University of Lincoln

Peter Cyril White

Jakob Howie Hjortkjaer

Jakob Howie Hjortkjær

A method for producing a silver colloid solution of highly stable resulting colloids includes adding an aqueous solution of a hydroxylamine salt to an aqueous solution of an alkali, and then dispersing into the mixture an aqueous solution of the metal ions, the hydroxylamine salt being selected such that the anion, when combined with the said metal ions, would form a metal salt having a very low solubility in water, wherein the metal ion solution is introduced into the mixture in such a manner that the metal ions are substantially dispersed throughout the mixture within one second. A maturing period, preferably at elevated temperatures, leads to a stable state.

Preparation of metal colloids

A method is described for producing a silver colloid solution comprised of highly stable resulting colloids, the method comprising: adding an aqueous solution of a hydroxylamine salt to an aqueous solution of an alkali, and then dispersing into the mixture an aqueous solution of the metal ions, the hydroxylamine salt being selected such that the anion, when combined with the said metal ions, would form a metal salt having a very low solubility in water, wherein the metal ion solution is introduced into the mixture in such a manner that the metal ions are substantially dispersed throughout the mixture within one second. A maturing period, preferably at elevated temperatures, leads to a stable state in which the characteristics of the colloid undergo no further changes, and it is preferred to make and store the colloid in a polystyrene container for greatest stability. The resulting colloids from such method exhibit high light-scattering properties of small particle size and low background fluorescence levels, with a long shelf life, making it particularly suitable for Raman spectroscopy.

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.

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Peter Cyril White