EP3881054A1

EP3881054A1 - An optical nano-manipulator for particles in a fluid

Info

Publication number: EP3881054A1
Application number: EP19885440.8A
Authority: EP
Inventors: Ambarish Ghosh; Souvik Ghosh
Original assignee: Indian Institute of Science IISC
Current assignee: Indian Institute of Science IISC
Priority date: 2018-11-14
Filing date: 2019-11-14
Publication date: 2021-09-22
Also published as: EP3881054A4; WO2020100077A1

Abstract

A Colloidal Optical Tweezer (CPT) 100 for use in a colloidal solution containing nano particlesis disclosed, comprising a disc 102 of plasmonic material coupled to an end of a dielectric nanorod 104. When a low power polarised laser beam is focussed on the CPT 100, the disc work as a plasmonic antenna to trap the nano particles based on a plasmonic gradient force of localized and enhanced electromagnetic intensity in optical near field generated by the discs, and the CPT100 is trapped to the light beam on account of far field optical forces acting on the dielectric nanorod as a result of the light beam. Steering the light beam enables movement of the CPT100 to desired locations where the trapped nano particles can be released. The CPT100 can work in any microfluidic chamber, i.e. does not require nano patterned surfaces.

Description

AN OPTICAL NANO-MANIPULATOR FOR PARTICLES IN A FLUID

TECHNICAL FIELD

[1] The present disclosure generally relates to the field of optical nanomanipulation. In particular, the present disclosure relates to a colloidal plasmonic tweezer designed to be used as a remotely controlled nano-manipulator.

BACKGROUND

[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] Manipulation of materials with light is a landmark invention that has led to many important breakthroughs in nanotechnology. Among the manipulation techniques, optical manipulation, such as by an optical tweezer, is by far most popular method and has the widest application. Optical tweezer, which is primarily a tightly focused laser beam, can trap and transport any particle in any fluid.

[4] The main feature that makes this technology unique is its ability to remotely control specific colloidal objects as desired, allowing independently controlled manipulation of individual specimens at any preferred location of a fluidic volume. Optical tweezers have been used to trap dielectric spheres, viruses, bacteria, living cells, organelles, small metal particles, and even strands of DNA. Applications include confinement and organization (e.g. for cell sorting), tracking of movement (e.g. of bacteria), application and measurement of small forces, and altering of larger structures (such as cell membranes).

[5] However, a drawback to this technology is that, due to diffraction, even limited focusing demands a high optical intensity to trap Nano scale objects. Further, due to diffraction, light cannot be focused to a sub-wavelength size, which sets the maximum focus achievable from a certain laser power.

[6] As an alternative, strongly localized and enhanced electromagnetic intensity in optical near-field is proposed, to overcome this fundamental restriction using plasmonic nanostructures due to their ability to squeeze light into nanometre-scale volume and enhance local field intensity. Plasmonic tweezers are undoubtedly much more efficient than optical tweezers in terms of optical power requirement and do not suffer from any size limitation. [7] However, the region of enhanced electromagnetic field gradient around a plasmonic nanostructure is localized within a small region, typically a small fraction of wavelength of the incident light. Accordingly, trapping relies on the probability of a particle diffusing into a small volume, which is an inefficient process in the absence of additional forces. Additionally, in these techniques traps are created at specific locations of a two- dimensional substrate that needs to be nano-pattemed. Therefore, unlike traditional laser tweezers these devices cannot be operated to selectively trap, dynamically transport and independently control target objects at bulk fluidic volume. The primary disadvantages of using plasmonic tweezers for optical manipulation are: (i) method is slow since it relies on diffusion of objects to the small trapping volume; (ii) requires a nanopatterned substrate which is a cumbersome task for scaling up; and iii) it is inefficient for transporting objects due to its static nature.

[8] There is therefore a need in the art for a nano-manipulator that can trap and transport particles with sufficient swiftness, and without a need for a nanopatterned substrate.

[9] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

[10] In some embodiments, the numbers expressing quantities or dimensions of items, 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 and attached claims 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-off techniques. 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 numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements. [11] As used in the description herein and throughout the claims that follow, the meaning of“a,”“an,” and“the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of“in” includes“in” and“on” unless the context clearly dictates otherwise.

[12] 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.

[13] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

OBJECTIVES OF THE INVENTION

[14] A general object of the present disclosure is to provide a system and method for optical manipulation that does not suffer from drawbacks of known systems and methods for optical manipulation.

[15] An object of the present disclosure is to provide a system and method for optical manipulation that uses low power optical illumination and yet do not suffer from drawbacks of plasmonic trapping.

[16] An object of the present disclosure is to provide a system and method that uses low power optical illumination for plasmonic trapping of nano particles, and yet allows mobility. [17] An object of the present disclosure is to provide a system and method for nano manipulation that integrates plasmonic and optical trapping to use low power optical illumination to trap nano particles as well as provide mobility for the trapped nano particles.

[18] An object of the present disclosure is to provide a system and method for nano manipulation that does not require a specialized substrate.

[19] An object of the present disclosure is to provide a system and method for nano manipulation that allows use of multiple laser beams

[20] Another object of the present disclosure is to provide a system and method for nano manipulation that provides flexibility in antenna design at different illumination.

[21] Another object of the present disclosure is to provide a system and method for nano manipulation that remote and independent control of movement of the trapped nano particles.

[22] Yet another object of the present disclosure is to provide a system and method for nano manipulation that allows selective manipulate of few or multiple nanoparticles

[23] Yet another object of the present disclosure is to provide a system and method for nano manipulation that is compatible for in-vivo applications.

[24] Yet another object of the present disclosure is to provide a system and method for nano manipulation that can be used in ionic fluids such as some of thebiofluids.

[25] Still another object of the present disclosure is to provide a system and method for nano manipulation that allows can be seamlessly integrated with existing optical tweezer equipment.

SUMMARY OF THE INVENTION

[26] Aspects of the present disclosure relate to optical manipulation of nano particles. In particular, the present disclosure provides a tweezer, a system and a method for optical manipulation using the disclosed tweezer. In an aspect, the disclosed tweezer for trapping and moving the nano particles integrates plasmonic and optical trapping, wherein plasmonic trapping is used for trapping of the nano particles to the tweezer, and the optical trapping uis used to trap the tweezer along with the nano particles trapped to the tweezer to the light beam. Thus, the disclosed plasmonic tweezer can be used in a colloidal solution containing the nano particles of interest and does not require any specialized substrate to manipulate the nano particles, therefore referred to as colloidal plasmonic tweezer.

[27] In an aspect the disclosed colloidal plasmonic tweezer for trapping and manipulatingnano particles in a colloidal solution, the plasmonic tweezer includes a nanorod made of a dielectric material; and a disc made of a plasmonic material. The disc is coupled to one end of the nanorod.

[28] In an aspect, the disc is configured to work as a plasmonic antenna to trap the nano particles using a plasmonic gradient force of localized and enhanced electromagnetic intensity in optical near field generated by the discs as a result of a light beam focussed on the colloidal plasmonic tweezer.

[29] In an aspect, the dielectric nanorod is configured such that the colloidal plasmonic tweezer is trapped to the light beam on account of far field optical forces acting on the dielectric nanorod as a result of the light beam, thereby enabling movement of the colloidal plasmonic tweezer by steering the light beam.

[30] The disc may be made of a plasmonic material selected from a group comprising Silver, Gold, Aluminium-doped Zinc Oxide, and Titanium nitride

[31] Diameter of the disc may be in the range of 200 to 300nm, and thickness of the disc may be the range of 40-60nm. In a preferred embodiment, the diameter of the disc is kept 250nm and the thickness of the disc is kept as 50nm.

[32] The nanorodmay be made of Silicon dioxide, and its length and diameter may be in the range of 2.00-3.00 pmand 40-60nm respectively. In a preferred embodiment, the length of the nanorod is kept 2.5 pm and the diameter of the nanorod is kept as 50 nm.

[33] An aspect of the present disclosure relates to a method for trapping and manipulatingnano particles using the disclosed colloidal plasmonic tweezer. The disclosed method allows use of multiple light beams, remote and independent control of movement of the trapped nano particles, and allows selective manipulate of few or multiple nano particles

[34] The disclosed method for trapping and manipulating nano particles includes the steps of: (a) providing a plurality of colloidal plasmonic tweezers in a colloidal solution that contains the nano particles to be manipulated; (b) focussing one or more light beams on one or more of the plurality of colloidal plasmonic tweezers Trapping one or more of the nano particles that are of interest by moving the one or more of the plurality of colloidal plasmonic tweezers close to the one or more nano particles of interest by steering the corresponding light beams; (c) moving each of the one or more of the plurality of colloidal plasmonic tweezers along with the trapped nano particles of interest to corresponding desired locations by steering the corresponding light beams; and (d) releasing the trapped nano particles at the desired location;

[35] In an aspect, the colloidal plasmonic tweezers include a disc of a plasmonic material coupled to one end of a long dielectric nanorod. The disc is configured to generate a plasmonic gradient force when illuminated with light thereby working as a plasmonic antenna to trap the nano particles;

[36] In an aspect, the one or more nano particles of interest are trapped by localized and enhanced electromagnetic intensity in optical near field generated by the discs of the one or more of the plurality of colloidal plasmonic tweezers as a result of the one or more light beams focussed thereon.

[37] In an aspect, the one or more of the plurality of colloidal plasmonic tweezers is moved by trapping the one or more of the plurality of colloidal plasmonic tweezers to the corresponding light beams based on the far field optical forces acting on the corresponding dielectric nanorods as a result of the corresponding light beams focussed on the colloidal plasmonic tweezers.

[38] The method may further include the step of providing a microfluidic chamber to hold the colloidal solution containing the nano particles to be manipulated and the plurality of colloidal plasmonic tweezers.

[39] The method may further include the step of providing one or more polarised laser sources to generate one or more light beams, the one or more polarised laser sources being coupled to an optical microscope.

[40] The method may further include the step of providing at least one galvo-mirror in paths of the light beams emanating from the one or more polarised laser sources to steer the light beams, wherein the at least one galvo-mirror enables steering the corresponding light beam remotely.

[41] The method may further include the step of sonicating the colloidal solution to distribute the plurality of colloidal plasmonic tweezers in the colloidal solution.

[42] Another aspect of the present disclosure relates to a system for trapping and manipulatingnano particles of interest, the system. The disclosed system allows remote and independent control of movement of the trapped nano particles, and is compatible for in-vivo applications. The system can be seamlessly integrated with existing optical tweezer equipment.

[43] The disclosed system for trapping and manipulating nano particles of interest includes: (a) a plurality of colloidal plasmonic tweezers suspended in a colloidal solution; and (b) one or more elliptically polarised laser sources to generate one or more elliptically polarized light beams. The one or more polarised laser sources are coupled to an optical microscope. [44] In an aspect, the colloidal plasmonic tweezers includes a disc made of a plasmonic material coupled to one end of a long nanorod made of a dielectric material; wherein the disc is configured to generate a plasmonic gradient force when illuminated by a light beam thereby working as a plasmonic antenna to trap the nano particles.

[45] In an aspect, the nano particles of interest are trapped by localized and enhanced electromagnetic intensity in optical near field generated by the discs of the one or more of the plurality of colloidal plasmonic tweezers as a result of the one or more light beams focussed thereon.

[46] In an aspect, the one or more of the plurality of colloidal plasmonic tweezers are moved by trapping the one or more of the plurality of colloidal plasmonic tweezers to the corresponding light beams based on the far field optical forces acting on the corresponding dielectric nanorods as a result of the corresponding light beams focussed on the colloidal plasmonic tweezers.

[47] The system may further include at least one galvo-mirror in path of each of the light beams emanating from the one or more polarised laser sources to remotely steer the light beams to remotely move of the one or more colloidal plasmonic tweezers trapped by the corresponding light beams.

[48] The one or more elliptically polarized laser light beams may be low power infrared lasers.

[49] The colloidal solution may be an ionic biofluid.

[50] The colloidal solution may be an in vivo biofluid.

[51] The colloidal solution may be based on any or a combination of hyaluronic gel and vitreous humour, and the trapping and manipulating nano particles of interest may be done in ex-Vivo conditions.

[52] The system may include a microfluidic chamber to hold the colloidal solution containing the nano particles to be trapped and manipulated.

BRIEF DESCRIPTION OF DRAWINGS

[53] The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present invention and, together with the description, serve to explain the principles of the present invention.

[54] FIG. 1A illustrates an exemplary representation of trapping of nano particles for nanomanipulation using by a plasmonic tweezer.FIG. IB illustrates an exemplary graph of localised surface plasmon resonance (LSPR) wavelength as a function of disk diameter and associated temperature rise due to light absorption.

[55] FIG. 1C illustrates thermal diffusivity (Brownian sensitivity) of a nanorod as a function of its length.

[56] FIG. ID illustrates an exemplary structure of the proposed Colloidal Plasmonic Tweezer (CPT), integrating the plasmonic nanodisc with a dielectric nanorod, and an SEM image of a plurality of CPTs attached to a substrate, in accordance with embodiments of the present disclosure.

[57] FIG. 2 illustrates an exemplary setup for the system for trapping and manipulating nano particles using the proposed CPT, in accordance with embodiments of the present disclosure.

[58] FIG. 3A illustrates anextinction cross section of plasmonic nanodisc in vertical and horizontal configurations, in accordance with an embodiment of the present disclosure.

[59] FIG. 3B illustrates differential orientation of CPT with respect to laser illumination, in accordance with an embodiment of the present disclosure.

[60] FIG. 3C illustrates trapping of polystyrene particles in plasmonic near-field for vertical and horizontal configurations, in accordance with an embodiment of the present disclosure.

[61] FIG. 3D illustrates a beam profile of the diffraction limited laser spot showing the region inaccessible by the trapped particle, in accordance with an embodiment of the present disclosure.

[62] FIG. 3E illustrates electric field intensity enhancement for the nanodisc in vertical configuration and horizontal configuration, in accordance with an embodiment of the present disclosure.

[63] FIG. 3F illustrates a histogram of fluctuations of the proposed CPT when trapped with a focused laser (vertical configuration) and defocussed laser (horizontal configuration), in accordance with an embodiment of the present disclosure.

[64] FIG. 4A illustrates a graph of minimum illumination intensity required to trap, as a function of bead size for vertical and horizontal configurations of the proposed CPT, in accordance with an embodiment of the present disclosure.

[65] FIG. 4B illustrates an exemplary plasmonic gradient force on a 200 nm polystyrene particle as a function of distance from the proposed nanodisc, in accordance with an embodiment of the present disclosure. [66] FIG. 4C illustrates a calculated temperature rise as a function of laser intensity for 400 nm and 1064 nm wavelength, in accordance with an embodiment of the present disclosure.

[67] FIG. 5A illustrates trapping and releasing of 100 nm fluorescent nano-diamonds in an ultra-low-density solution, in accordance with an embodiment of the present disclosure.

[68] FIG. 5B illustrates trapping, transporting and releasing of 300 nm fluorescent magnetic particles using two traps parallelly and independently, in accordance with an embodiment of the present disclosure.

[69] FIG. 6 illustrates an exemplary method flow diagram for the disclosed method for trapping and manipulating nano particles in a colloidal solution, in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

[70] The following is a detailed description of the 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 the 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.

[71] If the specification states a component or feature“may”,“can”,“could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.

[72] As used in the description herein and throughout the claims that follow, the meaning of“a,”“an,” and“the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of“in” includes“in” and“on” unless the context clearly dictates otherwise.

[73] Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. These exemplary embodiments are provided only for illustrative purposes and so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those of ordinary skill in the art. The invention disclosed may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Various modifications will be readily apparent to persons skilled in the art. The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Moreover, all statements herein reciting embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure). Also, the terminology and phraseology used is for the purpose of describing exemplary embodiments and should not be considered limiting. Thus, the present invention is to be accorded the widest scope encompassing numerous alternatives, modifications and equivalents consistent with the principles and features disclosed. For purpose of clarity, details relating to technical material that is known in the technical fields related to the invention have not been described in detail so as not to unnecessarily obscure the present invention.

[74] 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.

[75] In an aspect, the present disclosure provides a colloidal plasmonic tweezer) that can be moved by integrating it with laser tweezers for remote and independent control in nanomanipulation at similar power levels as current state of art plasmonic tweezers.

[76] FIG. 1A is a representation of trapping of nano particles for nanomanipulationby a plasmonic tweezer shown therein as a disc. When a light beam is focussed on the plasmonic material, a plasmonic gradient force of localized and enhanced electromagnetic intensity in optical near field is generated, which causes the plasmonic tweezer to work as a plasmonic antenna to trap the nano particles.

[77] In an embodiment, such nanomanipulation requires a suitable antenna where plasmonic enhancements are strong enough to support trapping, and the resonance wavelength of the antenna falls under the biological transparency window where absorption of light in biological matter is minimal. In an embodiment, the nanodisc geometry can be used where the localised surface plasmon resonance wavelength can be tuned with its size.

[78] FIG. IB illustrates an exemplary graph of localised surface plasmon resonance (LSPR) wavelength as a function of disk diameter. In an embodiment, it can be observed that the localised surface plasmon resonance (LSPR) wavelength increases linearly with size of the nanodiscs. In another embodiment, calculation of temperature enhancement due to light absorption in plasmonic nanostructures as a function of nanodisc size also suggests, from FIG. IB, that there can be a suitable wavelength band which is biologically favourable as well as optimized for reducing plasmonic heating. However, to trap a nano-antenna with a laser tweezer requires a large amount of power in order to overcome Brownian motion and achieve stable trapping; and this can lead to photodamage of the trapped specimen and amplified heating effects in the plasmonic tweezer.

[79] In another embodiment, in order to overcome the above stated issue, the plasmonic antenna can be combined with a bigger dielectric object which can be trapped with relative ease and steered inside a closed microfluidic chamber using a single beam optical tweezer without any detrimental effects to the plasmonic part.

[80] FIG. 1C illustrates thermal diffusivity (Brownian sensitivity) of a nanorod as a function of its length. In an exemplary embodiment, the rod has a fixed diameter of about 250 nm. It can be observed that there is an exponential dependence of thermal diffusivity with length of the rod.

[81] FIG. ID illustrates an exemplary structure of the proposed CPT, integrating the plasmonic nanodisc 102 with a dielectric nanorod 104. Also shown alongside is an SEM image showinga plurality of CPTs attached to a substratel08.As can be seen, the disc 102 is coupled to one end of the nanorod 104.

[82] In an aspect, the disc 102 may be configured to work as a plasmonic antenna to trap the nano particles, as shown in FIG. 1A, using a plasmonic gradient force of localized and enhanced electromagnetic intensity in optical near field generated by the discs as a result of a light beam focussed on the colloidal plasmonic tweezer. Suitable materials areSilver Gold, Aluminium-doped Zinc Oxide, and Titanium nitride etc. In a preferred embodiment, disc 102 is made of Silver.

[83] In an aspect, the dielectric nanorod is configured such that the colloidal plasmonic tweezer is trapped to the light beam on account of far field optical forces acting on the dielectric nanorod as a result of the light beam, thereby enabling movement of the colloidal plasmonic tweezer by steering the light beam. A suitable dielectric material for making the nanorod 104 is, but not limited to Silicon dioxide.

[84] In an embodiment, the diameter of the disc 102 may be in the range of 200 to 300 nm, and thickness of the disc 102 may be the range of 40-60 nm. Length and diameter of the nanorod 104 may be in the range of 2.00-3.00 pm and 40-60 nm respectively. In a preferred embodiment described in succeeding paragraphs, the length and diameter of the nanorodl04 are kept 2.5 pm and 50 nm respectively, and the diameter and thickness of the disc is kept 250 nm and 50 nm respectively.

[85] In an embodiment, a bottom-up approach is employed to design a hybrid metal - dielectric geometry consisting of a silver (Ag) nanodisc of about 250 nm diameter and 50 nm thickness integrated to a 2.5 pm long rod of diameter 250 nm, made of Silicon dioxide (Si02). The silver nanodisc plays a crucial role in generating plasmonic gradient force when illuminated with light, which acts as a plasmonic trap, whereas the dielectric part only facilitates optical confinement of the plasmonic tweezer itself.

[86] In another embodiment, the long dielectric nanorod 104 helps in reducing the optical power requirement by minimizing Brownian diffusion. The power requirement can be further reduced by combining a plasmonic element with the dielectric nanorod 104 as the effective optical volume increases due to increase in polarizability. In an aspect, it is well understood that metal nanoparticles can be captured more strongly than similar sized dielectric particle due to their higher polarizability. Therefore, the hybrid geometry allows the CPT 100 to be operated at low optical power.

[87] FIG. 2 illustrates an exemplary system for trapping and manipulating nano particles in a colloidal solution, using the proposed CPT, in accordance with embodiments of the present disclosure. The system 200 may comprise a microfluidic chamber 202 to hold a colloidal solution containing a plurality of the colloidal plasmonic tweezers 100 and nano particles 204 to be trapped and manipulated, anda laser source206 to generate an elliptically polarized light beam 212.The laser source 206 may be coupledan optical microscope 208. The system 200 may also comprise at least one galvo-mirror 210 in path of the light beam212 emanating from the laser source 206 to remotely steer the light beam 212.

[88] It is to be appreciated that while the exemplary illustration of FIG. 2 showes only one light source/laser, it is possible to have more than one light source/laser sources coupled to the microscope 208 to have more than one light beam 212. This shall help to simultaneously and independently move more than one CPTs trapped to the respective light beams 212 using the corresponding galvo-mirrors210.

[89] In an embodiment of implementation, the elliptically polarized laser light beam212 can be a low power infrared laser to enable in vivo use of the system 200. Thus, the colloidal solution can be an in vivo biofuel, such as an ionic biofluid.

[90] In an embodiment of implementation, the colloidal solution may be based on any or a combination of interesting fluids such as hyaluronic gel and vitreous humour, and the trapping and manipulating nano particles of interest may be done in ex- Vivo conditions. [91] In an embodiment, the experiments wereperformed using an elliptically polarised laser source (Nd:YAG; 1064 nm) 206 coupled to a standard optical microscope 208 using a 100X, 1.4NA oil immersion objective.

[92] In another embodiment, the laser spot size can be externally controlled using a telescopic lens assembly 214. Here, the focused laser/light beam 212 serves two purposes - simultaneously exciting and holding the CPT 100, which is designed in such a way that dielectric rod 104 acts as a passive element and does not affect the surrounding colloids.

[93] In another embodiment, the CPT 100 held at the laser focus can be manoeuvred precisely by moving the computer-controlled stage. Inside the laser focus, the CPT 100 can have two possible orientations - parallel and perpendicular, with respect to light propagation direction.

[94] FIG. 3A illustrates a scattering and absorption cross section of plasmonic nanodisc showing plasmon resonances at around 980 nm for in-plane polarisation . For out of plane polarization, there are four resonance peaks available.

[95] In another embodiment, for perpendicular configuration, multiple resonance modes are possible. In an exemplary embodiment, high energy (lower wavelength) modes are not used as silver becomes highly absorbing in that regime, and because of which low energy mode at infrared regime is preferred, which shows large electric field intensity enhancement. In another embodiment, the use of low power, infra-red lasers makes it compatible for delicate use such as for in-vivo applications.

[96] FIG. 3B illustrates differential orientation of CPT with respect to laser illumination. In an embodiment, the laser wavelength is chosen such that it lies to the slightly red-detuned side of the LSPR wavelength, resulting in attractive pulling force on the plasmonic disc towards the laser focus. Additionally, as metallic polarizability is higher compared to dielectric, the attraction is stronger on the metallic side. This brings a preferential vertical orientation of the CPT where the plasmonic nanodisc always stays at laser focus and the light polarization is in-plane to the nanodisc orientation.

[97] In an alternate embodiment, it is also possible to use a defocused laser spot, but preferable orientation is horizontal to the substrate. Alternately, any illumination with blue- detuned laser will repel the plasmonic part out of the focus and in that case dielectric part may be trapped in the laser focus.

[98] Referring to FIG. 2 again, the nanomanipulation is performed for both vertical and horizontal configurations inside a standard microfluidic chamber 202 made of glass. The microfluidic chamber 202 contains a suspension of CPTs and cargo in the form of colloidal particles. The CPTs are fabricated in large numbers and can be released by sonicating the substrate in a fluid.

[99] FIG. 3C illustrates trapping of polystyrene particles in plasmonic near-field for vertical and horizontal configurations. In an embodiment, the particles are trapped around the CPT, which is held at a diffraction limited laser focus with a fraction of a milliwatt, corresponding to an intensity 80 kW/cm2. The elliptically polarized light enhances the electric field around the nanodisc, imparting an attractive gradient force on the surrounding colloids and trapping is achieved without any need for substrate engineering.

[100] FIG. 3D illustrates a beam profile of the diffraction limited laser spot showing the region inaccessible by the trapped particle. It can be observed that the CPT stays at the centre of the laser focus, and therefore, peak intensity is forbidden to the tracer particles, which results in about 10 times reduction in total laser power falling on any individual colloid(for 400 nm particle).

[101] In another embodiment, in case of horizontal configuration, the defocused illumination is distributed on an area, with intensity equivalent to 20 kW/cm2. It can be noticed that particles again get captured around the nanodisc, but no trapping is observed along the direction of light propagation (z- axis), which can be attributed to zero field enhancement in that direction.

[102] FIG. 3E illustrates electric field intensity enhancement for the nanodisc in vertical configuration and horizontal configuration. In an embodiment, the polarization is in X-Y plane and the light propagation is along the Z-axis.

[103] FIG. 3F illustrates a histogram of fluctuations of the proposed CPT a focused laser (vertical configuration) and defocussed laser (horizontal configuration). In an embodiment, vertical configuration is advantageous for manipulation at micron-scale spatial resolution with greater control such as to move and collect target colloids.

[104] FIG. 4A illustrates a graph of minimum illumination intensity required to trap, as a function of bead size for vertical and horizontal configurations of the proposed CPT. In an embodiment, the minimum intensity to trap a particle with CPT increases as the bead size is decreased. It can also be noted that minimum trapping intensity required in vertical configuration with focused laser is nearly same for different size of particles and is also higher compared to the horizontal configuration. This is because minimum optical power required for laser trapping of CPTs is higher than the threshold intensity required for plasmonic trapping of the tracer colloids. Therefore, no size dependence can be observed on trapping intensity for vertical configuration. [105] FIG. 4B illustrates an exemplary plasmonic gradient force on a 200 nm polystyrene particle as a function of distance from the proposed nanodisc. In an embodiment, the intensity is kept constant at 30 kW/cm2 and this simulation is performed for both vertical and horizontal configurations along the X and Y directions. In another embodiment, it can be seen that the spatial extent of the trap becomes negligible beyond 50 nm from the CPT surface.

[106] FIG. 4C illustrates a calculated temperature rise as a function of intensity of wavelength. In an embodiment, in any plasmonic device, plasmon induced heating is an additional side-effect and can play a critical role in the trapping mechanism. In the proposed CPT, temperature is estimated to rise just a few degrees, up to an intensity of 100 kW/cm2 with 1064 nm laser.

[107] In another embodiment, the intensity level at 400 nm wavelength can cause at least 10 times higher temperature rise because of intrinsic loss in material.

[108] FIG. 5A illustrates trapping and releasing of 100 nm fluorescent nano-diamonds in an ultra-low-density solution. In an embodiment, The CPT was moved close to catch the nano-diamond without waiting for it to diffuse into the trap. Similarly, a collection of nano diamond is subsequently trapped, manoeuvred and released with a CPT in horizontal configuration. In this case, the sample stage is moved to take the plasmonic tweezer and the nano-diamonds in and out of illumination for subsequent trapping and releasing without modulating the trapping intensity.

[109] FIG. 5B illustrates trapping, transporting and releasing of 300 nm fluorescent magnetic particles. In an embodiment, the laser beam is focused using a fast scanning galvo- mirror 210, at two spots with each spot holding a CPT. Two magnetic particles are first captured in each of them. The tweezers are then independently manoeuvred to two different locations that are about 100 microns apart, where the particles are released one-by-one by turning the illumination off.

[110] FIG. 6 is an exemplary method flow diagram for the disclosed method for trapping and manipulating nano particles in a colloidal solution using the disclosed colloidal plasmonic tweezers. The disclosed method 600 may at step 602 include providing a plurality of colloidal plasmonic tweezers, such as colloidal plasmonic tweezers 100 shown at FIG. ID, in a colloidal solution that contains the nano particles to be manipulated. At step 604, the method 600 may include focussing one or more light beams, such as light beam 212 shown in FIG. 2, on one or more of the plurality of colloidal plasmonic tweezers 100, wherein trapping the colloidal plasmonic tweezers 100 to the corresponding light beams 212 is based on the far field optical forces acting on the dielectric nanorods 104 of the corresponding colloidal plasmonic tweezers 100 as a result of the corresponding light beams 212 focussed on the colloidal plasmonic tweezers 100.

[111] Step 606 of the method 600 may involve trapping of one or more of the nano particles, such as nono particles 204 shown in FIG. 2, that are of interest by moving the one or more of the colloidal plasmonic tweezers 100 close to the nano particles of interest 204 by steering the corresponding light beams 212.

[112] Step 608 of the method 600 may involve moving the one or more olloidal plasmonic tweezers 100 along with the trapped nano particles 204 of interest to corresponding desired locations by steering the corresponding light beams 212.

[113] Step 610 of the method 600 may involve releasing the trapped nano particles 204 at the desired location.

[114] In an embodiment, the method 600 may further include a step of providing a microfluidic chamber, such as microfluidic chamber 202 shown in FIG. 2, to hold the colloidal solution containing the nano particles 204 to be manipulated and the plurality of colloidal plasmonic tweezers 100.

[115] In an embodiment, the method 600 may further include a step ofproviding one or more polarised laser sources, such as laser source 206 shown in FIG. 2, to generate one or more light beams 212. The one or more polarised laser sources 206 may be coupled to an optical microscope, such as the optical microscope 206 shown in FIG. 2.

[116] In an embodiment, the method 600 may further include a step ofproviding at least one galvo-mirror, such as galvo-mirror 210, in paths of the light beams 212 emanating from the one or more polarised laser sources 206 to steer the light beams 212. The galvo- mirror 210 may enable steering the corresponding light beam remotely.

[117] In an embodiment, the method 600 may further include a step ofsonicating the colloidal solution to distribute the plurality of colloidal plasmonic tweezers 100 in the colloidal solution.

[118] Thus, the present disclosure provides a system for optical manipulation integrating a plasmonic tweezer with a conventional laser tweezer. Proposed colloidal plasmonic tweezer (CPT) bears a hybrid metal-dielectric design comprising a silver (Ag) nanodisc coupled to a Si02 nanorod. The proposed CPT can work in different configurations (vertical, horizontal) based on the type of illumination (red detuned, blue detuned), and can be used to trap and transport various nanomaterials such as nanoparticles, absorbing particles, fluorescent particles, magnetic particles etc. The hybrid dielectric -metal design results in minimal heating during operation of the CPT, allowing the CPT to be used for biofluids which are generally susceptible to photodamage. Further, the proposed CPT can be used with remote and independent control.

[119] Further, it is also possible to have two light beams used in conjunction with the CPTs, where one beam is used to trap the CPTs while the other is used to generate strong near field confinement around the CPTs. Accordingly, the first light beam can be used to manipulate the CPTs while the other one is used to trap colloids. For certain colloids, the second light beam can be used to heat the CPT so as to use thermophoretic attraction to bring the colloids close to CPT.

[120] In certain cases, the plasmonic effect can be obtained by alternate plasmonic materials, such as but not limited to TiN and AZO.

[121] In addition to microfluidic chambers, the CPTs can be operated in natural environments, including living biological cells, animals and plants.

[122] It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive patent matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “includes” and “including” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refer to at least one of something selected from the group consisting of A, B, C .... and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc. The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practised with modification within the spirit and scope of the appended claims. [123] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION

[124] The present disclosure provides a system and method for optical manipulation that does not suffer from drawbacks of known systems and methods for optical manipulation.

[125] The present disclosure provides a system and method for optical manipulation that uses low power optical illumination and yet do not suffer from drawbacks of plasmonic trapping.

[126] The present disclosure provides a system and method that uses low power optical illumination for plasmonic trapping of nano particles, and yet allows mobility.

[127] The present disclosure provides a system and method for nano manipulation that integrates plasmonic and optical trapping to use low power optical illumination to trap nano particles as well as provide mobility for the trapped nano particles.

[128] The present disclosure provides a system and method for nano manipulation that does not require a specialized substrate.

[129] The present disclosure provides a system and method for nano manipulation that allows use of multiple laser beams

[130] The present disclosure provides a system and method for nano manipulation that provides flexibility in antenna design at different illumination.

[131] The present disclosure provides a system and method for nano manipulation that remote and independent control of movement of the trapped nano particles.

[132] The present disclosure provides a system and method for nano manipulation that allows selective manipulate of few or multiple nano particles

[133] The present disclosure provides a system and method for nano manipulation that is compatible for in-vivo applications.

[134] The present disclosure provides a system and method for nano manipulation that can be used in ionic fluids such as some of the biofluids. [135] The present disclosure provides a system and method for nano manipulation that allows can be seamlessly integrated with existing optical tweezer equipment.

Claims

We Claim:

1. A colloidal plasmonic tweezer for trapping and manipulatingnano particles in a colloidal solution, the plasmonic tweezer comprising:

ananorod made of a dielectric material; and

a disc made of a plasmonic material, said disc coupled to one end of the nanorod;

wherein the disc is configured to work as a plasmonic antenna to trap the nano particles using a plasmonic gradient force of localized and enhanced electromagnetic intensity in optical near field generated by the discs as a result of a light beam focussed on the colloidal plasmonic tweezer; and

wherein the dielectric nanorod is configured such that the colloidal plasmonic tweezer is trapped to the light beam on account of far field optical forces acting on the dielectric nanorod as a result of the light beam, thereby enabling movement of the colloidal plasmonic tweezer by steering the light beam.

2. The colloidal plasmonic tweezer as claimed in claim 1, wherein the disc is made of a plasmonic material selected from a group comprising Silver, Gold, Aluminium-doped Zinc Oxide, and Titanium nitride.

3. The colloidal plasmonic tweezer as claimed in claim 1, wherein diameter of the disc is in the range of 200 to 300nm, and thickness of the disc is the range of 40-60nm.

4. The colloidal plasmonic tweezer as claimed in claim 1, wherein the nanorod is made of Silicon dioxide.

5. The colloidal plasmonic tweezer as claimed in claim 1, wherein length of the nanorod is in the range of 200-300 nm, and diameter of the nanorod is in the range of 40- 60nm.

6. A system for trapping and manipulatingnano particles of interest, the system comprising:

a plurality of colloidal plasmonic tweezers suspended in a colloidal solution; the colloidal plasmonic tweezers comprising a disc made of a plasmonic material coupled to one end of a long nanorod made of a dielectric material; wherein the disc is configured to generate a plasmonic gradient force when illuminated by a light beam thereby working as a plasmonic antenna to trap the nano particles; and one or more elliptically polarised laser sources to generate one or more elliptically polarized light beams, the one or more polarised laser sources being coupled to an optical microscope;

wherein the nano particles of interest are trapped by localized and enhanced electromagnetic intensity in optical near field generated by the discs of the one or more of the plurality of colloidal plasmonic tweezers as a result of the one or more light beams focussed thereon; and

wherein the one or more of the plurality of colloidal plasmonic tweezers are moved by trapping the one or more of the plurality of colloidal plasmonic tweezers to the corresponding light beams based on the far field optical forces acting on the corresponding dielectric nanorods as a result of the corresponding light beams focussed on the colloidal plasmonic tweezers.

7. The system for trapping and manipulatingnano particles of interest as claimed in claim 6, wherein the system comprises at least one galvo-mirror in path of each of the light beams emanating from the one or more polarised laser sources to remotely steer the light beams, thereby moving of the one or more colloidal plasmonic tweezers trapped by the corresponding light beams.

8. The system for trapping and manipulatingnano particles of interest as claimed in claim 6, wherein the one or more elliptically polarized laser light beams are low power infrared lasers.

9. The system for trapping and manipulatingnano particles of interest as claimed in claim 6, wherein colloidal solution is an ionic biofluid.

10. The system for trapping and manipulatingnano particles of interest as claimed in claim 8, wherein the colloidal solution is an in vivo biofluid.

11. The system for trapping and manipulatingnano particles of interest as claimed in claim 6, wherein the system comprises a microfluidic chamber to hold the colloidal solution containing the nano particles to be trapped and manipulated.

12. The system for trapping and manipulating nano particles of interest as claimed in claim 6, wherein colloidal solution is a based on any or a combination of hyaluronic gel and vitreous humour, and the trapping and manipulating nano particles of interest is done ex- Vivo conditions.

13. A method for trapping and manipulating nano particles, the method comprising the steps of: providing a plurality of colloidal plasmonic tweezers in a colloidal solution that contains the nano particles to be manipulated; the colloidal plasmonic tweezers comprising a disc of a plasmonic material coupled to one end of a long dielectric nanorod; wherein the disc is configured to generate a plasmonic gradient force when illuminated with light thereby working as a plasmonic antenna to trap the nano particles;

focussing one or more light beams on one or more of the plurality of colloidal plasmonic tweezers;

trapping one or more of the nano particles that are of interest by moving the one or more of the plurality of colloidal plasmonic tweezers close to the one or more nano particles of interest by steering the corresponding light beams, wherein the one or more nano particles of interest are trapped by localized and enhanced electromagnetic intensity in optical near field generated by the discs of the one or more of the plurality of colloidal plasmonic tweezers as a result of the one or more light beams focussed thereon;

moving each of the one or more of the plurality of colloidal plasmonic tweezers along with the trapped nano particles of interest to corresponding desired locations by steering the corresponding light beams; and

releasing the trapped nano particles at the desired location;

wherein the one or more of the plurality of colloidal plasmonic tweezers is moved by trapping the one or more of the plurality of colloidal plasmonic tweezers to the corresponding light beams based on the far field optical forces acting on the corresponding dielectric nanorods as a result of the corresponding light beams focussed on the colloidal plasmonic tweezers.

14. The method for trapping and manipulating nano particles as claimed in claim 13, comprising the step of providing a microfluidic chamber to hold the colloidal solution containing the nano particles to be manipulated and the plurality of colloidal plasmonic tweezers.

15. The method for trapping and manipulating nano particles as claimed in claim 13, comprising the step of providing one or more polarised laser sources to generate one or more light beams, the one or more polarised laser sources being coupled to an optical microscope.

16. The method for trapping and manipulating nano particles as claimed in claim 15, comprising the step of providing at least one galvo-mirror in paths of the light beams emanating from the one or more polarised laser sources to steer the light beams, wherein the at least one galvo-mirror enables steering the corresponding light beam remotely.

17. The method for trapping and manipulating nano particles as claimed in claim 13, comprising the step of sonicating the colloidal solution to distribute the plurality of colloidal plasmonic tweezers in the colloidal solution.