DESC:MICROFLUIDIC DEVICE FOR MULTI STAGE SEPARATION OF FLUIDS

FIELD OF INVENTION
The invention generally relates to the field of microfluidics and more particularly to an integrated microfluidic device for multistage separation of fluids.

BACKGROUND
Centrifugal Microfluidics platforms or lab-on-a-disc platforms are an evolving field of technology for biological analysis and offers many advantages over other microfluidic systems. In centrifugal microfluidics, channels are on a revolving platform which exerts a centrifugal force on the fluid to flow radially outward. However, integration of multiple functionalities on the same centrifugal microfluidic disc is difficult as the fluid flow cannot be stopped while the disc rotates. Hence, a valving mechanism is required to stop fluid even when the disc rotates and thus enable flow manipulation in the microfluidic circuit. There are several known valving techniques examples of which include but is not limited to capillary valves, hydro dynamic resistance valves, sacrificial valves, and siphon shape valves. However, the implementation of the designs of such a system increases fabrication steps and requires special attachments. Hence, there is a need for a microfluidic device that is easy to fabricate and enables one step separation of fluids.

BRIEF DESCRIPTION OF DRAWINGS
So that the manner in which the recited features of the invention can be understood in detail, some of the embodiments are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
FIG. 1 shows a schematic representation of a multistage microfluidic separation system, according to an embodiment of the invention
FIG. 2a shows a valve unit of the secondary separation phase, according to an embodiment of the invention.
FIG. 2b shows the calibration curve of valve units of the microfluidic systems at different locations on the microfluidic disc, according to an embodiment of the invention.

SUMMARY
One aspect of the invention provides a system for multistage separation of fluids. The system includes a centrifugal platform and a device mounted on the centrifugal platform. The device includes a primary separation phase having a microfluidic circuit and a secondary separation phase coupled to the primary separation phase. The secondary separation phase includes a plurality of microfluidic valves arranged radially in a series configuration, and a plurality of radially arranged collection ports provided downstream of the microfluidic valve for selective extraction of fluid. The spinning of the device on the platform results in multistage separation of the fluid.

DETAILED DESCRIPTION OF THE INVENTION
Various embodiments of the invention provide a method of obtaining a microfluidic separation unit. The method includes fabricating the master on a substrate like semiconductor, glass, ceramic or plastic wafer using standard photolithography process. The process of obtaining a microfluidic separation unit by photolithography, is described herein briefly. To create a stamp, PDMS is poured onto the master with microstructure and cured for a time duration of about 2hours to about 3 hours at a temperature range of about 60 ºC to about 70 ºC. The stamp is later bonded to glass by oxygen plasma to create a microfluidic circuit. Specifically, the circuit is formed on a disc capable of being mounted on a centrifugal platform. The multistage microfluidic separation system comprises of two separation phases. The two separation phases are a primary separation phase followed by a secondary separation phase. The primary separation phase involves initial separation of fluids into its components. The secondary separation involves sequential separation of further components of the fluid.
The primary separation is achieved through a microfluidic channel configured for direct separation. The separation is achieved either purely through frequency based separation or separation mediated through an intermediary dependent frequency separation.
In the secondary separation phase, the separation is achieved through series of separation units. The distance between any two consecutive separation unit progresses radially outwards from the first separation unit. The separation of components between two separation units occurs due to the construction of the separation unit and the frequency of the spin of the centrifugal platform. FIG. 1 shows a schematic representation of a multistage microfluidic separation system, according to an embodiment of the invention. The multistage microfluidic separation system includes a centrifugal platform and a device mounted on the centrifugal platform. The device includes a primary separation phase 101 where the primary separation is carried out. The primary separation phase 101 comprises of at least one inlet, at least one storage chamber and a separation channel. A sample of interest is dispensed into the storage chamber. The separation channel is connected to the secondary separation phase 103. The secondary separation phase comprises of a series of separation valves. Each separation valve comprises at least one inlet, at least one storage chamber, at least one collection chamber and a valve channel sandwiched between the storage chamber and the collection chamber. In one example of the invention, the collection chamber of the preceding valve acts as the storage chamber for the successive unit. The valve channel can be “V” shaped channel or any other design in which fluid is forced to move radially inward while the disc rotates. In one example of the invention the separation channel is a typical “U” shaped channel. The outlet of the separation channel is connected to at least one outlet channel 105. In one example of the invention, the separation channel is connected to an arced channel with center coinciding the center of the disc. The principle of separation in a single separation unit of the secondary separation phase 103 shall be explained herein below. FIG. 2a shows a valve unit of the secondary separation phase, according to an embodiment of the invention. In one example of the invention, the separation unit comprises of a storage chamber 201, a collection chamber 203 and a “U” shaped separation channel 205 sandwiched between the storage chamber 201 and the collection chamber 203. The storage chamber 201 is connected to an inlet 207. The collection chamber 203 is connected with outlet channels 209. The first outlet channel is positioned radially inwards to act as an air vent. The second channel is positioned radially outward and is configured for collecting the fluid from the collection chamber.
The channel 205 is positioned in a manner that the crest of the separation channel is radially aligned to the collection chambers. The radial distance of the storage chamber from the centre of the microfluidic device is r1. The radial distance of the crest position of the separation channel from the centre of the microfluidic device is r. The fluid flows from a position radially inward to outward governed by the equation:
P?r?r
Where r is the average position of the channel and ?r(?r = r-r1) is the difference in the liquid height. The difference in the liquid height creates excess pressure at the inlet chamber and pushes fluid to cross the crest due to pressure (P). The frequency at which the fluid crosses the crest is hereinafter referred to as the burst frequency(?). Once the burst frequency is reached, the fluid crosses the crest thereby leading to actuation. The siphoning may occur at a frequency relatively lower than the burst frequency. The design parameters are the position of the crest position (r) and the difference between the liquid height in the storage chamber and the crest (?r).
FIG. 2b shows the calibration curve of a separation unit of the microfluidic system at various positions on a microfluidic disc, according to an embodiment of the invention. The burst frequency (?) depends on the design through the equation:
??r?r
Example 1: Separation of components in blood
The multistage microfluidic separation system as explained briefly hereinabove is implemented in separation of components of blood. The individual circuits of plasma separation and sorting units are fixed on specific locations on the microfluidic device. The blood sample is stored in the storage chamber of the primary phase of the microfluidic separation. A frequency of about 1500 rpm is applied to separate the cells and plasma. The separated cells and plasma flow through the separation channel and are collected into the storage chamber of the first separation unit of the secondary separation phase. A burst frequency (?) of 2200rpm is applied to initiate the actuation of a first component of the blood through the first valve unit of the secondary separation phase. A second burst frequency (?) of about 3100 rpm is applied again to initiate a second actuation of the blood pallet. The above mentioned steps of applying a burst frequency to sequentially separate the individual components of the blood are repeated. The repetitive application of the burst frequency is dependent on the number of valve unit is on the disc which intern depends on the number of components desired to be separated. The outlet of the separation channel is connected to an arced channel with center coinciding the center of the disc in which the blood cell components experience secondary forces with centrifugal force and move towards different outlet based on the density and the size of the cell.
The invention as described herein briefly provides a method and a system for sequential separation of fluids. The system enablesmultistage separation of a mixed fluid on a single microfluidic platform, enables integration of multiple fluid processing units including but not limited to separation and mixing. The system also allows manipulation of fluid movements based on the frequency, instead of delay in fluid flow due to hydrodynamic resistance.
The invention can be modified according to the fluid used for multistage separation any photoresist on any substrate can be used to fabricate the device. The curing of the PDMS and the curing agent can be selected in any ratio, at different curing temperature and time. The versatility of such microfluidic devices can be improved by integrating spectroscopic technique such as Raman Spectroscopy. Integration of a plasmonic chip, which has metal nanostructures, aids in enhancement of Raman signal. The proposed fabrication technique enables to put large area SERS substrate effectively in microfluidics. Additionally, Raman spectrum can be obtained from the device itself without removing the separated fluid. Raman signal from the plasmonic substrate assists in the characterization of the separated fluid.
The aforesaid description is enabled to capture the nature of the invention. It is to be noted, however, that the aforesaid description and appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

,CLAIMS:We claim:
1. A system for multistage separation of fluids, the system comprising:
a centrifugal platform; and
a device mounted on the centrifugal platform, wherein the device includes a primary separation phase having a microfluidic circuit, a secondary separation phase coupled to the primary separation phase wherein the secondary separation phase includes a plurality of microfluidic valves arranged radially in a series configuration, and a plurality of radially arranged collection ports provided downstream of the microfluidic valve for selective extraction of fluid;
wherein, the spinning of the device on the platform results in multistage separation of the fluid.
2. The system as claimed in claim 1, wherein the fluid is biological fluid selected from a list comprising of blood, sputum, cerebro spinal fluid, semen.
3. The system as claimed in claim 1, wherein the microfluidic circuit comprises of a first storage chamber, at least one input port connected to the first storage chamber, at least one output port connected to the storage chamber, and a first separation channel formed out of the storage chamber.
4. The system as claimed in claim 1, wherein the secondary separation phase is connected to the primary separation phase through the separation channel.
5. The system as claimed in claim 1, wherein each of the microfluidic valve includes an inlet, a storage chamber distinct from the first storage chamber, a collection chamber and a separation channel having a construction distinct from the first separation channel connected between the storage chamber and the collection chamber.
6. The microfluidic valve as claimed in claim 4, wherein the distance between any two consecutive microfluidic valves progresses radially outwards from the first microfluidic valve.
7. The microfluidic valve as claimed in claim 4, wherein the separation channel is constructed to form a crest, the crest of the separation channel is radially aligned to the corresponding collection chamber of the given microfluidic valve.
8. The system as claimed in claim 1, wherein the first separation channel is connected to the inlet of the first microfluidic valve.
9. The microfluidic valve as claimed in claim 4, wherein the separation channel of the terminal microfluidic valve is connected to the radially arranged collection ports.
10. The system as claimed in claim 1, wherein the device is formed as a single unit and is capable of being mounted on the centrifugal platform.
11. The system as claimed in claim 1, wherein the separation of the fluid is achieved through a progression of frequency of rotation of the centrifugal platform.
12. The system as claimed in claim 1, wherein the primary separation of the fluid occurs at a base frequency that is dependent on the nature of the fluid selected.
13. The system as claimed in claim 1, wherein the secondary separation of the fluid is achieved at the plurality of microfluidic valves, wherein the separation of the fluid at each of the separation channel of the given microfluidic valve is dependent on a burst frequency specific to each of the separation channel, wherein the burst frequency is determined based on the radial distance of the separation channel from the centre of the centrifugal platform.

Bangalore NARENDRA BHATTA HL
4thJuly 2018 (INTELLOCOPIA IP SERVICES)
AGENT FOR APPLICANT