Sandwich SERS immunoassay of human immunoglobulin on silicon wafer compared to traditional SERS substrate, gold film

Likely the first application of silicon wafer as a substrate for sandwich immunoassay with Surface Enhanced Raman Scattering (SERS) detection is reported hereafter. Human immunoglobulin (hIgG) was used as a model biomarker in the simultaneous comparative assay on gold film and on Si wafer, an alternative (less expensive and potentially more resistant to surface contamination and non-specific binding) substrate. The Limits of Detection calculated from the data obtained with two-laser wavelength (633 nm and 785 nm) were about 1 × 10−12 mol of antigen or less for both substrates, which is close to the minimal detectable concentration of 30 pM. An approximately logarithmic response was observed across at least a factor of 133 in the dynamic range 0.03–4 nM. However, if four parametric logistic curve is used for the calibration, LOD on silicon would become significantly lower than LOD on gold (3 pM vs 28 pM). A much smaller slope of calibration plot was compensated by a significantly smaller standard deviation in the signal of the blank for the assay on silicon, as compared to the assay on gold. This report may encourage researchers to try silicon or other non-noble metal materials as SERS substrates for the detection of biomarkers.