Luminescent Gold Nanoclusters Research Articles

Dynamically-enhanced retention of gold nanoclusters in HeLa cells following X-rays exposure: A cell cycle phase-dependent targeting approach

Background and purposeCell cycle phase could affect the cellular uptake of nanoparticles. Based on the fact that ionizing radiation exposure can delay cell cycle progression including inducing G2/M phase arrest, we propose that ionizing radiation exposure is a cell cycle phase-dependent targeting approach for intracellular delivery of nano-agents in tumor cells. Materials and methodsWe synthesized luminescent gold nanoclusters (AuNCs) using a one-pot green synthetic method. Subsequently, we used the as-prepared AuNCs as both “nano-agents” and fluorescent trafficking probes for our study using human cervical carcinoma HeLa cells. Estimating the cellular uptake of AuNCs and cell cycle analysis were performed following X-rays irradiation and cell synchronization. ResultsOur work showed that X-rays irradiation could delay the division of HeLa cells and thereby enhance the retention of AuNCs in HeLa cells, which is a reverse strategy compared with other studies on synergistic nano-radiotherapy. Our results demonstrated that the cell cycle synchronization influenced the cellular uptake processes of AuNCs, suggesting that dynamic cell cycle progression could affect the cellular uptake kinetics of AuNCs. ConclusionWe consider that the radiation-induced cell division delay might provide a possible mechanism underlying the enhanced effect for the cellular uptake of AuNCs in irradiated HeLa cells.

Biocompatible glutathione-capped gold nanoclusters for dual fluorescent sensing and imaging of copper(II) and temperature in human cells and bacterial cells

Highly red luminescent gold nanoclusters (AuNCs) have been prepared at physiological temperature by using glutathione (GSH) as a stabilizing and capping agent in aqueous media. The resultant AuNCs have been characterized by photoluminescence and X-ray photoelectron spectroscopy, transmission electron microscopy and FTIR. The AuNCs exhibit red fluorescence with a quantum yield of 3.1 %, and fluorescence is strongly quenched by copper(II) ion due to aggregation. This finding is exploited in a fluorometric assay for Cu(II) that has a 2.8 nM detection limit. The method was applied to the determination of Cu(II) ion in (spiked) mineral water and Tai Lake water. In addition, the AuNCs display a strongly temperature-dependent emission that can be used for optical determination of temperature in the 0 to 60 °C range. We finally show that the AuNCs are viable nanomaterials for (a) plain imaging of Hep-2 cells by laser scanning confocal microscopy, and for (b) intracellular imaging of Cu(II) and of temperature in Hep-2 cells and E. coli.

Interactive luminescent gold nanocluster embedded dsDNA and cisplatin as model nanoparticles for cancer theranostics

Luminescent gold nanoclusters in DNA and cisplatin produced nanoparticle for theranostics.

A new and facile strategy for the one-pot fabrication of luminescent gold nanoclusters and their prospective application

Allium cepa L. peel, a common household waste material mediated fabrication of luminescent gold nanoclusters.

Decoupling the CO-Reduction Protocol to Generate Luminescent Au22(SR)18 Nanocluster

Development of efficient synthetic strategies for highly luminescent gold nanoclusters (Au NCs) requires a good understanding of their synthesis process and environmental factors involved which could affect their tailorability. In a recent study, we reported a new type of luminescent Au NCs featuring with the aggregation-induced emission (AIE) characteristic. This AIE-type luminescent Au NC has a molecular formula of Au22(SR)18 (SR denotes thiolate ligand), and it shows strong red emission at ∼665 nm with a high quantum yield of ∼8%. However, the formation process and reaction parameters that may affect the synthesis of Au22(SR)18 were not understood because of the lack of experimental evidence. Here, we revisit the synthetic protocol, a two-step carbon monoxide (CO) reduction method, to further understand the formation process of Au22(SR)18. First, we systematically investigate several reaction conditions (e.g., the solution pH and the duration of each step) that could affect the yield of red-emitting Au22(SR)18 in the protocol. Second, we use the time-course measurements of the optical properties (UV–vis absorption and photoemission) of the reaction solution to study the formation process of Au22(SR)18, which allows us to identify several key NC intermediates and makes possible the reconstruction of the formation process of red-emitting Au22(SR)18. Upon the basis of our experimental data, we propose a two-stage process for the growth of Au22(SR)18: (1) the reduction of Au(I)-thiolate complexes to form Au NCs with a narrow size distribution, which are subsequently focused to Au18(SR)14; and (2) a pH-induced aggregation of short Au(I)-thiolate complexes on Au18(SR)14, which are finally converted to Au22(SR)18. Our study suggests that the pH-induced aggregation of Au(I)-thiolate complexes on the in situ formed thiolated Au NCs could be an effective way to generate luminescent Au NCs with the AIE characteristic. This principle can also be used to synthesize other AIE-type metal NCs with strong luminescence.

A microwave-facilitated rapid synthesis of gold nanoclusters with tunable optical properties for sensing ions and fluorescent ink.

Luminescent glutathione-capped gold nanoclusters (GS-AuNCs) with tunable emissions have been efficiently synthesized by a solution-based microwave method.

Luminescent golden silk and fabric through in situ chemically coating pristine-silk with gold nanoclusters

Silk is an excellent natural material and has been used for a variety of applications. Modification of the pristine silk is usually needed depending on the intended purpose. The technical treatments involved in the modification not only should be easy, rapid, environmentally friendly, and cheap but should also retain the features of the pristine silk. Herein, we demonstrate that luminescent silk and fabric can be produced through nanotechnology. The surface of the natural silk fiber is chemically coated with luminescent gold nanoclusters (AuNCs) composed of tens to hundreds of Au atoms through a redox reaction between the protein-based silk and an Au salt precursor. The luminescent silk coated with AuNCs (called golden silk) possesses good optical properties, including a relatively long wavelength emission, high quantum yields, a long fluorescent lifetime, and photostability. Moreover, golden silk prepared this way has better mechanical properties than pristine silk, is better able to inhibit UV, and has lower toxicity in vitro. This work not only provides an effective strategy for in situ preparation of luminescent metal nanoclusters on a solid substrate but also paves the way for large-scale and industrialized production of novel silk-based materials or fabrics through nanotechnology.

A fluorescence detection of d-penicillamine based on Cu2+-induced fluorescence quenching system of protein-stabilized gold nanoclusters

In this contribution, a luminescent gold nanoclusters which were synthesized by bovine serum albumin as novel fluorescent probes were successfully utilized for the determination of d-penicillamine for the first time. Cupric ion was employed to quench the strong fluorescence of the gold nanoclusters, whereas the addition of d-penicillamine caused obvious restoration of fluorescence intensity of the Cu2+-gold nanoclusters system. Under optimum conditions, the increment in fluorescence intensity of Cu2+-gold nanoclusters system caused by d-penicillamine was linearly proportional to the concentration of d-penicillamine in the range of 2.0×10−5–2.39×10−4M. The detection limit for d-penicillamine was 5.4×10−6M. With the off–on fluorescence signal at 650nm approaching the near-infrared region, the present sensor for d-penicillamine detection had high sensitivity and low spectral interference. Furthermore, the novel gold nanoclusters-based fluorescent sensor has been applied to the determination of d-penicillamine in real biological samples with satisfactory results.

Understanding thiol-induced etching of luminescent gold nanoclusters

Electron injection from thiol ligands to Au8 clusters is a driving force for thiol-induced core etching of protein-stabilized Au8 clusters.

Assembling luminescent gold nanoclusters and amphiphilic polymeric nanocarriers for controlled drug release and optical imaging

Assembling luminescent gold nanoclusters and amphiphilic polymeric nanocarriers for controlled drug release and optical imaging

A ratiometric fluorescent probe for sensitive, selective and reversible detection of copper (II) based on riboflavin-stabilized gold nanoclusters

Most of the copper (II) fluorescent probes are based on the measurement of fluorescence at a single wavelength, which may be influenced by variations in the sample environment. To the end, the ratiometric fluorescent measurement, which involves the simultaneous measurement of two fluorescence signals at different wavelengths followed by calculation of their intensity ratio, can effectively eliminate the adverse effects on fluorescence signals and give greater precision to the data analysis relative to single-channel detection. In this work, we prepared novel luminescent gold nanoclusters (AuNCs) utilizing vitamin B2 (riboflavin) as stabilizer by a simple, rapid and one-pot green (low-toxicity materials use) procedure. The as-prepared riboflavin-AuNCs (Ri-AuNCs) solution can be luminescent exhibiting two fluorescence emission peaks at 530 nm and around 840 nm with excitation at 375 nm, however, in the presence of Cu(2+), the fluorescence of the Ri-AuNCs was found to be quenched at around 840 nm and enhanced at 530 nm by Cu(2+). The resultant ratiometric fluorescent response can provide a novel sensory probe for the determination of Cu(2+). The present probe had excellent selectivity in the presence of several cations. The probe revealed a detection limit of 0.9 μM of Cu(2+). Moreover, our proposed probe can reversibly switch between the "on" and "off" states through the addition of Cu(2+) and EDTA, which is reusable in practical application. Results and method reported here provide a unique strategy for performance of ratiometric assays demonstrated with a AuNCs-based fluorescent probe, which expands the application of AuNCs.

Imaging: PEGylated Luminescent Gold Nanoclusters: Synthesis, Characterization, Bioconjugation, and Application to One- and Two-Photon Cellular Imaging (Part. Part. Syst. Charact. 5/2013)

Biocompatible, near-infrared luminescent gold nanoclusters (AuNCs) are synthesized directly in water using PEG-dithiolane ligands terminating in either a carboxyl, amine, azide or methoxy group as presented by Igor L. Medintz and co-workers on page 453. Following bioconjugation testing, stability assays, and extensive characterization of their one- and two-photon absorption cross-section and emission, the AuNCs are demonstrated in high signal-to-noise one- and two-photon cellular imaging with mini mal cytoxicity.

Amphiphilic Polymeric Nanocarriers with Luminescent Gold Nanoclusters for Concurrent Bioimaging and Controlled Drug Release

AbstractMultifunctional theranostic systems with good biocompatibility, strong clinical imaging capability, and target specificity are the desired features of future medicine. Here, the design of a theranostic nanocomposite capable of simultaneous targeting and imaging of the cancer cells is presented. It releases its drug payload by a controlled release mechanism. The nanocomposite contains luminescent gold nanocluster (L‐AuNC) photostable and biocompatible diagnostic probes conjugated to a folic acid (FA)‐modified pH‐responsive amphiphilic polymeric system for controlled drug release. The nanocomposite uses a core‐satellite structure to encapsulate hydrophobic drugs and releases the drug payload in mildly acidic endosomal/lysosomal compartments by the action of the pH‐labile linkages in the polymer. In vivo studies show the selective accumulation of the FA‐conjugated nanocomposite in tumor tissues by folate‐receptor‐mediated endocytosis. These findings demonstrate the potential of the nanocomposite as a nontoxic, folate‐targeting, pH‐responsive drug carrier that is useful for the early detection and therapy of folate‐overexpressing cancerous cells.

PEGylated Luminescent Gold Nanoclusters: Synthesis, Characterization, Bioconjugation, and Application to One‐ and Two‐Photon Cellular Imaging

Biocompatible, near‐infrared luminescent gold nanoclusters (AuNCs) are synthesized directly in water using poly(ethylene glycol)‐dithiolane ligands terminating in either a carboxyl, amine, azide, or methoxy group. The ≈1.5 nm diameter AuNCs fluoresce at ≈820 nm with quantum yields that range from 4–8%, depending on the terminal functional group present, and display average luminescence lifetimes approaching 1.5 μs. The two‐photon absorption (TPA) cross‐section and two‐photon excited fluorescence (TPEF) properties are also measured. Long‐term testing shows the poly(ethylene glycol) stabilized AuNCs maintain colloidal stability in a variety of media ranging from saline to tissue culture growth medium along with tolerating storage of up to 2 years. DNA and dye‐conjugation reactions confirm that the carboxyl, amine, and azide groups can be utilized on the AuNCs for carbodiimide, succinimidyl ester, and CuI‐assisted cycloaddition chemistry, respectively. High signal‐to‐noise one‐ and two‐photon cellular imaging is demonstrated. The AuNCs exhibit outstanding photophysical stability during continuous‐extended imaging. Concomitant cellular viability testing shows that the AuNCs also elicit minimal cytotoxicity. Further biological applications for these luminescent nanoclustered materials are discussed.

Papain-directed synthesis of luminescent gold nanoclusters and the sensitive detection of Cu2+

Highly fluorescent papain stabilized gold nanoclusters (NCs) have been synthesized through a simple wet chemical route. Papain was used for the first time as an effective capping and reducing agent for these clusters. The optimal conditions for the synthesis of the gold nanoclusters, including the concentrations of papain and NaOH, reaction time and temperature, were investigated. The as-prepared Au clusters show intense red emission at ∼660nm (QY ∼4.3%) and are uniform in size. The clusters are quite stable and the intense red emission remained unchanged at a buffer pH range of 6–12. The fluorescent Au NCs were then used as a label-free probe for the sensitive detection of Cu2+. A limit of detection of 3nM was obtained. The sensing strategy is also highly selective against the various potential interference ions.

Fluorescence Intensity and Lifetime Cell Imaging with Luminescent Gold Nanoclusters

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.

Highly fluorescent gold nanoclusters based sensor for the detection of quercetin

In this contribution, novel luminescent gold nanoclusters were synthesized by utilizing bovine serum albumin as templates with a simple, rapid, and one-pot procedure. The as-prepared gold nanoclusters were highly dispersed in aqueous solution and emitted an intense red fluorescence under UV light (365 nm). They exhibited strong fluorescence and the maximum excitation and emission wavelengths were 480 and 613.5 nm. In addition, the bovine serum albumin-stabilized gold nanoclusters were successfully utilized as novel fluorescent probes for the detection of quercetin for the first time. It was found that the addition of quercetin induced the strong fluorescence intensity of the gold nanoclusters to decrease. The decrease in fluorescence intensity of the gold nanoclusters caused by quercetin allowed the sensitive detection of quercetin in the range of 8.9 × 10−8–1.8 × 10−4 mol L−1. The detection limit for quercetin is 1.8 × 10−8 mol L−1 at a signal-to-noise ratio of 3. The present sensor for quercetin detection possessed a low detection limit and wide linear range. In addition, the real samples were analyzed with satisfactory results.

Use of near-infrared luminescent gold nanoclusters for detection of macrophages

We determined the effect of aggregation and coating thickness of gold on the luminescence of nanoparticles engulfed by macrophages and in gelatin phantoms. Thin gold-coated iron oxide nanoclusters (nanoroses) have been developed to target macrophages to provide contrast enhancement for near-infrared optical imaging applications. We compare the brightness of nanoroses luminescent emissions in response to 635 nm laser excitation to other nanoparticles including nanoshells, nanorods, and Cy5 conjugated iron oxide nanoparticles. Luminescent properties of all these nanoparticles were investigated in monomeric and aggregated form in gelatin phantoms and primary macrophage cell cultures using confocal microscopy. Aggregation of the gold nanoparticles increased luminescence emission and correlated with increased surface mass of gold per nanoparticle (nanoshells 37 ± 14.30 × 10(-3) brightness with 1.23 × 10(-4) wt of gold (g)/nanoparticle versus original nanorose 1.45 ± 0.37 × 10(-3) with 2.10 × 10(-16) wt of gold/nanoparticle, p<0.05). Nanoshells showed greater luminescent intensity than original nanoroses or Cy5 conjugated iron oxide nanoparticles when compared as nanoparticles per macrophage (38 ± 10 versus 11 ± 2.8 versus 17 ± 6.5, p<0.05, respectively, ANOVA), but showed relatively poor macrophage uptake (1025 ± 128 versus 7549 ± 236 versus 96,000 nanoparticles/cell, p<0.05, student t-test nanoshells versus nanoroses). Enhancement of gold fluorescent emissions by nanoparticles can be achieved by reducing the thickness of the gold coating, by clustering the gold on the surface of the nanoparticles (nanoshells), and by clustering the gold nanoparticles themselves.

Microwave-assisted rapid synthesis of luminescent gold nanoclusters for sensing Hg2+ in living cells using fluorescence imaging

A microwave-assisted strategy for synthesizing dihydrolipoic acid (DHLA) capped fluorescent gold nanoclusters (AuNCs) has been developed. Irradiation with microwaves during synthesis enhanced the fluorescence quantum yield (QY) of AuNCs by about five-fold and shortened the reaction time from hours to several minutes. The as-synthesized DHLA-AuNCs possessed bright near-infrared fluorescence (QY: 2.9%), ultrasmall hydrodynamic diameter (3.3 nm), good colloidal stability over the physiologically relevant pH range of 5-10 as well as low cytotoxicity toward HeLa cells. Moreover, these DHLA-AuNCs were capable of sensing Hg(2+) through the specific interaction between Hg(2+) and Au(+) on the surface of AuNCs; the limit of detection (LOD) was 0.5 nM. A potential application in imaging intracellular Hg(2+) in HeLa cells was demonstrated by using spinning disc confocal microscopy.

Synthesis of hydrophobic gold nanoclusters: growth mechanism study, luminescence property and catalytic application

One-pot synthesis of well dispersed, size-controlled gold nanoparticles with the average size of 10–15 nm and luminescent gold nanoclusters with average size of 1.7–2.0 nm were successfully achieved by thermal decomposition of gold organometallic precursor CH3AuPPh3 in the presence of thiol surfactants in o-xylene. Only difference between the preparations of two types of Au nanoparticles is the amount of thiol surfactant employed. The mechanistic study of formation of gold nanoparticles was carried out by analyzing the samples at different reaction time intervals and revealed that two-staged growth process was involved. The nanoclusters showed strong red emission with the maximum intensity at about 600 nm. The maximum room temperature photoluminescence quantum yield was measured as 1.2%. The catalytic ability of the Au nanoclusters to promote Suzuki–Miyaura coupling involving the C–C bond formation was also investigated.