Towards the maximization of nanochannels blockage through antibody-antigen charge control: Application for the detection of an Alzheimer’s disease biomarker

Although size and charge effects in nanochannels have been previously approached for electrochemical immunosensing, as far as we know, thorough studies on the effect of both the antibody and the antibody/antigen immunocomplex charges at different pHs have not been deeply reported. In this context, we present here an unprecedented study of such parameters, applied also for the first time for the detection of an Alzheimer’s disease (AD) biomarker. AD detection is currently based in time consuming and expensive techniques, so that the development of alternative analytical strategies for facilitating its diagnosis is still a need. To reach that purpose, we propose here the development of a nanochannel-based system for the electrochemical monitoring of Tau protein, an important AD biomarker. Tau protein is selectively captured by specific antibodies immobilized in the inner walls of the nanochannels of nanoporous alumina membranes. The captured Tau protein blocks the nanochannel and difficulties the passage of red-ox indicator ions, which is voltammetrically monitored using an indium tin oxide/poly(ethylene terephthalate) (ITO/PET) electrode as transducer. The charges of both the antibody and the Tau antigen at different pHs and their effect on the diffusion of the red-ox indicator ions to the electrode are carefully evaluated to maximize the electrostatic blocking of the nanochannels upon the immunocomplex formation. The developed biosensing system allows the determination of Tau protein with a detection limit of 4.3 ng/mL, which is within the range of clinical interest, showing also excellent recovery percentages in human plasma samples.