Name: Plasmonic Trapping and Release of Nanoparticles in a Monitoring Environment (Video) | JoVE Journal
Uploaded: 2017-04-04T11:00:00.000+00:00
Duration: 9 min 13 s
Description: Learn plasmonic trapping and release of nanoparticles using a microchip with integrated tweezers for two-dimensional monitoring. This method enables quantitative measurement of maximal trapping forces for life science applications.

ai_agent_IP

ai_agent

maintenance

instantTrialDurationMinutes

isBiopharma

enableNewMyJoveSectionDesign

educationFeatures

seoMetaApi

ai_copilot_institution_blacklist

ai_chat_institution_blacklist

freeAccessWindow

ssoRoleCapture

scheduledMaintenanceBanner

joveLabsFeatures

disable_autoplay_for_bots

extended_trial_duration

5 minutes

This work was supported&#160;by the ICT R&#38;D program of MSIP/IITP (R0190-15-2040, Development of a contents configuration management system and a simulator for 3D printing using smart materials).

Caution: Please refer to all relevant material safety regulations before use. Several of the chemicals used in microchip fabrication are acutely toxic and carcinogenic. Please use all appropriate safety practices when performing the photolithography and etching processes, including the use of engineering controls (fume hood, hot plate, and aligner) and personal protective equipment (safety glasses, gloves, lab coat, full-length pants, and closed-toe shoes).
1. Fabrication of the PDMS Microchannel
<ol>
	<li>Fabrication of the microchannel mold by the photolithograph process
	<ol>
		<li>Completely remove foreign substances on the 4-inch Si wafer surface with piranha cleaning (Figure 1a). Mix sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) at a ratio of 3:1 to make the piranha solution in the dish. Mix by gradually adding small amounts of the strong acid (H2O2) to the weak acid (H2SO4); reversing this order may cause an explosion because of the highly reactive strong acid.</li>
		<li>Immerse the wafer in the piranha solution for 10 min. Subsequently, immerse the wafer in deionized (DI) water for 3 min to remove the remaining piranha solution. Rinse the wafer with flowing DI water for 10 s. Repeat the rinsing procedure 3 times and dry with N2 gas to remove the remaining DI.</li>
		<li>Place the wafer on a hot plate for 20 min at 180 &#176;C to further dehydrate the wafer.</li>
		<li>Pour 5 mL of the negative photoresist on top of the wafer and spin coat for 45 s at 1,500 rpm (Figure 1b); after spin coating, a photoresist bead is created at the wafer edge because of the relatively high viscosity of the photoresist.</li>
		<li>Balance the photoresist-coated wafer by planarization on a leveling stand for 5 h.</li>
		<li>Place the photoresist-coated wafer on a hot plate for 12 min at 65 &#176;C, 35 min at 95 &#176;C, and 12 min at 65 &#176;C (soft baking).</li>
		<li>Fix the film mask on the mask holder and the soft-baked wafer on the substrate stage of the aligner. Expose to ultraviolet (UV) light for 43 s at 650 mJ/cm2 to solidify the photoresist.</li>
		<li>Place the wafer on the hot plate for 5 min at 65 &#176;C, 15 min at 95 &#176;C, and 5 min at 65 &#176;C (post-exposure baking).</li>
		<li>Immerse the wafer in the photoresist developer for 30 min to remove unsolidified photoresist.</li>
		<li>Rinse the wafer with isopropyl alcohol (IPA) and dry with N2 gas to remove the remaining IPA.</li>
	</ol>
	</li>
	<li>Manufacture of the PDMS microchannel
	<ol>
		<li>Treat the surface of the wafer and the photoresist mold for 1 min at a power of 200 W using an atmospheric plasma machine25; the gas flows of CH4 and He should be 6 and 30 sccm, respectively. Perform this hydrophobic treatment to easily detach the polydimethylsiloxane (PDMS) microchannel from the surface of the wafer and photoresist mold (Figure 1c).</li>
		<li>Prepare the PDMS solution by mixing the PDMS base and curing agent at a ratio of 10:1. Stir the mixture for 2 min.</li>
		<li>Place the wafer inside a Petri dish (150 mm x 15 mm) and add 100 mL of the PDMS solution. Remove the bubbles that were created from stirring using a desiccator.</li>
		<li>Place the Petri dish in the oven for 2 h at 80 &#176;C to solidify the PDMS solution (Figure 1d and h).</li>
		<li>Cut along the contours of the PDMS microchannel with a razor blade and detach it from the wafer; the fabricated PDMS microchannel should have the following dimensions: 13 mm long, 300 &#181;m wide, and 150 &#181;m high (Figures 1e, f, and i). 
		NOTE: Two types of holes are produced by a micropuncture to insert the single-mode fiber (SMF) cable and the tubes (inlet and outlet) on the PDMS microchannel (Figure 1g). The SMF cable is used to emit the laser beam to the nanohole milled on the gold plate. The tube is used to insert/extract the particle solution to/from the PDMS microchannel.</li>
		<li>Puncture 1.5-mm inlet and outlet holes at each end of the PDMS microchannel. Puncture a 0.3-mm SMF cable hole at the center of the PDMS microchannel.</li>
	</ol>
	</li>
</ol>
2. Etching Process of the Gold Plate
<ol>
	<li>Prepare a commercially available gold plate with the dimensions of 25 x 6.25 mm2 (Figure 2a).</li>
	<li>Remove any foreign substances on the gold plate with the following cleaning procedures. Clean in the following order by immersing in acetone, methanol, and DI water for 5 min each.</li>
	<li>Rinse the gold plate 3 times with DI water for 10 s and dry the plate with N2 gas to remove the remaining DI water.</li>
	<li>Place the gold plate on a hot plate for 20 min at 180 &#176;C to completely remove any remaining moisture.</li>
	<li>Pour 0.5 mL of hexamethyldisilazane (HMDS) on the gold plate and spin coat for 40 s at 3,000 rpm.</li>
	<li>Pour 0.5 mL of positive photoresist on top of the spin-coated HMDS and spin coat for 40 s at 3,000 rpm (Figure 2b).</li>
	<li>Place the photoresist-coated gold plate on the hot plate for 90 s at 110 &#176;C (soft baking).</li>
	<li>Fix the film mask on the glass wafer and place the soft-baked gold plate on the substrate stage. Expose to UV light for 4.5 s at 64 mJ/cm2 to dissolve the photoresist.</li>
	<li>Immerse the gold plate in the photoresist developer for 1 min to remove the dissolved photoresist (Figure 2c). Rinse the gold plate with DI water and dry with N2 gas.</li>
	<li>Immerse the gold plate in the Au etchant for 45 s at an etching rate of 28 &#197;/s to remove the exposed Au (Figure 2d). Rinse the gold plate with DI water and dry with N2 gas.</li>
	<li>Immerse the gold plate in the Ti etchant for 5 s at an etching rate of 25 &#197;/s to remove the exposed Ti (Figure 2e). Rinse the gold plate with DI water and dry with N2 gas.</li>
	<li>Remove the remaining photoresist on the gold plate by immersing it in acetone, methanol, and DI water for 3 min each (Figure 2f); immerse the plate in the written order.</li>
	<li>Rinse the gold plate 3 times with DI water for 10 s. Dry with N2 gas to remove the DI water.</li>
	<li>Place the gold plate on the hot plate for 3 min at 120 &#176;C to completely remove the moisture; the produced gold block should be 400 x 150 &#181;m2 (Figure 2h).</li>
	<li>Mill a 400-nm nanohole using a focused ion beam (FIB) at the center of the gold block that was fabricated after etching (Figures 2g and i). Create a 370-nm circle pattern to focus on the gold block with an ion accelerating voltage of 30 kV at 28 pA for 3 s.</li>
</ol>
3. Assembly of the Microchip
<ol>
	<li>Treat the two surfaces of the PDMS microchannel and gold plate for 1 min with O2 plasma to attach them together with a plasma system at a power of 80 W and a pressure of 825 mTorr25. 
	NOTE: It is notably difficult to attach them with precision because the gold block and PDMS microchannel are on the micrometer level. Hence, use an aligner with a camera and a manual stage.</li>
	<li>Fix the glass wafer that is used to attach the film mask to the mask holder of the aligner (Figure 3a).</li>
	<li>Attach the O2-plasma-treated PDMS microchannel to the glass wafer; because the PDMS is hydrophilic, it will easily attach to the glass wafer without any adhesion solution. Fix the gold plate on the substrate stage of the aligner (Figure 3a).</li>
	<li>Locate the centers of the SMF cable hole and gold block, which are aligned on the same axis, using the camera on the aligner. Lift the manual stage to combine the two parts (Figures 3b and c).</li>
</ol>
4. Improvement of the Microchip Side Surface Roughness by PDMS Coating
NOTE: The gold plate with fixed dimensions of 400 x 150 &#181;m2 is relatively more difficult to cut out than the PDMS material. Therefore, to detach the PDMS microchannel from the wafer, a razor blade is used to cut out a larger piece than the gold plate. After combining the two parts, the excess parts of the PDMS relative to the gold plate must then be cut so that the inside of the channel can be observed from the side using a microscope (Figure 4a). However, the cut surface, which is used as a window, has a high surface roughness and consequently produces cloudy images of the particles that flow in the channel (Figure 4b). Coating with the PDMS solution is performed again to resolve this problem.
<ol>
	<li>Prepare the PDMS solution by mixing the PDMS base and curing agent at a 10:1 ratio and stir for 2 min.</li>
	<li>Pour 2 mL of the PDMS solution into the Petri dish and perform the spin coating for 30 s at 1,000 rpm (Figure 4c).</li>
	<li>Place the microchip surface that is going to be located on the microscope on the Petri dish (Figure 4d). Place the Petri dish in the oven for 1 h at 80 &#176;C to solidify the PDMS solution.</li>
	<li>Cut the border of the microchip and PDMS using a razor blade and subsequently detach it from the Petri dish (Figures 4e, f).</li>
</ol>
5. Laser Coupling to Insert the SMF Cable to the Microchip
NOTE: For the plasmonic tweezer system, an optical fiber incident laser with a 1,064-nm wavelength is used. The SMF cable is used because the diameter of the incident laser (5 mm) is too immense to emit the laser beam at the nanohole milled on the gold block (400 x 150 &#181;m2) in the microchip. The cladding diameter of the SMF cable is 125 &#181;m. Thus, the incident laser and SMF cable must be coupled.
<ol>
	<li>Connect a 40X objective lens to the microscope objective mount on the SMF coupler. Fix the SMF cable on the fiber clamp of the SMF coupler. Align the incident laser beam to fill in the back aperture of the objective lens.</li>
	<li>Focus the laser beam to the core of the SMF cable by adjusting the three-axis manual stage equipped on the SMF coupler.</li>
	<li>Insert the opposite end of the SMF cable into the SMF cable hole of the microchip. Measure the laser power prior to the insertion at the edge of the fiber cable, because the fixed fiber cable at the microchip cannot be detached.</li>
	<li>Seal the SMF cable hole using epoxy glue to block the leakage of the flowing particle solution from the gap between the SMF cable hole (300 &#181;m) and the cladding of the SMF cable (125 &#181;m); the end of the inserted fiber cable should not enter the microchannel to avoid the fluid flow. Manually align the fiber cable using visual feedback so that it is perpendicular to the gold block that hosts the nanohole.</li>
</ol>
6. Plasmonic Trapping of Single Fluorescent Polystyrene Particle in the Microchip
<ol>
	<li>Attach the syringe, which is filled with the particle solution, to a syringe micropump. Place the cover glass on the sample stage of the fluorescent microscope. Connect tubes to the inlet/outlet holes of the microchip. Place the PDMS-coated microchip surface on top of the cover glass.</li>
	<li>Position the microchip orthogonally to the 60X water immersion objective lens by observing the inside of the channel with the camera installed on the fluorescent microscope. Use transparent tape to fix the microchip in place. Connect the inlet tube of the microchip with the syringe needle.</li>
	<li>Insert the particle solution to the microchip by controlling the micropump at 20 &#181;m/s. At this moment, confirm that the fluorescent particle can be observed well in the channel when the fluorescent lamp is turned on.</li>
	<li>Wait until the particle solution exits from the outlet of the microchip. Set the speed to 3.4 &#181;m/s.</li>
	<li>Turn the laser source device so that it emits the laser into the nanohole; the fluorescent particle will be trapped at the rim of the nanohole.</li>
	<li>Ramp the fluid speed in increments of 0.4 &#181;m/s by controlling the micropump until the trapped particle escapes. Measure the fluid speed when the trapped particles escape. Obtain the maximal trapping force for each laser intensity using this measured fluid speed.</li>
</ol>

<ol><li>Crane, N. B., Onen, O., Carballo, J., Ni, Q., Guldiken, R. <a target="_blank" href="http://link.springer.com/article/10.1007/s10404-012-1060-1">Fluidic assembly at the microscale: progress and prospects.</a> Microfluid. Nanofluid. 14 (3), 383-419 (2013).</li>
<li>Yao, B., Luo, G. A., Feng, X., Wang, W., Chen, L. X., Wang, Y. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+microfluidic+device+based+on+gravity+and+electric+force+driving+for+flow+cytometry+and+fluorescence+activated+cell+sorting%5BTitle%5D)+AND+%22Lab+Chip%22%5BJournal%5D)">A microfluidic device based on gravity and electric force driving for flow cytometry and fluorescence activated cell sorting.</a> Lab Chip. 4 (6), 603-607 (2004).</li>
<li>Zhang, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((On-chip+manipulation+of+continuous+picoliter-volume+superparamagnetic+droplets+using+a+magnetic+force%5BTitle%5D)+AND+%22Lab+Chip%22%5BJournal%5D)">On-chip manipulation of continuous picoliter-volume superparamagnetic droplets using a magnetic force.</a> Lab Chip. 9 (20), 2992-2999 (2009).</li>
<li>Park, I. Y., Sung, S. Y., Lee, J. H., Lee, Y. G. <a target="_blank" href="http://iopscience.iop.org/article/10.1088/0960-1317/17/10/N03/pdf">Manufacturing micro-scale structures by an optical tweezers system controlled by five finger tips.</a> J. Micromech. Microeng. 17, N82-N89 (2007).</li>
<li>Kim, J. D., Hwang, S. U., Lee, Y. G. <a target="_blank" href="http://iopscience.iop.org/article/10.1088/0960-1317/22/10/105003">Traceable assembly of microparts using optical tweezers.</a> J. Micromech. Microeng. 22, 105003(2012).</li>
<li>Kim, J. D., Lee, Y. G. <a target="_blank" href="http://iopscience.iop.org/article/10.1088/0960-1317/23/6/065010">Construction and actuation of a microscopic gear assembly formed using optical tweezers.</a> J. Micromech. Microeng. 23, 065010(2013).</li>
<li>Kim, J. D., Choi, J. H., Lee, Y. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+measurement+of+the+maximal+forces+in+plasmonic+tweezers%5BTitle%5D)+AND+%22Nanotechnology%22%5BJournal%5D)">A measurement of the maximal forces in plasmonic tweezers.</a> Nanotechnology. 26 (42), 425203(2015).</li>
<li>Kim, J. D., Lee, Y. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Trapping+of+a+single+DNA+molecule+using+nanoplasmonic+structures+for+biosensor+applications%5BTitle%5D)+AND+%22Biomed.+Opt.+Express%22%5BJournal%5D)">Trapping of a single DNA molecule using nanoplasmonic structures for biosensor applications.</a> Biomed. Opt. Express. 5 (8), 2471-2480 (2014).</li>
<li>Quidant, R. <a target="_blank" href="https://www.cambridge.org/core/journals/mrs-bulletin/article/plasmonic-tweezersthe-strength-of-surface-plasmons/3637FF8C774139A6CCBD5666BC87F310">Plasmonic tweezers - the strength of surface plasmons.</a> MRS Bull. 37 (8), 739-744 (2012).</li>
<li>Juan, M. L., Gordon, R., Pang, Y., Eftekhari, F., Quidant, R. <a target="_blank" href="http://www.nature.com/nphys/journal/v5/n12/abs/nphys1422.html">Self-induced back-action optical trapping of dielectric nanoparticles.</a> Nat. Phys. 5, 915-919 (2009).</li>
<li>Pang, Y., Gordon, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Optical+trapping+of+12+nm+dielectric+spheres+using+double-nanoholes+in+a+gold+film%5BTitle%5D)+AND+%22Nano+Lett%22%5BJournal%5D)">Optical trapping of 12 nm dielectric spheres using double-nanoholes in a gold film.</a> Nano Lett. 11 (9), 3763-3767 (2011).</li>
<li>Tanaka, Y., Kaneda, S., Sasaki, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Nanostructured+potential+of+optical+trapping+using+a+plasmonic+nanoblock+pair%5BTitle%5D)+AND+%22Nano+Lett%22%5BJournal%5D)">Nanostructured potential of optical trapping using a plasmonic nanoblock pair.</a> Nano Lett. 13 (5), 2146-2150 (2013).</li>
<li>Kang, J. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Low-power+nano-optical+vortex+trapping+via+plasmonic+diabolo+nanoantennas%5BTitle%5D)+AND+%22Nat.+Commun%22%5BJournal%5D)">Low-power nano-optical vortex trapping via plasmonic diabolo nanoantennas.</a> Nat. Commun. 2, 582(2011).</li>
<li>Roxworthy, B. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Application+of+plasmonic+bowtie+nanoantenna+arrays+for+optical+trapping%2C+stacking%2C+and+sorting%5BTitle%5D)+AND+%22Nano+Lett%22%5BJournal%5D)">Application of plasmonic bowtie nanoantenna arrays for optical trapping, stacking, and sorting.</a> Nano Lett. 12 (2), 796-801 (2012).</li>
<li>Shoji, T., Tsuboi, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Plasmonic+optical+tweezers+toward+molecular+manipulation%3A+tailoring+plasmonic+nanostructure%2C+light+source%2C+and+resonant+trapping%5BTitle%5D)+AND+%22J.+Phys.+Chem.+Lett%22%5BJournal%5D)">Plasmonic optical tweezers toward molecular manipulation: tailoring plasmonic nanostructure, light source, and resonant trapping.</a> J. Phys. Chem. Lett. 5 (17), 2957-2967 (2014).</li>
<li>Pang, Y., Gordon, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Optical+trapping+of+a+single+protein%5BTitle%5D)+AND+%22Nano+Lett%22%5BJournal%5D)">Optical trapping of a single protein.</a> Nano Lett. 12 (1), 402-406 (2012).</li>
<li>Tsuboi, Y., et al. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/jz100659x">Optical trapping of quantum dots based on gap-mode-excitation of localized surface plasmon.</a> J. Phys. Chem. Lett. 1, 2327-2333 (2010).</li>
<li>Shoji, T., et al. <a target="_blank" href="https://www.ncbi.nlm.nih.gov/pubmed/23586869">Permanent fixing or reversible trapping and release of DNA micropatterns on a gold nanostructure using continuous-wave or femtosecond-pulsed near-infrared laser light.</a> J. Am. Chem. Soc. 135 (17), 6643-6648 (2013).</li>
<li>Grigrenko, A. N., Roberts, N. W., Dickson, M. R., Zhang, Y. <a target="_blank" href="http://www.nature.com/nphoton/journal/v2/n6/abs/nphoton.2008.78.html">Nanometric optical tweezers based on nanostructured substrates.</a> Nat. Photonics. 2, 365-370 (2008).</li>
<li>Righini, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Nano-optical+trapping+of+rayleigh+particles+and+escherichia+coli+bacteria+with+resonant+optical+antennas%5BTitle%5D)+AND+%22Nano+Lett%22%5BJournal%5D)">Nano-optical trapping of rayleigh particles and escherichia coli bacteria with resonant optical antennas.</a> Nano Lett. 9 (10), 3387-3391 (2009).</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/pubmed?term=((Transport+and+trapping+in+two-dimensional+nanoscale+plasmonic+optical+lattice%5BTitle%5D)+AND+%22Nano+Lett%22%5BJournal%5D)">Transport and trapping in two-dimensional nanoscale plasmonic optical lattice.</a> Nano Lett. 13 (9), 4118-4122 (2013).</li>
<li>Berthelot, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Three-dimensional+manipulation+with+scanning+near-field+optical+nanotweezers%5BTitle%5D)+AND+%22Nat.+Nanotechnol%22%5BJournal%5D)">Three-dimensional manipulation with scanning near-field optical nanotweezers.</a> Nat. Nanotechnol. 9 (4), 295-299 (2014).</li>
<li>Chen, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Enhanced+optical+trapping+and+arrangement+of+nano-objects+in+a+plasmonic+nanocavity%5BTitle%5D)+AND+%22Nano+Lett%22%5BJournal%5D)">Enhanced optical trapping and arrangement of nano-objects in a plasmonic nanocavity.</a> Nano Lett. 12 (1), 125-132 (2011).</li>
<li>Wang, K., Schonbrun, E., Steinvurzel, P., Crozier, K. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Trapping+and+rotating+nanoparticles+using+a+plasmonic+nano-tweezer+with+an+integrated+heat+sink%5BTitle%5D)+AND+%22Nat.+Commun%22%5BJournal%5D)">Trapping and rotating nanoparticles using a plasmonic nano-tweezer with an integrated heat sink.</a> Nat. Commun. 2, 469(2011).</li>
<li>Byun, D., Cho, S. J., Kim, S. <a target="_blank" href="http://iopscience.iop.org/article/10.1088/0960-1317/23/12/125010">Fabrication of a flexible penetrating microelectrode array for use on curved surfaces of neural tissues.</a> J. Micromech. Microeng. 23, 125010(2013).</li>
</ol>

The authors have nothing to disclose.

The SMF cable was inserted in the SMF cable hole on the microchip, as shown in the rectangular dot of Figure 6a. Because the SMF cable hole is larger than the cable diameter, epoxy glue was used to seal the gap to block the leakage of the flowing particle solution. Before the application of epoxy glue, the gold block and cable edge should be coaxially aligned by hand using a microscope. Although it is ideal for the inserted cable edge and the nanohole to be coaxially aligned, a slight misalignment can be...

The ability to manipulate microscale objects is an indispensable feature for many micro/nano experiments. Direct contact manipulations can damage the manipulated objects. Releasing the previously held objects is also challenging because of stiction problems. To overcome these issues, several indirect methods using fluidic1, electric2, magnetic3, or photonic forces4,5,6,7,8 have been proposed. Plasmonic tweezers that use photonic forces are based on the physics of extraordinary field enhancement several orders larger than the incident intensity9. This extremely strong field enhancement enables the trapping of extremely small nanoparticles. For example, it has been shown to immobilize and manipulate nanoscale objects, such as polystyrene particles7,10,11,12,13,14, polymer chains15, proteins16, quantum dots17, and DNA molecules8,18. Without plasmonic tweezers, it is difficult to trap nanoparticles because they quickly disappear before they are effectively examined or because they are damaged due to the high intensity of the laser.
Many plasmonic studies have used various nanoscale gold structures. We can categorize the gold structures as protruding nanodisk types12,13,14,15,19,20,21 or suppressed nanohole types7,8,10,11,22,23. In terms of imaging convenience, the nanodisk types are more suitable than the nanohole types because, for the latter, the gold substrates can obstruct the observation view. Moreover, the plasmonic trapping occurs near the plasmonic structure and makes observation even more challenging. To the best of our knowledge, plasmonic trapping on nanohole types was only verified using indirect scattering signals. However, no successful direct observations, such as microscopic images, have been reported. Few studies have described the position of trapped particles. One such result was presented by Wang et al. They created a gold pillar on a gold substrate and observed the particle motion using a fluorescent microscope24. However, this is only effective for monitoring lateral movements not in the direction parallel to the beam axis.
In this paper, we introduce new fluidic microchip design and fabrication procedures. Using this chip, we demonstrate the monitoring of plasmonically trapped particles, both in directions parallel and orthogonal to the plasmonic nanostructure. Furthermore, we measure the maximal force of the immobilized particle by increasing the fluid velocity to find the tipping velocity in the microchip. This study is unique because most studies on plasmonic tweezers cannot quantitatively show the maximal trapping forces used in their experimental setups.

<table><tbody><tr><td>Negative photoresist&amp;nbsp;</td><td>MicroChem</td><td>SU-8 2075</td><td></td></tr><tr><td>Developer</td><td>MicroChem</td><td>SU-8 Developer</td><td></td></tr><tr><td>Positive photoresist&amp;nbsp;</td><td>Merck Ltd.</td><td>AZ GXR-601</td><td></td></tr><tr><td>AZ Photoresist Developers</td><td>Merck Ltd.</td><td>AZ 300 MIF</td><td></td></tr><tr><td>HMDS</td><td>Merck Ltd.</td><td>AZ Adhesion Promoter</td><td></td></tr><tr><td>Aligner</td><td>Midas System</td><td>MDA 400M</td><td></td></tr><tr><td>Atmospheric plasma machine&amp;nbsp;</td><td>Atmospheric Process&lt;br/&gt; Plasma Co.</td><td>IDP-1000</td><td></td></tr><tr><td>Polydimethylsiloxane (PDMS)</td><td>Dow Corning</td><td>Sylgard 184 A/B</td><td></td></tr><tr><td>Gold coated test slides</td><td>EMF Co.</td><td>TA124(Ti/Au)</td><td></td></tr><tr><td>Au etchant&amp;nbsp;</td><td>Transene Inc.</td><td>TFA</td><td></td></tr><tr><td>Ti etchant&amp;nbsp;</td><td>Transene Inc.</td><td>TFT</td><td></td></tr><tr><td>40X objective lens&amp;nbsp;</td><td>Edmund Optics</td><td>40X DIN</td><td></td></tr><tr><td>60X water immersion&lt;br/&gt; objective lens&amp;nbsp;</td><td>Olympus</td><td>LUMPLFLN 60XW</td><td></td></tr><tr><td>Optical fiber incident laser&amp;nbsp;</td><td>IPG Photonic</td><td>YLR 10</td><td></td></tr><tr><td>SMF coupler</td><td>Thorlabs</td><td>MBT612D/M</td><td></td></tr><tr><td>Syringe micropump</td><td>Harvard</td><td>PC2 70-4501</td><td></td></tr><tr><td>Fluorescent microscope&amp;nbsp;</td><td>Olympus</td><td>IX-51</td><td></td></tr><tr><td>Plasma system</td><td>Femto Science Inc</td><td>CUTE-MPR</td><td></td></tr></tbody></table>

plasmonic trapping and release of nanoparticles in a monitoring environment

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.

The fabrication process of the PDMS microchannel and nanohole gold plate is shown in Figures 1 and 2. The method to combine the two parts and the actual microchip is shown in Figure 3. The PDMS was cut to reveal the inside of the channel from the side of the microchip. However, it was difficult to observe the particles flowing in the channel because of the surface roughness of the cutting plane. Therefore, we introduced the PDMS coating m...

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.

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

The overall goal of this experiment is to monitor particles in two dimensions, both parallel and orthogonal to the the symmetric axis of a plasmonic nanohole structure and to quantitatively estimate the maximum trapping force of the system. This method can help answer questions in the life sciences relating to rapid immunoassay development, cell and bacterial trapping, liposome analysis, and nanoparticle drug release studies. The main advantage of this technique is that it allows the monitoring of the particle motion in two dimensions, one in the laser beam axis, and the other in the direction orthogonal to it.To begin, fabricate the microchannel mold using standard photolithographic techniques and place the wafer into a 150 millimeter diameter Petri dish. Then, mix 10 parts PDMS base with one part curing agent and stir the mixture for two minutes. Once combined, pour 100 milliliters of the PDMS mixture over the wafer.Place the Petri dish into a vacuum chamber and pull a vacuum to remove any bubbles from the PDMS. Next, place the Petri dish in an oven for two hours at 80 degrees Celsius to solidify the PDMS solution. Once cool, remove the dish from the oven, and cut along the contours of the PDMS microchannel with a razor blade, and detach it from the wafer.Then, use a 1.5 millimeter biopsy punch to form 1.5 millimeter inlet and outlet holes at each end of the PDMS microchannel. Use a 0.3 millimeter punch to form a hole for the single-mode optical fiber cable at the center of the micro channel. Start by cleaning a commercially available gold plate as described in the accompanying text protocol.Then, place the plate onto spin coater, and pour 0.5 milliliters of hexamethyldisilazane onto the gold plate. Spin-coat the plate for 40 seconds at 3000 RPMs. Next, pour 0.5 milliliters of a positive photoresist on top of the spin-coated hexamethyldisilazane, and spin-coat the plate for an additional 40 seconds at 3000 RPMs.Remove the plate from the spin-coater, and place it on hot plate for 90 seconds at 110 degrees Celsius to soft-bake the photoresist. Then, use scotch tape to fix the film mask on the glass wafer, and place the soft-baked gold plate on the substrate stage. Expose the sample to UV light for 4 and a half seconds to dissolve the photoresist and create a gold rectangle that is 400 microns long by 150 microns wide.Next, immerse the gold plate in the photoresist developer for one minute to remove the dissolved photoresist. Then, rinse the gold plate with deionized water and dry it using nitrogen gas. Immerse the gold plate in the gold etchant for 45 seconds to remove the exposed gold layer.Then, rinse the gold plate with deionized water and dry it again using nitrogen gas. Next, immerse the plate in the titanium etchant for five seconds to remove the exposed titanium, then once more, rinse the gold plate with deionized water and dry it with nitrogen gas. Remove the remaining photoresist on the gold plate by immersing it sequentially in acetone, methanol, and finally deionized water for three minutes each.Rinse the plate three times with deionized water for 10 seconds each, and then dry the plate once more with nitrogen gas. Next, place the plate on hot plate for three minutes at 120 degrees Celsius to completely remove any remaining moisture. Using a focused ion beam, mill a 400 nanometer nanohole at the center of the fabricated gold block as described in the accompanying text protocol.Place both the PDMS microchannel and the gold plate into a plasma chamber. Treat the contacting surfaces for one minute using oxygen plasma. Fix the gold plate on the substrate stage of the aligner.Then, use the camera on the aligner to locate the centers of the SMF cable hole and the hole in the gold block so that they are aligned on the same axis. Lift the manual stage to combine the two parts. Next, pour two milliliters of a mixed PDMS solution into a Petri dish, and spin-coat the dish for 30 seconds at 1000 RPMs.Then, take the cut-out microchip and place the surface that is going to be located on the microscope into the PDMS that is on the Petri dish. Place the Petri dish in the oven for one hour at 80 degrees Celsius to solidify the PDMS solution. Once cooled, cut the border of the microchip and PDMS using a razor blade, and subsequently detach it from the Petri dish.First, connect a 40x objective lens to the microscope objective mount on the single mode optical fiber cable coupler. Next, fix the single mode optical fiber cable on the fiber clamp of the cable coupler. Align the incident laser beam to fill in the back aperture of the objective lens.Then, focus the laser beam to the core of the cable by adjusting the three axis manual stage equipped on the coupler. Measure the laser power prior to the insertion at the edge of the fiber cable, because the fixed fiber cable at the microchip cannot be detached. Then, insert the opposite end of the cable into the cable hole of the microchip.Manually align the fiber cable using visual feedback so that it is perpendicular to the gold block that hosts the nanohole. The end of the inserted fiber cable should not enter the microchannel so that it does not block the fluid flow. Finally, seal the cable hole using epoxy glue to block the leakage of the flowing particle solution from the 87.5 micrometer gap between the cable hole and the cladding of the optical fiber cable.Attach a syringe containing a solution of 100 nanometer diameter polystyrene particles to a syringe micropump. Next, connect tubes to the inlet and outlet holes of the microchip. Once connected, set the syringe pump to 20 micrometers per second and inject the particle solution into the microchip.Next, turn on the fluorescent lamp and confirm that the fluorescent particle can be observed in the channel. When the particle solution exits the outlet of the microchip, reduce the pump speed to 3.4 micrometers per second. Then, turn on the laser source so that it emits the laser into the nanohole.This will trap the fluorescent particle at the rim of the nanohole. Finally, ramp the fluid speed in increments of 0.4 micrometers per second by controlling the micropump until the trapped particle escapes. Use this information to obtain the maximal trapping force for each laser intensity.Shown here is an enlarged version of the microchannel setup showing the alignment of the parts and the location of the nanohole. As 100 nanometer fluorescent polystyrene particles flow through the microchannel, they become trapped by the laser at the nanohole. Untrapped particles are also shown as they flow past the nanohole, while the trapped particle stays in position.Once the flow speed was increased, the trapped particle was able to escape. After several practices, the procedures can be done within about 14 hours, if it is performed properly. While attempting this procedure, it is important to improve the microchip's size surface roughness of the PDMS coating.After watching this video, you should have a good understanding of how to monitor the particles in both parallel and orthogonal directions to the symmetric axis of a plasmonic nanostructure.

plasmonic-trapping-release-nanoparticles-monitoring

Research

JoVE Journal

Engineering

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.

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

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

Optical Trapping of Nanoparticles

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

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

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

Trapping of Micro Particles in Nanoplasmonic Optical Lattice

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.

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

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.

Monitoring Conformational Dynamics of Single Unmodified Proteins using Plasmonic Nanotweezers

Polycrystalline silicon thin-film solar cells on glass are fabricated by deposition of boron and phosphorous doped silicon layers followed by crystallisation, defect passivation and metallisation. Plasmonic light-trapping is introduced by forming Ag nanoparticles on the silicon cell surface capped with a diffused reflector resulting in ~45% photocurrent enhancement.

Polycrystalline Silicon Thin-film Solar cells with Plasmonic-enhanced Light-trapping

The system described herein employs a traditional optical trap as well as an independent holographic optical trapping line, capable of creating and manipulating multiple traps. This allows for the creation of complex geometric arrangements of refractive particles while also permitting simultaneous high-speed, high-resolution measurements of the activity of biological enzymes.

Construction of a High Resolution Microscope with Conventional and Holographic Optical Trapping Capabilities

We describe methods for the design, fabrication, and experimental characterization of plasmonic photoconductive emitters, which offer two orders of magnitude higher terahertz power levels compared to conventional photoconductive emitters.

Design, Fabrication, and Experimental Characterization of Plasmonic Photoconductive Terahertz Emitters

Silver nanowires can simultaneously transport electrons and optical information in the form of surface plasmons. A procedure is described here to realize such a shared circuitry and the limitations at propagating both information carriers are evaluated.

Evaluating Plasmonic Transport in Current-carrying Silver Nanowires

Learn plasmonic trapping and release of nanoparticles using a microchip with integrated tweezers for two-dimensional monitoring. This method enables quantitative measurement of maximal trapping forces for life science applications.

Plasmonic Trapping and Release of Nanoparticles in a Monitoring Environment

Explore More Videos