LAUSR

Electrochemiluminescence immunoassays are usually carried out through "on-electrode" strategy i.e., sandwich-type immunoassay format, the sensitivity of which is restricted by two key bottlenecks: (1) the number of signal labels is limited, and (2) only a part of signal labels could participate in the electrode reaction. In this perspective article, we discuss the development of "in-electrode" Faraday cage-type concept based immunocomplex immobilization strategy. The biggest difference from the traditional sandwich-type one is that, the designed "in-electrode" Faraday cage-type immunoassay uses a conductive two-dimensional (2-D) nanomaterial simultaneously coated with signal labels and recognition component as the detection unit, which could directly overlap on the electrode surface. In such a case, electrons could flow freely from the electrode to the detection unit, the outer Helmholtz plane (OHP) of the electrode is extended, and thousands of signal labels coated on the 2-D nanomaterial are all electrochemically "effective". Thus then, bottlenecks above-mentioned obstructing the improvement of the sensitivity in sandwich-type immunoassay are eliminated, and resulting much higher sensitivity of Faraday cage-type immunoassay can be obtained. And, the applications of the proposed versatile "in-electrode" Faraday cage-type immunoassay have been explored in the detection of target polypeptide, protein, pathogen and microRNA, with the detection sensitivity improved tens to hundreds of times. Finally, outlook and challenges in the field are summaried. The rise of Faraday cage-type electrochemiluminescence immunoassay (FCT-ECLIA) based biosensing strategies opens new horizons for wide range of early clinical identification and diagnostic applications.