Encapsulation of Luminescent Gold Nanoclusters into Synthetic Vesicles

Gold nanoclusters (Au NCs) are attractive luminescent nanoprobes for biomedical applications. In vivo biosensing and bioimaging requires the delivery of the Au NCs into subcellular compartments. In this view, we explore here the possible encapsulation of ultra-small-sized red and blue emitting Au NCs into liposomes of various sizes and chemical compositions. Different methods were investigated to prepare vesicles containing Au NCs in their lumen. The efficiency of the process was correlated to the structural and morphological aspect of the Au NCs' encapsulating vesicles thanks to complementary analyses by SAXS, cryo-TEM, and confocal microscopy techniques. Cell-like-sized vesicles (GUVs) encapsulating red or blue Au NCs were successfully obtained by an innovative method using emulsion phase transfer. Furthermore, exosome-like-sized vesicles (LUVs) containing Au NCs were obtained with an encapsulation yield of 40%, as estimated from ICP-MS.

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.

Augmented interaction of multivalent arginine coated gold nanoclusters with lipid membranes and cells

A library of ultra-small red photoluminescent gold nanoclusters (Au NCs) were synthesized with an increasing amount of positive charges provided by the addition of mono-, di- or trivalent-glutathione modified arginine peptides. We then studied how the arginine content impacted on the interaction of Au NCs with negatively charged artificial lipid bilayers and cell membranes. Results indicated that increasing the arginine content enhanced Au NCs' adsorption on lipid bilayers and on cell membranes followed by an increased cellular uptake in melanoma cells (COLO 829). Surprisingly, the presence of up to 40% serum for highly positively charged Au NCs did not hinder their interaction with lipid bilayers that contain glycolipids, suggesting a reduced opsonization of these Au NCs. In addition, these Au NCs are usually not toxic, except those with the highest arginine contents. Thus, controlled grafting of arginine peptides onto Au NCs is an elegant strategy to improve their binding and internalization by tumor cells while still keeping their anti-fouling properties.

Gold nanoclusters for biomedical applications: toward in vivo studies

In parallel with the rapidly growing and widespread use of nanomedicine in the clinic, we are also witnessing the development of so-called theranostic agents that combine diagnostic and therapeutic properties.

Recent advances in ultra-small fluorescent Au nanoclusters toward oncological research

Au nanoclusters possess a series of excellent properties owing to their size being comparable to the Fermi wavelength of electrons. For example, they show excellent biocompatibility, optical stability, large Stokes shift, intense size-dependent emission and monodispersion, and thus could effectively compensate for the shortcomings of traditional organic fluorescent dyes and fluorescent quantum. In this review, we detail the latest developments of Au nanoclusters employed in the field of biomedicine, especially in oncology research, by summarizing the application of imaging, sensing and drug delivery based on their excellent luminescent properties and unique structural features. We also discuss the significant work relating to Au NCs that now is being devoted in other therapeutic strategies, such as radiotherapy, photothermal therapy and photodynamic therapy, for example. It is anticipated that this review will provide new insights and theoretical guidance to allow the advantages of Au nanoclusters to be realized in oncotherapy.

Fluorescence-tunable copper nanoclusters and their application in hexavalent chromium sensing

Generally, metal nanoclusters are synthesized using only a single ligand. Thus, the properties and applications of these nanomaterials are limited by the nature of the ligand used. In this study, we have developed a new synthetic strategy to prepare bi-ligand copper nanoclusters (Cu NCs). These bi-ligand Cu NCs are synthesized from copper ions, thiosalicylic acid, and cysteamine by a simple one-pot method, and they exhibit high quantum yields (>18.9%) and good photostability. Most interestingly, the fluorescence intensities and surface properties of the Cu NCs can be tailored by changing the ratio of the two ligands. Consequently, the bi-ligand Cu NCs show great promise as fluorescent probes. Accordingly, the Cu NCs were applied to the inner-filter-effect-based detection of hexavalent chromium in water. A wide linear range of 0.1–1000 μM and a low detection limit (signal-to-noise ratio = 3) of 0.03 μM was obtained. The recoveries for the real sample analysis were between 98.3 and 105.0% and the relative standard deviations were below 4.54%, demonstrating the repeatability and practical utility of this assay.

Generally, metal nanoclusters are synthesized using only a single ligand.

Enhanced near infrared persistent luminescence of Zn2Ga2.98Ge0.75O8:Cr0.023+ nanoparticles by partial substitution of Ge4+ by Sn4+

Spinel-phase Zn₂Ga_2.98Ge_0.75–xSn_xO₈:Cr_0.02³⁺ (ZGGSO:Cr³⁺) nanoparticles with various Sn⁴⁺ concentrations were prepared by a hydrothermal method in combination with a post-annealing in vacuum at high temperature. For these nanoparticles, the observed near infrared (NIR) persistent luminescence peaked at ∼697 nm and originates from the ²E, ⁴T₂ (⁴F) → ⁴A₂ transitions of Cr³⁺ and the afterglow time exceeds 800 min. For both the interior and surface Cr³⁺ ions in the ZGGSO host, it can be found that the increased energy transfer from Cr³⁺ to the deep trap (anti-site defects, ) after the substitution of Ge⁴⁺ by Sn⁴⁺ plays a key role in enhancing the persistent luminescence of the ZGGSO:Cr³⁺ nanoparticles. Strikingly, this energy transfer process can be controlled through the variations in the crystal field strength and the trap depths. Our results suggest that not only Sn⁴⁺ substitution can improve in vivo bioimaging but also the existence of deep traps in ZGGSO:Cr³⁺ nanoparticles is helpful for retracing in vivo bioimaging at any time.

Distance between the ⁴T₂ energy level and traps depth can be modulated and the NIR persistent luminescence can be enhanced.

Recent advances in biomedical applications of fluorescent gold nanoclusters

Fluorescent gold nanoclusters (AuNCs) are emerging as novel fluorescent materials and have attracted more and more attention in the field of biolabeling, biosensing, bioimaging and targeted cancer treatment because of their unusual physicochemical properties, such as long fluorescence lifetime, ultrasmall size, large Stokes shift, strong photoluminescence, as well as excellent biocompatibility and photostability. Recently, significant efforts have been committed to the preparation, functionalization and biomedical application studies of fluorescent AuNCs. In this review, we have summarized the strategies for preparation and surface functionalization of fluorescent AuNCs in the past several years, and highlighted recent advances in the biomedical applications of the relevant fluorescent AuNCs. Based on these observations, we also give a discussion on the current problems and future developments of the fluorescent AuNCs for biomedical applications.

Multifunctional gold-based nanocomposites for theranostics

Although Au-particle potential in nanobiotechnology has been recognized for the last 15 years, new insights into the unique properties of multifunctional nanostructures have just recently started to emerge. Multifunctional gold-based nanocomposites combine multiple modalities to improve the efficacy of the therapeutic and diagnostic treatment of cancer and other socially significant diseases. This review is focused on multifunctional gold-based theranostic nanocomposites, which can be fabricated by three main routes. The first route is to create composite (or hybrid) nanoparticles, whose components enable diagnostic and therapeutic functions. The second route is based on smart bioconjugation techniques to functionalize gold nanoparticles with a set of different molecules, enabling them to perform targeting, diagnostic, and therapeutic functions in a single treatment procedure. Finally, the third route for multifunctionalized composite nanoparticles is a combination of the first two and involves additional functionalization of hybrid nanoparticles with several molecules possessing different theranostic modalities. This last class of multifunctionalized composites also includes fluorescent atomic clusters with multiple functionalities.

Biomedical applications of nano-titania in theranostics and photodynamic therapy

Titanium dioxide (TiO₂) is one of the most abundantly used nanomaterials for human life. It is used in sunscreen, photovoltaic devices, biomedical applications and as a food additive and environmental scavenger.

Lysozyme-stabilized Ag nanoclusters: synthesis of different compositions and fluorescent responses to sulfide ions with distinct modes

The effect of composition on the photoluminescence properties of lysozyme-stabilized Ag nanoclusters and their sensing modes for sulfide anions were studied.

Active tumor-targeting luminescent gold clusters with efficient urinary excretion

Novel active tumor targeting fluorescent gold nanoclusters are synthesized through a facile method.

Fluorescent gold nanoclusters for in vivo target imaging of Alzheimer's disease

Fluorescent gold nanoclusters forin vivotarget imaging provides a new way for rapid and early diagnosis of Alzheimer's disease.

Rapid tumor bioimaging and photothermal treatment based on GSH-capped red fluorescent gold nanoclusters

Au NCs used for fluorescent bioimaging and photothermal treatment through combining with porphyrin derivatives (TSPP).

Formation of fluorescent platinum nanoclusters using hyper-branched polyethylenimine and their conjugation to antibodies for bio-imaging

Fluorescent Pt NCs@PEI were formed in the cavities coiled by PEI ligands and bio-imaged HeLa cells via conjugation with antibodies.

Thiols-Induced Rapid Photoluminescent Enhancement of Glutathione-Capped Gold Nanoparticles for Intracellular Thiols Imaging Applications

The rapid detection and imaging of intracellular thiols is of great importance during the occurrence and development of some chronic diseases. Here we demonstrate the rapid thiols-induced photoluminescence (PL) enhancement of the low luminescent glutathione (GSH) stabilized Au nanoparticles, AuGSH (low). The dynamic PL investigation reveals that the PL enhancement fits a first-order reaction model. The X-ray photoelectron spectroscopic and mass spectroscopic results indicate that AuGSH (low) are mainly comprised of "thiols-insufficient" Au species and the additional thiols can efficiently attach to the "unsaturated" surface of Au nanoparticles, accompanied by significant PL enhancement. The noncytotoxic AuGSH (low) probe can be successfully applied for imaging of intracellular thiols. Generally, this work illustrates the great prospects of facile-prepared AuGSH (low) as a candidate for thiols labeling and imaging.

Multifunctional Au nanoclusters for targeted bioimaging and enhanced photodynamic inactivation of Staphylococcus aureus

A novel nanocluster platform is developed to combine intense red fluorescence of Au₂₅–BSA nanoclusters (QY ∼ 14%), biospecific binding to S. aureus due to human antistaphylococcal IgG, and photodynamic inactivation due to photosensitizer Photosens™.