FIELD OF THE INVENTION
The present invention relates to a system for optofluidically controlled fluid motion for variety of microscale applications. In particular, the invention is directed to a system for optofluidically controlled fluid motion involving UV light source adapted to alter the hydrophilic properties of the contacting surfaces to drive the fluid. Importantly, said optofluidically guided device of the invention makes use of the modification of the surface properties of coated substrate by selective exposure to UV light for flow diversion/actuation. The system of the invention would favour light influenced fluid motion/flow diversion, any branching configuration for flow diversions and valving using optofluidic mechanism. The optofluidic/light driven direction control of the fluid motion on photo responsive material in microscale applications with ease of integration and reconfigurablity especially in valve design is a distinct advantage of the invention for a number of microchannel based fluid flow control applications importantly in bio-medical and pharmaceutical industries.
BACKGROUND ART
It is well known optofluidics deals with unique optical properties of fluids in optical systems, including the fluid flow properties. Fluid-flow control is of specific concern in a number of applications where optofluidics have been utilized. In particular, fluid flow controlling mechanisms where the propagation of fluid in a particular direction is achieved utilizing direct or indirect effects of light either on the fluid itself or on the contacting solid interfaces has been attempted in macroscale. There are a few microscale applications in prior knowledge in the related field such as one having photosensitive nano-particles suspended in the fluids that are confined within microchannel.
The publication titled 'Optofluidic control using photothermal nanoparticles' by G.N. Liu et al, Nature Materials, 5, 27(2005) describes a method of actuating fluid flow through the use of PNP (photothermal gold nano-particles) and the use of laser light. The method mentioned is very costly to implement. For the applicability of wide range of fluids used, the method seems to have lot of demerits. Mixing PNP often may lead to contamination of biological species. The use of in situ lasers/UV light can also damage the biological tissue.

Another publication in related art is 'Developing optofluidic technology through the fusion of microfluidics and optics', Nature, 442, 381(2006) by D. Salties et al wherein mention is made about method for the fluid front being dragged in desired direction by the local heating of nano-particles. The evaporation of liquid taking place at the air-liquid interface followed by immediate condensation ahead of liquid front, such that the droplets formed on condensation merges with the main liquid body favor driving fluid in a particular direction.
An alternate embodiment of the optofluidically controlling of macroscale flow is mediated by optically created surface tension gradient. The hydrophobicity of the adjacent solid substrate is influenced when coated with materials sensitive to UV or blue light when exposed to, such materials comprising inorganic polymers e.g. photochromatic azobenzene, photo responsive pyrimidines or surfactants or semiconductor materials like zinc oxide or titanium dioxide, having band gap approximately close to the energy of UV light. One can refer to the prior art literature in these regard to study such hydrophobicity of materials such as in (a) Light-Driven motion of Liquids on a photo-responsive surface, Science, 288, 1624(2000) by K. Ichimura et al; (b) Reversible wettability of Photoresponsive Pyrimidine-coated surfaces, Langmuir, 15, 8923(1999) by S. Abbott et al; (c) Using light to control dynamic surface tensions of aqueous solutions of water soluble surfactants, Langmuir, 14, 4404(1999) by J. Y. Shin et al;(d) Photocatalytic activity and photoinduced hydrophilicity of titanium dioxide coated glass, Thin Solid Films, 351, 260(1999) by T. Watanabe et al;
Despite the said advancements in macro/microfluidic applications as stated above, specific use of optofluidics to develop flow controlling or diverting mechanisms in microscale applications has not been attempted to develop/configure valve means for microchannel based flow devices.
There has thus been a continuing need in the art of optofluidics to develop an effective microchannel based system wherein the optofluidic/photoresponsive property of substrate material is utilized effectively for microfluidic fluid flow diversion in desired direction to thereby designing a valve configuration in a simple, integrated and reconfigurable flow diverting microchannel based device adapted to suit a wide variety of microscale applications involving UV light-driven fluid motion with distinct operational advantage over the conventional mechanical or electrical valves for similar applications in a simple and cost effective manner.

OBJECTS OF THE INVENTION
It is thus the basic object of the present invention to develop a system for optofluidically controlled fluid motion for variety of microscale applications such as design a valve involving fabrication of a microchannel based fluid flow direction control in a simple and cost effective manner.
A further object of the present invention is directed to a system for optofluidically controlled fluid motion for variety of microscale applications wherein fabrication of said microchannel based flow passage may be of any shape involving flow diversion.
A still further object of the present invention is directed to a system for optofluidically controlled fluid motion for variety of microscale applications wherein rapid fabrication of said complex microchannel/microfluidic structure/device is possible involving fast , cost effective and well known pohotolithography and soft-lithography processes using selective substrate for desired UV light induced fluid flow diversion.
A still further object of the present invention is directed to a system for optofluidically controlled fluid motion for variety of microscale applications involving selective fabrication of photosensitive surfaces adapted to serve as the bottom surface of said microfluidic device which can be selectively exposed to UV light of desired characteristics to actuate flow direction control/valve actuation.
A still further object of the present invention is directed to a system for optofluidically controlled fluid motion for variety of microscale applications wherein said photoresponsive materials coated surfaces are usually made of metallic or semiconductor materials such that they become more hydrophilic when it is irradiated with or exposed to ultraviolet light, favoring optofluidic flow diversion.
A still further object of the present invention is directed to a system for optofluidically controlled fluid motion for variety of microscale applications involving fabrication of the microchannel walls to provide micro-confinement effects using standard photolithography or soft lithography techniques.

A still further object of the present invention is directed to a system for optofluidically controlled fluid motion for variety of microscale applications wherein fabrication of the microchannel involves simple thermal and/or chemical bonding of the surfaces coated with photoresponsive material to form the microfluidic flow device.
A still further object of the present invention is directed to a system for optofluidically controlled fluid motion for variety of microscale applications involving possible external fluidic connections through punched holes of selective size for inserting blunt end needles favoring inlet/outlet of the fluid medium to the microfuidic flow control device.
A still further object of the present invention is directed to a system for optofluidically controlled fluid motion for variety of microscale applications wherein any of the branches of the micro channel junction of the microfluidic device could be selectively exposed to UV light for desired duration for fluid flow towards the exposed side with no flow to the unexposed side of the junction, thus representing modification of the hydrophilic property of the photoresponsive substrate inducing fluid flow direction control/valve operation.
A still further object of the present invention is directed to a system for optofluidically controlled fluid motion for variety of microscale applications wherein the fluid medium injected in the microfluidic device used for optofluidic flow control is the de-ionized water.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a system for optofluidically controlled fluid motion for variety of microscale applications comprising,
a substrate coated with photosensitive material in combination with microstructures providing the desired microchannel for the fluid flow in confiinement;
provision of the fluid flow direction in the said microchannel involving atleast one inlet provision and atleast one outlet provision ;and

selective provision of light source dependent on the photosensitive material of the said substrate providing for the selective optofulidic control of the motion of the fluid in the said microchannel.
Another aspect of the present invention directed to a system for optofluidically controlled fluid motion wherein said photosensitive material comprises wide band gap materials.
A still further aspect of the present invention directed to a system for optofluidically controlled fluid motion wherein said wide band gap material comprise band gap of 3.2 eV which falls in UV range preferably including ZnO, Ti02.
A still further aspect of the present invention directed to a system for optofluidically controlled fluid motion wherein said light source comprises UV light source.
According to yet another aspect of the present invention directed to said system for optofluidically controlled fluid motion wherein said substrate comprises of anyone of glass, metallic or semiconductor material.
A still further aspect of the present invention directed to said system for optofluidically controlled fluid motion wherein said microstrutures providing for the microchannels comprise of photoresist with polymeric walls preferably poly-dimethylsiloxane (PDMS), isopropanol.
A still further aspect of the present invention directed to a system for optofluidically controlled fluid motion wherein said photoresist comprise SU-8, HPR,HNR,Microposit S1818 preferably SU-8.
A still further aspect of the present invention directed to a system for optofluidically controlled fluid motion wherein flow direction is dependant on the portion of the surface exposed using light and rate of flow can also be modulated using variation of intensity of light.
According to yet another important aspect of the present invention directed to a system for optofluidically controlled fluid motion comprising an optofluidic valve adapted to selectively allow passage of fluid flow based on said flow direction being dependant on the portion of

the surface exposed using light with or without means for rate of flow modulation involving selective variation of intensity of light.
Another aspect of the present invention directed to said system for optofluidically controlled fluid motion comprising branching configuration involving variable flow diversions and valving based on optofluidic mechanism.
Another aspect of the present invention directed to a system for optofluidically controlled fluid motion wherein choice of working fluid is provided based on the response of philia/phobia of the surface in response to exposure to UV light preferably de-ionized (Dl)-water and DMSO.
Another important aspect of the present invention is directed to a system for optofluidically controlled microfluidic valve, wherein the driving of fluid is controlled by the syringe pump or any alternative mechanism such as electric voltage / electrokinetics or even by optofluidics by exposing entry region to UV light.
According to yet another aspect of the present invention directed to said process for the manufacture of the system for system for optofluidically controlled fluid motion for variety microscale applications as claimed in anyone of claims comprising:
providing said substrate coated with photosensitive material in combination with microstructures providing the desired microchannel for the fluid flow in confiinement;
providing atleast one inlet provision and atleast one outlet provision ;and providing selective provision of light source dependent on the photosensitive material of the said substrate providing for the selective optofulidic control of the motion of the fluid in the said microchannel.
A still further aspect of the present invention is directed to a process , comprising
providing said substrate with desired coating of selective photosensitive material; fabricating microchannel of selective geometry by standard procedures preferably involving anyone of photolithography and soft lithography using said

selective,negative photoresist and polymer to achieve desired precision and high aspect ration of microchannel;
bonding said fabricated channel thermally or chemically with said substrate to form the microconfinement for desired optofluidic control for fluid flow diversion;
providing external inlet and outlets fluidic connections with punched holes of selective dimensions for desired injection and flow circulation of the fluid medium in said microfuidic device;
providing for said selectively disposed UV light sources of requisite energy adapted for selective exposure on the photoresponsive surface of the bottom substrate of the microfluidic system such as to modify the hydrophilic property of said surface causing the fluid medium to move to the exposed path and not to portions unexposed to UV light and thus providing the desired controlled optofluidic actuation of the fluid flow.
According to a further aspect of the present invention directed to a process wherein external fluidic connections are provided in the microfluidic channel by punching holes and inserting blunt end needles.
Further in said process of the invention wherein providing the microchannels on said substrate comprises the steps of :
Providing the pre-treated substrate ;
Coating the same with selective photoresist followed by soft baking comprising heating initially at about 60 to 70°C for a period of 5 to 10 minutes followed by 10 to 20 minutes at about 90 to 100°C;
exposing the photoresists to masks containing patterns of microchannels, developing and rinsing to obtain thus obtain moulds involving the microstructure/microchannels; pouring polymeric solution over the microchannels thus formed and heating for crosslinking followed by further hard baking and processing such as to obtain the desired structures on the substrate.

A still further aspect of the present invention is directed to said process wherein photoresists are exposed to masks containing patterns of microchannel printed over transparent sheets using high resolution printers and subjected to UV exposure such that the photoresist is developed and rinsed to obtain a master mould containing the microstructures and said polymer solution preferably PDMS solution is poured over it and heated for crosslinking (hardening) and is peeled off such that the polymer/ PDMS contain the depressions of the microstructure and is then bonded with the substrate with the surface coated by the wide band gap material, forming desired microchannel of desired configuration.
The details of the invention, its objects and advantages are explained hereunder in greater detail in relation to non-limiting exemplary illustrations as per the following accompanying figures:
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: is the illustration of the flow diagram showing the different steps involved in the fabrication of the substrate surface of selective T-configuration of the desired configuration of the microchannel according to the system of the invention;
Figure 2: is the schematic illustration of the top view of T-shaped junction of the microchannel fabrication on photoresponsive surfaces according to the system of the invention;
Figure 3: is the schematic illustration of the microfluidic device showing the selective provisioning of inlet and outlet connections to the fabricated T-shaped microchannels/microfluidic system of the invention.
Figure 4: is the schematic illustration of the optofluidically controlled microfluidic valve in 3D set up showing the flow of water as the fluid medium and operation of said device by the UV light driven fluid motion/valve actuation for desired flow diversion.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
As already described, the present invention relates to optofluidically controlled microfluidic system with means for light-driven fluid flow direction control in micro-confinement. The microfluidic flow control system of the invention adapted for the UV light influenced flow direction control of the fluid medium in the micro channel by way of selective exposure to the UV light on a photo responsive materials coated substrate to thereby modify the hydrophilic property of the contacting surfaces for desired microfluidic valve operation. The system of the invention as an illustrative embodiment can be selectively fabricated in junction configuration for selective flow diversion under the influence of modification of hydrophilic property of the photo responsive materials coated on the micro channel substrate surface at the bottom. The micro confinement of the channel is fabricated or the walls of the microchannel are fabricated involving rapid fabrication technique such as the standard photolithography and soft lithography processes.
Reference is first invited to the accompanying Figure 1 that illustrates the steps involved and the detailed methodology for fabrication of the microchannel to develop the microfluidic valve system according to the present invention. It is apparent from the sequential steps of the flow chart of Figure 1, that in the first step the substrate which is glass, metal or semiconductor material of desired thickness and dimensions, are pretreated prior to fabrication of confinements using standard photolithographic techniques.
Substrates (e.g. glass slides) are cleaned and dried prior to applying SU-8 2075 photoresist. After cleaning, it is coated with the SU-8 with spin coater - operating at 500 rpm for 5-10 seconds, with an acceleration of 1000 rpm/sec, followed by 2000 rpm for 30 seconds. It is followed by heating known as- soft baking at 65°C for 5 minutes and is followed by further heating for 10-20 minutess at 95°C. The coated and dried substrate is exposed to UV light with energy 215 mJ/cm2 for 20 secs under the mask which contains the T- channel pattern. After exposure, it is again baked which is post exposure bake' for 1-2 minutes at 65°C and 8-10 minutes at 95°C. It is then developed and rinsed in SU-8 developer solution and Isopropanol respectively. Finally it is hard baked to obtain the desired structures on the substrate.

In order to give confinement effects or in simple words to make three other walls for a microchannel soft lithographic technique is adopted as one of the possible routes to achives the same. Soft lithography technique provides a control of precision up to few microns (order of 10 microns) and high aspect ratio and hence is used for fabrication of the microchannels walls. Soft lithography allows rapid fabrication of complex microfluidic structures in flexible polymer substrates such as the one used in this process at a fraction of the cost of traditional glass or semiconductor manufacturing. It is the most recognized technique through out the world. Alternatively, techniques such as the lamination method, can also be used to produce confinement effects.
There are various mechanisms of driving flow in microscale. The present invention involves the modification of the surface properties with the use of light. The surface is coated using a photosensitive material (which has no relation with use of photoresist). Wide band gap materials like ZnO, Ti02 falls in this category are selectively applied in fabrication of the microfluidic device of the invention. They have a band-gap of 3.2 eV which eventually falls in the UV range. Hence, a surface is prepared by coating these materials over glass substrates. These surfaces are usually metallic or semiconductor or polymer or glass surfaces which have been coated with a material that becomes relatively more hydrophilic when it is irradiated with or exposed to ultra-violet light. These photosensitive surfaces serve as the bottom surface of the microfluidic device. The substrate surface thus prepared is an open surface and for the desired flow control experimentation, the flow has to be established in micro confinement.
The photoresist and polymer such as the poly-dimethylsiloxane (PDMS) are involved in order to provide confinement by creating microstructures using them. The selection of PDMS as the polymer substrate is desired on account of its optical transparency and good optical qualities. The photo-resists are exposed to masks containing patterns such as the T-shaped dividing junction of microchannel, printed over transparent sheets using high resolution printers. UV exposure is used to expose the photoresist over these masks (and this UV exposure has nothing to do with optofluidics and is a separate method of photolithography).
According to a non-limiting illustrative form, a T-shaped dividing junction is fabricated to replicate the microfluidic flow device and valve system. The photoresist is developed and rinsed which creates a master mould containing the microstructures (microchannel). PDMS solution is poured over it and heated for crosslinking (hardening) and finally PDMS is peeled

off. Now, this PDMS contain the depressions of the microstructure. It is then bonded with the substrate having its surface coated by the wide band gap material as already stated. The bottom surface of the microfluidic device is bonded thermally or chemically with metallic or glass surfaces confinement.
The accompanying Figure 2 schematically illustrates the T-shaped dividing junction for use as the microfluidic valve device following the steps as described above.
Reference is now invited to the accompanying Figure 3 that schematically illustrates the complete microfluidic valve system having inlet and outlet provision for working fluid circulation with controlled flow diversion. The external fluidic connections have been made in the device by punching holes and inserting blunt end 18 gauge needles. It is clearly apparent from the accompanying Figure 3, that the microfluidic device so fabricated is adapted to demonstrate the light-driven fluid motion on photo-responsive materials in microconfinement to design a valve for desired flow diversion. The fluid medium selected is injected through the inlet at the end of bottom leg of the T-shaped dividing junction and the two outlets are connected at the either extreme ends of the top of T-leg of the junction.
The choice of working fluid is dependant on the response of philia and phobia of the photoresponsive coating material of surface in response to the application of UV light. The present invention experimentally confirmed that DI(De-Ionized)-water and DMSO respond well for this phenomenon.
Reference is next invited to the accompanying Figure 4 that schematically illustrates the microfluidic valve system utilizing the selective T-shaped dividing junction in 3D view along with the interconnecting inlet and outlets for the fluid flow/circulation of the De-ionized water during the experimental flow control using the UV light source providing desired selective exposure to the photoresponsive substrate and to thereby modification of its hydrophilic property to effect controlled fluid flow diversion/valve actuation.
Once the entire set-up is assembled, only one of two branches of the T-shaped dividing junction was selectively exposed to ultra-violet (UV) light for 20 minutes. After exposure to UV light, fluid was driven through the microfluidic network by a syringe pump. Upon reaching the dividing T-shaped junction, the fluid flows towards the exposed side with no flow being observed to the unexposed side.

In the above discussed setup, the driving of flow of fluid was controlled by the syringe pump because only one of the branches were exposed to UV light, although any alternative mechanism can be utilised to drive the fluid flow e.g. use of electric voltage commonly known as Electrokinetics. Even, it can be achieved by the application of optofluidics itself, without the use of any kind of actuating mechanism, if the entry region is also exposed to UV light. This is achieved by the modification of the wetting characteristics of the surface in the entry region.
It is thus possible by way of the present invention to provide a system for optofluidically controlled microfluidic valve for controlled fluid flow in microchannel under the influence of selective exposure of the photoresponsive surface of substrate to UV light of selective wavelength range whereby the possible modification of the hydrophilic property of the substrate coating would favour fluid flow diversion in branched microchannel configuration to the desired direction that is exposed to UV light and not allowing flow to the unexposed branch of the microchannel and thus effecting said desired valve action/actuation. The microfluidic device of the present invention clearly ensure advantages of integration as well as reconfigurability. Integration makes the use of this technology easy to use in a microchannel with complex structures and array of networks. Often, other valves such as electrical or mechanical types, are difficult to integrate into systems of complex structure or complex microfluidic network. In comparison, optofluidic valves makes it easy as it involves the use of light which can be directed in any direction. Mechanical Valves are difficult to incorporate when there is multiple channel networks, while optofluidic valve bears no major disadvantage with the any form of complexity of networks. Moreover, it can be integrated into dimensions very small around or less than 1 micron, because light is used as a guiding device, which can be operated in such scales with the use of UV lasers. The present invention can thus be utilised with distinct advantage for a wide range of applications, mostly specific to the microscale. It can be utilised as a good replacement of the valves used in various different microfluidic circuits. In general, optofluidics can be utilised as a means of actuating flows with a good replacement of syringe/peristaltic pumps, especially in the fields of biomedical and pharmaceutical devices and methods.

WE CLAIM:
1. A system for optofluidically controlled fluid motion for variety of microscale
applications comprising,
a substrate coated with photosensitive material in combination with microstructures
providing the desired microchannel for the fluid flow in confiinement;
provision of the fluid flow direction in the said microchannel involving atleast one
inlet provision and atleast one outlet provision ;and
selective provision of light source dependent on the photosensitive material of the
said substrate providing for the selective optofulidic control of the motion of the fluid
in the said microchannel.
2. A system for optofluidically controlled fluid motion as claimed in claim 1 wherein said photosensitive material comprises wide band gap materials.
3. A system for optofluidically controlled fluid motion as claimed in claim 2 wherein said wide band gap material comprise band gap of 3.2 eV which falls in UV range preferably including ZnO,TiO2.
4. A system for optofluidically controlled fluid motion as claimed in anyone of claims 1 to 3 wherein said light source comprises UV light source.
5. A system for optofluidically controlled fluid motion as claimed in anyone of claims 1 to 4 wherein said substrate comprises of anyone of glass, metallic or semiconductor material.
6. A system for optofluidically controlled fluid motion as claimed in anyone of claims 1 to 4 wherein said microstrutures providing for the microchannels comprise of photoresist with polymeric walls preferably poly-dimethylsiloxane(PDMS), Isopropanol.
7. A system for optofluidically controlled fluid motion as claimed in claim 5 wherein said photoresist comprise SU-8, HPR,HNR,Microposit S1818 preferably SU-8.

8. A system for optofluidically controlled fluid motion as claimed in anyone of claims 1 to 7 wherein flow direction is dependant on the portion of the surface exposed using light and rate of flow can also be modulated using variation of intensity of light.
9. A system for optofluidically controlled fluid motion as claimed in anyone of claims 1 to 8 comprising an optofuidic valve adapted to selectively allow passage of fluid flow based on said flow direction being dependant on the portion of the surface exposed using light with or without means for rate of flow modulation involving selective variation of intensity of light.
10. A system for optofluidically controlled fluid motion as claimed in anyone of claims 1 to 9 comprising branching configuration involving variable flow diversions and valving based on optofludic mechanism.
11. A system for optofluidically controlled fluid motion as claimed in anyone of claims 1 to 10 wherein choice of working fluid is provided based on the response of philia/phobia of the surface in response to exposure to UV light preferably de-ionized (Dl)-water and DMSO.
12. A system for optofluidically controlled microfluidic valve, as claimed in anyone of Claims 1 to 11, wherein the driving of fluid is controlled by the syringe pump or any alternative mechanism such as electric voltage / electrokinetics or even by optofluidics by exposing entry region to UV light.
13. A process for the manufacture of the system for optofluidically controlled fluid motion for variety microscale applications as claimed in anyone of claims 1 to 10 comprising:
providing said substrate coated with photosensitive material in combination with
microstructures providing the desired microchannel for the fluid flow in
confiinement;
providing atleast one inlet provision and atleast one outlet provision ;and
providing selective provision of light source dependent on the photosensitive material
of the said substrate providing for the selective optofulidic control of the motion of
the fluid in the said microchannel.

14. A process as claimed in claim 11 comprising
providing said substrate with desired coating of selective photosensitive material; fabricating microchannel of selective geometry by standard procedures preferably involving anyone of photolithography and soft lithography using said selective,negative photoresist and polymer to achieve desired precision and high aspect ration of microchannel;
bonding said fabricated channel thermally or chemically with said substrate to form the microconfinement for desired optofluidic control for fluid flow diversion;
providing external inlet and outlets fluidic connections with punched holes of selective dimensions for desired injection and flow circulation of the fluid medium in said microfuidic device;
providing for said selectively disposed UV light sources of requisite energy adapted for selective exposure on the photoresponsive surface of the bottom substrate of the microfluidic system such as to modify the hydrophilic property of said surface causing the fluid medium to move to the exposed path and not to portions unexposed to UV light and thus providing the desired controlled optofluidic actuation of the fluid flow.
15. A process as claimed in anyone of claims 11 or 12 wherein external fluidic connections are provided in the microfluidic channel by punching holes and inserting blunt end needles.
16. A process as claimed in anyone of claims 11 to 13 wherein providing the microchannels on said substrate comprises the steps of :
Providing the pre-treated substrate ;
Coating the same with selective photoresist followed by soft baking comprising
heating initially at about 60 to 70 C for a period of 5 to 10 minutes followed by 10 to
20 minutes at about 90 to 100 C;
exposing the photoresists to masks containing patterns of microchannels, developing
and rinsing to obtain thus obtain moulds involving the microstructure/microchannels;

pouring polymeric solution over the microchannels thus formed and heating for crosslinking followed by further hard baking and processing such as to obtain the desired structures on the substrate.
17. A process as claimed in claim 14 wherein photo-resists are exposed to masks
containing patterns of microchannel printed over transparent sheets using high
resolution printers and subjected to UV exposure such that the photoresist is
developed and rinsed to obtain a master mould containing the microstructures and
said polymer solution preferably PDMS solution is poured over it and heated for
crosslinking (hardening) and is peeled off such that the polymer/ PDMS contain the
depressions of the microstructure and is then bonded with the substrate with the
surface coated by the wide band gap material, forming desired microchannel of
desired configuration.
18. A system for optofluidically controlled fluid motion for variety of microscale
applications and a method for its provision and application substantially as
hereindescribed with reference to the non limiting illustrative figures.

An optofluidically guided microfiuidic valve system adapted to selectively direct fluid flow in any junction based fluid flow in micro confinement and a method for such control of fluid flow direction. The microfiuidic system could be fabricated involving standard photolithography and soft lithography for forming microchannel walls. The optofluidically guided device makes use of the modification of the surface properties of coated substrate by selective exposure to UV light for flow diversion/actuation. The system would favour light influenced fluid motion/flow diversion, any branching configuration for flow diversions and valving using optofluidic mechanism. The optofluidic/light driven direction control of the fluid motion on photo responsive material in microscale applications with ease of integration and reconfigurablity especially in valve design is a distinct advantage for a number of microchannel based fluid flow control applications importantly in bio-medical and pharmaceutical industries.