Fast scan voltammetry-derived ultrasensitive Faraday cage-type electrochemical immunoassay for large-size targets

Electrochemical immunoassay (ECIA) is an important method for rapid, on-site detection of various analytes. However, its detection sensitivity is greatly limited by the traditional sandwich-type sensor construction mode, especially in the case of large-size targets such as pathogenic bacteria with micron size. Herein, we developed a Faraday cage-type sensing mode to build an electrochemical immunosensor based on a functionalized two-dimensional conductive nanomaterial, which could provide a platform to assemble a large number of electrochemical signal labels and a good support for the expansion of electrode surface. Electrons could flow between the electrode and the conductive nanomaterial and then exchange with all signal labels immobilized without the hindrance of non-conductive large-size targets, resulting in a significant signal amplification. In addition, first time integration with fast scan anodic stripping voltammetry (FSASV) allowed for further enhanced ECIA signal. Benefitting from both the Faraday cage-type sensing mode and the high scan rate 100 V s^-1 of FSASV, electrochemical signal was effectively amplified several hundred times with a limit of quantitation (LOQ) of 1 CFU mL^-1 for micron-sized pathogenic bacteria Vibrio parahemolyticus (VP). This work sheds lights on advancing the design of next-generation ECIA or other redox-related immunoassays with ultrahigh sensitivity, especially for large-size targets.