Aptasensor for the simple detection of ochratoxin A based on side-by-side assembly of gold nanorods

Abstract

A new optical aptasensor is described based on the side-by-side assembly of gold nanorods (GNRs) for the one-step determination of ochratoxin A (OTA), which is a mycotoxin identified as a contaminant in grains and wine throughout the world. A DNA aptamer against OTA exhibiting high affinity and binding specificity has already been used as a biorecognition element to improve detection. Here, thiol-modified DNA was decorated on the side sites of GNRs acting as probes. A linker DNA containing aptamer sequences against OTA hybridized with the DNA decorated on the GNRs. It was shown that the GNRs assembled side-by-side through DNA hybridization in the absence of OTA, exhibiting strongly enhanced optical properties. However, in the presence of OTA, the GNRs dispersed as a result of specific aptamer–OTA recognition and conformational changes in the aptamer. The resulting changes in the absorption spectra of the GNRs were used for sensing. A linear correlation was demonstrated between the absorbance of the GNRs at 708 nm and the concentration of OTA over the range 0.5–20 ng mL⁻¹. The limit of detection was 0.22 ng mL⁻¹ (3σ), which meets the demand for detection of the allowed concentrations of OTA in foods according to European Commission Regulations (2 ng g⁻¹). The selectivity and feasibility of the developed OTA aptasensor for the detection of OTA in red wine samples was also evaluated and it was shown to be a simple, efficient and cost-effective one-step detection method. This method is a promising tool in toxin screening to guarantee food safety and to minimize potential risks to human health.