Zeolitic imidazolate framework-8 encapsulating gold nanoclusters and carbon dots for ratiometric fluorescent detection of adenosine triphosphate and cellular imaging

A novel nanoprobe was prepared by encapsulating carbon dots (CDs) and gold nanoclusters (AuNCs) into zeolitic imidazolate framework-8 (ZIF-8) for sensitive detecting adenosine triphosphate (ATP). Under excitation at 360 nm, the obtained CDs/AuNCs@ZIF-8 nanoprobe exhibits dual-emissions at 469 nm and 660 nm, respectively, corresponding to the fluorescence emission of CDs and the aggregation-induced emission enhancement (AIEE) of AuNCs. The framework of ZIF-8 in this probe can be degraded by ATP due to the coordination competition of ATP and 2-Methylimidazole towards zinc ion (Zn2+), resulting in the release of CDs and AuNCs. The following dispersion of CDs would improve efficiencies of the fluorescence excitation and the consequent emission of CDs. On the contrary, the AIEE of AuNCs would be decreased spontaneously after the AuNCs originally restricted in ZIF-8 were allowed to escape. The intensity ratio of fluorescence at 469 nm to that at 660 nm (I469/I660) was conveniently employed as the response signal for representing the amount of ATP. This nanoprobe exhibits excellent sensitivity and selectivity toward ATP, with a limit of detection (LOD) of 0.061 μM. Besides, low cytotoxicity of this nanoprobe facilitates its application as a fluorescent indicator in fluorescence imaging of living cells. Encapsulating two types of fluorescent nanomaterials by a degradable ZIF-8 structure makes the ratiometric fluorescence response of the nanocomposite probe towards the target analyte that destroys the ZIF-8 structure possible, and simplifies the application of the probe.