Ratiometric Fluorescent Test Strips Based on Lysozyme-Stabilized Carbon Dots and Gold Nanoclusters Encapsulated in ZIF-8 for High-Selective Detection of Copper Ions

Although gold nanoclusters (AuNCs) are widely used in chemical sensing as a new type of luminescent nanoprobe, the metallophilic interaction between Hg2+ and Au+ on the surface of AuNCs will lead to fluorescence quenching, which will affect the detection of other metal ions based on AuNCs. Herein, a highly sensitive ratiometric fluorescent sensor was established for the detection of Cu2+ based on ZIF-8 encapsulating fluorescent nanoparticles. AuNCs and CDs were first coupled by lysozyme (LYZ) and then encapsulated in porous metal–organic frameworks of ZIF-8 by the LYZ-mediated process. The as-prepared CD@SiO2@AuNC@ZIF-8 could exhibit selective enrichment and specific response to Cu2+, resulting in the rational quenching of the fluorescence intensity of the AuNCs while the fluorescence intensity of CDs was stable and served as a background reference. The proposed method exhibited good linearity to Cu2+ concentration in the range of 0.04–4 μM and with a limit of detection of 33 nM. In addition, the prepared fluorescent test strips integrated with smartphone photo were further designed for the visual detection, which would greatly promote applications in Cu2+ monitoring.