Stepwise Centrifuge Classification Method for Citrate-Reduced Silver Nanoparticles to Decrease Size Variance.

Silver nanoparticle (AgNP) aqueous solutions are expected to be applied to various functional materials, such as highly sensitive molecule detection using surface-enhanced Raman scattering (SERS). However, the shape and size control of AgNPs for practical applications is challenging without any additional stabilizers in the chemical synthesis process. In this study, a stepwise centrifugal classification method was evaluated for its applicability to polydisperse particles from a mathematical model and employed to classify AgNPs that were reduced and stabilized using trisodium citrate. The AgNPs could be separated, and aqueous solutions with different particle size distributions could be obtained by varying the centrifugation time and speed. Centrifugation with several steps could effectively improve the uniformity of AgNPs, while the loss of AgNPs was prevented by redispersing the precipitate in a solution of the citrate ion as a stabilizer. Furthermore, since this shape-control method is performed without any additional stabilizers, the obtained silver nanoparticles are applicable to Raman scattering measurements, thereby contributing to an enhanced spectral resolution.