Significantly enhancing SERS sensitivity to distinguish pesticide concentrations at ppm levels in juices through inherent and added internal standards

Background

Surface-enhanced Raman scattering (SERS) aids in pesticide detection, including thiram. The U.S. Environmental Protection Agency has set a 7 ppm residue standard specifically for thiram. Nonetheless, conventional SERS methods often lack sensitivity at ppm levels. We introduce internal standards to overcome this limitation.

Methods

Initially, we assessed thiram concentrations in apple and orange juices using the SERS peak at 1383 cm^-1, denoted by its intensity as S₁₃₈₃. However, S₁₃₈₃ alone lacked sensitivity to ppm level variation. Apple juice exhibited a SERS peak at 732 cm^-1 (intensity denoted as S₇₃₂), serving as an inherent internal standard. The ratio of S₁₃₈₃ to S₇₃₂ could differentiate thiram concentrations by ∼1 ppm within the range of 1 × 10^-5 to 3 × 10^-5 M. Pure orange juice lacked a discernible SERS peak, necessitating an added internal standard. Adenine, with SERS intensity at 731 cm^-1 (S₇₃₁) and 1322 cm^-1 (S₁₃₂₂), was employed for this purpose. The combined use of S₁₃₈₃ and the ratios of S₁₃₈₃ to S₇₃₁ and S₁₃₈₃ to S₁₃₂₂ could distinguish thiram concentration differences by ∼1 ppm within the range of 1 × 10^-5 to 5 × 10^-5 M.

Significant findings

Our approach facilitates exceptional differentiation at the ppm level, enhancing pesticide detection for improved food safety and environmental health.