# Development of a biosensor for spectrophotometric determination of l-lactate in artificial saliva

## TL;DR

A new colorimetric biosensor was developed to detect l-lactate in artificial saliva using Fe3+ ions instead of traditional enzymes.

## Contribution

The study introduces a novel biosensor using Fe3+ ions with peroxidase-like activity for l-lactate detection.

## Key findings

- The biosensor has a linear detection range of 5 µM–20 µM l-lactate with a detection limit of 1.278 µM.
- Fe3+ ions effectively replace horseradish peroxidase in catalyzing TMB oxidation for l-lactate measurement.
- The method was successfully applied to artificial saliva samples with satisfactory results.

## Abstract

Analysis of critical biomarkers like l-lactate is extremely important in clinical practice. Herein, a non-invasive and sensitive colorimetric biosensor for accurate l-lactate determination has been developed. The proposed method demonstrates the ability of Fe3+ ions of iron(III) chloride to substitute the traditional horseradish peroxidase enzyme in the colorimetric determination of l-Lactate. The biosensor is based on the release of H2O2 by lactate oxidase enzyme (LOx) after 30 min incubation in a 37 °C water bath. Subsequently, H2O2 reacts with 3,3′,5,5′-tetramethylbenzidine substrate (TMB) catalyzed by Fe3+ ion utilizing its peroxidase-mimetic activity. Fe3+ ion has peroxidase-like activity which could rapidly catalyze the oxidation reaction of TMB by H2O2, producing a characteristic blue colored product at 30 °C water bath for 15 min. Based on the catalytic mechanism of fast electron transfer between TMB and H2O2 with the assistance of the intrinsic peroxidase-like activity of Fe3+ ion, a colorimetric biosensor for determination of l-lactate was developed. The obtained colored product of oxidized TMB could be measured spectrophotometrically at λmax 652 nm. The biosensor yielded a reproducible response over a linear range of 5 µM–20 µM of l-lactate with a limit of detection of 1.278 µM. Furthermore, satisfactory results were obtained upon application of the method to artificial saliva samples.

The online version contains supplementary material available at 10.1186/s13065-025-01718-5.