Paper and cloth-based microfluidic chips for rapid cysteine detection in deep-sea cold seeps

In this study, we developed a simple and cost-effective paper and cloth-based microfluidic fluorescence sensing device for the selective and quantitative detection of L-cysteine (L-Cys) in deep-sea water, addressing the need for efficient monitoring of this critical metabolite of deep-sea creatures which acts as a biomarker for tracking these organisms. The device employs gold nanoparticles (Au NPs) immobilized on a cloth-based substrate and rhodamine B (Rh B) molecules. In the presence of L-Cys, strong interactions between L-Cys and the Au NPs release Rh B molecules, restoring fluorescence proportional to the cysteine concentration. The device achieves a low detection limit of 0.52 nM with a dynamic range of 1-100 nM. It demonstrates excellent selectivity over other amino acids, stability over 30 days, and reproducibility. Its practical applicability was confirmed using deep-sea cold seep water samples, yielding recoveries of 98.07%-102.62%. Compared to existing methods, this platform offers enhanced portability, lower cost, and faster response, making it suitable for <i>in situ</i> environmental monitoring.