Competitive coordination assembly of light-degradable gold nanoclusters-intercalated metal organic frameworks for photoresponsive drug release

Controlled drug release with on demand holds great promise for cancer therapy. Light-degradable nanocarriers have gained increasing attention for designing controllable drug delivery systems due to their spatiotemporally controllable properties. Herein, a high luminescent and light-degradable nanocarrier is constructed by intercalating glutathione-capped gold nanoclusters (AuNCs) into zeolitic imidazolate framework-8 (ZIF-8) via competitive coordination assembly, named as AuNC@ZIF-8, for light-triggered drug release. Glutathione-capped AuNCs and 2-methylimidazole (MIm) competitively coordinated with Zn2+ to form AuNC@ZIF-8 via one step process in aqueous solution. Specifically, the obtained AuNC@ZIF-8 has a high quantum yield of 52.96 % and displays a distinctive property of photolysis. The competitive coordination interactions within AuNC@ZIF-8 were evidenced by X-ray diffraction and X-ray photoelectron spectroscopy, in which Zn2+ strongly coordinated with the N of MIm and weakly coordinated with the carboxyl/amino groups in glutathione of AuNCs. Under light irradiation, the Au-S bond on AuNCs breaks, enhancing the coordination ability between carboxyl/amino groups and Zn2+ enhance. This leads to the collapse of the crystal structure of AuNC@ZIF-8 and subsequent fluorescence quenching. Additionally, AuNC@ZIF-8 is successfully employed as luminescent nanocarriers of anticancer drugs to form drug-AuNC@ZIF-8, in which three typical anticancer drugs are selected due to different coordination interaction. The obtained smart drug-AuNC@ZIF-8 can be effectively internalized into HeLa cells and degraded in response to blue light, with negligible dark cytotoxicity and high light cytotoxicity. This study highlights the crucial role of competitive coordination interactions in synthesizing functional materials with fluorescence efficiency and photolytic properties.