Low Volume Whole Blood Sensor Biology Essay

The chief aim of this undertaking is focused on the development of a low-volume whole-blood detector that could revolutionize the consumption of cardiac point-of-care testing. Nano-structuring of fresh fluidic biosensors is envisaged for the development of such detectors, with good signal detectability utilizing micro-litre sums of patient blood sample. The fluidics system must filtrate out blood cells, to forestall them adhering to the detector, and falsifying the consequence. Typical utilizations include monitoring of cardiac enzymes, e.g. Troponin I, to assistance in the diagnosing of a cardiac onslaught, find the badness, and proctor recovery afterwards.

In this PhD undertaking, the chief accent was given to turn vertically aligned CNTs in assorted patternes and incorporate them into polymeric microfluidic channel. These CNT pillars can move as a micro-particle filtersinside fluidic channels. The procedure parametric quantity of thermic CVD and micro-cook plasma CVD to turn CNT of different aspect ratios on Si and vitreous silica substrates has been achieved. The fluidic channel with incorporate CNTs will so be sealed and characterised farther.

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1.2.2. Microfluidic channel for micro-particle filtering and flow control:

Microfluidic channels were prepared utilizing two different methods I ) On silicon/glass utilizing SU8 photoresists by maskless photo-lithography technique. two ) On polymeric substrate ( PMMA ) utilizing hot embossing technique. There devices were so farther characterised by mensurating the fluid flow speed inside the channels. CNTs were besides integrated into these channels as discussed earlier for micro-particle filtration. Simulation and modeling of fluid flow through a scope of suited geometries, and comparing with existent flow conditions, were undertaken at IIT, Bombay.

1.3. Literature Review on CNT growing

1.3.1 Catalyst pre-treatment

In the chemical vapour deposition method for the synthesis of CNTs, accelerator pretreatment plays really of import function in the growing procedure. Harmonizing to the reported literature summarised below, pretreatment of catalytic nanoparticles is of import to efficaciously synthesise CNTs. A figure of publications have been considered here which shows the importance of accelerator pre-treatment for CNT growing. Some of them are described as follows:

S. Hofmann et.al [ 1 ] shows that for Fe or Co accelerator, it is necessary to cut down the thickness to below 3 nanometers, to accomplish a passage from bamboo-like nanofibres with less than 40I?m diameter, to about 5 nm diameter MWCNTs, with between 2 to 5 walls. The latter MWCNTs grow more than 50 times faster, but the accelerator toxicants much more rapidly. Ni accelerator, nevertheless, did non demo such a growing passage, unless pre-treated with ammonium hydroxide – which implies that without ammonia pre-treatment Ni accelerator may good bring forth big nanofibres, instead than true MWCNTs.

M. Cantoro et Al [ 2 ] besides shows similar decisions about the effects of cut downing the Fe or Co accelerator thickness to less than 3 nanometer for about 5 nm MWCNT diameter. Chao Hsun Lin et Al [ 3 ] compares MPCVD and ECR-CVD growing of CNTs from thin foils of Fe, Co, and Ni. The bombardment energy of N plasma is found to be higher than for H plasma, so that the N plasma tends to clean the accelerator front surface better during deposition, maintaining it active for thirster. However, the higher bombardment energy of the N plasma tends to advance agglomeration of larger accelerator islands, taking to growing of bamboo-like CNTs.

S. Wang et al. [ 4 ] found that ammonia pre-treatment on comparatively thick ( & gt ; about 80 nanometers ) Fe accelerator movies gives about 10 to 25 nanometers atom size. The atom diameter increased with pre-treatment clip ( 10 mins. up to 30 mins. ) , as expected if island agglomeration is happening. For a scope of microwave powers between 200 – 600 W, for the ammonia pre-treatment, a distinguishable lower limit in atom diameter ( approximately15 nanometer ) occurred between 400 – 500 W. Similarly, CNTs were grown for a scope of microwave powers, with a distinguishable lower limit in nanotube diameter of 4 nanometers, at 500W. It clearly is necessary to optimize the microwave power for both the pre-treatment and the CNT growing procedure.

Last, the paper by H. Sato et Al, “ Consequence of accelerator oxidization on the growing of C nanotubes by thermic chemical vapor deposition ” [ 5 ] demonstrates that heat intervention of Fe accelerator on Si, in air at 700°C, before CNT growing, wholly oxidises the accelerator, interrupting it into islands which so do non farther agglomerate. It was found that a greater than 7 times increase in CNT growing rate was achieved by accelerator pre-oxidation – it is believed that the pre-treatment prevents the formation of a Fe silicide, which would suppress contact action.

1.3.2 CNT growing by TCVD

CVD is one of the popular technique for bring forthing CNTs. This technique uses a hydrocarbon in vapour signifier which is thermally decomposed in the presence of a metallic accelerator. It is besides normally known as thermal/catalytic CVD. Compared with other synthesis methods, CVD is a 1 of the simple and economic technique for synthesising CNTs at low temperature and ambient force per unit area, at the cost of crystallinity. It is various in that it harnesses a assortment of hydrocarbons in any province ( solid, liquid, or gas ) , enables the usage of assorted substrates, and allows CNT growing in a assortment of signifiers, such as pulverization, thin or thick movies, aligned or entangled, straight or coiled, or even a coveted architecture of nanotubes at predefined sites on a patterned substrate. It besides offers better control over growing parametric quantities. In fact, CVD has been used for bring forthing C fibrils and fibres since 1959 [ 6 ] . Using the same technique, shortly after the re-discovery of CNTs by Iijima, Endo et Al. [ 7 ] reported CNT growing from pyrolysis of benzine at 1100A°C, while Jose- Yacaman et Al. [ 8 ] formed clear coiling MWNTs at 700A°C from ethyne. In both instances, Fe nanoparticles were used as the accelerator. Later, MWNTs were besides grown from ethylene [ 9 ] , methane [ 10 ] and many other hydrocarbons. SWNTs were foremost produced by Dai et Al. [ 11 ] from disproportionation of CO at 1200A°C, catalyzed by Mo atoms. Subsequently, SWNTs were besides produced from benzine [ 12 ] , ethyne [ 13 ] , ethylene [ 14 ] , and methane [ 15, 16 ] utilizing assorted accelerators.

Fig. 1a shows a diagram of the apparatus used for CNT growing by CVD in its simplest signifier. The procedure involves go throughing a hydrocarbon vapour ( typically for 15-60 proceedingss ) through a tubing furnace in which a accelerator stuff is present at sufficiently high temperature ( 600-1200A°C ) to break up the hydrocarbon. CNTs grow over the accelerator and are collected, upon chilling the system to room temperature. In the instance of a liquid hydrocarbon ( benzine, intoxicant, etc. ) , the liquid is heated in a flask and an inert gas purged through it to transport the vapour into the reaction furnace. The vaporization of a solid hydrocarbon ( camphor, naphthalene, etc. ) can be handily achieved in another furnace at low temperature before the chief, high-temperature reaction furnace shown in Fig. 1a.

Fig. 1 ( a ) : Conventional diagram of a CVD apparatus. ( B ) Probable theoretical accounts for CNT growing [ R ] .

The accelerator stuff may besides be solid, liquid, or gas and can be placed inside the furnace or fed in from exterior. Pyrolysis of the accelerator vapour at a suited temperature liberates metal nanoparticles in situ ( the procedure is known as the drifting accelerator method ) . Alternatively, catalyst-plated substrates can be placed in the hot zone of the furnace to catalyse CNT growing. Catalytically decomposed C species of the hydrocarbon are assumed to fade out in the metal nanoparticles and, after making supersaturation, precipitate out in the signifier of a fullerene dome widening into a C cylinder ( like the upside-down trial tubing shown in Fig. 1b ) with no swinging bonds and, therefore, minimal energy [ 17,18 ] . When the substrate-catalyst interaction is strong, a CNT grows up with the accelerator atom rooted at its base ( known as the ‘base growing theoretical account ‘ ) . When the substrate-catalyst interaction is weak, the accelerator atom is lifted up by the turning CNT and continues to advance CNT growing at its tip ( the ‘tip growing theoretical account ‘ ) . Formation of SWNTs or MWNTs is governed by the size of the accelerator atom. Broadly talking, when the atom size is a few nanometres, SWNTs signifier, whereas particles a few 10s of nanometres broad favour MWNT formation. The three chief parametric quantities for CNT growing in CVD are the hydrocarbon, accelerator, and growing temperature. General experience is that low-temperature CVD ( 600-900A°C ) outputs MWNTs, whereas a higher temperature ( 900-1200A°C ) reaction favours SWNT growing, bespeaking that SWNTs have a higher energy of formation ( presumptively owing to their little diameters, which consequences in high curvature and high strain energy ) . This could explicate why MWNTs are easier to turn from most hydrocarbons than SWNTs, which can merely be grown from selected hydrocarbons ( e.g. CO, CH4, etc. , that have a sensible stableness in the temperature scope of 900-1200A°C ) .

Common efficient precursors of MWNTs ( e.g. ethyne, benzine, etc. ) are unstable at higher temperatures and lead to the deposition of big sums of carbonous compounds other than CNTs. Passage metals ( Fe, Co, Ni ) are the most normally used accelerators for CNT growing, since the stage diagram of C and these metals suggests finite solubility of C in these passage metals at high temperatures. This leads to the formation of CNTs under the growing mechanism outlined above. Solid organometallocenes ( ferrocene, cobaltocene, nickelocene ) are widely used as accelerator stuffs because they liberate metal atoms in situ that expeditiously catalyze CNT growing. The accelerator atom size has been found to order the tubing diameter. Hence, metal nanoparticles of controlled size can be used to turn CNTs of controlled diameter [ 19 ] . Thin movies of accelerator coated onto assorted substrates have besides proved successful in accomplishing unvarying CNT sedimentations [ 20 ] . In add-on, the stuff, morphology, and textural belongingss of the substrate greatly affect the output and quality of the resulting CNTs. Zeolite supports with accelerators in their nanopores have resulted in significantly higher outputs of CNTs with a narrow diameter distribution [ 21 ] . Alumina stuffs are reported to be better accelerator supports than silicon oxide owing to their strong metal-support interaction, which allows high metal scattering and, therefore, a high denseness of catalytic sites [ 22 ] . Such interactions prevent metal species from aggregating and organizing unwanted big bunchs that lead to graphite atoms or faulty MWNTs. The key to obtaining high outputs of pure CNTs is accomplishing hydrocarbon decomposition on accelerator sites entirely and avoiding self-generated pyrolysis. It is singular that passage metals have proven to be efficient accelerators non merely in CVD but besides in arc-discharge and optical maser methods. This indicates that these seemingly different methods might hold a common growing mechanism for CNTs, which is non yet clear. CNTs have been successfully synthesized utilizing organometallic compounds ( nickel phthalocyanine [ 23 ] and ferrocene [ 24 ] ) as carbon-cum-catalyst precursors, though the as-grown CNTs were largely metal encapsulated. The usage of ethyl alcohol has drawn attending for synthesising SWNTs at comparatively low temperatures ( approximately850A°C ) on Fe-Co impregnated zeolite supports and Mo-Co coated quartz substrates [ 25-27 ] . Recently, a tree merchandise, camphor, has been used to bring forth high outputs of high-purity MWNTs [ 28-30 ] . Because of the low accelerator demand with camphor, as-grown MWNTs are the least contaminated with metal, while the O atoms present in camphor aid oxidise formless C in situ [ 31 ] . CVD is ideally suited to turning aligned CNTs on coveted substrates for specific applications, which is non executable by discharge or optical maser methods. Li et Al. [ 32 ] have grown heavy MWNT arrays on Fe-impregnated mesoporous silicon oxide prepared by a sol-gel procedure, Terrones et Al. [ 33 ] have produced CNTs on Co-coated vitreous silica substrates via CVD of a triazene compound with about no by-products, while Pan et Al. [ 34 ] have reported the growing of aligned CNTs of more than 2 millimeter in length over mesoporous substrates from ethyne. Highly aligned nanotubes for electronics have been grown from acetylene [ 35 ] utilizing a Co accelerator impregnated in alumina nanochannels at 650A°C, while pillars of parallel CNTs have been grown from ethene on Fe-patterned Si home bases at 700A°C for field emanation applications [ 30 ] . Bearing in head that pyrolysis of a xyleneferrocene mixture leads to the growing of perpendicular CNTs on vitreous silica [ 36 ] , Ajayan and coworkers have produced organized assemblies of CNTs on thermally oxidized Si wafers [ 37,38 ] . Since CVD is a good known and good established industrial procedure, CNT production is easy to scale up. MWNTs of controlled diameter are being produced in big measures ( approximately100 g/day ) from ethyne utilizing nanoporous stuffs as the accelerator support [ 39 ] . Wang et Al. [ 40 ] have developed a nano-agglomerate fluidized-bed reactor ( a vitreous silica cylinder 1 m long and 0.25 m broad ) in which the uninterrupted decomposition of ethene gas on an Fe/alumina accelerator at 700A°C produces a few kgs of MWNTs per hr with a reported pureness of 70 % . Dai ‘s group has scaled up SWNT production from methane utilizing a Fe-Mo bimetallistic accelerator supported on a sol-gel derived alumina-silica multicomponent stuff [ 41 ] . However, Smalley ‘s lab still leads the manner in the mass production of SWNTs ( approximately10 g/day ) by the high force per unit area C monoxide ( HiPco ) technique [ 42 ] . In this method, a Fe pentacarbonyl accelerator liberates Fe atoms in situ at high temperatures, while a high force per unit area of CO ( approximately30 standard pressure ) enhances the C feedstock manifolds, which significantly speeds up the disproportionation of CO molecules into C atoms and accelerates SWNT growing. Apart from large-scale production, CVD besides offers the possibility of turning individual nanotubes for usage as investigation tips in atomic force microscopes ( AFM ) or as field emitters in negatron microscopes. Hafner et Al. [ 43 ] have grown individual SWNTs and MWNTs ( 1-3 nanometer in diameter ) rooted in the pores of Si tips suited for AFM imaging. In another attack, individual SWNTs are grown straight onto pyramids of Si cantilever-tip assemblies [ 44 ] . In this instance, a SWNT grown on the Si surface ( controlled by the accelerator denseness on the surface ) protrudes from the vertex of the pyramid. As-grown CNT tips are smaller than automatically assembled nanotube tips by a factor of three and enable significantly improved declaration. CVD-produced CNTs have great promise for the fiction of sophisticated instruments and nanodevices.

1.3.3 CNT growing by MPCVD

At present, there are a limited figure of mentions to individual wall CNTs grown by MPCVD. W.L. Wang et Al in the paper “ Low temperature growing of single-walled C nanotubes: little diameters with narrow distribution ” [ 45 ] , shows the successful growing of nanotubes with a diameter scope of about 1.0 nm A± 0.23 nanometers compared with a typical mean figure of about 1.6 nanometers for CNTs grown by thermic CVD. Bimetallic Fe-Mo nanoparticles were used as the accelerator, but on porous MgO pulverization, instead than a solid substrate, likely because of the purpose to divide the CNTs from the surface, and sublimate them ( by HCl acid ) for farther analysis in the HRTEM.

Thermal CVD is typically carried out at 800A°C. However it was found that the diameter of SWCNTs grown by MPCVD could be reduced as temperature reduced, from 700A°C down to 500A°C. It was besides found, from Raman informations, that both the D set increased in strength, and the RBM mode signal became weaker ( and noisier ) , as the temperature decreased from 700A°C to 500A°C. Below 500A°C, small SWCNT growing occurred, the movies being largely formless or nanocrystalline C, and nanofibres. However, it is promoting to cognize that smaller diameter SWCNTs are possible by MPCVD, in instance it becomes a demand to turn higher bandgap SWCNTs with a position to accomplishing shorter wavelength visible radiation end product ( presuming metallic contacts that align to the bandgap mid-points can be made for wider bandgap stuff ) .

In the following paper, “ Role of thin Fe accelerator in the synthesis of dual and individual wall C nanotubes via microwave chemical vapor deposition ” [ 46 ] by Y. Y. Wang et Al, is interesting for a figure of grounds ; foremost, vertically aligned SW and DW CNT growing by MPCVD is demonstrated, and confirmed by Raman analysis. The RBMs show distinct mensurable extremums, and the D set extremums are really much lower than the G set extremums, corroborating good quality tubing growing. These CNTs were grown in an ASTeX 1.5kW microwave CVD reactor, similar to the MPCVD beginning at Nanotechnology and Integrated Bio-Engineering Centre ( NIBEC ) . A 180 nm SiO2 bed on the Si wafer substrate was used to forestall formation of an Fe silicide, which would suppress catalyst action. Interestingly, instead than pre-treat with a plasma, the substrates were foremost annealed in vacuity for 10 mins. at about 850A°C, to organize nanoislands, as confirmed by AFM. The substrate was so introduced into the MPCVD chamber a short H explosion was used to light the plasma, and the H force per unit area was maintained throughout the growing, while ethyne and ammonium hydroxide was introduced. The ammonium hydroxide was used to reactively etch formless C and graphite-like stuff which can organize during deposition, and limit the formation of the coveted CNTs.

Mentions:

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17. R. T. K Baker, In Chemistry and Physics of Carbon, P. L. Walker, and P. A. Thrower,

Marcel Dekker, New York, ( 1978 ) , 14

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22. N. Nagaraju, et Al. J. Mol. Catal. A ( 2002 ) 181 ( 1-2 ) , 57

23. M. Yudasaka, et Al. Carbon ( 1997 ) 35 ( 2 ) , 195

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32. W. Z. Li, et Al. Science ( 1996 ) 274, 1701

33. M. Terrones, et Al. Nature ( 1997 ) 388, 52

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3.0 Introduction to microfluidics

3.1 Introduction

Microfluidics is the scientific discipline of design, fabrication and formulating of devices and processes that trade with nanolitres of fluid. These devices range with dimensions from millimetres down to microns. Therefore the fabrication processes involved differ greatly from devices on the macroscale. The system behavior is affected when the dimensions of the device become comparable to the atom size of the fluid passing through. Common fluids used in microfluidics include protein or antibody solutions, blood samples, buffer solutions and bacterial or cell suspensions. The usage of microfluidic devices to carry on biomedical research has a figure of important advantages over other methods ;

The sum of reagents needed to obtain a diagnosing is comparatively little due to the little dimensions involved.

The fiction methods used to build microfluidic devices are comparatively inexpensive and are easy mass produced.

The fiction of extremely complex lad-on-a-chip devices is accomplishable which allows for faster diagnosing and removes the demand for laboratory analysis.

Microfluidics fluid flow is based on a classical country of fluid kineticss: low-Reynolds-number flows. Flow in a microfluidic channel is described as holding a low Reynolds figure & lt ; 100.

The Reynolds figure is dependent on viscousness, fluid denseness, comparative length graduated table and mean speed. When the Reynolds figure is low as it is in microfluidic systems the turbulency is minimum. This means that the flow happens in a comparatively predictable mode. The fluid moves through a microfluidic system utilizing capillary forces. It occurs when the adhesive molecular forces are stronger than the cohesive intermolecular forces present in the fluid. However this may be an oversimplified model.The visual aspect of smaller and smaller devices has introduced many different variables such as ;

Surface tenseness which itself is affected by surface raggedness, electrical effects and new wave der Waals forces.

Complicated 3D patterning of the surface of the device

The presence of suspended atoms which are comparable in size to the dimensions of the device.

The challenge of developing a device such as these is to use and understand these complex variables and pull strings them to one ‘s advantage. On the device which will be developed, the fluid will be driven through the system by two different forces. Gravity will coerce the bead to come in the capillary channel at one terminal and so capillary action will pull the fluid through the system.

3.2 Literature Review on Microfluidics

3.2.1 General Microfluidic Theory

J. Lammertyn et Al, [ 1 ] shows the development of a convection-diffusion-reaction theoretical account to imitate the behavior of a flow inject analysis biosensor with regard to flux rate, fluidic channel dimensions, flow cell geometry, volume of substrate and the fluid used. This paper looks at the fluid flow utilizing Navier-Stokes equations and Michaelis-Menten dynamicss. A speed flow profile was obtained and force per unit area driven fluidics and standard flow was compared. It was found that this modeling attack has a high potency in the design and development of high truth biosensors, irrespective of the enzyme chosen.

B. Kuswandi et Al [ 2 ] trades with the application of optical feeling systems in microfluidic devices. It is a reappraisal of the optical detection attack for microfluidic devices, both the off bit attack ( macroscale optical substructure coupled externally to the device ) and on bit attack ( which comprises the integrating of micro optical maps into the microfluidic device. It was found that detector size and form deeply affect the sensing bounds due to analyte conveyance restriction. The reappraisal concludes with an appraisal of future waies of on bit integrated optical feeling microfluidic devices. I included this paper as it gives an overview of a different usage of microfluidics and helps demo how relevant these devices will be in medical specialty in the hereafter.

P. Gould et Al [ 3 ] discussed the possible, commercially, of microfluidic devices. Microfluidic lab-on-a-chip devices can incorporate everything needed to examine the tiniest of liquid samples and do a diagnosing. Microfluidic devices can be active ( necessitating external control ) or inactive ( wholly self contained devices ) . These points are individual usage devices designed to be discarded after one usage. They so need to be inexpensive and easy to fabricate. This paper inside informations the etching and lithography techniques that can be used to make a device. It talks about devices which can be designed with electronic devices impeded that manipulate an electric field and can travel and procedure nanolitres samples through capillary circuitry. It besides discusses the country of nanofluidics, utilizing dimensions comparable to the size of the molecules in inquiries these molecules can be manipulated and squeezed so utilizing cardinal parametric quantities such as visible radiation at certain wavelengths and this can be used to separate between different molecular types. The of import factor as this paper states is traveling these devices from the experimental and proficient country into the commercial sphere and turning it into a successful merchandise.

P. Woias et Al [ 4 ] explained old 30yrs of microfluidic promotion and where it will head in the hereafter. Get downing in the 1970s a steadily turning and amazing diverseness of fresh thoughts and attacks to fabrication engineering and applications have been coming to the bow in the development of MEMS devices. It deals specifically with the micropumps country of microfluidics and discusses the possible applications for this country in the hereafter such as biochemical detection. Microfluidics promotion will go on to fuel the development of micropump systems in the hereafter. I reviewed this paper as it gives an overview of the history and advancement of micropumps which is closely entwined with microfluidics and helps exemplify the enormousness of the research country.

H.A. Stone et al [ 5 ] gives a brief overview of the chief countries of microfluidics and the natural philosophies and variables involved in making such a device. Many microfluidic devices have been developed over the past several old ages and these systems are going more and more of import to the biomedical and pharmaceutical industries, every bit good as other countries outside these two chief research subjects. The ability to implement modeling on the nanoscale, make a device in the lab-on-a-chip construct, control and heighten chemical reactions, develop commixture and separation procedures will offer research chances in the hereafter and will so take onto commercial chances for the successful devices. It inside informations the countries which still need to be researched farther such as ; molecular interactions, surface forces and fluid flow. Again this article is of involvement to this study as it gives a brief overview of the workings and natural philosophies involved in a microfluidic device.

T. Gervais et Al [ 6 ] investigated mass conveyance and surface reactions in microfluidic systems in this paper. It deals with analysis of diffusion and laminar flow convection when combined with surface reactions relevant to microchemical checks. Analytic solutions for the concentration Fieldss are compared to anticipations from 2D computing machine theoretical accounts which are normally used to construe these consequences. Particular accent was placed on the word picture of conveyance in shallow microfluidic channels. Two cardinal parametric quantities relevant to on-board bit biochemical checks and microfluidic detectors were studied and compiled ; capture fraction of the majority analyte and the impregnation clip graduated table at the reactive surface. This paper is relevant because it looks at the criterion modeling for microfluidic systems to see merely how accurate it is in the country of a biosensor.

3.2.2 Production Techniques

A.Pepin et al [ 7 ] describes the fiction of microfluidic devices for biomolecule separation utilizing an array of chiseled nanostructures. Two types of pattern reproduction of the same device constellation are considered, based on different methods of processing. The 1st attack uses a tri-layer nanoimprint lithography procedure to model a SiO2 substrate on top of which is stuck a plastic screen home base. The 2nd method involved straight forming thermoplastic polymer pellets to organize majority home bases that are so thermally bonded together. The fancied devices were characterised by epifluorescence microscopy, utilizing a fluorescein solution to track leaks and unstable incursion. The findings of the study are those nanofluidic devices are accomplishable and could be manufactured for mass production.

C-H Wu and C-H Chen [ 8 ] described a new method for fabricating a microfluidic construction on a polymer substrate is investigated in this paper. It uses an optical phonograph record ( Cadmium ) procedure to forestall harm to the mirror home base of the mold. The rhythm clip has besides been reduced in comparing to the conventional methods by agencies of a new chilling system. The molding system is comprised of a stamper and a vacuity system to fall in the mold insert with the mold. The clip to alter the mold is hence dramatically reduced. It reduces the clip required from several hours to a few proceedingss. The experiments demonstrated that this method is suited for mass production. This shows another method for making a microfluidic construction on a substrate.

The first paper to cover with SU-8 as a substance to make a microfluidic device was by J.M. Ruano-Lopez et Al. [ 9 ] SU-8 is a photodefinable epoxy and in this paper it was used to incorporate optical detectors and microfluidic constructions. The bit consists of optical detectors, wave guides and sealed microfluidic channels patterned in SU-8 on a Si substrate. It describes the SU-8 fiction procedure which will be discussed in great item subsequently in this study. The microchannels were sealed by low temperature adhesive bonding of the SU8 patterned movies at a wafer degree. The fiction procedure was found to be fast, consistent, CMOS compatible and a simple manner to develop a lab on a bit device. The fiction procedure discussed is of great involvement to this paper as it detail the SU-8 procedure carried out which, more than probably, will be the method used.

Ten Sun.et al [ 10 ] developed a new method for rapid prototyping of difficult polymer microfluidic systems utilizing solvent imprinting and bonding. A bed of SU-8 photoresist was patterned on glass as a templet for solvent imprinting. Poly ( methyl methacrylate ) ( PMMA ) was exposed to acetonitrile and so had the SU-8 templet pressed into the surface, which provided suitably imprinted channels and a suited surface for adhering. A PMMA screen home base was fabricated in a similar mode and bonded together at room temperature at appropriate force per unit area. The entire fiction clip was 15mins and the SU-8 templet could be used to created about 30 PMMA french friess. The lengths and deepnesss of channels were investigated to detect the repeatability. This new dissolver imprinting and adhering attack significantly simplified the fiction procedure for constructions in polymers such as PMMA.

L.Yu, & A ; F.E.H Tay et Al [ 11 ] proposed an adhesive bonding technique at wafer degree once more utilizing SU-8 as the structural stuff. The adhesive was imprinted onto one of the surfaces and the purpose was to bond the two surfaces utilizing a low temperature method. It used three chief stairss ; First the adhesive bed is deposited onto the adhering surface by contact forming onto the SU-8 photoresist. The wafers are so placed in contact and aligned. In the concluding measure the bonding is performed between 100oC and 200oC at a force per unit area of 1000N in a vacuity. This procedure was successfully tested in the fiction procedure of a dielectrophoretic device.

B. Bilenberg et Al [ 12 ] , investigates an adhesive bonding technique for wafer degree waterproofing of SU-8 based lab-on-a-chip Microsystems. Microfluidic channels were created utilizing a standard lithography procedure in SU-8 photoresist and sealed with a pyrex glass palpebra by agencies of an intermediate bed of PMMA. This bonding technique was compared with SU-8 bonding and it was found that the slow flow of SU-8 resist during the sealing procedure caused the channels to be filled with resist. The adhering strengths of both methods were tested and it was found that PMMA has a bonding strength of around 16MPA when bonded under a force of 2000N and a temperature of 120oC. This method is assuring for the devices that will be developed in this thesis and the method used by this thesis will be investigated further in experiments carried out in the lab at NIBEC.

J.S. Liu et al [ 13 ] shows Fabrication of microchannels on PMMA substrates utilizing fresh microfabrication techniques are investigated in this paper. The image of microchannels is transferred from a Si maestro home base utilizing hot stamping methods. The Si maestro is electrostatically bonded to a Pyrex glass wafer which improves the device output from 20 per maestro to over 100. This paper is chiefly concerned with soft lithography techniques. However this method will non be used in my Ph.d.

D.P. Poenar et al [ 14 ] studies on the creative activity of a microfluidic device from glass substrates that will be used to characterize cells utilizing electric resistance spectrometry. The device is constructed from two glass wafers. The underside wafer has microfluidic channels and electrodes while the upper wafer has recesss and mercantile establishments. The chief focal point of this paper was the fiction of the device, foremost, successfully using a through-wafer moisture etch to model recesss and mercantile establishments on the lid wafer. Second, modeling electrodes in the microfluidic channel on the bottom wafer. Finally adhering was carried out utilizing an intermediate bonding bed ( paralyene C ) which requires a low bonding temperature, short clip period for bond to take consequence and high bond strength.

3.3 Carbon Nanotube Integration

S.G.Wang et al [ 15 ] , showed the synthesis of Multi-walled C nanotubes ( MWNTs ) in this paper on Si substrate utilizing nickel accelerator with thickness varied from 2nm to 30 nanometers utilizing microwave plasma chemical vapor deposition. The word picture consequences obtained from this work showed that the diameter of produced MWNTs decreased with thickness of the nickel accelerator bed. MWNTs of 8nm have been obtained utilizing a nickel accelerator bed of 2nm.

R. Pcionek, D.M. Aslam and D. Tomanek [ 16 ] investigates the variables involved in the synthesis of CNTs. Nanotubes with diameters runing from 20nm to 400nm and densenesss runing from 108-109cm-2, were produced on metal coated Si by MPCVD. The forms and sizes of the nanostructures depended on growing status and pre or station intervention of the samples. Presence of N in the growing or pre-growth atmosphere increased the denseness and perpendicular growing rate of the nanotubes. The growing rate on Nickel is slower than the growing rate on Iron and eventually an supersonic intervention of nanotubes in methyl alcohol is demonstrated.

J.Y Kim et Al [ 17 ] , discusses integrating SWNTs into a poly ( dimethylsiloxane ) ( PDMS ) based microfluidic channel. An 80I?m midst horseshoe shaped SWNT microblock which had been physically immobilised with glucose oxidase ( GOx ) and horseradish peroxidase ( HRP ) was fabricated utilizing a PDMS mold. The fancied SWNT microblock was incorporated into a microfluidic channel for the bioreaction on a microscale. This microfluidic device was tested for the spectroscopic glucose sensing and the consequences showed that the glucose can be detected linearly in a broad scope of concentrations. This shows the CNTs can be used in concurrence with a microfluidic device to make a biosensor.

G. Chen [ 18 ] focal points on recent progresss in fiction of electrochemical sensors in micro chip and microfluidics utilizing CNT in this reappraisal paper. The topic covered include CNT based electrochemical sensors in micro chip capillary cataphoresis ( CE ) , CNT based electrochemical sensors in conventional CE B doped diamond electrochemical sensors in micro chip CE and B doped diamond electrochemical sensors in conventional CE. The belongingss found make CNTs and B doped diamond promising stuffs in the countries of electrochemical sensing in microfluidic analysis systems.

J. Xu et Al [ 19 ] , manufacture a C nanotube/polystyrene composite electrodes were as sensitive amperometric sensors of capillary cataphoresis ( CE ) for the finding of rutin and quercetin in Flos Sophorae Immaturus. The composite electrode was fabricated on the footing of unmoved polymerization of a mixture of CNT and cinnamene in the microchannel of a piece of amalgamate silicon oxide capillary under heat. The surface morphologies were investigated utilizing a scanning negatron microscope. The public presentation of this alone system has been demonstrated by dividing and observing rutin and quercetin. The system demonstrated long term stableness, duplicability and shows a batch of possible to be sued in a broad scope of applications in microfluidic analysis and flow injection analysis.