Preparation and characterisation of a stable silver colloid for SER(R)S spectroscopy

A method for the reproducible preparation of a silver colloid with strong surface-enhanced Raman scattering (SERS) properties, good stability with a zeta potential of -55mV and a shelf life exceeding 1year is reported. The mean particle size is 20nm with a narrow size distribution of 10-30nm. The colloid is produced by the reduction of silver nitrate with hydroxylamine phosphate to give a negatively charged phosphate surface on the silver particles. This is an ultrafast room temperature reaction and with controlled rapid addition and dispersion of reagents, very reproducible batches of colloid can be prepared making it suitable for commercial applications of Surface enhanced resonance Raman scattering(SER(R)S) spectroscopy. The stability of the colloid is attributed to the extremely low solubility product (K-sp) of silver phosphate. Characterisation and stability study data for this colloid have been obtained by ultraviolet-visible spectroscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, particle size analysis and SERS analyses using a 514nm laser on a Raman spectrometer. A SERS method to detect and to identify riboflavin in a vitamin B complex tablet is reported to illustrate a SERS application based upon the use of this silver colloid. Copyright (c) 2013 John Wiley & Sons, Ltd.