| Summary: | Electrochemical impedance spectroscopy (EIS) has been one of the most intensively studied electrochemical techniques for biosensing in recent decades. However, despite its great potential, real applications of EIS sensors still remain not as widely spread as other techniques because there are many factors that govern impedimetric signals. In particular, features such as the probe coverage density on the sensor surface, as well as the target size, charge and conformation, can assume significant importance. The aim of this study was to analyse both the limitations and the potential solutions for maximizing the EIS signals in certain possible systems which are characterised by having different types of target to detect. In order to reproduce different conditions, four types of molecular targets have been taken in consideration. These provided example systems where the approach for the development of an EIS sensor varied considerably. In the first system the importance of the surface conditions of an aptasensor for prostate specific antigen (PSA) using Faradaic processes was reported. It was demonstrated that the effect of the target binding combined with the relative surface charge modification can diminish the EIS signals. In the second system, a strategy for improving the sensitivity and selectivity of the assay for drug discovery applications was demonstrated. This was obtained by adopting ferrocene-crowned gold nanoparticles that specifically bind to the molecular targets and induced a transition from non-Faradaic to Faradaic processes. In the last two example systems, particular attention has also been given to non-Faradaic processes which are the least exploited in EIS systems although the technique can be simpler to implement compared to Faradaic EIS. Moreover, with non-Faradaic processes more effective results can be achieved under some specific conditions, such as exploiting the size and charge of molecular targets. On such premises, the current work wants to serve as a reference for overcoming the limitations met in several EIS systems and hopefully contribute as a support for enhancing the fields of applications of EIS sensors.
|
|---|
