Ultrasensitive electrochemical aptasensor for ochratoxin A detection using AgPt bimetallic nanoparticles decorated iron-porphyrinic metal-organic framework for signal amplification

An ultrasensitive electrochemical ochratoxin A (OTA) aptasensor was designed using AgPt bimetallic nanoparticles decorated iron-porphyrinic metal-organic framework (PCN-223-Fe) as electrochemical tracer. PCN-223-Fe was synthesized with zirconium ion as node and iron-porphyrin as linker, and in situ supported with PtAg bimetallic nanoparticles to obtain AgPt/PCN-223-Fe composite. Spindle-shaped AgPt/PCN-223-Fe was characterized by electron microscopies, X-ray diffraction and X-ray photoelectron spectroscopy. Due to the synergistic effect, AgPt/PCN-223-Fe modified electrode exhibited enhanced electrocatalytic activity to oxygen reduction. Sequentially, AgPt/PCN-223-Fe was combined with streptavidin (SA) to prepare electrochemical tracer. SA/AgPt/PCN-223-Fe introduced into the electrode surface capturing OTA aptamer through the recognition of biotin and streptavidin, which lead to a strong electrochemical signal from oxygen reduction. When OTA existed in solution, the aptamer was bonded with OTA preferentially, and electrochemical signal reduced. The proposed approach showed a wide linear range from 20 fg mL(-1) to 2 ng mL(-1) and a low detection limit of 14 fg mL(-1) (S/N = 3). Meanwhile, the aptasensor showed good reproducibility, stability and selectivity, which was successfully applied for OTA detection in red wine and corn samples. This strategy broadens application of metal-organic frameworks, and could be used for other toxins detection.