Preparation of stable silver colloids

A method is described for producing highly stable silver colloidal solutions by reducing silver nitrate with lithium citrate. In the method, the main steps consist of: (a) heating a first quantity of water to a first predetermined temperature; (b) adding a second quantity of silver nitrate to the water; (c) heating the mixture to a second predetermined temperature; (d) adding a third quantity of an aqueous lithium citrate solution to the mixture; (e) maintaining the mixture at the second predetermined temperature for a predetermined time; and (f) cooling the mixture. The mixing process is accompanied by constant stirring. The colloid exhibits high light-scattering properties and intense SERS or SERRS spectra with low background fluorescence levels and a long shelf life, making it particularly suitable for Raman spectroscopy.