A New Method for Fast Preparation of Highly Surface-Enhanced Raman Scattering (SERS) Active Silver Colloids at Room Temperature by Reduction of Silver Nitrate with Hydroxylamine Hydrochloride

A very effective and simple way to produce silver colloids for surface-enhanced Raman scattering (SERS) is reported. Reduction of silver nitrate with hydroxylamine hydrochloride at alkaline pH and at room temperature yields highly sensitive SERS colloids within a short time. The so-produced colloids can be used for SERS spectroscopy immediately after preparation. The overall procedure is fast, simple, and characterized by a high preparation success rate. Changing the mixing order and rate of the two involved solutions, silver nitrate and hydroxylamine hydrochloride containing sodium hydroxide, one can control the size and dispersion of the produced colloids. The obtained colloids have been characterized by UV−vis spectroscopy, transmission electron microscopy, and SERS using a 1064 nm laser line on a Fourier transform and a 785 nm laser line on a dispersive Raman spectrometer. The SERS enhancement factor of the hydroxylamine-reduced silver colloids was tested using crystal violet, rhodamine 6G, methylene blue, and 9-aminoacridine. It was found that for both excitation lines sensitivities comparable to those achievable with a Lee−Meisel silver colloid were obtained thus rendering the new colloid advantageous because of its significantly simpler and faster synthesis.