Label-free fluorescence aptasensor for ochratoxin A using crystal violet as displacement-type probe

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• A label-free fluorescent aptasensor was developed for the detection of OTA. • Crystal violet (CV) as a displacement-type fluorescent probe was discovered for OTA aptasensor. • The rapid and high sensitivity detection of OTA in actual red wine was achieved. • An assay kit is developed base on this method, which meet the maximum permissible specified in European Commission. • The designed assay kit showed broad prospects in portable systems and in-field monitoring. Ochratoxin A (OTA) is a widespread, highly toxic, and harmful mycotoxin. It is commonly found in contaminated crops and foods by a fungal infection. Therefore, to avoid the risk of OTA consumption, rapid and sensitive detection methods are highly required. This report proposes a novel label-free fluorescence aptasensor for the immediate, and highly sensitive detection of OTA in red wine by utilizing crystal violet (CV) as a displacement-type fluorescence probe. CV can interact with OTA aptamer in the absence of its target, thus inducing its folding into an antiparallel G-quadruplex, while CV stacks onto the two external G-tetrads of OTA aptamer engendering a strong fluorescence. However, in the presence of OTA, the CV-aptamer complex will be dissociated, thus decreasing the fluorescence intensity. The experimental data denote that the limit of detection of the developed label-free fluorescence aptasensor achieved 0.56 nmol/L, and the linear range was from 0.56 to 7.8 nmol/L. Moreover, an assay kit was designed based on this method, representing a promising strategy for portable systems and in-field monitoring.