A Centrifugation-based Method for Preparation of Gold Nanoparticles and its Application in Biodetection

Gold nanoparticles (AuNPs) have found widespread applications in lifesciences. While synthesis of monodispersed AuNPs has been fairly convenient by usingchemical reduction of chloroauric acid by sodium citrate, we found that AuNPs of highquality and high concentrations were not readily obtained via this method. As an example,we showed that monodispersed 13-nm AuNPs were readily synthesized at relatively lowconcentrations (e.g. 3.5 nM); in contrast, 13-nm AuNPs of 17 nM obtained by the directreduction method were irregularly shaped and not well dispersed. In this work, wedemonstrated that AuNPs of high concentration could be prepared by a two-step approach,i.e. chemical reduction at low concentrations and subsequent centrifugation. Compared tothe direct reduction method, this new two-step method led to AuNPs with high saltresistance and high stability, which are essential for the preparation of DNA-AuNPsconjugates for DNA biodetection.