Research has proved that the molecular structures of pesticides determine their stability and persistence, and most of them are difficult to excrete from the human body through the digestive system. Pesticide residues in fruits and vegetables cause chronic poisoning and can induce many chronic diseases. Thiram is a representative dithiocarbamate (DTC) fungicide with a strong protective effect, which can control white rot and anthracnose in fruit. Thiram should be used rationally; if it is widely used with other DTC pesticides, it can elicit nervous system, endocrine-disrupting, and carcinogenic effects, raising concerns for human health . Pesticide residues are very harmful, and even at trace levels can increase physical burden and even severely disrupt ecosystems [2, 3]. The development of strategies to monitor the application of pesticides is of primary importance.
At present, many methods are available for detecting thiram, including fluorimetry , colorimetry , high-performance liquid chromatography , electrochemical analysis, and spectrophotometry. Surface-enhanced Raman scattering spectroscopy is a detection method based on molecular vibrations that can be used for trace analysis [7, 11, 14, 15, 18, 23–25, 28]. Electromagnetic enhancement arising from the local surface plasmon resonance of neighboring precious metal particles  and chemical enhancement caused by metal nanostructures and electric charge are the main mechanisms of Raman enhancement. The applicability of SERS depends on the design and realization of suitable substrates. Traditional rigid SERS substrates [9, 10, 12] require a complex pretreatment process, are not amenable to non-invasive detection, and can no longer meet the needs of rapid detection of pesticides on site. Newly emerging flexible substrates, such as cellulose [17, 25, 29–31], polymer films [26, 27, 32–39, 43], and other flexible materials [13, 16, 40–42], can be formed into variable shapes. Most flexible substrates can be applied as swabs to detect pesticides [14–22, 29], but many methods are costly and complicated to operate.
Face masks have become more and more important part of daily life. Here, we have successfully prepared a PDA/AgNPs substrate on face masks. Dopamine self-polymerizes in an alkaline environment to form a PDA layer bearing a large number of phenolic hydroxyl and amino functional groups, which can bind silver ions. Furthermore, PDA has some reducing ability, and can reduce silver ions to silver nanoparticles. In deatail, we have employed SEM to characterize the morphology of the substrate, and XPS to analyze the elemental composition. The FM/PDA/AgNPs substrate displays high uniformity and sensitivity for the detection of NBA molecules. In addition, in order to verify its practical application and reproducibility on various curved surfaces, the FM/PDA/AgNPs substrate has been used to detect thiram residues on fruits. The results prove that the substrate can realize waste utilization, is characterized by a simple preparation method, low production cost, high sensitivity, high uniformity, and reproducibility, and provides a potential platform for efficient and flexible SERS sensors for use in biochemical identification.