# Rigor & Reproducibility: pH Adjustments of Papain with L-Cysteine Dissociation Solutions and Cell Media Using Phenol Red Spectrophotometry

## TL;DR

This paper introduces a simple and reliable method to adjust and monitor pH in cell dissociation solutions using phenol red, improving cell viability and research reproducibility.

## Contribution

A spectrophotometric pH adjustment method for low-volume dissociation media using phenol red is introduced, validated against traditional pH probes.

## Key findings

- Phenol red spectrophotometry reliably adjusts pH in low-volume dissociation solutions to physiological levels (~7.4).
- Unadjusted papain-based dissociation media with L-cysteine can be acidic (pH 6.6), reducing cell viability.
- The method supports consistent pH documentation, enhancing reproducibility in cell isolation and downstream applications.

## Abstract

Phenol red is a widely used, low-cost, label-free colorimetric pH indicator that bridges traditional colorimetric assays with modern quantitative imaging and cell-based screening platforms. Its protonation-dependent absorbance shift (430–560 nm) allows for the real-time monitoring of extracellular acidification, which indirectly reflects cellular metabolism, growth, and respiration. Although phenol red lacks the molecular specificity of genetically encoded or fluorogenic biosensors, it remains useful in systems where pH changes are effective proxies for physiological processes. Existing tissue digestion protocols often overlook key parameters, especially pH control and enzyme cofactor use. This study presents a straightforward, spectrophotometric method to monitor and adjust the pH of low-volume (1 mL) buffered enzymatic dissociation media using phenol red and a plate reader. We titrated dissociation solutions to physiological pH (~7.4) using spectrophotometric pH measurements validated against conventional glass pH probe readings, confirming method reliability. Accurate pH assessment is critical for isolating viable primary cells for downstream applications such as tissue engineering, single-cell omics, and neurophysiological assays. We highlight that papain-based dissociation media supplemented with L-cysteine can be acidic (pH 6.6) if unadjusted, compromising cell viability. This accessible approach enhances reproducibility by promoting pH documentation concerning dissociation conditions that contribute to advancing consistency in biomedical, cellular, neuronal, and tissue engineering research.