Wafer-scale fibrous SERS substrates allow label-free, portable detection of food adulteration and diagnosis of pesticide poisoning

Herein, a method for constructing three-dimensional (3D) fibrous surface-enhanced Raman scattering (SERS) substrates was developed. This strategy enables the wafer-scale, direct formation of monolayer gold nanoparticles (Au NPs) on filter paper. The process begins with coating of the fiber surface with perfluorooctyltrichlorosilane (FOS) to manipulate the surface energy. During subsequent sputter deposition, the large difference in surface energy between the Au atoms and the FOS-modified fibers leads to the thermodynamically driven formation of discrete Au NPs, thereby generating an abundance of hotspots. Moreover, the Au NP–decorated paper maintained its great hydrophobicity, condensing the analyte molecules nearby hot spots after solvent evaporation. In addition, the 3D fibrous structure provided a large detection space to efficiently utilize the large depth of field of a portable Raman spectrometer. These features resulted in the as-designed SERS paper having high sensitivity, with the enhancement factor reaching 1.63 × 10⁸ and the detection limit reaching the nanomolar level when using a portable 785-nm Raman spectrometer. We used this approach for the trace-level, label-free detection of a diverse range of substances as well as their practical on-site detection in multiple-component systems, including illegal rhodamine B in commercial beverages and lethal paraquat in poisoning patients.