Electrochemical Sensing on a Nanostructured Silicon Mass Spectrometry Surface

Mass Spectrometry (MS) is a widely used analytical tool that provides quantitive information (molecule weight and intensity) of the analyte. Nanostructured silicon-based surface-assisted desorption/ionization mass spectrometry (LDI-MS) provides matrix-free and high sensitivity advantages. However, the mass spectrometer is a large and expensive tool limiting the onsite screening or point-of-care testing applications. Electrochemical sensing, on the other hand, is a simple and less-expensive detection method that can be used as portable onsite screening purposes. If the nanostructure silicon (nSi) surface can be used for electrochemical sensing, it opens the possibility of using nSi surface for both electrochemical sensing and Mass Spectrometry (MS) detection. Therefore, in this paper, we demonstrate the feasibility of using nSi surface for electrochemical sensing. Effects of the major nSi surface process parameters, including metal-assisted etching time and electroless Au decoration/deposition time to the electrochemical was evaluated.

Synthesis and Simulation of Nano-Composite Metamaterial for Broadband Negative Refractive Index in Visible Spectral Regime

In this paper, a nano-metamaterial with the structure of Ag-SiO2-PbTe is proposed that has a random arrangement in the host medium of expanded polystyrene (foam) for the realization of a broadband negative refractive index at the visible spectrum. The negative refractive index for the purposed meta-material was obtained from the plasmonic resonance in the core and outer layer for both electric and magnetic components of light. Here, we use different radii for the outer layer of nanoparticles to create the broadband negative permeability. In this way, the doped semiconductor nanoparticles are included in the host medium to create the broadband negative permittivity. The overlap between the spectrum of the negative permittivity and permeability introduces the broadband negative refractive index at the visible band. The novel introduced structure creates the broadband negative refractive index and it is simple and practical for fabrication. For the realization of the proposed material, synthesis and characterization of the designed nanocomposite structure are investigated. To this end, the absorption and the transmission coefficients of the synthesized material are measured and compared with theoretical results. The obtained results indicate that the numerical simulations using Mie theory have good agreement with the experimental results.

Effect of Gold Nanoparticle Aggregation on the Kinetic Aspect of AuNPs/DNA Interactions

Since successful therapy for curing cancer and others genetic diseases requires the transport of DNA into the cell by delivery vehicles, the understanding of the factors that control the complexation and condensation of the DNA is a key problem. During the last decade, researchers have developed some uses of nanoparticles-DNA systems, the majority of these studies dealing with NPs, which are covalently bound to the DNA. However, the kinetic aspect of AuNPs/DNA system by non-covalent interactions is less explored. Moreover, the role of high salt concentrations in these studies is of great interest due to the majority of nanoparticles have a great tendency to aggregate upon exposure to biological medium, significantly alter the uptake extent, rate, and mechanism of AuNPs/DNA interaction. As a contribution to this field, we have studied kinetics aspects of the binding of small tiopronin gold nanoparticles, AuNPs, to double stranded DNA in at high salt concentration by using the stopped-flow technique. The kinetic curves are biexponential and reveal the presence of two kinetic steps. Moreover, AFM studies reveal AuNPs aggregation in the presence of high salt content, while the same particle are well-dispersed in water. A two-step series mechanism reaction scheme was proposed. According to the reaction scheme, the formation of an intermediate complex formed by aggregated gold nanoparticles and DNA precedes the rate-determining step of the reaction.