SERS based aptasensor for ochratoxin A by combining Fe₃O₄@Au magnetic nanoparticles and Au-DTNB@Ag nanoprobes with multiple signal enhancement

A SERS-based aptasensor for ochratoxin A (OTA) is described. It is making use of Fe₃O₄@Au magnetic nanoparticles (MGNPs) and of Au@Ag nanoprobes modified with the Raman reporter 5,5-dithiobis-(2-nitrobenzoic acid; DTNB). Au-DTNB@Ag NPs were modified with the OTA aptamer (aptamer-GSNPs) and used as Raman signal probes. The SERS peak of DTNB at 1331 cm^-1 was used for quantitative analysis. MGNPs modified with cDNA (cDNA-MGNPs) were used as capture probes and reinforced substrates. When the Au-DTNB@Ag-Fe₃O₄@Au complexes are formed through oligonucleotide hybridization, the Raman signal intensity of the Raman probe is significantly enhanced. If the OTA concentration in samples increases, more Raman signal probes (aptamer-GSNPs) will dissociate from the cDNA-MGNPs because more OTA aptamer is bound by OTA. This leads to a lower Raman signal after magnetic separation. Under the optimal conditions, the detection limit for OTA is 0.48 pg·mL^-1 based on 3σ criterion. This is attributed to the multiple Raman signal enhancement and the good performance of the OTA aptamer. The good recovery and accuracy of the assay was confirmed by evaluating spiked samples of wine and coffee. Graphical abstract Schematic of an aptamer based SERS assay for OTA by integrating Fe₃O₄@AuNPs (MGNPs) with Au-DTNB@Ag NPs with multiple signal enhancement. Aptamer modified Au-DTNB@Ag NPs are used as Raman probes, and MGNPs modified with cDNA are used as capture probes and reinforced substrates.