Colloidal AuNPs were prepared according to the literature by reaction
of sodiumcitrate solution and HAuCl4 solutionwhichwas previously
heated up to 60 °C. Briefly, 0.5ml of 1% (w/v) sodium citrate solution
as reducing agent was added dropwise to 50 ml of 0.01% (w/v)
HAuCl4·3H2O