Sodium alginate hydrogelation mediated paper-based POCT sensor for visual distance reading and smartphone-assisted colorimetric dual-signal determination of L-lactate

Herein, we presented a paper-based POCT sensor based on lactate dehydrogenase-mediated alginate gelation combined with visual distance reading and smartphone-assisted colorimetric analysis dual-signal to determine the concentrations of L-lactate in yogurt samples. In this research, L-lactate was transformed to pyruvate by lactate dehydrogenase. The pyruvate then triggered the gelation of the sol mixture, increasing the viscosity (ηs) of the mixture, which showed a decrease in diffusion diameter on the paper-based sensor. Also, protons from pyruvate accelerated the degradation of Rhodamine B, causing color fading of the mixture, which could be analyzed by a RGB analysis application software. Under the optimal experimental conditions, the linear ranges of the visual distance reading and smartphone-assisted colorimetric analysis were 0.1-15 μM for the former and 0.3-15 μM for the latter, and the detection limits were 0.03 μM and 0.07 μM, respectively. As a proof-of-concept application, we then exploited the paper-based sensor to determine the concentrations of L-lactate in yogurt samples. The results from the dual-signal paper-based sensor are consistent with the ones from HPLC analysis. In short, this study developed a simple, convenient, cost-effective and feasible method for the quantitative detection of L-lactate in real samples.