THORNTON, Catherine (Singleton Park, Swansea SA2 8PP, GB)
IGIC, Petar (Singleton Park, Swansea SA2 8PP, GB)
HOLLAND, Paul Michael (Singleton Park, Swansea SA2 8PP, GB)
THORNTON, Catherine (Singleton Park, Swansea SA2 8PP, GB)
IGIC, Petar (Singleton Park, Swansea SA2 8PP, GB)
1. A lab on a chip device including a microchip having a first and a second surface, the first surface having at least one opening in proximity to one or more electrodes on the first surface, with the at least one opening having a dielectric contained therein which forms a base of the opening, characterized in that the second surface has at least one channel that extends into the microchip such that a terminal wall of the at least one channel abuts against the base of the at least one opening, the channel forming an optical passage extending into the microchip such that a sample placed on the first surface and extending over the at least one opening can be viewed through said optical passage.
2. A lab on a chip device according to claim 1 , wherein the area where the terminal wall of a channel in the second surface abuts an opening in the first service provides an optical window through the microchip.
3. A lab on a chip device according to claim 1 or claim 2, wherein the side walls of the opening in the upper surface are substantially parallel to one another.
4. A lab on a chip according to any preceding claim wherein the side walls of the channel in the lower surface are angled to one another with the channel being wider at the lower surface of the microchip than at the base of the opening in the upper surface.
5. A lab on a chip according to any preceding claim wherein the side walls of the opening include an anti-reflective coating on the surfaces of said side walls.
6. A lab on a chip device according to any preceding claim wherein the microchip if formed of a substrate that is predominantly silicon based.
7. A lab on a chip according to any preceding claim wherein the microchip has a chamber attached to the surface of the chip to receive a sample.
8. A lab on a chip according to claim 6, wherein the chamber a microchamber.
9. A lab on a chip according to any preceding claim wherein the electrodes and openings containing the dielectric in the first surface are in an array.
10. A lab on a chip according to any of claims 1 to 7 wherein an electrode extends around the periphery of an opening containing the dielectric.
1 1 . A bioanalytical system including circuitry connected to a lab on a chip according to any preceding claim.
12. A method of making a lab on a chip microchip having a first and a second surface, wherein an opening is formed in the first surface of the chip and filled with a dielectric material, at least two electrodes are formed adjacent the opening characterized in that a channel is formed in the second surface and aligned with the opening thereby providing an optical passage extending into the microchip.
FIELD OF INVENTION
The present invention relates to a Lab on a Chip (LOAC) device and in particular but not exclusively to a LOAC device used as a bioanalytical device with optical transparent characteristics.
BACKGROUND TO THE INVENTION
The following discussion of the background to the invention is intended to facilitate an understanding of the present invention. However, it should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was published, known or part of the common general knowledge in any jurisdiction as at the priority date of the application.
Advances in the semiconductor industry have led to the development of new microchip processing technologies that have allowed the continued miniaturisation of electronic and mechanical devices. Photolithography and chemical etching techniques have enabled the fabrication of miniaturised and self contained chemical analysis systems formed on microchips and such systems are termed Micro Total Analysis Systems (pTASs). Much of the research on pTASs initially focused on creating channels in the substrates on microchips where micro-fluidic chemical or biological samples could be manipulated using capillary electrophoresis in a controlled manner.
The ability to fabricate micron scale 2-dimensional arrays of sensors on silicon or glass substrates using photolithography or printing techniques enabled the invention of the DNA Microarray. This was used initially for genomics research and utilised a chip substrate surface modified to anchor the complementary reporter oligonucleotides in place. Whilst many Microarrays are passive and the biological information of interest is typically collected externally by fluorescence or chemiluminescence techniques, the term Lab-On-A-Chip (LOAC) evolved to describe
l systems where increased functionality was integrated into the chip. This included components from the developing area of MicroElectroMechanical Systems (MEMS) such as micro-pumps or valves used for micro-fluidic control and various sensor technologies.
LOAC devices can allow biological investigation at the single cell or sub-cellular level. Such a chip would require the ability to sort cells by type, separate them and deliver them in a controlled manner to an experimental micro-site for experimentation and analytical investigation. Whilst well known cell sorting techniques that are suitable for chip integration such as fluorescence and magnetic activated cell sorting (FACS and MACS) are effective, they suffer from the general requirement to modify the cells by staining with dyes or antibodies and hence increase the complexity of the experimentation and analysis tools.
The present invention seeks to overcome the problems associated with the prior art by providing a portable, standardized, cost effective and rapid system for analyzing biological samples.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a lab on a chip device including a microchip having a first and a second surface, the first surface having at least one opening in proximity to one or more electrodes on the first surface, with the at least one opening having a dielectric contained therein which forms a base of the opening, characterized in that the second surface has at least one channel that extends into the microchip such that a terminal wall of the at least one channel abuts against the base of the at least one opening, the channel forming an optical passage extending into the microchip such that a sample placed on the first surface and extending over the at least one opening can be viewed through said optical passage. It is envisaged that the area where the terminal wall of a channel in the second surface abuts an opening in the first service provides an optical window through the microchip.
Preferably the sides of the opening in the upper surface are substantially parallel to one another.
It is preferred that the sides of the channel in the lower surface are angled to one another with the channel being wider at the lower surface of the microchip than at the base of the opening in the upper surface.
Preferably the microchip if formed of a substrate that is predominantly silicon based.
It is preferred that the microchip has a chamber attached to the surface of the chip to receive a sample.
Preferably the chamber is in the form of a microchamber.
It is envisaged that the electrodes and openings containing the dielectric in the first surface are formed in an array.
Alternatively am electrode extends around the periphery of an opening containing the dielectric.
According to a second aspect of the invention there is provided a method of making a lab on a chip microchip having a first and a second surface, wherein an opening is formed in the first surface of the chip and filled with a dielectric material, at least two electrodes are formed adjacent the opening characterized in that a channel is formed in the second surface and aligned with the opening thereby providing an optical passage extending into the microchip.
It can be seen that the present invention provides a robust technology platform that combines the advantages of a transparent substrate for 'top down' AFM (and other) probing with 'bottom up' epi-fluorescence and other microscopy techniques whilst maintaining a silicon substrate for on-chip' functionality would allow untold possibilities for highly advanced biological experimentation using multiple analytical tools.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment of the invention will now be described by way of example only with reference to and as illustrated in the accompanying figures, in which:
Figure 1 : shows a cross section of a device according to an embodiment of the invention;
Figure 2: shows a sequence of steps in the manufacture of a device according to an embodiment of the invention
Figure 3: shows a plan view of possible optical layouts for a device according to an embodiment of the invention; and
Figure 4: shows a schematic drawing of a LOAC according to an embodiment of the invention having metal electrode connections, Si0 2 top trench fill and micro-fluidic chamber.
Other arrangements of the invention are possible and, consequently, the accompanying drawings are not to be understood as superseding the generality of the preceding description of the invention.
DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION
A microchip that provides the LOAC device according to the present invention is generally shown as 1 in Figure 1. Figure 1 shows the cross-sectional view of the microchip, which in this case is provided in the form of a silicon wafer. The microchip has an upper surface 2 and a lower surface 3. The upper surface 2 has at least one opening 4 which extends into the microchip and the opening has side walls 41 and a base 42 extending between the side walls and which forms the bottom of the opening or trench. The side walls 41 are substantially perpendicular to the base 42. The opening can be filled with a dielectric such as silicon dioxide. The channel extends a small finite distance through the thickness of the microchip. A typical distance would be l Omicrons. . The walls of the opening have a coating 43 which is an antireflective coating that can reflect light passing through the LOAC and optimize light transmission so samples on the chip can be seen as clearly as possible. The lower surface has a channel 5 in the lower surface 3 of the microchip. The channel has side walls 51 which are angled so that the mouth of the channel which is at the surface 3 of the microchip is larger than the end wall 52 of the channel which meets the base 42 of the opening 4. The base 42 and end wall 52 meet and form a dividing wall between the opening and channel.
The opening 4 is aligned with the channel 5. The channel and/or the opening are formed by aligned etching from the top to the bottom of the wafer. The opening is filed with a dielectric. However, the channel allows for an optically transparent path from the bottom of the wafer to the top. The channel will allow the aspirations of cell separation and manipulation on the top surface of the microchip using techniques such as dielectrophoresis. The microchip can include or be connected to integrated control circuitry. The use of an integrated LOAC which has an optical path that can pass through the chip allows for the combined AFM and optical technique investigation from the top and bottom of the wafer simultaneously.
Identifying cells and manipulating position by using electrical field based techniques such as electrophoresis and dielectrophoresis is highly suitable for LOAC as the cell requires no pre-treatment and suffers minimal physical interaction during the cell separation and delivery to the experimental micro-site. As most cells are electrically neutral, dielectrophoresis (DEP) can be utilised to good effect. DEP is a phenomenon where a physical force is exerted on a neutrally charged particle that is placed in a spatially non-uniform electrical field. In the case of a cell located in a liquid medium then the cell may move towards an increasing field strength, positive DEP (pDEP) or alternatively towards a decreasing negative field negative DEP (nDEP) depending upon the physical properties of the cell and medium, and epi- fluorescence microscopy from underneath.
The microchip may be a CMOS technology silicon microchip having an array of channels (for example a 300x300 array) and software is used to control actuation electrodes allowing DEP control of up to 9000 living cells. The chip has actuator control electronics integrated into it, together with: memory and photodiodes to detect micro-site cell occupancy. This technology allows for the ability to control the co- localisation of two different cells for studies relating to cell interactions.
Alternatively microbeads can be used which are coated with known antibodies or other cell stimuli and these microbeads can be manipulated using DEP forces to develop analyze cell function in health and disease.
Figure 2 shows a cross-sectional view of the proposed core processing steps that will be used to fabricate the initial concept structure and the steps are numbered 2.1 to 2.6 The techniques used in the manufacture of the microchips include e-beam and Mine photolithography, plasma resist strip, chemical cleans, Plasma Enhanced Chemical Vapour Deposition (PECVD) , silicon plasma etch and Deep Re-active Ion Etch (DRIE). The process has been designed to be completely compatible with an industrial CMOS process to allow full chip integration in future projects and technology transfer work.
Firstly, as shown in diagram 2.1, openings 4 are etched into the upper surface 2 of the microchip 1. The positioning of the openings can be controlled using software that controls etching devices such as an e-beam tool. The mask that is used to locate the openings is based on the requirements for position of the cells and for the investigative techniques used to analyze them. Once etched, the openings are filled with a dielectric 6 such as SiO 2 by techniques including as Chemical Vapour Deposition or Spin-On-Glass. The thickness of the S1O2 windows will only be in the order of several microns and therefore transmission should be extremely high across the visible and UV spectrum of interest regardless of deposition morphology. Once the openings 4 have been etched on the upper surface of the microchip, and filed with dielectric, metal is deposited on the surface of the microchip and areas are again etched to leave discrete areas of metal 7 that will provide the location of the circuitry on the chip and this is shown in diagram 2.2. A further dielectric layer 8 of S1O2 is put down and there is further etching to form recesses 9 which sit over the areas of metal 7 and this is shown in diagram 2.3 As shown in diagram 2.4, electrodes 10 are connected to the discrete areas of metal. The electrodes form a contact area on the chip. This etching again uses a mask to form areas where metal that will form electrodes is deposited. As shown in diagram 2.5, channels 11 are etched in the lower surface of the microchip, which align with the openings 4 in the upper surface. A further dielectric layer 12 is formed on the upper surface of the microchip as shown in diagram 2.6. A microfluidic chamber 13 is then formed over the dielectric, preferably using a commonly used photo-resist process such as SU8 to produce structures such as microfluidic chambers requiring high aspects ratios and micro-fluidic device containment.
Using etching with the facility to have integrated circuitry means that the LOAC structure of the present invention will be easy to manufacture. The silicon substrate will have etched holes or windows in a continuous honeycomb like structure and as such will have good mechanical stability.
Figures 3a and 3b show the arrays that can be used. Figure 3a shows a hexagonal electrode array with electrodes 10 and optical window 11 whilst Figure 3b places the etched windows inside the metal electrode. It is envisaged that other arrangements could be used for optimal control of the cells.
Typically an array of optical windows and electrodes will be used as such arrays are useful for the manipulation of T cells. The metal interconnects are connected to bond pads outside the area of the array. The devices are attached to a surface such as a transparent glass substrate by bonding agents that are selected so as not to obstruct optical pathways. Typically epoxy resins are used. Conductive wires such as gold wire bonds will electrically connect the chip to the substrate or package. Separate or integrated electronic controller circuitry will be used to connect to the package and subsequently control the voltage and frequency to each electrode allowing experimentation on cell separation and positioning
Figure 4 shows use of a device according to an embodiment of the invention. An atomic force microscope 14 is positioned above the microfluidic chamber 13 that is positioned on the microchip 1. The microfluidic chamber 13 holds a sample in solution, which may be an aqueous solution, and in this case the sample is a T-cell suspension 16 in liquid medium. Fluorescence signals 17 are transmitted through the medium and the S1O2 layer 12 on the microchip. Metal electrodes 10 are used for DEP positioning. It is possible to position cells above the metal electrodes used for dielectrophoretic control but a transparent window is required beneath the cell for investigation by microscopy and spectroscopy.
The electrode shape, size and position relative to the T cell in addition to the voltage, frequency and the liquid medium used for suspension of the cell in the microfluidic chamber have an effect on the positioning of the cells on the LOAC.
A Perkin Elmer spectrophotometer will be used to measure the transmission spectrum between 200nm - 2500nm and the microscope objective is shown as 15. Of particular interest is the wavelength range between 400nm and 1000nm that contains the various laser excitation and emission wavelengths of the fluorophores typically used for biological investigation. S1O2 can exist in several forms such as Silica or Quartz with varying optical transmission characteristics.
The use of a Complementary Metal Oxide Semiconductor (CMOS) compatible process to fabricate the new LOAC structure enables scope for future On chip' integration of analytical techniques combined with the processing power of integrated silicon chip technology. This invention provides a novel technology platform that can be developed with future innovations leading to new tools and thereby better understanding of the immunological response that underpins many disease states including allergy, diabetes and cancer.
The term "chip" or "microchip" or "microfluidic chip" as used herein means a microfluidic device generally containing a multitude of microchannels and chambers that may or may not be interconnected with one another. Typically, such biochips include a multitude of active or passive components such as microchannels, microvalves, micropumps, biosensors, ports, flow conduits, filters, fluidic interconnections, electrical interconnections, microelectrodes and related control systems.
Throughout this document, unless otherwise indicated to the contrary, the terms "comprising", "consisting of, and the like, are to be construed as non-exhaustive, or in other words, as meaning "including, but not limited to".
It should be noted that the above mentioned embodiments illustrate rather than limits the invention and that alterations or modifications are possible without departing from the scope of the invention as described. It is also to be noted that the invention covers not only individual embodiments but also combinations of any of the embodiments as described.