An aptamer sensor based on peroxidase-like AgNPs@MOF for SERS and colorimetric dual-mode detection of sulfadimethoxine

An AgNPs@MOF bifunctional nanocomposite (combining peroxidase-like catalytic properties and surface-enhanced Raman activity substrate) was synthesized. The material can decompose H₂O₂ to produce hydroxyl radicals (˙OH), which oxidize the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) from its colorless, Raman-silent form to a blue-colored, Raman-active oxidized product (ox-TMB). The peroxidase-like activity of AgNPs@MOF is suppressed when the sulfadimethoxine (SDM) specific aptamer is adsorbed onto its surface. However, upon binding with the target SDM molecule, the aptamer forms a stable complex and detaches from AgNPs@MOF, thereby restoring the nanomaterial's catalytic function. This mechanism enabled the design of a dual-mode aptamer sensor (aptasensor) based on surface-enhanced Raman spectroscopy (SERS) and colorimetry (UV-vis) for SDM detection. The optimized SERS technique displayed a linear detection range of 6.00-200.00 ng mL⁻¹ with an LOD of 0.96 ng mL⁻¹, whereas the colorimetric approach had a linear range of 24.00-200.00 ng mL⁻¹ and a LOD of 2.19 ng mL⁻¹. The developed aptasensor successfully detected SDM in fortified milk and mutton samples, showing excellent specificity and acceptable recovery rates. Compared to single-mode detection systems, this dual-mode analytical platform offers enhanced reliability and can be modified for different antibiotic detection through substitution of specific aptamers. Consequently, the developed aptasensor shows promising applications for monitoring trace-level antibiotics in food safety analysis.