An ultrasensitive non-noble metal colorimetric assay using starch-iodide complexation for Ochratoxin A detection.

Colorimetric sandwich-type biosensors that can both provide sensitivity competitive with fluorescence-based approaches, and leverage reagents that are cost-effective, widely available and as safe as possible, are highly sought after. Herein, we demonstrate an alternative highly-sensitive colorimetric method for paper-based sandwich-type biosensing that uses starch–iodide complexation to simplify practical biosensing using ubiquitous reagents. Targeting the mycotoxin ochratoxin A (OTA), a covalently-immobilised OTA antibody on a cellulose surface captures OTA and forms a sandwich with OTA aptamer-conjugated glucose oxidase. Adding the chromogenic reagents at an optimized concentration, a distinct blue color develops within 30 min, offering excellent contrast with the clear/white of the negative sample. With a sampling volume down to just 5 μL, the assay exhibits concentration limits of detection and quantitation of 20 and 320 pg mL−1, respectively, and a linear range from 10−1 to 105 ng mL−1 (R2 = 0.997). The method displays excellent selectivity against related mycotoxins, excellent %recovery (95–117%) and robust operation in complex matrices (beer, urine and human serum), with no significant difference versus gold-standard liquid chromatography. Along with its excellent analytical performance, this assay benefits from non-toxic and extremely cheap reagents that can be safely disposed of in the field, and presents an attractive alternative to toxic dyes and nanoparticles. Image 1 • Novel colorimetric antibody-aptamer sandwich assay using starch-iodine complexation. • Central composite design for fast and efficient sensor optimization. • Ultrasensitive detection of OTA using PADs with LoD of 20 pg mL−1 using 5 μL. • Applied for OTA detection in beverages, urine and human serum. [ABSTRACT FROM AUTHOR]