Y. T. Y. desidera ringraziare finanziamento dal Ministero della scienza e della tecnologia in numeri di sovvenzione più 105-2221-E-007-MY3 e dal National Tsing Hua University sotto grant numeri 105N518CE1 e 106N518CE1.

1. Setup ottico Nota: il principio dell'apparato ottico è illustrato nella Figura 1.
<ol><li>Set up ottico pinzetta kit (vedere la Tabella materiali) e il modulo di fluorescenza (Vedi Tabella materiali) secondo i loro manuali. Collegare una fonte di 470 nm blu luce che emettono luce a diodi (LED) al modulo fluorescente.</li>
	<li>Sostituire l'alta apertura numerica (NA) (NA = 1.25, ingrandimento 100 x) obiettivo a immersione in olio tramite un funzionamento di lungo distanza obiettivo del microscopio (WD) (lunghezza focale 3,6 mm, WD = 10.6 mm, NA = 0.5).</li>
	<li>Rimuovere la lente nella sezione di espansione di larghezza del kit assemblato per raggiungere sciolto di messa a fuoco del fascio laser.</li>
	<li>Disabilita l'alimentazione e la corrente per il laser a diodi di lunghezza d'onda 980 nm e uso la carica accoppiata fotocamera del dispositivo (CCD) per assicurarsi che il raggio laser è allineato correttamente. 
	Nota: Se il raggio laser è ben allineato, la telecamera CCD leggerà un posto gaussiano.</li>
</ol> 2. Nanofabbricazione <ol><li>Marker Fabrication. 
	Nota: I marcatori aiuterà a posizionare la serie di nanoplasmonic durante il processo di fabbricazione e l'esperimento successivo intrappolamento. Il processo dettagliato è illustrato in complementare figura 1.
	<ol><li>Film di ossido di stagno (ITO) di cauzione 40 nm indio su un vetrino coprioggetti spessore 0,17 mm con sputtering. 
		Nota: La pellicola di ITO aiuterà gli elettroni di scarico durante il processo di Litografia di fascio elettronico successivi.</li>
		<li>Spin cappotto uno strato di 8 µm di photoresist positivo con spin velocità 4000 giri/min e tempo 30 s con una macchina a spin.</li>
		<li>Soft cuocere il campione a 90 ° C per 5 min e allineare il campione con strato di fotoresist per marcatore ed esporre il campione ai raggi UV per 80 s nell'assetto maschera.</li>
		<li>Immergere il campione nello sviluppatore di photoresist per 130 s.</li>
		<li>Depositare uno strato di 2 nm di cromo e uno strato di 40 nm di oro sul campione mediante evaporazione termica. 18</li> <li>immergere il campione in acetone e posizionarlo in un pulitore ad ultrasuoni operanti a 43 kHz e 150 W per 5 min per lift off.</li>
	</ol></li> <li>Fabbricazione di Nanoplasmonic matrice <ol><li>cappotto Spin uno strato di e-fascio resistere PMMA 120K con velocità di rotazione di 5000 giri/min per 30 s su una macchina a rotazione. Cuocere il campione a 160 ° C per 3 min su una piastra calda.</li>
		<li>Spin cappotto un altro strato di fotoresist e-fascio PMMA 960K con velocità di centrifuga 5000 giri/min per 30 s su una macchina a rotazione. Cuocere il campione a 160 ° C per 3 min su una piastra calda.</li>
		<li>Scrittore di fascio elettronico di uso per esporre il fascio elettronico resistere con accelerazione tensione 30 kV e dosaggio 400 C/cm 2.</li>
		<li>Depositare uno strato di 40 nm di oro in un evaporatore termale.</li>
		<li>Immergere il campione in acetone e posizionarlo in un pulitore ad ultrasuoni per 5 min per lift off.</li>
	</ol></li></ol> 3. Esempio di sistema e la sua taratura della temperatura di raffreddamento Nota: il campione in fase di progettazione di raffreddamento è mostrato complementare figura 2.
<ol><li>Rendendo il circuito di pilotaggio per esempio raffreddamento <ol><li>posto le resistenze, transistor a giunzione bipolare e transistori di effetto di campo di ossido di metallo di potere sul circuito stampato personalizzato seguendo lo schema di circuito di complementare figura 3 . Saldare tutti questi componenti con saldatore.</li>
		<li>Cavi di connessione tra la porta di controllo del circuito e scheda elettronica di controllo. Collegare i cavi tra la porta di uscita del circuito stampato ed elemento di (TEC) raffreddamento termoelettrico. Posizionare l'elemento TEC sul palco campione con d'affondamento di calore. 
		&#8203; Nota: The TEC elemento ha un buco al centro per permettere il fascio laser di passare attraverso.</li>
		<li>Connect fili da circuito stampato a 5 V di alimentazione. Utilizzare il lungimirante fotocamera a raggi infrarossi per controllare la temperatura per controllare se il raffreddamento termoelettrico è correttamente raffreddando.</li>
	</ol></li> <li>Calibrazione di temperatura misurata in lungimirante termometro a infrarossi telecamera e resistenza temperatura detector (RTD).
	<ol><li>Posizionare il Termometro RTD su un vetrino coprioggetto vuoto e applicare una piccola quantità di pasta termica su di esso per garantire il corretto contatto termico tra il Termometro RTD e il vetrino coprioggetti.</li>
		<li>Modificare l'impostazione di potenza di uscita del circuito di controllo elettronico a TEC elemento modificando il duty cycle di impostazione di modulazione larghezza impulso e attendere 3 minuti per assicurarsi che la temperatura allo stato stazionario è raggiunto. Leggere la temperatura utilizzando il Termometro RTD.</li>
		<li>Disabilita la telecamera a infrarossi che guarda avanti e monitor della temperatura. Ripetere questa operazione con diverse impostazioni di potenza di uscita per ottenere la curva di calibrazione di temperatura. Una curva di calibrazione temperatura rappresentativa è mostrata in complementare figura 4. 
		Nota: È fondamentale fare calibrazione tra Termometro RTD e la telecamera a infrarossi lungimirante, perché la lettura della temperatura della telecamera a raggi infrarossi previsionale dovrà essere accurata per garantire la corretta temperatura.</li>
	</ol></li></ol> 4. Cattura di microparticelle <ol><li>diluire micro particelle di polistirene di µm di diametro 2 in acqua deionizzata in un microcentrifugetube con rapporto adeguato volume. 
	Nota: La concentrazione di micro particelle può essere regolata secondo l'obiettivo dell'esperimento. Mentre la concentrazione più bassa consente un intervallo di tempo campione tra gli eventi di intrappolamento di singola particella, maggiore concentrazione accorcerà il tempo per intrappolamento delle particelle più. Per il trapping di singola particella, una concentrazione tipica è ~0.05% (w/v).</li>
	<li>Mettere il campione con matrice di nanoplasmonic sul palco e accendere un 470 nm LED come la sorgente di luce di fluorescenza e impostare manualmente la potenza di 5 mW per l'imaging del campo luminoso.</li>
	<li>Utilizzare il marcatore per individuare la matrice nanoplasmonic, allineare il campione e la telecamera CCD per assicurarsi che la matrice sia nel centro della regione di interesse sullo schermo del computer.</li>
	<li>Dispensare 10 µ l del diluito micro particelle di diametro 2 µm sul campione con una pipetta.</li>
	<li>Accendere il rifornimento corrente per il diodo laser di lunghezza d'onda 980 nm per eccitare la risonanza plasmonica della matrice con una potenza nella gamma ~ 1 mW a 10 mW.</li>
	<li>Accendere manualmente l'alimentazione alla scheda elettronica di controllo per raffreddare il campione ad un stato stazionario temperatura ~ 4 ° C.</li>
	<li>Nel software visualizzatore, scegliere il &#34; registrare video &#34; sequenza per aprire la finestra di dialogo di registrazione. Fare clic sul &#34; record &#34; pulsante per avviare la registrazione 1.5 del moto delle particelle micro a un frame rate di 10 fotogrammi/s sopra il campione sotto l'influenza del raggio laser utilizzando la telecamera CCD video. Fare clic sul &#34; stop &#34; pulsante per interrompere la registrazione. Guarda il Video 1.</li>
</ol>

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	<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. 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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. 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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. 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La procedura qui descritta consente al lettore di riprodurre in modo affidabile la registrazione dei colori su una base quotidiana. Regola empirica generale per progettare un reticolo ottico utilizzabile è quello di utilizzare una dimensione paragonabile per plasmoniche nanoarray, interdisc distanza e intrappolati dimensione delle particelle. Rispetto ad una singola, isolata Nanostrutture plasmoniche, il design di grata ottica in collaborazione con l'alto potere ottico accordato dal raffreddamento il campione a ~ 4 ° C...

L'intrappolamento ottico di particelle micro-scala è stato originariamente sviluppato da Arthur Askin agli inizi del 1970. Mai fin dalla sua invenzione, la tecnica è stata sviluppata come un versatile strumento per micro - e nanomanipulation1,2. Optical trapping base lontano dal campo-principio di messa a fuoco è intrinsecamente limitato dalla diffrazione nel suo confinamento spaziale, in cui la forza di intrappolamento diminuisce drammaticamente convenzionale (seguente un ~unalegge3 per una particella di raggio un) 3. per superare tali limiti di diffrazione, i ricercatori hanno sviluppato tecniche di intrappolamento ottico vicino-campo basati sul campo ottico evanescente utilizzando Nanostrutture plasmoniche metallico e, inoltre, l'intrappolamento di nanoscala oggetti verso il basso per singole molecole proteiche, è stata dimostrata4,5,6,7,8,9,10,11. Inoltre, il reticolo ottico plasmonico viene creato da matrici di periodici plasmoniche di conferire il trasporto a lungo raggio di micro e nanoparticelle e più particelle impilamento11,12. È uno dei principali ostacoli per interrompere la cattura in un reticolo ottico photothermal convezione e sono stati compiuti sforzi per delucidare i suoi effetti da diversi gruppi14,15,16,17. Utilizzando la funzione di Green, Valerio et al hanno calcolato un profilo di temperatura modellando ogni Nanostrutture plasmoniche come un riscaldatore di punto ed ha quindi convalidato sperimentalmente loro modello14. Gruppo di Toussant ha misurato anche la convezione indotta da plasmon con particella velocimetry15. Gruppo dell'autore ha anche caratterizzato il trasporto sia di campo vicino e convezione e ha dimostrato una strategia ingegneria per sopprimere photothermal convezione16,17.
Qui presentiamo la progettazione di una configurazione ottica e una procedura dettagliata in particolare per gli esperimenti dell'intrappolamento con grata ottica plasmonica. Il potenziale ottico è stato creato da illuminare una matrice di oro nanodiscs con un fascio gaussiano vagamente focalizzato. Uno schema per sopprimere la convezione photothermal dal raffreddarsi il campione ad una temperatura bassa (~ 4 ° C) per il trapping ottimale è anche descrivere qui17. Sotto approssimazione di Boussinesq, una stima dell'ordine di grandezza per la convezione naturale velocità u è data da u ~L2 gβΔT / v, dove L è la scala di lunghezza della sorgente di calore e Δ T è l'aumento della temperatura rispetto al riferimento a causa del riscaldamento.  g e β sono l'accelerazione gravitazionale e coefficiente di espansione termica, rispettivamente. A temperature vicine ai 4 ° C, la densità del mezzo acqua esibisce la dipendenza dalla temperatura anomala e questo si traduce in un coefficiente di dilatazione termica quasi zero e, quindi, una convezione photothermal infinitamente piccolo.

<table><tbody><tr><td>Thermoelectric cooling element</td><td>Thorlabs</td><td>TEC 1.4-6</td><td>TEC element for sample cooling</td></tr><tr><td>RTD thermometer</td><td>Omega Engineering</td><td>RTD Thermometer 969C</td><td></td></tr><tr><td>Forward looking infrared camera</td><td>FLIR&amp;nbsp;</td><td>FLIR One</td><td>IR camera for temperature monitoring</td></tr><tr><td>light emitting diode light source</td><td>Touchbright</td><td></td><td>Light source for illumination for fluorescent imaging</td></tr><tr><td>Long working distance objective</td><td>Olympus</td><td>LMPLFLN</td><td>For illuminating the sample and imaging</td></tr><tr><td>Optical trap kit</td><td>Thorlabs</td><td>OTKB/M</td><td></td></tr><tr><td>Cover slip</td><td></td><td></td><td>thickness 0.17 mm</td></tr><tr><td>Scanning electron microscope</td><td>Hitachi</td><td>SEM-Hitachi S3400N</td><td></td></tr><tr><td>Electron beam blanker</td><td>DEBEN</td><td>PCD beam blanker</td><td>the blanker is added to the scanning electron microscope&amp;nbsp;</td></tr><tr><td>Thermal evaporator</td><td>SYSKEY Technology</td><td></td><td></td></tr><tr><td>Mask aligner</td><td>Karl Suss</td><td>MJB 3</td><td>For marker fabrication</td></tr><tr><td>Electron beam resist</td><td>Sigma Alrich</td><td>PMMA 120K</td><td>For e-beam lithography</td></tr><tr><td>Electron beam resist</td><td>Sigma Alrich</td><td>PMMA 960K</td><td>For e-beam lithography</td></tr><tr><td>Fluoresent labeled polystyrene microspheres</td><td>Polyscience</td><td></td><td>2 um diameter</td></tr><tr><td>Bipolar transistor</td><td>Mouser</td><td>2N3904</td><td>quantity 2 for TEC driver circuit</td></tr><tr><td>Bipolar transistor</td><td>Mouser</td><td>2N3906</td><td>quantity 2 for TEC driver circuit</td></tr><tr><td>MOSFET power transistor</td><td>Mouser</td><td>IRF5305</td><td>quantity 2 for TEC driver circuit</td></tr><tr><td>MOSFET power transistor</td><td>Mouser</td><td>IRF131ON</td><td>quantity 2 for TEC driver circuit</td></tr><tr><td>10 kOhm resistor</td><td>Mouser</td><td></td><td>quantity 6 for TEC driver circuit</td></tr><tr><td>910 Ohm resistor</td><td>Mouser</td><td></td><td>quantity 2 for TEC driver circuit</td></tr><tr><td>Photoresist</td><td>Microchemicals</td><td>AZ4620</td><td>For marker fabrication</td></tr><tr><td>Acetone</td><td>Sigma Alrich</td><td></td><td>For marker fabrication</td></tr><tr><td>Fluorescence Module for the OTKB/M, Metric Threads</td><td>Thorlabs</td><td>OTKB-FL/M</td><td></td></tr><tr><td>Fluorescent filter set</td><td>Thorlabs</td><td>MDF-FITC</td><td>For Fluorescein Isothiocyanate (FITC)</td></tr><tr><td>Ultrasonic cleaner</td><td>Delta</td><td>DC150H</td><td>For the lift off step</td></tr></tbody></table>

trapping of micro particles in nanoplasmonic optical lattice

La pinzetta ottica plasmonica è stata sviluppata per superare i limiti di diffrazione delle pinzette ottiche convenzionali campo lontano. Plasmonica reticolo ottico è costituito da una matrice di nanostrutture, che esibiscono una varietà di intrappolamento e comportamenti di trasporto. Segnaliamo le procedure sperimentali per intrappolare micro-particelle in un reticolo ottico semplice quadrato nanoplasmonic. Descriviamo anche l'installazione di ottica e la nanofabbricazione di una matrice di nanoplasmonic. Il potenziale ottico è creato da illuminare una matrice di nanodiscs d'oro con un fascio gaussiano di 980 nm lunghezza d'onda ed eccitante risonanza plasmonica. Il moto delle particelle è monitorato da formazione immagine di fluorescenza. Uno schema per sopprimere photothermal convezione anche descritto per aumentare la potenza ottica utilizzabile per il trapping ottimale. Soppressione della convezione è realizzata il campione a bassa temperatura di raffreddamento, ed utilizzando il coefficiente di dilatazione termica quasi zero di un mezzo di acqua. Trasporto di singola particella sia più dell'intrappolamento delle particelle sono segnalati qui.

Traiettorie di singola particella sono state registrate da una telecamera CCD nel nostro esperimento e le immagini sono state poi elaborate con un programma personalizzato per estrarre traiettoria16 di ogni particella. Risultati rappresentativi vengono visualizzati in Figura 3 e Video 1 per micro-sfere con diametro di 2 µm. più orpelli di particelle all'interno del reticolo ottico sono stati osservati. Successive imm...

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Trapping of Micro Particles in Nanoplasmonic Optical Lattice

Descriviamo una procedura per intercettare otticamente micro-particelle in grata ottica nanoplasmonic.

Intrappolamento delle Micro particelle in grata ottica Nanoplasmonic

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

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Video: Trapping of Micro Particles in Nanoplasmonic Optical Lattice

Optical Trapping of Nanoparticles

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping and manipulating small biological particles. Ashkin and co-workers first demonstrated optical tweezers using a single focused beam1. The single beam trap can be described accurately using the perturbative gradient force formulation in the case of small Rayleigh regime particles1. In the perturbative regime, the optical power required for trapping a particle scales as the inverse fourth power of the particle size. High optical powers can damage dielectric particles and cause heating. For instance, trapped latex spheres of 109 nm in diameter were destroyed by a 15 mW beam in 25 sec1, which has serious implications for biological matter2,3.
A self-induced back-action (SIBA) optical trapping was proposed to trap 50 nm polystyrene spheres in the non-perturbative regime4. In a non-perturbative regime, even a small particle with little permittivity contrast to the background can influence significantly the ambient electromagnetic field and induce a large optical force. As a particle enters an illuminated aperture, light transmission increases dramatically because of dielectric loading. If the particle attempts to leave the aperture, decreased transmission causes a change in momentum outwards from the hole and, by Newton's Third Law, results in a force on the particle inwards into the hole, trapping the particle. The light transmission can be monitored; hence, the trap can become a sensor. The SIBA trapping technique can be further improved by using a double-nanohole structure.
The double-nanohole structure has been shown to give a strong local field enhancement5,6. Between the two sharp tips of the double-nanohole, a small particle can cause a large change in optical transmission, thereby inducing a large optical force. As a result, smaller nanoparticles can be trapped, such as 12 nm silicate spheres7 and 3.4 nm hydrodynamic radius bovine serum albumin proteins8. In this work, the experimental configuration used for nanoparticle trapping is outlined. First, we detail the assembly of the trapping setup which is based on a Thorlabs Optical Tweezer Kit. Next, we explain the nanofabrication procedure of the double-nanohole in a metal film, the fabrication of the microfluidic chamber and the sample preparation. Finally, we detail the data acquisition procedure and provide typical results for trapping 20 nm polystyrene nanospheres.

The following setup approach details low power optical trapping of dielectric nanoparticles using a double-nanohole in metal film.

Trapping ottica di nanoparticelle

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping ...

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Three-dimensional Optical-resolution Photoacoustic Microscopy

Optical microscopy, providing valuable insights at the cellular and organelle levels, has been widely recognized as an enabling biomedical technology. As the mainstays of in vivo three-dimensional (3-D) optical microscopy, single-/multi-photon fluorescence microscopy and optical coherence tomography (OCT) have demonstrated their extraordinary sensitivities to fluorescence and optical scattering contrasts, respectively. However, the optical absorption contrast of biological tissues, which encodes essential physiological/pathological information, has not yet been assessable. 
The emergence of biomedical photoacoustics has led to a new branch of optical microscopy optical-resolution photoacoustic microscopy (OR-PAM)1, where the optical irradiation is focused to the diffraction limit to achieve cellular1 or even subcellular2 level lateral resolution. As a valuable complement to existing optical microscopy technologies, OR-PAM brings in at least two novelties. First and most importantly, OR-PAM detects optical absorption contrasts with extraordinary sensitivity (i.e., 100%). Combining OR-PAM with fluorescence microscopy3 or with optical-scattering-based OCT4 (or with both) provides comprehensive optical properties of biological tissues. Second, OR-PAM encodes optical absorption into acoustic waves, in contrast to the pure optical processes in fluorescence microscopy and OCT, and provides background-free detection. The acoustic detection in OR-PAM mitigates the impacts of optical scattering on signal degradation and naturally eliminates possible interferences (i.e., crosstalks) between excitation and detection, which is a common problem in fluorescence microscopy due to the overlap between the excitation and fluorescence spectra. 
Unique for optical absorption imaging, OR-PAM has demonstrated broad biomedical applications since its invention, including, but not limited to, neurology5, 6, ophthalmology7, 8, vascular biology9, and dermatology10. In this video, we teach the system configuration and alignment of OR-PAM as well as the experimental procedures for in vivo functional microvascular imaging.

Optical-resolution photoacoustic microscopy (OR-PAM) is an emerging technology capable of imaging optical absorption contrasts in vivo with cellular resolution and sensitivity. Here, we provide a visualized instruction on the experimental protocols of OR-PAM, including system configuration, system alignment, typical in vivo experimental procedures, and functional imaging schemes.

Tridimensionale con risoluzione ottica Microscopia fotoacustico

Optical microscopy, providing valuable insights at the cellular and organelle levels, has been widely recognized as an enabling biomedical technology. As ...

Bioingegneria

Utilization of Plasmonic and Photonic Crystal Nanostructures for Enhanced Micro- and Nanoparticle Manipulation

A method to manipulate the position and orientation of submicron particles nondestructively would be an incredibly useful tool for basic biological research. Perhaps the most widely used physical force to achieve noninvasive manipulation of small particles has been dielectrophoresis(DEP).1 However, DEP on its own lacks the versatility and precision that are desired when manipulating cells since it is traditionally done with stationary electrodes. Optical tweezers, which utilize a three dimensional electromagnetic field gradient to exert forces on small particles, achieve this desired versatility and precision.2 However, a major drawback of this approach is the high radiation intensity required to achieve the necessary force to trap a particle which can damage biological samples.3 A solution that allows trapping and sorting with lower optical intensities are optoelectronic tweezers (OET) but OET's have limitations with fine manipulation of small particles; being DEP-based technology also puts constraint on the property of the solution.4,5
This video article will describe two methods that decrease the intensity of the radiation needed for optical manipulation of living cells and also describe a method for orientation control. The first method is plasmonic tweezers which use a random gold nanoparticle (AuNP) array as a substrate for the sample as shown in Figure 1. The AuNP array converts the incident photons into localized surface plasmons (LSP) which consist of resonant dipole moments that radiate and generate a patterned radiation field with a large gradient in the cell solution. Initial work on surface plasmon enhanced trapping by Righini et al and our own modeling have shown the fields generated by the plasmonic substrate reduce the initial intensity required by enhancing the gradient field that traps the particle.6,7,8 The plasmonic approach allows for fine orientation control of ellipsoidal particles and cells with low optical intensities because of more efficient optical energy conversion into mechanical energy and a dipole-dependent radiation field. These fields are shown in figure 2 and the low trapping intensities are detailed in figures 4 and 5. The main problems with plasmonic tweezers are that the LSP's generate a considerable amount of heat and the trapping is only two dimensional. This heat generates convective flows and thermophoresis which can be powerful enough to expel submicron particles from the trap.9,10 The second approach that we will describe is utilizing periodic dielectric nanostructures to scatter incident light very efficiently into diffraction modes, as shown in figure 6.11 Ideally, one would make this structure out of a dielectric material to avoid the same heating problems experienced with the plasmonic tweezers but in our approach an aluminum-coated diffraction grating is used as a one-dimensional periodic dielectric nanostructure. Although it is not a semiconductor, it did not experience significant heating and effectively trapped small particles with low trapping intensities, as shown in figure 7. Alignment of particles with the grating substrate conceptually validates the proposition that a 2-D photonic crystal could allow precise rotation of non-spherical micron sized particles.10 The efficiencies of these optical traps are increased due to the enhanced fields produced by the nanostructures described in this paper.

Plasmonic tweezers and photonic crystal nanostructures are shown to produce useful enhancements in the efficiency and orientation control of optically trapping micro- and nano-particles.

L&#39;utilizzo di nanostrutture di cristallo plasmoniche e fotonici per Enhanced manipolazione micro e nanoparticelle

A method to manipulate the position and orientation of submicron particles nondestructively would be an incredibly useful tool for basic biological ...

Analyzing the Movement of the Nauplius 'Artemia salina' by Optical Tracking of Plasmonic Nanoparticles

We demonstrate how optical tweezers may provide a sensitive tool to analyze the fluidic vibrations generated by the movement of small aquatic organisms. A single gold nanoparticle held by an optical tweezer is used as a sensor to quantify the rhythmic motion of a Nauplius larva (Artemia salina) in a water sample. This is achieved by monitoring the time dependent displacement of the trapped nanoparticle as a consequence of the Nauplius activity. A Fourier analysis of the nanoparticle&#39;s position then yields a frequency spectrum that is characteristic to the motion of the observed species. This experiment demonstrates the capability of this method to measure and characterize the activity of small aquatic larvae without the requirement to observe them directly and to gain information about the position of the larvae with respect to the trapped particle. Overall, this approach could give an insight on the vitality of certain species found in an aquatic ecosystem and could expand the range of conventional methods for analyzing water samples.

Analyzing the Movement of the Nauplius 'Artemia salina' by Optical Tracking of Plasmonic Nanoparticles

We use optical tracking of plasmonic nanoparticles to probe and characterize the frequency movements of aquatic organisms.

Analizzando il movimento del Nauplius &#39;<em&gt; Artemia salina</em&gt; &#39;Di monitoraggio ottico di nanoparticelle plasmoniche

We demonstrate how optical tweezers may provide a sensitive tool to analyze the fluidic vibrations generated by the movement of small aquatic organisms. A ...

Fabrication and Operation of a Nano-Optical Conveyor Belt

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological and physical sciences over the past few decades. The progress made in this field invites further study of even smaller systems and at a larger scale, with tools that could be distributed more easily and made more widely available. Unfortunately, the fundamental laws of diffraction limit the minimum size of the focal spot of a laser beam, which makes particles smaller than a half-wavelength in diameter hard to trap and generally prevents an operator from discriminating between particles which are closer together than one half-wavelength. This precludes the optical manipulation of many closely-spaced nanoparticles and&#160;limits the&#160;resolution of optical-mechanical systems. Furthermore, manipulation using focused beams requires beam-forming or steering optics, which can be very bulky and expensive. To address these limitations in the system scalability of conventional optical trapping our lab has devised an alternative technique which utilizes near-field optics to move particles across a chip. Instead of focusing laser beams in the far-field, the optical near field of plasmonic resonators produces the necessary local optical intensity enhancement to overcome the restrictions of diffraction and manipulate particles at higher resolution. Closely-spaced resonators produce strong optical traps which can be addressed to mediate the hand-off of particles from one to the next in a conveyor-belt-like fashion. Here, we describe how to design and produce a conveyor belt using a gold surface patterned with plasmonic C-shaped resonators and how to operate it with polarized laser light to achieve super-resolution nanoparticle manipulation and transport. The nano-optical conveyor belt chip can be produced using lithography techniques and easily packaged and distributed.

The scalability and resolution of conventional optical manipulation techniques are limited by diffraction. We circumvent the diffraction limit and describe a method of optically transporting nanoparticles across a chip using a gold surface patterned with a path of closely spaced C-shaped plasmonic resonators.

Fabbricazione e funzionamento di un nano-ottica Nastro trasportatore

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological ...

Optical Trap Loading of Dielectric Microparticles In Air

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly scattered dielectric microparticles adhered to a glass substrate are momentarily detached using ultrasonic vibrations generated by a piezoelectric transducer (PZT). Then, the optical beam focused on a selected particle lifts it up to the optical trap while the vibrationally excited microparticles fall back to the substrate. A particle may be trapped at the nominal focus of the trapping beam or at a position above the focus (referred to here as the levitation position) where gravity provides the restoring force. After the measurement, the trapped particle can be placed at a desired position on the substrate in a controlled manner. 
In this protocol, an experimental procedure for selective optical trap loading in air is outlined. First, the experimental setup is briefly introduced. Second, the design and fabrication of a PZT holder and a sample enclosure are illustrated in detail. The optical trap loading of a selected microparticle is then demonstrated with step-by-step instructions including sample preparation, launching into the trap, and use of electrostatic force to excite particle motion in the trap and measure charge. Finally, we present recorded particle trajectories of Brownian and ballistic motions of a trapped microparticle in air. These trajectories can be used to measure stiffness or to verify optical alignment through time domain and frequency domain analysis. Selective trap loading enables optical tweezers to track a particle and its changes over repeated trap loadings in a reversible manner, thereby enabling studies of particle-surface interaction.

A protocol for launching and stably trapping selected dielectric microparticles in air is presented.

Optical Trappola Caricamento di dielettrico microparticelle in aria

We demonstrate a method to trap a selected dielectric microparticle in air using radiation pressure from a single-beam gradient optical trap. Randomly ...

Plasmonic Trapping and Release of Nanoparticles in a Monitoring Environment

Plasmonic tweezers use surface plasmon polaritons to confine polarizable nanoscale objects. Among the various designs of plasmonic tweezers, only a few can observe immobilized particles. Moreover, a limited number of studies have experimentally measured the exertable forces on the particles. The designs can be classified as the protruding nanodisk type or the suppressed nanohole type. For the latter, microscopic observation is extremely challenging. In this paper, a new plasmonic tweezer system is introduced to monitor particles, both in directions parallel and orthogonal to the symmetric axis of a plasmonic nanohole structure. This feature enables us to observe the movement of each particle near the rim of the nanohole. Furthermore, we can quantitatively estimate the maximal trapping forces using a new fluidic channel.

A microchip fabrication process that incorporates plasmonic tweezers is presented here. The microchip enables the imaging of a trapped particle to measure maximal trapping forces.

Plasmonico cattura e rilascio di nanoparticelle in un ambiente di monitoraggio

Plasmonic tweezers use surface plasmon polaritons to confine polarizable nanoscale objects. Among the various designs of plasmonic tweezers, only a few ...

Construction and Operation of a Light-driven Gold Nanorod Rotary Motor System

The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and artificial nanomotors and may provide new routes towards single cell analysis, studies of non-equilibrium thermodynamics, and mechanical actuation of nanoscale systems. A facile way to drive rotation is to use focused circularly polarized laser light in optical tweezers. Using this approach, metallic nanoparticles can be operated as highly efficient scattering-driven rotary motors spinning at unprecedented rotation frequencies in water.
In this protocol, we outline the construction and operation of circularly-polarized optical tweezers for nanoparticle rotation and describe the instrumentation needed for recording the Brownian dynamics and Rayleigh scattering of the trapped particle. The rotational motion and the scattering spectra provides independent information on the properties of the nanoparticle and its immediate environment. The experimental platform has proven useful as a nanoscopic gauge of viscosity and local temperature, for tracking morphological changes of nanorods and molecular coatings, and as a transducer and probe of photothermal and thermodynamic processes.

Plasmonic gold nanorods can be trapped in liquids and rotated at kHz frequencies using circularly-polarized optical tweezers. Introducing tools for Brownian dynamics analysis and light scatteringspectroscopy leads to a powerful system for research and application in numerous fields of science.

Costruzione e funzionamento di un sistema motore basato su luce oro Nanorod Rotary

The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and ...

Monitoring Conformational Dynamics of Single Unmodified Proteins using Plasmonic Nanotweezers

Current single-molecule techniques to characterize proteins typically require labels, tethers, or the use of non-native solution conditions. Such changes can alter protein biophysics and reduce the usefulness of the data acquired. Plasmonic nanotweezers is a technique that uses localized surface plasmon resonance (LSPR) on gold nanostructures to enhance the electric field within a confined hotspot region. This field enhancement allows for the use of low laser powers to trap single nanoparticles far smaller than conventional optical tweezers, down to only a few nanometers in diameter, such as single proteins. Trapping of single protein molecules within the hotspot region induces a shift in the local refractive index (nprotein &#62; nwater), altering light scattering as a product of the molecule&#39;s polarisability, which is affected by its volume, shape anisotropy, and refractive index. An avalanche photodiode (APD) collects the subsequent changes in light scattering. These alterations can then be analyzed to determine changes in the trapped molecule, including its size, global conformation, and dynamics of conformational change over time. The incorporation of microfluidics within the system allows for controlled environmental changes and real-time monitoring of their subsequent effects on the molecule. In this protocol, we demonstrate the steps to trap single protein molecules, alter their environmental solution conditions, and monitor their corresponding conformational changes using a plasmonic nanotweezers system.

Plasmonic nanotweezers use localized surface plasmon resonance in gold nanostructures to trap single nanoparticles, including proteins, within a nanometer-scale optical field. Changes in the scattered signal reveal protein presence and conformational dynamics, enabling monitoring without fluorophore modifications or surface tethering.

Monitoraggio della dinamica conformazionale di singole proteine non modificate mediante Nanotweezers plasmonici

Current single-molecule techniques to characterize proteins typically require labels, tethers, or the use of non-native solution conditions. Such changes ...

Optical Trapping of Plasmonic Nanoparticles for In Situ Surface-Enhanced Raman Spectroscopy Characterizations

Surface-enhanced Raman spectroscopy (SERS) enables the ultrasensitive detection of analyte molecules in various applications due to the enhanced electric field of metallic nanostructures. Salt-induced silver nanoparticle aggregation is the most popular method for generating SERS-active substrates; however, it is limited by poor reproducibility, stability, and biocompatibility. The present protocol integrates optical manipulation and SERS detection to develop an efficient analytical platform to address this. A 1064 nm trapping laser and a 532 nm Raman probe laser are combined in a microscope to assemble silver nanoparticles, which generate plasmonic hotspots for in situ SERS measurements in aqueous environments. Without aggregating agents, this dynamic plasmonic silver nanoparticle assembly enables an approximately 50-fold enhancement of the analyte molecule signal. Moreover, it provides spatial and temporal control to form the SERS-active assembly in as low as 0.05 nM analyte-coated silver nanoparticle solution, which minimizes the potential perturbation for in vivo analysis. Hence, this optical trapping-integrated SERS platform holds great potential for efficient, reproducible, and stable molecular analyses in liquids, especially in aqueous physiological environments.

Optical Trapping of Plasmonic Nanoparticles for In Situ Surface-Enhanced Raman Spectroscopy Characterizations

The present protocol describes a convenient approach to integrating optical trapping and surface-enhanced Raman spectroscopy (SERS) to manipulate plasmonic nanoparticles for sensitive molecular detection. Without aggregating agents, the trapping laser assembles plasmonic nanoparticles to enhance the SERS signals of target analytes for in situ spectroscopic measurements.

Intrappolamento ottico di nanoparticelle plasmoniche per la caratterizzazione della spettroscopia Raman potenziata dalla superficie in situ

Surface-enhanced Raman spectroscopy (SERS) enables the ultrasensitive detection of analyte molecules in various applications due to the enhanced electric ...

Intrappolamento delle Micro particelle in grata ottica Nanoplasmonic

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