This work is supported by Ministry of Science and Technology under NSC-101-2923-M-002-001-MY3 and NSC-102-2112-M-002-018-MY3. This research is also supported by the Japan Society for the Promotion of Science (JSPS) through the &#8220;Funding Program for Next Generation World-Leading Researchers (NEXT Program),&#8221; initiated by the Council for Science and Technology Policy (CSTP) and JSPS Asian CORE Program.

1. GNS Sample Preparation
<ol>
	<li>Before preparing the sample, sonicate 1 ml GNS colloid solution for at least 15 min at about 40 kHz to prevent particle aggregation, which may cause the LSPR peak to shift.</li>
	<li>Drop 100-200 &#181;l of GNS colloid onto a slide glass with commercial magnesium aluminum silicate (MAS) coating to fix the GNSs.</li>
	<li>After at least 1 min, remove the extra colloid by flushing with distilled water. The waiting time depends on the required distribution density of the GNSs. Typically, 1-3 min results in a suitable density that enables the particles to be easily identified since most of them are isolated from each other. Significant aggregation may occur if the waiting time is too long.</li>
	<li>Dry the sample by purging with nitrogen gas.</li>
	<li>(Optional) To map the GNSs on the glass with high resolution, perform scanning electron microscopy (SEM) at this stage23. An example image is provided in Figure 1, showing the characteristic density of GNSs. Use a field emission SEM to acquire the image. Once oil is added onto the sample (next step), it will be difficult to remove the oil and observe the sample with SEM.</li>
	<li>Add a drop of oil with the same refractive index onto the sample to cover the GNSs and to eliminate the strong reflection from the glass substrate.</li>
	<li>Place a cover glass on top of the sample and seal it with nail polish.</li>
	<li>Wait at least 5 min until the nail polish dries. The sample is ready now.</li>
</ol>
2. Alignment of Home-built Confocal Microscope
<ol>
	<li>See Figure 2 for the scheme of setup. Align the white light illumination path of the microscope body itself. Turn on the halogen light source of the microscope, and follow the microscope manufacturer&#8217;s manual to achieve the K&#246;hler illumination condition. Ensure that the white halogen light beams are nearly parallel at the back of aperture of the objective, partially reflected by the 50/50 beamsplitter, and then propagate toward the laser.</li>
	<li>Turn on the galvano mirrors to ensure that they remain at the correct initial position, that is, at the center of the scanning range.</li>
	<li>Place at least two targets, made by a thin sheet of paper with concentric rings on it, along the halogen light path, and align them with the halogen beam.</li>
	<li>To perform imaging, select the 532 nm laser. To perform spectroscopy measurements, select the super-continuum laser. During the alignment, the power of the lasers should be less than 10 &#956;W at the back aperture of the objective to avoid nonlinearity. Then, collimate the incident laser beam opposite to the outgoing halogen beam with the aid of the two targets. When this process is complete, the coarse alignment of the laser beam has been achieved.</li>
	<li>Align the laser beam through the center of the back aperture of the objective lens. Typically, use an oil-immersion objective. Add a drop of oil between the oil-immersion objective lens and the GNS sample. Use a photomultiplier tube (PMT) as the detector to collect the scattering signals of the GNSs.</li>
	<li>Place a 20-&#181;m-diameter pinhole in front of the PMT to block out-of-focus scattering signals. Turn on the galvano mirrors and PMT (via home-built software), adjust the pinhole position and height of the sample stage to maximize the backscattering signals of the GNSs, and then observe an individual GNS on a computer screen. A sample xy image of the GNSs with correct alignment is shown in Figure 2B.</li>
	<li>Slightly change the height of the sample stage to check the concentricity of the focus. If it is not concentric, adjust the beam with the two mirrors in front of the scanner until the center of the GNS remains at the same position while the height of the sample stage is changed. Make sure that the xz image of the PSF is similar to Figure 2C to ensure correct beam alignment. Process these two images with low-pass and Gaussian smooth filters.</li>
</ol>
3. Characterization of Scattering Nonlinearity
<ol>
	<li>At low excitation intensity (less than 104 W/cm2), acquire an image of gold nanoparticles by following protocol 2.6.</li>
	<li>Open the image in ImageJ (or any other image analysis software). Draw a line across one of the GNSs in the image (see Figure 2B), and use Analysis -&#62; Plot profile of the ImageJ tools to retrieve the scattering intensity profile. Fit the profile of the chosen PSF by a Gaussian function: 
	<img alt="Equation 2" src="/files/ftp_upload/53338/53338eq2.jpg" /> 
	where y is the PMT readout value, y0 is the background value (if any), A is the peak amplitude, w is the width, x is the spatial coordinate, and xc is the center coordinate of the Gaussian function. The FWHM of the corresponding PSF is (&#189;ln2)w. Based on the numerical aperture (NA) of the objective, the theoretical FWHM of the confocal PSF can be estimated to be approximately 0.43l/NA, where l is the excitation wavelength. Compare these two numbers to check the alignment of the imaging system.</li>
	<li>Increase the excitation intensity by manually changing the neutral density (ND) filter in Figure 2A, and record the backscattering images at each intensity level. Take the value of the scattering signal from the center of each GNS at different excitation intensities, and plot the curve of scattering signals versus excitation intensities. Check the linearity of the first few points, which should exhibit a linear relationship when the excitation intensity is adequately low. Draw a line based on linear fitting of the first few points. If the scattering intensities of the subsequent points drop below this linear trend, saturation has occurred.</li>
	<li>After observing saturable scattering, gradually decrease the intensity below the saturation threshold, and image the same GNSs again to ensure the reversibility of the nonlinear behaviors.</li>
</ol>
4. Measurement of a Scattering Spectrum of a Single Gold Nanosphere
<ol>
	<li>To measure the backscattering spectrum from a single GNS, use the super-continuum laser as the laser source. The initial wavelength of the laser ranges from 450 nm to 1,750 nm. To remove the excess infrared power that might cause damage to the sample and the optical components, place one or two mirrors right after the super-continuum laser to reflect the visible light, and use beam dumps to collect the excess infrared light.</li>
	<li>Follow the alignment procedures in Section 2 to direct the super-continuum laser into the laser scanning confocal microscope. Use a broadband 50/50 BS to ensure spectral coverage across the whole visible range.</li>
	<li>Acquire an image of the GNSs on glass. Locate a single GNS in the image, and fix the focus of the incident broadband light on the particle.</li>
	<li>Use a flipping mirror in front of the PMT to direct the backscattering signal toward the spectrometer, which is equipped with a charge-coupled device, and then take a spectrum of the selected single GNS. Be careful that the spectrum here is a mixture of GNS scattering and background due to reflections from other surfaces.</li>
	<li>Switch back to the PMT detector, and take another image to confirm that the particle position has not changed. Then, shift the focus to a point at which no particle is present. Switch back to the spectrometer, and take one more spectrum, which represents the background.</li>
	<li>Subtract the background spectrum from step 4.5 from the spectrum from step 4.4 to obtain a clear backscattering spectrum of a single GNS.</li>
</ol>
5. Alignment of SAX Microscope
<ol>
	<li>See Figure 3 for the scheme of the SAX microscope, where an ideal sinusoidal temporal modulation is obtained from the beat frequency between two acousto-optic modulators (AOMs). First, adjust the beam size of the laser to meet the requirement of the subsequent AOMs. Split the 532 nm laser light into two beams by using a 50/50 beam splitter.</li>
	<li>Guide the two beams through the two AOMs, with one beam passing through each AOM. The modulating frequencies of the two AOMs must be different. For example, one may be at 40.000 MHz and the other at 40.010 MHz, yielding a difference frequency of 10 kHz. This difference frequency will be the fundamental modulation frequency fm for the SAX signals.</li>
	<li>Take the first-order diffracted beams from both AOMs, and combine the two beams by using another 50/50 beam splitter. Adjust the mirrors after the AOMs to collimate the two beams.</li>
	<li>Add a photodetector that is connected to an oscilloscope to monitor the temporal modulation. Split a small portion of the laser with a slide glass, and send it to the photodetector, as shown in Figure 3. With correct modulation and beam overlapping, observe sinusoidal intensity modulation at the main frequency fm, similar to that of the waveform shown in Figure 4. 
	Note: The background of the modulation needs to be as low as possible to achieve the maximum modulation depth. In addition, use the Fourier analysis function of the oscilloscope to check that the harmonic distortion of the modulation is diminishing. To achieve successful SAX implementation, ensure a perfect sinusoidal excitation intensity modulation with minimized initial nonlinearity.</li>
	<li>Disconnect the electric output of the photodetector from the oscilloscope and connect to the reference input of a lock-in amplifier.</li>
	<li>As shown in Figure 3, align the laser beam into the confocal system following the previous protocols. Here, connect the electric output of the PMT to the lock-in amplifier as the signal input.</li>
	<li>Use a blank cover glass as the sample, and check the linearity of the electric detection system by gradually increasing the excitation power,, as shown in Figure 5, where the detector is linear below a readout value of 1-V. In all subsequent measurements, take care to restrain the readout to below this value.</li>
	<li>Set the output of the lock-in amplifier to export the absolute magnitude of the voltage signal. By changing the harmonic component setting at the reference channel, obtain the amplitudes of the SAX signals, A1, A2, and so on.</li>
	<li>Export the linear and nonlinear signals from the lock-in amplifier to a data acquisition card, which also receives the driving voltage signals of the raster scanning galvano mirrors. With the aid of a customized Labview program, synchronize the signals of the lock-in amplifier and the galvano mirrors to form an image.</li>
	<li>To optimize the signal-to-noise ratio in the images, select appropriately the pixel acquisition and integration times of the lock-in amplifier. For example, when the main modulation frequency fm of the excitation is 10 kHz, that is, when the period is 100 &#181;sec, set the integration time of the lock-in amplifier to be at least three times longer than the period. Adding the time of the galvano mirror movement, the acquisition speed is set at 1,500 pixels per second in the SAX imaging mode.</li>
</ol>

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The authors declare that they have no competing financial interests.

In the protocol, there are several critical steps. First, when preparing the samples, the density of nanoparticles should not be too high, to avoid plasmonic coupling among particles. If two or more particles are very close to each other, the coupling results in the LSPR wavelength shifting toward longer wavelengths, thus significantly reducing the nonlinearity. However, this imaging technique actually maps the distribution of plasmonic modes, instead of the particles themselves. Therefore, it is expected that with an ap...

The study of plasmonics has attracted great interest due to its applications in many different fields1-4. One of the most investigated fields in plasmonics is surface plasmonics, in which the collective oscillation of conduction electrons couples with an external electromagnetic wave at an interface between a metal and dielectric. Surface plasmonics has been explored for its potential applications in subwavelength optics, biophotonics, and microscopy5,6. The strong field enhancement in the ultra-small volume of metallic nanoparticles due to localized surface plasmon resonance (LSPR) has attracted extensive attention, not only because of its exceptional sensitivity to particle sizes, particle shapes, and the dielectric properties of the surrounding medium7-10, but also because of its ability to boost inherently weak nonlinear optical effects11. The exceptional sensitivity of LSPR is valuable for bio-sensing and near-field imaging techniques12,13. On the other hand, the enhanced nonlinearity of plasmonic structures can be utilized in photonic integrated circuits in applications such as optical switching and all-optical signal processing14,15. It is well known that the plasmonic absorption is linearly proportional to the excitation intensity at low intensity levels. When the excitation is strong enough, the absorption reaches saturation. Intriguingly, at higher intensities, the absorption increases again. These nonlinear effects are called saturable absorption (SA)15-17 and reverse saturable absorption (RSA)18, respectively.
It is known that due to the LSPR, scattering is particularly strong in plasmonic structures. Based on fundamental electromagnetics, the response of scattering versus incident intensity should be linear. However, in nanoparticles, scattering and absorption are closely linked via the Mie theory, and both can be expressed in terms of real and imaginary parts of the dielectric constant. Under the assumption that a single GNS behaves as a dipole under light illumination, the scattering coefficient (Qsca) and absorption coefficient (Qabs) from a single plasmonic nanoparticle according to the Mie theory can be expressed as19
<img alt="Equation 1" src="/files/ftp_upload/53338/53338eq1.jpg" />
where x is 2&#960;a/&#955;, a is the radius of the sphere, and m2 is &#949;m/&#949;d. Here, &#949;m and &#949;d correspond to the dielectric constants of the metal and of the surrounding dielectrics, respectively. Since the form of the scattering coefficient is similar to that of the absorption coefficient, it is therefore expected to observe saturable scattering in a single plasmonic nanoparticle20.
Recently, nonlinear saturable scattering in an isolated plasmonic particle was demonstrated for the first time21. It is remarkable that at deep saturation, the scattering intensity in fact decreased slightly when the excitation intensity increased. Even more remarkably, when the excitation intensity continued increasing after the scattering became saturated, the scattering intensity rose again, showing the effect of reverse saturable scattering20. Wavelength- and size-dependent studies have shown a strong relationship between LSPR and nonlinear scattering21. The intensity and wavelength dependences of plasmonic scattering are very similar to those of absorption, suggesting a common mechanism underlying these nonlinear behaviors.
In terms of applications, it is well known that nonlinearity helps to improve optical microscopy resolution. In 2007, saturated excitation (SAX) microscopy was proposed, which can enhance resolution by extracting the saturated signal via a temporal sinusoidal modulation of the excitation beam22. SAX microscopy is based on the concept that, for a laser focal spot, the intensity is stronger at the center than at the periphery. If the signal (either fluorescence or scattering) exhibits saturation behavior, the saturation must start from the center, while the linear response remains at the periphery. Therefore, if there is a method to extract only the saturated part, it will leave only the central part while rejecting the peripheral part, thus effectively enhancing the spatial resolution. In principle, there is no lower resolution limit in SAX microscopy, as long as deep saturation is reached and there is no sample damage due to the intense illumination.
It has been shown that the resolution of fluorescence imaging can be significantly enhanced by utilizing the SAX technique. However, fluorescence suffers from the photobleaching effect. Combining the discovery of scattering nonlinearity and the concept of SAX, super-resolution microscopy based on scattering can be realized21. Compared to conventional super-resolution microscopies, the scattering-based technique provides a novel non-bleaching contrast method. In this paper, a step-by-step description is given to outline the procedures required to obtain and extract the nonlinearity of plasmonic scattering. Methods of identifying scattering nonlinearities introduced by changing the incident intensity are described. More details will be provided to unravel how these nonlinearities affect images of single nanoparticles and how spatial resolution can be enhanced accordingly by the SAX technique.

<table>
	<tbody>
		<tr>
			<td>microscope body</td>
			<td>Olympus, Japan</td>
			<td>BX-51</td>
			<td></td>
		</tr>
		<tr>
			<td>objective lens</td>
			<td>Olympus, Japan</td>
			<td>UPlanSapo, 100X, NA 1.4</td>
			<td></td>
		</tr>
		<tr>
			<td>80-nm gold colloid</td>
			<td>BBI Solutions, UK</td>
			<td>EM.GC80</td>
			<td></td>
		</tr>
		<tr>
			<td>supercontinuum laser</td>
			<td>Fianium, United Kingdom</td>
			<td>SC400-2-PP</td>
			<td></td>
		</tr>
		<tr>
			<td>broadband dielectric mirrors</td>
			<td>Thorlabs, USA</td>
			<td>BB1-E02</td>
			<td></td>
		</tr>
		<tr>
			<td>field emission SEM</td>
			<td>JEOL, Japan</td>
			<td>JSM-6330F</td>
			<td>optional</td>
		</tr>
		<tr>
			<td>spectrometer</td>
			<td>Andor Technology, UK</td>
			<td>Shamrock 163</td>
			<td></td>
		</tr>
		<tr>
			<td>&#160;charge-coupled device</td>
			<td>Andor Technology, UK</td>
			<td>iDus DV420A-OE</td>
			<td></td>
		</tr>
		<tr>
			<td>acousto-optic modulators</td>
			<td>&#160;IntraAction Corp., USA</td>
			<td>AOM-402AF1</td>
			<td></td>
		</tr>
		<tr>
			<td>lock-in amplifier</td>
			<td>Stanford Research Systems, USA</td>
			<td>SR-830</td>
			<td></td>
		</tr>
		<tr>
			<td>MAS-coated slide glass</td>
			<td>Matsunami Glass, Japan,</td>
			<td>S9215</td>
			<td></td>
		</tr>
	</tbody>
</table>

measurement of scattering nonlinearities from a single plasmonic nanoparticle

Plasmonics, which are based on the collective oscillation of electrons due to light excitation, involve strongly enhanced local electric fields and thus have potential applications in nonlinear optics, which requires extraordinary optical intensity. One of the most studied nonlinearities in plasmonics is nonlinear absorption, including saturation and reverse saturation behaviors. Although scattering and absorption in nanoparticles are closely correlated by the Mie theory, there has been no report of nonlinearities in plasmonic scattering until very recently. 
Last year, not only saturation, but also reverse saturation of scattering in an isolated plasmonic particle was demonstrated for the first time. The results showed that saturable scattering exhibits clear wavelength dependence, which seems to be directly linked to the localized surface plasmon resonance (LSPR). Combined with the intensity-dependent measurements, the results suggest the possibility of a common mechanism underlying the nonlinear behaviors of scattering and absorption. These nonlinearities of scattering from a single gold nanosphere (GNS) are widely applicable, including in super-resolution microscopy and optical switches. 
In this paper, it is described in detail how to measure nonlinearity of scattering in a single GNP and how to employ the super-resolution technique to enhance the optical imaging resolution based on saturable scattering. This discovery features the first super-resolution microscopy based on nonlinear scattering, which is a novel non-bleaching contrast method that can achieve a resolution as low as l/8 and will potentially be useful in biomedicine and material studies.

Figure 6 shows the measured spectrum from an 80 nm GNS. A calculated curve based on the Mie theory is given in the same plot, showing excellent agreement. The LSPR peak is around 580 nm. In the following experiment, the laser wavelength was 532 nm, which was chosen as it is located inside the plasmonic band to enhance optical scattering with plasmonic effect and enable scattering saturation21.
Figure 7 presents scattering images of a single gold nan...

Watch this Scientific Journal Video about Measurement of Scattering Nonlinearities from a Single Plasmonic Nanoparticle at JoVE.com

Measurement of Scattering Nonlinearities from a Single Plasmonic Nanoparticle

Saturable and reverse saturable scattering were discovered in isolated plasmonic particles and adopted as a novel non-bleaching contrast method in super-resolution microscopy. Here the experimental procedures of detecting and extracting nonlinear scattering are explained in detail, as well as how to enhance resolution with the aid of saturated excitation microscopy.

Plasmonics, which are based on the collective oscillation of electrons due to light excitation, involve strongly enhanced local electric fields and thus ...

measurement-scattering-nonlinearities-from-single-plasmonic

Research

JoVE Journal

Engineering

12.8K Views.  National Taiwan University. Saturable and reverse saturable scattering were discovered in isolated plasmonic particles and adopted as a novel non-bleaching contrast method in super-resolution microscopy. Here the experimental procedures of detecting and extracting nonlinear scattering are explained in detail, as well as how to enhance resolution with the aid of saturated excitation microscopy. 

Video: Measurement of Scattering Nonlinearities from a Single Plasmonic Nanoparticle

Measuring Spatially- and Directionally-varying Light Scattering from Biological Material

Light interacts with an organism's integument on a variety of spatial scales. For example in an iridescent bird: nano-scale structures produce color; the milli-scale structure of barbs and barbules largely determines the directional pattern of reflected light; and through the macro-scale spatial structure of overlapping, curved feathers, these directional effects create the visual texture. Milli-scale and macro-scale effects determine where on the organism's body, and from what viewpoints and under what illumination, the iridescent colors are seen. Thus, the highly directional flash of brilliant color from the iridescent throat of a hummingbird is inadequately explained by its nano-scale structure alone and questions remain. From a given observation point, which milli-scale elements of the feather are oriented to reflect strongly? Do some species produce broader "windows" for observation of iridescence than others? These and similar questions may be asked about any organisms that have evolved a particular surface appearance for signaling, camouflage, or other reasons.
In order to study the directional patterns of light scattering from feathers, and their relationship to the bird's milli-scale morphology, we developed a protocol for measuring light scattered from biological materials using many high-resolution photographs taken with varying illumination and viewing directions. Since we measure scattered light as a function of direction, we can observe the characteristic features in the directional distribution of light scattered from that particular feather, and because barbs and barbules are resolved in our images, we can clearly attribute the directional features to these different milli-scale structures. Keeping the specimen intact preserves the gross-scale scattering behavior seen in nature. The method described here presents a generalized protocol for analyzing spatially- and directionally-varying light scattering from complex biological materials at multiple structural scales.

We present a non-destructive method for sampling spatial variation in the direction of light scattered from structurally complex materials. By keeping the material intact, we preserve gross-scale scattering behavior, while concurrently capturing fine-scale directional contributions with high-resolution imaging. Results are visualized in software at biologically-relevant positions and scales.

Light interacts with an organism's integument on a variety of spatial scales. For example in an iridescent bird: nano-scale structures produce color; the ...

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

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on photoconduction, which has been one of the most commonly used techniques for terahertz generation 1-8. Terahertz generation in a photoconductive emitter is achieved by pumping an ultrafast photoconductor with a pulsed or heterodyned laser illumination. The induced photocurrent, which follows the envelope of the pump laser, is routed to a terahertz radiating antenna connected to the photoconductor contact electrodes to generate terahertz radiation. Although the quantum efficiency of a photoconductive emitter can theoretically reach 100%, the relatively long transport path lengths of photo-generated carriers to the contact electrodes of conventional photoconductors have severely limited their quantum efficiency. Additionally, the carrier screening effect and thermal breakdown strictly limit the maximum output power of conventional photoconductive terahertz sources. To address the quantum efficiency limitations of conventional photoconductive terahertz emitters, we have developed a new photoconductive emitter concept which incorporates a plasmonic contact electrode configuration to offer high quantum-efficiency and ultrafast operation simultaneously. By using nano-scale plasmonic contact electrodes, we significantly reduce the average photo-generated carrier transport path to photoconductor contact electrodes compared to conventional photoconductors 9. Our method also allows increasing photoconductor active area without a considerable increase in the capacitive loading to the antenna, boosting the maximum terahertz radiation power by preventing the carrier screening effect and thermal breakdown at high optical pump powers. By incorporating plasmonic contact electrodes, we demonstrate enhancing the optical-to-terahertz power conversion efficiency of a conventional photoconductive terahertz emitter by a factor of 50 10.

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.

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on ...

Visible-light Induced Reduction of Graphene Oxide Using Plasmonic Nanoparticle

Present work demonstrates the simple, chemical free, fast, and energy efficient method to produce reduced graphene oxide (r-GO) solution at RT using visible light irradiation with plasmonic nanoparticles. The plasmonic nanoparticle is used to improve the reduction efficiency of GO. It only takes 30 min&#160;at RT by illuminating the solutions with Xe-lamp, the r-GO solutions can be obtained by completely removing gold nanoparticles through simple centrifugation step. The spherical gold nanoparticles (AuNPs) as compared to the other nanostructures is the most suitable plasmonic nanostructure for r-GO preparation. The reduced graphene oxide prepared using visible light and AuNPs was equally qualitative as chemically reduced graphene oxide, which was supported by various analytical techniques such as UV-Vis spectroscopy, Raman spectroscopy, powder XRD and XPS. The reduced graphene oxide prepared with visible light shows excellent quenching properties over the fluorescent molecules modified on ssDNA and excellent fluorescence recovery for target DNA detection. The r-GO prepared by recycled AuNPs is found to be of same quality with that of chemically reduced r-GO. The use of visible light with plasmonic nanoparticle demonstrates the good alternative method for r-GO synthesis.

A simple protocol for the preparation of reduced graphene oxide using visible light and plasmonic nanoparticle is described.

Present work demonstrates the simple, chemical free, fast, and energy efficient method to produce reduced graphene oxide (r-GO) solution at RT using ...

A System to Create Stable Nanoparticle Aerosols from Nanopowders

Nanoparticle aerosols released from nanopowders in workplaces are associated with human exposure and health risks. We developed a novel system, requiring minimal amounts of test materials (min. 200 mg), for studying powder aerosolization behavior and aerosol properties. The aerosolization procedure follows the concept of the fluidized-bed process, but occurs in the modified volume of a V-shaped aerosol generator. The airborne particle number concentration is adjustable by controlling the air flow rate. The system supplied stable aerosol generation rates and particle size distributions over long periods (0.5-2 hr and possibly longer), which are important, for example, to study aerosol behavior, but also for toxicological studies. Strict adherence to the operating procedures during the aerosolization experiments ensures the generation of reproducible test results. The critical steps in the standard protocol are the preparation of the material and setup, and the aerosolization operations themselves. The system can be used for experiments requiring stable aerosol concentrations and may also be an alternative method for testing dustiness. The controlled aerosolization made possible with this setup occurs using energy inputs (may be characterized by aerosolization air velocity) that are within the ranges commonly found in occupational environments where nanomaterial powders are handled. This setup and its operating protocol are thus helpful for human exposure and risk assessment.

We designed and developed an effective nanopowder aerosolization setup and operating protocol. The system generated nanoparticle aerosols with stable number concentrations and size distributions for long durations, requiring only small quantities of test material (min. 200 mg).

Nanoparticle aerosols released from nanopowders in workplaces are associated with human exposure and health risks. We developed a novel system, requiring ...

Testing of Nanoparticle Release from a Composite Containing Nanomaterial Using a Chamber System

With the rapid development of nanotechnology as one of the most important technologies in the 21st century, interest in the safety of consumer products containing nanomaterials is also increasing. Evaluating the nanomaterial release from products containing nanomaterials is a crucial step in assessing the safety of these products, and has resulted in several international efforts to develop consistent and reliable technologies for standardizing the evaluation of nanomaterial release. In this study, the release of nanomaterials from products containing nanomaterials is evaluated using a chamber system that includes a condensation particle counter, optical particle counter, and sampling ports to collect filter samples for electron microscopy analysis. The proposed chamber system is tested using an abrasor and disc-type nanocomposite material specimens to determine whether the nanomaterial release is repeatable and consistent within an acceptable range. The test results indicate that the total number of particles in each test is within 20% from the average after several trials. The release trends are similar and they show very good repeatability. Therefore, the proposed chamber system can be effectively used for nanomaterial release testing of products containing nanomaterials.

Nanoparticle release is tested using a chamber system that includes a condensation particle counter, an optical particle counter and sampling ports to collect filter samples for microscopy analysis. The proposed chamber system can be effectively used for nanomaterial release testing with a repeatable and consistent data range.

With the rapid development of nanotechnology as one of the most important technologies in the 21st century, interest in the safety of consumer products ...

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.

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.

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

Scanning Light Scattering Profiler (SLPS) Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light scattering from intraocular lenses (IOLs) using goniophotometer principles. This protocol describes the SLSP platform and how it employs a 360&#176; rotational photodetector sensor that is scanned around an IOL sample while recording the intensity and location of scattered light as it passes through the IOL medium. The SLSP platform can be used to predict, non-clinically, the propensity for current and novel IOL designs and materials to induce light scatter. Non-clinical evaluation of light scattering properties of IOLs can significantly reduce the number of patient complaints related to unwanted glare, glistening, optical defects, poor image quality, and other phenomena associated with the unintended light scattering. Future studies should be conducted to correlate SLSP data with clinical results to help identify which measured light scatter is most problematic for patients that have undergone cataract surgery subsequent to IOL implantation.

Scanning Light Scattering Profiler SLPS Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

This protocol describes the scanning light scattering profiler (SLSP) that enables the full-angle quantitative evaluation of forward and backward scattering of light from intraocular lenses (IOLs) using goniophotometer principles.

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light ...

Standardized Method for Measuring Collection Efficiency from Wipe-sampling of Trace Explosives

One of the limiting steps to detecting traces of explosives at screening venues is effective collection of the sample. Wipe-sampling is the most common procedure for collecting traces of explosives, and standardized measurements of collection efficiency are needed to evaluate and optimize sampling protocols. The approach described here is designed to provide this measurement infrastructure, and controls most of the factors known to be relevant to wipe-sampling. Three critical factors (the applied force, travel distance, and travel speed) are controlled using an automated device. Test surfaces are chosen based on similarity to the screening environment, and the wipes can be made from any material considered for use in wipe-sampling. Particle samples of the explosive 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) are applied in a fixed location on the surface using a dry-transfer technique. The particle samples, recently developed to simulate residues made after handling explosives, are produced by inkjet printing of RDX solutions onto polytetrafluoroethylene (PTFE) substrates. Collection efficiency is measured by extracting collected explosive from the wipe, and then related to critical sampling factors and the selection of wipe material and test surface. These measurements are meant to guide the development of sampling protocols at screening venues, where speed and throughput are primary considerations.

Optimized sampling protocols and the development of new wipe materials can be facilitated by standardized measurements of collection efficiency from wipe-sampling. Our approach for sampling trace explosives uses an automated device to control speed, force, and distance during wipe-sampling followed by extraction of collected explosives.

One of the limiting steps to detecting traces of explosives at screening venues is effective collection of the sample. Wipe-sampling is the most common ...

Micro/Nano-scale Strain Distribution Measurement from Sampling Moir&#233; Fringes

This work describes the measurement procedure and principles of a sampling moir&#233; technique for full-field micro/nano-scale deformation measurements. The developed technique can be performed in two ways: using the reconstructed multiplication moir&#233; method or the spatial phase-shifting sampling moir&#233; method. When the specimen grid pitch is around 2 pixels, 2-pixel sampling moir&#233; fringes are generated to reconstruct a multiplication moir&#233; pattern for a deformation measurement. Both the displacement and strain sensitivities are twice as high as in the traditional scanning moir&#233; method in the same wide field of view. When the specimen grid pitch is around or greater than 3 pixels, multi-pixel sampling moir&#233; fringes are generated, and a spatial phase-shifting technique is combined for a full-field deformation measurement. The strain measurement accuracy is significantly improved, and automatic batch measurement is easily achievable. Both methods can measure the two-dimensional (2D) strain distributions from a single-shot grid image without rotating the specimen or scanning lines, as in traditional moir&#233; techniques. As examples, the 2D displacement and strain distributions, including the shear strains of two carbon fiber-reinforced plastic specimens, were measured in three-point bending tests. The proposed technique is expected to play an important role in the non-destructive quantitative evaluations of mechanical properties, crack occurrences, and residual stresses of a variety of materials.

A sampling moir&#233; technique featuring 2-pixel and multi-pixel sampling methods for high-accuracy strain distribution measurements at the micro/nano-scale is presented here.

This work describes the measurement procedure and principles of a sampling moir&#233; technique for full-field micro/nano-scale deformation measurements. ...