The invention relates to a system for the detection and/or measurement of the optical absorption and/or fluorescence of a fluid sample.

Background of the Invention

Optical techniques are important in fluid characterization. The properties that are normally characterized are optical absorption, fluorescence, scattering, reflectance, polarisation, for example linear or circular polarisation, and refractive index. Such characterization is used in diagnostic processes in many fields: medicine, as an aid to the diagnosis of diseases; food processing, as an aid to quality control and counterfeit detection; and industrial quality control, as an aid to ensure production consistency. Other fields include forensic applications and contaminant detection.

Current optical fluid analysis can be performed on the fluids as they are or by looking at changes thereof. Such changes can be either spontaneous or induced by one or more chemical reactions, including exposure to air or induced by temperature. Such analysis can either be performed by detection (the fluid exhibits / does not exhibit a certain property) or by measurement (how large is the property? How much does the property change? How fast, or according to what time dependence, does the property change?). The measurement can be absolute or relative.

Instruments for performing optical fluid analysis can be self-contained with, for example, an on-board processor for providing a test result. Alternatively, they may be externally connected to a computer. The fluid under examination is typically contained in a measurement device. Disposable devices are often used for in-field applications. These typically rely on fluidic channels manufactured by micro-fabrication. When fluidic channels are used, the sample is generally applied to an inlet channel using an external sampling device. If needed, reagents are stored in separate reservoirs, whether integrated, on disposables, or external.

Summary of the Invention

According to the present invention, there is provided a system for detecting and/or measuring an optical property of a fluid sample, the system comprising a porous material that draws fluid into itself and defines a sample collection and test region; at least one optical source for illuminating the test region and at least one optical detector for detecting light from

i the test region, wherein the porous material and at least one of the source and detector are integrally formed.

The optical property may be absorption and/or fluorescence and/or refractive index and/or optical scattering and/or reflectance and/or polarisation, for example linear or circular polarisation. Light from the region may be one or more of: light through the region; light coming back or reflected from the region; light generated in the region.

By using a porous material to draw fluid into a sample region, there is provided a very simple device in which a sample can be analysed without requiring microfluidic channels and/or pumps for driving fluid into a test area, thereby avoiding the need for complex micro- fabrication techniques. This means that the device can be mass-produced relatively cheaply.

The porous material may be such that the sample is drawn into the region by capillary action.

The at least one optical source and/or at least one optical detector may be attached to the porous material and/or region.

The porous material may contain one or more reagents.

The at least one optical source and/or the at least one optical detector may contain one or more organic/inorganic semiconductor materials.

The at least one optical source may be selected from: an inorganic light emitting diode, an organic light emitting diode, an inorganic superluminescent diode, an inorganic device emitting by amplified spontaneous emission, an inorganic device emitting by amplified spontaneous emission, a lamp, a chemiluminescent material, an inorganic laser and an organic laser.

The at least one optical detector may be selected from: an inorganic photodiode, an organic photodiode, an inorganic photocell, an organic photocell, an inorganic photoresistor, an organic photoresistor, an inorganic charge injection device, an organic charge injection device, an inorganic charge coupled device, an organic charge coupled device, an inorganic FET or CMOS based detector, an organic FET or CMOS based detector, a photomultiplier, an avalanche detector, a vidicon, a thermally sensitive photodetector. The at least one optical source and/or at least one detector may emit / be responsive to a selected wavelength. The at least one optical source and/or at least one detector may emit / be responsive to a selected polarisation, for example a linear or circular polarisation.

The least one optical source may emit light at a plurality of different wavelengths. The at least one source may comprise multiple emitters. The multiple emitters may emit light at a plurality of different wavelengths.

The at least one optical source may emit light continuously. The at least one optical source may emit pulsed light. The at least one optical source may emit light that varies in time with a predetermined temporal behaviour.

The system may include means to determine if the sample has filled the porous region to such an extent to allow the measurement or detection.

The optical property measured and/or detected may be at least one of absorption and/or fluorescence and/or refractive index and/or optical scattering and/or reflectance and/or polarisation, for example linear or circular polarisation.

The system may include a power supply for supplying power to the at least one source and/or at least one detector.

The system may include a processor for controlling at least one source and/or analysing an output from the at least one detector. The processor may be operable to provide one or more test results.

Means may be provided for varying a spatial emission pattern of the at least one source and/or the spatial sensitivity of at least one detector.

The porous material and at least one of the source and detector may be part of a removable insert for inclusion in a tester device.

The porous material may be in the form of a layer or sheet. The porous material may be sandwiched between two layers of materials, preferably two layers of transparent material. At least part of the porous material may be exposed so that fluid under test can be applied to it. At least one edge or surface or side portion of the porous material may be exposed.

According to another aspect of the invention there is provided insert for use in the system of the first aspect of the invention, the insert comprising a porous material for drawing fluid into itself, the porous material defining a sample collection and test region, and at least one of an optical source for illuminating the test region and an optical detector for detecting light from the test region.

The porous material and at least one of the optical source and the optical detector may be in the form of sheet or layer or sheets or layers. The porous material may be sandwiched between two layers of materials, preferably two layers of transparent material.

At least part of the porous material may be exposed so that fluid under test can be applied to it. At least one edge or surface or side portion of the porous material may be exposed.

A power source may be provided for the source and/or detector. Equally, a processor for processing signals received at the detector may be provided for processing signals received at the detector.

Brief Description of the Drawings

Various aspects of the invention will now be described by way of example only with reference to the accompanying drawings, of which:

Figure 1 is a block diagram of a first optical test device; Figure 2 is a block diagram of a second optical test device, and

Figure 3 is a block diagram of a third optical test device.

Detailed Description of the Drawings

Figure 1 shows an optical test device 10 that has a porous paper layer 12 between an organic light emitting diode (OLED) 14 and an organic photodiode (OPD) 16. The OLED 14 and the OPD 16 are each formed as thin layers of roughly equal size, and similar area to that of the paper layer 12. Descriptions of suitable OLEDs and OPDs can be easily found in the literature. The three layers 12, 14 and 16 are attached so that they constitute a single layered device 10, the parts forming a single integral device, with the porous material 12 between the OLED 14 and OPD 16 defining a sample collection and test area, with at least one side of the porous material being exposed. Attachment of the three layers can be done by glue, ultrasonic bonding, thermal treatment, or the paper 12 can be passivated on its sides using an inert transparent material, such as plastic sheet or glass, and the devices 14,16 fabricated directly on the passivation layer. The device 10 can be made at low cost and so can be treated as a single use, disposable device.

Dispersed in the porous paper layer 12 is a reagent or combination thereof. In one example, the reagent may tint a biological fluid in the presence of a particular substance. If the emission wavelength of the OLED14 is appropriately chosen, when the OLED 14 emits light, the amount of light detected by the detector 16 depends on the tinting on the fluid and so the presence or otherwise of the particular substance. Alternatively, the reagent may alter its fluorescence in the presence of a substance in the biological fluid or render the biological fluid appropriately fluorescent in presence of such substance. When the fluorescent material is exposed to the light emitted by the OLED 14, it causes a fluorescent emission, which can be detected by the detector 16. In this case, the detector should be sensitive to the fluoresced light and not the light from the OLED 14, and so the OLED 14 should be selected to emit at a wavelength to which 16 is not sensitive. Examples of reagents for detecting substances in specific fluids by tinting or by fluorescence are well known.

Fluid 20 is applied to any exposed side of the porous layer 12. The porous layer 12 is such that it draws the sample fluid into the region between the OLED 14 and the photodiode 16, where it can be tested. During testing, the OLED 14 is switched on and the light emitted passes through the layer 12 and reaches the OPD 16. Data from the OPD 16 is passed to a measurement device 18, preferably handheld, which processes and displays the signal / result of the test. Measurement devices of this nature are well known in the art. The processing depends on the nature of the optical test being done.

Figure 2 shows another optical test and measurement device 22. In this case, a disposable test insert 24 is used. This has a layer of porous material 25, for example compressed chalk powder, between two layers 27 and 28. Layer 27 is transparent, while layer 28 is an OLED, transparent over a range of wavelengths. Again, a description of such OLEDs can be commonly found in the literature. The three layers 25, 27 and 28 are attached so that they constitute a single integral device 10, with at least one side of the porous material 25 being exposed. The porous material may be sandwiched between the transparent layer 27 and the OLED 28 or formed as an integral part thereof as part of the manufacturing process. The transparent layer 27 and the OLED 28 are substantially the same size as the porous layer, although a small lip 26 of porous material is exposed and extends beyond the end of the insert to facilitate application of the fluid. The porous material 25 between the transparent layer 27 and the OLED 28 defines a sample collection and test area. As before, dispersed in the porous layer 25 is a reagent that can react in some way with the biological fluid, for example, to detect another substance. As a specific example, it will be assumed that the reagent changes colour in the presence of the substance of interest.

The insert 24 is fitted into a readout head 30 containing two inorganic light emitting diodes (LEDs) 32, 34 and an inorganic photodiode 36. A first one of the light emitting diodes 32 has an emission wavelength that exhibits a high difference in optical absorption between the two different colours the layer 25 can take. Likewise, the OLED 28 has an emission wavelength that exhibits a high difference in optical absorption between the two different colours. The second LED 34 has an emission wavelength that exhibits a low difference in optical absorption between the two different colours the layer 25 can take. The emission wavelengths of the first and second LEDs 32 and 34 are also chosen to be within the transparency range of the OLED 28. As before, the device is used in conjunction with a measurement device 40, preferably handheld, that powers the LEDs, and processes and displays the signal / result of the test based on data from the photodiode 36.

Fluid 42 is applied to the lip 26 of the porous layer 25 and is drawn by the material into the region between the transparent layers 27, 28. Ideally, the porous layer 25 is such as to draw the fluid in to such an extent that a sufficient area for carrying out the test is covered. In some cases, the material is such that most of its surface area is covered. This maximises the sample test region. In absence of the substance, the colour of the layer soaked with fluid, and therefore the optical transmittance of such layer at a selected wavelength, differs from the colour (transmittance) in presence of the substance. The first LED 32, whose emission wavelength exhibits a high difference in optical absorption between the two different colours the layer can take, is switched on. The light emitted by the first LED 32 passes through the layer, and reaches the photodiode where it is detected. Because of the colour difference of the porous layer, the photodiode 36 detects a different light intensity in the presence and in the absence of the substance. Similarly, the OLED 28, whose emission wavelength exhibits a high difference in optical absorption between the two different colours the layer can take, is switched on. The light emitted by the OLED 28 passes through the layers 26 and 27, and reaches the photodiode where it is detected. Because of the colour difference of the porous layer, the photodiode 36 detects again a different light intensity in the presence and in the absence of the substance. The second LED 34, whose emission wavelength is chosen to exhibit a low difference in optical absorption between the two different colours the layer can take, is then switched on. The light emitted by the second LED 34 passes through the layer, and reaches the detector. Because of the low sensitivity to the colour difference of the porous layer, the detected light intensity does not depend on the presence or absence of the substance. This allows a calibration of the transmission of the device, thus permitting a comparison with the light detected coming from the first LED 32 and/or from the OLED 28, and subsequent measurement of transmission of the sample. It also allows confirmation that the sample has filled the porous region to such an extent as to allow the system to work because the transmission of the porous region of the sample will change when the sample is drawn into it.

Alternative measurement and/or detection methods that rely on the geometry in Figure 2, may require calculations on the signals detected as a response to the light emitted by 32 and 34, such as, for example, taking the ratio, the product, the sum or the difference between such signals. By appropriately choosing the emission wavelength of at least one of the first LED 32, the second LED 34 and the OLED 28 with respect to the wavelength sensitivity of the photodiode 36, whether by an appropriate choice of the devices and/or by interposition of optical filters, fluorescence may be measured or detected alongside or as an alternative to optical absorption.

Alternatively or additionally, where the LEDs 32 and 34 and the OLED 28 emit polarised light, for example linearly or circularly polarised light, with respect to the polarisation sensitivity of the photodiode 36, whether by an appropriate choice of the devices and/or by interposition of optical filters, polarisation may be measured or detected alongside or as an alternative to optical absorption and/or fluorescence. The same operating principles can be applied by integrating sources 32, 34 and /or detector 36 into the insert 24. In this case devices 32, 34 or 36 can use organic or inorganic semiconductors.

The porous material of the devices of Figures 1 and 2 draws fluid into it without the need for measures to enhance the capillary action (such as a pump or porosity gradient) so as to substantially fill a sample test and collection region. To test whether a porous material is appropriate for use in these devices, any standard porosity test could be applied. For example, a liquid, representative of the sample composition, may be put in an open vessel and a strip of a candidate porous medium immersed vertically in the liquid. The liquid should be drawn by capillarity into the medium to a pre-determined height, for example at least 0.5 mm, above the surface of the liquid remaining in the vessel. Additionally or alternatively, a strip of the material may be exposed to a gas. In the event that within a set time, for example 100 seconds, the gas has permeated at least a set amount, for example 10% of the medium cavities, the material may be used.

Alternatively, the porous material may be manufactured using a material that contains a plurality of cavities or channels, filling the whole region and guaranteeing that they can draw the fluid into the region by a combination of appropriate wetting properties and appropriate geometry. For example, this can be done by specifying that a given amount (for example 50%) of such cavities or channels have a volume comprised between given limits (for example 0.001 and 0.5 mm ³ ) and that the contact angle between the fluid and the material constituting the porous region does not exceed a given value (for example, 89.5 degrees). In any event, the porosity of the material has to be such as to effectively draw fluid into the region between the optical emitter and detector.

Figure 3 shows yet another optical test device. This has an insert 44 that has a layer of porous material 49, for example compressed chalk powder, between layers 47 and 48, the layers 47, 48 and 49 being attached so as to form a integral unit, with at least one side of the porous material 49 being exposed. Layer 47 is transparent, while layer 48 comprises a region 45 that behaves dually as OLED and as an optical photodiode OPD, transparent on a given number of wavelengths. A description of such mixed-mode OLEDs/OPDs can be found in the article by A.K. Pandey and J. M . Nunzi in Advanced Materials, volume 19, page 3613 (2007). An emitter 46 and a detector 48 are located on either side of the insert 44.

The emitter and detector 46, 48 and the region 45 have multiple emitting and sensing areas, according to a preconfigured geometry, such as, for example, pixel arrays, or areas with different shapes, each area optionally emitting and/or sensing on a wavelength range independent from the other areas. An advantage of this is that a pre-determined spatial emission and/or sensitivity pattern can be defined. A further advantage is that region 45, being transparent only on a number of wavelengths, can optionally act as optical filter. Alternatively, where the emitting and/or sensing areas can be selectively enabled or controlled, the devices can be spatially selective. In another possible embodiment, the optical devices 46, 48, 45 may each have independently emitting and detecting areas. In this case, reflectance, backscattering, and/or back-detected fluorescence may also be measured (light paths 50 and/or 52).

The device of the present invention can be used to test numerous substances, where "substance" is intended in its broadest meaning of single chemical species, or mixture of chemical species, or of subcomponent (live or dead cells, specific cellular membranes and/or nuclei and/or other cellular components), dispersed particles of a specific type, etc. In particular, it can be used to aid the detection of a human, animal or vegetal disease; contaminants; anomalies in the manufacturing or processing of a sample; variations in the manufacturing or processing of a sample; fraudulent manufacturing or processing of the sample; erroneous or false declarations over the nature or composition of the sample, etc. The device can be handheld / portable and so is suitable for many different applications.

A skilled person will appreciate that variations of the disclosed arrangements are possible without departing from the invention. For example, although organic and inorganic LEDs and photodiodes are described, any suitable detector could be used, such as a photocell, a photoresistor, a charge injection device, a charge coupled device, a CMOS based detector, a photomultiplier, an avalanche detector, a thermally sensitive optical detector. Equally, a chemiluminescent reagent could be dispersed in the porous layer, the chemiluminescent reagent being such that on contact with a particular fluid the reagent emits light. Accordingly, the above description of the specific embodiment is made by way of example only and not for the purposes of limitation. It will be clear to the skilled person that minor modifications may be made without significant changes to the operation described.