Flexible, Ultrasensitive and High-practical Paper/f-TiO2/Ag SERS Chips for On-site, Rapid and Accurate Detection of Tricyclazole Pesticide in Agricultural Products

Abstract Surface-enhanced Raman scattering (SERS) sensing is a powerful and important analytical technique in agriculture and food. Designing flexible SERS substrates that ensure both high sensor efficiency and feasibility in field analysis is highly desirable as it can bring the SERS technique closer to practical applications. Here, we demonstrate a designed Paper/f-TiO2/Ag structure, a flexible, ultrasensitive, and highly practical SERS chip, created by enhancing the self-assembly of Ag nanoparticles on a cellulose fiber matrix through the bridging of smart functionalized TiO2 nanomaterial (f-TiO2), which demonstrates superior detection capability for the hazardous plant protection agent tricyclazole (TCZ) on crops using an advanced, simple, and highly efficient analytical technique. Despite its straightforward fabrication process via a solvent immersion method, the intrinsic smart surface properties of the TiO2 bridging material – both hydrophilic and hydrophobic – enable the uniform and dense self-assembly of hydrophilic Ag nanoparticles (NPs) on the cellulose fiber paper substrate. This innovative design provides superior sensing efficiency for TCZ molecules with a detection limit reaching 2.1 × 10-9 M, a remarkable improvement compared to Paper/Ag substrates lacking f-TiO2 nanomaterials, which register at 10-5 M. This flexible SERS substrate also exhibits very high reliability as indicated by its excellent reproducibility and repeatability with relative standard deviations (RSD) of only 5.93% and 4.73%, respectively. Characterized by flexibility and a water-attractive yet non-soluble surface, the flexible Paper/f-TiO2/Ag chips offer the convenience of direct immersion into the analytical sample, facilitating seamless target molecule collection while circumventing interference signals. Termed the "dip and dry" technique, its advantages in field analysis are indisputable, boasting in-situ deployment, simplicity, and high efficiency, while minimizing interference signals to negligible levels. Through the application of this advanced technique, we have successfully detected TCZ in two high-value crops, ST25 rice, and dragon fruit, achieving excellent recovery values ranging from 90 to 128%. This underscores its immense potential in ensuring food quality and safety. As a proof of concept, flexible Paper/f-TiO2/Ag SERS chips, with a simple fabrication process, advanced analytical technique, and superior sensing efficiency, bring SERS one step closer to field applications beyond the laboratory.