Gold-nanoparticle-based colorimetric array for detection of dopamine in urine and serum.

A highly selective method is presented for the colorimetric determination of dopamine (DA) using gold nanoparticles (AuNPs). DA caps on the surface of AuNPs (DA-AuNPs) induces the aggregation of AuNPs in alkaline solution. The DA-AuNPs are modified by the hydrolysate of thioglycolic acid (TGA(2)(-)) through Au-S bonds. The aggregation of AuNPs is accelerated by TGA(2-), due to the strong hydrogen-bonds (NH⋯OC and OH⋯OC) formed between TGA(2)(-) and DA. Upon the addition of DA, the solution shows a color change from red to purple (or yellow), which is also monitored to detect DA in human urine and fetal bovine serum samples. Here, the limits of colorimetric detection are as low as 10(-7)M observed in Milli-Q water, urine and serum. Based on UV-vis absorption spectra, the limits of detection have been calculated to be 3.3×10(-8)M, 1.0×10(-7)M and 9.4×10(-8)M in Milli-Q water, urine, and serum, respectively. All the limits of detection are lower than the lowest abnormal concentrations of DA in urine (5.7×10(-7)M) and blood (1.6×10(-5)M). The good linear ranges from 0 to 10(-6)M are used for the quantitative assay of DA in urine and serum samples. The applicability of our detection system is also verified by analysis of DA in urine and serum samples. The developed approach is without using complex financial instruments.

Plasmonic enhancement of the upconversion fluorescence in YVO4:Yb³âº, Er³âº nanocrystals based on the porous Ag film.

The upconversion luminescence (UCL) enhancement based on the surface plasmonic resonance (SPR) of noble metals is a promising way to improve UCL efficiency. However, it is still a challenge to achieve stable and effective UCL enhancement. Here, we present the preparation of the porous Ag/YVO4:Yb(3+), Er(3+) composite film via a simple double annealing method. It is exciting to observe that a maximum 36-fold ((2)H11/2-(4)I15/2) and 30-fold ((4)S3/2-(4)I15/2) UCL enhancement in the porous Ag/YVO4:Yb(3+), Er(3+) composite film, attributed to the effective coupling between SPR and the excitation light by adjusting the SPR peak to the excitation wavelength, controlling the effective coupling distance and improving the scattering-absorption ratio. Furthermore, the enhancement factor strongly depended on the excitation power and the Er(3+) concentration.

Geometries, stabilities and electronic properties of beryllium-silicon Be2Si(n) clusters.

The equilibrium geometries, growth patterns, stabilities, and electronic properties of bimetallic Be2Si(n) (n = 1-11) clusters are systematically investigated at the B3LYP/6-311G(d) level of theory. Harmonic vibrational analysis has been performed to assure that the optimized geometries are stable. The optimized results suggest that the three-dimensional structures are observed for the most stable isomers of Be2Si(n) clusters when n > 2. The calculated vertical ionization potential for the lowest-energy isomers are comparable to the experimental values of Si(n+2). According to the averaged binding energy, fragmentation energy, second-order energy difference and HOMO-LUMO gaps calculations, we identify that the Be2Si2 and Be2Si5 clusters are more stable, and Be atoms doping enhance the chemical reactivity of the Si n host. The natural population and natural electron configuration analyses indicate that the Be atoms possess positive charge at n = 1-5 but negative charge at n = 6-11. The chemical hardness of Be2Si(n) clusters show three local maxima at n = 2, 5, and 9, whereas three local minima are found for the corresponding chemical potential, meaning these clusters are more stable than their neighboring cluster sizes.

Multiple-image encryption and authentication with sparse representation by space multiplexing.

A multiple-image encryption and authentication approach by space multiplexing has been proposed. The redundant spaces in the previous security systems employing sparse representation strategy are optimized. With the proposal the information of multiple images can be integrated into a synthesized ciphertext that is convenient for storage and transmission. Only when all the keys are correct can the information of the primary images be authenticated. Computer simulation results have demonstrated that the proposed method is feasible and effective. Moreover, the proposal is also proved to be robust against occlusion and noise attacks.