Achieving very low levels of detection: an improved surface-enhanced raman scattering experiment for the physical chemistry teaching laboratory

This experiment was designed and successfully introduced to complement the nanochemistry taught to undergraduate students in a useful and interesting way. Colloidal Ag nanoparticles were synthesized by a simple, room-temperature method, and the resulting suspension was then used to study the surface-enhanced Raman scattering (SERS) of methylene blue. The colloid was also characterized by UV–visible spectroscopy, and these results were used to help explain some of the observed SERS features. The students looked at the effects of concentration and acquisition time on the measured SERS spectra, and the final part of the experiment was based around using their newly acquired knowledge to investigate the lowest concentration of methylene blue that could be detected. Concentrations of 5 × 10^-10 M were routinely achieved. The combination of UV–visible spectroscopy, SERS, and nanochemistry made for an interesting and thought-provoking laboratory experience.