A colorimetric indicator-displacement assay based on stable Cu selective carbon dots for fluorescence turn-on detection of pyrophosphate anions in urine.

Determination of PPi levels in urine represents a measurable factor for diagnostic, treatment, and monitoring of urolithiasis. Owing to the quenching ability of Cu on fluorescent carbon dots (CDs) and strong binding affinity between Cu and PPi, we develop a new off-on assay for PPi detection using newly BPHA CDs (BPHA: N,N-bis(pyridin-2-ylmethyl)hexan-1-amine). The fluorescence intensity of BPHA CDs was significantly quenched by Cu ("off") through forming BPHA CDs/Cu complexes and the fluorescence intensity of BPHA CDs /Cu system was completely resumed by PPi ("on") owing to the release of free Cu.