S-doped carbon dots capped ZnCdTe quantum dots for ratiometric fluorescence sensing of guanine

Quantum dots (QDs)-based ratiometric fluorescence probe have drawn extensive attention in recent years. However, intrinsic dual-emitting QDs were rarely reported, and most of them were based on the metal doped-QDs. Herein, an intrinsic dual-emitting ZnCdTe QDs were synthesized by using fluorescence S doped-carbon dots (CDs) as capping ligands for the first time in this work, two emission peaks (derived from CDs and QDs respectively) were observed in CDs-ZnCdTe QDs and the probe showed excellent stability and optical properties. Moreover, we found that the fluorescence emission of QDs could be quenched by guanine via excited state electron transfer or the aggregation of QDs, but the emission of CDs remained stable, thus we successfully developed a ratiometric probe for the determination of guanine. Under optimized conditions, the detection limit of guanine was 0.076 mu mol.L-1 (3 sigma/k), with a linear range from 0.25 to 40.0 mu mol.L-1. The smart ratiometric fluorescence probe was demonstrated for the detection of guanine in DNA samples with satisfactory recoveries ranging from 96.95 to 102.50%, indicating it was a promising biosensor for highly selectively and sensitively determination of guanine.