“…The method is still widely applied (Sreethawong et al, 2011; Liu R. et al, 2013; Tran Thi Minh et al, 2013; Wang H. et al, 2013; He et al, 2016; Ilieva et al, 2016; Liu et al, 2016; Mishra et al, 2016; Li et al, 2018; Patil et al, 2018). It consists on having an aqueous solution of HAuCl 4 and water-soluble metal salts, such as a nitrate, being poured into an aqueous alkaline solution (Na 2 CO 3 and/or NH 4 OH) and stirred for a few minutes.…”