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The direct reduction of graphene oxide (GO) by hydroiodic acid is an established method to produce iodine functionalized reduced GO (I-rGO). However, the stability of the iodine species within I-rGO upon heating and dispersing into different solvents, as required for many applications, has not been examined. Herein we examined the stability of I-rGO and utilized it to promote self-assembled nanoenergetic composites. I-rGO intercalated with polyiodide was found to be unstable at elevated temperature and when dispersed in organic solvents. The I-rGO exhibited excellent dispersion in dimethylformamide but resulted in a loss of iodine content as exfoliation released weakly-bound intercalated iodine species. The dispersed I-rGO was utilized as a scaffold to self-assemble I-rGO/Al and I-rGO/Al/Bi2O3 nanoenergetic composites. The I-rGO both prevented the phase separation of Al and Bi2O3 particles and provided a source for reactive iodine to etch the alumina shell surrounding Al fuel nanoparticles. Differential scanning calorimetry showed that the use of the I-rGO assembly template reduced the temperature of initiation and peak reaction and produced 70% greater energy release than randomly mixed Al/Bi2O3 nanoenergetic powder. In fact, 95% of the exothermal energy released by the reaction occurred while Al was in the solid state, suggesting that the reaction between free iodine and alumina was significant enough to greatly reduce the diffusion barrier between solid Al fuel and surrounding oxidizer. Further, the underlying conductive I-rGO scaffold reduces electrostatic discharge sensitivity of the nanoenergetic composite by almost four orders of magnitude.

Since the development of fluoroimmunoassays, researchers have sought a method of substantially enhancing fluorescence intensity to extend the limits of detection to new levels of sensitivity. Surface plasmon resonance (SPR) and metal enhanced fluorescence has long been a topic of research and has led to the development of prism- and grating-based SPR systems. However, with the wide coupling range and ease of exciting SPR on plasmonic gratings with a simple microscope objective, they have tremendous potential for revolutionizing the fields of plasmonics, fluorescence, and sensors. In an effort to better understand the influence of grating profile and metal film properties on the extraordinary fluorescence enhancement capabilities of plasmonic gratings, a novel microcontact printing process and different metal deposition techniques were used to fabricate silver gratings with varying grain diameters, roughnesses, heights, and duty cycles using thermal evaporation and RF sputtering. The resulting plasmonic gratings exhibited fluorescence enhancements up to 116× that of dye-coated glass slides using an epifluorescence microscope, much higher than more expensive prism-based SPR systems. This silver grating represents an extraordinary opportunity to quickly and easily enhance fluorescence and widen the detection limits of common fluorescence based assays with little to no equipment modification.

Plasmonic gratings with incorporated nanoprotrusions can replace traditional imaging substrates to extend the current detection limitations of fluoroimmunoassays and enable sub-diffraction limit image resolution.

We present an indium tin oxide/polymethylsilsesquioxane (ITO/PMSSQ) photonic crystal (PC) with grating structure. This topography exhibits multiple coupling resonances in specific regions of the solar spectrum, which can be controlled by tuning the angle and polarization of incident light as demonstrated through simulation and experimental results. The ITO/PMSSQ grating structures are prepared by simple soft lithography procedures using commercial HD-DVD and Blu-ray as template molds. The surface topography also includes geometrical singularities such as nanogaps and nanocones, which lead to further enhanced light trapping characteristics. Together, these singularity-embedded photonic crystal gratings result in concentrated electromagnetic fields at the aforementioned singularities, which could be especially helpful in separating the tightly bonded excitons in organic solar cells. Simulation shows an absorption enhancement over the full spectral range of ITO PCs-based solar cells with substantial increases closer to the band edge under s-polarized light.

Classical methods for enhancing the electromagnetic field from substrates for spectroscopic applications, such as surface-enhanced Raman spectroscopy (SERS), have involved the generation of hotspots through directed self-assembly of nanoparticles or by patterning nanoscale features using expensive nanolithography techniques. A novel large-area, cost-effective soft lithographic technique involving glancing angle deposition (GLAD) of silver on polymer gratings is reported here. This method produces hierarchical nanostructures with high enhancement factors capable of analyzing single-molecule SERS. The uniform ordered and patterned nanostructures provide extraordinary field enhancements that serve as excitatory hotspots and are herein interrogated by SERS. The high spatial homogeneity of the Raman signal and signal enhancement over a large area from a self-assembled monolayer (SAM) of 2-naphthalenethiol demonstrated the uniformity of the hotspots. The enhancement was shown to have a critical dependence on the underlying nanostructure via the surface energy landscape and GLAD angles for a fixed deposition thickness, as evidenced by atomic force microscopy and scanning electron microscopy surface analysis of the substrate. The nanostructured surface leads to an extremely concentrated electromagnetic field at sharp nanoscale peaks, here referred to as 'nano-protrusions', due to the coupling of surface plasmon resonance (SPR) with localized SPR. These nano-protrusions act as hotspots which provide Raman enhancement factors as high as 108 over a comparable SAM on silver. Comparison of our substrate with the commercial substrate Klarite™ shows higher signal enhancement and minimal signal variation with hotspot spatial distribution. By using the proper plasmon resonance angle corresponding to the laser source wavelength, further enhancement in signal intensity can be achieved. Single-molecule Raman spectra for rhodamine 6G are obtained from the best SERS substrate (a GLAD angle of 60°). The single-molecule spectrum is invariant over the substrate, due to the patterned ordered nanostructures (nano-protrusions).

We developed a novel plasmonic grating platform as a fluorescence-based temperature sensor for in-situ imaging of localized temperature and dynamic mapping of temperature in nanoscale due to photothermal heating of aluminum nanoparticles. Al/polymer nanoenergetics films with temperature sensitive dyes (Rhodamine 6G) were prepared and calibrated to obtain temperature-dependent dye fluorescence intensity. A tunable laser heating setup was developed for microscope imaging. We monitored the in-situ laser heating on Al/polymer/R6G systems by microscope and then constructed the spatial thermal mapping over time. Based on the fluorescence microscopic imaging, we can monitor Al nanoparticles movement and morphology changes for Al/polymer/Rhodamine 6G systems induced by laser heating. Al nanoparticles play an important role in laser heating due to the plasmonic, interband and intraband absorption characteristics of Al nanoparticles. Plasmonic grating platforms can not only significantly enhance the photothermal heating of Al compared with glass platforms, but also act as superlensing for sub-diffraction limited imaging of nanoparticles.

Surface reactions between heated aluminum nanoparticles (Al NPs) and thin α-MoO3 sheets are investigated. Localized photothermal heating on Al NP clusters is provided by a Raman spectrometer laser, while enhanced heating rates and imaging resolution are enabled by the use of a plasmonic grating substrate. Prominent linear reaction zones extending from Al NPs in the 〈001〉 crystal direction are observed on the surface of the host MoO3 sheets after heating. Raman spectroscopy and x-ray diffraction indicate that α-Al2O3 is generated within these extended reacted regions, while AFM and SEM indicate that the topology of the reaction regions are indistinguishable from the MoO3 host. We hypothesize that these Al2O3 zones are formed by surface diffusion and subsequent sub-surface adsorption of heated Al adatoms along the low-energy 〈001〉 MoO3 direction. Understanding and controlling these reaction mechanisms could lead to enhanced combustion of Al/MoO3 nanothermite systems.

Ultra-broadband strong absorption over 92% covering the infrared wavelength range of 1~6μm is demonstrated by using the tapered hyperbolic Au-SiO2 multilayer waveguides on glass substrates. Such broadband absorption is formed by the stop-light modes at various wavelengths located at different waveguide widths. A planar hyperbolic waveguide model is built to determine the stop-light modes by considering both forward and backward guided modes. The stop-light modes located inside the Au-SiO2 multilayer waveguide are simulated at the absorption peaks by reducing the Au loss. Tapered multilayer waveguides with varying top widths are further simulated, fabricated and measured, indicating the almost linear relation between the waveguide width and the stop-light wavelength. Moreover, the broadband absorption of tapered waveguide is proved to be angle-insensitive and polarization-independent, and the heat generation and temperature increase are also discussed.

We report the cost-effective fabrication of a plasmonic grating for improved light coupling in a fluorescence-based sensor platform by a simple micro-contact printing technique. The fluorescence of Rhodamine 6G (R6G) film on gratings was enhanced by up to 239-fold with respect to glass using a fluorescence microplate reader. The silver gratings are made suitable for use in biological buffers by a protective alumina layer. The platform has been optimized to detect Interferon-gamma (IFN δ ), a commonly used biomarker for M. tuberculosis infection and other autoimmune diseases, with an immunofluorescence assay. The platform demonstrates 500 fg/ml limit of detection (LOD) while commercial enzyme-linked immunosorbent assays (ELISA) report 2 pg/mL LOD. The extraordinary fluorescence enhancement was compared with simulation result to predict and support the experimental analysis. These results can be used to expand the platform for numerous fast, robust, sensitive biosensors.

The optical nonlocality in metal-dielectric multilayer metamaterials is characterized experimentally as a function of the angle of incidence with respect to the TE-polarized incident light. The physical mechanism of the difference between the nonlocal effective permittivity and the effective-medium-theory-based effective permittivity depending on the incident angle is theoretically revealed through the analysis of the band structure, the dispersion relation, and the iso-frequency contours according to the transfer-matrix method. Such effective permittivity difference is also retrieved in the metal-dielectric multilayers based on the measured transmission and reflection spectra.

The optical nonlocalities in metal-dielectric multilayer metamaterials are characterized as functions of incident angles for different polarizations. The measured epsilon-near-zero frequency shifts due to nonlocal effects agree with the theoretical analysis developed from transfer-matrix method.

This paper describes a tilted-target RF magnetron sputter deposition system to grow nanoparticles in a controlled way. With detailed characterization of ultra-high density (up to 1.1 × 10¹³ cm⁻²) and ultra-small size Pt nanoparticles (0.5-2 nm), it explains their growth and crystalline properties on amorphous Al₂O₃ thin films. It is shown that Pt nanoparticle size and number density can be precisely engineered by varying selected experimental parameters such as target angle, sputtering power and time of deposition to control the energy of the metal atoms in the deposition flux. Based on rate equation modelling of nanoparticle growth, three distinct growth regimes, namely nucleation dependent, coalescence dependent and agglomeration dependent regimes, were observed. The correlation between different nanoparticle growth regimes and the consequent crystal structure transformation, non-crystalline clusters → single crystalline nanoparticles → polycrystalline islands, is also discussed.

Epsilon-near-zero (ENZ) metamaterial slabs at visible frequencies based on metal-dielectric multilayers are experimentally realized. Transmission, reflection and absorption spectra are measured and used to determine the complex refractive indices and the effective permittivities of the ENZ slabs, which agree with the results obtained from both the numerical simulations and the optical nonlocalities analysis. Furthermore, light propagation in ENZ slabs and directional emission from ENZ prisms are also analyzed. The accurate determination of the ENZ wavelength for metal-dielectric multilayer metamaterial slabs is important for realizing many unique applications, such as phase front manipulation and enhancement of photonic density of states., Comment: 9 pages, 5 figures

We have developed and tested transparent microelectrode arrays capable of simultaneous amperometric measurement of oxidizable molecules and fluorescence imaging through the electrodes. Surface patterned microelectrodes were fabricated from three different conducting materials: Indium-tin-oxide (ITO), nitrogen-doped diamond-like carbon (DLC) deposited on top of ITO, or very thin (12 - 17 nm) gold films on glass substrates. Chromaffin cells loaded with lysotracker green or acridine orange dye were placed atop the electrodes and vesicle fluorescence imaged with total internal reflection fluorescence (TIRF) microscopy while catecholamine release from single vesicles was measured as amperometric spikes with the surface patterned electrodes. Electrodes fabricated from all three materials were capable of detecting amperometric signals with high resolution. Unexpectedly, amperometric spikes recorded with ITO electrodes had only about half the amplitude and about half as much charge as those detected with DLC or gold electrodes, indicating that the ITO electrodes are not as sensitive as gold or DLC electrodes for measurement of quantal catecholamine release. The lower sensitivity of ITO electrodes was confirmed by chronoamperometry measurements comparing the currents in the presence of different analytes with the different electrode materials.

Electrochemical microelectrodes are commonly used to detect spikes of amperometric current that correspond to exocytosis of oxidizable transmitter from individual vesicles, i.e., quantal exocytosis. We are developing transparent multi- electrochemical electrode arrays on microchips in order to automate measurement of quantal exocytosis. Here we report development of an improved device to target individual cells to each microelectrode in an array. Efficient targeting (~75%) is achieved using cell-sized micro-well traps fabricated in SU-8 photoresist together with patterning of poly (L-lysine) in register with electrodes to promote cell adhesion. The surface between electrodes is made resistant to cell adhesion using poly (ethylene glycol) in order to facilitate movement of cells to electrode “docking sites”. We demonstrate the activity of the electrodes using the test analyte ferricyanide and perform recordings of quantal exocytosis from bovine adrenal chromaffin cells on the device. Multiple cell recordings on a single device demonstrate the consistency of spike measurements and multiple recordings from the same electrodes demonstrate that the device can be cleaned and reused without degradation of performance. The new device will enable high-throughput studies of quantal exocytosis and may also find application in rapidly screening drugs or toxins for effects on exocytosis.

Electrochemical microelectrodes are commonly used to detect spikes of amperometric current that correspond to exocytosis of oxidizable transmitter from individual vesicles, i.e., quantal exocytosis. We are developing transparent multi- electrochemical electrode arrays on microchips in order to automate measurement of quantal exocytosis. Here we report the development of an improved device to target individual cells to each microelectrode in an array. Efficient targeting (∼75%) was achieved using cell-sized micro-well traps fabricated in SU-8 photoresist together with patterning of poly (L-lysine) in register with electrodes to promote cell adhesion. The surface between electrodes was made resistant to cell adhesion using poly (ethylene glycol) grafted to a poly (dopamine) adhesive in order to facilitate movement of cells to electrode microwells. We demonstrated the activity of the electrochemical microelectrodes using the test analyte ferricyanide and perform recordings of quantal exocytosis from bovine adrenal chromaffin cells on the devices. Dozens of cell recordings on a single device illustrated the consistency of recordings and multiple recordings from the same electrode demonstrated that the device could be cleaned and re-used without degradation of performance. The novel device will enable high-throughput studies of quantal exocytosis and may also have applications in rapidly screening drugs or toxins for effects on exocytosis. (Supported by NIH R01 NS048826.)

We are developing transparent multi- electrochemical electrode arrays on microchips in order to automate measurement of quantal exocytosis. Design goals are that one and only one cell be positioned directly over each electrode and working electrodes have μm-scale dimensions in order to resolve pA-level currents. Patterning of cell-adhesion molecules in register with electrodes using conventional photolithographic approaches is problematic because organic solvents can disable sensitive biomolecule films. We report the parylene “dry liftoff” approach pioneered by Ilic and Craighead (Biomed Microdev 2: 317, 2000) can be used to pattern single cell-electrode pairs on the chip. A 1 μm-thick parylene C film is deposited on the multi-electrode array and S1813 photoresist is spin coated onto the device and patterned. The unprotected parylene over the electrodes is then removed using Reactive Ion Etch. Poly-l-lysine (PLL) is then added to promote cell attachment. Chromaffin cells are loaded on the chip in standard culture media and left in an incubator overnight. Finally, the parylene film is peeled off to remove excess cells and PLL, leaving tightly adhered chromaffin cells at the desired locations. Importantly, we find that promoting cell attachment with PLL films does not passivate the electrochemical electrodes. Experiments are in process to explore an alternative approach whereby PLL is patterned using the dry liftoff approach but cells are added after peel off of the parylene. With this approach, cell attachment to inactive areas of the chip is blocked by using “cytophobic” materials such as Teflon AF. This alternative approach may allow efficient targeting of cells at lower cell densities as cells migrate from cytophobic areas to the electrode binding sites (Supported by NIH BRP grant RO1 NS048826).

In a survey for beta-thalassemia carrier status among students in the State of Punjab in India, a surprisingly large number were found to have an elevated red cell volume over 99 fl. The finding was predominantly but not exclusively in females. Similar student surveys from other states showed less macrocytosis. Follow-up tests in a group of affected students were carried out. Volunteers were asked to modify their diet then after six months they were provided with oral vitamin B12. The resulting changes are reported and the implications of the probable vitamin B12 and or folic acid deficiency are considered.

Single-electron transistors incorporating single ∼1 nm gold nanocluster (AuNCs) and pentacene as a complex charge transport system have been used to study the quantum Coulomb blockade and its single electron tunnelling behaviour at room temperature (RT) (300 K). Monodisperse ultra-small (0.86 ± 0.30 nm) AuNCs were deposited by the tilted-target sputtering technique into 12 nm nanogaps fabricated by high-resolution e-beam lithography. Tunnelling resistance was modulated to ∼10(9) Ω by addition of a pentacene layer, allowing clear observation of quantum staircases and Coulomb oscillations with on/off current modulation ratio of ∼100 in RT current-voltage measurements. The electron addition energy and average quantized energy level spacing were found to be 282 and 80.4 meV, respectively, which are significantly larger than the thermal energy at 300 K (25.9 meV).