Silver nanocubes/nano mica platelets flexible nanohybrid substrates modified by zinc oxide quantum dots with synergistic 3D lightning rod effect, and electromagnetic and chemical enhancements for highly sensitive SERS bacterial biosensor

This study utilized a polyol-mediated synthesis method to prepare silver nanocubes (AgNCs) of different sizes. Subsequently, the AgNCs were stably adsorbed onto the surfaces of nano mica platelets (NMPs) via one-step synthesis to form AgNC/NMP nanohybrid surface-enhanced Raman spectroscopy (SERS) substrates with a three-dimensional (3D) lightning rod effect. The NMPs (thickness: 1–3 nm; length and width: approximately 300 nm) had a high surface-area-to-volume ratio and numerous hydroxyl groups on their surfaces, which provided the AgNCs with a good platform for stabilization and growth. When used in surface-enhanced Raman scattering for the biomolecular detection of adenine, the AgNC/NMP nanohybrids exhibited a better limit of detection (LOD) concentration of 10⁻¹⁰ M compared with AgNCs, an enhancement factor (EF) of 4.38 × 10⁹, and a relative standard deviation of 8.52 %. This may be attributed to the hot spots generated along the z-axis by the AgNC/NMP nanohybrids, which created a 3D hot spot effect. The AgNC/NMP nanohybrids also demonstrated an LOD of 10² CFU/mL in the detection of Staphylococcus aureus. To further improve detection sensitivity and biocompatibility, the AgNC/NMP nanohybrids were modified with zinc quantum dots (ZnO QDs) for the synthesis of AgNC/NMP/ZnO QD nanohybrids. When used for the biodetection of adenine, the ZnO-QD-modified nanohybrids exhibited a higher signal intensity compared with the AgNC/NMP nanohybrids, with an increase in the EF to 6.37 × 10⁹. The increase in intensity was attributed to the chemical enhancement effect in SERS. Excellent characteristic signals were also obtained when the AgNC/NMP/ZnO QD nanohybrids were used for the detection of the other three bases of DNA. Finally, the good biocompatibility and large specific surface area of the ZnO QDs enhanced the effects of SERS in bacterial detection, with a further decrease in the LOD to 10 CFU/mL. This also demonstrates that the prepared nanohybrid substrates were highly suitable for use in rapid and sensitive SERS biodetection.