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.