FRET-Based\nDual-Color Carbon Dot Ratiometric Fluorescent\nSensor Enables the Smartphone-Integrated Device for Noninvasive and\nPortable Diagnosis of Chronic Kidney Disease

Cystatin C (Cys C), a crucial renal disease marker for\nchronic\nkidney disease (CKD), plays a vital role in early diagnosis and treatment\nguidance. However, most current methods for detecting Cys C rely on\na single signal and find it difficult to perform noninvasive and portable\ndiagnosis. Here, we developed a ratiometric fluorescent carbon dot\n(CD) detection system for point-of-care testing (POCT) of Cys C through\nfluorescence resonance energy transfer (FRET). The detection is based\non the hydrolysis effect of papain on a bovine serum albumin (BSA)\nscaffold and the specific inhibitory effect of Cys C on papain, endowing\nhigh-resolution color variance. Moreover, a low-cost, portable, yet\nreliable smartphone-assisted miniaturized device for real-time quantitative\nPOCT of Cys C has been developed with a limit of detection (LOD) as\nlow as 0.4 μg/mL. This sensing platform can effectively differentiate\npatients from healthy volunteers, which facilitates self-screening\nfor healthy individuals and home monitoring for CKD patients.