Cascade recognition-enabled portable fluorescent sensor for specific detection of lysozyme in tear samples

Accurate detection of decreased tear lysozyme (LYZ) levels, a diagnostic biomarker for dry eye disease (DED), is critical for early intervention. Conventional LYZ detection requires bulky instruments; emerging aptamer/electrochemical methods are costly and complex. To address these challenges, we designed a portable fluorescent sensor using boron-doped red-emitting carbon dots (B-RCDs) via a three-step cascade recognition mechanism: electrostatic pre-enrichment, dynamic quenching, and boronate ester recognition. This cascade enables sensitive and selective detection of LYZ in human tear samples. Under optimal conditions, the sensor exhibits a linear response from 10 to 90 μg/mL with a LOD of 0.026 μg/mL, outperforming most reported CD-based probes. The sensor shows excellent anti-interference performance, with recoveries of 88.70%-106.30% (RSD < 4.0%) in real tear samples, consistent with standard turbidimetric results. Furthermore, a filter paper strip integrated with a smartphone-assisted color analysis module (Manhattan distance calibrated) achieves visual point-of-care LYZ detection within 5 min. This work provides a portable platform for point-of-care DED screening and a generalizable cascade recognition strategy for glycoprotein detection.