Gold nanoclusters are emerging as new materials for biomedical applications because of promises offered by their ultrasmall size and excellent biocompatibility. Here, the synthesis and optical and biological characterizations of a highly luminescent folate-functionalized Au22 cluster (Au22-FA) are reported. The Au22-FA clusters are synthesized by functionalizing the surface of Au22(SG)18 clusters, where SG is glutathione, with benzyl chloroformate and folate. The functionalized clusters are highly water-soluble and exhibit remarkably bright luminescence with a quantum yield of 42%, significantly higher than any other water-soluble gold clusters protected with thiolate ligands. The folate groups conjugated to the gold cluster give rise to additional luminescence enhancement by energy transfer sensitization. The brightness of Au22-FA is found to be 4.77 mM−1 cm−1, nearly 8-fold brighter than that of Au22(SG)18. Further biological characterizations have revealed that the Au22-FA clusters are well-suited for bioimaging. The Au22-FA clusters exhibit excellent photostability and low toxicity; nearly 80% cell viability at 1000 ppm of the cluster. Additionally, the Au22-FA clusters show target specificity to folate-receptor positive cells. Finally, the time-course in vivo luminescence images of intravenous-injected mice show that the Au22-FA clusters are renal-clearable, leaving only 8% of them remained in the body after 24 h post-injection.
Bibliographical noteFunding Information:
D.L. acknowledges support by the Korea CCS R&D Center (KCRC) grant (NRF-2014M1A8A1074219), the NRF grant (NRF-2014R1A2A1A11051032 and 2009-0093823), and the Yonsei University Future-leading Research Initiative of 2014.
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All Science Journal Classification (ASJC) codes
- Biomedical Engineering
- Pharmaceutical Science