Luminescent Gold Research Articles

Luminescent Gold Nanoparticles with Controllable Hydrophobic Interactions.

The construction of luminescent gold nanoparticles (AuNPs) with highly redshifted emission in the second near-infrared window (NIR-II) and good biocompatibility is still challenging. Herein, using an amphiphilic block copolymer (ABC) template with controllable hydrophobic interactions in the diverse forms of unimers and micelles, we report a facile strategy for redshifting the emission and enhancing the biological interactions of luminescent AuNPs. While the uniform clusters of NIR-II AuNPs are formed in situ inside the hydrophobic cores of ABC micelles with strong interparticle hydrophobic interactions and enhanced emission at 1080 nm with a high quantum yield (QY) of 1.6%, the rigid NIR-II AuNPs are generated with strong intraparticle hydrophobic interactions as ABC unimers on the surface, leading to a redshifted emission of 1280 nm with a QY of 0.25% and enhancing the affinities toward injured intestinal mucosa in colitis imaging. These findings open new possibilities for the design of highly redshifted luminescent AuNPs with enhanced biological interactions.

Au⋅⋅⋅H−C Interactions Support a Robust Thermally Activated Delayed Fluorescence (TADF) Gold(I) Complex for OLEDs with Little Efficiency Roll‐Off and Good Stability

AbstractThe practical use of luminescent mononuclear gold(I) complexes as optoelectronic materials has been limited by their inferior stability. Herein we demonstrate a strategy to improve the stability of gold(I) complexes which display thermally activated delayed fluorescence (TADF). A highly rigid and groove‐like σ‐donating aryl ligand has been used to form dual Au⋅⋅⋅H−C hydrogen bonds. The secondary metal‐ligand interactions have been authenticated by single‐crystal structure, NMR spectroscopy and theoretical simulations. The TADF AuI complex exhibits appealing emission properties (photoluminescence quantum yield=76 %; delayed fluorescence lifetime=1.2 μs) and much improved thermal and photo‐stability. Vacuum‐deposited organic light‐emitting diodes (OLEDs) show promising electroluminescence with a maximum external quantum efficiency (EQE) over 23 % and negligible efficiency roll‐off even at 10 000 cd m−2. An estimated LT50 longer than 77 000 h with initial luminance of 100 cd m−2 reveals good operational stability. This work suggests a way for design of stable luminescent gold(I) complexes.

Au⋅⋅⋅H-C Interactions Support a Robust Thermally Activated Delayed Fluorescence (TADF) Gold(I) Complex for OLEDs with Little Efficiency Roll-Off and Good Stability.

The practical use of luminescent mononuclear gold(I) complexes as optoelectronic materials has been limited by their inferior stability. Herein we demonstrate a strategy to improve the stability of gold(I) complexes which display thermally activated delayed fluorescence (TADF). A highly rigid and groove-like σ-donating aryl ligand has been used to form dual Au⋅⋅⋅H-C hydrogen bonds. The secondary metal-ligand interactions have been authenticated by single-crystal structure, NMR spectroscopy and theoretical simulations. The TADF AuI complex exhibits appealing emission properties (photoluminescence quantum yield=76 %; delayed fluorescence lifetime=1.2 μs) and much improved thermal and photo-stability. Vacuum-deposited organic light-emitting diodes (OLEDs) show promising electroluminescence with a maximum external quantum efficiency (EQE) over 23 % and negligible efficiency roll-off even at 10 000 cd m-2 . An estimated LT50 longer than 77 000 h with initial luminance of 100 cd m-2 reveals good operational stability. This work suggests a way for design of stable luminescent gold(I) complexes.

Ligand evolution of luminescent gold nanoclusters: from amino acids to proteins

<p indent="0mm">Gold nanoclusters are known as emerging ultra-small-sized luminescent nanomaterials with the characteristics of strong photobleaching resistance, large Stokes shifts, good biocompatibility and low toxicity. Up to now, the development of emissive gold nanoclusters has experienced several stages, which are closely related to the study of ligands. Based on the evolution of ligands, this review focuses on how ligands from amino acids, peptides to proteins are used to synthesize photoluminescent gold nanoclusters and to fabricate biosensors. The content of this review includes synthesis methods, luminescence mechanism and stimuli-responsive properties of gold nanoclusters. The effects of different ligands on gold nanoclusters are discussed separately, and the current challenges and the future development direction in the field of gold nanoclusters are proposed.

Luminescent gold nanoclusters as a signal reporter for cytochrome c assay with a double signal amplification strategy

AbstractQuantitative determination of serum cytochrome c (Cyt c) is of importance in the regular medical assessment of cancer diseases. This work reported a new fluorescence method for the determination of Cyt c with glutathione‐protected gold nanoclusters (GSH‐AuNCs) as a signal reporter. Cyt c was observed to quench the fluorescence of GSH‐AuNCs due to its electron‐rich structure. This inhibitory effect was further strengthened by its peroxidase mimetic catalytic activity on hydrogen peroxide (H2O2)‐mediated oxidation of GSH‐AuNCs. The inhibitory efficiency was linearly related to Cyt c concentrations ranging from 10.0 to 700.0 nM with a limit of detection of 2.7 nM (3sb/S). The relative standard deviation was 3.6% for Cyt c at a 40.0 nM concentration level (n = 11). The practical application of the method was evaluated by the determination of Cyt c in spiked human serum samples. The recoveries were within the range from 92.6 to 104.8%, suggesting its potential application in biomedical and clinical diagnosis.

Luminescent Gold Nanoclusters Interacting with Synthetic and Biological Vesicles.

According to their high electron density and ultrasmall size, gold nanoclusters (AuNCs) have unique luminescence and photoelectrochemical properties that make them very attractive for various biomedical fields. These applications require a clear understanding of their interaction with biological membranes. Here we demonstrate the ability of the AuNCs as markers for lipidic bilayer structures such as synthetic liposomes and biological extracellular vesicles (EVs). The AuNCs can selectively interact with liposomes or EVs through an attractive electrostatic interaction as demonstrated by zetametry and fluorescence microscopy. According to the ratio of nanoclusters to vesicles, the lipidic membranes can be fluorescently labeled without altering their thickness until charge reversion, the AuNCs being located at the level of the phosphate headgroups. In presence of an excess of AuNCs, the vesicles tend to adhere and aggregate. The strong adsorption of AuNCs results in the formation of a lamellar phase as demonstrated by cryo-transmission electron microscopy and small-angle X-ray scattering techniques.

Bis-Schiff base linkage-triggered highly bright luminescence of gold nanoclusters in aqueous solution at the single-cluster level

Metal nanoclusters (NCs) have been developed as a new class of luminescent nanomaterials with potential applications in various fields. However, for most of the metal NCs reported so far, the relatively low photoluminescence quantum yield (QY) in aqueous solution hinders their applications. Here, we describe the utilization of bis-Schiff base linkages to restrict intramolecular motion of surface motifs at the single-cluster level. Based on Au22(SG)18 (SG: glutathione) NCs, an intracluster cross-linking system was constructed with 2,6-pyridinedicarboxaldehyde (PDA), and water-soluble gold NCs with luminescence QY up to 48% were obtained. The proposed approach for achieving high emission efficiency can be extended to other luminescent gold NCs with core-shell structure. Our results also show that the content of surface-bound Au(I)-SG complexes has a significant impact on the PDA-induced luminescence enhancement, and a high ratio of Au(I)-SG will be beneficial to increasing the photoluminescence intensity of gold NCs.

Synthesis and application of concanavalin A-conjugated green luminescent gold nanoparticle/fluorescent polydopamine nanoparticles for specific differentiation of cancer cells from normal cells using glycan bioreceptors

Glycan receptor is a cell-surface bioreceptor which has been expressed on the membrane of several cancer cells. This bioreceptor was employed for different medicinal disciplines such as drug-delivery, sensing, etc. In this work, concanavalin A (Con A)-conjugated green luminescent gold nanoparticle/fluorescent polydopamine nanoparticles (FPNPs) were synthesized and utilized for bioimaging of the glycan bioreceptor-positive breast cancer cells. The produced AuNPs/Cysteine/FPNPs/Con A NPs showed a specific manner towards biorecognition of glycan receptor-overexpressed MCF 7 cancer cells through Con A and glycan receptor interactions. Fluorescence microscope and flow cytometry techniques were employed to evaluate the accuracy of the bioimaging process. Furthermore, the specific attachment of AuNPs/Cysteine/FPNPs/Con A NPs to the MCF 7 cancer cells was tested using HEK 293 normal cells as a negative control. Viability results proposed that the AuNPs/Cysteine/FPNPs/Con A NPs are biocompatible at levels up to 100 μg/mL. This nanoparticle showed some advantageous features such as high stability, favorable emission wavelength, and low toxicity, enabling for application of in vivo bioimaging of MCF 7 tumoral cells.

Phase transferring luminescent gold nanoclusters via single-stranded DNA

Phase transferring luminescent gold nanoclusters via single-stranded DNA

Front Cover: Heterobimetallic Ln(III)‐Containing Materials Based on One‐Dimensional Aurophilic Chains of Gold(I) Dithiolate Dimers and Their Vapochromic Response to DMF (Eur. J. Inorg. Chem. 14/2022)

The Front Cover shows the luminescence turn-on response of a gold(I)-containing dithiolate complex after exposure to dimethylformamide (DMF) vapor. The switch represents the toggleable nature of this response, as the complex is non-luminescent in the absence of DMF. The intensity of the luminescence depends on the concentration of DMF present. The structure of the luminescent gold(I) dithiolate is depicted, with chains affixed to the gold(I) atoms, symbolic of the aurophilic interactions binding each monomeric unit into polymeric one-dimensional chains. Notably, in these materials, the observed emission energy may be dependent on more than just the length of the aurophilic interactions. More information can be found in the Research Article by D. B. Leznoff and co-workers.

Dual-readout fluorescence quenching immunochromatographic test strips for highly sensitive simultaneous detection of chloramphenicol and amantadine based on gold nanoparticle-triggered photoluminescent nanoswitch control

Herein, a novel fluorescence quenching immunochromatographic test strip (FQICTS) for simultaneous detection of chloramphenicol (CAP) and amantadine (AMD) was developed on the basis of inner filter effect (IFE), with the combination of gold nanoparticles (AuNPs) and highly luminescent green-emitting gold nanoclusters (AuNCs) as the IFE quencher/donor pair. The AuNPs could quench the excitation light and emission light of AuNCs and achieve a high IFE efficiency due to dual spectral overlapping. Under optimal conditions, the “turn-on” mode of the AuNCs-based dual-readout FQICTS showed good linearity for CAP detection in chicken samples from 0.05 ng/g to 10 ng/g, with a limit of detection (LOD) of 0.043 ng/g. The linear range of AMD is 0.5–50 ng/g, with LOD of 0.45 ng/g. The visual LODs of CAP and AMD in “turn-on” mode were 200 and 10 times lower than that in “turn-off” mode, respectively. The “turn-on” mode of FQICTS showed high recovery for detecting CAP (82.5–94.5%) and AMD (81.9–110.7%) spiked into chicken samples. The performance and practicability of the established method were verified with commercial enzyme-immunoassay kits, and good correlations were observed. Overall, the newly developed AuNCs-based dual-readout FQICTS is a promising on-site screening tool for rapid, high-sensitivity detection of multiple food contaminants in practical applications.

Enzymatic digestion of luminescent albumin-stabilized gold nanoclusters under anaerobic conditions: clues to the quenching mechanism

Enzymatic digestion of albumin-conjugated gold nanoclusters (AuNCs) decreases their luminescence, regardless of oxygen presence. Our study points to agglomeration of AuNCs as the main process underlying the proteolysis-induced quenching.

Facile construction of highly luminescent and biocompatible gold nanoclusters by shell rigidification for two-photon pH-edited cytoplasmic and in vivo imaging.

Gold nanoclusters (AuNCs), as a novel fluorescent material, have been extensively explored and developed for bioimaging because of their attractive advantages such as ultrasmall size, low toxicity and exceptional two-photon excitation properties. However, it still remains a challenge to produce water-soluble, biocompatible and ultrabright AuNCs. Herein, we report on a novel one-pot synthesis of highly luminescent and biocompatible AuNCs by using polyvinyl pyrrolidone (PVP), a water-soluble polymer, to rigidify the primary stabilizing layer (shell) that is composed of 6-aza-2-thiothymine (ATT) ligands bound to the particle. Such shell-rigidification resulted in a significant enhancement of the fluorescence efficiency, reaching a quantum yield of 39% under the best conditions, about 35-fold increase from the intrinsically weak fluorescence of the AuNCs stabilized by only ATT. The fluorescence enhancement mechanism was systematically characterized, and the results indicate that PVP coating rigidifies the ATT ligand shell through steric hindrance and reduces the nonradiative relaxation of the excited states. The biocompatible PVP-AuNCs were further examined for two-photon cellular and sentinel lymph node (SLN) bioimaging, and we observed pH-dependent cytoplasmic images and intense green fluorescence in SLN and lymphatic vessels.

Highly luminescent gold nanocluster assemblies for bioimaging in living organisms.

Fluorescent gold nanoclusters are promising nanomaterials for biomedical applications but confronted with low emission efficiency and poor surface functionality. Herein, three kinds of highly luminescent and functionalized gold nanocluster nano-assembled structures were fabricated by poly-l-arginine surface engineering for luminescence improvement. The assembly is employed for imaging the glutathione molecule in cells and living organisms with low background and high sensitivity.

Surface-regulated injection dose response of ultrasmall luminescent gold nanoparticles.

With the rapid growth of the use of renal-clearable nanomedicines in disease targeting and therapy, a fundamental understanding of their injection dose responses is of great importance for future translation to clinical settings. Using glutathione-coated gold nanoparticles (GS-AuNPs) as a renal-clearable nanomedicine model for the construction of ultrasmall AuNPs with different serum protein binding abilities, we discover that the concentration-dependent serum protein binding capabilities endow GS-AuNPs with a more sensitive response to injection dose than NPs resistant to serum protein binding, resulting in greatly improved tumor-targeting efficiencies during both single and repeated low-dose injections; the performance is also distinct from nonrenal-clearable AuNPs coated with serum protein, which show decreased tumor-targeting efficiency with a decrease in the injection dose.

The Sensitization of Scintillation in Polymeric Composites Based on Fluorescent Nanocomplexes.

The sensitization of scintillation was investigated in crosslinked polymeric composite materials loaded with luminescent gold clusters aggregates acting as sensitizers, and with organic dye rhodamine 6G as the emitting species. The evolution in time of the excited states population in the systems is described by a set of coupled rate equations, in which steady state solution allowed obtainment of an expression of the sensitization efficacy as a function of the characteristic parameters of the employed luminescent systems. The results obtained indicate that the realization of sensitizer/emitter scintillating complexes is the strategy that must be pursued to maximize the sensitization effect in composite materials.

Green synthesis of highly luminescent gold nanoclusters and their application in sensing Cu(II) and Hg(II)

A novel synthetic strategy for high luminescent gold nanoclusters (AuNCs) based on coffee Arabica seeds extract (CASE) is presented in this work. We have designed and developed a green technique that enhanced the selectivity of gold nanoclusters towards Cu(II) and Hg(II) ions. The coffee extract was used as a stabilizer and reducing agent in the synthesis process of AuNCs. The as-prepared AuNCs were characterized in terms of size, surface modification, and composition utilizing different advanced techniques. The CASE-AuNCs responded to these significant metal ions through the quenching phenomenon of the AuNCs fluorescence. EDTA and sodium borohydride were utilized as masking agents. Further, EDTA is bind to Cu(II) ion forming a metal complex and shielding the quenching effect of Cu(II) ions on CASE-AuNCs fluorescence through electron or energy transfer. Besides, Hg(II) is reduced to mercury Hg0 in the presence of sodium borohydride and prevents the quenching effect of Hg(II)-CASE-AuNCs system. Thus, considerable selectivity of AuNCs was achieved towards these two metal ions allowing sensitive determination even one of these metal ions coexists in the environment. The AuNCs have detection limits for Cu(II) and Hg(II) in nanomolar level. The as-prepared CASE-AuNCs were used successfully to detect Cu(II) and Hg(II) ions in real samples.

In situ synthesis of red fluorescent gold nanoclusters with enzyme-like activity for oxidative stress amplification in chemodynamic therapy

Chemodynamic therapy (CDT) has attracted tremendous interest in cancer therapy because it is independent of oxygen and photoirradiation. However, the therapeutic efficacy of CDT is restricted by insufficient H2O2 levels in tumor cells. Herein, employing endogenous GSH as a template and cationic polymeric chitosan (CS) as crosslinker and stabilizer exhibiting easy cell uptake, red luminescent gold nanoclusters (denoted CS-GSH@AuNCs) were successfully synthesized in HeLa cells. The in situ synthesized CS-GSH@AuNCs exhibited both superoxidase dismutase (SOD) and peroxidase (POD)-like activity, which could promote the production of H2O2 from superoxide anion radicals (O2•−) and then •OH. The combination of GSH elimination and H2O2 elevation boosted the generation of •OH, which could trigger cancer cell apoptosis and death. The enzyme-like activity of CS-GSH@AuNCs could be effectively activated under acidic conditions, and showed a high killing effect on tumor cells but minimal toxicity to normal cells. The developed GSH consumption and •OH promotion theranostic platform is an innovative route for enhanced CDT by the amplification of oxidative stress.

Versatile Emissive Three‐Coordinated Gold(I) Systems‐Properties and Perspectives

AbstractTrigonal planar coordination at gold allows phosphorescent 3MC transitions, not expected for luminescent mononuclear linear gold complexes. The careful selection and nature of the ancillary ligands bonded to gold, being fluorophore groups or not emissive ligands may cause a distortion of ideal trigonal planar coordination favoring different origins for the emissions. Consequently, intraligand (IL) or charge transfer (CT) transitions may be present and besides the expected phosphorescent MC transitions, fluorescence or thermally activated delayed fluorescence (TADF) may be the origin of the luminescence. In addition of the advantages of triplet population and deactivation via phosphorescent or delayed fluorescence processes, these systems are very versatile and may show interesting properties such as mechanochromism and vapochromism and, consequently, have revealed as promising candidates for optical applications. The objective of this review is to provide an overview of the reported luminescent three‐coordinated gold systems and to get insight into their emissive properties.

Water-soluble luminescent gold nanoclusters reduced and protected by histidine for sensing of barbaloin and temperature

In terms of the vital functions of barbaloin, it is necessary to develop a selective and sensitive detection means in barbaloin sensing to replace the previous defective analytical methods. Herein, the water-soluble luminescent gold nanoclusters (Au NCs) with good emission character were firstly established for barbaloin detection with high efficiency. The small size and stable probe was synthesized through one-pot way by protecting and reducing of histidine (His). The characterization results revealed that the quenching mechanism was mainly attributed to the inner filter effect (IFE). The His-Au NCs displayed high selectivity to barbaloin against interferes and a good linear relationship existed in the range of 0.5–150 μM. More importantly, the probe was successfully employed to detect barbaloin in bovine serum samples with satisfactory recoveries and the excellent performance was also obtained from temperature sensing. This novel detection platform expanded the analytical methods for barbaloin based on fluorescence properties.