C₆₀ Mediated Ion Pair Interaction for Label-Free Electrochemical Immunosensing with Nanoporous Anodic Alumina...

Label-free biosensing based on the nanoporous anodic alumina (NAA) membrane emerged as a versatile biosensing platform in the recent decade. In the present work, we developed a new immunosensing strategy based on the nanochannels of NAA and the ion pair interaction mediated by electrochemistry of C₆₀. The NAA served as the matrix for the immobilization of the capture antibodies. The incubation of target antigens resulted in the formation of the immunocomplexes and thus an increase of the steric hindrance of the nanochannels. Therefore, the concentration of the redox probe transported through the nanochannels decreases, which can be detected at the working electrode modified with C₆₀. Herein, we initially found that the cathodic peak ascribed to the reduction of C₆₀ to C₆₀^- was obviously enhanced by the presence of the redox probe K₃[Fe(CN)₆] and which was contributed to the formation of a ternary ion association complex among C₆₀, tetraoctylammonium bromide, and K₃[Fe(CN)₆]. Therefore, the transportation of K₃[Fe(CN)₆] though the NAA-based bionanochannels can be detected by a C₆₀ modified electrode with an amplified signal. Choosing human epididymis protein 4 (HE4) as the model target, a linear range of 1.0 ng mL^-1 to 100 ng mL^-1 can be established between the peak current obtained from the differential pulse voltammetric response of the platform and the concentration of HE4. The detection limit was 0.2 ng mL^-1. This study not only provides a new avenue to develop the other nanochannel-based biosensing platform for a variety of other disease biomarkers but also contributes to the electrochemistry of fullerene.