Silver Nanoparticle-Enhanced Resonance Raman Sensor of Chromium(III) in Seawater Samples

Tris(hydroxymethyl)aminomethane ethylenediaminetetraacetic acid (Tris-EDTA), upon binding Cr(III) in aqueous solutions at pH 8.0 on silver nanoparticles (AgNPs), was found to provide a sensitive and selective Raman marker band at ~563 cm(−1), which can be ascribed to the metal-N band. UV-Vis absorption spectra also supported the aggregation and structural change of EDTA upon binding Cr(III). Only for Cr(III) concentrations above 500 nM, the band at ~563 cm(−1) become strongly intensified in the surface-enhanced Raman scattering spectra. This band, due to the metal-EDTA complex, was not observed in the case of 50 μM of K(+), Cd(2+), Mg(2+), Ca(2+), Mn(2+), Co(2+), Na(+), Cu(2+), NH(4)(+), Hg(2+), Ni(2+), Fe(3+), Pb(2+), Fe(2+), and Zn(2+) ions. Seawater samples containing K, Mg, Ca, and Na ion concentrations higher than 8 mM also showed the characteristic Raman band at ~563 cm(−1) above 500 nM, validating our method. Our approach may be useful in detecting real water samples by means of AgNPs and Raman spectroscopy.