Silver mirror for enhancing the detection ability of near-infrared diffuse reflectance spectroscopy

Near-infrared diffuse reflectance spectroscopy (NIRDRS) has been proved to be a convenient and fast quantitative method for complex samples. The sensitivity or the detection limit, however, has been the obstacle in practical uses, although great efforts have been made through experimental and chemometric approaches. Due to the strong reflectivity of silver in near-infrared region, a novel method that utilizes silver layer as the adsorption substrate was developed to enhance the detection ability of NIRDRS in this study. For investigating the enhancement effect of the method, lysozyme samples with different concentrations were spotted on the silver layer and NIR spectra were measured. Then quantitative determination was performed using multivariate calibration. For comparison, the comparative experiment was performed using the copper sheet as the substrate. The results show that the intensity of diffuse reflection can be enhanced, and the background variation was reduced by taking the mirror layer as the substrate. A linear variation was obtained between the concentrations and the intensities of the spectral response at a wavenumber. Using multivariate calibration for quantitative analysis, the optimal PLS model was obtained. The maximum deviation of the prediction results can be as low as 12.8 mu g. Therefore, this study made a progress for NIRDRS technique in microanalysis.