title: Fluorescence Intensity and Lifetime Cell Imaging with Luminescent Gold Nanoclusters.
abstract: In this article, luminescent properties of gold nanoclusters (AuNCs) were studied at the single nanoparticle level and also used as novel imaging agents in cell media. Two types of water-soluble AuNCs which were stabilized with a monolayer composed of either mercaptosuccinic acid (MSA) or tiopronin thiolate ligands were synthesized by a chemical reduction reaction. These AuNCs were determined to have an average core diameter of less than 2 nm. On a time-resolved confocal microscope, the emission signals from the single AuNCs were distinctly recordable. The quantum yields of these AuNCs were measured to be ca. 5%. The lifetime of these AuNCs is also much longer than the lifetime of cellular autofluorescence in lifetime cell imaging as well as the lifetime of organic dye Alexa Fluor 488. After being derivatized with polyethylene glycol (PEG) moieties, the AuNCs were uploaded efficiently in the HeLa cells. Fluorescence intensity and lifetime cell images were recorded on the time-resolved confocal microscope in which the emission from the AuNCs was readily differentiated from the cellular autofluorescence background because of their relatively stronger emission intensities and longer lifetimes. These loaded nanoclusters in the cells were observed to widely distribute throughout the cells and especially densely loaded near the cell nucleuses. The AuNCs in the cells were also tested to have a better photostability relative to the organic fluorophores under the same conditions. We thus conclude that the AuNCs have a great potential as novel nanoparticle imaging agents, especially as lifetime imaging agents, in fluorescence imaging applications. We also prospect much broader applications of these AuNCs after further improvements of their luminescence quantum yields.
authors.affiliation: Center for Fluorescence Spectroscopy, University of Maryland School of Medicine, Department of Biochemistry and Molecular Biology, 725 West Lombard Street, Baltimore, Maryland 21201, United States.
authors.forename: Jian
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Center for Fluorescence Spectroscopy, University of Maryland School of Medicine, Department of Biochemistry and Molecular Biology, 725 West Lombard Street, Baltimore, Maryland 21201, United States.
authors.forename: Yi
authors.initials: Y
authors.lastname: Fu
authors.affiliation: Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States.
authors.forename: Cecil V
authors.initials: CV
authors.lastname: Conroy
authors.affiliation: Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States.
authors.forename: Zhenghua
authors.initials: Z
authors.lastname: Tang
authors.affiliation: Division of Molecular Pathology, Department of Pathology, University of Maryland School of Medicine, 10 South Pine Street, Baltimore, Maryland 21201, United States.
authors.forename: Ge
authors.initials: G
authors.lastname: Li
authors.affiliation: Division of Molecular Pathology, Department of Pathology, University of Maryland School of Medicine, 10 South Pine Street, Baltimore, Maryland 21201, United States ; Department of Microbiology-Immunology, University of Maryland School of Medicine, 10 South Pine Street, Baltimore, Maryland 21201, United States ; Institute of Human Virology, University of Maryland School of Medicine, 10 South Pine Street, Baltimore, Maryland 21201, United States.
authors.forename: Richard Y
authors.initials: RY
authors.lastname: Zhao
authors.affiliation: Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States.
authors.forename: Gangli
authors.initials: G
authors.lastname: Wang