This work was supported by the Knut and Alice Wallenberg Foundation, the Swedish Research Council and the Chalmers Area of Advance Nanoscience and Nanotechnology.

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The authors have nothing to disclose.

The optical trapping setup described in this protocol is built around a commercial inverted microscope and uses red laser light. However, the techniques outlined are versatile and can be used to construct circularly polarized optical tweezers around most commercial or home-built microscopes, both upright and inverted, with only slight alterations. The trapping laser wavelength can be chosen within a wide visible-NIR spectrum, as long as the rest of the optical components and detectors are functional at this specific wavelength. Nevertheless, when choosing a laser wavelength, the size and spectral vicinity to resonances of the particles to be manipulated should be considered because this will affect the optical trapping forces and rotation performance2,5, the magnitude of photothermal effects1, and the trapping stability26. We have previously successfully worked with circularly polarized laser tweezers using laser wavelengths of 660, 785, 830, and 1064 nm.
One of the most important components of the optical trapping setup is the microscope objective. The objective in this protocol is a dry objective with NA = 0.95. The use of a dry objective is experimentally a simpler realization of the setup; however, it does lead to optical aberrations due to refraction in the sample cell interfaces. In the present case, the result is a slightly enlarged focus spot (~1.2 &#181;m) compared to the diffraction limit (~0.4 &#181;m), but this does not significantly change the general or rotary performance of the platform. In principal, a wide range of microscope objectives can be used, provided they have good transmission at the trapping wavelength, good polarization maintenance and long enough working distance to perform trapping through a microscope cover slip and layer of water. In case of 2D trapping, the NA can be relatively low, which makes the entire experiment simpler and provides cleaner circular polarization in the focus. However, higher laser powers might be required than in case of a high NA objective. In our experience, the best performance for trapping, rotation and dark-field spectroscopy is obtained with objectives with NA 0.7-0.95, but it is possible to use lower as well as higher NA objectives.
To obtain good photon correlation measurements of rotary motion, a fast single-pixel detector is needed. Choose a detector with a bandwidth at least two, preferably ten, times higher than the expected rotation frequency multiplied by the shape degeneracy factor and high sensitivity at the trapping wavelength used. Amplified Si photodetectors, single photon counting APDs, and PMTs have been used with success in different setups in our laboratories. Additional information, for example on trap stiffness, can be obtained by measuring and analyzing particle translational displacement using well-established techniques such as power spectral analysis5. A number of previous publications describe different variants of this technique38,39. DF spectroscopy can be performed using a wide range free-space or fiber coupled spectrometers and the choice should be based on the spectral range and wavelength and temporal resolution needed for the planned study.
When performing a trapping experiment, additional particles may accidentally enter the trap. This can be detected by monitoring the rotation frequency, which will fluctuate strongly due to the disturbance. Visual inspection by DF microscopy can be used to verify the presence of an additional particle, in which case the stage can be moved to avoid further disturbance or the experiment needs to be restarted.
The system described above is a simple and efficient way to realize 2D confinement and rotation of metallic nanoparticles. However, for some applications, the extra degree of freedom for manipulation that comes with 3D trapping is important, and the current configuration is therefore a limitation. However, 3D confinement and rotation might be achievable by utilizing counter propagating laser tweezers or more exotic trapping configurations.
Although the particle and system parameters discussed here can be optimized to reduce photothermal heating to below ~15 K4, the temperature increase associated with plasmonic excitation of metal nanoparticles can be problematic in certain applications. A possible route towards further heat reduction is to use high-index dielectric nanoparticles instead of plasmonic particles. Such particles support strong Mie-type scattering resonances but at the same time exhibit low intrinsic absorption coefficients. We have recently been able to manufacture colloidal resonant Si nanoparticles that might prove useful in this respect40,41.

The methods presented in this article replicates those used in our previous work1 to study nanoscale photothermal effects influencing light-driven gold nanorod rotary motors. Variants of the experimental platform has been used in several related publications2,3,4,5,6,7,8,9.
Optical tweezers are widely used for controlling position, force and linear momentum transfer at small length scales in physics, biology, and engineering10,11,12,13,14. Angular momentum carried by circularly polarized light can be employed for additional motion control because it continuously transfer torque to trapped objects15. By combining optical linear and angular momentum transfer, it is then possible to construct non-invasive rotary nanomotors with potential for diverse applications, such as drug delivery into single cells16,17, nanoscale surgery18, and active nanofluidics19, amongst others.
By using metallic nanoparticles as the subject of light driven manipulation, one can exploit the advantages of localized surface plasmon resonances (LSPR&#39;s), which provide large optical cross sections, high sensitivity to environmental changes, and large field enhancements20,21,22,23. This has led to a wealth of studies at the boundary between plasmonics and optical manipulation8,24,25,26,27. The strong light-matter interaction provided by LSPR has enabled us to design a platform where circularly polarized laser tweezers are capable of driving gold nanorods to spin at record rotation frequencies in water2. By tracking the Brownian motion of a rotating nanorod, detailed information about its environment and temperature can be obtained3,5. Simultaneous spectroscopic analysis provides an additional independent information channel for analysing local temperature and the morphological stability of the rotating nanorod1. A range of systems and configurations have been used for studying and applying rotary motion in optical tweezers, generating important insights within the field15,28,29,30,31,32. However, most of these studies have dealt with objects several micrometers in diameter while a single nanorod gives access to the nanometer size regime. Furthermore, when gold nanorods are used as the rotary nanomotor, torque is efficiently transferred mainly via scattering2,33. This decreases the risk of overheating the trapped particle3,34,35.
In the following method, we outline the steps required to build a system capable of efficient optical trapping and rotation of metal nanoparticles. The gold nanorods considered in these studies have high scattering cross sections, and the radiation pressure turns out to be stronger than the counteracting gradient force in the propagation direction. To still confine the particles in 3D, we utilize the force balance between Coulomb repulsion from a glass surface and the laser scattering force in the propagation direction. This 2D-trapping configuration greatly expands the range of trappable particles, as compared to standard 3D optical tweezers, and it can be easily combined with dark-field optical imaging and spectroscopy.
A trapped and rotating metal nanoparticle interacts with its environment, and detailed information about this interaction is contained in its motion and spectral properties. After describing how to construct the circularly polarized optical tweezers, we therefore also outline how to integrate instrumentation for probing rotational dynamics and for measuring Rayleigh scattering spectra in the experimental setup. The result is a versatile platform for studies of nanoscale rotation phenomena in physics, chemistry, and biology.
This protocol assumes that the researcher has access to suitable colloidal metal nanoparticles, preferably single crystalline gold nanorods. Gold nanorods can be purchased from specialized companies or synthesized in house using wet-chemistry methods. The nanorods used in our experiments were made by the seed-mediated growth method described in Ye et al. 201336. It is advantageous if the morphology and optical properties of the nanoparticles are well characterized, for example using scanning electron microscopy (SEM) and optical extinction measurements. Figure 1 displays data recorded from such measurements for representative nanorod types1.
An outline of the protocol is as follows: In the first section, we describe the construction of the optical tweezers based on circular polarization. In the second section, we describe how to extract information from the nanomotor by recording its rotational dynamics and scattering properties. The rotation frequency and the rotational Brownian motion of the trapped particle is measured using photon correlation spectroscopy by projecting backscattered laser light filtered through a linear polarizer on a fast single-pixel detector3. By fitting the data to a theoretical autocorrelation function, both the rotation frequency and the decay time of the rotational Brownian diffusion can be extracted2,3. The optical properties of the trapped and rotating nanoparticle are measured using dark field spectroscopy, which provides complementary information on the particle and its environment. In the third section, we describe the experimental procedure for the trapping and rotation of gold nanorods.
The protocol described up to this point is a straightforward path to a functioning circularly polarized optical tweezers system for nanoparticle rotation. However, sometimes issues arise that demand additional attention. In the fourth section, we outline a few of the common problems that we have encountered and how to address them. These include issues related to nanoparticle optical properties leading to poor trap stability (4.1), low rotation frequencies due to suboptimal circular polarization caused by beamsplitter birefringence (4.2), sticking of nanoparticles at the glass surface due to insufficient Coulomb repulsion (4.3), and deviation from the characteristic autocorrelation signal (4.4).

<table border="0" cellpadding="0" cellspacing="0" width="935">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Gold nanoparticles</td>
			<td style="width:167px;"></td>
			<td style="width:195px;"></td>
			<td style="width:373px;">Purchased or home-grown</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:201px;">Commersial inverted microscope</td>
			<td style="width:167px;">Nikon</td>
			<td style="width:195px;">Eclipse TI</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:23px;width:201px;">Trapping laser</td>
			<td style="width:167px;">Cobolt</td>
			<td style="width:195px;">Flamenco 05-01&#160;</td>
			<td>660 nm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Objective</td>
			<td style="width:167px;">Nikon</td>
			<td style="width:195px;">CFI Plan Apo Lambda 40X</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Laser safety googles</td>
			<td style="width:167px;">Thorlabs</td>
			<td style="width:195px;">LG4</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:201px;">Assorted optomechanical components for mounting optics.</td>
			<td style="width:167px;"></td>
			<td style="width:195px;"></td>
			<td style="width:373px;">A range of mounts, posts and components from any company</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Lens 1 Keplarian telescope</td>
			<td style="width:167px;">Thorlabs</td>
			<td style="width:195px;">AC254-035-A-ML</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Lens 2 Keplarian telescope</td>
			<td style="width:167px;">Thorlabs</td>
			<td style="width:195px;">LA1725-A-ML</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Silver coated mirrors</td>
			<td style="width:167px;">Thorlabs</td>
			<td style="width:195px;">PF10-03-P01</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Kinematic mirror mounts</td>
			<td style="width:167px;">Thorlabs</td>
			<td>KM100</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Translation stage</td>
			<td style="width:167px;">Thorlabs</td>
			<td>PT1/M</td>
			<td>Quantity: 2</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">50/50 R/T Beamsplitter</td>
			<td style="width:167px;">Chroma</td>
			<td style="width:195px;">21000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">CMOS camera</td>
			<td style="width:167px;">Andor</td>
			<td style="width:195px;">Zyla 5.5</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:201px;">Quarter waveplate (QWP, &#955;/4)</td>
			<td style="width:167px;">Thorlabs</td>
			<td style="width:195px;">AQWP05M-600</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Power meter</td>
			<td style="width:167px;">Thorlabs</td>
			<td>PM100USB</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Photodiode Power Sensors</td>
			<td style="width:167px;">Thorlabs</td>
			<td>S121C</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Linear polarizer</td>
			<td style="width:167px;">Thorlabs</td>
			<td style="width:195px;">LPVIS050</td>
			<td style="width:373px;">For laser polarization measurement</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">360&#176; rotation mount</td>
			<td style="width:167px;">Thorlabs</td>
			<td style="width:195px;">RSP1/M</td>
			<td style="width:373px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:23px;width:201px;">Half waveplate (HWP, &#955;/2)</td>
			<td style="width:167px;">Thorlabs</td>
			<td style="width:195px;">AHWP05M-600</td>
			<td style="width:373px;">Used if polarization is not sufficient with only QWP</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:22px;width:201px;">Oil DF condenser</td>
			<td style="width:167px;">Nikon</td>
			<td style="width:195px;">C-DO Dark Field Condenser Oil&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">30/70 R/T Beamsplitter</td>
			<td style="width:167px;">Chroma</td>
			<td style="width:195px;">21009</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Fast Si detector</td>
			<td style="width:167px;">Thorlabs</td>
			<td style="width:195px;">PDA36A-EC</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Data Acquisition Module</td>
			<td style="width:167px;">National Instruments</td>
			<td style="width:195px;">USB-6361</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Fiber 400 &#181;m core size</td>
			<td style="width:167px;">Thorlabs</td>
			<td>M74L01</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">xy-translation mount</td>
			<td style="width:167px;">Thorlabs</td>
			<td>LM1XY/M</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Linear polarizer</td>
			<td style="width:167px;">Thorlabs</td>
			<td style="width:195px;">LPVIS050</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Spectrometer</td>
			<td style="width:167px;">Princeton Instruments&#160;</td>
			<td style="width:195px;">IsoPlane SCT320&#160;</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:201px;">CCD camera for spectrometer</td>
			<td style="width:167px;">Princeton Instruments&#160;</td>
			<td style="width:195px;">PyLoN&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Notch filter</td>
			<td style="width:167px;">Semrock</td>
			<td>NF03-658E-25</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Notch filter</td>
			<td style="width:167px;">Thorlabs</td>
			<td style="width:195px;">NF658-26</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ultrasonic cleaner bath</td>
			<td style="width:167px;">Branson</td>
			<td style="width:195px;">Branson 3510&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Microscope slide</td>
			<td style="width:167px;">Ted Pella</td>
			<td style="width:195px;">260202</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">No. 1.5 Coverslips</td>
			<td style="width:167px;">VWR</td>
			<td style="width:195px;">630-2873</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Aceton</td>
			<td style="width:167px;"></td>
			<td style="width:195px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Isopropanol</td>
			<td style="width:167px;"></td>
			<td style="width:195px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Basic detergent</td>
			<td style="width:167px;">Hellma</td>
			<td style="width:195px;">Hellmanex III</td>
			<td>Cleaning if particle sticking is an issue</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Secure-Seal Spacer</td>
			<td style="width:167px;">Thermo Fisher</td>
			<td style="width:195px;">S24735</td>
			<td>Spacer tape with hole, for making sample cell</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Immersion Oil</td>
			<td style="width:167px;">Zeiss</td>
			<td style="width:195px;">444960-0000-000&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">PS beads</td>
			<td style="width:167px;">Microparticles GmbH</td>
			<td style="width:195px;">PS-R-5.0</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Spectrophotometer</td>
			<td style="width:167px;">Agilent</td>
			<td style="width:195px;">Cary 5000 UV-Vis-NIR</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">SEM</td>
			<td style="width:167px;">Zeiss</td>
			<td style="width:195px;">Ultra 55 FEG SEM</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:201px;">Tweezers</td>
			<td style="width:167px;"></td>
			<td style="width:195px;"></td>
			<td>Any brand</td>
		</tr>
	</tbody>
</table>

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.

The rotation and rotational Brownian motion of a gold nanorod that is properly trapped in the circularly polarized laser tweezers can be probed by recording light scattering intensity fluctuations (Figure 3a) using a single-pixel detector. An autocorrelation spectrum of this signal contains an oscillatory component, similar to the one shown in Figure 3b. which can be fit to a theoretical autocorrelation function. The fitting allows extraction of the rotation frequency and the autocorrelation decay time, which is related to the rotational Brownian fluctuations, of the nanorod.
As mentioned in the protocol (instruction 4.4.2), it is essential to use a sufficiently thick fiber core to collect the backscattered laser light for photon correlation spectroscopy. If this is not the case, an additional decay term related to particle translation in and out of the probe volume will be present in the correlation function, see Figure 4. Through careful analysis, this could provide more information about the system; however, it complicates the analysis of the rotational Brownian dynamics contained in the data.
To obtain correct DF scattering spectra from trapped nanoparticles, as described in section 3.5, the raw spectral data needs to be calibrated. This is done by recording the illumination lamp spectrum as well as a background spectrum (Figure 5a). When focusing intense laser light at a glass surface, such as the substrate against which the nanorods are trapped, some fluorescence might be generated (see the red spectral contribution in the background spectrum of Figure 5a). This fluorescence contamination can be reduced by using fused silica substrates. However, it is anyway highly recommended to record a background spectrum with empty optical tweezers at the correct laser power. When a scattering spectrum is recorded and all spectral components not related to the actual nanoparticle scattering have been compensated for, the spectrum can be fitted in energy scale with a bi-Lorentzian fitting function to extract information related to the LSPR peak positions (Figure 5b).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57947/57947fig1.jpg" /> 
Figure 1: SEM images and ensemble extinction spectra for two representative nanoparticle batches. a) Scale bar is 200 nm. b) The blue/red bordered SEM images in a) correspond to the red/blue spectrum, respectively. The spectral peaks related to the transverse and longitudinal LSPRs are clearly distinguishable. <a href="https://www.jove.com/files/ftp_upload/57947/57947fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57947/57947fig2.jpg" /> 
Figure 2: Schematic illustration of optical tweezers setup for nanoparticle rotation measurements. Laser light is collimated and expanded through a Keplerian telescope, and subsequently guided to the objective through the use of two movable mirrors (M1, M2) and a beamsplitter (BS). Two waveplates in the laser path optimize the circular polarization of the optical tweezers (&#955;/2, &#955;/4). Backscattered laser light can be collected after a linear polarizer for photon correlation spectroscopy and rotational dynamics measurements. After removing the laser light, scattered white light is guided to a spectrometer or a camera. <a href="https://www.jove.com/files/ftp_upload/57947/57947fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/57947/57947fig3.jpg" /> 
Figure 3: Representative intensity and autocorrelation data with curve fit for a trapped and rotating nanorod. a) Intensity fluctuations recorded by the single pixel detector after a linear polarizer for 1s, and a zoomed in plot of the fluctuations. b) Autocorrelated data of intensity fluctuation for a rotating gold nanorod (blue points), collected from backscattered laser light. The data shows an oscillation that decays after a few periods. The oscillation is related to the rotation frequency of the nanorod, whereas the decay is due to rotational Brownian motion. A fit to the theoretical autocorrelation function is performed (red line) to extract a rotation frequency of f = 24285 &#177; 45 Hz and a correlation decay time of &#964;0 = 40.9 &#177; 1.06 &#181;s. The f and &#964;0 uncertainties represent 95% confidence intervals of the fit, which has a coefficient of determination (R2) of 0.9877. <a href="https://www.jove.com/files/ftp_upload/57947/57947fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/57947/57947fig4.jpg" /> 
Figure 4: Issue with a too small probe volume in photon correlation spectroscopy measurements. a) Autocorrelation data for a rotating gold nanorod, collected using a thick (400 &#181;m, blue data) and a thin (62.5 &#181;m, red data) fiber. Collection using a thick fiber ensures that the nanorod is always confined within the probe volume and that the autocorrelation function measures rotational dynamics only. An additional decay term due to translational Brownian motion is present when the probe volume is insufficient. In b) and c), schematic illustrations of the effect and images of the back-illuminated collection region are shown. Scale bars are 2 &#181;m. <a href="https://www.jove.com/files/ftp_upload/57947/57947fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/57947/57947fig5.jpg" /> 
Figure 5: Exemplary dark field scattering spectra recorded for a gold nanorod optically trapped by 660 nm laser light. The spectral region 630-670 nm (1.85-1.97 eV) is distorted due to notch filters needed to block the trapping laser light. a) Raw scattering spectra (dark blue) displaying features that are not inherent to the scattering of the particle and should be calibrated for. These include the background spectrum (red), which contains autofluorescence excited by the highly focused laser light, and the white light excitation spectrum (orange, recorded without notch filter). After calibration, the corrected scattering spectrum (light blue) shows two distinct LSPR peaks as expected. The arrows indicate the scale for each spectrum. b) Scattering spectrum for a trapped nanorod (blue points) together with a fit to the bi-Lorentzian model function (red) with its components (light blue and orange). The distorted spectral region is disregarded in the fitting of the data and the fit has an R2 of 0.9975. <a href="https://www.jove.com/files/ftp_upload/57947/57947fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Construction and Operation of a Light-driven Gold Nanorod Rotary Motor System at JoVE.com

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

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.

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

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Unit 1

Moment of Inertia

Rotation and Rigid Bodies

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8.7K 조회수.  Chalmers University of Technology. 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.

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

Synthesis and Operation of Fluorescent-core Microcavities for Refractometric Sensing

This paper discusses fluorescent core microcavity-based sensors that can operate in a microfluidic analysis setup. These structures are based on the formation of a fluorescent quantum-dot (QD) coating on the channel surface of a conventional microcapillary. Silicon QDs are especially attractive for this application, owing in part to their negligible toxicity compared to the II-VI and II-VI compound QDs, which are legislatively controlled substances in many countries. While the ensemble emission spectrum is broad and featureless, an Si-QD film on the channel wall of a capillary features a set of sharp, narrow peaks in the fluorescence spectrum, corresponding to the electromagnetic resonances for light trapped within the film. The peak wavelength of these resonances is sensitive to the external medium, thus permitting the device to function as a refractometric sensor in which the QDs never come into physical contact with the analyte. The experimental methods associated with the fabrication of the fluorescent-core microcapillaries are discussed in detail, as well as the analysis methods. Finally, a comparison is made between these structures and the more widely investigated liquid-core optical ring resonators, in terms of microfluidic sensing capabilities.

Fluorescent-core microcavity sensors employ a high-index quantum-dot coating in the channel of silica microcapillaries. Changes in the refractive index of fluids pumped into the capillary channel cause shifts in the microcavity fluorescence spectrum that can be used to analyze the channel medium.

Refractometric 감지 용 형광 코어 Microcavities의 합성 및 운영

This paper discusses  fluorescent core microcavity-based sensors that can operate in a microfluidic  analysis setup. These structures are based on the ...

연구

공학

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

High resolution microscope systems with optical traps allow for precise manipulation of various refractive objects, such as dielectric beads 1 or cellular organelles 2,3, as well as for high spatial and temporal resolution readout of their position relative to the center of the trap. The system described herein has one such "traditional" trap operating at 980 nm. It additionally provides a second optical trapping system that uses a commercially available holographic package to simultaneously create and manipulate complex trapping patterns in the field of view of the microscope 4,5 at a wavelength of 1,064 nm. The combination of the two systems allows for the manipulation of multiple refractive objects at the same time while simultaneously conducting high speed and high resolution measurements of motion and force production at nanometer and piconewton scale.

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.

기존 및 홀로 그래픽 광학 트래핑 기능과 고해상도 현미경의 구조

High resolution microscope systems with optical traps allow for precise manipulation of various refractive objects, such as dielectric beads 1 or cellular ...

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.

나노 광학 컨베이어 벨트의 제작 및 운영

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

Detection and Recovery of Palladium, Gold and Cobalt Metals from the Urban Mine Using Novel Sensors/Adsorbents Designated with Nanoscale Wagon-wheel-shaped Pores

Developing low-cost, efficient processes for recovering and recycling palladium, gold and cobalt metals from urban mine remains a significant challenge in industrialized countries. Here, the development of optical mesosensors/adsorbents (MSAs) for efficient recognition and selective recovery of Pd(II), Au(III), and Co(II) from urban mine was achieved. A simple, general method for preparing MSAs based on using high-order mesoporous monolithic scaffolds was described. Hierarchical cubic Ia3d wagon-wheel-shaped MSAs were fabricated by anchoring chelating agents (colorants) into three-dimensional pores and micrometric particle surfaces of the mesoporous monolithic scaffolds. Findings show, for the first time, evidence of controlled optical recognition of Pd(II), Au(III), and Co(II) ions and a highly selective system for recovery of Pd(II) ions (up to ~95%) in ores and industrial wastes. Furthermore, the controlled assessment processes described herein involve evaluation of intrinsic properties (e.g., visual signal change, long-term stability, adsorption efficiency, extraordinary sensitivity, selectivity, and reusability); thus, expensive, sophisticated instruments are not required. Results show evidence that MSAs will attract worldwide attention as a promising technological means of recovering and recycling palladium, gold and cobalt metals.

Because of the importance and extensive use of palladium, gold and cobalt metals in high-technology equipment, their recovery and recycling constitute an important industrial challenge. The metal recovery system described herein is a simple, low-cost means for the effective detection, removal, and recovery of these metals from the urban mine.

감지 및 팔라듐의 복구, 도시 광산에서 금과 코발트 금속은 나노 수레 바퀴 모양의 기공 지정 소설 센서 / 흡착제를 사용하여

Developing low-cost, efficient processes for recovering and recycling palladium, gold and cobalt metals from urban mine remains a significant challenge in ...

Non-aqueous Electrode Processing and Construction of Lithium-ion Coin Cells

Research into new and improved materials to be utilized in lithium-ion batteries (LIB) necessitates an experimental counterpart to any computational analysis. Testing of lithium-ion batteries in an academic setting has taken on several forms, but at the most basic level lies the coin cell construction. In traditional LIB electrode preparation, a multi-phase slurry composed of active material, binder, and conductive additive is cast out onto a substrate. An electrode disc can then be punched from the dried sheet and used in the construction of a coin cell for electrochemical evaluation. Utilization of the potential of the active material in a battery is critically dependent on the microstructure of the electrode, as an appropriate distribution of the primary components are crucial to ensuring optimal electrical conductivity, porosity, and tortuosity, such that electrochemical and transport interaction is optimized. Processing steps ranging from the combination of dry powder, wet mixing, and drying can all critically affect multi-phase interactions that influence the microstructure formation. Electrochemical probing necessitates the construction of electrodes and coin cells with the utmost care and precision. This paper aims at providing a step-by-step guide of non-aqueous electrode processing and coin cell construction for lithium-ion batteries within an academic setting and with emphasis on deciphering the influence of drying and calendaring.

Non-aqueous electrode processing is central to the construction of coin cells and the evaluation of new electrode chemistries for lithium-ion batteries. A step-by-step guide to the basic practices needed as an electrochemical engineer working with batteries in an academic experimental setting is furnished.

리튬 이온 코인 셀의 비수 전극 가공 및 건설

Research into new and improved materials to be utilized in lithium-ion batteries (LIB) necessitates an experimental counterpart to any computational ...

Preparation of ZnO Nanorod/Graphene/ZnO Nanorod Epitaxial Double Heterostructure for Piezoelectrical Nanogenerator by Using Preheating Hydrothermal

Well-aligned ZnO nanostructures have been intensively studied over the last decade for remarkable physical properties and enormous applications. Here, we describe a one-step fabrication technique to synthesis freestanding ZnO nanorod/graphene/ZnO nanorod double heterostructure. The preparation of the double heterostructure is performed by using thermal chemical vapor deposition (CVD) and preheating hydrothermal technique. In addition, the morphological properties were characterized by using the scanning electron microscopy (SEM). The utility of freestanding double heterostructure is demonstrated by fabricating the piezoelectric nanogenerator. The electrical output is improved up to 200% compared to that of a single heterostructure owing to the coupling effect of the piezoelectricity between the arrays of ZnO nanorods on the top and bottom of graphene. This unique double heterostructure have a tremendous potential for applications of electrical and optoelectrical devices where the high number density and specific surface area of nanorod are needed, such as pressure sensor, immuno-biosensor and dye-sensitized solar cells.

One-step fabrication method for obtaining freestanding epitaxial double heterostructure is presented. This approach could achieve ZnO coverage with a higher number density than that of the epitaxial single heterostructure, leading to a piezoelectric nanogenerator with an increased output electrical performance.

예열 열수를 사용하여 Piezoelectrical 나노 발전기에 대한의 ZnO 나노 막대 / 그래 핀 / ZnO의 나노로드 에피 택셜 더블 헤테로 구조의 제조

Well-aligned ZnO nanostructures have been intensively studied over the last decade for remarkable physical properties and enormous applications. Here, we ...

Fabrication and Operation of Acoustofluidic Devices Supporting Bulk Acoustic Standing Waves for Sheathless Focusing of Particles

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must be smaller than the incident wavelength of sound and the width of the fluidic channels are typically tens to hundreds of micrometers across, acoustofluidic devices typically use ultrasonic waves generated from a piezoelectric transducer pulsating at high frequencies (in the megahertz range). At characteristic frequencies that depend on the geometry of the device, it is possible to induce the formation of standing waves that can focus particles along desired fluidic streamlines within a bulk flow. Here, we describe a method for the fabrication of acoustophoretic devices from common materials and clean room equipment. We show representative results for the focusing of particles with positive or negative acoustic contrast factors, which move towards the pressure nodes or antinodes of the standing waves, respectively. These devices offer enormous practical utility for precisely positioning large numbers of microscopic entities (e.g., cells) in stationary or flowing fluids for applications ranging from cytometry to assembly.

Acoustofluidic devices use ultrasonic waves within microfluidic channels to manipulate, concentrate and isolate suspended micro and nanoscopic entities. This protocol describes the fabrication and operation of such a device supporting bulk acoustic standing waves to focus particles in a central streamline without the aid of sheath fluids.

제조 및 Acoustofluidic 장치의 작동은 입자의 초점 쉬스에 대한 대량 음향 서 파도 지원

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must ...

Expression of Cementitious Pore Solution and the Analysis of Its Chemical Composition and Resistivity Using X-ray Fluorescence

The goal of this method is to determine the chemical composition and electrical resistivity of cementitious pore solution expressed from a fresh paste sample. The pore solution is expressed from a fresh paste sample using a pressurized nitrogen gas system. The pore solution is then immediately transferred to a syringe to minimize evaporation and carbonation. After that, assembled testing containers are used for the X-ray fluorescence (XRF) measurement. These containers consist of two concentric plastic cylinders and a polypropylene film which seals one of the two open sides. The pore solution is added into the container immediately prior to the XRF measurement. The XRF is calibrated to detect the main ionic species in the pore solution, in particular, sodium (Na+), potassium (K+), calcium (Ca2+), and sulfide (S2-), to calculate sulfate (SO42-) using stoichiometry. The hydroxides (OH-) can be calculated from a charge balance. To calculate the electrical resistivity of the solution, the concentrations of the main ionic species and a model by Snyder et al. are used. The electrical resistivity of the pore solution can be used, along with the electrical resistivity of concrete, to determine the formation factor of concrete. XRF is a potential alternative to current methods to determine the composition of pore solution, which can provide benefits in terms of reduction in time and costs.

This protocol describes the procedure to express fresh pore solution from cementitious systems and the measurement of its ionic composition using X-ray fluorescence. The ionic composition can be used to calculate pore solution electrical resistivity, which can be used, together with concrete electrical resistivity, to determine the formation factor.

The goal of this method is to determine the chemical composition and electrical resistivity of cementitious pore solution expressed from a fresh paste ...

Large Area Substrate-Based Nanofabrication of Controllable and Customizable Gold Nanoparticles Via Capped Dewetting

Recent scientific advances in the utilization of metallic nanoparticle for enhanced energy conversion efficiency, improved optical device performance, and high-density data storage have demonstrated the potential benefit of their use in industrial applications. These applications require precise control over nanoparticle size, spacing, and sometimes shape. These requirements have resulted in the use of time and cost intensive processing steps to produce nanoparticles, thus making the transition to industrial application unrealistic. This protocol will resolve this issue by providing a scalable and affordable method for the large-area production of nanoparticle films with improved nanoparticle control compared to the current techniques. In this article, the process will be demonstrated with gold, but other metals can also be used.

This protocol details a novel nano-manufacturing technique that can be used to make controllable and customizable nanoparticle films over large areas based on the self-assembly of dewetting of capped metal films.

큰 면적 기판 기반 Nanofabrication 출장 Dewetting 통해 제어 하 고 사용자 정의 금 나노 입자의

Recent scientific advances in the utilization of metallic nanoparticle for enhanced energy conversion efficiency, improved optical device performance, and ...

A Rapid Method for Modeling a Variable Cycle Engine

The variable cycle engines (VCE) that combine the advantages of turbofan and turbojet engines, are widely considered to be the next generation aircraft engines. However, developing VCE requires high costs. Thus, it is essential to build a mathematical model when developing an aircraft engine, which may avoid a large number of real tests and reduce the cost dramatically. Modeling is also crucial in control law development. In this article, based on a graphical simulation environment, a rapid method for modeling a double bypass variable cycle engine using object-oriented modeling technology and modular hierarchical architecture is described. Firstly, the mathematical model of each component is built based on the thermodynamic calculation. Then, a hierarchical engine model is built via the combination of each component mathematical model and the N-R solver module. Finally, the static and dynamic simulations are carried out in the model and the simulation results prove the effectiveness of the modeling method. The VCE model built through this method has the advantages of clear structure and real-time observation.

Here, we present a protocol to build a component-level mathematical model for a variable cycle engine.

가변 사이클 엔진 모델링을 위한 신속한 방법

The variable cycle engines (VCE) that combine the advantages of turbofan and turbojet engines, are widely considered to be the next generation aircraft ...