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A facile, dialysis-based synthesis of stable near infrared (nIR) absorbing plasmonic gold nanoparticles (λ_max = 650–1000 nm) will increase the yield of nIR particles and reduce the amount of gold colloid contaminant in the product mixture.

Chloroauric acid and sodium thiosulfate were reacted using a dialysis membrane as a reaction vessel. Product yield and composition was determined and compared to traditional synthesis methods. The product particle distribution, yield, and partitioning of gold between dispersed product and membrane-adsorbed gold were determined.

The synthesis results in polydisperse particle suspensions comprised of 70% spheroid-like particles, 27% triangular plates, and 3% rod-like structures with a 3% batch-to-batch variation and a prominent nIR absorption band with λ_max = 650–1000 nm. The amount of small gold colloid (λ_max = 530 nm; d < 10 nm) in …