Thin-Layer Behavior in Carbon Nanopipettes. Understanding the Iontronic-Electronic Contributions

Abstract

Nanopipettes with carbon-coated inner surfaces (carbon nanopipettes, CNPs) have attracted considerable attention due to their exceptional sensitivity and potential in electroanalytical applications. The nanoconfinement of the sample solution within the CNP facilitates a thin-layer electrochemical regime, in which ion and electron transferences are inherently coupled. This feature allows exhaustive oxidation/reduction of certain analytes within typical electroanalytical time scales, offering unprecedented opportunities for nanoscale sensing. Despite this promising advantage, a detailed understanding of how measurement dimensions and experimental conditions influence key electrochemical responses remains significantly underexplored. Effectively, conventional electrochemical methods frequently struggle with decoupling ionic and redox contributions, which are critical for understanding the performance toward optimal exploitation. For the first time, cyclic voltammetry (CV), numerical simulations, and electrochemical impedance spectroscopy (EIS) are combined to systematically investigate the interplay between ion transport and electron transfer in the electrochemical behavior of CNPs. CV experiments were used to assess essential parameters under varying electrolyte compositions, solution depths, and scan rates, achieving signal-to-noise ratio enhancements of over 10-fold and submicromolar detection of the redox couple at the rationalized conditions. Complementarily, it is demonstrated that EIS can resolve the nanofluidic behavior by deconvoluting iontronic and electronic contributions, opening an option to be investigated more extensively in future research. The present study not only provides insights into the unique thin-layer electrochemical behavior of CNPs but also establishes the feasibility of simultaneously obtaining iontronic and electronic information with a single setup. This dual capability is poised to advance both related applications, e.g., sensing, (bio)­catalysis, imaging, and fundamental directions in nanoelectrochemistry.