WO2015001286A1

WO2015001286A1 - Biosensor

Info

Publication number: WO2015001286A1
Application number: PCT/GB2014/000260
Authority: WO
Inventors: Owen GUY
Original assignee: Swansea University
Current assignee: Swansea University
Priority date: 2013-07-01
Filing date: 2014-06-27
Publication date: 2015-01-08
Anticipated expiration: 2016-01-01
Also published as: GB201311760D0; GB201601669D0; GB2530700A

Abstract

A sensor (1) is formed of a graphene or silicon based nanostructure (10) having a flow path (21) which may be a channel or nanowire. The flow path is functionalised to attract certain molecules. The flow path has contacts (22) at either and the loading of the functionalised flow path alters the charge on that path and gives a measurement of the molecules. The sensor can provide a particularly sensitive device which can monitor a number of biomolecules in real-time, and in particular molecules associated with stress.

Description

Biosensor

Field of the invention

The present disclosure relates to a biosensor which is functionalised and in particular but not exclusively the biosensor is used to monitor hormones, and in particular those related to stress.

Background of the invention

Sensors for detecting biological molecules, termed biosensors, are widely used. A large variety of biosensors have been developed for sensing or detecting biological molecules (organic molecules produced by or occurring in organisms) with increasing resolution and specificity. The term biological molecules includes, but is not limited to polymeric molecules occurring in nature and their analogues, such as proteins, polysaccharides, and nucleic acids as well as small molecules such as primary metabolites, secondary metabolites, and natural products.

Many biosensors rely on the general principle of generating an electrical signal if the presence or absence of a biological molecule is detected. Structured semiconductor materials are in some cases used to form channels or other structures at the micrometer scale (micro-scale) or nanometer scale (nano-scale).

Sensors that include graphene have been used. Graphene is a planar sheet of carbon atoms forming a honey-comb shaped crystal lattice and has gained increasing interests for its electronic properties. However graphene is generally not the preferred choice of material for biological applications because of its low affinity for biological monitoring. Structures that are similar to graphene have also been used, such as carbon nanotubes, graphite and fullerenes but again there are biocompatibility issues which are based on the physical properties including the shape or length of structures such as nanotubes.

To deal with biocompatibility issues or for applications in sensors, surfaces of material such as graphene are chemically modified or functionalised but to date known processes have only been able to detect material such as molecule/markers in the body which are at larger concentrations i.e. above nano molar concentrations. A particular area where the detection of biological molecules in the body is important is the area of stress analysis. The chemicals associated with stress in the body are very particular to an individual. Cortisol (a steroid hormone produced by the adrenal glands in response to stress) is elevated in the body and increased levels are related to increased risk of heart disease and high blood pressure. Similarly low levels of steroids in the body can be problematical too. Cortisol levels in saliva, are normally between 3 nM and 27 nM, and can be significantly higher in stress suffers. However, what is an elevated level for one individual may be quite normal and not potentially detrimental to health for another individual. Stress costs the UK economy £26bn and affects many people's quality of life. To date, sensors have involved taking a sample in a hospital or medical practitioner environment and then having the sample analysed either as an individual test or by sending off the sample to be analysed in a laboratory. The taking of the sample can lead to increased stress and also if the sample is not analysed immediately the levels of markers in the sample, can decay, leading to a false indication of the true levels of indicators for the individual from whom the sample is taken. The usefulness of the results of sample analysis being available significantly after the individual performing the test is also an issue. Ideally, test results should be available immediately after taking a stress test to get a meaningful picture of the condition of an individual at a point in time. Also, currently there is no means for analysing stress levels for an individual and determining whether this is a normal level for that individual or whether it is an aberration from what is normal and so potential detrimental to health. In particular there are no means of monitoring stress in real time over a particular time period so that trends in stress levels can be evaluated.

The present invention seeks to overcome the problems of the prior art by providing a very sensitive biosensor that can operate if required in real time to give a selective measurement of the amount or concentration of biological molecules in the body. In addition the invention provides a way of determining anomalies in the levels of chemicals in the body and so gives an early indication of potential health risks.

Summary of the invention

According to a first aspect of the invention there is provided a sensor for detecting the presence of at least one biological molecule, the sensor comprising: - a flow path

- at least two electric contacts arranged in contact with the flow path for determining a conductivity of a sample material including said at least one biological molecule in said flow path; and

- at least one linker attached to at least a portion of the flow path, wherein the at least one linker has a binding affinity for the at least one biological molecule, said biological molecule being associated with stress in the body.

Preferably, the flow path is provided by a graphene body having a surface with a channel etched in said surface to form the flow path.

Alternatively, it is envisaged that the flow path is a silicon nanowire that is used as the conductive sensor channel for the substrate material. The silicon nanowire can carry a current that is use to detect the sample material in the flow path.

It is preferred that the graphene body is arranged on a non conductive surface. Such non conductive substrates include materials based on silicon such as silicon dioxide, silicon nitride, silicon carbide or polymers such as Polydimethylsiloxane (PDMS).

In a preferred arrangement the at least two electrical contacts are arranged at opposite ends of the flow path.

It may be that the sensor has at least three electrical contacts.

It is envisaged that in one arrangement two contacts are arranged at opposite ends of the flow path, and a third contact is arranged either in a lateral position relative to the flow path forming a lateral transistor structure or the third contact is on the back of the substrate so providing a field path or back-gate transistor structure.

It is envisaged that a further electrical contact which acts as a reference electrode, counter or auxiliary electrode. Preferably, the further contact is incorporated onto the same wafer as the sensor device or is fabricated on a separate substrate.

It is envisaged that the contacts are produced on the substrate by lithographically or by printing, e.g. 3D printing.

It is envisaged that the at least one linker includes an amine group or a carboxy group.

It is anticipated that the at least one linker may be a linker molecule or a group of molecules. The at least one linker may comprise at least one of an aniline, a diazonium ion or diazonium salt, APTES (3-Aminopropyl)triethoxysilane (APTES), or other amine or carboxy terminated moiety compounds and a sensing molecule.

Preferably the at least one linker is selected from one or more of a receptor molecule, an amino acid, an enzyme, an antibody for the at least one biological molecule.

The sensing molecule may be at least one of a biomarker, a receptor, an amino acid, an enzyme, or an antibody for the at least one biological molecule

Preferably the at least on linker is a receptor for a biological molecule associated with stress in the body.

It is preferred that the receptor is an antibody bioreceptor for Cortisol. Binding of Cortisol to its complementary antibody, produces a detectable electrical change in the flow channel formed of nano wires or nanochannels.

It is envisaged that the stress associated biological molecule is one or more of Cortisol, Serotonin, Adrenaline, Nor-adrenaline, Dopamine, Human Growth Hormone (HgH), Oxytocin, Melatonin or, Dehydroepiandrosterone (DHEA). It is envisaged that the sensor may be a multichannel sensor having one or more flow paths, each being able to carry a separate sample material and each having a linker for a specified biological molecule.

It is preferred that the flow paths are arranged in pairs, with one of the pair of flow paths providing a control and the other flow path of the pair being arranged to monitor a sample material from an individual. The control measurement allows for the delineation between responses of a device to non specific interactions compared with the response of the device to a specific chemical in a biological fluid, for example a target biomolecule such as Cortisol.

It is envisaged that the sensor is in communication with a data recorder that can analyse the relative levels of the biological molecules for the individual.

It is preferred that the sensor is combined with microfluidics that can receive a flow of saliva from the individual for detection and analysis of the biological molecule.

Preferably the sensor is provided as a patch that can be releasably secured to the body and which can receive a flow through of blood from the individual and which can analyse several biological molecules at the same time. Patch type sensors are particularly suited to blood monitoring devices.

As an alternative the sensor is provided as an implant which can receive a flow through of blood from the individual and which can analyse several biological molecules on the one sensor.

It is envisaged that the analysis can be carried out for a number of biological molecules on the one sensor at the same time. By analysing several materials at a single period in time then it is possible to gain an overall picture of the chemical/biological profile of an individual at a set period in time. The profile can give an indication of the different enzymes/hormones steroids that are associated with a particular aspect of that individual and their relative levels in the body for that individual. It is envisaged that the measurement may be in real time. If measurements are carried out in real time then a profile of the hormonal/enzymatic characteristics of that individual may be monitored over time.

Short description of the Figures

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 perspective view of a multichannel graphene or silicon nanowire sensor according to an embodiment of the invention;

Figure 2 shows: an individual nanowire device;

Figure 3a shows: a schematic of a process for the functionalization of graphene or silicon nanowire according to an embodiment of the invention;

Figure 3b shows: a schematic process for the functionalization of graphene or silicon using APTES solution

Figure 4 shows: a top view of a microfluidic sensor package;

Figure 5 shows: a perspective view of a sensor and multichannel graphene or silicon nanowire layer;

Figure 6 shows: a cross section of a nanostructure incorporated in a sensor; and Figure 7 shows: a sensor implemented as a nano- transmitter. Detailed description of an example of the Invention

The microchannel part of a sensor is illustrated in Figure 1, and this structure is generally shown as 1 in the figure. The structure consists of a substrate 10 and there is a plurality of nanostructures 20 on the substrate. The nanostructures are generally in alignment forming blocks 11, 12 of nanostructures with insulators between them. Each nanostructure is formed of a nano-channel 21 between two metal contacts 22. Figure 2 shows an individual nanostructure with a representation of the microchannel being functionalised with a functionalised surface 23. Current is passed between the two metal contacts, through the nanochannel. The nano-channel is typically made from graphene (on a silicon carbide substrate). The sensor can be graphene or a silicon nanowire (SiNW) with the channel being functionalised (represented by 23) with a bioreceptor such as an antibody. The bioreceptor may be an antibody, enzyme or other protein or nucleic acid. This antibody specifically and selectively detects the disease biomarker (D).

In Figure 1, we also see that there can be a plurality of sensors arranged on a substrate to form a pattern. The pattern comprises a plurality of graphene channels 20 which may be of different channel widths to illustrate that the sensor according to the invention is equally applicable with different channel dimensions. A sensor usually comprises one channel and two or more metal contacts or electrodes 22. The graphene channels and thus the individual sensors are separated by a silicon dioxide (Si0₂) layer providing electric insulation 15 between the metal contacts and the graphene channels. The metal contacts or metal electrodes may be silver probes or may be made from other metals such as, for example, titanium, nickel, copper, gold or aluminium. The metal contacts may or may not be in contact with the graphene channel. The electrodes may have different shapes such as triangles or squares. The shape of the metal contacts or electrodes may be adapted to the specific needs of a specific biosensor. A measurement channel made from graphene is formed between two of the electrodes. The two electrodes are arranged at opposite ends of the channel. As an example, some of the channels may comprise a third electrode arranged at one side of the channel for operating these sensors as a lateral transistor.

If a SiC substrate is used it can be semiconducting or semi-insulating, or a combination of semiconducting or semi-insulating depending on the conductivity. The difference in conductivity arises from doping of the SiC as known in the art. If there are an excess of one type of impurity or dopant atom in the SiC, the SiC the conductivity will be increased and the SiC substrate becomes semi-conducting. If there is little or no excess, the SiC will be virtually insulating or semi-insulating. The graphene layer is grown, for example by epitaxial growth or sublimation growth, on the SiC substrate. The graphene layer may, for example have the shape of a graphene channel. The two metal contacts 22 are arranged on top of the graphene layer and form end points of the graphene channel 21. The metal contacts may be electrodes and can be made of silver material or any other material known in the art. A metallic back electrode can be provided on the back surface of the SiC substrate and this may be of the same material as the metal contacts 22. However it could be the case that the electrode and contact are of different material.

As an alternative example the sensor comprises a SiC substrate with a back side electrode and a semi-insulating SiC layer is arranged on the silicon carbide substrate and a graphene layer is arranged (i. e. grown) on top of the semi-insulating SiC layer. The semi-insulating layer electrically isolates the highly conductive graphene layer from the SiC substrate. If the SiC substrate is conductive, some of the current in any graphene device could potentially travel through the SiC substrate. Semi-insulating SiC can also be used as the SiC substrate and metal contacts and are arranged on top of the graphene layer.

The graphene channel 21 may have a thickness or channel width about 20 nm to about 200 nm, although thicker channels may be used, i.e. up to 400nm. The length of the channel may vary from about 200 nm to 10 μιη. The structured graphene channel may therefore be termed a "nano-channel". However, for some applications, the graphene channel may be made larger and thus be at the micrometer scale or sub- millimetre scale. The graphene channel may be open at the topside to allow access of biological molecules to the graphene channel. It may also be that fluid is allowed to access the graphene channel via sealed microfluidic channels.

The two metal contacts or metal electrodes 22 may be much larger in size compared to the width of the graphene channel. The dimension of the metal contacts or metal electrodes may have a surface area of, for example, about 20 to 50 μιη². However, different electrode sizes can be used. Using a back electrode allows the operation of the graphene channel as a field effect transistor. However, the electric properties of the graphene channel may also be determined by measuring the electrical resistance of, a current passing through, the impedance of other parameters of the graphene channel. The measurement of the electrical property can rely on the principle that the electrical property changes if a biological molecule or a plurality of biological molecules binds to the graphene channel. This change in the electrical property may be detected as an electrical signal which can be further amplified. A back electrode may be omitted depending on the electrical property to be detected and the type of sensor that is to be used. The graphene channel is functionalized to enable the binding or attachment of specific biological molecules.

The channel structures shown as examples in Figure 1 may be formed as graphene layer or multi-layer epitaxial graphene grown using epitaxial growth. The layer thickness may be between one and about 10 atomic layers or more.

The graphene layer may be grown on a substrate using CVD and used on the substrate or transferred onto another substrate for use.

Typically, growth and fabrication processes involved in the manufacture of a graphene structure involve sublimation growth of graphene on SiC substrate. The SiC substrate may be a commercially available SiC wafer. The growth process comprises sublimation of silicon from the first few surface layers of the SiC substrate. Carbon atoms left behind after silicon sublimation, reconstruct themselves into a hexagonal graphene structure. The growth process involves heating the SiC substrate at between about 1000 and 1800°C . under vacuum conditions, for example ultra high vacuum conditions with pressures lower than 10^"9 mbar. An alternative growth process involves higher temperatures (for example up to about 1500 to 1700°C or more) and higher pressures. For example, an epitaxial graphene layer is grown on the SiC substrate by annealing SiC under ultra high vacuum (UHV) conditions, for example for about 10 minutes at about 1250°C. The temperature and time duration may be varied to control the thickness of the graphene layer. The grapheme layer may also be grown using an atmosphere such as Argon.

The graphene layer is then patterned by depositing a layer of electron beam resist and subsequently patterning using electron beam lithography. The resist is developed and the exposed graphene is then etched away using an oxygen plasma etch. After striping the remaining resist, graphene channels remain on the SiC substrate. The metal electrodes can then be fabricated by depositing a thin film of metal from 100 nm to 1 um in thickness. A Photoresist is then deposited on top of the metal layer and patterned using a standard photolithography process. Finally the thin film of metal is etched, leaving behind the final device structures.

The alternative sensor, fabricated using a SiNW may be fabricated using asilicon on insulator wafer and etching a silicon nanowire structure from the silicon layer - leaving a Silicon nanowire on an insulating silicon dioxide layer. The silicon nanowire can be patterened using electron beam lithography or photolithography followed by silicon etching using dry plasma etching or wet chemical etching. Following this process metal contacts are deposited and contacted to the silicon nanowires.

The attachment of the bioreceptor onto the graphene (or SiNW) surface requires two parallel processes: (i) the surface modification and (ii) the subsequent antibody attachment. The antibody may be attached using the diazonium chemistry as shown in Figure 3a or using (3-Aminopropyl)triethoxysilane)APTES attachment chemistry Figure 3b.

The graphene channels may be chemically functionalized to have a binding affinity for the biological molecule. The binding affinity may be specific for the biological molecule to be detected with the sensor. The biological molecule to be detected is also termed target molecule and for stress analysis the molecule is typically a steroid, for example Cortisol. A possible mechanism for nitrobenzene attachment to graphene and subsequent electrochemical reduction to aniline is the attachment of a diazonium salt. The diazonium salt is attached to the graphene surface in order to attach a nitrobenzene or a nitrobenzene derivate to the graphene surface. The nitro group of the nitrobenzene may than be reduced to an amine, such as phenyl amine (IV). The resulting nitrophenyl amine has an amine group that can be used as such as a linker.

To increase sensitivity and specificity of the sensor, a sensing molecule can be attached to the amine group of the aniline or to the carboxyl group of the benzoic acid. The sensing molecules may comprise a biomarker, a receptor, an antibody, an amino acid, an enzyme or any other biological molecule appropriate for specifically binding a target molecule, for example a molecule associated with stress such as a corticosteroid. As the receptor molecule is highly specific to the target molecule, only these target molecules will bind to the sensing molecule and thus to the graphene surface, thereby changing the electrical properties of the graphene surface. Other biological molecules or any other molecule coming into contact with the graphene surface or the receptor molecule will not bind specifically or covalently to the graphene surface or the sensing molecule and have little effect or no effect on the electrical properties of the graphene surface.

The graphene may also be functionalized using ethandiamine for the linker and the ethandiamine may be attached to carboxylated graphene or graphene oxide to give amine functionalised graphene to which a sensing molecule can be bound.

The graphene may also be functionalized by a NH₃ plasma treatment of the graphene surface.

Appropriate amendments may be made to optimize the sensor for specific applications and make the appropriate modification to the functionalization and the shape and dimensions of the graphene structures. For example, a higher sensitivity may be reached if smaller graphene channels are used.

An alternative functionalization process, is performed by firstly terminating the silicon or graphene with -OH groups, for example, using the Fenton reaction, then reacted with 3- Aminopropyl-triethoxysilane (APTES) in order to obtain an amine-terminated surface. In order to be able to react with the surface amine groups, the carboxylic acids on the antibody are activated. However, in order to prevent the antibody from cross-linking, the majority of amine groups on the antibody are blocked using Di-tert-butyl dicarbonate. The antibody can now be reacted with the amine on the surface. The groups blocking the amines on the antibody are subsequently removed by mild acidic treatment. The functionalisation reaction may be carried out in situ i.e. in the microfluidic channel. To do this requires a three electrode device and this avoids using additional and external Ag/AgCl and Platinum wire electrodes because the 3 electrodes are thus integrated into one unit.

As shown in Figure 4, the nanostructures 10 may be placed in a housing 30 formed of a surround 32 which formed a border around the nanostructures. A dividing surface 35 can form a border between separate micro channels 21. The dividers provide an opening to each separated micro channel and so a sample can be placed on each separate micro channel. Each micro channel may be functionalised with different bioreceptors or it could be that different levels of the same bioreceptor are used for each channel so a comparative or qualitative study of samples can be made. A control could be provided in one channel to show levels that are considered to be in a normal range so an indication can be given if the levels measured are outside those that would be considered normal, either for the population as a whole or based on previous readings for that individual.

Figure 5 shows a complete sensor having a lid 31 which is formed of the surround 32 and dividers 35 as shown in Figure 4. The lid 31 may be secured to a base 36. A nanostructure 10 may be placed between the lid 31 and base 36. A window 34 in the lid provides access to the nanostructure 10 having micro channels 2 land contacts 22.

In Figure 6 we a cross section through a sensor where there is a silicon carbide substrate 310 and a graphene layer 320 which is grown on top of the semi-insulating layer 360. Metal contacts 331 and 332 are on top of the graphene layer 320 and back side electrode 340 forms a thirds contact.

Figure 7 shows a substrate 550 with a graphene channel 520 between metal contacts of electrodes 531 and 532. The third contact is a gate contact 535 which means that the sensor may be operated as a lateral field transistor which changes its electrical properties when one or more biological molecules are attached to the graphene channel 510. A back electrode as shown in Figure 6, may or may not be present.

The lid may have an electrode incorporated into it that can be used either during the functionalization process or during the sample measurement process. This electrode may be produced lithographically or printed and may be comprised of a metal such as Al, Au, Pt, Ni, Ti, Cu, Ag or a conductive material such as graphite, graphene, carbon nanotubes (CNTs) or conductive polymers.

The sensor may also have a power supply such as a battery and may also include a transmitter 37 that can send data information to a receiver. This arrangement allows for the sensor to be attached to the body for a period of time and the window 24 can include a needle or array of micro needles (not shown) that are in contact with the interstitial fluid in the skin of an individual. The sensor may include an alternative microfluidic system which can deliver fluids such as saliva, blood, urine, interstitial fluid or other bodily fluids onto the sensor. The sensor can then take measurements of particular components in the body over a period of time to provide a measurement of levels of molecules over a period of time.

The sensors can be used to evaluate corticosteroid hormones such as Cortisol and

Serotonin and also in addition other stress hormone markers including Adrenaline, Nor adrenaline, Dopamine, and Human Growth Hormone (HgH), Oxytocin, Melatonin, Dehydroepiandrosterone (DHEA). Using a multiplex sensor having isolated separate microfluidic channels for each compound to be measured means that an overall picture of an individual's stress levels can be measured.

It is envisaged that the sensor can be incorporated in a hand held device that medical practitioners can use or it can be included in an implant for continual monitoring of the body. The device allows for the detection of sub nano Molar concentrations of Cortisol and the sensor can be calibrated for clinically relevant concentration ranges.

It is envisaged that the sensor can be integrated with a microfluidic device with the sensor being part of a disposable sensor package, where the part of the sensor coming into contact with body fluids can be removed once used and disposed of. In addition the sensor can be integrated with hand held electronics where the sensor can be inserted in a reader, much like a "biochip credit card" using hand-held "card reader" so that results of the sampling can be read and if necessary analyzed.

The sensor can be used for the testing of saliva, urine, and interstitial fluid samples as well as analysis of blood samples.

The nano-biosensor is particularly useful for the rapid detection of stress hormones that can be at very low levels in the body, Further, nanowires and/or nano-channels have extremely high surface to volume ratios, making them extremely sensitive to interactions with their surfaces. In combination with excellent electronic conduction properties, this makes nano-channel sensors ideal for the detection of biomarkers at very low concentrations. In addition because nano-channel electrochemical sensors are being used, a number of current-voltage measurements over a defined time period can be taken to observe trends in levels of compounds in the body. This yields information on the change of resistance over time so providing information on diffusion controlled reactions which means that quantitative information and not just qualitative can be obtained.

Furthermore, other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangements of the exemplary embodiments without departing from the scope of the invention as expressed.

Claims

1. A sensor for detecting the presence of at least one biological molecule, the sensor comprising:

- a flow path

2. A sensor according to claim 1, wherein the flow path is provided by a graphene body having a surface with a channel etched in said surface to form the flow path.

3. A sensor according to claim 2, wherein the graphene is arranged on a non conductive surface.

4. A sensor according to claim 3, wherein the non conductive substrate is selected from one or more of silicon dioxide, silicon nitride, silicon carbide or Polydimethylsiloxane (PDMS) or chemical vapour deposition (CVD) graphene on an insulating substrate.

5. A sensor according to claim 1, wherein the flow path is a silicon nanowire that is used as the conductive sensor channel for the substrate material.

6. A sensor according to any preceding claim wherein at least two electrical contacts are arranged at opposite ends of the flow path.

7. A sensor according to any of claims 1 to 5, wherein the sensor has at least three electrical contacts.

8. A sensor according to claim 7, wherein two contacts are arranged at opposite ends of the flow path, and a third contact is arranged either in a lateral position relative to the flow path forming a lateral transistor structure or the third contact is on the back of the substrate so providing a field path or back-gate transistor structure.

9. A sensor according to any preceding claim including a further electrical contact which acts as a reference electrode, counter or auxiliary electrode.

10. A sensor according to claim 9, wherein the further contact is incorporated onto the same wafer as the sensor device or is fabricated on a separate substrate.

11. A sensor according to and preceding claim wherein the contacts are produced on the substrate by lithography or by printing.

12. A sensor according to any preceding claim wherein the at least one linker includes an amine group or a carboxy group.

13. A sensor according to claim 12, wherein the at least one linker is selected from one or more of an aniline, a diazonium ion or diazonium salt, APTES (3- Aminopropyl)triethoxysilane (APTES), or other amine or carboxy terminated moiety compounds and a sensing molecule.

14. A sensor according to claim 12, wherein the at least one linker is selected from one or more of a receptor molecule, an amino acid, an enzyme, an antibody for the at least one biological molecule.

15. A sensor according to claim 13, wherein the sensing molecule is at least one of a biomarker, a receptor, an amino acid, an enzyme, or an antibody for the at least one biological molecule

16. A sensor according to any preceding claim wherein the at least on linker is a receptor for one or more stress associated biological molecules associated with stress in the body.

17. A sensor according to claim 16, wherein the stress associated biological molecule is one or more of Cortisol, Serotonin, Adrenaline, Nor-adrenaline, Dopamine, Human Growth Hormone (HgH), Oxytocin, Melatonin or, Dehydroepiandrosterone (DHEA).

18. A senor according to any preceding claim having one or more flow paths, each being able to carry a separate sample material and each having a linker for a specified biological molecule.

19. A sensor according to claim 18, wherein the flow paths are arranged in pairs, with one of the pair of flow paths providing a control for a level of the biological molecule and the other flow path of the pair being arranged to monitor a sample material from an individual.

20. A sensor according to any preceding claim which has communication means so that information can be stored and/or sent that can analyse the relative levels of the biological molecules for the individual.

21. A sensor according to any preceding claim that can be releasably secured to the body and which can receive a flow through of blood from the individual and which can analyse several biological molecules at the same time.

22. A sensor according to any of claims 1 to 21 provided as an implant which can receive a flow through of blood from the individual and which can analyse several biological molecules on the one sensor.

23. A sensor according to any preceding claim where flow paths can be functionalised so that each flow path can analyse a separate biological molecule at the same time.

24. A sensor according to any preceding claim having recording means so that measurements can be carried out in real time over a particular period to provide a real time than a profile of the hormonal/enzymatic characteristics of an individual.

25. Use of a sensor according to any preceding claim as an analyser for stress hormones in an individual.

26. A sensor substantially as described herein with reference to and as illustrated in the accompanying figures.