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. The fluorescence turn-off/on approach showed a highly selective response to PPi over the large family of other anions. The detection limits were 0.094 μM for Cu and 0.025 μM for PPi, respectively. A wide linear range for PPi was up to 4400 μM. The indicator displacement assay (IDAs) using pyrocatechol violet (PV) as a colorimetric indicator was carried out to detect PPi with the naked eyes. The "off-on" fluorescent sensor based on BPHA CDs shows many merits, including convenient operation, cost-saving, high sensitivity, selectivity, stability and wide detecting range, which is applied to PPi detection in human urine sample.