Au@Fe3O4 nanocomposites as conductive bridges coupled with a bi-enzyme-aided system to mediate gap-electrical signal transduction for homogeneous aptasensor mycotoxins detection

A novel gap-electrical homogeneous aptasensor based on Au@Fe3O4 nanocomposites as conducive bridges coupled with a bi-enzyme-aided system is developed for mycotoxins assay. Herein, exonuclease I (Exo I) and terminal deoxyribonucleotidyl transferase (TdT) constitute a bi-enzyme-aided system, which efficiently regulates the quantity of deoxyribonucleic acid (DNA) on Au@Fe3O4 nanocomposites surface, which in turn influences the conductivity of Au@Fe3O4 nanocomposites. In this strategy, ochratoxin A (OTA) is used as the model mycotoxin. In the presence of OTA, Exo I in the bi-enzyme system can degrade DNA on Au@Fe3O4 nanocomposites surface. After multiple cycles, no DNA remains on Au@Fe3O4 surface. After transferred onto the interdigitated electrodes surface, the Au@Fe3O4 particles are directly assembled under an external magnetic field and a conducive network with high conductance is formed. Conversely, the absence of OTA produces a large amount of single stranded DNA (ssDNA) accumulated on Au@Fe3O4 surface with the aid of TdT in the bi-enzyme system. The poor conductivity of ssDNA contributes to low conductance of the interdigitated electrode. Under the optimal experimental conditions, the developed homogeneous gap-electrical aptasensor has high sensitivity and selectivity for OTA determination in real samples. These performances suggest the great potential for this developed strategy in screening of carcinogenic mycotoxins and food safety evaluation.