SERS Performance\nFactor: A Convenient Parameter for\nthe Enhancement Evaluation of SERS Substrates

Surface-enhanced\nRaman spectroscopy (SERS), with molecular\nfingerprint\ninformation and single-molecule sensitivity, has been widely used\nfor qualitative and quantitative analysis in various fields. Plenty\nof nanostructured plasmonic materials have been fabricated to achieve\nhigh SERS activity. Currently, great difficulty lies in evaluating\nthe SERS performance among substrates, making it difficult to standardize.\nAddressing this problem, this work proposed the SERS performance factor\n(SPF=ΔISERSΔCSERS/ΔIRamanΔCRaman) as a practically operational parameter\nto evaluate the sensitivity of SERS substrates. Experimentally, <i>SPF</i> can be obtained by taking the ratio of the slopes (i.e.,\nthe sensitivity) for concentration-dependent SERS and normal Raman\nmeasurements in the linear range of the intensity response under \nidentical experimental conditions. Theoretically, <i>SPF</i> quantitatively describes the overall contribution to the SERS performance,\n(i.e., the electromagnetic (EM) enhancement of the SERS substrate\nand the interfacial interaction between the probe and substrate).\nThe use of <i>SPF</i> as the criterion for evaluating the\nSERS performance was validated on Au nanoparticles in colloidal and\nsolid states, where the tendency of <i>SPF</i> is consistent\nwith that of the sensitivity of the probe molecules. Derived from\nthe typically used surface enhancement factor EF in which accurate\nparameters are hardly achievable and different from concentration-dependent\nanalytical enhancement factor AEF, <i>SPF</i> distinguishes\nitself with a simpler calculation and thereby offers a convenient\nand reliable protocol for the evaluation of the performance of different\nSERS substrates, which is very important to the practical application\nof SERS.