In-situ growth and application of cotton swab-Ag composite as flexible and wipeable surface enhanced Raman scattering substrate

In order to detect pesticide residues on the surface of fruits, the flexible and wipeable Ag/cotton swab surface enhanced Raman scattering (SERS) substrate was prepared by in-situ growth process. By adjusting the concentration of silver nitrate in the growth medium, plasmonic cotton swab composite with uniform and dense Ag nanoparticles was obtained. The scanning electron microscopy, transmission electron microscopy, fourier transform infrared and thermogravimetric analysis indicated that the Ag nanoparticles were decorated on the surface of cotton swab. Nile Blue was used as a probe molecule to evaluate the SERS performance of Ag/cotton swab, furthermore the composite was employed for detecting thiram. The results show that the Ag nanoparticles with size 50 to 70 nm are uniformly distributed on the surface of cotton fiber. The Ag/cotton swab composite exhibits excellent SERS uniformity, with a relative standard deviation of 3.72%. The detection limit for Nile Blue is lower than 10⁻⁷ mol/L. The plasmonic Ag/cotton swab presented excellent flexibility and adsorption capability, which enable to adsorb and detect pesticide residue from irregular surface of pear directly by simple swabbing process, the sensiti-vity could achieve 10⁻⁶ mol/L. The manufacturing method can be easily extended to other cellulosic compounds, such as absorbent cotton and paper. This research proposes a new method to manufacture cost-effective, environmentally friendly and flexible SERS substrates.