Filter paper loaded with Ag nanocubes serves as a SERS platform for detecting thiram in fruit

The polyol reduction method has performed well in Ag nanocube (AgNC) synthesis but is hindered by high-temperature requirements, impacting environmental sustainability and economy. Using polyethylene glycol (PEG)/deionized water as a solvent mitigates these issues, by leveraging PEG’s high solubility, bio-compatibility, low cost, and redox properties. The synthesis conditions were optimized, resulting in relatively uniform AgNC. The synthetic AgNC were loaded on porous, cheap, flexible and biocompatible filter paper (FP) by a simple self-assembly, and the formed flexible substrate (AgNC@FP) was used for surface-enhanced Raman scattering (SERS) detection. The AgNC@FP substrate had a high enhancement factor (EF) of 9.8 × 10 7 , with a detection limit of Rhodamine 6G (R6G) of 5.2 × 10 -12 M. Meanwhile, the substrate showed good reproducibility and stability, with a relative standard deviation (RSD) of 5.9 % and a decrease in Raman signal strength of only 25 % after 30 days. Furthermore, the direct sampling of apples and pears from their surface thereby enables the rapid identification of ultra-low thiram residue concentrations, with a sensitivity of 8.3 × 10 -7 M. The high SERS enhancement factor and sensitivity were attributed to the result of the high hot spot density generated by the FP surface, excellent uniformity and superior sample collection efficiency. It can therefore be concluded that this flexible AgNC@FP substrate, which is manufactured at a low cost and allows for label-free SERS detection, represents a promising SERS platform for analytical and biosensing applications.