Highly SERS active composite of silver nanospheres-decorated Ag nanostar/ZIF-8 for determination of diquat and thiram residues

In surface-enhanced Raman scattering (SERS) measurements, the creation of “hot spots” and the effective concentration of analytes in these areas are crucial for enhancing detection sensitivity. In this work, a novel composite with highly SERS activity, Ag nanospheres decorated Ag nanostar/ZIF-8 composite (Ag NS/ZIF-8/Ag) was achieved via first coating the Ag nanostars with the metal-organic framework ZIF-8, known for its strong molecular adsorption capabilities, followed by the electrostatic self-assembly of Ag nanospheres. The composites produce numerous hotspots due to the abundant plasmonic nanogaps, including the interstitial space between the Ag nanostar and Ag nanospheres, as well as internanogaps between neighboring Ag nanospheres, resulting in outstanding SERS performance. It was successfully applied for the quantitative and simultaneous detection of diquat and thiram in fruit juice, achieving detection limits of 5.0 × 10⁻⁸ mol/L and 1 × 10⁻⁸ mol/L, respectively, with recovery rates ranging from 86.6 % to 118.4 %. Notably, under UV light exposure, the composite was able to degrade pesticides efficiently within 80 min. Additionally, its reusability was demonstrated by sustaining strong SERS activity over five continuous detection cycles. These results emphasize the capability of Ag NS/ZIF-8/Ag composites for sensitive pesticide detection via SERS.