Ultrasensitive and reusable Cu2O/Ag composite SERS substrates for trace thiram detection

Abstract

Due to its distinctive molecular recognition, high detection sensitivity, and in situ detectability, the surface-enhanced Raman scattering (SERS) spectroscopic technique has been widely applied as an effective analytical method for the detection of trace hazardous substances. In this study, we successfully fabricated Cu₂O/Ag composite substrates by employing a simple electrochemical deposition of Cu₂O film followed by magnetron sputtering deposition of Ag nanoparticles. The as-prepared substrates exhibited excellent SERS performance with remarkable sensitivity and reusability due to the synergetic effect of electromagnetic enhancement from Ag nanoparticles and chemical enhancement resulting from the charge transfer effect. Upon optimizing the amount of post-deposited Ag nanoparticles, the Cu₂O/Ag-90 composite substrate showed a good linear relationship between SERS intensities and the logarithmic concentration within the range of 10⁻⁵ M to 10⁻¹⁰ M for rhodamine 6G, a representative dye analyte. Furthermore, the limit of detection could be lowered down to 10⁻¹⁰ M. Moreover, the as-prepared Cu₂O/Ag-90 composite substrate displayed outstanding reproducibility in SERS signals with a calculated relative standard deviation of approximately 6.6%. To evaluate its capability in detecting hazardous substances, we selected pesticide thiram as a model analyte that can be detected at concentrations as low as 10⁻⁸ M in ethanol solution and 10 ppb in soil, both significantly lower than the national standard. Under the irradiation of a xenon lamp, the Cu₂O/Ag-90 composite substrate achieved complete catalytic degradation of the organic dye molecule R6G within 100 min while maintaining good SERS activity even after three cycles. This work demonstrates that the semiconductor and the noble metal composite substrate can effectively enhance the SERS activity of semiconducting SERS substrates, enabling rapid detection of pesticides.