Preparation of stable, reproducible silver colloids for use as surface-enhanced resonance Raman scattering substrates

A flow system for the production of stable, reproducible batches of silver colloid for use as substrates for surface-enhanced resonance Raman spectroscopy (SERRS) is described. The colloids were prepared by borohydride reduction of silver nitrate and subsequent stabilization was achieved by adding trisodium citrate. The batches of colloid produced were analyzed using UV-visible spectroscope and their suitability for use as SERRS substrates was assessed using 3,5-dimethoxy-4-(5'-azobenzotriazole)phenylamine as the analyte. SERRS analysis was carried out using a flowcell. Using the method described, batches of silver colloid were prepared that were stable for at least five months and when used as SERRS substrates resulted in a relative standard deviation in SERRS intensity of 3,5dimethoxy-4-(5'-azobenzotriazole)phenylamine of 6.6% between colloid batches. The robustness of the system for production of stable, reproducible colloids was assessed using experimental design. The final method proposed enables reproducible, time-stable colloid to be made in a simple manner, thus eliminating one of the major problems associated with the use of SERRS detection in analytical procedures.