Y. T. Y. would like to acknowledge funding support from the Ministry of Science and Technology under grant numbers MOST 105-2221-E-007-MY3 and from the National Tsing Hua University under grant numbers 105N518CE1 and 106N518CE1.

1. Optical Setup
Note: The principle of the optical setup is illustrated in Figure 1.
<ol>
	<li>Set up the optical tweezer kit (see the Table of Materials) and the fluorescence module (see Table of Materials) as per their manuals. Connect a 470 nm blue light emitting diode (LED) light source to the fluorescent module.</li>
	<li>Replace the high numerical aperture (NA) (NA= 1.25, magnification 100x) oil immersion objective by a l...

<ol>
	<li>Ashkin, A., Dziedzic, J. M., Bjorkholm, J. E., Chu, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Observation+of+a+single-beam+gradient+force+optical+trap+for+dielectric+particles.">Observation of a single-beam gradient force optical trap for dielectric particles.</a> Opt.Lett. 11, 288-290 (1986).</li><li>Grier, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+revolution+in+optical+manipulation.">A revolution in optical manipulation.</a> Nature. 424, 21-27 (2003).</li><li>Wright, W. H., Sonek, G. J., Berns, M. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Radiation+on+trapping+forces+with+optical+tweezers.">Radiation on trapping forces with optical tweezers.</a> Appl. Phys. Lett. 63, 715-717 (1993).</li><li>Kawata, S., Tani, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optically+driven+Mie+particles+in+an+evanescent+field+along+a+channel+waveguide.">Optically driven Mie particles in an evanescent field along a channel waveguide.</a> Opt. Lett. 21, 1768-1770 (1996).</li><li>Yang, A. H. J., Moore, S. D., Schmit, B. S., Klug, M., Lipson, M., Erickson, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+Manipulation+of+nanoparticles+and+biomolecules+in+sub-wavelength+slot+waveguides.">Optical Manipulation of nanoparticles and biomolecules in sub-wavelength slot waveguides.</a> Nature. 457, 71-75 (2009).</li><li>Lin, S., Schonbrun, E., Crozier, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+manipulation+with+planar+silicon+microring+resonators.">Optical manipulation with planar silicon microring resonators.</a> Nano Lett. 10, 2408-2411 (2010).</li><li>Mandal, S., Serey, X., Erickson, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanomanipulation+using+silicon+photonic+crystal+resonators.">Nanomanipulation using silicon photonic crystal resonators.</a> Nano Lett. 2010 (10), 99-104 (2010).</li><li>Lin, S., Crozier, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Planar+silicon+microrings+as+wavelength-+multiplexed+optical+traps+for+storing+and+sensing+particles.">Planar silicon microrings as wavelength- multiplexed optical traps for storing and sensing particles.</a> Lab Chip. 11, 4047-4051 (2011).</li><li>Juan, M. L., Righini, M., Quidant, M., R, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasmonic+nano+optical+tweezers.">Plasmonic nano optical tweezers.</a> Nat. Photon. 5, 349-356 (2011).</li><li>Huang, J. S., Yang, Y. -. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+origin+and+future+of+plasmonic+optical+tweezer.">The origin and future of plasmonic optical tweezer.</a> Nanomaterials. 5, 1048-1065 (2015).</li><li>Pang, Y., Gordon, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+trapping+of+single+protein.">Optical trapping of single protein.</a> Nano Lett. 12, 402-406 (2012).</li><li>Chen, K. Y., Lee, A. T., Hung, C. C., Huang, J. S., Yang, Y. -. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transport+and+trapping+in+two-dimensional+nanoscale+plasmonic+optical+lattice.">Transport and trapping in two-dimensional nanoscale plasmonic optical lattice.</a> Nano Lett. 13, 4118-4122 (2013).</li><li>Cuche, A., Stein, B., Canguier-Durand, A., Devaux, E., Genet, C., Ebbesen, T. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Brownian+motion+in+a+designer+force+field:+Dynamical+effects+of+negative+refraction+on+nanoparticles.">Brownian motion in a designer force field: Dynamical effects of negative refraction on nanoparticles.</a> Nano Lett. 12, 4329-4332 (2012).</li><li>Baffou, G., Berto, P., Urena, E. B., Quidant, R., Monnert, S. J., Polleux, J., Righeault, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photoinduced+heating+of+nanoparticle+arrays.">Photoinduced heating of nanoparticle arrays.</a> ACS Nano. 8, 6478-6488 (2013).</li><li>Roxworthy, B. J., Bhuiya, A. M., Vanka, S. P., Toussant, K. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+and+controlling+plasmon-induced+convection.">Understanding and controlling plasmon-induced convection.</a> Nat. Commun. 5, (2014).</li><li>Yang, T. P., Yossifon, G., Yang, Y. -. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+the+near-field+and+convectional+transport+behavior+of+micro+and+nano+particles+in+nanoscale+plasmonic+optical+lattice.">Characterization of the near-field and convectional transport behavior of micro and nano particles in nanoscale plasmonic optical lattice.</a> Biomicrofluidics. 10, 034102 (2016).</li><li>Chen, Y. -. C., Yossifon, G., Yang, Y. -. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Supression+of+phtothermal+convection+of+micro+particles+in+two+dimensional+nanoplamonic+optical+lattice.">Supression of phtothermal convection of micro particles in two dimensional nanoplamonic optical lattice.</a> Appl. Phys. Lett. 109, 201111 (2016).</li><li>Smith, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Thin film deposition: principles and practice. , (1995).</li><li>Zehtabi-Oskuie, A., Bergeron, J. G., Gordon, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flow-dependent+double-nanohole+optical+trapping+of+20+nm+polystyrene+nanospheres.">Flow-dependent double-nanohole optical trapping of 20 nm polystyrene nanospheres.</a> Sci. Rep. 2, 966 (2012).</li><li>Zhang, W., Huang, L., Santschi, C., Martin, O. J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Trapping+and+sensing+10+nm+metal+nanoparticles+using+plasmonic+dipole+antennas.">Trapping and sensing 10 nm metal nanoparticles using plasmonic dipole antennas.</a> Nano Lett. 10, 1006-1011 (2010).</li><li>Pang, Y., Gordon, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+trapping+of+12+nm+dielectric+spheres+using+double-nanoholes+in+a+gold+film.">Optical trapping of 12 nm dielectric spheres using double-nanoholes in a gold film.</a> Nano Lett. 2011 (11), 3763-3767 (2011).</li></ol>

The procedure described here enables the reader to reliably reproduce trapping on a daily basis. A general empirical guideline to design a usable optical lattice is to use a comparable size for plasmonic nanoarray, interdisc distance, and trapped particle size. Compared to a single, isolated plasmonic nanostructure, the optical lattice design in conjunction with the high optical power afforded by cooling the sample to ~4 &#176;C used here greatly enhances the trapping probability. If well separated, plasmonic nanostructu...

The optical trapping of micro-scale particles was originally developed by Arthur Askin in the early 1970s. Ever since its invention, the technique has been developed as a versatile tool for micro- and nanomanipulation1,2. Conventional optical trapping based on the far-field focusing principle is inherently limited by the diffraction in its spatial confinement, wherein the trapping force decreases dramatically (following an ~a3 law for a particle of radius a)3. To overcome such diffraction limits, researchers have developed near-field optical trapping techniques based on the evanescent optical field using plasmonic metallic nanostructures and, furthermore, the trapping of nanoscale objects down to single protein molecules has been demonstrated4,5,6,7,8,9,10,11. Moreover, the plasmonic optical lattice is created from arrays of periodic plasmonic nanostructures to confer long range transport of micro- and nanoparticles and multiple particle stacking11,12. One major obstacle to disrupt trapping in an optical lattice is photothermal convection and efforts have been made to elucidate its effects by several groups14,15,16,17. Using Green&#39;s function, Baffou et al. have calculated a temperature profile by modeling each plasmonic nanostructure as a point heater and then experimentally validated their model14. Toussant&#39;s group has also measured the plasmon-induced convection with particle velocimetry15. The author&#39;s group has also characterized both near-field and convectional transport and demonstrated an engineering strategy to suppress photothermal convection16,17.
Here we present the design of an optical setup and a detailed procedure specifically for trapping experiments with plasmonic optical lattice. The optical potential was created by illuminating an array of gold nanodiscs with a loosely focused Gaussian beam. A scheme to suppress the photothermal convection by cooling down the sample to a low temperature (~4 &#176;C) for optimal trapping is also describe here17. Under Boussinesq approximation, an order of magnitude estimate for the natural convection velocity u is given by u ~L2 g&#946;&#916;T / v, where L is the length scale of the heat source and &#916;T is the temperature increase relative to the reference due to the heating. &#160;g and &#946;&#160;are the gravitational acceleration and thermal expansion coefficient, respectively. At temperatures near 4 &#176;C, the density of the water medium exhibits anomalous temperature dependence and this translates into a near-zero thermal expansion coefficient and, therefore, a vanishingly small photothermal convection.

<table style="border-collapse:collapse;width:629pt" width="839">
	<colgroup>
		<col style="width:207pt" width="276" />
		<col style="width:131pt" width="174" />
		<col style="width:122pt" width="162" />
		<col style="width:170pt" width="227" />
	</colgroup>
	<tbody>
		<tr height="21" style="height:15.75pt">
			<td class="xl69" height="21" style="width:207pt;height:15.75pt" width="276">Thermoelectric cooling element</td>
			<td class="xl69" style="width:131pt" width="174">Thorlabs</td>
			<td class="xl69" style="width:122pt" width="162">TEC 1.4-6</td>
			<td class="xl70" style="width:170pt" width="227">TEC element for sample cooling</td>
		</tr>
		<tr height="42" style="height:31.5pt">
			<td class="xl69" height="42" style="width:207pt;height:31.5pt" width="276">RTD thermometer</td>
			<td class="xl69" style="width:131pt" width="174">Omega Engineering</td>
			<td class="xl69" style="width:122pt" width="162">RTD Thermometer 969C</td>
			<td class="xl70"></td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl69" height="21" style="width:207pt;height:15.75pt" width="276">Forward looking infrared camera</td>
			<td class="xl69" style="width:131pt" width="174">FLIR&#160;</td>
			<td class="xl69" style="width:122pt" width="162">FLIR One</td>
			<td class="xl70">IR camera for temperature monitoring</td>
		</tr>
		<tr height="46" style="height:34.5pt">
			<td class="xl69" height="46" style="width:207pt;height:34.5pt" width="276">light emitting diode light source</td>
			<td class="xl69" style="width:131pt" width="174">Touchbright</td>
			<td class="xl69" style="width:122pt" width="162"></td>
			<td class="xl69" style="width:170pt" width="227">Light source for illumination for fluorescent imaging</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl69" height="21" style="width:207pt;height:15.75pt" width="276">Long working distance objective</td>
			<td class="xl69" style="width:131pt" width="174">Olympus</td>
			<td class="xl69" style="width:122pt" width="162">LMPLFLN</td>
			<td class="xl70">For illuminating the sample and imaging</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl69" height="21" style="width:207pt;height:15.75pt" width="276">Optical trap kit</td>
			<td class="xl69" style="width:131pt" width="174">Thorlabs</td>
			<td class="xl69" style="width:122pt" width="162">OTKB/M</td>
			<td class="xl70"></td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl71" height="21" style="height:15.75pt">Cover slip</td>
			<td class="xl69" style="width:131pt" width="174"></td>
			<td class="xl69" style="width:122pt" width="162"></td>
			<td class="xl69" style="width:170pt" width="227">thickness 0.17 mm</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl71" height="21" style="height:15.75pt">Scanning electron microscope</td>
			<td class="xl69" style="width:131pt" width="174">Hitachi</td>
			<td class="xl69" style="width:122pt" width="162">SEM-Hitachi S3400N</td>
			<td class="xl69" style="width:170pt" width="227"></td>
		</tr>
		<tr height="44" style="height:33.0pt">
			<td class="xl71" height="44" style="height:33.0pt">Electron beam blanker</td>
			<td class="xl69" style="width:131pt" width="174">DEBEN</td>
			<td class="xl69" style="width:122pt" width="162">PCD beam blanker</td>
			<td class="xl69" style="width:170pt" width="227">the blanker is added to the scanning electron microscope&#160;</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl71" height="21" style="height:15.75pt">Thermal evaporator</td>
			<td class="xl69" style="width:131pt" width="174">SYSKEY Technology</td>
			<td class="xl69" style="width:122pt" width="162"></td>
			<td class="xl69" style="width:170pt" width="227"></td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl71" height="21" style="height:15.75pt">Mask aligner</td>
			<td class="xl69" style="width:131pt" width="174">Karl Suss</td>
			<td class="xl69" style="width:122pt" width="162">MJB 3</td>
			<td class="xl69" style="width:170pt" width="227">For marker fabrication</td>
		</tr>
		<tr height="24" style="height:18.0pt">
			<td class="xl69" height="24" style="width:207pt;height:18.0pt" width="276">Electron beam resist</td>
			<td class="xl69" style="width:131pt" width="174">Sigma Alrich</td>
			<td class="xl69" style="width:122pt" width="162">PMMA 120K</td>
			<td class="xl69" style="width:170pt" width="227">For e-beam lithography</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl69" height="21" style="width:207pt;height:15.75pt" width="276">Electron beam resist</td>
			<td class="xl69" style="width:131pt" width="174">Sigma Alrich</td>
			<td class="xl69" style="width:122pt" width="162">PMMA 960K</td>
			<td class="xl70">For e-beam lithography</td>
		</tr>
		<tr height="42" style="height:31.5pt">
			<td class="xl69" height="42" style="width:207pt;height:31.5pt" width="276">Fluoresent labeled polystyrene microspheres</td>
			<td class="xl69" style="width:131pt" width="174">Polyscience</td>
			<td class="xl69" style="width:122pt" width="162"></td>
			<td class="xl70">2 um diameter</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl69" height="21" style="width:207pt;height:15.75pt" width="276">Bipolar transistor</td>
			<td class="xl69" style="width:131pt" width="174">Mouser</td>
			<td class="xl69" style="width:122pt" width="162">2N3904</td>
			<td class="xl70">quantity 2 for TEC driver circuit</td>
		</tr>
		<tr height="28" style="height:21.0pt">
			<td class="xl69" height="28" style="width:207pt;height:21.0pt" width="276">Bipolar transistor</td>
			<td class="xl69" style="width:131pt" width="174">Mouser</td>
			<td class="xl69" style="width:122pt" width="162">2N3906</td>
			<td class="xl70">quantity 2 for TEC driver circuit</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl69" height="21" style="width:207pt;height:15.75pt" width="276">MOSFET power transistor</td>
			<td class="xl69" style="width:131pt" width="174">Mouser</td>
			<td class="xl69" style="width:122pt" width="162">IRF5305</td>
			<td class="xl70">quantity 2 for TEC driver circuit</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl69" height="21" style="width:207pt;height:15.75pt" width="276">MOSFET power transistor</td>
			<td class="xl69" style="width:131pt" width="174">Mouser</td>
			<td class="xl69" style="width:122pt" width="162">IRF131ON</td>
			<td class="xl70">quantity 2 for TEC driver circuit</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl69" height="21" style="width:207pt;height:15.75pt" width="276">10 kOhm resistor</td>
			<td class="xl69" style="width:131pt" width="174">Mouser</td>
			<td class="xl69" style="width:122pt" width="162"></td>
			<td class="xl70">quantity 6 for TEC driver circuit</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl69" height="21" style="width:207pt;height:15.75pt" width="276">910 Ohm resistor</td>
			<td class="xl69" style="width:131pt" width="174">Mouser</td>
			<td class="xl69" style="width:122pt" width="162"></td>
			<td class="xl70">quantity 2 for TEC driver circuit</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl69" height="21" style="width:207pt;height:15.75pt" width="276">Photoresist</td>
			<td class="xl69" style="width:131pt" width="174">Microchemicals</td>
			<td class="xl69" style="width:122pt" width="162">AZ4620</td>
			<td class="xl70">For marker fabrication</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl69" height="21" style="width:207pt;height:15.75pt" width="276">Acetone</td>
			<td class="xl69" style="width:131pt" width="174">Sigma Alrich</td>
			<td class="xl69" style="width:122pt" width="162"></td>
			<td class="xl70">For marker fabrication</td>
		</tr>
		<tr height="41" style="height:30.75pt">
			<td class="xl69" height="41" style="width:207pt;height:30.75pt" width="276">Fluorescence Module for the OTKB/M, Metric Threads</td>
			<td class="xl69" style="width:131pt" width="174">Thorlabs</td>
			<td class="xl69" style="width:122pt" width="162">OTKB-FL/M</td>
			<td class="xl69" style="width:170pt" width="227"></td>
		</tr>
		<tr height="49" style="height:36.75pt">
			<td class="xl69" height="49" style="width:207pt;height:36.75pt" width="276">Fluorescent filter set</td>
			<td class="xl69" style="width:131pt" width="174">Thorlabs</td>
			<td class="xl69" style="width:122pt" width="162">MDF-FITC</td>
			<td class="xl70">For Fluorescein Isothiocyanate (FITC)</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl70" height="21" style="height:15.75pt">Ultrasonic cleaner</td>
			<td class="xl69" style="width:131pt" width="174">Delta</td>
			<td class="xl70">DC150H</td>
			<td class="xl70">For the lift off step</td>
		</tr>
	</tbody>
</table>

trapping of micro particles in nanoplasmonic optical lattice

The plasmonic optical tweezer has been developed to overcome the diffraction limits of the conventional far field optical tweezer. Plasmonic optical lattice consists of an array of nanostructures, which exhibit a variety of trapping and transport behaviors. We report the experimental procedures to trap micro-particles in a simple square nanoplasmonic optical lattice. We also describe the optical setup and the nanofabrication of a nanoplasmonic array. The optical potential is created by illuminating an array of gold nanodiscs with a Gaussian beam of 980 nm wavelength, and exciting plasmon resonance. The motion of particles is monitored by fluorescence imaging. A scheme to suppress photothermal convection is also described to increase usable optical power for optimal trapping. Suppression of convection is achieved by cooling the sample to a low temperature, and utilizing the near-zero thermal expansion coefficient of a water medium. Both single particle transport and multiple particle trapping are reported here.

Single particle trajectories were recorded by a CCD camera in our experiment and the images were then processed with a custom program to extract each particle&#39;s trajectory16. Representative results are displayed in Figure 3 and Video 1 for micro-spheres with diameters of 2 &#181;m. Multiple particle trappings inside the optical lattice were observed. Successive images extracted from a representative motion video of...

Watch this Scientific Journal Video about Trapping of Micro Particles in Nanoplasmonic Optical Lattice at JoVE.com

Trapping of Micro Particles in Nanoplasmonic Optical Lattice

We describe a procedure to optically trap micro-particles in nanoplasmonic optical lattice.

The plasmonic optical tweezer has been developed to overcome the diffraction limits of the conventional far field optical tweezer. Plasmonic optical ...

The overall goal of this experiment is to demonstrate how to trap microparticles with plasmonic optical lattices with a technique that suppresses photothermal convection. The main feature of this technique is that we use the array of plasmonic nanostructures to enhance the trapping efficiency. Also we use a unique brewing property of water, 0%thermal expansion coefficient at low temperature to suppress the photothermal convection.Demonstrating this procedure will be Dinesh Bhalothia, a grad student from my laboratory. The setup for the experiment builds on a optical tweezer kit. This modified optical tweezer kit with a florescence module is ready on a breadboard.An LED and a diode laser provide light for florescence and manipulation. Mirrors direct light through an objective lens. The objective focuses the light on a sample stage which also serves as a heat sink.A CCD camera captures images from the sample. These elements are more evident in this schematic. A 470 nanometer blue LED is the light source for the florescence module.A 980 nanometer laser diode provides laser light in loose focus for manipulation. The lens is a long working distance microscope objective. Activity on the sample stage is recorded by a CCD camera.Turn on the power supply and current for the 980 nanometer laser diode. Use the CCD camera to check the laser beam alignment. If the beam is well aligned, the camera image will be a Gaussian spot.Turn off the laser for the next steps. An important aspect of the setup is the cooling system. The sample stage is a heat sink designed to accommodate a thermoelectric cooler.Work with the system electronics to prepare to add the thermoelectric cooler. There is a custom driver circuit for this experiment. Make the connections between the driver circuit and the electronic control board.Next, get a thermoelectric cooling element that will fit in the sample stage and with a hole in it to allow the laser beam through. Connect the output of the driver circuit to the thermoelectric cooling element. Move the cooling element to the sample stage.Before continuing, connect the driver circuit to a five volt power supply. To monitor the temperature, use a forward-looking infrared camera, and check that the system is cooling properly before proceeding. For this, use a resistance thermometer unit and its sensor.Begin with the sensor on a glass cover slip. Transfer the sensor and cover slip to the sample stage. Apply a small amount of thermal paste to ensure thermal contact.There, put the the assembly in contact with the stage. At the controls, adjust the power to the thermoelectric cooling element. After three minutes, read the temperature using the resistance temperature detector thermometer.In addition, record the temperature with the forward-looking infrared camera. Repeat these two measurements at various output power settings to obtain a temperature calibration curve similar to this one. Calibration is essential.Before proceeding, shut off the power to the thermoelectric cooler. The final element of the setup is the nanoplasmonic array. The slide cover has a custom fabricated array and is ready to mount in the experiment.This scanning electron microscope image of the array provides more detail. It is an array of about 16 micrometers square of 22 by 22 gold nanodiscs. Each nanodisc has a thickness of 40 nanometers and a diameter of 550 nanometers.The center to center distance between discs is 750 nanometers. Put the slide cover with the nanoplasmonic array on the sample stage. It should be in contact with the thermoelectric cooler.Next, set up the light source. Turn on the florescent light source, and set the power to five milliwatts for bright field imaging. Monitor the CCD image while manipulating the slide.Use the marker on the slide to locate and align the array. Make sure the array is in the center of the region of interest on the computer screen. Now, turn to the sample for the experiment.It is a mixture of two micrometer diameter polystyrene particles in deionized water. Use a micropipette to dispense 10 microliters onto the nanoarray slide. Move to the current supply of the 980 nanometer laser diode.Turn it on to excite the plasmonic resonance of the array. Then work with the power supply for the cooling system to achieve a temperature of four degrees Celsius. Finally, start recording video of the microparticles with the CCD camera.This is an example of the video recorded during an experiment with two micrometer polystyrene spheres. The optical power of the 980 nanometer wavelength laser used for plasmonic resonance excitation is five milliwatts. Note the particles cluster in a hexagonal, close-packed structure.These still images are of the accumulated trapped microparticles over time. Again, the hexagonal close-pack structure is clear. Images such as these can provide data to produce a plot of the number of trapped microparticles as a function of time.These five colored curves are examples of microparticle trajectories that can be extracted from the recorded video using image processing techniques, and the centroid algothrithm. The scale bar represents two micrometers. The procedure reported here enables a researcher to reproduce trapping on a daily basis.While attempting this procedure, it's important to remember to use the infrared camera to monitor the sample temperature to avoid the sample breakage. After its development, this technique pave the way for researchers in the field of optical trapping to study a larger class of transport phenomena in plasmonic optical lattice. After watching this video, you should have a good understanding of how to do the optical trapping with the plasmonic optical lattice,

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6.5K vistas.  National Tsing Hua University. The overall goal of this experiment is to demonstrate how to trap microparticles with plasmonic optical lattices with a technique that suppresses photothermal convection. The main feature of this technique is that we use the array of plasmonic nanostructures to enhance the trapping efficiency. Also we use a unique brewing property of water, 0%thermal expansion coefficient at low temperature to suppress the photothermal convection.Demonstrating this procedure will be Dinesh Bhalothia, a...