There are several methods reported to reduce silver ion into zero-valent silver atoms:
*Chemical Reduction. Chemical reductants can reduce silver ions into silver nanoclusters. Some examples of chemical reductants are sodium borohydride (NaBH) and sodium hypophosphite (NaPOH.HO). For instance, Dickson and his research team have synthesized silver nanoclusters in DNA using sodium borohydride. 
*Electrochemical Reduction. Silver nanoclusters can also be reduced electrochemically using reductants in the presence of stabilizing agents such as  and tetrabutylammonium.
*Photoreduction. Silver nanoclusters can be produced using ultraviolet light, visible or infrared light. The photoreduction process has several advantages such as avoiding the introduction of impurities, fast synthesis, and controlled reduction. For example Diaz and his co-workers have used visible light to reduce silver ions into nanoclusters in the presence of a PMAA polymer. Kunwar et al produced silver nanoclusters using infrared light.
*Other reduction methods. Silver nanoclusters are also formed by reducing silver ions with gamma rays, microwaves, or ultrasound. For example silver nanoclusters formed by gamma reduction technique in aqueous solutions that contain sodium polyacrylate or partly carboxylated polyacrylamide or glutaric acids. By irradiating microwaves Linja Li prepared fluorescent silver nanoclusters in PMAA, which typically possess a red color emission. Similarly Suslick et al. have synthesized silver nanoclusters using high ultrasound in the presence of PMAA polymer.