Gold@silver nanodumbbell based inter-nanogap aptasensor for the surface enhanced Raman spectroscopy determination of ochratoxin A

Highlights: • A plasmonic nanogap Au@Ag nanodumbbell structure was prepared for OTA assay. • The inter-nanogap structure generated more hot spots to enhance the Raman intensity. • The limit of detection of OTA was as low as 0.007 ng mL⁻¹. • The SERS method could be utilized in real sample detection. Here, a plasmonic nanogap structure was fabricated with its specific surface enhanced Raman spectroscopy (SERS) effect to construct an aptasensor for the sensitive detection of ochratoxin A (OTA). Gold nanorod (AuNR) were synthesized first by seed-mediated method. Then, silver was reduced and grown on its surface. In the presence of glycine, Ag⁰ was preferred to grow at both ends of AuNR to form Au@Ag nanodumbbell (Au@AgND). The thiolated OTA aptamer and its complementary sequence were modified on Au@AgND respectively using Ag-SH bond. Under the base complementary pairing principle, Au@AgND assembly formed with certain inter distances. The inter-nanogap structure generated more hot spots which enhanced the Raman signal of 4-hydroxybenzoic acid (4-MBA) immobilized on Au@AgND. When OTA was present, the aptamer preferentially combined to OTA and the Au@AgND assembly disintegrated. Thus, the SERS signal of 4-MBA decreased. Under the optimal conditions, the OTA concentrations were inversely proportional to SERS signal. The linear range was 0.01 ng/mL-50 ng/mL and the limit of detection (LOD) was 0.007 ng/mL. The method can be successfully applied to the detection of real sample (beer/peanut oil).