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The Use of a Combination of a Sugar and Surfactant to Stabilize an Au Nanoparticle Dispersion against Aggregation during Freeze-Drying.

Drying a suspension of nanoparticles typically results in the irreversible aggregation of nanoparticles although solutions that contain unstable ingredients are often converted into dried powders to prolong their shelf-lives. In this study, the use of a combination of a surface active agent and sugar was investigated with regard to avoiding the aggregation of nanoparticles during drying. Suspensions of Au nanoparticles (~60 nm diameter, AuNPs) were freeze-dried in the presence of different combinations of various sugars with a surfactant. Sucrose monopalmitate (SEC16) was mainly used as the surfactant, based on a comparison of anti-aggregation effects conferred by various surfactants. The freeze-dried AuNPs suspension was then reconstituted, and the avoidance of AuNPs aggregation was then examined. The results demonstrated that the use of a combination of a small amount of SEC16 and a sugar resulted in a greater redispersibility of AuNPs after freeze-drying than when the individual components were used. Repetition tests of freeze-drying and reconstitution were conducted. The sucrose/SEC16 mixture was freeze-dried on an electroless-plated Au film and then analyzed by Infrared spectroscopy. Strong interactions between the SEC16 and the Au surface were detected and these interactions appear to play a crucial role in the anti-aggregation of AuNPs during freeze-drying.