Quantification of ochratoxin A in a coffee sample utilizing an electrochemical aptasensor fabricated through encapsulation of toluidine blue within a Zn-based metal-organic framework

Abstract

An electrochemical aptasensor has been developed specifically for the sensitive and selective determination of ochratoxin A (OTA), one of the most important mycotoxins. The aptasensor utilizes a glassy carbon electrode that has been modified with toluidine blue (TB) encapsulated in a Zn-based metal-organic framework (TB@Zn-MOF). The results demonstrate that in the presence of OTA, the peak current of the differential pulse voltammogram (DPV) related to TB oxidation is notably decreased. The changes in the oxidation peak current of TB encapsulated in Zn-MOF, both in the absence and presence of OTA, serve as an analytical signal for accurately measuring its concentration. With the proposed aptasensor, OTA can be determined within a linear concentration range 1.0 × 10^-4 - 200.0 ng mL^-1, with a detection limit of 2.1 × 10^-5 ng mL^-1. The aptasensor design is suitable for measuring OTA concentration in coffee powder samples. This represents the first report to utilize TB@Zn-MOF in designing an applicable aptasensor to OTA measurement. The high porosity of the Zn-MOF allows for a large number of TB molecules to be encapsulated in its cavities, while its large surface area enables more OTA aptamers to be immobilized on the electrode surface. These two key features significantly enhance the sensitivity of the aptasensor in measuring OTA concentration.

Keywords: Differential pulse voltammetry; Electrochemical aptasensor; Modified glassy carbon electrode; Ochratoxin A; Toluidine blue; Zn–based metal organic framework.