Molecular-receptor-specific, non-toxic, near-infrared-emitting Au cluster-protein nanoconjugates for targeted cancer imaging
TL;DR: Receptor-targeted cancer detection using Au clusters is demonstrated on FR(+ve) oral squamous cell carcinoma (KB) and breast adenocarcinoma cell MCF-7, where the FA-conjugated Au(25) clusters were found internalized in significantly higher concentrations compared to the negative control cell lines.
Abstract: Molecular-receptor-targeted imaging of folate receptor positive oral carcinoma cells using folic-acid-conjugated fluorescent Au(25) nanoclusters (Au NCs) is reported. Highly fluorescent Au(25) clusters were synthesized by controlled reduction of Au(+) ions, stabilized in bovine serum albumin (BSA), using a green-chemical reducing agent, ascorbic acid (vitamin-C). For targeted-imaging-based detection of cancer cells, the clusters were conjugated with folic acid (FA) through amide linkage with the BSA shell. The bioconjugated clusters show excellent stability over a wide range of pH from 4 to 14 and fluorescence efficiency of approximately 5.7% at pH 7.4 in phosphate buffer saline (PBS), indicating effective protection of nanoclusters by serum albumin during the bioconjugation reaction and cell-cluster interaction. The nanoclusters were characterized for their physico-chemical properties, toxicity and cancer targeting efficacy in vitro. X-ray photoelectron spectroscopy (XPS) suggests binding energies correlating to metal Au 4f(7/2) approximately 83.97 eV and Au 4f(5/2) approximately 87.768 eV. Transmission electron microscopy and atomic force microscopy revealed the formation of individual nanoclusters of size approximately 1 nm and protein cluster aggregates of size approximately 8 nm. Photoluminescence studies show bright fluorescence with peak maximum at approximately 674 nm with the spectral profile covering the near-infrared (NIR) region, making it possible to image clusters at the 700-800 nm emission window where the tissue absorption of light is minimum. The cell viability and reactive oxygen toxicity studies indicate the non-toxic nature of the Au clusters up to relatively higher concentrations of 500 microg ml(-1). Receptor-targeted cancer detection using Au clusters is demonstrated on FR(+ve) oral squamous cell carcinoma (KB) and breast adenocarcinoma cell MCF-7, where the FA-conjugated Au(25) clusters were found internalized in significantly higher concentrations compared to the negative control cell lines. This study demonstrates the potential of using non-toxic fluorescent Au nanoclusters for the targeted imaging of cancer.
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TL;DR: In this critical review, recent advances in sub-nanometre sized metal clusters (Au, Ag, Cu, etc.) including the synthetic techniques, structural characterizations, novel physical, chemical and optical properties and their potential applications are discussed in detail.
Abstract: Sub-nanometre sized metal clusters, with dimensions between metal atoms and nanoparticles, have attracted more and more attention due to their unique electronic structures and the subsequent unusual physical and chemical properties. However, the tiny size of the metal clusters brings the difficulty of their synthesis compared to the easier preparation of large nanoparticles. Up to now various synthetic techniques and routes have been successfully applied to the preparation of sub-nanometre clusters. Among the metals, gold clusters, especially the alkanethiolate monolayer protected clusters (MPCs), have been extensively investigated during the past decades. In recent years, silver and copper nanoclusters have also attracted enormous interest mainly due to their excellent photoluminescent properties. Meanwhile, more structural characteristics, particular optical, catalytic, electronic and magnetic properties and the related technical applications of the metal nanoclusters have been discovered in recent years. In this critical review, recent advances in sub-nanometre sized metal clusters (Au, Ag, Cu, etc.) including the synthetic techniques, structural characterizations, novel physical, chemical and optical properties and their potential applications are discussed in detail. We finally give a brief outlook on the future development of metal nanoclusters from the viewpoint of controlled synthesis and their potential applications.
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886 citations
TL;DR: This review focuses on recent advances in Au NCs based sensing and imaging systems between 2012 and 2014 and examines their potential for the analysis of environmental and biological samples.
Abstract: F gold nanoclusters (Au NCs) or nanodots (NDs) with sizes smaller than 3 nm are a specific type of gold nanomaterials. In this review, Au NCs are used to represent fluorescent Au nanomaterials with sizes smaller than 3 nm. Unlike the most popular and well-known spherical, large gold nanoparticles, Au NCs do not exhibit surface plasmon resonance (SPR) absorption in the visible region but have fluorescence in the visible to near-infrared (NIR) region. With advantages of long lifetime, large Stokes shift, and biocompatibility, Au NCs have become interesting sensing and imaging materials. Although Au NCs prepared from Au in the presence of small thiol compounds such as 2-phenylethanethiol (PhCH2CH2SH) have been reported over the past decade, 5 their use for bioapplications have not been well recognized, mainly because of their low quantum yield (usually less than 1%), poor water dispersibility, photo and chemical instability, and difficulty for conjugation. In the past decade, many strategies for the preparation of stable, water dispersible, highly fluorescent, and biocompatible Au NCs have been reported. There are two major categories elucidating the recent advanced techniques for the preparation of Au NCs. The first category is through etching of larger sizes of nonfluorescent gold nanoparticles (Au NPs) by thiol compounds such as mercaptopropionic acid. The second category is from reduction of Au in the presence of a ligand or template (protein) such as bovine serum albumin (BSA). The optical properties of biocompatible Au NCs are dependent on their size, surface ligand or template, and the surrounding medium, and thus they can be studied to develop sensitive and selective sensing and imaging systems for the detection of various analytes. The growing popularity of Au NCs in analytical applications has been realized in these few years. Several excellent review papers dealing with Au NCs from the viewpoint of analytical chemistry have been reported to highlight their potential for the analysis of environmental and biological samples. This review focuses on recent advances in Au NCs based sensing and imaging systems between 2012 and 2014. Current challenges and future prospects of Au NCs for fundamental studies and analytical applications will be provided.
683 citations
TL;DR: In vivo applications of noble metal nanoparticles (NPs), another promising nanomedicine in biomedical imaging, drug delivery, antibacterial and photothermal therapy, are still severely hampered by their slow renal clearance and high nonspecific accumulations.
Abstract: Developing functional nanomaterials with efficient renal clearance is of fundamental importance to their in vivo biomedical applications.[1] Ideal nanomaterial based contrast agents should be effectively cleared out of the body, have little accumulation in organs and show minimum interference with other diagnostic tests.[1c, 1e, 2] While significant progress has been made toward the creation of fluorescent quantum dots with efficient renal clearance,[2] in vivo applications of noble metal nanoparticles (NPs), another promising nanomedicine in biomedical imaging, drug delivery, antibacterial and photothermal therapy,[3] are still severely hampered by their slow renal clearance and high nonspecific accumulations in the reticuloendothelial system (RES) organs (e.g. liver, spleen) after systematic administration.[4] Although NPs with hydrodynamic diameter (HD) smaller than 10 nm are generally considered being stealthy to the RES organs, they are still often found in the liver.[2a] For example, nearly ~50% of 1.4 nm gold NPs (AuNPs) were found in the liver and only ~9% of them can be excreted into urine in 24 hours after intravenous (IV) injection.[4b] Therefore, developing metal NPs with efficient renal clearance and fundamental understanding of key factors in renal clearance are highly desirable.
394 citations
TL;DR: The synthesis of fluorescent Au NCs by using insulin as a template is reported for the first time, and the resulting protein–Au NC nanocomposites are able to retain bioactivity, so that the associated biological role can be pursued by various imaging techniques.
Abstract: Fluorescent nanomaterials have received great attention and have been intensively studied, because of their unique optical and photophysical properties, as replacements for conventional organic dyes in optical cell imaging. Although semiconductor quantum dots show promising signals in biomedical imaging, their high inherent cytotoxicity and self-aggregation inside living cells fatally limit pragmatic biomedical applications. Fluorescent nanoclusters (NCs), in contrast, exhibit superior properties such as low toxicity and high biocompatibility. Among the various NCs, much effort has been dedicated to the study of fluorescent Au NCs. Au NCs carry quantum-mechanical properties when their sizes are comparable to or smaller than the Fermi wavelength (ca. 1 nm) of conductive electrons. The fluorescent Au NCs, with their ultrafine size, do not disturb the biological functions of the labeled bioentities; therefore, there is great potential to develop Au NCs as a new luminescent label. For example, Lin et al. successfully used water-soluble fluorescent Au NCs capped with dihydrolipoic acid (AuNC@DHLA) and modified with polyethylene glycol (PEG), bovine serum albumin (BSA), and streptavidin for cell bioimaging. Compared with organic-monolayer-protected Au NCs, the usage of proteins as a green-chemical reducing and stabilizing agent is advantageous because their complex 3D structures can withstand a wide range of pH conditions. Accordingly, Au NC synthesis with BSA and lysozyme has been reported and applied to several devices, such as nanosensors of Hg, CN , and H2O2. [12] Very recently, through the conjugation of BSA–Au NCs to folic acid, targetspecific detection of cancer-cell imaging has been demonstrated. Also, BSA–Au NCs have been applied in MDAMB-45 and HeLa tumor xenograft model imaging. Nevertheless, up to this stage, there has been a lack of reports on bioactive protein-directed fluorescent Au NCs that can still preserve their own biological role. Conversely, using Au nanoparticles encapsulated in certain enzymes, several reports claimed significant changes of enzymatic functionality. The goal of this project is thus to search for a bioactive protein to exploit as a template to direct the growth of fluorescent Au NCs. The resulting protein–Au NC nanocomposites are able to retain bioactivity, so that the associated biological role can be pursued by various imaging techniques. Among a number of proteins of vital importance, insulin is of prime interest. Insulin is a polypeptide hormone comprising only 51 amino acids. Its function primarily lies in the regulation of insulin-responsive tissues and it is also directly/indirectly related to many diseases, including diabetes, Alzheimer s disease, obesity, and aging. Its signaling pathway controls the growth of an organism, and hence exerts a profound influence on metabolism and reproduction. Herein, we report for the first time the synthesis of fluorescent Au NCs by using insulin as a template. The resulting insulin–Au NCs exhibit intense red fluorescence maximized at 670 nm and, more importantly, retain their bioactivity and biocompatibility. Several key experiments have been performed in vitro and/or in vivo to assess their viability and versatility. Detailed synthetic procedures are elaborated in the Supporting Information. In brief, by mixing insulin and HAuCl4 in Na3PO4 buffer by continuously stirring at 4 8C for 12 h, reddish luminescent insulin–Au NCs were readily prepared. The crude product was then purified by centrifugal filtration (4000g) for 30 min with a cutoff of 5 kDa to obtain the insulin–Au NCs for subsequent applications. The absorption and photoluminescence emission spectra of insulin–Au NCs are shown in Figure 1. The emission quantum yield Ff was determined to be 0.07, with observed lifetimes fitted to be 439 ns (4%) and 2041 ns (96%). The inset of Figure 1 displays a high-resolution transmission electron microscopy (HRTEM) image of insulin–Au NCs. From the respective histograms, the as-prepared insulin– Au NCs revealed a spherical shape and good size uniformity (for size distribution, see Figure S1 in the Supporting Information). The diameters of insulin–Au NCs, upon averaging over 100 particles, were calculated to be (0.92 0.03) nm (mainly for Au NCs). The hydrodynamic radii of [*] C.-L. Liu, Y.-H. Hsiao, Dr. C.-W. Lai, C.-W. Shih, Y.-K. Peng, Dr. K.-C. Tang, H.-W. Chang, Prof. P.-T. Chou Department of Chemistry, National Taiwan University 1, Section 4, Roosevelt Road, Taipei 10617 (Taiwan) Fax: (+886)2-369-5208 E-mail: chop@ntu.edu.tw
386 citations
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TL;DR: In this article, the authors focus on the properties of quantum dots and their ability to join the dots into complex assemblies creates many opportunities for scientific discovery, such as the ability of joining the dots to complex assemblies.
Abstract: Current research into semiconductor clusters is focused on the properties of quantum dots-fragments of semiconductor consisting of hundreds to many thousands of atoms-with the bulk bonding geometry and with surface states eliminated by enclosure in a material that has a larger band gap. Quantum dots exhibit strongly size-dependent optical and electrical properties. The ability to join the dots into complex assemblies creates many opportunities for scientific discovery.
10,737 citations
TL;DR: Investigation and spectroscopic measurements indicate that the QD-tagged beads are highly uniform and reproducible, yielding bead identification accuracies as high as 99.99% under favorable conditions.
Abstract: Multicolor optical coding for biological assays has been achieved by embedding different-sized quantum dots (zinc sulfide-capped cadmium selenide nanocrystals) into polymeric microbeads at precisely controlled ratios. Their novel optical properties (e.g., size-tunable emission and simultaneous excitation) render these highly luminescent quantum dots (QDs) ideal fluorophores for wavelength-and-intensity multiplexing. The use of 10 intensity levels and 6 colors could theoretically code one million nucleic acid or protein sequences. Imaging and spectroscopic measurements indicate that the QD-tagged beads are highly uniform and reproducible, yielding bead identification accuracies as high as 99.99% under favorable conditions. DNA hybridization studies demonstrate that the coding and target signals can be simultaneously read at the single-bead level. This spectral coding technology is expected to open new opportunities in gene expression studies, high-throughput screening, and medical diagnostics.
2,722 citations
TL;DR: A simple, one-pot, "green" synthetic route, based on the "biomineralization" capability of a common commercially available protein, bovine serum albumin (BSA), has been developed for the preparation of highly stable Au nanocrystals (NCs) with red emission and high quantum yield.
Abstract: A simple, one-pot, "green" synthetic route, based on the "biomineralization" capability of a common commercially available protein, bovine serum albumin (BSA), has been developed for the preparation of highly stable Au nanocrystals (NCs) with red emission and high quantum yield.
2,215 citations
TL;DR: This work has shown how the emission wavelength of quantum-dot nanocrystals can be continuously tuned by changing the particle size, and a single light source can be used for simultaneous excitation of all different-sized dots.
2,066 citations