Self-assembled dual-emissive nanoprobe with metal−organic frameworks as scaffolds for enhanced ascorbic acid and ascorbate oxidase sensing

Abstract

Schematic representation of the synthesis of QDs/CDs@MOFs nanoprobe and its application for sensing. • The QDs/CDs@MOFs nanoprobe was synthesized by a facile one-pot strategy. • The QDs/CDs@MOFs nanoprobe had the advantages of MOFs and ratiometric sensors. • The utilization of MOFs to capsulate QDs and CDs can prevent their agglomeration. • AA and AAO detection were realized based on “off-on” and “off-on-off” strategy. Herein, a ratiometric fluorescent nanoprobe was successfully fabricated through incapsulating quantum dots (QDs) and carbon dots (CDs) into the cavities of zeolitic imidazolate framework-8 by self-assembly, which generated QDs/CDs@MOFs. The QDs/CDs@MOFs nanoprobe combined the properties of metal − organic frameworks (MOFs) and ratiometric fluorescent nanoprobe, thus it possessed following advantages including strong adsorption and enrichment ability for the analytes, and the ability of eliminating interferences of environmental and instrumental factors. The fluorescence of QDs loaded in the cages of ZIF-8 was initially quenched by mercury ions. However, mercury ions could be reduced to mercury atom by ascorbic acid (AA), leading to the restoration of QDs fluorescence. Moreover, under the catalysis of ascorbate oxidase (AAO), AA was oxidized to dehydroascorbic acid that couldn’t reduce mercury ions, resulting in the fluorescence of QDs quenched again. Simultaneously, the fluorescence of CDs loaded in the ZIF-8 was not affected under above procedures. Hence, with QDs serving as reporter signal and CDs acting as stable reference signal, a ratio fluorescence platform was constructed for sensitive determination of AA and AAO with the linear calibration in the range of 0.01−0.2 μM and 0.05–4 U·L −1 and the detection limit of 4 nM and 0.02 U·L −1 , respectively.