Electrochemical SERS Sensing Using CVD-Grown Tungsten Diselenide as a Substrate

Recently, WSe2 has attracted attention as a promising candidate for surface-enhanced Raman spectroscopy (SERS) application due to its anisotropic structure and unique electrical and optical properties; however, achieving large-area, high-quality continuous films of WSe2 remains challenging. Here, we successfully synthesized centimeter-scale WSe2 films on Si and W-foil substrates via the chemical vapor deposition technique. These films serve as effective SERS substrates for the detection of biomolecules (bilirubin, B12, and dopamine). Our study achieves notably higher sensitivity of WSe2/W-foil as SERS substrate at room temperature with a limit of detection of 2.3× 10–11 M for bilirubin, 9.9 × 10–10 M for vitamin B12, and 9.09 × 10–7 M for dopamine as per IUPAC recommendation, as compared to the WSe2/Si substrate. The WSe2/W-foil shows near single-molecule detection of bilirubin and vitamin B12 due to efficient charge transfer between WSe2 and the analyte molecules. We further quantified the degree of charge transfer between biomolecules and WSe2 substrates. The high degree of charge transfer values (ρCT ∼ 0.84, 0.82, and 0.74) is obtained for bilirubin, vitamin B12, and dopamine adsorbed on WSe2/W-foil, respectively, compared to the WSe2/Si substrate (ρCT ∼ 0.83, 0.78, and 0.71). We also demonstrate the improved SERS activity at lower temperatures due to the increase in the photoinduced charge transfer (PICT) process. The enhancement in sensitivity of the SERS substrate was also examined by application of electrochemical (EC) potential in EC-SERS, which can be attributed to the higher charge transfer near the oxidation potential, stronger chemical adsorption of analyte molecules, and alterations in molecular orientation and surface packing density upon electrochemical modulation.