Toward the Development of Ultrasensitive Detectors for Environmental Applications: A Kinetic Study of Cr(III) Monitoring in Water Using EDTA and SERS Techniques.

We report for the first time kinetic studies on chromium(III) detection in aqueous solution using citrate-capped silver nanoparticles (AgNPs) and the surface-enhanced Raman spectroscopy (SERS) technique. Moreover, we have shown an important effect of adding ethylenediaminetetraacetic acid (EDTA) on the enhancement and the stability of the Raman signal. The origin of the SERS signal was attributed to the coordination of Cr(III) by citrate/EDTA molecules and the formation of hot spots on aggregated AgNPs. Depending on the mixing method of Cr(III) and EDTA with AgNPs, the temporal SERS spectral features reveal a Prout-Tompkins or a Langmuir kinetic detection model. The UV-visible data, the temporal response of the Raman signal, and the scanning electron microscopy analysis have allowed us to elucidate the mechanism of Cr(III) detection. We observed that mixing simultaneously Cr(III), AgNPs, and EDTA leads to the most stable and intense time-dependent SERS signal. The obtained results should open the way to perform kinetic studies on different host-guest interactions in solution using the SERS technique.