# In Situ Determination of Chlorella Concentration Using Single Entity Electrochemistry

## TL;DR

This paper introduces an electrochemical method to detect and measure Chlorella algae in real time, aiding in early algal bloom monitoring.

## Contribution

A novel electrochemical strategy using single-particle collision at an ultramicroelectrode for real-time Chlorella detection and sizing.

## Key findings

- Collision frequency at the UME correlates with Chlorella concentration and can be calibrated.
- Migration effects enhance detection sensitivity for negatively charged microalgae.
- COMSOL simulations help estimate cell size from collision data.

## Abstract

Harmful algal blooms pose significant risks to water resource management and aquatic ecosystem health, rendering early detection of algal bloom proliferation essential. In this study, we present an electrochemical strategy for the real-time detection of individual Chlorella cells using the single-particle collision method at an ultramicroelectrode (UME). The detection principle relies on monitoring changes in the redox probe flux at the UME induced by attachment of the target. Both diffusional and migrational transport were considered to promote particle collision at the UME. Detection sensitivity for negatively charged microalgae was enhanced by exploiting migration effects. To control migration strength, neutral and charged redox probes were selected, and the ionic strength was adjusted to tune electrostatic attraction, yielding microalgae capture on the UME with a collision frequency that depended on the solution composition. Conversely, migration was suppressed by increasing the ionic strength, and inverse migration was implemented, and resulting collision responses were compared. Furthermore, COMSOL Multiphysics simulations were used to estimate the size of detected Chlorella cells. The collision frequencies expected from diffusion and migration were compared with the experimental values, and a calibration curve relating collision frequency to Chlorella concentration was established. Consequently, this methodology provides a promising platform for the early monitoring of algal blooms by simultaneously determining microalgal size and concentration.