Synthesis of hydrophilic Ag₂Se quantum dots optically optimized by multivariate strategies: an easy one-pot approach

Near-infrared-emitting quantum dots (QDs) are very interesting for (bio)medical uses because they penetrate biological tissues more deeply and emit light in the biological diagnostic window, that is, the region from 650 to 1450 nm. Among the semiconductors with appropriate band gaps to provide photoluminescence at wavelengths longer than 650 nm, silver chalcogenides are distinguished mainly by being environmentally friendly. This work proposes the use of experimental design techniques to optimize a one-pot aqueous procedure to synthesize photoluminescent silver selenide (Ag₂Se) QDs capped with mercaptosuccinic acid (MSA). The best conditions found were Ag/Se and MSA/Ag molar ratios of 8 : 1 and 6 : 1, respectively, pH 5.0, and stirring for 20 minutes at 60 °C. The Ag₂Se nanocrystals synthesized under those experimental parameters showed a photoluminescence quantum yield of 16.3%, absorption edge at 583 nm, and emission within the biological diagnostic window, at 789 nm, with orthorhombic crystal structure and an average diameter of 5.7 nm.