A PMMA@Ti₃C₂T_x-Ag array-structured SERS platform for sensitive detection of pesticide residues on fruit surfaces

The rapid identification and quantitative detection of pesticides on a portable device is of vital importance for food safety evaluation and human health protection. However, conventional strategies for realizing the reliable, portable and sensitive detection of target analytes are still challenging. In this work, the ordered polymethyl methacrylate (PMMA) microspheres array were employed as template to fabricate PMMA@Ti₃C₂T_x. Silver nanoparticles (AgNPs) were then uniformly immobilized onto the composite substrate through an in-situ route, generating abundant electromagnetic hotspots. Benefiting from the synergistic electromagnetic and chemical enhancement, a high-performance PMMA@Ti₃C₂T_x-Ag composite array SERS substrate was successfully fabricated. The prepared array substrate exhibits excellent SERS performance with good uniformity (relative standard deviation, RSD < 5%) and satisfactory stability. It achieves the detection concentration of 10^-9 M for probe molecules of crystal violet (CV) and 4-aminothiophenol (4-ATP). For pesticide detection using standard solutions, the substrate realizes trace detection of diquat and triazophos down to 10^-8 M, while the detection concentration for thiram is 10^-7 M. Taking advantage of the unique molecular fingerprint signature of SERS, the platform enables simultaneous identification of various pesticide molecules. Further practical tests were carried out to perform in-situ analysis of pesticide residues on the surfaces of blueberries and cherry tomatoes. The detectable concentrations of target pesticides are well below the maximum residue limits stipulated by the European Union, demonstrating the great potential of the SERS platform for rapid screening applications in food safety monitoring. These results indicate the promising potential of the sensing platform for rapid on-site monitoring of pesticide residues in complex food matrices. For the spiked fruit-surface experiments, diquat and triazophos were detected down to 10^-7 M, whereas thiram was detected at 10^-6 M.