Dual-emission carbon dots based ratiometric fluorescent sensor with opposite response for detecting copper (II)

Herein, carbon dots with intrinsic dual-emission fluorescence (d-CDs) at 360 nm (F360) and 530 nm (F530) under excitation of 320 nm were prepared by microwave-assisted heat treatment of o-phenylenediamine (OPD). Cu2+ could be effectively captured by the d-CDs via coordinating with the nitrogen lone pair of –NH2 to form a complex (Cu2+-OPD) by electron pair sharing. The complex can efficiently quench the fluorescence of F360 by through-bond energy transfer (TBET) and meanwhile selectively enhance the fluorescence of F530 by inhibiting the occurrence of photoinduced electron transfer (PET). The unique opposite response of the d-CDs toward Cu2+ could produce a large change to the value of F360/F530 and thus the d-CDs were utilized to fabricate a ratiometric fluorescent sensor to detect Cu2+ with a wide linear range of 0.8–55.0 μmol L−1 and a low limit of detection (LOD) of 44.63 nmol L−1 (R2 = 0.9989). Recoveries of 95.8–102.3% with relative standard deviations (RSD) < 6.7% were achieved in spiked food samples. Moreover, this sensor possessed excellent selectivity and sensitivity for the quantitative determination of Cu2+, indicating its promising potentials for constructing a reliable and convenient approach for quick pre-warning of Cu2+.