Mercaptopyrimidine-templated gold nanoclusters for antithrombotic therapy

Here we report for the first time that mercaptopyrimidine-templated gold nanoclusters (DAMP-AuNCs) can be used as a novel anticoagulant candidate for the design of antithrombotic drugs. Anticoagulant mechanisms revealed that DAMP-AuNCs significantly inhibited thrombus formation by interacting with fibrinogen. Carrageenan-induced mice tail thrombosis model experiments showed that DAMP-AuNCs had antithrombotic efficacy comparable to heparin in vivo. More importantly, these ultrasmall AuNCs possess excellent blood compatibility and only induce negligible bleeding side effects. Our study is a successful attempt at developing novel antithrombotic agents with high biosafety.

Antibacterial Carbon Dots-Based Composites

The emergence and global spread of bacterial resistance to conventionally used antibiotics have highlighted the urgent need for new antimicrobial agents that might replace antibiotics. Currently, nanomaterials hold considerable promise as antimicrobial agents in anti-inflammatory therapy. Due to their distinctive functional physicochemical characteristics and exceptional biocompatibility, carbon dots (CDs)-based composites have attracted a lot of attention in the context of these antimicrobial nanomaterials. Here, a thorough assessment of current developments in the field of antimicrobial CDs-based composites is provided, starting with a brief explanation of the general synthesis procedures, categorization, and physicochemical characteristics of CDs-based composites. The many processes driving the antibacterial action of these composites are then thoroughly described, including physical destruction, oxidative stress, and the incorporation of antimicrobial agents. Finally, the obstacles that CDs-based composites now suffer in combating infectious diseases are outlined and investigated, along with the potential applications of antimicrobial CDs-based composites.

Progress on photocatalytic semiconductor hybrids for bacterial inactivation

Due to its use of green and renewable energy and negligible bacterial resistance, photocatalytic bacterial inactivation is to be considered a promising sterilization process. Herein, we explore the relevant mechanisms of the photoinduced process on the active sites of semiconductors with an emphasis on the active sites of semiconductors, the photoexcited electron transfer, ROS-induced toxicity and interactions between semiconductors and bacteria. Pristine semiconductors such as metal oxides (TiO₂ and ZnO) have been widely reported; however, they suffer some drawbacks such as narrow optical response and high photogenerated carrier recombination. Herein, some typical modification strategies will be discussed including noble metal doping, ion doping, hybrid heterojunctions and dye sensitization. Besides, the biosafety and biocompatibility issues of semiconductor materials are also considered for the evaluation of their potential for further biomedical applications. Furthermore, 2D materials have become promising candidates in recent years due to their wide optical response to NIR light, superior antibacterial activity and favorable biocompatibility. Besides, the current research limitations and challenges are illustrated to introduce the appealing directions and design considerations for the future development of photocatalytic semiconductors for antibacterial applications.

Photoluminescent Nanoparticles for Chemical and Biological Analysis and Imaging

Research related to the development and application of luminescent nanoparticles (LNPs) for chemical and biological analysis and imaging is flourishing. Novel materials and new applications continue to be reported after two decades of research. This review provides a comprehensive and heuristic overview of this field. It is targeted to both newcomers and experts who are interested in a critical assessment of LNP materials, their properties, strengths and weaknesses, and prospective applications. Numerous LNP materials are cataloged by fundamental descriptions of their chemical identities and physical morphology, quantitative photoluminescence (PL) properties, PL mechanisms, and surface chemistry. These materials include various semiconductor quantum dots, carbon nanotubes, graphene derivatives, carbon dots, nanodiamonds, luminescent metal nanoclusters, lanthanide-doped upconversion nanoparticles and downshifting nanoparticles, triplet-triplet annihilation nanoparticles, persistent-luminescence nanoparticles, conjugated polymer nanoparticles and semiconducting polymer dots, multi-nanoparticle assemblies, and doped and labeled nanoparticles, including but not limited to those based on polymers and silica. As an exercise in the critical assessment of LNP properties, these materials are ranked by several application-related functional criteria. Additional sections highlight recent examples of advances in chemical and biological analysis, point-of-care diagnostics, and cellular, tissue, and in vivo imaging and theranostics. These examples are drawn from the recent literature and organized by both LNP material and the particular properties that are leveraged to an advantage. Finally, a perspective on what comes next for the field is offered.

The synthesis of novel fluorescent bimetal nanoclusters for aqueous mercury detection based on aggregation-induced quenching

In this research, new bimetal nanoclusters (DAMP-AuAg BNCs) with 4,6-diamino-2-mercaptopyrimidine (DAMP) as a reducing agent and stabilizer ligand were exploited. The nanoclusters displayed excellent fluorescent properties, very small size, good stability, and water solubility. It was found that the as-prepared DAMP-AuAg BNCs exhibited strong fluorescent emission at 640 nm under an excitation wavelength of 473 nm with a large Stokes shift of 167 nm, and the red fluorescence could be readily quenched with aqueous Hg²⁺. The DAMP-AuAg BNCs showed good specificity and sensitivity toward Hg²⁺ in aqueous solution, and the fluorescence analysis of Hg²⁺ showed a wide linear range from 0.85 μM to 246 μM and a detection limit of 20 nM. It is demonstrated that strong Hg²⁺-Au⁺ interactions led to the aggregation of nanoclusters, which caused the quenching of the fluorescence, and the affinity of Hg²⁺ for nitrogen should also be considered. Due to the relevant good performance of DAMP-AuAg BNCs, they were applied to the fluorescence analysis of Hg²⁺ in real water samples and were found to be a potential fluorescent sensor for aqueous mercury ions.

Gold nanoclusters treat intracellular bacterial infections: Eliminating phagocytic pathogens and regulating cellular immune response

Intracellular bacterial infection is underlying many serious human disorders, leading to high morbidity and mortality. The development of safe and efficient therapeutic agents is the most effective solutions to combat intracellular bacterial infections. Recently, ultrasmall gold nanoclusters (AuNCs) have emerged as an innovative nanoantibiotics against multidrug-resistant bacterial infections due to their inherent antibacterial activity. However, the therapeutic effects of AuNCs on intracellular bacterial infections and their effects on host cells still remain unvisited. Here, we demonstrate the therapeutic potential of 4,6-diamino-2-mercaptopyrimidine-functionalized AuNCs (AuDAMP) for intracellular multidrug-resistant infections in a co-culture model of macrophages and methicillin-resistant Staphylococcus aureus (MRSA). The AuNCs were found to show a superior intracellular antibacterial capability, which can eliminate most of the MRSA phagocytosed by macrophages, and without exhibiting obvious cytotoxicity on host RAW 264.7 macrophages at tested concentrations. More importantly, treatment of AuDAMP exerts critical roles on enhancing the innate immune response to defend against pathogens invading inside the host cells and alleviating the bacterial infection-induced inflammatory response to avoid pyroptosis by up-regulating significantly xenophagy level in macrophages. Taken together, our results suggest that AuNCs hold great potential for the treatment of intracellular bacterial infections.

Cytidine-gold nanoclusters as peroxidase mimetic for colorimetric detection of glutathione (GSH), glutathione disulfide (GSSG) and glutathione reductase (GR)

Abnormal levels of glutathione (GSH) and glutathione oxidized (GSSG) usually relates to some diseases, thus quantifying the amount of GSH or GSSG is of great significance. A label-free sensing assay based on the enzyme-mimicking property of Cytidine-Au nanoclusters (Cy-AuNCs) was demonstrated for colorimetric detection of GSH, GSSG and glutathione reductase (GR). Firstly, obvious blue color accompanied with an absorption peak at 652 nm was observed due to the high peroxidase-like activity of Cy-AuNCs toward 3,3',5,5'-tetramethylbenzidine (TMB). Then, in the presence of target, the mimetic activity of Cy-AuNCs could be strongly inhibited and used to achieve the visualization detection. The inhibition effect arose from the surface interaction between GSH and Cy-AuNCs. Linear relationships between absorbance response and concentration were obtained between 0 and 0.4 mM for GSH, 0-2.5 mM for GSSG and 0-0.2 U/mL for GR. The limit of detection (LOD) was calculated as low as 0.01 mM, 0.03 mM and 0.003 U/mL for GSH, GSSG and GR, respectively. Furthermore, the proposed method displayed rapid response, easy procedure and high selectivity.

Ultrasmall Au nanoclusters for bioanalytical and biomedical applications: the undisclosed and neglected roles of ligands in determining the nanoclusters' catalytic activities

Significantly different from conventional Au nanoparticles, ultrasmall Au nanoclusters (NCs) consisting of several to about a hundred Au atoms with a size below 2 nm exhibit a strong quantum confinement effect, and possess an intriguing molecular-like highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) transition, quantized charging, intrinsic chirality, and special fluorescence properties, as well as high catalytic activities. In virtue of their unique molecular-like electronic structure, remarkable physicochemical properties, mild preparation conditions and good biocompatibility, Au NCs have been having a profound impact on bioanalytical and biomedical applications, such as biosensing, biological imaging, cell markers, drug delivery, photodynamic/photothermal therapy, and biomedical toxicology. As an indispensable part of Au NCs, shell ligands not only stabilize and protect the structure of Au NCs, but also have an important influence on the structure and biocatalytic activities of Au NCs. Nevertheless, the effect of shell ligands on the biocatalytic activities of Au NCs has not been paid much attention or even ignored. In this Focus article, thus, the structure and biocatalytic activities of Au NCs are discussed from the perspective of the shell ligands. Particular emphasis is directed to the discussion and exploration of the undisclosed and neglected roles of shell ligands in the biocatalytic activities of Au NCs, which are of fundamental importance to the unraveling of charge transfer behaviors and biocatalytic processes of Au NCs. In addition, the future directions to explore the mechanism of shell ligands affecting the biocatalytic activities of Au NCs, such as surface ligand engineering of Au NCs, advanced surface/interface in situ characterization techniques, theoretical analysis, and the nanobiology of Au NCs, are also put forward.

Zinc-Ion-Induced Aggregation of Gold Clusters for Visible-Light-Excitation-Based Fluorimetric Discrimination of Geometrical Isomers

Herein, we report discrimination of dicarboxylic acids - fumaric acid (FA) and maleic acid (MA) - exhibiting geometrical isomerism, using nanoclusters based luminescent probe having excitation under broad day light. The luminescent probe was designed via complexation reaction between zinc ions and ligands (mercaptopropioinc acid; MPA) stabilizing the gold nanoclusters. This resulted in formation of nanoaggregates exhibiting bright green luminescence upon excitation at 450 nm capable of discriminating between FA and MA upto nanomolar level. The basis of discrimination has been attributed to deprotonation of FA and MA following interaction with MPA moieties present on the surface of the nanoaggregates and being governed by the stability of the respective conjugate base of the geometrical isomers of the dicarboxylic acids. As a consequence of different extent of deprotonation of FA and MA upon interaction with the cluster aggregates, different effect on the luminescence of the aggregates was observed, thus enabling discernible fluorimetric discrimination between FA and MA under visible light excitation.

Gold Nanoclusters for Bacterial Detection and Infection Therapy

Infections caused by antibiotic-resistant bacteria have become one of the most serious global public health crises. Early detection and effective treatment can effectively prevent deterioration and further spreading of the bacterial infections. Therefore, there is an urgent need for time-saving diagnosis as well as therapeutically potent therapy approaches. Development of nanomedicine has provided more choices for detection and therapy of bacterial infections. Ultrasmall gold nanoclusters (Au NCs) are emerging as potential antibacterial agents and have drawn intense attention in the biomedical fields owing to their excellent biocompatibility and unusual physicochemical properties. Recent significant efforts have shown that these versatile Au NCs also have great application potential in the selective detection of bacteria and infection treatment. In this review, we will provide an overview of research progress on the development of versatile Au NCs for bacterial detection and infection treatment, and the mechanisms of action of designed diagnostic and therapeutic agents will be highlighted. Based on these cases, we have briefly discussed the current issues and perspective of Au NCs for bacterial detection and infection treatment applications.

A novel near-infrared fluorescent probe for the dynamic monitoring of the concentration of glutathione in living cells

In this study, a water-soluble, near-infrared fluorescent probe (EQR-S) was designed for the measurement of the glutathione (GSH) concentration. Responses of different interfering substances to the developed probe were investigated, and the luminescence mechanism was examined by theoretical calculations. Results revealed that EQR-S can be applied for the rapid, sensitive determination of the GSH concentration with a detection limit of 69 nM. Based on the above advantages, EQR-S was successfully applied to investigate the fluctuation in the GSH concentration of living cells under high-temperature stress.

Gold Nanoparticles Cure Bacterial Infection with Benefit to Intestinal Microflora

Antibiotics that are most used to cure bacterial infections in the clinic result in the imbalance of intestinal microflora, destroy the intestinal barrier, and induce bacterial resistance. There is an urgent need for antibacterial agent therapy for bacterial infections that does not destroy intestinal microflora. Herein, we applied 4,6-diamino-2-pyrimidinethiol (DAPT)-coated Au nanoparticles (D-Au NPs) for therapy of bacterial infection induced by Escherichia coli ( E. coli) in the gut. We cultured D-Au NPs and E. coli in an anaerobic atmosphere to evaluate their bactericidal effect. We studied the microflora, distribution of Au, and biomarkers in mice after a 28-day oral administration to analyze the effect of Au NPs on mice. D-Au NPs cured bacterial infections more effectively than levofloxacin without harming intestinal microflora. D-Au NPs showed great potential as alternatives to oral antibiotics.

Poly(β-cyclodextrin) enhanced fluorescence coupled with specific reaction for amplified detection of GSH and trypsin activity

Schematic illustration of the construction process of a specific-reaction assay coupled with βCDP-induced signal amplification platform.