# Cobalt ferrite magnetic nanoparticles as stirring actuators to improve UV–Vis spectroelectrochemical measurements in normal reflection mode

## TL;DR

This paper introduces a new method using magnetic nanoparticles to improve UV–Vis spectroelectrochemical measurements in normal reflection mode.

## Contribution

A novel measuring cell with cobalt ferrite nanoparticles enhances mass transport and signal strength in normal reflection SEC.

## Key findings

- Cobalt ferrite magnetic nanoparticles improve mass transport in normal reflection SEC measurements.
- The new method increases both electrochemical and optical signals in the Fe(III)/(II)-orthophenanthroline system.
- The approach uses a modified measuring cell with a magnetic stirrer to enhance diffusion layer renewal.

## Abstract

Spectroelectrochemical (SEC) measurements using UV–Vis radiation in normal reflection mode (or normal configuration) are less sensitive than parallel approaches, since the volume of sample monitored has a much lower proportion of the diffusion layer created by the electrochemical processes, i.e., the region where relevant optical changes take place. In contrast, the normal configuration is more robust and reproducible and, as of today, is the only commercially available. This work presents a strategy to enhance normal reflection SEC measurements of Fe(III)/(II)-orthophenanthroline system using a screen-printed carbon electrode (SPCE), improving competitiveness with parallel designs. This method required the design of a new measuring cell based on the geometry of the commercial one, but replacing the eight magnets by a non-magnetic closing system. The developed approach involves adding cobalt ferrite magnetic nanoparticles (CoFe2O4 MNPs) to the analyte solution and coupling the SEC cell to a conventional magnetic stirrer. The resulting nanostirring, driven by MNPs movement, enhances mass transport toward the electrode. This accelerates diffusion layer renewal, leading to a noticeable increase of both electrochemical and optical signals.

The online version contains supplementary material available at 10.1007/s00604-025-07351-2.