Quantitative SERS analysis based on multiple-internal-standard embedded core-shell nanoparticles and spectral shape deformation quantitative theory

Due to the practical impossibility in controlling the number and distribution of "hot spots" on or close to the surfaces of enhancing substrates, internal standards are generally used to improve the accuracy and precision of quantitative surface-enhanced Raman spectroscopy (SERS). Traditional internal standard methods based on either univariate ratiometric models or conventional multivariate calibration models can use the information of only one characteristic SERS peak of only one internal standard, which weakens the efficiency of traditional internal standard methods in improving the quantitative results of SERS assays. In this contribution, the concept of using multiple internal standards was introduced for the first time to quantitative SERS assays by incorporating a unique spectral shape deformation (SSD) quantitative theory with multiple-internal-standard embedded core-shell nanoparticles. The quantification of phosmet residues on apple skins by SERS technique with Au-core/Ag-shell nanoparticles embedded with both 2-MB and PATP as enhancing substrate was used to illustrate the applicability of the proposed strategy. Experimental results demonstrated that the proposed multiple-internal-standard strategy based on SSD achieved much more accurate and precise concentration predictions for phosmet residues on apple skin than traditional single-internal-standard methods based on either univariate ratiometric calibration models or conventional multivariate calibration models. The SERS quantitative results of the multiple-internal-standard strategy were comparable to those obtained by LC-MS/MS. The average relative deviation between the quantitative results of the proposed method and those of ICP-MS was about 8%. The good accuracy of the proposed method makes it a promising alternative for quantitative SERS assays.