Abstract
—The development of sensitive analytical methods is of prime importance for the detection of pesticide residues on the surfaces of fruits and vegetables at extremely low concentrations. Here, we synthesized Ag-decorated three-dimensional ZnO nanoflowers (ZnO@Ag) composed of ultrathin nanosheets as surface-enhanced Raman spectroscopy (SERS) substrates. Combined with the finite-difference time-domain (FDTD) method, it is proven that the ultrathin nanosheets greatly improve the electromagnetic coupling between the two metal nanoparticles due to the high refractive index of ZnO and generate new “hot spots”. The nanosheets also endow the incident light with multiple reflections to motivate the local electromagnetic field. The substrate presents high sensitivity and the enhancement factor was as high as 2.98 × 107 utilizing R6G as probe molecules. The detection concentration of thiram and malachite green (MG) solutions can reach 10−10 M and 10−9 M, respectively. For the real-life sample assays, the substrate can simultaneously detect the two pesticides on apple skin with high sensitivity. The research also reveals the importance of semiconductors toward the local electromagnetic field enhancement in noble metal-semiconductor substrates, benefiting the realization of highly sensitive SERS substrates and the wide application of the SERS technology in real-world scenarios.
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