Search

The purpose of this paper is to provide an in-depth review of plasmonic metal nanoparticles made from rhodium, platinum, gold, or silver. We describe fundamental concepts, synthesis methods, and optical sensing applications of these nanoparticles. Plasmonic metal nanoparticles have received a lot of interest due to various applications, such as optical sensors, single-molecule detection, single-cell detection, pathogen detection, environmental contaminant monitoring, cancer diagnostics, biomedicine, and food and health safety monitoring. They provide a promising platform for highly sensitive detection of various analytes. Due to strongly localized optical fields in the hot-spot region near metal nanoparticles, they have the potential for plasmon-enhanced optical sensing applications, including metal-enhanced fluorescence (MEF), surface-enhanced Raman scattering (SERS), and biomedical imaging. We explain the plasmonic enhancement through electromagnetic theory and confirm it with finite-difference time-domain numerical simulations. Moreover, we examine how the localized surface plasmon resonance effects of gold and silver nanoparticles have been utilized for the detection and biosensing of various analytes. Specifically, we discuss the syntheses and applications of rhodium and platinum nanoparticles for the UV plasmonics such as UV-MEF and UV-SERS. Finally, we provide an overview of chemical, physical, and green methods for synthesizing these nanoparticles. We hope that this paper will promote further interest in the optical sensing applications of plasmonic metal nanoparticles in the UV and visible ranges. [ABSTRACT FROM AUTHOR]

Citrate-capped silver nanoparticles (Ag@Cit NPs) were synthesized by a simple plasma-assisted reduction method. Homogenous colloidal Ag@Cit NPs solutions were produced by treating a A g N O 3 -trisodium citrate-deionized water with an atmospheric-pressure argon plasma jet. The plasma-synthesized Ag@Cit NPs exhibited quasi-spherical shape with an average particle diameter of about 5.9−7.5 nm, and their absorption spectra showed surface plasmon resonance peaks at approximately 406 nm. The amount of Ag@Cit NPs increased in a plasma exposure duration-dependent manner. Plasma synthesis of Ag@Cit NPs was more effective in the 8.5 cm plume jet than in the shorter and longer plume jets. A larger amount of Ag@Cit NPs were produced from the 8.5 cm plume jet with a higher pH and a larger number of aqua electrons, indicating that the synergetic effect between plasma electrons and citrate plays an important role in the plasma synthesis of Ag@Cit NPs. Plasma-assisted citrate reduction facilitates the synthesis of Ag@Cit NPs, and citrate-capped nanoparticles are stabilized in an aqueous solution due to their repulsive force. Next, we demonstrated that plasma-synthesized Ag@Cit NPs exhibited a significant degradation of methylene blue dye. [ABSTRACT FROM AUTHOR]

To understand the killing mechanism of fungal spores by plasma treatment, the optical, structural, and biological properties of the insect pathogenic fungus Cordyceps bassiana spores were studied. A nonthermal atmospheric-pressure plasma jet (APPJ) was used to treat the spores in aqueous solution. Optical emission spectra of the APPJ acquired in air indicated emission peaks corresponding to hydroxyl radicals and atomic oxygen. When the APPJ entered the aqueous solution, additional reactive species were derived from the interaction of plasma radicals with the aqueous solution. Fluorescence and absorption spectroscopy confirmed the generation of hydroxyl radicals and hydrogen peroxide in the plasma-activated water (PAW). Spore counting showed that plasma treatment significantly reduced spore viability. Absorption spectroscopy, circular dichroism (CD) spectroscopy, and agarose gel electrophoresis of the DNA extracted from plasma-treated spores showed a reduction in spore DNA content. The magnitude of the dip in the CD spectrum was lower in the plasma-treated spores than in the control, indicating that plasma treatment causes structural modifications and/or damage to cellular components. Tryptophan fluorescence intensity was lower in the plasma-treated spores than in the control, suggesting that plasma treatment modified cell wall proteins. Changes in spore viability and DNA content were attributed to structural modification of the cell wall by reactive species coming from the APPJ and the PAW. Our results provided evidence that the plasma radicals and the derived reactive species play critical roles in fungal spore inactivation. [ABSTRACT FROM AUTHOR]

Plasma-activated water (PAW) has emerged as a platform for sterilizing fungal pathogens. In this study, we investigated the influence of PAW on black melanized spores of Aspergillus brasiliensis to explore the mechanism of fungal spore inactivation. PAW was prepared by activating deionized water with a nonthermal atmospheric pressure air plasma jet (soft plasma jet). The concentrations of H 2 O 2 and N O x in the PAW treated by the soft plasma jet for 3 min were 50 μ M and 1.8 mM , respectively, and the pH of the PAW was 3.10. The reactive oxygen and nitrogen species (RONS) in the PAW increased with longer plasma activation time. After being treated for 30 min in the PAW with a plasma activation time of 3 min, the spore viability dramatically dropped to 15%. The viabilities of 0.3% H 2 O 2 - and 0.3% H N O 3 -treated spores were 22% and 42%, respectively. The breakage of the spore cell wall by the PAW was revealed in scanning electron microscope images and flow cytometry measurements. Disruption of cell wall integrity provides a path for intracellular components to escape and RONS of the PAW can attack intracellular components directly. Degradation of high molecular genomic DNA was also observed by agarose gel electrophoresis. These results suggest that long-lived reactive species generated in the PAW play an important role in the inactivation of melanized fungal spores. Consequently, PAW produced by a soft plasma jet can be applied to sterilize bioprotective walled fungal spores in a relatively large volume. [ABSTRACT FROM AUTHOR]

The linear and nonlinear optical properties of one-dimensional photonic crystals containing ZnO defects were studied by linear absorption spectroscopy and the femtosecond Z-scan technique. Photonic crystals containing ZnO defects, (Ta2O5/SiO2)5/ZnO/(SiO2/Ta2O5)5, were prepared using electron-beam deposition and magnetron sputtering. The transmission spectra of these photonic crystals revealed a defect mode resonance and a broad photonic band gap. The observed transmission spectra could be described by applying the optical transfer matrix formalism to the multilayer structure. When compared with the Z-scan curve of the ZnO film, that of the resonant photonic crystal exhibited a larger transmittance dip. The enhancement of the nonlinear absorption in the resonant photonic crystal is due to the strong confinement of the optical field. [ABSTRACT FROM AUTHOR]

Atmospheric-pressure A r plasma jets are known to be detrimental to Cordyceps pruinosa spores. However, it is not clear what kinds of reactive species are more effective with regard to fungal cell death. Herein, we study which reactive species plays pivotal roles in the death of fungal spores using an electric shock-free, atmospheric-pressure air plasma jet, simply called soft plasma jet. Plasma treatment significantly reduced the spore viability and damaged fungal DNA. As observed from the circular dichroism spectra, scanning electron microscope images, and flow cytometric measurements, cell wall integrity was decreased by reactive oxygen and nitrogen species (RONS) from the plasma itself and the plasma-activated water. Consequently, degradation of the spore cell wall allows RONS from the plasma to reach the intracellular components. Such plasma-induced intracellular RONS can attack spore DNA and other intracellular components, as confirmed by electrophoresis analysis and phosphorylated histone measurement. In addition, weakening of the spore cell wall allowed for the loss of intracellular components, which can lead to cell death. Plasma radicals were investigated by measuring the optical emission spectrum of the soft plasma jet, and intracellular reactive oxygen species were confirmed by measuring the fluorescence of 2′, 7′-dichlorodihydrofluorescein-diacetate ( H 2 D C F - D A )-stained spores. The soft plasma jet generated considerable amounts of H 2 O 2 and N O x but a very small number of O H radicals as compared to the atmospheric-pressure A r plasma jet; this indicates that plasma-induced long-lived reactive species ( H 2 O 2 and N O x ) play an important role in the weakening of spore cell walls and cell death. [ABSTRACT FROM AUTHOR]

A magnetic grating with a periodicity of 2 μm was generated by selective crystallization of an amorphous Cu2MnSn thin film using femtosecond laser pulses. By irradiating the amorphous Cu2MnSn thin film with two-beam interference pattern of femtosecond laser pulses, alternating bands of ferromagnetic and paramagnetic phases were produced. The crystallized region was composed of ferromagnetic Cu2MnSn grains, whereas the amorphous region remained paramagnetic. Because crystallized Cu2MnSn is the only ferromagnetic phase that can be produced by heat-treatment of the amorphous Cu2MnSn thin film, a magnetic grating with high definition was produced. Moreover, the periodicity of the modulated structure can be reduced down to a submicrometer scale and extended to two dimensions so that the technique could be potentially utilized for magnetic patterning. [ABSTRACT FROM AUTHOR]

Femtosecond laser-interference induced amorphization (FLIA) was used to form a spatially periodic magnetic structure by selectively amorphizing the surface of bulk Co2MnSi. Regularly spaced alternating lines with a periodicity of 2 μm were produced by FLIA. Magnetic force microscopy of the samples clearly revealed one-dimensional periodic magnetic domains resulting from the modulated surface structure which was confirmed by transmission electron microscopy. The periodicity of the modulated structure can be further decreased or the process can be modified to write two-dimensional pattern so that the resulting magnetic structure can be potentially utilized for a permanent magnetic identification. [ABSTRACT FROM AUTHOR]

In this study, we have studied the scavenging effects of radical scavengers (ascorbic acid and mannitol) on •OH radicals generated inside water by an atmospheric pressure plasma jet. Plasma was generated by using a sinusoidal power supply (applied voltage: 2.4 kV, frequency: 40 kHz) at a constant argon gas flow rate of 400 sccm and it was characterized by electrical and optical measurements. The technique of ultra-violet (UV) absorption spectroscopy was applied to investigate the effects of scavenging at 3, 6 and 9 mm depths below the water surface by using terephthalic acid as a •OH radical sensitive probe. Also, the effects of scavenging were studied by changing the concentration of radical scavengers and plasma exposure time. For both radical scavengers, the reduced concentrations of •OH radicals were found to decrease with increasing depths as their production would also be reduced by decreasing intensities of plasma-initiated UVs with increasing depths. The effectiveness of ascorbic acid on the scavenging of •OH radicals appeared much stronger than mannitol at all depths inside water since the deprotonated form of ascorbic acid consumes two •OH radicals whereas mannitol consumes only one. Also, the reduced concentration of OH radicals with addition of scavengers was found to be increased under longer plasma exposure time even though the generation of OH radicals were also increased. The detailed mechanism on the formation of •OH radicals inside water has been discussed along with the causes of scavenging. These results can be an important milestone in the applications of non-thermal plasma sources requiring the reduction of •OH radicals. [ABSTRACT FROM AUTHOR]

Femtosecond laser-interference crystallization (FLIC) was used to form a spatially periodic magnetic structure by selectively crystallizing a paramagnetic amorphous Co2MnSi thin film. Regularly spaced alternating lines of polycrystalline and microcrystalline regions with a periodicity of 2 μm were produced by FLIC. The crystalline region composed of ∼100-nm-sized grains contained a nonequilibrium ferromagnetic phase intermixed with β-Mn. The areas between the crystallized lines also received sufficient energy, crystallizing into a microcrystalline state with its grain size ranging from 1 to 5 nm. The magnetic force microscopy of the samples clearly revealed the one-dimensional periodic magnetic domains resulting from the modulated microstructure. [ABSTRACT FROM AUTHOR]

New photopolymers were designed and prepared using the thermoplastic and photoreactive binders. Poly (vinylacetate-co-vinylalcohol) was used as a thermoplastic polymer binder and 3-isopropenyl-α,α-dimethylbenzyl isocyanate (m-TMI) was tethered to the side chain of the above polymer. The holographic gratings were successfully fabricated in these photopolymer film samples by conventional optical interference method. The dynamic behaviors of the grating formation were studied with the change of exposure intensity. The effect of photoreaction between the polymer binder and the newly-formed polymer in the constructive region on the diffraction behavior and its stability was also investigated. [ABSTRACT FROM AUTHOR]

This research investigated the capture of nitrate by magnesium ions in plasma-activated water (PAW) and its antifungal effect on the cell viability of the newly emerged mushroom pathogen Cryptococcus pseudolongus. Optical emission spectra of the plasma jet exhibited several emission bands attributable to plasma-generated reactive oxygen and nitrogen species. The plasma was injected directly into deionized water (DW) with and without an immersed magnesium block. Plasma treatment of DW produced acidic PAW. However, plasma-activated magnesium water (PA-Mg-W) tended to be neutralized due to the reduction in plasma-generated hydrogen ions by electrons released from the zero-valent magnesium. Optical absorption and Raman spectra confirmed that nitrate ions were the dominant reactive species in the PAW and PA-Mg-W. Nitrate had a concentration-dependent antifungal effect on the tested fungal cells. We observed that the free nitrate content could be controlled to be lower in the PA-Mg-W than in the PAW due to the formation of nitrate salts by the magnesium ions. Although both the PAW and PA-Mg-W had antifungal effects on C. pseudolongus, their effectiveness differed, with cell viability higher in the PA-Mg-W than in the PAW. This study demonstrates that the antifungal effect of PAW could be manipulated using nitrate capture. The wide use of plasma therapy for problematic fungus control is challenging because fungi have rigid cell wall structures in different fungal groups. [ABSTRACT FROM AUTHOR]

Polyethylene glycol-functionalized gold nanoparticles (Au@PEG NPs) were prepared by a simple plasma-assisted method without additional reducing chemicals. After irradiating tetrachloroauric acid (HAuCl4) and polyethylene glycol (PEG) in aqueous medium with an argon plasma jet, the gold precursor transformed into an Au@PEG NP colloid that exhibited surface plasma resonance at 530 nm. When the plasma jet entered the water, additional reactive species were induced through interactions between plasma-generated reactive species and aqueous media. Interaction of the gold precursor with the plasma-activated medium allowed the synthesis of gold nanoparticles (AuNPs) without reductants. The plasma-synthesized Au@PEG NPs had a quasi-spherical shape with an average particle diameter of 32.5 nm. The addition of PEG not only helped to stabilize the AuNPs but also increased the number of AuNPs. Au@PEG NP-loaded paper (AuNP-paper) was able to detect the degradation of rhodamine B, therefore, indicating that AuNP-paper can act as a surface-enhanced Raman scattering platform. Dye degradation by plasma treatment was investigated by optical absorption and Raman spectroscopy. The method proposed for the fabrication of Au@PEG NPs is rapid, low-cost, and environment-friendly and will facilitate the application of plasma-synthesized nanomaterials in sensors. [ABSTRACT FROM AUTHOR]

Poly(2-fluoro-1,4-phenylenevinylene), PFPV, and its copolymers have been synthesized via water soluble precursor route and their electrical and optical propreties were measured. It seems that electron-withdrawing fluorine substituent on phenylene ring increases the band-gap of PFPV and it affects electrical and optical properties. The conductivity values of FeCl-doped drawn polymer films ranged from 10 to 10 Scm depending on their composition, and were 10 times larger than those of undrawn ones. The χ value for undrawn PFPV, using THG technique at 1907nm fundamental wavelength, was 4.76x10 esu. [ABSTRACT FROM AUTHOR]

In this research, we successfully fabricated ZnO-nanorod grating by carrying out femtosecond-laser modification of the seed layer. First, a Ag-doped ZnO seed layer was deposited on a glass substrate by dc/rf magnetron co-sputtering, in which rf and dc power sources were utilized for the ZnO and the Ag targets, respectively. Next, a seed grating was produced on the seed layer by using the two-beam interference of femtosecond-laser pulses. Finally, a ZnO-nanorod grating was grown on the seed grating by chemical bath deposition in an aqueous solution of Zn(NO3)2 and hexamethyltetramine. The scanning-electron-microscopy images indicate that the ZnO-nanorod grating can be regarded as a spatially periodic structure consisting of alternating bands of ZnO nanorods with relatively large and small diameters. The selected-area electron-diffraction patterns of the seed grating reveal that the formation of the ZnO-nanorod grating is attributable to the spatially selective modification of the seed layer produced by femtosecond-laser pulses. [ABSTRACT FROM AUTHOR]

Nanocrystalline silicon gratings were fabricated by applying both femtosecond-laser-interference crystallization and post thermal annealing to amorphous silicon (a-Si) nanoclusters embedded within a silicon nitride matrix. Catalytic chemical vapor deposition was used to fabricate the embedded a-Si nanoclusters, and the formation of a-Si nanoclusters was confirmed by photoluminescence spectroscopy. The femtosecond laser interference technique was employed to produce a seed pattern for the spatially-selected crystallization of a-Si nanoclusters. Micro-Raman spectroscopy and selected-area electron diffraction, together with high-resolution transmission-electron microscopy, show that nanocrystalline silicon gratings were formed through an amorphous-to-crystalline transformation with femtosecond laser pulses, and that the degree of crystallization was enhanced by applying post thermal annealing to the seed gratings. [ABSTRACT FROM AUTHOR]

9-(2-Ethyl-hexyl)-3-[2-(4-methanesulfonyl-phenyl)vinyl]-9H-carbazole (EHCS) was synthesized as a monolithic photorefractive molecule forming low T[sub g](∼25 °C) organic glass. It showed distinct photoconductivity due to the carbazole moiety and the optical nonlinearity by the push-pull structure. The EHCS glass showed excellent optical quality and great stability as the ethylhexyl group effectively suppressed the crystallization in the films. Also, the extremely simple structure of EHCS contributed to a very high chromophore concentration. This single-component photorefractive glass of EHCS showed large net gain (56.3 cm-1) and diffraction efficiency (12%). Photorefractivity of EHCS glass was greatly improved by doping with a small amount (<1%) of 2,4,7-trinitrofluorenone (TNF). The two-beam coupling gain of samples with TNF was 113 cm-1 and the diffraction efficiency was 29%. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]