Dual hot-spot SERS test strip for picomole level analysis of thiram

The misuse and improper disposal of thiram pesticide present significant health and environmental risks, emphasizing the need for highly sensitive detection methods, particularly in food safety. In this study, we introduce a novel approach for thiram detection using surface-enhanced Raman scattering (SERS) test strips with dual hot-spots. Thiram prevents Ag⁺ from acting as specific bridging molecules in a SERS hotspots model. Initially, the aggregation of 4-aminothiophenol (4-ABT) functionalized silver nanoparticles (AgNPs@4-ABT) can be efficiently triggered by Ag⁺ ions, simultaneously enhancing the SERS signal of 4-ABT. However, the introduction of thiram inhibits the aggregation of Ag NPs@4-ABT, leading to a reduction in the SERS signal. Based on this principle, we have developed a SERS analysis method for detecting thiram in solution. To address the reliance on initial signal intensity, we translocated the detection system onto cotton fabric. This adjustment not only amplifies the initial signal through the physical aggregation of nanoparticles, creating secondary hotspots, but also improves portability and reduces resource consumption. Compared to the single hotspot solution model, our dual hotspot configuration significantly enhances sensitivity due to the stronger initial signal, achieving an impressive broad linear detection range from 5 × 10⁻⁵ to 5 × 10⁻¹¹ M. This range substantially outperforms the linear range of Ag NPs@4-ABT alone, which spans from 5 × 10⁻⁵ to 10⁻⁸ M. The SERS test strips exhibit a detection limit as low as 2.56 × 10⁻¹² M, enabling picomolar level analysis. This innovative dual hotspot SERS approach provides a powerful tool for sensitive and practical detection of thiram in safety-critical applications.