A simple two-step seed-mediated method has been developed to synthesize chitosan (CS)-supported core–shell metal nanoparticles (NPs) in aqueous solution. CS-supported copper NPs (CS–Cu NPs), when treated with silver nitrate (AgNO₃) solution, resulted in Ag shells on Cu NP cores in the composite. The Cu@Ag NPs in the CS composite were characterized and found to be spherical in shape with an average particle size of 14.0 ± 3.4 nm. The antibacterial efficacy of the CS–Cu@Ag NP composite was evaluated on Gram-negative Escherichia coli and Gram-positive Bacillus cereus bacteria using turbidity measurement as well as flow-cytometry. Results demonstrated enhanced bactericidal activity of the composite. Analytical techniques, used to elucidate the mode of bactericidal action, revealed that the superior antibacterial activity of the CS–Cu@Ag NP composite was due to synergistic effects of CS and Cu@Ag NPs. The proposed mode of antibacterial action involves the electrostatic binding of CS to the bacterial cell wall and simultaneous interaction of Cu@Ag NPs with membrane proteins leading to perforation of the cell membrane and release of intracellular material.

Temperature dependent aggregation reaction of partially bare gold nanoparticles showed a first order kinetics and prevalence of reaction limited colloidal aggregation with an activation energy equal to 36.2 ± 3.0 kJ mol⁻¹.

The presence of citrate-stabilized gold nanoparticles (cit-Au NPs) significantly enhanced the specific activity of α-amylase, which could also be modulated by varying the concentration of the enzyme, while keeping the NP concentration constant. Also, the lowest concentration (0.175 μg mL⁻¹) at which the Michaelis–Menten behavior of the enzyme could clearly be observed in the presence of NPs was much less than that in their absence. At higher protein concentrations the activity decreased monotonically until it reached nearly the same as that of free enzyme, while exhibiting Michaelis–Menten kinetics at all concentrations. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) based particle size analyses indicated increased agglomeration of the NPs with increased protein concentration. The results have been explained based on a model which considered the presence of enzyme bound to NP and that available for enhanced catalysis, enzyme bound to NP but unavailable due to being buried inside the agglomerate and the free enzyme.

Single-particle level white-light-emitting carbon dots via a one-step microwave synthesis.

Programmed assembly of “few atom” quantum clusters may offer superior physicochemical properties of the new material in comparison to the constituents. We report the formation of a luminescent crystalline inorganic complex, consisting of Zn²⁺ ions and L-histidine plus mercaptopropionic acid stabilized Au₁₄ nanoclusters, with a complexation constant of (9.7 ± 6.6) × 10⁶ M⁻¹. Analytical investigations, supported by computational modelling, indicated the hexagonal structure of the crystal. The crystalline complex exhibited superior luminescence in comparison to ligand stabilized gold nanoclusters. Importantly, the complex stored hydrogen reversibly at room temperature, accompanied by change in the luminescence playing the role of sensing. The hydrogen adsorption capacity of the complex was determined to be 0.244 mM per gram of the complex at 20 °C and 20 bar.