Quasi-spherical silver nanoparticles: Aqueous synthesis and size control by the seed-mediated Lee–Meisel method

Silver nanoparticles (AgNPs) are attracting tremendous attention in biomedicine, and their related performances are shape and size-dependent. For biomedical applications, water-soluble AgNPs are necessary. However, aqueous syntheses of AgNPs with controlled shape and size are relatively difficult as the balance between nucleation and growth is hard to regulate. This paper describes a robust method for controllable synthesis of quasi-spherical AgNPs based on the combination of the seed-mediated growth and the Lee–Meisel method by thermal reduction of AgNO3 with citrate. In the presented method, citrate-stabilized AgNPs with tunable sizes up to 80 nm were achieved through one-step or stepwise growth process using qualified spherical 4 nm AgNPs as starter seeds. Specially, the two main difficulties (formation of nanorods and secondary nucleation during the growth stage) in the previous studies have been effectively overcome by tailoring the experimental parameters such as the reaction temperature and the seed amount, without extra additives, pH adjustment, and laser treatment. The crucial factors that affect the uniformity of the resulting AgNPs are discussed.

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► Qualified Ag nanoparticles of 4 nm were reproducibly obtained in water.
► Quasi-spherical Ag nanoparticles with controlled sizes were obtained in water.
► Formation of nanorods and secondary nucleation were effectively overcome.
► No extra additives, pH adjustment, and laser ablation are needed.
► The ratio of monomer to seed is critical to control of the final particles.