This work was supported by the National Research Foundation of Korea (2013R1A1A1061387) and KU-KIST research fund.

1. Preparation of Precursor
<ol>
	<li>Preparation of graphene oxide (GO):
	<ol>
		<li>GO preparation using modified Hummer&#8217;s method14
		<ol>
			<li>Add 3.0 g of graphite flakes to a mixture of concentrated H2SO4/H3PO4 (360:40 ml) at RT. (Note: Special care has to be taken while using strong acids H2SO4 and H3PO4.)</li>
			<li>Add KMnO4 (18.0 g) slowly with stirring and cooling in an ice bath to maintain the temperature of reaction mixture at &#60; 35 &#176;C. (The solution become sticky with increased reaction time, need to use proper method to maintain efficient stirring.) (Note: Special care has to be taken while adding KMnO4 due to exothermic reaction.)</li>
			<li>Stir for 12 hr at 50 &#176;C and then cool to RT and pouring reaction mixture onto ice (400 ml) containing 30% H2O2 (3 ml).</li>
			<li>Filter the reaction mixture using a metal U.S. Standard testing sieve (300 &#181;m) to remove unreacted graphite and centrifuge the filtrate (4,722 x g speed for 2 hr) to remove the supernatant.</li>
			<li>Repeat the centrifugation step with 200 ml of water, 200 ml of 30% HCl, 200 ml of ethanol, and distilled water again until pH of solution reach at 5.0&#8211;6.0.</li>
			<li>Lyophilize the final solutions to produce a fluffy GO powder.</li>
			<li>In order to make nanosized GO solution, dissolve 20 mg of GO powder in 40 ml of triple distilled water (&#62; 18 M&#937;), and then exfoliate by prolonged sonication (35% amplitude, 500 W, 2 hr) until the entire size distribution become below 150 nm, then centrifuge it two times (10,625 x g speed, 15 min) to remove precipitates (un-exfoliated large GO sheets).&#160;&#160;</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Preparation of plasmonic nanoparticle
	<ol>
		<li>Preparation of AuNPs
		<ol>
			<li>Citrate-stabilized spherical shape gold nanoparticle (AuNPs, O.D. = 1.0) of 30 nm particles size was used for r-GO reduction.</li>
		</ol>
		</li>
		<li>Preparation of AuNRs15
		<ol>
			<li>Prepare the seed solution by adding a freshly prepared 0.6 ml ice-cold solution of NaBH4 solution (0.01 M) into an aqueous mixture solution compose of 0.25 ml of HAuCl4 (0.01 M) and 9.75 ml of cetyltrimethylammonium bromide (CTAB, 0.1 M).</li>
			<li>Stir the resulting mixture vigorously for 0.5 min and then keep it at 28 &#176;C for 3 hr.</li>
			<li>Prepare the growth solution by mixing 475 ml of CTAB (0.1 M), 3 ml of AgNO3 (0.01 M) and 20 ml of HAuCl4 (0.01 M).</li>
			<li>Then add freshly prepared 3.2 ml of ascorbic acid (0.01 M) to the mixture followed by the addition of 0.8 ml of an aqueous HCl (1.0 M) solution.</li>
			<li>In the final step add 3.2 ml of seed solution to the growth solution at 28 &#176;C and subject the reaction mixture to quick inversion for few seconds. Finally, keep the resulting mixture undisturbed for at least 6 hr.</li>
			<li>Analyze the prepared AuNRs with UV-Visible spectroscopy for absorption maxima (&#955;max) and TEM analysis (typically the &#955;max and aspect ratio was found to be 730 nm and 3.5, respectively).</li>
		</ol>
		</li>
		<li>Preparation of AuNSs16
		<ol>
			<li>Prepare aqueous stock solution of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) with concentration of 100 mM, and adjust the pH to 7.4 at 25 &#176;C by adding 1.0 M NaOH solution.</li>
			<li>Mix 20 ml of phosphate buffer (100 mM) with 30 ml of 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid (100 mM).</li>
			<li>Then add 500 &#181;l of gold(III) chloride trihydrate (20 mM) to the above mixture and keep at 28.5 &#176;C for 30 min in water bath. Solution color changes from light yellow to greenish blue after 30 min could be observed.</li>
			<li>Centrifuge the solution at 8,928 x g speed for 30 min and disperse the precipitates in distilled water.</li>
			<li>Finally, analyze the prepared AuNSs with UV-Visible spectroscopy for absorption maxima (&#955;max) and TEM analysis for particles size confirmation which is found to be 740 nm and 30 nm, respectively.&#160;&#160;</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
2. Preparation of r-GO Using Visible Light and AuNPs
<ol>
	<li>Add 1 ml of plasmonic nanoparticles (Abs 1.0 at 520 nm for AuNPs, Abs 1.0 at 750 nm for AuNRs, and Abs 1.0 at 730 nm for AuNSs, respectively) and 100 &#181;l of ammonium hydroxide (28%, w/v%) to 10 ml of GO solution (OD 1.0 at 230 nm, 0.125 mg ml-1) placed in a Pyrex glass reactor equipped with a water-circulating jacket.</li>
	<li>Irradiate the mixture with Xe lamp (power density of 1.56 W cm-2) for 30 min with water circulation through water-circulating jacket to maintain the temperature at 25 &#176;C and then centrifuge the solution at 10,625 x g speed for 15 min to remove gold nanoparticles.</li>
	<li>Take the supernatant containing the prepared r-GO to analyze with UV-Visible spectrophotometer (r-GO should show the distinctive absorption band at 270 nm) in the range of 200&#8211;900 nm.</li>
</ol>
3. Target DNA Detection Using r-GO Solution17
<ol>
	<li>For fluorescence quenching, add 20 &#181;l of 10-6 M Cy3-modified ssDNA (5&#39;-ATC CTT ATC AAT ATT TAA CAA TAA TCC CTC-Cy3-3&#39;) into GO or r-GO solution containing 25 &#181;l of GO (0.125 mg ml-1) or r-GO (0.125 mg ml-1) in 1,955 &#181;l of 0.3 M PBS solution (10 mM phosphate buffer, 0.3 M NaCl) and incubate for 10 min at RT.</li>
	<li>Measure the fluorescence intensity of these samples with spectrofluorometer (&#955;ex= 529 nm).</li>
	<li>For Target Detection, add 200 &#181;l of target oligonucleotide solution (5&#39;- GAG GGA TTA TTG TTA AAT ATT GAT AAG GAT- 3&#39;) in three different concentrations (10-6 M, 10-7 M, 10-8 M) into the GO or r-GO solution containing 20 &#181;l of 10-6 M ssDNA-Cy3, 25 &#181;l of GO or r-GO (0.125 mg ml-1), and 1,755 &#181;l of 0.3 M PBS for fluorescence recovery experiment.17 
	Notes: 
	Light Sources &#38; Reactor 
	Visible light (400&#8211;780 nm) source. Visible light irradiate through Pyrex glass reactor (window diameter = 1.1 cm) containing GO solution using Xe lamp (1.56 W/cm2 power). The photon energy applied to the reactor is calculated to be 4.8 &#215; 1021 photons per min (Figure 2A-2C). 
	Near-infrared (NIR) laser. NIR laser (window diameter = 13.2 cm) with power density of 0.36 W/cm2, and operating wavelength of 808 nm has been used as the source of near-infrared light for GO reduction reactions (Figure 2E). The photon energy is calculated to be 2.43 &#215; 1021 photons per min. 
	Reactor: Pyrex glass reactor (window diameter = 1.1 cm; reaction volume = 10 ml) equipped with a water-circulating jacket is used for both visible light and NIR light irradiated GO reduction reactions (Figure 2F).</li>
</ol>

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We have nothing to disclose.

Visible light irradiation onto GO solution for 30 min with gold nanoparticles (AuNPs, AuNSs &#38; AuNRs) showed the rapid color changes from light yellow-brown to black color (Figure 1). To obtain highly pure r-GO product in high yield, there are two important factors need to follow. One is the use of AuNPs as an efficient plasmonic catalyst, since AuNPs can strongly absorb the visible light among other structures (i.e., AuNRs, AuNSs). Another is the use of nanosized GO solution to obtain nanopa...

The first developed scotch-tape based method1 and chemical vapor deposition2 were excellent methods to produce the pristine state of a graphene, but the large scale graphene synthesis or graphene layer formation on the surface with wide area have been regarded as a key limitation of previous methods.3 One of possible solution for large scale r-GO synthesis will be wet-chemical synthetic method which first requires the reactions with strong oxidants, extensive physical treatment such as sonication to produce GO sheet, and finally the reduction of oxygen functionalities such as hydroxy, epoxide and carbonyl groups in GO is essential in order to recover its original physical properties.4 Mostly, the reduction of GO was carried out with either chemical method using hydrazine or its derivatives5 or by thermal treatment method (550&#8211;1,100 &#176;C) in an inert or reducing atmosphere.6
These processes require the toxic chemicals, long reaction time and high temperature which increased total energy demand for r-GO synthesis.7 While the photo-irradiating reduction processes such as UV-induced,8 photo-thermal process using a pulsed xenon flash,9 pulsed laser assisted10 and photo-thermal heating with camera flash lights11 have also been reported for the preparation of r-GO. In general, the low conversion efficiency of the photo-induced methods propagated to the use of UV or pulsed laser irradiation that can deliver high photon energy. The low photon energy of visible light limits its use and not attracted much for r-GO synthesis. Excellent light absorption properties of plasmonic nanoparticles in the visible and/or NIR regions can greatly improve the current drawbacks of the use of visible light for r-GO synthesis.12,13 Mild reaction conditions, short reaction time and limited use of toxic chemicals could make the visible light induced plasmon assisted photocatalytic reduction of GO as a useful alternative method.
In present method, we describe the efficient and simple r-GO synthetic method using plasmonic nanoparticles and visible light. The reaction progress was found to be strongly dependent on the structures of plasmonic nanoparticles such as spherical gold nanoparticles (AuNPs), gold nanorods (AuNRs), and gold nanostars (AuNSs). The use of AuNPs showed the most efficient reduction of GO and the nanoparticles are easily removable and recyclable for the repeated use (Figure 1). The r-GO synthesized using visible light and AuNPs showed almost equal quality compared with the r-GO prepared by well-known chemical method (hydrazine) as demonstrated by use of various analytical measurements and the fluorescence quenching/recovery based DNA detection method.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Cy3 modifeid ssDNA</td>
			<td>IDT(Iowa, USA)</td>
			<td></td>
			<td>HPLC purified by IDT</td>
		</tr>
		<tr>
			<td>Gold nanoparticles (30 nm)</td>
			<td>Ted Pella, Inc(Redding, CA, USA).</td>
			<td>15706-20</td>
			<td>colloidal solution</td>
		</tr>
		<tr>
			<td>4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid (HEPES) (99.5%)</td>
			<td>Sigma-Aldrich (St. Louis, MO, USA)</td>
			<td>7365-45-9</td>
			<td></td>
		</tr>
		<tr>
			<td>Gold(III)Chloride Hydrate (99.999%)</td>
			<td>Sigma-Aldrich (St. Louis, MO, USA)</td>
			<td>&#160;27988-77-8</td>
			<td>strongly hygroscopic</td>
		</tr>
		<tr>
			<td>Sodium Borohydride (99.99%)</td>
			<td>Sigma-Aldrich (St. Louis, MO, USA)</td>
			<td>16940-66-2</td>
			<td></td>
		</tr>
		<tr>
			<td>Hexadecyltrimethylammonium bromide (&#8805;99%)</td>
			<td>Sigma-Aldrich (St. Louis, MO, USA)</td>
			<td>57-09-0</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Ascorbic Acid(&#8805;99.0%)</td>
			<td>Sigma-Aldrich (St. Louis, MO, USA)</td>
			<td>50-81-7</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Chloride (99.5%)</td>
			<td>Sigma-Aldrich (St. Louis, MO, USA)</td>
			<td>7647-14-5</td>
			<td></td>
		</tr>
		<tr>
			<td>Silver Nitrate&#160; (&#8805;99.0%)</td>
			<td>Sigma-Aldrich (St. Louis, MO, USA)</td>
			<td>7761-88-8</td>
			<td></td>
		</tr>
		<tr>
			<td>Graphite</td>
			<td>Sigma-Aldrich (St. Louis, MO, USA)</td>
			<td>7782-42-5</td>
			<td></td>
		</tr>
		<tr>
			<td>Sulfuric acid</td>
			<td>Sigma-Aldrich (St. Louis, MO, USA)</td>
			<td>7664-93-9</td>
			<td></td>
		</tr>
		<tr>
			<td>Phophoric acid</td>
			<td>Sigma-Aldrich (St. Louis, MO, USA)</td>
			<td>7664-38-2</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium permanganate</td>
			<td>Sigma-Aldrich (St. Louis, MO, USA)</td>
			<td>7722-64-7</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrogen peroxide</td>
			<td>JUNSEI</td>
			<td>23150-0350</td>
			<td></td>
		</tr>
		<tr>
			<td>Ammonium hydroxide</td>
			<td>Sigma-Aldrich (St. Louis, MO, USA)</td>
			<td>1336-21-6</td>
			<td></td>
		</tr>
		<tr>
			<td>Xe-lamp</td>
			<td>&#160;Cermax, Waltham, USA</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>NIR Laser</td>
			<td>Class-IV, Sanctity Laser, Shanghai, China&#160;</td>
			<td></td>
			<td>6W (output power)</td>
		</tr>
		<tr>
			<td>UV-Vis spectrophotometer&#160;</td>
			<td>S-3100, SINCO, South Korea</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Transmission Electron Microscopy</td>
			<td>H-7650, Hitachi, Japan</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Spectro Fluorometer</td>
			<td>Jasco FP-6500, Tokyo, Japan</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>X-ray Photoelectron Spectrometer</td>
			<td>AXIS&#8211;NOVA, KRATOS Inc., UK</td>
			<td></td>
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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.

Figure 1 shows the overall scheme for visible light and plasmonic nanoparticle based r-GO reduction reaction. Figure 2 shows the instrumental setup for the reactions. After reaction, it is required the centrifugation step to remove the used photocatalyst (AuNSs, AuNRs, or AuNPs) as shown in Figure 3A. The HRTEM analysis shows the complete removal of nanoparticles in the supernatant (r-GO) (Figure 3B), which is also possible to confirm with UV-Visible ana...

Watch this Scientific Journal Video about Visible-light Induced Reduction of Graphene Oxide Using Plasmonic Nanoparticle at JoVE.com

Visible-light Induced Reduction of Graphene Oxide Using Plasmonic Nanoparticle

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 ...

visible-light-induced-reduction-graphene-oxide-using-plasmonic

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JoVE Journal

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14.4K Views.  Korea University. A simple protocol for the preparation of reduced graphene oxide using visible light and plasmonic nanoparticle is described.

Video: Visible-light Induced Reduction of Graphene Oxide Using Plasmonic Nanoparticle

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 ...

Evaluating Plasmonic Transport in Current-carrying Silver Nanowires

Plasmonics is an emerging technology capable of simultaneously transporting a plasmonic signal and an electronic signal on the same information support1,2,3. In this context, metal nanowires are especially desirable for realizing dense routing networks4. A prerequisite to operate such shared nanowire-based platform relies on our ability to electrically contact individual metal nanowires and efficiently excite surface plasmon polaritons5 in this information support. In this article, we describe a protocol to bring electrical terminals to chemically-synthesized silver nanowires6 randomly distributed on a glass substrate7. The positions of the nanowire ends with respect to predefined landmarks are precisely located using standard optical transmission microscopy before encapsulation in an electron-sensitive resist. Trenches representing the electrode layout are subsequently designed by electron-beam lithography. Metal electrodes are then fabricated by thermally evaporating a Cr/Au layer followed by a chemical lift-off. The contacted silver nanowires are finally transferred to a leakage radiation microscope for surface plasmon excitation and characterization8,9. Surface plasmons are launched in the nanowires by focusing a near infrared laser beam on a diffraction-limited spot overlapping one nanowire extremity5,9. For sufficiently large nanowires, the surface plasmon mode leaks into the glass substrate9,10. This leakage radiation is readily detected, imaged, and analyzed in the different conjugate planes in leakage radiation microscopy9,11. The electrical terminals do not affect the plasmon propagation. However, a current-induced morphological deterioration of the nanowire drastically degrades the flow of surface plasmons. The combination of surface plasmon leakage radiation microscopy with a simultaneous analysis of the nanowire electrical transport characteristics reveals the intrinsic limitations of such plasmonic circuitry.

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.

Plasmonics is an emerging technology capable of simultaneously transporting a plasmonic signal and an electronic signal on the same information ...

Development of a 3D Graphene Electrode Dielectrophoretic Device

The design and fabrication of a novel 3D electrode microdevice using 50 &#181;m thick graphene paper and 100 &#181;m double sided tape is described. The protocol details the procedures to construct a versatile, reusable, multiple layer, laminated dielectrophoresis chamber. Specifically, six layers of 50 &#181;m x&#160;0.7 cm x&#160;2 cm graphene paper and five layers of double sided tape were alternately stacked together, then clamped to a glass slide. Then a 700 &#956;m diameter micro-well was drilled through the laminated structure using a computer-controlled micro drilling machine. Insulating properties of the tape layer between adjacent graphene layers were assured by resistance tests. Silver conductive epoxy connected alternate layers of graphene paper and formed stable connections between the graphene paper and external copper wire electrodes. The finished device was then clamped and sealed to a glass slide. The electric field gradient was modeled within the multi-layer device. Dielectrophoretic behaviors of 6 &#956;m polystyrene beads were demonstrated in the 1 mm deep micro-well, with medium conductivities ranging from 0.0001 S/m to 1.3 S/m, and applied signal frequencies from 100 Hz to 10 MHz. Negative dielectrophoretic responses were observed in three dimensions over most of the conductivity-frequency space and cross-over frequency values are consistent with previously reported literature values. The device did not prevent AC electroosmosis and electrothermal flows, which occurred in the low and high frequency regions, respectively. The graphene paper utilized in this device is versatile and could subsequently function as a biosensor after dielectrophoretic characterizations are complete.

A microdevice with high throughput potential is used to demonstrate three-dimensional (3D) dielectrophoresis (DEP) with novel materials. Graphene nanoplatelet paper and double sided tape were alternately stacked; a 700 &#956;m micro-well was drilled transverse to the layers. DEP behavior of polystyrene beads was demonstrated in the micro-well.

The design and fabrication of a novel 3D electrode microdevice using 50 &#181;m thick graphene paper and 100 &#181;m double sided tape is described. The ...

Writing and Low-Temperature Characterization of Oxide Nanostructures

Oxide nanoelectronics is a rapidly growing field which seeks to develop novel materials with multifunctional behavior at nanoscale dimensions. Oxide interfaces exhibit a wide range of properties that can be controlled include conduction, piezoelectric behavior, ferromagnetism, superconductivity and nonlinear optical properties. Recently, methods for controlling these properties at extreme nanoscale dimensions have been discovered and developed. Here are described explicit step-by-step procedures for creating LaAlO3/SrTiO3 nanostructures using a reversible conductive atomic force microscopy technique. The processing steps for creating electrical contacts to the LaAlO3/SrTiO3 interface are first described. Conductive nanostructures are created by applying voltages to a conductive atomic force microscope tip and locally switching the LaAlO3/SrTiO3 interface to a conductive state. A versatile nanolithography toolkit has been developed expressly for the purpose of controlling the atomic force microscope (AFM) tip path and voltage. Then, these nanostructures are placed in a cryostat and transport measurements are performed. The procedures described here should be useful to others wishing to conduct research in oxide nanoelectronics.

Oxide nanostructures provide new opportunities for science and technology. The interfacial conductivity between LaAlO3 and SrTiO3 can be controlled with near-atomic precision using a conductive atomic force microscopy technique. The protocol for creating and measuring conductive nanostructures at LaAlO3/SrTiO3 interfaces is demonstrated.

Oxide nanoelectronics is a rapidly growing field which seeks to develop novel materials with multifunctional behavior at nanoscale dimensions.  Oxide ...

Synthesis and Functionalization of 3D Nano-graphene Materials: Graphene Aerogels and Graphene Macro Assemblies

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. Additionally, most reported graphene assemblies are held together through physical interactions (e.g., van der Waals forces) rather than chemical bonds, which limit their mechanical strength and conductivity. This video method details recently developed strategies to fabricate mass-producible, graphene-based bulk materials derived from either polymer foams or single layer graphene oxide. These materials consist primarily of individual graphene sheets connected through covalently bound carbon linkers. They maintain the favorable properties of graphene such as high surface area and high electrical and thermal conductivity, combined with tunable pore morphology and exceptional mechanical strength and elasticity. This flexible synthetic method can be extended to the fabrication of polymer/carbon nanotube (CNT) and polymer/graphene oxide (GO) composite materials. Furthermore, additional post-synthetic functionalization with anthraquinone is described, which enables a dramatic increase in charge storage performance in supercapacitor applications.

This video method describes the synthesis of high surface area, monolithic 3D graphene-based materials derived from polymer precursors as well as single layer graphene oxide.

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. ...

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.

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 ...

Iridium Oxide-reduced Graphene Oxide Nanohybrid Thin Film Modified Screen-printed Electrodes as Disposable Electrochemical Paper Microfluidic pH Sensors

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use integrated paper microfluidic electrochemical pH sensor for resource-limited settings. Taking advantages from both pH meters and strips, the pH sensing platform is composed of hydrophobic barrier-patterned paper micropad (&#181;PAD) using polydimethylsiloxane (PDMS), screen-printed electrode (SPE) modified with IrO2-graphene films and molded acrylonitrile butadiene styrene (ABS) plastic holder. Repetitive cathodic potential cycling was employed for graphene oxide (GO) reduction which can completely remove electrochemically unstable oxygenated groups and generate a 2D defect-free homogeneous graphene thin film with excellent stability and electronic properties. A uniform and smooth IrO2 film in nanoscale grain size is anodically electrodeposited onto the graphene film, without any observable cracks. The resulting IrO2-RGO electrode showed slightly super-Nernstian responses from pH 2-12 in Britton-Robinson (B-R) buffers with good linearity, small hysteresis, low response time and reproducibility in different buffers, as well as low sensitivities to different interfering ionic species and dissolved oxygen. A simple portable digital pH meter is fabricated, whose signal is measured with a multimeter, using high input-impedance operational amplifier and consumer batteries. The pH values measured with the portable electrochemical paper-microfluidic pH sensors were consistent with those measured using a commercial laboratory pH meter with a glass electrode.

The study demonstrates the growth of iridium oxide-reduced graphene oxide (IrO2-RGO) nanohybrid thin films on irregular and rough screen-printed carbon substrate through a green electrochemical synthesis, and their implementation as a pH sensor with a patterned paper-fluidic platform.

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use ...

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.

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

Multifunctional Hybrid Fe2O3-Au Nanoparticles for Efficient Plasmonic Heating

One of the most widely used methods for manufacturing colloidal gold nanospherical particles involves the reduction of chloroauric acid (HAuCl4) to neutral gold Au(0) by reducing agents, such as sodium citrate or sodium borohydride. The extension of this method to decorate iron oxide or similar nanoparticles with gold nanoparticles to create multifunctional hybrid Fe2O3-Au nanoparticles is straightforward. This approach yields fairly good control over Au nanoparticle dimensions and loading onto Fe2O3. Additionally, the Au metal size, shape, and loading can easily be tuned by changing experimental parameters (e.g., reactant concentrations, reducing agents, surfactants, etc.). An advantage of this procedure is that the reaction can be done in air or water, and, in principle, is amenable to scaling up. The use of such optically tunable Fe2O3-Au nanoparticles for hyperthermia studies is an attractive option as it capitalizes on plasmonic heating of gold nanoparticles tuned to absorb light strongly in the VIS-NIR region. In addition to its plasmonic effects, nanoscale Au provides a unique surface for interesting chemistries and catalysis. The Fe2O3 material provides additional functionality due to its magnetic property. For example, an external magnetic field could be used to collect and recycle the hybrid Fe2O3-Au nanoparticles after a catalytic experiment, or alternatively, the magnetic Fe2O3 can be used for hyperthermia studies through magnetic heat induction. The photothermal experiment described in this report measures bulk temperature change and nanoparticle solution mass loss as functions of time using infrared thermocouples and a balance, respectively. The ease of sample preparation and the use of readily available equipment are distinct advantages of this technique. A caveat is that these photothermal measurements assess the bulk solution temperature and not the surface of the nanoparticle where the heat is transduced and the temperature is likely to be higher.

Multifunctional Hybrid Fe2O3-Au Nanoparticles for Efficient Plasmonic Heating

We describe the synthesis and properties of multifunctional Fe2O3-Au nanoparticles produced by a wet chemical approach and investigate their photothermal properties using laser irradiation. The composite Fe2O3-Au nanoparticles retain the properties of both materials, creating a multifunctional structure with excellent magnetic and plasmonic properties.

One of the most widely used methods for manufacturing colloidal gold nanospherical particles involves the reduction of chloroauric acid (HAuCl4) to ...

Advanced Compositional Analysis of Nanoparticle-polymer Composites Using Direct Fluorescence Imaging

The fabrication of polymer-nanoparticle composites is extremely important in the development of many functional materials. Identifying the precise composition of these materials is essential, especially in the design of surface catalysts, where the surface concentration of the active component determines the activity of the material. Antimicrobial materials which utilize nanoparticles are a particular focus of this technology. Recently swell encapsulation has emerged as a technique for inserting antimicrobial nanoparticles into a host polymer matrix. Swell encapsulation provides the advantage of localizing the incorporation to the external surfaces of materials, which act as the active sites of these materials. However, quantification of this nanoparticle uptake is challenging. Previous studies explore the link between antimicrobial activity and surface concentration of the active component, but this is not directly visualized. Here we show a reliable method to monitor the incorporation of nanoparticles into a polymer host matrix via swell encapsulation. We show that the surface concentration of CdSe/ZnS nanoparticles can be accurately visualized through cross-sectional fluorescence imaging. Using this method, we can quantify the uptake of nanoparticles via swell encapsulation and measure the surface concentration of encapsulated particles, which is key in optimizing the activity of functional materials.

Here we present a reliable method to monitor the incorporation of nanoparticles into a polymer host matrix via swell encapsulation. We show that the surface concentration of cadmium selenide quantum dots can be accurately visualized through cross-sectional fluorescence imaging.