Au–Ag alloy nanoparticles, synthesized using wolfberry fruit extract, showed linearly tunable photocatalytic activity through changing alloy composition and synthesis parameters.

A prospective diagnosis method for coronary heart disease (CHD) using human urine based on surface-enhanced Raman spectroscopy (SERS) is proposed, and could provide valuable information for judging whether to perform percutaneous coronary intervention (PCI) in clinics. Here, urine samples from 87 patients with CHD, including patients with PCI before operation (degree of cardiovascular congestion above 70%) and without PCI (degree of cardiovascular congestion under 70%), and 20 healthy humans were measured using SERS. Principal component analysis (PCA) combined with linear discriminant analysis (LDA) was employed to analyze the SERS spectra, revealing that the classification sensitivity and specificity were 90% and 78.9%, respectively, and the absolute value for loading of PC1 at 1509 cm-1 was the largest. Since platelet-derived growth factor-BB (PDGF-BB) is closely related to CHD, PDGF-BB aqueous solutions with various concentrations (1, 0.5, 0.1, 0.05 and 0.01 ppm) and a mixture of healthy human urine and PDGF-BB aqueous solutions were then investigated in this work, and it was found that the Raman peak at 1509 cm-1 may be attributed to PDGF-BB. Moreover, the measured SERS spectra of all the urine samples from the 87 patients with CHD were compared with the clinical data provided by a hospital, and it was revealed that the appearance of a peak at 1509 cm-1 in the SERS spectra was in good agreement with the results of coronary angiography tests when cardiovascular congestion was above 70%. This indicated that the classification sensitivity and specificity were 87.9% and 87.0%, respectively, through identification of the Raman peak at 1509 cm-1.

Au-Ag alloy nanoparticles (NPs) less than 10 nm in size were synthesized using sucrose as a reductant and surfactant. Au-Ag alloy NPs with a homogeneous composition were continuously obtained by changing the synthesis time from 2 to 40 min in one pot. Based on the UV-Vis, ICP, TEM, HR-TEM, EDX and SAED analyses, the synthesis mechanism of Au-Ag alloy NPs was deduced. Under hydrolysis conditions, sucrose showed a stronger reducibility compared with glucose, fructose and their mixture. And the as-prepared Au-Ag alloy NPs exhibited a superior photocatalytic activity and stability for the reduction of 4-nitrophenol due to the abundant hydroxyl groups of sucrose and the synergistic effect between Au and Ag elements. The rate constant of 4-nitrophenol reduction could be linearly controlled by the composition of Au-Ag alloy NPs or their synthesis time. It was indicated that the photocatalytic activity of Au-Ag alloy NPs could be predetermined as early as their synthesis process. The above methods of controlling the rate constant provide promising routes for other photocatalytic reactions using bimetallic NPs as photocatalysts.