A microfluidic paper-based distance-readout immunosensor for visual quantification of Salmonella typhimurium

This article presents a microfluidic paper-based distance readout immunosensor for the quantitative monitoring of Salmonella typhimurium (S. Typhimurium) levels. By integrating paper-microfluidics, carbon nanomaterials, and a sandwich-formatted immunological technique, the developed immunosensor provides a linear range of 10.0-200.0 CFU mL^-1 (R² = 0.9970) with a detection limit (LOD) of 10.0 CFU mL^-1 for S. Typhimurium detection. Furthermore, the method demonstrated excellent selectivity, with no interference from the tested bacteria strains and chemical compounds, as well as remarkable precision with the highest relative standard deviation (RSD) of 3.8%. It also exhibited high accuracy and precision for S. Typhimurium monitoring in both food and water samples. The obtained results were comparable to those of the conventional plate culture method at the 95% confidence level by a t-test, demonstrating the reliability and analytical validity of the proposed method. Moreover, our technique is simpler and cheaper to operate than previous immunoassay techniques that rely on costly instruments for signal measurement and external magnetic separation. Therefore, this distance-based immunosensing platform shows great promise as a simple and effective analytical tool for S. Typhimurium across various sample matrices, making it highly deployable in real-world applications and resource-limited settings.