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

•Strongly enhancing SERS sensitivity for detecting ppm-level thiram in fruit juices.•Utilizing either inherent or added internal standards for precise thiram detection.•Apple juice (inherent internal standard) with SERS peak for thiram sensing in it.•Adenine as added internal standard for thiram sensing in orange juice.•Both internal standards distinguishing thiram concentrations, ∼1 ppm difference. 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. 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. Our approach facilitates exceptional differentiation at the ppm level, enhancing pesticide detection for improved food safety and environmental health. [Display omitted]