Smartphone-assisted antifouling colorimetric aptasensor for ultrasensitive ochratoxin A detection in coffee

A smartphone-assisted colorimetric aptasensor was constructed for the detection of ochratoxin A (OTA) utilizing Au/CeO₂/rGO nanohybrid. The sensor integrates aptamer-functionalized Au/Fe 3 O 4 (Apt/Au/Fe 3 O 4 ) as recognition elements. The complementary-chain-modified Au/CeO₂/rGO (cDNA/Au/CeO₂/rGO) act as nanozyme catalyst for signal amplification through the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to blue-colored ox-TMB. The detection mechanism relies on competitive binding between OTA and cDNA/Au/CeO 2 /rGO to Apt/Au/Fe 3 O 4 . Upon OTA introduction, OTA preferentially binds to Apt/Au/Fe 3 O 4 . These Apt/Au/Fe 3 O 4 are magnetically separated and introduced into the cDNA/Au/CeO 2 /rGO suspension. Unbound Apt/Au/Fe 3 O 4 interacts with cDNA/Au/CeO 2 /rGO. After magnetic separation, the residual cDNA/Au/CeO 2 /rGO concentration in supernatant exhibits a correlation with the OTA concentration. This design effectively eliminates potential interference from the intrinsic color of coffee, significantly improving the accuracy of colorimetric detection. The aptasensor demonstrated superior selectivity towards OTA with a detection limit of 27.3 pg mL −1 . This specificity was validated against interference, with recovery rates of 102.1–117.4 % in coffee, as confirmed by ELISA.