Biocompatible gold nanoclusters: synthetic strategies and biomedical prospects

Design a Friendly Nanoscale Chemical Sensor Based on Gold Nanoclusters for Detecting Thiocyanate Ions in Food Industry Applications

The surfactant cetyltrimethylammonium bromide (CTAB) induces the aggregation of gold nanoclusters (GNCs), leading to the development of a proposed fluorometric technique for detecting thiocyanate (SCN-) ions based on an anti-aggregation mechanism. This approach is straightforward to execute, highly sensitive, and selective. A significant quenching effect occurs in fluorescence upon using the aggregation agent CTAB in GNCs synthesis, resulting in a transition from intense red fluorescence to dim red. The decrease in fluorescence intensity of GNCs in the presence of CTAB is caused by the mechanism of fluorescence quenching mediated by aggregation. As the levels of SCN- rise, the fluorescence of CTAB-GNCs increases; this may be detected using spectrofluorometry or by visually inspecting under UV irradiation. The recovery of red fluorescence of CTAB-GNCs in the presence of SCN- enables the precise and discerning identification of SCN- within the concentration range of 2.86-140 nM. The minimum detectable concentration of the SCN- ions was 1 nM. The selectivity of CTAB-GNCs towards SCN- ions was investigated compared to other ions, and it was demonstrated that CTAB-GNCs exhibit exceptional selectivity. Furthermore, we believe that CTAB-GNCs have novel possibilities as favorable sensor candidates for various industrial applications. Our detection technique was validated by analyzing SCN- ions in milk samples, which yielded promising results.

Precision nanoengineering for functional self-assemblies across length scales

As nanotechnology continues to push the boundaries across disciplines, there is an increasing need for engineering nanomaterials with atomic-level precision for self-assembly across length scales, i.e., from the nanoscale to the macroscale. Although molecular self-assembly allows atomic precision, extending it beyond certain length scales presents a challenge. Therefore, the attention has turned to size and shape-controlled metal nanoparticles as building blocks for multifunctional colloidal self-assemblies. However, traditionally, metal nanoparticles suffer from polydispersity, uncontrolled aggregation, and inhomogeneous ligand distribution, resulting in heterogeneous end products. In this feature article, I will discuss how virus capsids provide clues for designing subunit-based, precise, efficient, and error-free self-assembly of colloidal molecules. The atomically precise nanoscale proteinic subunits of capsids display rigidity (conformational and structural) and patchy distribution of interacting sites. Recent experimental evidence suggests that atomically precise noble metal nanoclusters display an anisotropic distribution of ligands and patchy ligand bundles. This enables symmetry breaking, consequently offering a facile route for two-dimensional colloidal crystals, bilayers, and elastic monolayer membranes. Furthermore, inter-nanocluster interactions mediated via the ligand functional groups are versatile, offering routes for discrete supracolloidal capsids, composite cages, toroids, and macroscopic hierarchically porous frameworks. Therefore, engineered nanoparticles with atomically precise structures have the potential to overcome the limitations of molecular self-assembly and large colloidal particles. Self-assembly allows the emergence of new optical properties, mechanical strength, photothermal stability, catalytic efficiency, quantum yield, and biological properties. The self-assembled structures allow reproducible optoelectronic properties, mechanical performance, and accurate sensing. More importantly, the intrinsic properties of individual nanoclusters are retained across length scales. The atomically precise nanoparticles offer enormous potential for next-generation functional materials, optoelectronics, precision sensors, and photonic devices.

Functional Materials for Subcellular Targeting Strategies in Cancer Therapy: Progress and Prospects

Neoadjuvant and adjuvant therapies have made significant progress in cancer treatment. However, tumor adjuvant therapy still faces challenges due to the intrinsic heterogeneity of cancer, genomic instability, and the formation of an immunosuppressive tumor microenvironment. Functional materials possess unique biological properties such as long circulation times, tumor-specific targeting, and immunomodulation. The combination of functional materials with natural substances and nanotechnology has led to the development of smart biomaterials with multiple functions, high biocompatibilities, and negligible immunogenicities, which can be used for precise cancer treatment. Recently, subcellular structure-targeting functional materials have received particular attention in various biomedical applications including the diagnosis, sensing, and imaging of tumors and drug delivery. Subcellular organelle-targeting materials can precisely accumulate therapeutic agents in organelles, considerably reduce the threshold dosages of therapeutic agents, and minimize drug-related side effects. This review provides a systematic and comprehensive overview of the research progress in subcellular organelle-targeted cancer therapy based on functional nanomaterials. Moreover, it explains the challenges and prospects of subcellular organelle-targeting functional materials in precision oncology. The review will serve as an excellent cutting-edge guide for researchers in the field of subcellular organelle-targeted cancer therapy.

Towards site-specific emission enhancement of gold nanoclusters using plasmonic systems: advantages and limitations

Photoluminescent gold nanoclusters are widely seen as a promising candidate for applications in biosensing and bioimaging. Although they have many of the required properties, such as biocompatibility and photostability, the luminescence of near infrared emitting gold nanoclusters is still relatively weak compared to the best available fluorophores. This study contributes to the ongoing debate on the possibilities and limitations of improving the performance of gold nanoclusters by combining them with plasmonic nanostructures. We focus on a detailed description of the emission enhancement and compare it with the excitation enhancement obtained in recent works. We prepared a well-defined series of gold nanoclusters attached to gold nanorods whose plasmonic band is tuned to the emission band of gold nanoclusters. In the resultant single-element hybrid nanostructure, the gold nanorods control the luminescence of gold nanoclusters in terms of its spectral position, polarization and lifetime. We identified a range of parameters which determine the mutual interaction of both particles including the inter-particle distance, plasmon-emission spectral overlap, dimension of gold nanorods and even the specific position of gold nanoclusters attached on their surface. We critically assess the practical and theoretical photoluminescence enhancements achievable using the above strategy. Although the emission enhancement was generally low, the observations and methodology presented in this study can provide a valuable insight into the plasmonic enhancement in general and into the photophysics of gold nanoclusters. We believe that our approach can be largely generalized for other relevant studies on plasmon enhanced luminescence.

In-situ bio-assembled specific Au NCs-Aptamer-Pyro conjugates nanoprobe for tumor imaging and mitochondria-targeted photodynamic therapy

Mitochondrion has emerged as a promising drug target for photodynamic therapy (PDT), due to its significant role in supporting life activities and being reactive oxygen species (ROS)-sensitive. Herein, we establish a new strategy that in-situ bio-synthesized Au NCs combine with mitochondria-targeted aptamer-Pyro conjugates (ApPCs) for specific tumor imaging and PDT. The prepared ApPCs can serve as template for the in-situ bio-synthesis of Au NCs, thereby facilitating the generation of Au NCs-ApPCs assemblies in unique tumor microenvironment. Compared with highly negatively charged ApPCs, bio-synthesized nanoscale Au NCs-ApPCs assemblies are conducive to cell uptake, which consequently benefits the delivery of ApPCs. After dissociated from Au NCs-ApPCs, internalized ApPCs can selectively accumulate in mitochondria and generate excess ROS to disrupt the mitochondrial membrane upon irradiation, thus inducing efficient cell killing. In vitro assays demonstrated that the fluorescent Au NCs-ApPCs assemblies could be specifically produced in cancerous cells, indicating the specific tumor imaging ability, while intracellular ApPCs co-localized well with mitochondria. CCK-8 results revealed over 80% cell death after PDT. In vivo study showed that fluorescent Au NCs-ApPCs assemblies were exclusively generated in tumor and achieved long-term retention; tumor growth was significantly inhibited after 15-day PDT treatment. All these evidences suggest that in-situ bio-synthesized Au NCs-ApPCs assembly is a potent mitochondria-targeted nanoprobe to boost the PDT efficacy of cancers.

Tailoring the Electron-Phonon Interaction in Au25(SR)18 Nanoclusters via Ligand Engineering and Insight into Luminescence

Understanding the electron-phonon interaction in Au nanoclusters (NCs) is essential for enhancing and tuning their photoluminescence (PL) properties. Among all the methods, ligand engineering is the most straightforward and facile one to design Au NCs with the desired PL properties. However, a systematic understanding of the ligand effects toward electron-phonon interactions in Au NCs is still missing. Herein, we synthesized four Au₂₅(SR)₁₈^- NCs protected by different -SR ligands and carefully examined their temperature-dependent band-gap renormalization behavior. Data analysis by a Bose-Einstein two-oscillator model revealed a suppression of high-frequency optical phonons in aromatic-ligand-protected Au₂₅ NCs. Meanwhile, a low-frequency breathing mode and a quadrupolar mode are attributed as the main contributors to the phonon-assisted nonradiative relaxation pathway in aromatic-ligand-protected Au₂₅ NCs, which is in contrast with non-aromatic-ligand-protected Au₂₅ NCs, in which tangential and radial modes play the key roles. The PL measurements of the four Au₂₅ NCs showed that the suppression of optical phonons led to higher quantum yields in aromatic-ligand-protected Au₂₅ NCs. Cryogenic PL measurements provide insights into the nonradiative energy relaxation, which should be further investigated for a full understanding of the PL mechanism in Au₂₅ NCs.

The Recent Development of Multifunctional Gold Nanoclusters in Tumor Theranostic and Combination Therapy

The rising incidence and severity of malignant tumors threaten human life and health, and the current lagged diagnosis and single treatment in clinical practice are inadequate for tumor management. Gold nanoclusters (AuNCs) are nanomaterials with small dimensions (≤3 nm) and few atoms exhibiting unique optoelectronic and physicochemical characteristics, such as fluorescence, photothermal effects, radiosensitization, and biocompatibility. Here, the three primary functions that AuNCs play in practical applications, imaging agents, drug transporters, and therapeutic nanosystems, are characterized. Additionally, the promise and remaining limitations of AuNCs for tumor theranostic and combination therapy are discussed. Finally, it is anticipated that the information presented herein will serve as a supply for researchers in this area, leading to new discoveries and ultimately a more widespread use of AuNCs in pharmaceuticals.

Glutathione-capped gold nanoclusters as near-infrared-emitting efficient contrast agents for confocal fluorescence imaging of tissue-mimicking phantoms

An innovative research has been conducted focused on demonstrating the ability of novel dual-emissive glutathione-stabilized gold nanoclusters (GSH-AuNCs) to perform bright near-infrared (NIR)-emitting contrast agents inside tissue-mimicking agarose-phantoms via two complementary confocal fluorescence imaging techniques. First, using a new and fast microwave-assisted approach, we synthesized photostable dual-emitting GSH-AuNCs with an average size of 3.2 ± 0.4 nm and NIR emission quantum yield of 9.9%. Steady-state fluorescence measurements coupled with fluorescence lifetime imaging microscopy (FLIM) assays performed on lyophilized GSH-AuNCs revealed that the obtained GSH-AuNCs exhibit PL emissions at 610 nm (red PL) and, respectively, 800 nm (NIR PL) in both solution and powder solid-state. Time-resolved fluorescence measurements showed that the two PL components are characterized by average lifetimes of 407 ns (red PL) and 1821 ns (NIR PL), respectively. Additionally, due to a partial overlap between the red PL and the absorption of the NIR PL, an energy transfer between the two coexisting emissive centers was discovered and confirmed via steady-state and time-resolved fluorescence measurements. Furthermore, the FLIM analysis performed on powder GSH-AuNCs under 640 nm, an excitation more suitable for bioimaging applications, revealed a homogeneous and photostable NIR PL signal from GSH-AuNCs. Finally, the ability of GSH-AuNCs to operate as reliable NIR-emitting contrast agents inside tissue-mimicking agarose-phantoms was demonstrated here for the first time via complementary FLIM and re-scan confocal fluorescence imaging techniques. In consequence, GSH-AuNCs show great promise for future in vivo imaging applications via confocal fluorescence microscopy.

Nanoligomers Targeting Human miRNA for the Treatment of Severe COVID-19 Are Safe and Nontoxic in Mice

The devastating effects of the coronavirus disease 2019 (COVID-19) pandemic have made clear a global necessity for antiviral strategies. Most fatalities associated with infection from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) result at least partially from uncontrolled host immune response. Here, we use an antisense compound targeting a previously identified microRNA (miRNA) linked to severe cases of COVID-19. The compound binds specifically to the miRNA in question, miR-2392, which is produced by human cells in several disease states. The safety and biodistribution of this compound were tested in a mouse model via intranasal, intraperitoneal, and intravenous administration. The compound did not cause any toxic responses in mice based on measured parameters, including body weight, serum biomarkers for inflammation, and organ histopathology. No immunogenicity from the compound was observed with any administration route. Intranasal administration resulted in excellent and rapid biodistribution to the lungs, the main site of infection for SARS-CoV-2. Pharmacokinetic and biodistribution studies reveal delivery to different organs, including lungs, liver, kidneys, and spleen. The compound was largely cleared through the kidneys and excreted via the urine, with no accumulation observed in first-pass organs. The compound is concluded to be a safe potential antiviral treatment for COVID-19.

Gold labelling of a green fluorescent protein (GFP)-tag inside cells using recombinant nanobodies conjugated to 2.4 nm thiolate-coated gold nanoparticles

Advances in microscopy technology have prompted efforts to improve the reagents required to recognize specific molecules within the intracellular environment. For high-resolution electron microscopy, conjugation of selective binders originating from the immune response arsenal to gold nanoparticles (AuNPs) as contrasting agents is the method of choice to obtain labeling tools. However, conjugation of the minimal sized 15 kDa nanobody (Nb) to AuNPs remains challenging in comparison to the conjugation of 150 kDa IgG to AuNPs. Herein, effective Nb-AuNP assemblies are built using the selective and almost irreversible non-covalent associations between two peptide sequences deriving from a p53 heterotetramer domain variant. The 15 kDa GFP-binding Nb is fused to one dimerizing motif to obtain a recombinant Nb dimer with improved avidity for GFP while the other complementing dimerizing motif is equipped with thiols and grafted to a 2.4 nm substituted thiobenzoate-coordinated AuNP via thiolate exchange. After pegylation, the modified AuNPs are able to non-covalently anchor Nb dimers and the subsequent complexes demonstrate the ability to form immunogold label GFP-protein fusions within various subcellular locations. These tools open an avenue for precise localization of targets at high resolution by electron microscopy.

Intrinsic Photoluminescence of Solid-State Gold Nanoclusters: Towards Fluorescence Lifetime Imaging of Tissue-Like Phantoms Under Two-Photon Near-Infrared Excitation

Gold nanoclusters (AuNCs) have attracted extensive attention as light-emissive materials with unique advantages such as high photostability, large Stoke shifts and low toxicity. However, a better understanding of their solid-state photoluminescence properties is still needed. Herein, we investigated for the first time the intrinsic photoluminescence properties of lyophilized bovine serum albumin stabilized AuNCs (BSA-AuNCs) via fluorescence lifetime imaging microscopy (FLIM) studies performed under both one and two photon excitations (OPE and TPE) on individual microflakes, combined with fluorescence spectroscopic investigations. Both in solution and solid-state, the synthesized BSA-AuNCs exhibit photoluminescence in the first biological window with an absolute quantum yield of 6% and high photostability under continuous irradiation. Moreover, under both OPE and TPE conditions, solid BSA-AuNCs samples exhibited a low degree of photobleaching, while FLIM assays prove the homogeneous distribution of the photoluminescence signal inside the microflakes. Finally, we demonstrate the ability of BSA-AuNCs to perform as reliable bright and photostable contrast agents for the visualization of cancer tissue mimicking agarose-phantoms using FLIM approach under non-invasive TPE. Therefore, our results emphasize the great potential of the as synthesized BSA-AuNCs for ex vivo and in vivo non-invasive NIR imaging applications.

Glutathione Disulfide as a Reducing, Capping, and Mass-Separating Agent for the Synthesis and Enrichment of Gold Nanoclusters

Water-soluble nanoclusters, which are facilely enrichable without changes in the original properties, are highly demanded in many disciplines. In this contribution, a new class of gold nanoclusters (AuNCs) was synthesized using glutathione disulfide (GSSG) as a reducing and capping agent under intermittent heating mode. The as-prepared GSSG–AuNCs had a higher quantum yield (4.1%) compared to the conventional glutathione-protected AuNCs (1.8%). Moreover, by simply introducing the GSSG–AuNC solution to acetonitrile at a volume ratio of 1:7, a new bottom phase was formed, in which GSSG–AuNCs could be 400-fold enriched without changes in properties, with a percentage recovery higher than 99%. The enrichment approach did not need additional instruments and was potentially suitable for large-scale enrichment of nanoclusters. Further, density functional theory calculations indicated that the hydrogen bonding between GSSG and acetonitrile plays a key role for the bottom phase formation. Our work suggests that the highly emissive GSSG–AuNCs possess great potential not only in fluorescent measurements but also in other scenarios in which high-concentration AuNCs may be needed, such as catalysis, drug delivery, and electronic and optical industries.

Current Biomedical and Diagnostic Applications of Gold Micro and Nanoparticles

Production of particles and their adaptation in the pharmacology became an object of interest, and they are the currently introduced therapies based on the use of micro and nanoparticles. The use of gold particles is not an exception. This review has focused on the application of gold micro and nanoparticles in pharmacology and biomedicine. The particles can be used for diagnosis respective theranostic of cancer, rheumatoid arthritis and as antimicrobial means. Besides these applications, specifications of gold, gold particles, and colloidal gold manufacturing and their comparison with the solid gold, are described as well. This review is based on a survey of actual scientific literature.

CoFe2O4-Quantum Dots for Synergistic Photothermal/Photodynamic Therapy of Non-small-Cell Lung Cancer Via Triggering Apoptosis by Regulating PI3K/AKT Pathway

Non-small-cell lung cancer (NSCLC) has become the second most diagnosed malignant tumors worldwide. As our long-term interests in seeking nanomaterials to develop strategies of cancer therapies, we herein constructed novel CoFe2O4-quantum dots (QDs) with outstanding synergistic photothermal/photodynamic property which suppressed NSCLC efficiently without apparent toxicity. We showed that the combination of CoFe2O4-QDs + NIR treatment induces apoptosis of NSCLC cells. In addition, the CoFe2O4-QDs + NIR treatment also promotes reactive oxygen species generation to trigger cell death through regulating PI3K/AKT pathway. Moreover, the CoFe2O4-QDs + NIR treatment successfully eliminates tumor xenografts in vivo without apparent toxic effects. Taken together, we reported that the novel nanomaterials CoFe2O4-QDs could exhibit enhanced synergistic photothermal therapy and photodynamic therapy effect on killing NSCLC without toxicity, which could be a promising photosensitizer for NSCLC therapy.

Self-assembled anionic and cationic Au nanoparticles with Au nanoclusters for the exploration of different biological responsiveness in cancer therapy

Self-assembly overcomes the biodegradation resistance of some traditional inorganic drug carriers. Herein, we prepared self-assembled Au nanocluster-based nanoparticles with different sizes and charges based on solvent- and cation-induced self-assembly nanotechnology as anti-cancer drug vehicles to solve the potential metabolism problems of solid gold nanoparticles. We also systematically explored the responsiveness of cancer cells to self-assembled Au nanocluster-based nanoparticles with different sizes and surface modified properties. We discovered that self-assembled nanoparticles inherited molecular-like properties of small-size Au NCs and exhibited an aggregation-induced emission (AIE) phenomenon with intense luminescence. Self-assembled Au nanocluster-based nanoparticles (Au NPs and cAu NPs) taking advantage of their size and positive charge exhibited better cell uptake than Au NCs. Encouraged by the excellent biological compatibility and cell uptake of these nanomaterials, we prepared drug-loaded nanomaterials by diffusion absorption and hydrophobic-induced embedding. cAu NPs@DOX showed an excellent anti-cancer effect owing to efficient cell internalization; Au NPs@DOX exhibited slow release of cargo drugs which might be significant to in vivo drug delivery. This work plays a crucial role in the rational design of self-assembled multifunctional gold-based nanoparticles in the application of nanomaterial-assisted multifunctional drug delivery systems (DDSs).

The Au25(pMBA)17Diglyme Cluster

A modification of Au₂₅(pMBA)₁₈ that incorporates one diglyme ligand as a direct synthetic product is reported. Notably the expected statistical production of clusters containing other ligand stoichiometries is not observed. This Au₂₅(pMBA)₁₇diglyme product is characterized by electrospray ionization mass spectrometry (ESI-MS) and optical spectroscopy. Thiolate for thiolate ligand exchange proceeds on this cluster, whereas thiolate for diglyme ligand exchange does not.

Principles and Applications of Single Particle Tracking in Cell Research

It is a tough challenge for many decades to decipher the complex relationships between cell behaviors and cellular physical properties. Single particle tracking (SPT) with high spatial and temporal resolution has been applied extensively in cell research to understand physicochemical properties of cells and their bio-functions by tracking endogenous or exogenous probes. This review describes the fundamental principles of SPT as well as its applications in intracellular mechanics, membrane dynamics, organelles distribution, and processes of internalization and transport. Finally, challenges and future directions of SPT are also discussed.

Advances in inorganic-based colloidal nanovehicles functionalized for nitric oxide delivery

Nitric oxide (NO) is an important pharmaceutical agent of considerable therapeutic interest ascribed to its vasodilative, tumoricidal and antibacterial effects. Rapid development of functional nanomaterials has provided opportunities for us to achieve controllable exogenous delivery of NO. In the current review, a variety of functionalized colloidal nanovehicles that have been developed to date for nitric oxide delivery are reported. Specifically, we focus on inorganic nanomaterials such as semiconductor quantum dots, silica nanoparticles, upconversion nanomaterials, carbon/graphene nanodots, gold nanoparticles, iron oxide nanoparticles as the functional or/and supporting materials to carry NO donors. N-diazeniumdiolates, S-nitrosothiols, nitrosyl metal complexes and organic nitrates as main types of NO donors have their own unique properties and molecular structures. Conjugating the NO donors of different forms with appropriate nanomaterials results in NO delivery nanovehicles capable of releasing NO in a dose-controllable or/and on-demand manner. We also consider the therapeutic applications of those NO delivery nanovehicles, especially their applications for cancer therapy. In the end, we discuss possible future directions for developing exogenous NO delivery systems with more desired structure and improved performance. This review aims to offer the readers an overall view of the advances in functionalized colloidal nanovehicles for NO delivery. It will be attractive to scientists and researchers in the areas of material science, nanotechnology, biomedical engineering, chemical biology, etc.

Advances in biomedical and pharmaceutical applications of protein-stabilized gold nanoclusters

The interest in using gold nanoclusters (AuNCs) as imaging probes is growing, covering wide ranges of applications. The stabilization of AuNCs with protein ligands enhances their biomedical and pharmaceutical applications. This is due to the biocompatibility, water solubility and bioactivity of proteins. Different factors can control the optical properties of AuNCs such as protein size, amino acids content and conformational structure. Controlling the synthesis conditions can result in tuning the AuNCs excitation, emission, fluorescence intensity and physicochemical properties to fulfill different applications. NIR-emitting protein-stabilized AuNCs are promising as imaging agents for targeting and visualization of cancer in vitro and in vivo. They are promising to be included as an important part of multifunctional theranostic nanosystems, due to their potential dual functions as imaging and photosensitizing agent for photodynamic therapy. Additionally, the protein around AuNCs represents a rich environment of active functional groups that are susceptible for conjugation with various biomolecules. Protein-AuNCs can act as fluorescent probes for rapid and selective analysis of different analytes in solution, cells or biological fluids. In conclusion, the variability of protein-AuNC applications can advance research in different biomedical and pharmaceutical fields.

Bovine Serum Albumin-Conjugated Red Emissive Gold Nanocluster as a Fluorescent Nanoprobe for Super-resolution Microscopy

The gold nanocluster (GNC), because of its interesting photoluminescence properties and easy renal clearance from the body, has tremendous biomedical applications. Unfortunately, it has never been explored for super-resolution microscopy (SRM). Here, we present a protein-conjugated red emissive GNC for super-resolution radial fluctuation (SRRF) of the lysosome in HeLa cells. The diameter of the lysosome obtained in SRRF is ∼59 nm, which is very close to the original diameter of the smallest lysosome in HeLa cells. Conjugation of protein to GNC aided in the specific labeling of the lysosome. We hope that GNC not only will replace some of the common dyes used in SRM but due to its electron beam contrast could also be used as a multimodal probe for several other correlative bioimaging techniques.

Fabrication of gold-calcium phosphate composite nanoparticles through coprecipitation mediated by amino-terminated polyethylene glycol

Calcium phosphate (CaP) nanoparticles immobilizing gold (Au) nanocrystals (Au-CaP composite nanoparticles) would be useful in diagnoses and/or treatments with Au nanocrystals. In this study, we achieved the rapid one-pot fabrication of such nanoparticles via coprecipitation in labile supersaturated CaP solutions by using appropriate Au sources, namely, Au nanocrystals coated with amino-terminated polyethylene glycol (PEG). In this process, amino groups at the PEG terminal played a crucial role in the coprecipitation with CaP through affinity interactions, and thus in the formation of Au-CaP composite nanoparticles; however, the molecular weight of the PEG chain was not a controlling factor in the coprecipitation. The important role of the functional groups at the PEG terminal was suggested by comparison with Au nanocrystals coated with carboxyl- and methoxy-terminated PEG, both of which barely coprecipitated with CaP and failed to form Au-CaP composite nanoparticles. Au nanocrystals coated with amino-terminated PEG were immobilized on the CaP nanoparticles, thereby regulating their size (∼140 nm in hydrodynamic diameter) and their dispersion in water. This coprecipitation process and the resulting Au-CaP composite nanoparticles have great potential in biomedical applications.

Ultrasmall Gold Nanoparticles Coated with Zwitterionic Glutathione Monoethyl Ester: A Model Platform for the Incorporation of Functional Peptides

Ultrasmall gold nanoparticles (AuNPs) are an emerging class of nanomaterials exhibiting distinctive physicochemical, molecular, and in vivo properties. Recently, we showed that ultrasmall AuNPs encompassing a zwitterionic glutathione monoethyl ester surface coating (AuGSHzwt) were highly resistant to aggregation and serum protein interactions. Herein, we performed a new set of biointeraction studies to gain a more fundamental understanding into the behavior of both pristine and peptide-functionalized AuGSHzwt in complex media. Using the model Strep-tag peptide (WSHPQFEK) as an integrated functional group, we established that AuGSHzwt could be conjugated with increasing numbers of Strep-tags by simple ligand exchange, which provides a generic approach for AuGSHzwt functionalization. It was found that the strep-tagged AuGSHzwt particles were highly resistant to nonspecific protein interactions and retained their targeting capability in biological fluid, displaying efficient binding to Streptactin receptors in nearly undiluted serum. However, AuGSHzwt functionalized with multiple Strep-tags displayed somewhat lower resistance to protein interactions and lower levels of binding to Streptactin than monofunctionalized AuGSHzwt under given conditions. These results underscore the need for optimizing ligand density onto the surface of ultrasmall AuNPs for improved performance. Collectively, our findings support ultrasmall AuGSHzwt as an attractive platform for engineering functional, protein-mimetic nanostructures capable of specific protein recognition within the complex biological milieu.

Activating a Silver Lipoate Nanocluster with a Penicillin Backbone Induces a Synergistic Effect against S. aureus Biofilm

Many antibiotic resistances to penicillin have been reported, making them obsolete against multiresistant bacteria. Because penicillins act by inhibiting cell wall production while silver particles disrupt the cell wall directly, a synergetic effect is anticipated when both modes of action are incorporated into a chimera cluster. To test this hypothesis, the lipoate ligands (LA) of a silver cluster (Ag29) of known composition (Ag29LA12)[3-] were covalently conjugated to 6-aminopenicillanic acid, a molecule with a β-lactam backbone. Indeed, the partially conjugated cluster inhibited an Staphylococcus aureus biofilm, in a dose-response manner, with a half-maximal inhibitory concentration IC50 of 2.3 μM, an improvement over 60 times relative to the unconjugated cluster (IC50 = 140 μM). An enhancement of several orders of magnitude over 6-APA alone (unconjugated) was calculated (IC50 = 10 000 μM). Cell wall damage is documented via scanning electron microscopy. A synergistic effect of the conjugate was calculated by the combination index method described by Chou-Talalay. This hybrid nanoantibiotic opens a new front against multidrug-resistant pathogens.