An easy synthesis of autofluorescent alloyed silver-gold nanoparticles

A one-pot synthesis of fluorescent bimetallic silver-gold nanoparticles in aqueous medium is presented. Carboxylic acid-functionalized nanoparticles were prepared with different metal compositions from 90 : 10 to 10 : 90 (n : n) for silver : gold with a diameter of 1.8 ± 0.4 nm. Pure silver and gold nanoparticles were prepared for comparison. Spectroscopic analyses showed that the ligand, i.e. 11-mercaptoundecanoic acid, binds to the particle surface by the thiol group, leaving the carboxylic acid accessible for further functionalization, e.g. by suitable coupling reactions. Nanoparticles with a silver content up to 60 : 40 showed autofluorescence with a large Stokes shift of about 250-300 nm (maximum wavelength of the emission between 608 nm and 645 nm). The intracellular localization of bimetallic silver-gold nanoparticles was studied in HeLa cells by confocal laser scanning microscopy (CLSM). The alloyed silver-gold nanoparticles showed no significant cytotoxicity at a metal concentration of 5 μg mL^-1 for 24 h, but were cytotoxic to some degree at 50 μg mL^-1 at higher silver content.