Silver Nanocube-Decorated PVDF Membranes for SERS Substrates

In this study, we report that silver nanocubes (AgNCs) can be synthesized via the silver mirror reaction (SMR) within 1 min. To extend the reaction time, the sharp-edge AgNCs quickly denucleated and collapsed into small spherical Ag nanoparticles and became aggregates. Based on this discovery, we developed an easy-to-make membrane-based surface-enhanced Raman scattering (SERS) substrate with superior sensitivity and reproducibility. The entire fabrication process, including AgNC synthesis from SMR, membrane pretreatment, and AgNC deposition on the membrane by suction filtration, was completed within 30 min. The SERS intensity of R6G increased 48-fold after the pretreatment of the polyvinylidene difluoride (PVDF) membrane with methanol and NaCl aqueous solutions. The PVDF-based SERS substrate successfully verified attomolar (aM) sensitivity to R6G using 3 × 3 μL of an aqueous sample on a 3 × 3 mm² substrate. To validate the practicality of the developed SERS substrate as a SERS sensor, it was applied to the detection of malachite green, cocaine, 2,6-pyridinedicarboxylic acid, and tetracycline, with limits of detection of 10 ppb, 1 ppm, 1 ppm, and 1 ppm, respectively. However, the SERS substrate maintained up to 80% sensitivity for only 3 days. Fortunately, a freshly prepared SERS substrate can be quickly fabricated on demand; thus, shelf-life or long-term stability is no longer a concern.