Au Film–Au@Ag Core–Shell Nanoparticle Structured Surface-Enhanced Raman Spectroscopy Aptasensor for Accurate Ochratoxin A Detection

As a powerful toxin that could cause fatal death, the detection of ochratoxin A (OTA) has gained much attention in the fields of environmental and food sciences. In this study, an internal standard (IS) aptasensor was synthesized through a facile and scalable method to enhance the sensitivity and quantativity of OTA detection. The substrates were formed through hybridization of modified aptamers on Au@Ag core–shell nanoparticles (NPs) and Au films at a silicon surface. Incorporated with 4-ATP and 4-NTP as an internal standard, OTA recognition of such aptamers could cause NP release and signal losses. Utilizing the strong peaks at 1078 and 1335 cm^–1, which represent 4-ATP and 4-NTP, respectively, the intensity ratio of I₁₀₇₈/I₁₃₃₅ could delegate the OTA concentration in a ratiometric manner. Therefore, the highest ratio of I₁₀₇₈/I₁₃₃₅ represents the lowest concentration of OTA, and a lower ratio means a higher OTA concentration. Quantitatively, the high consistency for OTA detection was achieved through correction of signal losses by IS references with an R² of 0.993 and RSD of 0.94%, and the OTA detection limit of 5 pM was achieved. Herein, such an IS aptasensor provides a reliable and scalable detection platform for various molecules in a continuous and high-throughput manner and holds great promise in future quantitative SERS measurements.