G-Quadruplex/Hemin Self-Assembly Powered Homogeneous Electrochemical/Visual Sensor for Efficient and Reliable Detection of Ochratoxin A

Electrochemical (EC) aptasensors stand out in ochratoxin A (OTA) detection due to their rapid analysis capabilities. However, existing EC aptasensors rely on layer-by-layer assembly techniques for immobilization. Thus, developing a simple technique that can efficiently and accurately detect OTA remains a significant challenge. Herein, an homogeneous EC/visual sensor is developed to achieve an efficient and reliable detection of OTA. First, gold nanoparticles grown on mesoporous polydopamine nanoparticles (AuNPs@mPDA) serve as nanocontainers for hemin encapsulation. OTA aptamers and SH-complementary DNA (SH-cDNA) act as a “biogate” to encapsulate hemin. The presence of OTA can trigger the opening of the biogate, releasing hemin, which then self-assembles into G-quadruplex/hemin DNAzyme (GQH). GQH acts as the electron transfer mediator, generating an EC signal. Meanwhile, GQH catalyzes colorimetric substrates, and the resulting visual response can be rapidly assessed for OTA contamination using a portable colorimeter. Overall, this homogeneous strategy and dual-signal mode effectively circumvent the errors induced by environmental factors and the tedious electrode preparation, thereby significantly enhancing the efficiency and reliability of detection. The proposed homogeneous sensor can sensitively electrochemically detect OTA in the range from 1 pg/mL to 500 ng/mL via the EC method and visually within the range from 100 pg/mL to 500 ng/mL. Furthermore, this sensor has exhibited satisfactory performance in the detection of OTA in complex food matrices, highlighting its potential in food safety monitoring.