Novel ratiometric probe based on the use of rare earth-carbon dots nanocomposite for the visual determination of doxycycline.

Rare earth-carbon dots (RE-CDs) hybrid nanomaterials with the merits of both RE and CDs have rapidly emerging as highly promising functional materials in biochemical analysis. In this work, a new kind of water-soluble RE-CDs nanocomposite (CDs@CaF2:Eu3+) was developed for the ratiometric determination of doxycycline (DOX). The CDs@CaF2:Eu3+ under the excitation at 365 nm displayed blue emission of CDs at 440 nm and no obvious emission of Eu3+. With the addition of DOX, substantial fluorescence quenching of the CDs at 440 nm and enhancement of Eu3+ at 613 nm were observed, resulting in a ratiometric fluorescent response toward DOX. A wide linear range from 0.1 µM to 30 µM was achieved in the detection of DOX with a lowest detection limit of 43 nM. In particular, the probe could discriminate DOX from other tetracycline antibiotics through unique fluorescence response. Moreover, we have successfully applied the method for the determination of DOX in milk and honey samples.