Yongan Tang

A Review on Preparation and Applications of Silver-Containing Nanofibers

Silver-containing nanofibers are of great interest recently because of the dual benefits from silver particles and nanofibers. Silver nanoparticles are extensively used for biomedical applications due to the antibacterial and antiviral properties. In addition, silver nanoparticles can excite resonance effect of light trapping when pairing with dielectric materials, such as polymer. Comparing to the traditional fabrics, polymer nanofibers can provide larger number of reaction sites and higher permeability contributed to their high surface-to-volume ratio and high porosity. By embedding the silver nanoparticles into polymer nanofiber matrix, the composite is promising candidates for biomaterials, photovoltaic materials, and catalysts. This work demonstrates and evaluates the methods employed to synthesize silver nanoparticle-containing nanofibers and their potential applications.

Optical switching in a resonant Fabry-Perot saturable absorber

We experimentally demonstrate optical switching in a Fabry–Perot saturable absorber using a pump–probe technique. The saturable absorbers are multiple quantum wells, 35 and 42 pairs of alternating layers of 7 nm thick compressively strained Ga0.42In0.58AsP. These quantum wells are separated by 8 nm thick InP barriers. The reflectivity of these samples as a function of the input optical power is theoretically and experimentally investigated. A switching rate of better than 20 MHz is observed. This optical switching is based on the mechanism of controlling the reflectivity of the Fabry–Perot saturable absorber, while operating at its resonant wavelength, by the pump power. Optical switching speed of 10 ns is possible.

Metallic nano-structures for polarization-independent multi-spectral filters

Cross-shaped-hole arrays (CSHAs) are selected for diminishing the polarization-dependent transmission differences of incident plane waves. We investigate the light transmission spectrum of the CSHAs in a thin gold film over a wide range of features. It is observed that two well-separated and high transmission efficiency peaks could be obtained by designing the parameters in the CSHAs for both p-polarized and s-polarized waves; and a nice transmission band-pass is also observed by specific parameters of a CSHA too. It implicates the possibility to obtain a desired polarization-independent transmission spectrum from the CSHAs by designing their parameters. These findings provide potential applications of the metallic nano-structures in optical filters, optical band-pass, optical imaging, optical sensing, and biosensors.

Metallic nano-particles for trapping light

We study metallic nano-particles for light trapping by investigating the optical absorption efficiency of the hydrogenated amorphous silicon thin film with and without metallic nano-particles on its top. The size and shape of these nano-particles are investigated as to their roles of light trapping: scattering light to the absorption medium and converting light to surface plasmons. The optical absorption enhancement in the red light region (e.g., 650nm) due to the light trapping of the metallic nano-particles is observed when a layer of metallic nano-particle array has certain structures. The investigation of the light with incident angles shows the importance of the coupling efficiency of light to surface plasmons in the metallic nano-particle light trapping.PACS73.20.Mf, 42.25.s, 88.40.hj

Superior Antibacterial Activity of Photochemical Synthesized Ag-CNTComposites and their Synergistic Effects in Combination with otherAntimicrobial Agents

Silver nanoparticle-modified multiwalled carbon nanotubes (MWCNTs) nanocomposites (AgCNTs) were synthesized by photochemical reduction method, their antimicrobial effect on both Gram negative and Gram positive bacteria, using E. coli and Bacillus anthracis as model bacteria, respectively, were investigated. The results indicated that AgCNTs exhibited more potent antibacterial effects against both Gram negative and Gram positive bacterium compared to Ag nanoparticles (Ag NPs). The minimal inhibitory concentrations (MICs) of AgCNTs against E. coli cells (0.5 μg/mL) and B. anthracis cells (0.8 μg/mL) was 1/20 times and 1/17.5 of the MICs of Ag NPs against E. coli and B. anthracis, respectively. Further study on the antibacterial effect of combination treatment of AgCNTs with oxidizing antimicrobial agents (NaOCl or H2O2) to E. coli cells indicated a partial synergistic or a synergistic effect using the fractional inhibitory concentration (FIC) index test or isololograms. The combination treatment of AgCNTs with a natural peptide, nisin, also exhibited enhanced inhibitory effect on E. coli growth, as significant delays in growth of E. coli cells treated by the combination of 0.2 μg/mL AgCNTs and 4 or 8 μg/mL nisin was observed compared to AgCNTs alone nisin alone treatment. The synergistic or enhanced effect of the combination of AgCNTs with other antimicrobial relied on the combination of different action mechanisms in which AgCNTs played a role to damage cell membrane which allowed easier access for other small antimicrobial molecules to penetrate into cells. Such combination strategy could be broadly applicable to the improvement of existing antimicrobial methods or design/discover new effective antimicrobial agents/methods.

Electrospun Polymer Nanofibers Decorated with Noble Metal Nanoparticles for Chemical Sensing

The integration of different noble metal nanostructures, which exhibit desirable plasmonic and/or electrocatalytic properties, with electrospun polymer nanofibers, which display unique mechanical and thermodynamic properties, yields novel hybrid nanoscale systems of synergistic properties and functions. This review summarizes recent advances on how to incorporate noble metal nanoparticles into electrospun polymer nanofibers and illustrates how such integration paves the way towards chemical sensing applications with improved sensitivity, stability, flexibility, compatibility, and selectivity. It is expected that further development of this field will eventually make a wide impact on many areas of research.

Antibacterial effects of carbon dots in combination with other antimicrobial reagents

This study was designed to investigate the antimicrobial effects of CDots in combination with other antimicrobial reagents, including H2O2, Na2CO3, and AcOH (acetic acid). CDots were synthesized and passivated with 2,2’-(ethylenedioxy)bis(ethylamine) (EDA). The minimal inhibitory concentration (MIC) of CDots was 64 μg/mL on both Gram negative bacteria E.coli cells and Gram positive bacteria Bacillus subtilis cells. When CDots were combined with H2O2, antibacterial synergistic effects were observed based on the fractional inhibitory concentration (FIC) index, and further confirmed by an isobologram analysis and viable cell number counting methods. With the combination treatment of 10 μg/mL CDots with 8.82 mM H2O2, the viable E.coli cell numbers decreased 2.46 log, which was significant lower than the log reduction from 8.82 mM H2O2 (1.57 log) or 10 μg/mL CDots (0.14 log) treatment alone. However, the combination of CDots with Na2CO3 or AcOH did not show synergistic effects, instead, exhibiting indifference effects according to the FIC index. This study indicated that the combination of CDots with their synergistic antimicrobial reagents, such as H2O2, could reach the goal of inhibiting bacteria growth by using lower concentration of each individual chemical in the combination than using one chemical treatment alone, reduce the risks imposed on environmental health and the possibilities of the development of microbial resistances.

ANTIMICROBIAL EFFECTS OF CARBON NANOTUBES

Inactivation of pathogens from environment and inhibition of biofilm formation on various surfaces are important for biosafety, biosecurity and public health. Carbon nanotubes (CNTs) possess antimicrobial effects in addition to their unique optical, electrical, mechanical and thermal properties. This review summarizes the antimicrobial effects of single walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) in suspensions and on CNT contained surfaces. To increase antimicrobial effects, CNT composites containing other antimicrobial reagents are introduced. Also described are the possible antimicrobial mechanisms of CNTs.

Comparison of wavelength conversion in SOA and EDFA fiber ring systems

We report on two types of wavelength conversion techniques that are based on gain saturation effect in semiconductor optical amplifier (SOA) and erbium doped fiber amplifier (EDFA). In these amplifiers the gain saturation occurs when the optical density at the gain medium is high enough to result in depletion of the population inversion by stimulated emission. In each case, the fiber ring laser is assembled using a variable fiber coupler, a narrowband optical filter and the gain medium. For external input power values higher than the determined threshold value of the ring resonator, the gain will be saturated. Because the wavelength of the external laser is different from the oscillating wavelength of the ring resonator, the optical power at the output of the resonator is drastically decreased (low-state). On the other hand, when the input of the external laser is below the threshold value the output power of the resonator increases (high-state). In our experiment the operating wavelengths of the ring resonators are 1314 nm and 1553 nm for the SOA and EDFA respectively. The input signal is modulated around the threshold value for frequencies of 20 MHz and 1 MHz and resonator lengths of around 8 m and 16 m for the SOA and EDFA cases respectively. Both systems exhibit high contrast modulation of 41 dB and 33 dB at the output port for the low/high states of the SOA and EDFA ring lasers respectively.

LIGHT PROPAGATING IN METAL SUB-WAVELENGTH-HOLE ARRAYS

We investigate the light propagating through a sub-wavelength-hole array in a thin gold film. The extraordinary light transmission (ELT) of the metallic array is observed. This ELT is due to the localized plasmon polaritons, whose production are dependent on the polarization of the light, the periodicity of the array, the features of the hole, and the thickness of the gold film. These parameters of the metallic structures are investigated through the finite difference time domain method. It is possible to obtain a desired transmission spectrum from the sub-wavelength-hole array by designing these parameters.