A laser beam shot at a gold surface reflects back a signal more than a million times stronger than other metals. This phenomenon, known as Surface-Enhanced Raman Scattering (SERS), is now being used to identify trace amounts of unknown materials placed atop a gold holder.
Uncovering these minute amounts can be critical to forensic criminal investigations, environment studies and medical experiments.
SERS was first used to study the adsorption of gases or liquids on surfaces. Recently, it was discovered that when specific compounds are attached to a gold-reflective surface, the reflected signal is then capable of identifying the presence of specific material. The discovery is now forming the basis for a new, extremely sensitive system of chemical investigation.
The preparation of the gold surface for the Raman analysis is critical to its success. The U.S. Navy SPAWAR Systems Centre in San Diego, Calif., discovered a silica-like compound that, when applied to the glass sample holder, will firmly hold colloidal-sized gold particles. Once attached to the glass, the gold particles are coated with a compound that will adsorb the specific, but as yet unidentified, chemical contaminant, which is then recognized from its SERS spectrum.
Gold is preferred because it will not react with the coating or with the adsorbed contaminants, and therefore will not change their character. The gold substrates can be used in either a flowing liquid or gas stream. The system can be tuned to detect specific contaminants in parts per million or parts per billion.
Detection Limit, a company based in Laramie, Wyo., markets a portable self-contained system, about the size of a bread box, which is easily operated for routine analysis. The new laser-based Detection Limit system is finding important applications in medicine, forensics, chemistry (both liquid and gas analysis), environmental control, scientific research and the classroom. It is ideally suited for routine quality-assurance and process monitoring.
— The preceding is an excerpt from Gold News, published by the Gold Institute, based in Washington, D.C.
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