# 2PP-Hydrogel Covered Electrodes to Compensate for Media Effects in the Determination of Biomass in a Capillary Wave Micro Bioreactor

## TL;DR

This paper introduces a new electrode design for microbioreactors that improves biomass measurement accuracy by compensating for changes in the culture medium.

## Contribution

A novel hydrogel-covered electrode setup is developed to isolate biomass signals from medium effects in microbioreactors.

## Key findings

- The sensor measured yeast biomass from 1 to 20 g L−1.
- It compensated for conductivity changes between 5 to 15 mS cm−1.
- The hydrogel method is suitable for broader biosensing applications.

## Abstract

Microbioreactors increase information output in biopharmaceutical screening applications because they can be operated in parallel without consuming large quantities of the pharmaceutical formulations being tested. A capillary wave microbioreactor (cwMBR) has recently been reported, allowing cost-efficient parallelization in an array that can be activated for mixing as a whole. Although impedance spectroscopy can directly distinguish between dead and viable cells, the monitoring of cells in suspension within bioreactors is challenging because the signal is influenced by the potentially varying properties of the culture medium. In order to address this challenge, an impedance sensor consisting of two sets of microelectrodes in a cwMBR is presented. Only one set of electrodes was covered by a two-photon cross-linked hydrogel to become insensitive to the influence of cells while remaining sensitive to the culture medium. With this impedance sensor, the biomass of Saccharomyces cerevisiae could be measured in a range from 1 to 20 g L−1. In addition, the sensor can compensate for a change in the conductivity of the suspension of 5 to 15 mS cm−1. Moreover, the two-photon cross-linking of hydroxyethyl starch methacrylate hydrogel, which has been studied in detail, recommends itself for even much broader sensing applications in miniaturized bioreactors and biosensors.