# Covalent and Site-Specific Immobilization of a Fluorogenic Sensor Protein on Cellulose-Based Paper for Detection of Lactate in Cell Culture Media

## TL;DR

This paper presents a paper-based sensor using fluorescent proteins to detect lactate in cell culture media, offering a new method for monitoring metabolic states.

## Contribution

The study introduces a novel covalent and site-specific immobilization method for fluorogenic sensor proteins on cellulose-based paper.

## Key findings

- Immobilizing the proteins on paper does not hinder their lactate binding ability.
- The sensor successfully detects lactate in cell culture supernatant under various conditions.
- The fluorescent readout provides a reliable and visual method for lactate detection.

## Abstract

Lactate is a key metabolite with applications ranging from monitoring training efficiency to early sepsis detection and monitoring the metabolic state of cell cultures. In this study, a paper-based lactate sensor utilizing a fluorescent readout was developed. Unlike common lactate dehydrogenase (LDH)-based methods, these sensors use a green fluorescent protein (GFP) or mApple-coupled lactate binding domain, which provides a fluorescent readout upon lactate binding. We demonstrate that immobilizing these proteins on paper does not affect their ability to bind lactate and produce a fluorescent readout, by monitoring lactate levels in the cell culture supernatant applying different cell culture conditions.