An ON/OFF Aptasensor for Detection of AFB1 Based on pH-sensitive Polymer and GO Composite

In this work, a novel ON/OFF aptasensor was designed with a composite film consisting of carboxylated graphene oxide (GO) and poly(4-vinyl pyridine) (P4VP) for the accurate and sensitive detection of AFB1. The "on" and "off" behavior of the electrochemical sensor could be controlled by the pH sensitive P4VP. Through continuous switching of solution pH value below and above pKa of P4VP (pKa = 4.9), the conversion in the reversible electron transfer between protonized or deprotonized P4VP and the electrochemical probe was used to control the "ON" and "OFF" state of the electrochemical sensor. The condition was optimized when the electrochemical sensor is kept "ON" state, finding that the aptasensor showed highest current signal and the best electrochemical performance at pH = 4. Here the addition of P4VP not only could significantly improve the current signal at pH = 4 but also increase the stability of the modified electrode. Carboxylated GO was able to form an amide linkage with an amino-modified aptamer to fix the aptamer more firmly and increase the immobilized quantity of aptamer. On the basis of the excellent electrochemical performance of GO-P4VP composite, the designed biosensor exhibited a wide linear range from 0.01 to 50 ng ml−1 and a low detection limit of 14.75 pg ml−1.