Monodisperse Ag Nanoparticle-Decorated Bacterial Nanocellulose as Flexible Surface-Enhanced Raman Scattering Sensors for Trace Detection of Toxic Thiram

Surface-enhanced Raman spectroscopy (SERS) is becoming an attractive technique for applications in food safety detection, environmental monitoring, disease diagnosis, and molecular identification. However, SERS substrates often suffer from low sensitivity, poor signal homogeneity, and stability. Herein, solution-processable monodisperse Ag nanoparticles (M-AgNPs) with an average diameter of 66 nm are synthesized by a size-controllable seeded-growth method. Furthermore, the M-AgNPs were coated on the surface of bacterial nanocellulose (BNC) to form flexible monodisperse Ag nanoparticles@bacterial nanocellulose (M-Ag@BNC) SERS sensors by a simple vacuum-assisted filtration. The SERS performance of flexible M-Ag@BNC substrates with various M-Ag loadings is systematically investigated. Due to the highly homogeneous distribution of M-AgNPs, the optimal M-Ag-12@BNC SERS sensor exhibits high sensitivity with a detection sensitivity of 10^-13M for methylene blue, excellent reproducibility (relative standard deviation (RSD) = 4.48%), and prominent storage stability (over 20 days). Besides, the hydrophilic BNC with good permeability and adsorption properties can absorb target molecules in the high-density hot-spot regions to further enhance SERS performance. Finite-difference time domain (FDTD) is also used to simulate and verify the strong electric field distribution of a M-AgNP-based SERS sensor. Finally, the M-Ag-12@BNC SERS sensor is successfully applied to detect pesticide residues on irregular fruit surfaces by a simple and feasible paste-and-read method. The sensitivity of a flexible M-Ag@BNC SERS sensor for thiram is up to 10^-8M. The flexible, ultrasensitive, and stable M-Ag@BNC SERS sensor exhibits potential applications in trace identification of hazardous organic molecules.