DIAGNOSTIC DEVICE

Field of the invention

The present invention relates to a diagnostic device, More particularly, the present invention relates to a diagnostic device comprising porous silicon. Yet more particularly, the present invention relates to a diagnostic device, comprising porous silicon, for analysing a body fluid of an animal or human.

The present invention further relates to a separation device. More particularly, the present invention relates to a separation device comprising porous silicon.

Background of the invention

Rapid processing and analysis of bodily fluids, in particular blood, presents significant technical challenges yet the benefits and applications of being able to do so are considerable, ranging from dialysis treatment of patients with renal failure, to purification and concentration of blood components for therapeutic purposes to monitoring of physiological conditions such as glucose in diabetics, or onset of heat in farm animals to disease diagnosis.

To date, such processing and analysis is typically carried out by bulky equipment in a laboratory or clinic. Body fluid may be excreted and collected or extracted, stabilised, transported and then subjected to various processing and analysis techniques such as addition of buffers, centrifugation, filtration, chromatography, mass spectrometry, and immunological assays.

Because so many steps are involved in processing and analysing bodily fluids, miniaturisation of equipment has not been possible. Such miniaturisation could allow processing and analysis to become mobile, point-of-care, or even wearable. It is only recently, with the significant advancement of a number of key technologies including microfluidic technology, cheap high powered computing power, MEMS technology, and nanotechnology that such devices can now be commercially produced.

Sensor arrays have been developed for the analysis of gaseous, and liquid samples, arrays operating on liquid samples typically being termed 'electronic tongues' or 'e- tongues'.

Each sensor, of an array, will commonly generate a signal in response to a number of different components of the substance to be analysed. In order to identify the presence of a specific analyte, or combination of analytes, it is necessary to compare the characteristic signal profile generated by the entire array with a pre-established database of reference profiles.

Somewhat analogous to matching a suspect's fingerprint in a police database, the pattern matching software matches the electronic fingerprint produced by the sensing array to stored profiles previously generated using known, or otherwise verified samples.

It has proved to be extremely difficult to construct small, robust arrays of sufficient sensitivity, with each element in the array having sufficient variation from other elements in its response to stimuli. It has also been problematic to construct sensors that can remain highly sensitive to analytes of interest while not becoming fouled or otherwise disrupted by contaminants or other substances not of interest in the sample.

Isolation or separation of components from bodily fluids, in particular blood, is often an essential precursor step to the analysis and therapeutic applications. Separation techniques include: filtration, evaporation, distillation, fermentation, sedimentation, skimming, centrifugation, electrophoresis and chromatography.

Typical analyses include measurements of key fluid constituents to determine health, disease or productivity status in humans or animals, such as: blood panel, blood typing, glucose, cholesterol, blood gases, hematocrit, coronary disease markers, cancer markers, and others from blood; urea, key metabolites and infectious organisms from urine; infectious agents from saliva or phlegm; digestive problems, ulcers and infectious agents from gastric juices; state of nutrition, fat and protein levels from milk.

Typical therapeutic applications include: purification of blood products from whole blood for later administration to a patient, including plasma, red blood cells, platelet rich plasma, clotting factors, albumin, growth factors, immunoglobulins; extraction of microcomponents

from milk or colostrum including proteins, growth factors, immunological factors, enzymes and lipids; filtering of micro-organisms or toxins from blood products or milk prior to administration or consumption; sorting of sperm from ejaculate for breeding and insemination purposes.

The following prior art may be relevant to the present invention.

WO 03075745, describes a method of contacting an array of sensors with a sample from a mammal suspected of having a disease or condition to generate a silicon sensor array response profile. US2005164320 describes a method of rapid characterization of multi- analyte fluids, that involves the use of a light source, and a sensor array. US 20030004402 describes a method of classifying a biological state from biological data by the detection of discriminatory patterns where the discriminatory pattern describes a biological state.

S E Letant et a! have published, in Sensors and Actuators B 69 (2000) 193-198, a paper that describes changes in reflectivity and photoluminescence spectra of porous silicon chips. US 6,780,649 describes a method for detecting a test analyte by irradiating a porous semiconductor material modified with at least one recognition element. A paper by C Baratto et al (Sensors 2002, 2, 121-126) describes the use of a porous silicon microcavity.

Chemical detection using porous silicon is described in papers by De Stefano, Moretti et al (IEEE Transactions on Nanotechnology 2004, 3, 49-54), Sailor et al (Science 1997, 278, 840-843), Mathew and Alocilja (IEEE 2003, 293-298) and Bow, Kwok and Poon et al (IEEE 1999, 80-83).

US 6,699,392 describes a method to fabricate a silicon chromatographic column. US 2004154972 describes a method for forming an anti-microbial filter for a micro-fluidic system including a silicon-based filter membrane. EP 0912223 describes methods for microfabricating filters constructed with permeable polysilicon membranes. DE 10055872 and US 2004203239 provide background information concerning the use of porous silicon as a means of separating or resolving components in a fluid. The use of porous silicon to improve on-chip chromatography is described in the paper "Porous silicon as a stationary phase for shear-driven chromatography", Clicq et al, Journal of Chromatography A 1032 (2004) 185-191. The microfluidic separation of test samples from non-test samples (in particular, blood) on a disposable chip is described in the paper by Ahn, Choi et al

(Proceedings of the IEEE 2004, 92, 154-173). US 2005/0019956 describes an optical sensor for monitoring molecular binding interactions the sensor comprising porous silicon. WO 04111612 describes a method for simultaneously detecting and separating an analyte using a porous silicon matrix. US 6,248,539 describes a means for detecting shifts in Fabry-Perot fringes using a porous semiconductor. EP 1 484 599 describes a biosensor comprising a porous matrix.

It is an objective of the present invention to solve at least some of the above mentioned problems. It is a further objective of the present invention to provide a new diagnostic device that will allow rapid and accurate identification and quantification of one or more substances in a fluid. It is a yet further objective of the present invention to provide a new diagnostic device that will allow the effective detection of disease and/or conditions in human and/or animal subjects.

Summary of the invention

According to a first aspect the invention provides a diagnostic device for analysing one or more test substances, the device comprising:

(a) a silicon sample interaction means for, when in use, interacting with the or at least one of the test substances; (b) a signal generation means for interrogating the sample interaction means, and for generating a test signal in response to the interrogation of the sample interaction means; and (c) a signal processing means for processing the test signal.

According to a further aspect, the invention provides a separation device for separating one or more test substances from a mixture, the separation device comprising a silicon separation means having a silicon sample interaction means for, when in use, interacting with the or at least one of the test substances, the silicon separation means having structure and composition such that, when in use, at least part of the or at least one of the test substances is separated from said mixture by interaction with the interaction means.

According to a further aspect, the invention provides a combined diagnostic and separation device comprising the diagnostic device, and the separation device as defined in the above aspects of the invention.

The combined diagnostic and separation device may have a construction and be arranged such that at least part of the, or at least one of the, test substances that has been separated by the separation device, is introduced to the diagnostic device for analysis.

According to a further aspect, the invention provides a silicon sample interaction means comprising a porous silicon region.

According to a further aspect, the invention provides a method of fabricating a silicon sample interaction means comprising the step of etching a sample of silicon to form a silicon sample interaction means comprising porous silicon region.

According to a further aspect the invention provides an attachable diagnostic and/or separation device comprising a diagnostic device and/or separation device as defined in the above aspects of the invention, and a means of attaching the device to the body of an animal or human.

According to a further aspect the invention provides an implantable diagnostic and/or separation device comprising a diagnostic device and/or separation device as defined in the above aspects of the invention.

Detailed description of the invention

A detailed description of the invention will now be provided.

Test substances

The or at least one of the test substances may comprise one or more of: blood, sweat, saliva, tears, mucus, urine, breast milk, regurgitant, ejaculate, interstitial fluid, pus, phlegm, • gastro-intestinal juices, breath, biopsy fluid, bronchial washings, breath condensate. The or at least one of the test substances may comprise one or more body fluids. A body fluid

may be a fluid that is excretable from a human or animal. A body fluid may be a fluid that is extractable from a human or animal.

The body fluid may comprise one or more of the following: saline, blood products, vaccines, growth factors, immunological factors, iodinated dyes or any other liquid products which are clinically administered to a human or animal.

The or at least one of the test substances may comprise a fluid derived from one or more of the following: a tissue sample, a biopsy sample, hair, fecal matter, bone, cartilage, marrow, shell, skin, hide and fur.

The or at least one of the test substances may comprise one or more components of one or more of: blood, sweat, saliva, tears, mucus, urine, breast milk, regurgitant, ejaculate, interstitial fluid, pus, phlegm, gastro-intestinal juices, breath, biopsy fluid, bronchial washings, breath condensate. The or at least one of the test substances may comprise one or more components of one or more body fluids.

The or at least one of the test substances may comprise one or more substances that are characteristic of one or more of the following conditions: cancer, neurological disease, cardiovascular disease, genetic disorders, asthma, diabetes, organ malfunction, systemic disease, infection, autoimmune disease, stress, exhaustion, reaction to drug or alcohol, allergic reaction, respiratory condition, gastro-intestinal condition, abnormal activity or failure of organs or glands, pregnancy, physical injury, burn, hypothermia, altitude sickness, decompression illness, sunstroke, abnormal blood pressure or heart rate, rash, pain, cramp, nausea, diarrhea, and congestion.

Silicon sample interaction means

The silicon sample interaction means may comprise a silicon sensor array having a multiplicity of silicon sensors. The silicon sample interaction means may comprise one or more silicon sensors.

The silicon sample interaction means may comprise a porous silicon region and a non- porous silicon region.

The silicon sample interaction means may comprise a porous silicon region and a non- porous silicon region, the porous region comprising a multiplicity of silicon elements. The silicon sample interaction means may comprise a porous silicon region and a non-porous silicon region, the porous region comprising a multiplicity of porous silicon elements.

Each silicon element may comprise a silicon sensor. Each silicon element may comprise porous silicon. Each silicon sensor may comprise a porous silicon element.

Each porous silicon element may have an element interface area that is located between the non-porous silicon region and the porous silicon region. Each element interface area may be spatially separate from the adjacent element interface area or areas. Each silicon element may be spatially separate from the adjacent silicon element or elements. Each element interface area may lie substantially in a single plane, Each porous silicon element may protrude from a substrate. Each porous silicon element may lie in an element cavity formed in the substrate. Each porous silicon element may be integral with the walls of the element cavity. The volume occupied by at least one of the porous silicon elements may be less than the cavity in which it is located. Each of the porous silicon elements may be * integral with the substrate. The substrate may comprise silicon.

The volume of at one porous silicon element may differ from that of its adjacent silicon element or elements. The mean pore size of at least one porous silicon element may differ from that of its adjacent element or elements. The porosity of at least one porous silicon element may differ from that of its adjacent element or elements.

At least some of the porous silicon elements may lie on a single element axis, and the volume occupied by each element may vary along the length of the element axis. At least some of the porous silicon elements may lie on a single element axis, and the mean pore size of each element may vary along the length of the element axis. At least some of the porous silicon elements may lie on a single element axis, and the porosity of each element may vary along the length of the element axis.

The volume of at least one of the elements on a single element axis may be less than half the volume of the or one of the other elements on the same single element axis.

At least some of the porous silicon elements may lie on a first element axis, and the volume occupied by each element may vary along the length of the first element axis. At least some of the porous silicon elements may lie on a first element axis, and the mean pore size of each element may vary along the length of the first element axis. At least some of the porous silicon elements may lie on a first element axis, and the porosity of each element may vary along the length of the first element axis.

At least some of the porous silicon elements may lie on a second element axis, and the volume occupied by each element may vary along the length of the second element axis. At least some of the porous silicon elements may lie on a second element axis, and the mean pore size of each element may vary along the length of the second element axis. At least some of the porous silicon elements may lie on a second element axis, and the porosity of each element may vary along the length of the second element axis.

The first and second element axes may be substantially perpendicular to each other. The first and second element axes may each be a straight line. The first element axis may have a length between 0.01 mm and 10 cm. The first element axis may have a length between 0.01 mm and 1 cm. The second element axis may have a length between 0.01 mm and 10 cm. The second element axis may have a length between 0.01 mm and 1 cm.

The volume of at least one of the silicon elements may be less than half the volume of at least one of the other silicon elements. The volume of at least one of the porous silicon elements may be less than half the volume of at least one of the other porous silicon elements.

A first porous silicon element and a second porous silicon element may lie on a single element axis that is a straight line. The mean pore size of the first porous silicon element may be between 1.1 and 1 x 10 ³ times greater than the mean pore size of the second porous silicon element. The porosity of the first porous silicon element may be between 1.1 and 9 times greater than the porosity of the second porous silicon element. Between 5 and 1000 porous silicon elements may lie on a single element axis that is a straight line. Greater than 1000 porous silicon elements may lie on a single element axis that is a straight line.

The silicon sample interaction means may comprise porous silicon interaction layer having an interaction layer surface. The silicon sample interaction means may comprise a silicon sensor, the silicon sensor comprising a porous silicon interaction layer,

The porous silicon interaction layer may have a planar interaction layer surface. The porous silicon interaction layer may have a convex interaction layer surface. The porous silicon interaction layer may be tapered. The porous silicon interaction layer may comprise a tapered region. The porous silicon interaction layer may comprise a first planar interaction layer surface and a second planar interaction layer surface. The first planar interaction layer surface may have a first normal line that is normal to the first planar interaction layer surface. The second planar interaction layer surface may have a second normal line that is normal to the second planar interaction layer surface.

The smallest angle between the first normal line and the second normal line may be between 90 degrees and 0.1 degrees. The smallest angle between the first normal line and the second normal line may be between 85 degrees and 0.1 degrees. The smallest angle between the first normal line and the second normal line may be between 45 degrees and 0.1 degrees. The smallest angle between the first normal line and the second normal line may be between 10 degrees and 2 degrees. The smallest angle between the first normal line and the second normal line may be between 5 degrees and 0.5 degrees.

The porous silicon interaction layer may comprise a high porosity region and a low porosity region, the porosity of the high porosity region being greater than the porosity of the low porosity region. The high porosity region may comprise a high porosity volume, having a volume greater than 0.1 mm ³ . The low porosity region may comprise a low porosity volume, having a volume greater than 0.1 mm ³ .

The porosity of the high porosity volume, of the porous silicon interaction layer, may be between 1.1 and 9 times greater than the porosity of the low porosity volume, of the porous silicon interaction layer.

The porous silicon interaction layer may comprise a high pore size region and a low pore size region, the high pore size region having a higher mean pore diameter than that of the low pore size region. The high pore size region may comprise a high pore size volume,

having a volume greater than 0.1 mm ³ . The low pore size region may comprise a low pore size volume, having a volume greater than 0.1 mm ³ .

The mean pore size of the high pore size volume may be between 1.1 and 1 x 10 ³ times greater than the mean pore size of the low pore size volume.

The porous silicon interaction layer may be integral with a silicon substrate. The silicon substrate may be substantially planar. The porous silicon interaction layer may be integral with a silicon substrate that is substantially planar, and the maximum depth of the silicon interaction layer, measured along a line that is perpendicular to the silicon substate, may be between 1 micron and 10,000 microns. The porous silicon interaction layer may be integral with a silicon substrate that is substantially planar, and the maximum depth of the silicon interaction layer, measured along a line that is perpendicular to the silicon substate, may be between 1 micron and 1 ,000 microns. The porous silicon interaction layer may be integral with a silicon substrate that is substantially planar, and the maximum depth of the silicon interaction layer, measured along a line that is perpendicular to the silicon substate, may be between 1 micron and 500 microns.

The silicon sensor array may comprise between 2 x 10° and 1 x 10 ⁶ silicon sensors. The silicon sensor array may comprise between 2 x 10° and 1 x 10 ³ silicon sensors. The silicon sensor array may comprise between 10 and 1 ,000 silicon sensors. The silicon sensor array may comprise between 100 and 500 silicon sensors.

The silicon sensor array may comprise one or more non-silicon sensors.

The silicon sensor array may have a structure, and be arranged such that there are between 2 x 10° and 1 x 10 ⁶ silicon sensors contained within a volume of 5 mm ³ . The silicon sensor array may have a structure, and be arranged such that there are between 2 x 10° and 1 x 10 ³ silicon sensors contained within a volume of 5 mm ³ . The silicon sensor array may have a structure, and be arranged such that there are between 2 x 10° and 500 silicon sensors contained within a volume of 5 mm ³ .

The or at least one of the silicon sensors may comprise an electrical silicon sensor having one or more silicon electrical contacts, each silicon electrical contact being in electrical contact with the silicon from which the silicon sensor is at least partly formed. The or at

least one of the electrical contacts may comprise one or more of: a metal, a semiconductor, and an electrolyte. The or at least one of the electrical silicon sensors may comprise a silicon pn junction. The or at least one of the electrical silicon sensors may comprise a transistor. The or at least one of the electrical silicon sensors may comprise a silicon field effect transistor. The or at least one of the silicon sensors may comprise electroluminescent porous silicon. The electroluminescent porous silicon may comprise a multiplicity of quantum wires. The or at least one of the electrical silicon sensors may comprise a variable resistor. The or at least one of the electrical silicon sensors may incorporate a polymer or a conducting polymer.

The or at least one of the silicon sensors may comprise an optical silicon sensor.

The or at least one of the optical silicon sensors may comprise a porous silicon mirror. The or at least one of the silicon mirrors may comprise a multiplicity of porous silicon layers. The or at least one of the silicon mirrors may comprise alternating layers of high and low porosity porous silicon, the combined high and low porosity layers forming a Bragg stack mirror. Each of the high porosity layers of the silicon mirror may have a porosity between 40% and 90%, each of the low porosity layers of the silicon mirror may have a porosity between 20% and 60%.

The or at least one of the optical silicon sensors may comprise photo-luminescent porous silicon. The photo-luminescent porous silicon may comprise a multiplicity of quantum wires.

The or at least one of the optical silicon sensors may comprise an ellipsometer.

The silicon sensor array may comprise a substrate and a multiplicity of mechanical silicon sensors, the substrate and each of the mechanical sensors having a structure and being arranged such that each of the mechanical sensors is moveable relative to the substrate. The or at least one of the mechanical silicon sensors may comprise a silicon cantilever. The or at least one of the mechanical silicon sensors may comprise a variable frequency vibrator.

The or at least one of the silicon sensors may comprise one or more of the following: one or more silicon plates, one or more silicon membranes, one or more silicon wires, one or

more silicon fibres, one or more silicon channels, one or more silicon wells, one or more silicon particles, one or more silicon columns, one or more silicon cantilevers.

The silicon sensor array may comprise a substrate, each silicon sensor being attached to, and/or integral with, the substrate. The substrate may comprise a silicon substrate. The substrate may comprise a plastic substrate. Each silicon sensor may be spatially separate from its neighbouring sensor or sensors. The substrate and each sensor may be arranged such that there are between 1 and 100 sensors per 1 mm ² of substrate surface area. The substrate and each sensor may be arranged such that there are between 1 and 100 sensors per 10mm ² of substrate surface area. The substrate and each sensor may be arranged such that there are between 1 and 100 sensors per 0.1 mm ² of substrate surface area.

For the purposes of this specification the term "sensor array" does not imply a particular spatial arrangement of sensors. For example, a sensor array, according to the present invention, need not comprise a substrate.

The substrate may have a substantially planar surface having an area between 0.01 mm ² and 100 cm ² . The substrate may have a substantially planar surface having an area between 0.1 mm ² and 10 cm ² . The substrate may have a substantially planar surface having an area between 0.05mm ² and 2 cm ² . The substrate may have a substantially planar surface having an area between 1 mm ² and 5 cm ² .

The silicon sensor array may comprise two or more substrates, some of the silicon sensors being arranged, and/or formed, on each of the substrates. Each of the substrates may comprise silicon.

The or at least one of the silicon sensors may have a largest dimension in the range 1 nm to 1 cm. The or at least one of the silicon sensors may have a largest dimension in the range 10Onm to 1 mm. The or at least one of the silicon sensors may have a largest dimension in the range 0.001 mm to 1 mm.

The silicon sensor array may comprise: one or more sensor groups of optical silicon sensors, and/or one or more sensor groups of electrical silicon sensors, and/or one or more sensor groups of mechanical sensors.

The silicon sensor array may comprise sensors that are a combination of one or more of electrical, optical or mechanical silicon sensors,

The or at least one of the sensor groups may have a different chemical composition to the other sensor groups. The or at least one of the sensor groups may have a different morphology to the other sensor groups.

The silicon sample interaction means may form part of a silicon separation means. The silicon separation means may comprise a chromatographic device. The silicon separation means may comprise one or more of: a layer chromatography device, a gas chromatography device, a column chromatography device, a high pressure liquid chromatography device, an ion chromatography device, and a gel permeation chromatography device. The silicon separation means may comprise a filtration device. The silicon separation means may comprise one or more of: a diffusion membrane, an osmosis membrane, a reverse osmosis membrane, a multi-step filter, and a bio-active filter.

The silicon sample interaction means may comprise one or more silicon filters each silicon filter having a multiplicity of silicon pores, each silicon pore being at least partly formed from silicon. The silicon sample interaction means may comprise one or more silicon chambers, the or each silicon chamber being at least partly formed from silicon. The silicon sample interaction means may comprise one or more silicon channels, the or each silicon channel being at least partly formed from silicon. The silicon sample interaction means may comprise one or more silicon capillaries, the or each silicon capillary being at least partly formed from silicon. The silicon sample interaction means may comprise one or more silicon osmotic membranes, the or each silicon osmotic membrane being at least partly formed from silicon. The silicon sample interaction means may comprise one or more silicon particles, the or each silicon particle being at least partly formed from silicon. The silicon sample interaction means may comprise one or more silicon valves, the or each silicon valve being at least partly formed from silicon. The sample interaction means may comprise one or more silicon fibres, the or each silicon fibre being at least partly formed from silicon.

The silicon sample interaction means may comprise one or more of the following: one or more silicon plates, one or more silicon membranes, one or more silicon wires, one or more silicon fibres, one or more silicon channels, one or more silicon wells, one or more silicon particles, one or more silicon columns, one or more silicon cantilevers.

The silicon sample interaction means may comprise one or more of: acetyltributyl citrate, acetyltriethyl citrate, aliphatic polyesters, calcium carbonate, carbomers, carboxymethylcellulose sodium, cellulose acetate, cellulose acetate phthalate, cetyl alcohol, chitosan, ethylcellulose, fructose, gelatin, glycerin, glyceryl behenate, glyceryl palmitostearate, guar gum, hydroxyethyl cellulose, hydroxyethylmethyl cellulose, hydroxypropyl cellulose, hypromellose, hypromellose acetate succinate, hypromellose phthalate, isomalt, latex particles, maltitol, maltodextrin, methylcellulose, poloxamer, polydextrose, polyethylene glycol, polymethacrylates, polyvinyl acetate phthalate, polyvinyl alcohol, potassium chloride, povidone, shellac, shellac with stearic acid, sucrose, sureteric, titanium dioxide, titanium oxide, tributyl citrate, triethyl citrate, vanillin, wax (camauba), wax (microcrystalline), wax (white), wax (yellow), xylitol, zein, and/or corn protein, ammonium alginate, calcium carbonate, chitosan, chlorpheniramine maleate, copovidone, dibutyl phthalate, dibutyl sebacate, diethyl phthalate, dimethyl phthalate, ethyl lactate, ethylcellulose, gelatin, glucose (liquid), hydroxyethyl cellulose, hydroxypropyl cellulose, hypromellose, hypromellose acetate succinate, maltodextrin, polydextrose, polyethylene glycol, polyethylene oxide, polymethacrylates, poly(methyl vinyl ether/maleic anhydride), polyvinyl acetate phthalate, triethyl citrate, and/or vanillin.

Silicon

The silicon components of the present invention include: a silicon sensor array, a silicon interaction means, a silicon separation means, a silicon sensor, a silicon substrate, a silicon membrane, a silicon filter, a silicon chamber, a silicon pore, a silicon channel, a silicon particle, and a silicon fibre. Each of the silicon components comprise silicon. The silicon may be selected from one or more of: bulk crystalline silicon, polycrystalltine silicon, amorphous silicon, porous silicon, derivatized silicon, semiconductor silicon, elemental silicon, metallurgical grade silicon, and nanocrystalline silicon.

The silicon sample interaction means may comprise a silicon surface, which is at least partly formed from silicon. The silicon surface may comprise a derivatized silicon surface,

which is at least partly formed from derivatized silicon. Each of the above mentioned silicon components may comprise a silicon surface, which is at least partly formed from silicon.

The silicon may comprise silicon that has been doped with one or more of: boron, phosphorus, arsenic, and antimony. The silicon may comprise one or more of: silicon oxide, a surface layer of silicon oxide, and partially oxidised silicon. The silicon may comprise hydrogen terminated silicon.

The porous silicon may comprise microporous silicon having a pore size less than 20 A. The porous silicon may comprise mesoporous silicon having a pore size between 20 A and 500 A. The porous silicon may comprise macroporσus silicon having a pore size greater than 500 A.

The porous silicon may have a porosity between 2% and 99.9%. The porous silicon may have a porosity between 4% and 90%. The porous silicon may have a porosity between 4% and 70%. The porous silicon may have a porosity between 50% and 95%. The porous silicon may have a porosity between 20% and 60%.

For the absence of doubt the term "derivatized silicon" includes derivatized porous silicon.

The derivatized silicon may comprise one or more of: an organic compound, a biomolecule, an oligonucleotide, RNA, DNA, mRNA, an antibody, an antigen, an aptamer, a protein, an enzyme, a hormone, a lipid, a monomer, a polymer, a gel, a sugar, a carbohydrate, an inorganic, a catalyst, a salt, an ions, a cation, an anion, a metal, a non- metal, a silicate, a metallic complex, a metalo-porphyrin, a dye, a luminescent, a fluorescent, a chelating agent, .an acid, a base, a reducing agent, an oxidising agent.

The derivatized silicon may comprise one or more of: a oligonucleotide fragment, an RNA fragment, a DNA fragment, a mRNA fragment, an antibody fragment, an antigen fragment, an aptamer fragment, a protein fragment, an enzyme fragment, a hormone fragment, a lipid fragment, a sugar fragment, and a carbohydrate fragment.

The or at least one of the silicon sensors may comprise derivatized silicon. The or at least one of the silicon sensors may comprise derivatized porous silicon. The sensor array may

comprise between 2 and 10 types of derivatized silicon. The sensor array may comprise between 10 and 100 types of derivatized silicon. The sensor array may comprise between 10 and 1 ,000 types of derivatized silicon.

Each type of derivatized silicon may comprise a substance that differs from that of the other types of derivatized porous silicon.

Interaction of silicon sample interaction means with the test substance or substances

Interaction of the or at least one of the test substances with the silicon sample interaction means may comprise one or more of: chemical reaction with the or at least one of the test substances, chemical bonding to the or at least one of the test substances, covalent bonding to the or at least one of the test substances, ion exchange with the or at least one of the test substances, non-covalent association with the or at least one of the test substances, catalytic action on the or at least one of the test substances, adsorption of the or at least one of the test substances, mechanical interaction with the or at least one of the test substances, absorption of the or at least one of the test substances, and at least partial erosion of the silicon interaction means by the test substance.

Adsorption of the or at least one of the test substances may comprise adsorption of the or at least one of the test substances to the silicon surface. If the silicon interaction means comprises derivatized silicon, adsorption of the or at least one of the test substances may comprise adsorption of the or at least one of the test substances to the derivatized silicon surface.

Bonding to the or at least one of the test substances may comprise bonding between the test substance and the silicon surface. If the silicon interaction means comprises derivatized silicon, bonding to the or at least one of the test substances may comprise bonding between the test substance and the derivatized silicon surface.

If the or at least one of the test substances comprises a multiplicity of test substance particles, then mechanical interaction with the or at least one of the test substances may comprise collision between the surface of the silicon interaction means and at least some of the test substance particles.

If the or at least one of the test substances comprises a multiplicity of test substance molecules, then mechanical interaction with the or at least one of the test substances may comprise collision between the surface of the silicon interaction means and at least some of the test substance molecules.

If the silicon interaction means comprises porous silicon then absorption of the or at least one of the test substances may comprise passage of the or at least one of the test substances into at least some of the pores of the porous silicon.

If the silicon interaction means comprises polycrystalline silicon, then absorption of the or at least one of the test substances may comprise passage of the or at least one of the test substances into at least some of the grain boundaries of the polycrystalline silicon.

If the silicon interaction means comprises a multiplicity of silicon particles, then absorptrion of the or at least one of the test substances may comprise passage of the or at least one of the test substances into the spaces between the silicon particles.

If the silicon interaction means forms part of a combined diagnostic and separation device, then the silicon interaction means may have a dual function, being involved with both separation of the or one of the test substances, and analysis of the or at least one of the test substances.

If the silicon sample interaction means comprises derivatised silicon having one or more chemical groups boded to the surface of the silicon, then the interaction may comprise the breaking of at least some of the chemical bonds. Said bond breaking step may comprise the step of at least some of the test substance molecules reacting with the silicon and/or at least some of the chemical groups.

Some molecules and/or chemical groups are known to quench photoluminescence and/or electroluminescence of porous silicon. If a quenching group is bonded to the porous silicon, then reaction of the silicon sample interaction means with one or more components of the test substance may result in bonds being broken between the quenching group and the silicon. After the bonds have been broken, the group is removed from the vicinity of the porous silicon, thereby reducing quenching. Such a reaction may result in an increase in

photoluminescence or electroluminescence generated by the test signal generation means.

Jest signal generation means

Interaction of the or at least one of the test substances with the silicon sample interaction means may result in a change in the electrical properties of the silicon sample interaction means. Interaction of the or at least one of the test substances with the silicon sample interaction means may result in a change in the optical properties of the silicon sample interaction means. Interaction of the or at least one of the test substances with the silicon sample interaction means may result in a change in the optical reflectance of the silicon sample interaction means.

Interaction of the or at least one of the test substances with the silicon sample interaction means may result in a change in the photoluminescence properties of the silicon sample interaction means. Interaction of the or at least one of the test substances with the silicon sample interaction means may result in a change in the refractive index of the silicon sample interaction means. Interaction of the or at least one of the test substances with the silicon sample interaction means may result in a change in the electroluminescence properties of the silicon sample interaction means.

If the silicon sample interaction means comprises porous silicon, then some molecules of the test substance may be excluded from some pores because they are too large. If the silicon sample interaction means comprises a multiplicity of porous silicon elements, each silicon element having a unique pore structure, then each silicon element may interact differently with the test substance and a spatial pattern will be generated.

If the silicon sample interaction means comprises one or more optical silicon sensors, then the signal generation means may comprise one or more light sources. The or at least one of the light sources may comprise one or more of: a laser, an LED array, an ultraviolet lamp. The LED may have a construction such that it is able to operate over a range of wavelengths.

The or at least one of the light sources may be arranged such that, when in use, at least some of the light from the light source impinges upon the or at least one of the optical silicon sensors.

Interaction of the or at least one of the test substances may result in a change in the photoluminescence of the or at least one of the silicon sensors. The test signal may comprise electromagnetic radiation generated by the or at least one of the optical silicon sensors.

Interaction of the or at least one of the test substances may cause a change in the reflectivity of the or at least one of the silicon sensors. The test signal may comprise electromagnetic radiation reflected from the or at least one of the optical silicon sensors. Porous silicon mirrors and thin layers of porous silicon reflect radiation and are often brightly coloured. Interaction of the porous silicon with a test substance may affect the optical properties of the porous silicon, inducing a colour change that is characteristic of the substance.

If the or at least one of the silicon sensors comprises an electrical silicon sensor, then the signal generation means may comprise one or more interrogation electronic circuits. The or at least one of the electronic circuits may apply a potential difference across at least one of the electrical silicon sensors.

Interaction of the or at least one of the test substances with the or at least one of the silicon sensors may result in a change in the electrical properties of the or at least one of the silicon sensors. Interaction of the or at least one of the test substances with the or at least one of the silicon sensors may result in a change in the electroluminescent properties of the or at least one of the silicon sensors.

The test signal may comprise an electrical current that has passed through the or at least one of the electrical silicon sensors. The test signal may comprise a potential difference between two points in or on the or at least one of the silicon electrical sensors. The test signal may comprise a potential measured at a point in or on the or at least one of the silicon electrical sensors. The test signal may comprise radiation that has been generated by electroluminescence of the or at least one of the electrical silicon sensors.

Signal processing means

If the or at least one of the silicon sensors comprises an electrical silicon sensor then the signal processing means may comprise one or more of:

(a) an ammeter for measuring an electrical current passing through the silicon sensor;

(b) a potentiometer for measuring a potential at a point on or in the silicon sensor; and

(c) a voltage meter for measuring the potential difference between two points in or on the silicon sensor.

If the or at least one of the silicon sensors comprises an optical silicon sensor, then the signal processing means may comprise one or more of:

(a) a photodiode;

(b) a photodiode array; and (c) a charge-couple device (CCD)

If the or at least one of the silicon sensors comprises a mechanical silicon sensor, then the signal processing means may comprise one or more of:

(a) deflection based vibrometer; (b) deflection based differential capacitance device;

(c) reflectometry based optical device for measurement of displacement;

(d) a microcantilever;

(e) Differential thermometer; and

(f) Differential pressure gauge.

The signal processing means may further comprise a data processing means for processing information derived from the test signal.

If the silicon interaction means comprises an optical silicon sensor, then information may be derived from variation in radiation that has been generated by photoluminescence by the or at least one of the optical silicon sensors; said variation resulting from interaction of the or at least one of the test substances with the silicon interaction means. Information may be derived from variation in photoluminescence efficiany, or a variation in the wavelengths of photoluminescence, as a result of interaction between the silicon sample interaction means and the test substance.

If the silicon interaction means comprises an optical silicon sensor, then information may be derived from variation in radiation that has been reflected from the or at least one of the optical silicon sensors; said variation resulting from interaction of the or at least one of the test substances with the silicon interaction means.

If the silicon interaction means comprises an electrical silicon sensor, then information may be derived from variation in current that has passed through the or at least one of the electrical silicon sensors; said variation resulting from interaction of the or at least one of the test substances with the silicon interaction means.

If the silicon interaction means comprises an electrical silicon sensor, then information may be derived from variation in the potential measured at a point in or on the or at least one of the electrical silicon sensors, said variation resulting from interaction of the or at least one of the test substances with the silicon interaction means.

The test signal may comprise a number of test signal components. Each signal component may be generated by one or more of the silicon sensors. Each signal component may be generated by one or more of the sensor groups.

At least one of the signal components may comprise an optical component generated by ^' one or more of the optical sensors. At least one of the signal components may comprise an electrical component generated by one or more of the electrical sensors. At least one of the signal components may comprise a mechanical component generated by one or more of the mechanical sensors.

At least one of the signal components may comprise a derivatized component generated by one or more derivatized silicon sensors, the or each derivatized silicon sensor comprising derivatized silicon. At least one of the signal components may comprise a first derivatized component generated by one or more first derivatized silicon sensors, the or each first derivatized silicon sensor comprising a first type of derivatized silicon. At least one of the signal components may comprise a second derivatized component generated by one or more second derivatized silicon sensors, the or each second derivatized silicon sensor comprising a second type of derivatized silicon.

The data processing means may comprise a database that contains data that is representative of the or at least one of the test substances.

The set of test signal components generated by a particular test substance may be characteristic of that test substance. The set of test signal components for a particular test substance may be unique for that test substance.

The data processing means may comprise a database that contains a multiplicity of sets of signal component data, each set of signal component data being representative of a particular test substance.

Comparison of a set of test signal component with the data contained in the database may allow characterisation of the one or more test substances. If the test substance is a body fluid that has been taken from, or emitted by, an animal or human, then such characterisation of the test substance may allow identification of a medical or other condition.

The use of silicon and particularly porous silicon is of particular value in this regard. This is because silicon may be formed into electronic and optical components that have dimensions of a few microns or less than a micron, A variety of different silicon sensors, or groups of sensors, may therefore be located on a single substrate, allowing a variety of tests to be carried out on the body fluid sample. Porous silicon is a preferred material for many such tests because it has a large surface area that allows high levels of interaction with the test substance.

Separation of the or at least one of the test substances

The silicon sample interaction means may form part of a silicon separation means having structure and composition such that, when in use, at least part of the or at least one of the other test substances is at least partly separated from said mixture.

Prior to separation, the mixture comprises the one or more test substances to be separated from the mixture.

The mixture may comprise one or more of: blood, sweat, saliva, tears, mucus, urine, breast milk, regurgitant, ejaculate, interstitial fluid, pus, phlegm, breath condensate, and gastrointestinal juice.

The mixture may comprise one or more of: a body fluid selected from one or more of: blood, sweat, saliva, tears, mucus, urine, breast milk, regurgitant, ejaculate, interstitial fluid, pus, phlegm, gastro-intestinal juices, and breath condensate. The body fluid may be a fluid excreted and/or extracted from a human or animal.

Interaction of the or at least one of the test substances with the silicon sample interaction means may cause the or at least one of the test substances to be separated from the or at least one of the non-test substances.

Therefore separation may result from one or more of: chemical bonding to the or at least one of the test substances, covalent bonding to the or at least one of the test substances, adsorption of the or at least one of the test substances, mechanical interaction with the or at least one of the test substances, and absorption of the or at least one of the test substances.

Adsorption of the or at least one of the test substances, to the silicon surface may retard passage across the silicon surface, of the or at least one of the test substances, relative that of the or at least one of the other substances present in the mixture.

Adsorption of the or at least one of the test substances, to the derivatized silicon surface may retard passage across the derivatized silicon surface, of the or at least one of the test substances, relative that of the or at least one of the other substances present in the mixture.

Bonding of the or at least one of the test substances, to the silicon surface may retard passage across the silicon surface, of the or at least one of the test substances, relative that of the or at least one of the other substances present in the mixture.

Bonding of the or at least one of the test substances, to the derivatized silicon surface may retard passage across the derivatized silicon surface, of the or at least one of the test

substances, relative that of the or at least one of the other substances present in the mixture.

Mechanical interaction of the or at least one of the test substances, with the silicon surface may retard passage across the silicon surface, of the or at least one of the test substances, relative that of the or at least one of the other substances present in the mixture.

Absorption of the or at least one of the test substances, by the silicon from which the silicon surface is formed may retard passage across the silicon surface, of the or at least one of the test substances, relative that of the or at least one of the other substances present in the mixture.

For each of the above examples, the test substance is retarded relative to another substance, thereby causing separation. It will be appreciated that separation may also occur as a result of retardation of one or more of the other substances present in the mixture.

Etching a sample of silicon to form a porous silicon region

The silicon sample interaction means may be fabricated by the step of (x) etching a sample of silicon to form a porous silicon region.

The sample of silicon may be etched in such a way that a tapered layer of porous silicon is formed. The sample of silicon may be etched in such a way that a porous silicon region having curved layer surface is formed.

The sample of silicon may comprise a multiplicity of silicon elements and the sample of silicon may be etched in such a way that a multiplicity of porous silicon elements are formed, each porous silicon element having a different element volume to its neighbouring element or elements.

The etching step (x) may comprise the step of (ai) lowering the sample of silicon into an HF solution.

The etching step (x) may comprise the step of (ai) lowering the sample of silicon into an HF solution, and the method of fabrication may further comprise the step (bi), performed after step (ai), of raising the sample of silicon until at least part of the silicon is removed from the HF solution.

The method of fabrication may comprise the step (ci), performed after (bi) of rotating the sample about an axis, and the etch step (x) may further comprise (di), performed after step (ci) of lowering the sample of silicon into an HF solution.

The method of fabrication may comprise the step (ei), performed after step (di) of at least partly removing the sample of silicon from the HF solution.

The method may comprise the further step (y) of anodising the sample of silicon.

The step (y) may be performed prior to, during, and/or after step (ai). The step (y) may be performed prior to, during, and/or before step (di).

The etching step (x) may comprise the step of (aii) raising the level of an HF solution so that it at least partly immerses the sample of silicon.

The etching step (x) may comprise the step (aii) of raising the level of an HF solution so that it at least partly immerses the sample of silicon, and the fabrication method may further comprise the step (bii), performed after the step (aii), of lowering the level of an HF solution so that the sample of silicon is at least partly removed from the HF solution.

The fabrication method may comprise the step (cii), performed after step (bii) of rotating the sample about an axis, and the etch step (x) may comprise the step (dii), performed after step (cii) of lowering the sample of silicon into an HF solution.

The fabrication method may comprise the further step (eii), performed after step (dii) of lowering the level of the HF solution so that the sample of silicon is at least partly removed from the HF solution.

The step (y) may be performed prior to, during, and/or after step (aii). The step (y) may be performed prior to, during, and/or before step (dii).

The etching step (x) may at least partly comprise the anodisation step (y). The step (y) may comprise the step of using a cathode and applying a negative bias to the cathode and a positive bias to the anode,

The sample of silicon may comprise porous silicon prior to the etching step (x),

The HF solution may comprise one or more of: methanol, ethanol, ethanoic acid, methanoic acid, and water.

The silicon sample may comprise a layer of porous silicon having a uniform depth, and the HF concentration of the HF solution, and steps (ai) and (bi) may be performed in such a way that uniform depth layer of porous silicon is etched to produce a layer of porous silicon that has a depth which tapers. The direction of taper may be along a line that is parallel to the direction in which silicon was lowered into the HF solution in step (ai).

The silicon sample may comprise a layer of porous silicon and the HF concentration of the HF solution, and steps (ai) and (bi) may be performed in such a way that the layer of porous silicon is etched such that the mean pore size, and/or porosity, of the porous silicon decreases with distance in one direction along a straight line.

The silicon sample may comprise a layer of porous silicon having a uniform depth, and the HF concentration of the HF solution, and steps (aii) and (bii) may be performed in such a way that uniform depth layer of porous silicon is etched to produce a layer of porous silicon that has a depth which tapers. The direction of taper may be along a line that is parallel to the direction in which level of the HF solution was raised in step (aii).

The silicon sample may comprise a layer of porous silicon, and the HF concentration of the HF solution, and steps (aii) and (bii) may be performed in such a way that the layer of porous silicon is etched to produce a layer of porous silicon is etched such that the mean pore size, and/or porosity, of the porous silicon decreases with distance in one direction along a straight line.

The silicon sample may comprise a layer of porous silicon having a uniform depth, and the HF concentration of the HF solution, and steps (ai), (bi), (ci), (di), and (ei) may be

performed in such a way that uniform depth layer of porous silicon is etched to produce a layer of porous silicon that has a depth which tapers. The direction of taper may be along a first line that is parallel to the direction in which silicon was lowered into the HF solution in step (ai) and along a second line that is parallel to the direction in which the silicon was lowered into the HF solution in step (di).

The step (ai) direction may be substantially perpendicular to the step (di) direction.

The silicon sample may comprise a layer of porous silicon, and the HF concentration of the HF solution, and steps (aii), (bii), (cii), (dii), and (eii) may be performed in such a way that the layer of porous silicon is etched to produce a layer of porous silicon that has a depth which tapers. The direction of taper may be along a line that is parallel to the direction in which silicon was lowered into the HF solution.

The step (aii) direction may be substantially perpendicular to the step (dii) direction.

The sample of silicon may comprise a silicon wafer having an upper face and a lower face. The upper face and lower face may each be substantially planar. The upper face and lower face may be substantially parallel to each other. The upper face and lower face may each have the same surface area. The upper and lower face may each be circular. The upper and lower face may each be square.

The step (ai) may comprise the step of lowering the silicon wafer into the solution in such a way that one face of the wafer is substantially perpendicular to the meniscus of the HF solution.

The step (aii) may comprise the step of raising the level of the HF solution in such a way that one face of the wafer is substantially perpendicular to the meniscus of the HF solution.

The step (ci) may comprise the step of rotating the silicon wafer about an axis that is perpendicular to one face of the wafer. The wafer may be circular and (ci) axis of rotation may pass through the centre of the wafer's circular cross section. The wafer may be square and (ci) axis of rotation may pass through the centre of the wafer's square cross section.

The step (cii) may comprise the step of rotating the silicon wafer about an axis that is perpendicular to one face of the wafer. The wafer may be circular and (cii) axis of rotation may pass through the centre of the wafer's circular cross section. The wafer may be square and (cii) axis of rotation may pass through the centre of the wafer's square cross section.

The cathode may be angled relative to the plane of one face of the silicon wafer. The cathode may comprise a planar section that is at substantially planar. The smallest angle between the planar cathode section and the face of the wafer that is closest to the cathode may be between 15 degrees and 60 degrees. The smallest angle between the planar cathode section and the face of the wafer that is closest to the cathode may be between 5 degree and 45 degrees. The smallest angle between the planar cathode section and the face of the wafer that is closest to the cathode may be between 2 degree and 45 degrees. The smallest angle between the planar cathode section and the face of the wafer that is closest to the cathode may be between 10 degrees and 45 degrees.

The concentration of the HF solution may be between 5 wt% HF and 60 wt% HF. The concentration of the HF solution may be between 10 wt% HF and 60 wt% HF. The concentration of the HF solution may be between 25 wt% HF and 60 wt% HF.

Means of attaching the device to the body of an animal or human.

The means of attaching the diagnostic and/or separation device to the body of an animal or human may comprise a tape and/or sheet and/or fabric and/or plastic material. The attachment means may comprise an adhesive and/or flexible band and/or flexible garment. The garment may be designed to surround part of the animal or human body, for example the garment may be a glove or sleeve or cuff or head band or wrist band or arm band. The attachment means may comprise a solid object. The attachment means may be a ring, or necklace, or bracelet.

Examples

The invention will now be described, by way of example only, with reference to the following figures:

Figure 1 shows a separation device according to the present invention; Figure 2 shows part of a separation device according to the present invention; and Figure 3 part of a wafer and a planar cathode section that may be used to anodise the wafer.

The examples will be divided into two sections concerning: (a) separation techniques; and (b) fabrication and operation of sensor arrays.

Separation techniques

A separation device, according to the present invention, may comprise a silicon sample interaction means comprising a micromachined silicon membrane having pores having a uniform circular cross section, each cross section having a single diameter. The micromachined membrane may be placed at an angle intersecting a silicon channel through which a test substance is flowing.

The surface chemistry of the micromachined silicon membrane may be modified to increase or decrease its hydrophilic properties, ionic charge properties, or other physical properties that would affect the passage of the test substance through the pores.

A further separation device, according to the present invention, may comprise a silicon sample interaction means comprising a micromachined silicon membrane having a number of pores each pore having a uniform circular cross section. The diameters of the pores may vary from pore to pore such that a test substance that flows across one of the surfaces of the membrane encounters in succession pores having an decreasing diameter. This structure would allow test substances that comprise a number of particulate components, each component comprising particles of a particular size, to be separated at different locations in the membrane. Once separated in this way further processing and/or analysis may occur.

A further separation device according the present invention may comprise homogenous porous silicon particles contained in a column or channel. As a test substance passes through the channel, particles of the test substance that are small enough to enter the pores experience longer transit times than larger particles, thus effecting separation. The

pore size and/or porosity may be varied depending upon the test substances to be separated, and depending upon the particular application.

The surface chemistry of the porous silicon particles, contained in the column or channel, may be chemically modified to increase or decrease hydrophilic properties, ionic charge properties, or other physical properties that would affect the rate of passage of different particles through the column or channel.

Porous silicon particles may be tagged or coated with different molecules that facilitate placement of porous silicon particles having a particular pore size and/or porosity at particular location of a column or channel. Such molecules may be monomers which would covalently link the beads to each other and the channel walls after polymerisation, or short complimentary oligonucleotide sequences which would accomplish the same task.

The pore size and/or porosity of the porous silicon particles may vary with their location in the channel or column.

A further separation device, according to the present invention, may comprise a silicon channel filled with beads, the walls of the channel being porosified, the pore size and/or porosity varying with the location in the silicon channel. As a test substance passes through the silicon channel, particles of the test substance that are small enough to enter the pores experience longer transit times than larger particles, thus effecting separation.

One problem with many prior art cellular filter membranes is that the edges where a pore begins are sharp and cell membranes can rupture when fluid pressure and flow forces them against these edges. Micro-machined silicon membranes may comprise pores having rounded edges by initially etching, by standard techniques, at a larger diameter than the pore size and graduating the diameter down to the required size over a relatively short depth.

When the leading edge of a test substance first encounters a micromachined silicon membrane, surface tension and turbulence can impede the fluid entering and traversing the pores. Surface chemistry modifications may be required to increase the wettability of the pores and improve filter function. Similarly porous silicon particles that may initially be full of air need may have to be wetted with the eluant to ensure proper function. Chemically

modifying the internal as well as external surfaces of the pores by oxidation or other means to increase wettability may be essential for separation of aqueous solutions.

A further separation device, according to the present invention, may comprise a silicon sample interaction means comprising porous silicon, at least some of the pores of the porous silicon containing a porous gel and/or polymer. Such a gel and/or polymer may alter the retardation properties, with regard to a test substance, of the silicon sample interaction means.

Figure 1 shows a separation device, according to the present invention, generally indicated by 11. The device 11 comprises a multiplicity of channels 12, each channel containing porous silicon particles, the particles not being shown in figure 1. The device 1 1 further comprises an injection means 13, a multiplicity of channel junctions 14, and a number of detectors 15, each detector 15 being located at one end of one of the channels 12. In an alternative embodiment, detectors may be placed at the junctions 14.

Figure 2 shows part of a separation device generally indicated by 21 , according to the present invention, comprising a conical porous silicon filter 22 and a silicon channel 23 having a spiral groove 24. One common problem with prior art filters, especially those designed to separate biological cells and structures of different sizes, is clogging of pores by larger cells, with fluid pressure keeping the cells pressed against the membrane thereby blocking further flow through the filter. The groove 24, which has been formed in the silicon walls of the channel 23, may introduce turbulence to a fluid test substance that passes through the channel, thereby tending to prevent blockage of the conical porous silicon filter 22.

A combined diagnostic and separation device according to the present invention may comprise a series of porous silicon membranes, each membrane in the series progressively having smaller pore sizes such that fractions of a test substance are trapped in the inter-membrane spaces. Drains on the sides of these inter-membrane spaces may then direct these fractions to different parts of the device for further processing and/or analysis.

Intermittent or continuous mechanical vibration of filter porous silicon membranes may assist in dislodging components that are clogging pores. Vibration may be effected through incorporating piezo-electric elements into the membrane construction, using rapid thermal cycles to cause membrane support structures to vibrate or by using acoustic vibration as described below.

Sound waves generated by piezo-electric components or porous silicon thermal ultrasound transducers may be directed either at filter porous silicon membranes to cause mechanical vibration of the filter to counteract clogging or they may be directed at the fluid flow itself, to generate turbulence or to generate standing waves such that components of different densities are separated into different parts of the fluid flow.

The combined separation and diagnostic device, according to the present invention, may comprise a channel in which a multiplicity of photoluminescent porous silicon particles are located. A number of test substances may be passed through the channel, and interaction of the test substances with the porous silicon particles may result in separation of the substances. The porous silicon may be interrogated with ultraviolet light, and information about the test substance that is located at a particular location in the channel may be derived from the photoluminescence of the porous silicon.

Fabrication and operation of sensor arrays

(A) Fabrication of a silicon interaction means by ion implantation

A 0.1 ohm cm p- Si wafer may have its front face patterned by standard photolithographic techniques. The wafer having an HF resistant photoresist such as silicon carbide, silicon nitride, polycrystalline silicon on oxide, or SU-8 resist. The photoresist pattern may result in 1 cm ² squares each containing 1600 pixels, each pixel having a dimension of 200 microns by 200 microns and having a 50 micron wide masked border. The number of pixelated squares that may be formed on the surface of the wafer will depend upon the wafer size. Both faces of the entire wafer may then be subjected to boron ion implantation, at an energy in the range 20 to 500 KeV. The un-pattemed face may be subjected to a relatively high dose (1 x 10 ¹⁵ to 1 x 10 ¹⁶ cm ^"2 ) of unfocussed irradiation. The patterned face may be subjected to focussed, rastered ion beam implantation so that each pixel receives a different dose of boron within the range 1 x 10 ¹² to 1 x 10 ¹⁶ cm ^"2 . The implanted boron may

then be electrically activated by a rapid thermal anneal in the 950 to 1250 C temperature range resulting in a p+/p-/p+ wafer configuration with spatially varying resistivity on the patterned face.

The patterned face of the wafer may then be anodised in an HF solution, by a standard technique, employing a uniform current density across the surface of the wafer, Such anodisation will yield a variation of porosity and pore size with location on the surface of the wafer, Each pixel will have a different pore size and/or porosity from its neighbouring pixel or pixels. This variation in morphology, results from the dependence of the porosification process of the resistivity of each pixel. In this way a silicon sensor array may be fabricated having 1600 silicon sensors, each silicon sensor comprising a porous silicon element.

(B) Fabrication of a silicon interaction means by graded chemical etching

A further wafer may be patterned, by standard techniques, so that one face has a number of pixels formed on it, each pixel being a square of sides equal to 5mm. The wafer may be p-type and have a resistivity of 0.01 ohm cm. The patterned wafer may be subjected to anodisation, by a standard technique, in an HF based electrolyte so that a layer of porous silicon is formed from each pixel. The porosity may be between 25 and 55%. The wafer may then be suspended over a HF-based chemical leaching solution; the patterned surface may be perpendicular to the surface of the leaching solution. A stepping motor may then be employed to lower the wafer into and then out of the etching solution, the velocity of the wafer may be between 0.1 and 10 mm per minute. Once the wafer has been immersed and removed from the etching solution it may be rotated through 90 degrees about the axis of its circular cross-section, while maintaining the patterned surface perpendicular to the surface of the etching solution. It may then be lowered into and removed from the etching solution. In this way a silicon sensor array having silicon elements, each element having a different porosity to their neighbouring element or elements may be achieved as a result of the different etch time for each pixel. Porosities in the range 25 to 85 % may be achieved.

(C) Fabrication of a silicon interaction means by oriented electrode anodisation

A p-type silicon wafer having a resistivity of 0,01 ohm cm was front face patterned (for example a 10mm x 10mm step and repeat pattern). The wafer was then anodised in an HF based electrolyte using a structured platinum electrode in close proximity to the wafer surface. The cathode comprises a number of substantially planar cathode sections, each planar section corresponding to one of the 10 mm squares of the wafer. Figure 3 shows such a wafer square 31 and a planar cathode section 32. The footprint of each cathode section 32, on the wafer should approximately be the same area and location as each corresponding wafer square 31 ,

Each cathode section is electrically connected to the other cathode sections. The different distances between the cathode section 32 and the patterned wafer square 31 result in differences in current flow and in different parts of the wafer square being porosified in a different way. Each wafer square has been patterned to produce a multiplicity of silicon elements and porosification by this type of anodisation will result in the fabrication of an array of porous silicon elements, each element having a unique porous silicon properties. For example an element may have a different porosity to its neighbour, or it may have a different depth of porosification.

(D) Fabrication of porous silicon having improved photoluminescence quantum efficiency

A p-type silicon wafer having a resistivity between 1 and 10 ohm cm and having an aluminized back contact may be anodised in a single electrochemical cell such that a porosity of 40% to 70% and a thickness of 5 to 25 microns is achieved. The electrolyte employed for the anodisation may comprise equal volumes of ethanol and 50% wt HF, The anodised wafer may then be placed in a pressure vessel loaded with deionised water, and heated to 150 - 300 C for 1 - 3 hours. This heating causes the pressure to equilibrate in the range 1 to 5 MPa. After cooling to room temperature the wafer may be removed from the vessel. The passivation treatment yields high photoluminescence quantum efficiency porous silicon. Luminescence is in the range 600 to 900 nm with external quantum efficiency of up to 20%. This high pressure steam treatment is described by Gelloz et al in Appl. Phys. Lett. 87, 031107 (2005) which is incorporated by reference in its entirety.

(E) Fabrication of a silicon interaction means by electrochemical fabrication of a porous silicon region having variable depth

An anodic bias may be applied to a wafer during the filling and/or emptying of an electrolytic cell with an HF-based electrolyte. The wafer may be suspended vertically in a double cell anodisation kit in which the front reservoir of the cell is filled from the bottom up. Variation in transit time of the meniscus across the wafer surface, in the range 10 seconds to 10 minutes, is achieved by varying the pumping speed of peristaltic pumps used to circulate the HF solution. The anodic bias may be removed as soon as the cell is full of electrolyte. In this way a silicon interaction layer may be fabricated.

(F) Operation of an array of porous silicon optical sensors

An array of optical silicon sensors, each silicon sensor comprising photoluminescent porous silicon, may be of value in the analysis of a test substance. Each porous silicon sensor may have a different pore size distribution from its neighbour. Such difference in size distribution may result in the physical exclusion, from some of the pores, of biomolecules contained in the test substance.

A subset of the biomolecules contained in the test substance may induce quenching or peak shifting of visible photoluminescence, by the introduction of non-radiative processes.

The covalent attachment of a quencher molecule to an optical porous silicon sensor may result in quenching of the photoluminescence of the porous silicon. The interaction with a test substance, via partial wetting, chemical reaction with the quencher molecule, or corrosion of the silicon skeleton, may release the quencher molecule into solution, inducing the activation of visible photoluminescence. For example a gold nanoparticle may be peptide linked to the porous silicon.

Pholuminescence may be excited using an LED and/or an ultraviolet lamp. A silicon photodiode array may be employed to capture an image of the photoluminescecnt intensity produced by an array of porous silicon optical sensors. Mapping software algorithms, such as Principal Component Analysis may be used to compare those patterns obtained from different test substances.

A test substance to be analysed may be allowed to equilibriate with an array of porous silicon and may induce a colour change. The colour change may result from a change in optical constant from partial wetting of the porous silicon by the test substance, deposition of specific organic molecules from the test substance, corrosion of the silicon skeleton by the test substance, or a combination of these effects.

The resulting patterns of colour may be analysed using inexpensive digital camera technology. An artificial neural network with fuzzy logic may be trained to interpret the pattern from body fluids of healthy patients. The patterns derived from test substances may then be compared and significant deviations correlated with physiological conditions.