# Fundamental Insights into Nanoconfined Devices by Using Electrochemical Impedance Spectroscopy

## TL;DR

This paper shows how electrochemical impedance spectroscopy can reveal key properties of nanoconfined devices, offering new insights for sensor development.

## Contribution

The study demonstrates the effectiveness of EIS and ECS in analyzing nanoscale electrochemical systems with high precision.

## Key findings

- EIS and ECS can estimate ion and electron transfer resistances, double-layer, and redox capacitance in carbon-coated nanopipettes.
- Capacitance-based analysis can detect redox species at concentrations below 10 μM, indicating potential for sensing applications.
- EIS effectively monitors surface modifications, showing significant resistance changes upon protein adsorption.

## Abstract

Despite electrochemical impedance spectroscopy (EIS)
being a powerful
tool to inspect phenomena that occur at different time scales, its
application to nanofluidic devices remains underexplored. In this
study, we investigate the electrochemical behavior of glass nanopipettes
internally coated with a carbon layer (CNPs, 60 nm radius) using EIS
and electrochemical capacitance spectroscopy (ECS) to decouple ion
transport from redox reactions. Through systematic measurements under
varied conditions, we demonstrate herein that EIS and ECS can facilitate
the estimation of key parameters, such as ion and electron transfer
resistances, double-layer capacitance, and redox capacitance, by employing
equivalent electrical circuits. Complementary methods, i.e., the distribution
of relaxation times and differential capacitance, provide consistent
values of resistances and capacitances compared to equivalent circuit
analysis (<5% of difference between both methods) without predefined
circuit assumptions, offering further insight into time constants
and CNP resistance. Moreover, we underline the effectiveness of capacitance-based
analysis in detecting redox species within the CNP domain at concentrations
<10 μM, suggesting significant potential for sensing applications.
Also, EIS effectively monitors surface modifications in the presence
of nonredox-active compounds, as demonstrated using bovine serum albumin.
Thus, protein adsorption led to a slight increase of 16 mV in peak
separation in voltammetry; whereas EIS displayed a significant increase
in both electron transfer resistance (from 0.88 to 18.4 MΩ)
and ion resistance (from 8.55 to 10.6 MΩ). Overall, our findings
underscore the potential of EIS in nanoscale electrochemistry, providing
a valuable platform for fundamental studies and sensor development
in nanoconfined domains.