CLIAMS:1. A portable handheld device for on-chip biosynthesis of nanoparticles, the device comprising:
a microfluidic chip comprising a first microfluidic channel that is configured to receive a precursor at a first inlet, and a second microfluidic channel that is configured to receive a reducing agent at a second inlet; the first and second microfluidic channels joining together to form at least one reaction channel configured with micro-mixing geometry to allow reaction between the precursor and the reducing agent to form metal nanoparticles at room temperature, wherein the reaction channel is connected to an outlet channel; and
a vacuum based pumping system coupled with the outlet channel of the microfluidic chip to induce suction of the precursor and of the reducing agent through the inlets of the first and the second microfluidic channels, wherein the first and the second microfluidic channels are dimensioned to control flow of the precursor and of the reducing agent to their respective desired values; and wherein the reducing agent is a plant extract.
2. The device of claim 1, wherein the device further comprises a synthesized nanoparticle collection unit configured between the outlet channel and the vacuum based pumping system, and wherein the collection unit is a pluggable and removable microfluidic system.
3. The device of claim1, wherein the plant extract is obtained by boiling leaves of Partheniumhisterophorus or Lawsoniainermis.
4. The device of claim 1, wherein the at least one reaction channel is serpentine in nature with length in the range of 5 – 60 cm and width in the range of 10-1000 µm.
5. The device of claim 1, wherein width of the first and the second microfluidic channels and of the outlet channel is in the range of 10 µm to 500 µm.
6. The device of claim 1, wherein said microfluidic chip is made of polydimethylsiloxane.
7. The device of claim 1, wherein said microfluidic chip is made of glass or an optically transparent material Polymethyl methacrylate (PMMA).
8. A method for synthesizing metal nanoparticles comprising steps of:
Providinga portable handheld device for on-chip biosynthesis of nanoparticles, the device comprising:
a microfluidic chip comprising at least a first microfluidic channel, that is configured to receive a precursor at a first inlet and a second microfluidic channel configured to receive a reducing agent at a second inlet; the first and second microfluidic channels joining together to form at least one reaction channel configured with micro-mixing geometry to allow reaction between the precursor and the reducing agent to form metal nanoparticles at room temperature wherein the reaction channel connected to an outlet channel;
a vacuum based pumping system coupled to the outlet channel of the microfluidic chip to induce suction of the precursor and of the reducing agent through the inlets of the first and the second microfluidic channels wherein the first and the second microfluidic channels are dimensioned to control flow of the precursor and of the reducing agent to their respective desired values; and
a pluggable and removablesynthesized nanoparticle collection unit configured between the outlet channel and the vacuum based pumping system;
positioning in a first reservoir,the precursor at the first inlet of the first microfluidic channel;
positioning in a second reservoir the reducing agent at the second inlet of the second microfluidic channel;
priming the vacuum based pumping system to generate a vacuum to facilitate suction of the precursor and the reducing agent through the first and the second inlets of the first and the second microfluidic channels and further induce their flow through the least one reaction channel;
unplugging the synthesized nanoparticle collection unit from the device after requisite reaction time.
9. The method of claim 8, wherein the precursor is a salt form of a metal selected from the group consisting of gold, silver, cobalt, copper, platinum and palladium.
10. The method of claim 9, wherein the salt is selected from the group consisting of sulphates, silicates, nitrates, nitrides, oxides, sulfides and chlorides.
11. The method of claim 7, wherein the flow rate of the precursor is in the range of from 500 µL/min to 2000 µl/min, and wherein the flow rate of the reducing agent is in the range of from 0.1 µL/min to 50 µl/min.
12. The method of claim 11, wherein there ducingagentis a plant extract prepared by boiling leaves of Partheniumhisterophorus or Lawsoniainermisin water to extract water soluble components.
,TagSPECI:FIELD OF THE INVENTION
[1] The present disclosure pertains to technical field of nanotechnology. In particular, the present disclosure pertains to continuous flow microfluidic system and method of on-chip biosynthesis of nanoparticles using such microfluidic system at room temperature.

BACKGROUND OF THE INVENTION
[2] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[3] Metal nanoparticles such as gold, silver, copper, iron, palladium, platinum, zinc, aluminium, titanium, etc. are used in wide range of applications such as drug delivery, diagnosis, sensors, water purification, effluent treatment, electronics, solar cell, etc. Several new apparatuses and processes have been developed recently for synthesis of metal nanoparticles. For example, microwave assisted co-precipitation, hydrothermal method, sol-gel process, sonication method, vapour deposition, mechanical attrition, etc. have been employed to synthesize metal nanoparticles.
[4] However, most of the methods known in the art require complex instrumentation, very expensive equipment, and most of them involve high pressure and temperature. Further, the known micro reactors and mixing schemes demonstrate a number of deficiencies when considered for purpose of nanoparticle generation. For example, some of the methods lack ability to control generation and growth of nanocrystals which results in wide distribution of nanoparticle size.
[5] Hydrothermal synthesis of metal nanoparticles employs high process temperature and pressure. The wet chemical synthesis techniques such as sol-gel and co-precipitation require the presence of strong reducing agents such as sodium borohydride which is very hazardous in nature. Further, some of the known methods also require stirring using magnetic bar at any point of reaction step or shaking.
[6] Microfluidic on-chip synthesis of metal nanoparticles and nanowires has been developed in the art using different synthetic chemicals. These methods often involve reduction of the relevant metal salts or decomposition of organometallic precursor by the synthetic reducing agents in presence of a suitable surfactant that is expensive. Further, most of these synthetic reducing agents are carcinogenic and hazardous to the environment, and also the microfluidic synthetic methods using these chemicals require high process temperature.
[7] Biosynthesis of metal nanoparticles has also been developed in the art using tubular-fluidic system that employs tubular coils immersed in beakers to increase or decrease the temperature. Further, the biosynthesis techniques known in the art require heating of the reactor system since they employ sundried leaf powder based extract for the synthesis.
[8] There is thus a need in the art for a microfluidic/reactor system for synthesizing metal nanoparticles which is simple in construction, highly energy efficient, produces nanoparticles at room temperature and also facilitates precise control over growth and size distribution of resulting particles. Also, there is a need for a method of synthesizing metal nanoparticles that is rapid, inexpensive, environment friendly, reproducible and devoid of hazardous chemicals.
[9] The present invention satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the prior art.

OBJECTS OF THE INVENTION
[10] It is an object of the present disclosure to provide a portable hand held device for synthesizing nanoparticles that facilitates precise control over growth and size distribution of resulting particles.
[11] It is a further object of the present disclosure to provide a device for synthesizing nanoparticles that facilitates precise control over flow rates of metal precursor and reducing agent during the course of particle production run.
[12] It is another object of the present disclosure to provide a device for synthesizing nanoparticles that facilitates particle production at ambient temperature.
[13] It is another object of the present disclosure to provide a method for synthesizing nanoparticles that is completely devoid of hazardous chemicals and thereby making the process pollution free and environment friendly.
[14] It is another object of the present disclosure to provide a method that facilitates continuous production of nanoparticles with high reproducibility, yield and homogeneity.
[15] It is another object of the present disclosure to provide a simple and economic method of synthesizing nanoparticles.

SUMMARY OF THE INVENTION
[16] Aspects of the present disclosure relate to a hand held portable device for synthesizing nanoparticles. In an aspect the disclosed device is based on microfluidic chip that facilitates precise control over growth and size distribution of resulting particles and also enables production of nanoparticles at room temperature. It is to be understood that though the present disclosure describes various embodiments with reference to synthesis of metal nanoparticles using a plant extract as reducing agent, it is possible to use the disclosed embodiments for other processes after suitable modifications that would be apparent to persons skilled in art and all such applications are well within the scope of the present disclosure.
[17] In an embodiment the microfluidic chip can incorporate a first channel having a first inlet, a second channel having a second inlet, a reaction section positioned downstream from the first and the second channels, wherein the reaction section comprises at least one reaction channel provided with at least one micromixing section, and an outlet channel fluidly coupled to the at least one reaction channel and positioned downstream from the reaction section.
[18] According to embodiments of the present disclosure, the microfluidic chip can be formed of glass or an optically transparent polymeric material such as Polymethyl methacrylate (PMMA). The reaction channel can be serpentine in nature with effective length in the range of 5 – 60 cm and width in the range of 10-1000 µmµm. The width of the first channel, second channel and outlet channel can preferably be in the range of 10 µm to 500 µm.
[19] In an embodiment, the device can further incorporate a vacuum based pumping system to facilitate flow of fluids through the microfluidic channels configured on the microfluidic chip wherein the vacuum based pumping system can be configured to the outlet channel and can among various option comprise a syringe that can be pulled and locked in position to create suction to suck fluids through the first and second inlets of the first and second channels and make the fluids flow through the first and second channels and the reaction channel.
[20] In an embodiment, the first and the second channels can be dimensioned to control the flow of fluids under the suction of the vacuum based pumping system at their respective desired flow rates wherein the desired flow rate can depend on metal nanoparticles to be synthesized and choice of corresponding precursor and reducing agent. In an aspect, microfluidic chips can be fabricated to meet the requirement of synthesizing different nanoparticles of different metals using different combinations of the precursor and the reducing agent.
[21] In an embodiment, the device can further incorporate means to collect synthesized nanoparticles. The means to collect synthesized nanoparticles can be configured between the outlet channel and the syringe of the vacuum based pumping system and can prevent the synthesized nanoparticles from traveling to the syringe/pumping system. In an aspect the means to collect synthesized nanoparticles (also referred to as collection unit/device or collection and storage device/unit and the terms used interchangeably hereinafter) can be a removable and externally plugged in microfluidic device designed to act as a synthesized nanoparticle collection unit and can be unplugged after each synthesis. In an aspect the collection device can prevent dismantling and changing/cleaning of individual units of the nanoparticle synthesis device after each use.
[22] In another aspect, the present disclosure provides a method for synthesizing metal nanoparticles, wherein the method can include steps of: (a) providing a device for synthesizing metal nanoparticles wherein the device cancomprise: a microfluidic chip having a first channel having a first inlet, a second channel having a second inlet and a reaction section positioned downstream from the first and second channels, wherein the first channel and the second channel are dimensioned to control flow rates of fluids through them to the reaction section and wherein the reaction section comprises at least one reaction channel provided with at least one micromixing section; and an outlet channel fluidly coupled to the at least one reaction channel and positioned downstream from the reaction section; a vacuum based pumping system to facilitate flow of fluids through the microfluidic channels; and a means to collect synthesized nanoparticles configured between the outlet channel and the vacuum based pumping system wherein the means can be a microfluidic device designed to act as a synthesized nanoparticle collection unit; (b) positioning a first reservoir containing solution of a metal precursor into the first inlet, (c) positioning a second reservoir containing a reducing agent into the second inlet, (d) priming the vacuum based pumping system by pulling and locking a syringe of the vacuum based pumping system to facilitate flow of the metal precursor and the reducing agent through the first and the second microfluidic channels and into the reaction channel at respective desired flow rates and (e) unplugging the collection unit into which the synthesized metal nanoparticles have collected.
[23] In one embodiment, the metal precursor can be a salt form of a metal selected from the group consisting of gold, silver, cobalt, copper, platinum and palladium. The salt form can be sulphates, silicates, nitrates, nitrides, oxides, sulfides or chlorides.
[24] In another embodiment, the reducing agent used in the synthesis of metal nanoparticlescan be a plant extract and can be prepared by boiling leaves of a plant in water to extract water soluble components.
[25] In yet another embodiment, the plant extract can be prepared by boiling leaves of Partheniumhisterophorus or Lawsoniainermis in water.
[26] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[27] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[28] FIG. 1 illustrates an exemplary schematic general arrangement for a portable handheld device for synthesis of metal nanoparticles in accordance with embodiments of the present disclosure.
[29] FIG. 2A and FIG. 2B illustrate an exemplary working model of the portable handheld device for synthesis of metal nanoparticles in accordance with embodiments of the present disclosure.
[30] FIG. 3 illustrates a preferred configuration of a microfluidic chip for synthesizing metal nanoparticles in accordance with embodiments of the present disclosure.
[31] FIG. 4 depicts an exemplary experimental setup for synthesis of metal nanoparticles in accordance with embodiments of the present disclosure.
[32] FIG. 5illustrates an exemplary optical microscope image showing reddish brown solution of silver nanoparticles formed at the junction of first and second inlet channels of the microfluidic system carrying silver nitrate and Partheniumhisterophorus leaf extract, in accordance with embodiments of the present disclosure.
[33] FIG. 6illustrates exemplary images of embodiments of the master mould fabricated using photo-lithography process of the synthesized metal nanoparticles collection and storage device in accordance with embodiments of the present disclosure.
[34] FIG. 7 is an UV-VIS spectroscopy showing 416nm SPR peak of silver nanoparticles synthesized within the microfluidic system in accordance with embodiments of the present disclosure.
[35] FIG. 8A to FIG. 9F illustrate exemplary Atomic Force Microscopic images (2D and 3D) from different angles of silver nanoparticles synthesized in accordance with embodiments of the present disclosure.
[36] FIG. 9A to FIG. 9Fillustrate exemplary High Resolution Transmission Electron Microscopic images of silver nanoparticles at different scales, synthesized in accordance with embodiments of the present disclosure.
[37] FIG. 10illustrates an exemplary Nanoparticle Size Histogram depicting the size range of silver nanoparticles synthesized in accordance with embodiments of the present disclosure.
[38] FIG. 11illustrates an exemplary FTIR spectroscopy image of silver nanoparticles synthesized in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION
[39] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[40] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[41] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[42] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[43] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
[44] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
[45] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[46] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[47] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[48] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[49] Embodiments of the present disclosure relate to a device to synthesize metal nanoparticles. In an aspect the disclosed device is a hand held portable device and the synthesis of nanoparticles takes place at room temperature without any other aid such as ultrasonic or microwaves making the synthesis process very simple and fast.
[50] In an embodiment, the disclosed device is based on a microfluidic chip and further comprises vacuum based pumping system that facilitates flow of required fluids through microfluidic channels of the microfluidic chip.
[51] In an embodiment, the microfluidic channels of the microfluidic chip can be configured to control the flow of the required fluids through the channels at their respective desired values to facilitate precise control over growth and size distribution of nanoparticles synthesized during the processsimultaneously avoiding any wastage.
[52] In an embodiment, the device can incorporate a collection unit into which the synthesized metal nanoparticles can get collected. The collection unit can be a removable and externally plugged in microfluidic device designed to act as a synthesized nanoparticle collection unit and can be unplugged after each synthesis. In an aspect the collection device can prevent dismantling and changing/cleaning of individual units of the nanoparticle synthesis device after each use.
[53] In an embodiment, the present disclosure provides a method of bio synthesis of metal nanoparticles using a precursor and a reducing agent that can be a plant extract. The precursor can be a salt form of a metal selected from the group consisting of gold, silver, cobalt, copper, platinum and palladium. The salt form can be sulphates, silicates, nitrates, nitrides, oxides, sulfides or chlorides.
[54] In another embodiment, the plant extract used as reducing agent in the synthesis of metal nanoparticles can be prepared by boiling leaves of a plant in water to extract water soluble components. In an aspect use of a plant extract as a reducing agent can prevent use of chemicals that are carcinogenic and hazardous to the environment.
[55] In yet another embodiment, the plant extract can be prepared by boiling leaves of Partheniumhisterophorus or Lawsoniainermis in water.
[56] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
[57] Referring to FIG. 1 that discloses an exemplary schematic general arrangement for a portable handheld device 100 for synthesis of metal nanoparticles in accordance with embodiments of the present disclosure. The device 100 can comprise a microfluidic chip 102(also referred simply as chip), a vacuum based pumping system that can be syringe 104 which can be pulled to create vacuum and locked in position to facilitate suction and flow of required fluids through the channels of the microfluidic chip 102. The device can further incorporate reservoirs such as a leaf extract reservoir 110 and a precursor reservoir 108 wherein these reservoirs can be configured at inlets of the channels of the microfluidic chip 102 to help suction of the leaf extract and the precursor under influence of the vacuum generated by the vacuum based pumping system. The device 100 can additionally incorporate a collection unit 106 to collect and store the synthesized nanoparticles.
[58] FIG. 2A and FIG. 2B illustrate images 200 and 250 of an exemplary working model of the portable handheld device for synthesis of metal nanoparticles in accordance with embodiments of the present disclosure. The different constituents i.e. the microfluidic chip 102, syringe 104 and reservoirs 108 and 110 of the device 100 can be configured on a casing 202 to make the device 100 portable. FIG. 2B illustrates an image 250 of the device 100 held in hand to put its size in relative perspective. As can be seen that the device is truly portable and hand held and does not require any additional external means such as heating means or ultrasonic or microwaves to synthesize metal nanoparticles.
[59] FIG. 3 illustrates a preferred configuration 300 of the microfluidic chip 102 for synthesizing metal nanoparticles in accordance with embodiments of the present disclosure. The microfluidic chip 102 can comprise a first channel 302 having a first inlet 306, and a second channel 304 having a second inlet 308. The first and second channels can lead to a reaction section 310 in which chemical reaction between the reactants can take place. The reaction section 310 can include at least one reaction channel 312 that can provide aging length for the growing nanoparticles. The reaction channel 312 can be provided with at least one micromixing section 314 that can have a specific flow design throughout the flow path to enhance mixing of the reactants. The microfluidic chip102 can include at least one outlet or exit channel 316 through which the synthesized nanoparticles may exit the chip102. The outlet channel 316 can be fluidly coupled to the reaction channel 312 and can be positioned downstream from the reaction section 310.
[60] The microfluidic chip 102 may be formed of any material that is suitable for use in synthesis of nanoparticles and it can be fabricated using any method known in relevant art. In a preferred embodiment, the microfluidic chip 102 can be fabricated on glass using through femto second laser inscriptions followed by HF etching. Alternatively, an optically transparent polymeric material such as but not limited to Polymethyl methacrylate (PMMA) can also be used.
[61] In an embodiment, the first channel 302 and the second channel 304 can be dimensioned to control the flow of fluids under the suction of the vacuum based pumping system at their respective desired flow rates wherein the desired flow rate can depend on metal nanoparticles to be synthesized and choice of corresponding precursor and reducing agent. In an aspect, microfluidic chips can be fabricated to meet the requirement of synthesizing different nanoparticles of different metals, of different sizes using different combinations of the precursor and the reducing agent and, therefore, it is to be appreciated that FIG. 3 is purely exemplary and the features of the microfluidic chip102, such as, the inlets 306 and 308, outlet 316, reaction channel 312 and the micromixing section 314 can take any other size, length and shape desired to suite the intended purpose and use.
[62] In an exemplary embodiment, length of inlet channels302 and 304 can be in the range of 100 – 2000 microns and width 10 – 1000 microns. Further micro mixer – reaction channel 312/314 can be of serpentine channel geometry with overall reactor channel cross section of 1.6 cm x 7 cm and width of the channel can be 100 microns with the expansion chamber width of 400 microns.
[63] In an embodiment, the micromixing section 314 can be a thin and long channel in which complete mixing of reactants i.e. the metal precursor and plant extract can occur in approximately less than one second. The micromixing section 314 can have a specific flow design throughout the flow path to enhance mixing of the reactants. The micromixing section 314 can have a planar geometry that enables effective mixing of the metal precursor and the plant extract within a very small foot-space and thereby reducing the quantity of reagents required to synthesize metal nanoparticles.
[64] The reactants such as the metal precursor and the reducing agent can be sucked into the microfluidic chip102 through the inlets 306 and 308 under influence of vacuum generated by suitable means. It is to be understood that though in the exemplary embodiment a syringe 104 has been used for the purpose, any other means such as a peristaltic pump, a vacutainer, an aspirator or a vacuum pump can be used for the purpose without any limitation. The reactants can get combined in the reaction channel 312 for effecting chemical reactions which may take place at a very fast rate. In an embodiment, the reaction time for formation of metal nanoparticles can be less than one second. The flow rates of the reactants can be precisely controlled by configuring the microfluidic channels with appropriate dimensions. In an exemplary embodiment, the optimal flow rate of metal precursor can be in the range of from 500 µl/min to 2000 µl/min, while the flow rate of plant extract can from 0.1 µl/min to 50 µl/min.
[65] FIG. 4 depicts an exemplary experimental setup 400 for synthesis of metal nanoparticles using the disclosed microfluidic chip 102 in accordance with embodiments of the present disclosure. In the experiment the synthesis of nanoparticles is being observed by an optical microscope 402. In the exemplary experimental set up, silver nitrate was used as the precursor and Partheniumhisterophorus leaf extract was used as a reducing agent to synthesize silver nanoparticles.
[66] FIG. 5illustrates an exemplary optical microscope image 500at junction of first channel 302 and the second channel 304 of the microfluidic chip 102during the exemplary experiment of the FIG. 4. The exemplary optical microscope image 500shows reddish brown solution of silver nanoparticles formed at the junction.
[67] FIG. 6illustrates an exemplary image 600 of the master mould of the synthesized nanoparticles collection and storage device fabricated using photo-lithography process in accordance with embodiments of the present disclosure. The synthesized nanoparticles collection and storage device 106 can be prepared using soft-lithography processes and can be configured between the outlet channel 316 of the chip 102 and the syringe 104 of the vacuum based pumping system and can prevent the synthesized nanoparticles from traveling to the syringe. In an aspect the synthesized nanoparticles collection/storage unit 106 can be a removable and externally plugged-in microfluidic device and can be unplugged after each synthesis. In an aspect the collection device can prevent dismantling and changing/cleaning of individual units of the nanoparticle synthesis device after each use. The collection unit 106 can have an input 602 that can be connected to the outlet channel 316 and an outlet 604 that can be connected to the syringe 104. In an embodiment the collection unit can be made of thin PDMS membrane and thickness of the thin membrane can be in the range of 10microns to 200 microns. FIG. 6 illustrates two alternate embodiments of the master mould of the synthesized nanoparticles collection and storage device of thickness 150 microns and 200 microns.
[68] In an embodiment, the chip 102 can incorporate an additional third channel with an additional third inlet. The third channel and corresponding inlet can be used for cleaning and flushing the micro channels of the chip 102 if desired.
[69] In another aspect, the present disclosure provides a method for synthesizing metal nanoparticles, wherein the method can include steps of: (a) providing a device 100 for synthesizing metal nanoparticles comprising: a microfluidic chip102having a first channel 302 having a first inlet 306 , a second channel 304 having a second inlet 308 and a reaction section 310 positioned downstream from the first channel 302and second channel 304, wherein the first channel 302 and the second channel 304 are dimensioned to control flow rates of fluids through them to the reaction section and wherein the reaction section 310 comprises at least one reaction channel 312 provided with at least one micromixing section 314 and an outlet channel 316 fluidly coupled to the at least one reaction channel 312 and positioned downstream from the reaction section 310; a vacuum based pumping system 104 to facilitate flow of fluids through the microfluidic channels; and a means to collect synthesized nanoparticles such as the collection unit 106 configured between the outlet channel 316 and the vacuum based pumping system 104 wherein the means can be a microfluidic device designed to act as a synthesized nanoparticle collection unit; (b) positioning a first reservoir 108 containing solution of a metal precursor into the first inlet 306, (c) positioning a second reservoir 110 containing a reducing agent into the second inlet 308, (d) priming the vacuum based pumping system 104 by pulling and locking a plunger of the vacuum based pumping system 104 to facilitate flow of the metal precursor and the reducing agent through the first and the second microfluidic channels and into the reaction channel 312 at respective desired flow rates and (e) unplugging the collection unit 106 into which the synthesized metal nanoparticles have collected.
[70] In one embodiment, the metal precursor can be dissolved in a suitable solvent to produce a solution which in turn can be placed into the first reservoir 108 and configured with the first inlet 306. The metal precursor can be a salt form of a metal selected from the group consisting of gold, silver, cobalt, copper, platinum and palladium. The salt form can be sulphates, silicates, nitrates, nitrides, oxides, sulfides or chlorides.
[71] In another embodiment, the reducing agent in the synthesis of metal nanoparticles can be placed in the second reservoir 110 and configured with the second inlet 308. In an embodiment, the reducing agent can be a plant extract and can be prepared by boiling leaves of a plant in water to extract water soluble components.
[72] In yet another embodiment, the plant extract can be prepared by boiling leaves of Partheniumhisterophorus or Lawsoniainermis in water.
[73] The reactants can mix together at the intersection of the first and second inlet channels and the resulting combination may then pass into reaction channels 312 through micromixing section 314. Nanoparticles can grow to their final size in the reaction channels 312 and the resulting particles can get collected in the collection unit 106.

EXAMPLES
[74] The present disclosure is further explained in the form of following examples. However, it is to be understood that the foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.
[75] On-chip synthesis of silver nanoparticles at room temperature using Partheniumhisterophorususing the device 100 of the present disclosure: Plant extract was prepared by boiling 30 grams of leaves of Partheniumhisterophorus (a notorious weed) in 100 ml de-ionized water for one hour. The extract was filtered through Whatman Paper and stored at 4oC. The pH of the leaf extract was adjusted to 10 by the addition of 0.1N NaOH. 1mM of aqueous silver nitrate solution was received into the first inlet 306 and the pH adjusted leaf extract was received in the second inlet 308 of the microfluidic chip102 at different flow rates using syringe pumps fitted with 1 ml syringes. The optimal flow-rates for on-chip biosynthesis of silver nanoparticles were found to be 1000 µl/min for metal precursor and 20 µl/min for Parthenium leaf extract. Formation of silver nanoparticles was visually observed by the color change at the junction of the two inlets of the microfluidic system. FIG. 5 depicts an optical microscope image showing reddish brown solution of silver nanoparticles being formed at the junction of first and second inlet channels of the microfluidic system. Flow rates were optimized by way of analyzing the Surface Plasmon Resonance (SPR) band of the obtained silver nanoparticles.
[76] Microliter volumes of silver nanoparticles as obtained above were taken in a 96 well plate and subjected to UV-VIS absorption spectroscopy scan from 300 nm to 800 nm using the TECAN 200 INFINITE plate reader. As shown in FIG. 7, silver nanoparticles formed at the optimized flow rates (1000:20 µl/min) had a narrow peak at 416 nm.
[77] Initial morphological characterization of the silver nanoparticles was done using Atomic Force Microscopy (using Nanowizard AFM of JPK INSTRUMENTS) at different angles in tapping mode and the results have been provided in FIG. 8A to FIG. 8D.
[78] Further, size and shape of the above synthesized silver nanoparticles were confirmed by using High Resolution Transmission Electron Microscopy (FEI TECNAI) at size scales of 200 nm, 100 nm, 20 nm, 20nm and 5 nm (FIG.9A to FIG.9F). Fringe pattern observed at 5 nm scale was analyzed using Image J and the pitch of the pattern was found to be 0.23nm (FIG.9E), which matched with the d-spacing of silver nanoparticles for crystal lattice plane. Selected Area Electron Diffraction (SAED) pattern was obtained for the synthesized silver nanoparticles showing distinct rings having d-spacing value of 0.235 nm for crystal lattice plane [111] and 0.144 nm for crystal lattice plane [220] (Figure 9F). By analyzing HR-TEM image of the silver nanoparticles using MATLAB, it was found that the majority of the nanoparticles size lied between 4nm to 6nm as shown in FIG. 10.
[79] Fourier Transformation Infrared spectroscopy (FTIR) of the leaf extract, and the synthesized silver nanoparticles were generated to determine the reducing mechanism of the biosynthetic method and the FTIR data has been provided in FIG. 11. The FTIR data helped to identify the interaction of nanoparticles and to identify the possible biomolecules responsible for capping and efficient stabilization of the silver nanoparticles synthesized using the leaf extracts. Table 1 below provides the FTIR bands of the leaf extract and the silver nanoparticles, from which the functional groups involved in the formation of the silver nanoparticles can be inferred.

Partheniumhisterophorus leaf extract (cm-1)
Silver nanoparticles (cm-1)
Functional Groups involved
3432 3436 N-H Stretch
2090 2092 C=N Stretch
1636 1637 Amide I band
1404 1405 -C-O- Stretch (Tertiary alcohols)
1328 1320 C-N Stretch (Aromatic amines)
1257 1254 =C-O- (Polyols)
672 670 Aromatic compounds

Table 1

[80] The bands observed at 1636 cm-1 in the leaf extract aroused from carbonyl group and it was shifted to 1637 cm-1 in the nanoparticles which suggested that carbonyl groups present in the leaf extract may have interacted with the nanoparticles. The band at 3400-3500 cm-1 was characteristic of the O-H stretching vibration of the alcoholic compounds. The observation of bands at 1405 cm-1 and 1328 cm-1 in the leaf extract and the slight shift of these bands in the nanoparticles might be attributed due to the C=O, C-N stretching vibrations of the alcohols and the aromatic amine groups. The bonds or functional groups such as –C=C-, -C-O-, and –C-O-C- were derived from the compounds present in the leaf extract of Partheniumhisterophorus.
[81] It was assumed that water soluble compounds such as flavanoids, terpenoids are the capping ligands of the nanoparticles. The band at 1257 cm-1 confirmed the presence of C-O groups from polyols. The shift of this band was attributed to the reduction of metal ions coupled with the oxidation of phenolic components of polyols. The band at 672 cm-1 in the leaf extract was shifted to 670 cm-1 and the decrease in the transmittance in the nanoparticles indicated the possible involvement of some aromatic compounds present in the leaf extract in the reduction of metal ions.

ADVANTAGES OF THE PRESENT INVENTION
[82] The present disclosure provides a portable hand held device for synthesizing nanoparticles that facilitates precise control over growth and size distribution of resulting particles.
[83] The present disclosure provides a device that enables rapid production of nanoparticles with continuous throughput.
[84] The present disclosure provides a device that produces nanoparticles with uniform size distribution.
[85] The present disclosure provides a device that facilitates production of nanoparticles at ambient temperature.
[86] The present disclosure provides a device that incorporates a nanoparticle collection unit that can be plugged and removed after the synthesis process.
[87] The present disclosure provides a device that requires very less amount of metal precursor and reducing agent to synthesize microliter nanoparticles for applications requiring less volume of nanoparticles such as sensing and bio bar-coding.
[88] The present disclosure provides a method for synthesizing nanoparticles which employs plant extracts as reducing agents and is completely devoid of hazardous chemicals, thereby making the process pollution free and environment friendly.
[89] The present disclosure provides a method for synthesizing nanoparticles which does not involve stirring or shaking and thereby making the process energy efficient.
[90] The present disclosure provides a method for synthesizing nanoparticles, wherein the reaction time for formation of the nanoparticles is shorter compared to the known methods.
[91] The present disclosure provides a method that facilitates continuous production of metal nanoparticles with high reproducibility, yield and homogeneity.