Development of coinage metal nanoclusters as antimicrobials to combat bacterial infections

Infection microenvironment-triggered nanoparticles eradicate MRSA by thermally amplified chemodynamic therapy and M1 macrophage

It is of great significance to develop a novel approach to treat bacterial infections, as the frequent misuse of antibiotics leads to the serious problem of bacterial resistance. This study proposed antibiotic-free antibacterial nanoparticles for eliminating methicillin-resistant Staphylococcus aureus (MRSA) based on a multi-model synergistic antibacterial ability of chemodynamic therapy (CDT), photothermal effect, and innate immunomodulation. Specifically, a polydopamine (PDA) layer coated and Ag nanoparticles loaded core-shell structure Fe3O4 nanoparticles (Fe3O4@PDA-Ag) is prepared. The Fe3O4 catalyzes H2O2 present in acidic microenvironment of bacterial infection into more toxic reactive oxygen species (ROS) and synergizes with the released Ag ions to exert a stronger bactericidal capacity, which can be augmented by photothermal action of PDA triggered by near-infrared light and loosen the biofilm by photothermal action to promote the penetration of ROS and Ag ion into the biofilm, result in disrupting biofilm structure along with killing encapsulated bacteria. Furthermore, Fe3O4@PDA-Ag exerts indirect antibacterial effects by promoting M1 macrophage polarizing. Animal models demonstrated that Fe3O4@PDA-Ag effectively controlled MRSA-induced infections through photothermal enhanced CDT, Ag+ releasing, and macrophage-mediated bactericidal properties. The acid-triggered antibacterial nanoparticles are expected to combat drug-resistant bacteria infection.

Antibiotic Alternatives: Multifunctional Ultra-Small Metal Nanoclusters for Bacterial Infectious Therapy Application

The prevalence of major bacterial infections has emerged as a significant menace to human health and life. Conventional treatment methods primarily rely on antibiotic therapy, but the overuse of these drugs has led to a decline in their efficacy. Moreover, bacteria have developed resistance towards antibiotics, giving rise to the emergence of superbugs. Consequently, there is an urgent need for novel antibacterial agents or alternative strategies to combat bacterial infections. Nanoantibiotics encompass a class of nano-antibacterial materials that possess inherent antimicrobial activity or can serve as carriers to enhance drug delivery efficiency and safety. In recent years, metal nanoclusters (M NCs) have gained prominence in the field of nanoantibiotics due to their ultra-small size (less than 3 nm) and distinctive electronic and optical properties, as well as their biosafety features. In this review, we discuss the recent progress of M NCs as a new generation of antibacterial agents. First, the main synthesis methods and characteristics of M NCs are presented. Then, we focus on reviewing various strategies for detecting and treating pathogenic bacterial infections using M NCs, summarizing the antibacterial effects of these nanoantibiotics on wound infections, biofilms, and oral infections. Finally, we propose a perspective on the remaining challenges and future developments of M NCs for bacterial infectious therapy.

Chemically Tailored Single Atoms for Targeted and Light-Controlled Bactericidal Activity

Single-atom (SA) nanoparticles exhibit considerable potential in terms of photothermal properties for bactericidal applications. Nevertheless, the restricted efficacy of their targeted and controlled antibacterial activity has hindered their practical implementation. This study aims to overcome this obstacle by employing chemical modifications to tailor SAs, thereby achieving targeted and light-controlled antimicrobial effects. By conducting atomic-level modifications on palladium SAs using glutathione (GSH) and mercaptophenylboronic acid (MBA), their superior targeted binding capabilities toward Escherichia coli cells are demonstrated, surpassing those of SAs modified with cysteine (Cys). Moreover, these modified SAs effectively inhibit wound bacteria proliferation and promote wound healing in rats, without inducing noticeable toxicity to major organs under 808 nm laser irradiation. This study highlights the significance of chemical engineering in tailoring the antibacterial properties of SA nanoparticles, opening avenues for combating bacterial infections and advancing nanoparticle-based therapies.

An ultra-small fluorescence zero-valent iron nanoclusters selectively kill gram-positive bacteria by promoting reactive oxygen species generation

A list of the most dangerous bacteria that are multiple-drug resistance has been published by WHO, among which are various Gram-positive bacteria related with serious healthcare and community-associated infection. An effort is called for developing new strategies to combat the resistance, and nanomaterial-based approaches provide an ideal potential to mitigate the antimicrobial resistance as an alternative to antibiotics. Nanoscale zero-valent iron particles exhibited a good antimicrobial activity by triggering Fenton reaction, however, no zero-valent iron nanoclusters are developed as antimicrobial medical materials. In this work, a novel ultra-small zero-valent iron nanoclusters (usZVIN) was synthesized by one-step reduction in aqueous solutions, which exhibited bright red fluorescence at 616 nm. Interestingly, the usZVIN displayed an excellent selectively antibacterial activity against Gram-positive bacteria, and little effects on Gram-negative bacteria. The killing efficiency of usZVIN against S. aureus can reach 100 % with a concentration of 40 μg mL^-1 after 1 h incubation, whereas there is no killing effect of usZVIN against E.coli even with a concentration of 900 μg mL^-1 for 4 h. The antimicrobial mechanism of usZVIN was demonstrated to be the intracellular reactive oxygen species (ROS) production triggered by usZVIN due to its excellent peroxidase-like activity. Collectively, our findings suggested that usZVIN is a good medical-material candidate for fighting against Gram-positive bacterial infections, especially when we need leave beneficial Gram-negative bacteria intact.

Emerging Strategies in Enhancing Singlet Oxygen Generation of Nano-Photosensitizers Toward Advanced Phototherapy

The great promise of photodynamic therapy (PDT) has thrusted the rapid progress of developing highly effective photosensitizers (PS) in killing cancerous cells and bacteria. To mitigate the intrinsic limitations of the classical molecular photosensitizers, researchers have been looking into designing new generation of nanomaterial-based photosensitizers (nano-photosensitizers) with better photostability and higher singlet oxygen generation (SOG) efficiency, and ways of enhancing the performance of existing photosensitizers. In this paper, we review the recent development of nano-photosensitizers and nanoplasmonic strategies to enhance the SOG efficiency for better PDT performance. Firstly, we explain the mechanism of reactive oxygen species generation by classical photosensitizers, followed by a brief discussion on the commercially available photosensitizers and their limitations in PDT. We then introduce three types of new generation nano-photosensitizers that can effectively produce singlet oxygen molecules under visible light illumination, i.e., aggregation-induced emission nanodots, metal nanoclusters (< 2 nm), and carbon dots. Different design approaches to synthesize these nano-photosensitizers were also discussed. To further enhance the SOG rate of nano-photosensitizers, plasmonic strategies on using different types of metal nanoparticles in both colloidal and planar metal-PS systems are reviewed. The key parameters that determine the metal-enhanced SOG (ME-SOG) efficiency and their underlined enhancement mechanism are discussed. Lastly, we highlight the future prospects of these nanoengineering strategies, and discuss how the future development in nanobiotechnology and theoretical simulation could accelerate the design of new photosensitizers and ME-SOG systems for highly effective image-guided photodynamic therapy.

Cytokine Regulation and Fast Inflammation Resolution in Early Rheumatoid Arthritis by Cerium-Modified Gold Nanoclusters

Rheumatoid arthritis (RA) is an incurable chronic disorder that may induce autoinflammation and serious pain in the joints. Early diagnosis and treatment are important for RA prognosis. However, there is a lack of effective and objective diagnostic approaches. Levels of several immunity cytokines were found to change for patients with early RA, including IL-6, TNF-α, and IL-17 in serum. We assumed a combined change of these cytokines could predict early RA, and a total of 37 outpatients were found. After these patients with early symptoms had been followed for more than one year, 32 clinical cases of RA were diagnosed. The accuracy rate of the current method is >86%. We assumed the symptom relief could be achieved by regulating these cytokines and serum lipid-associated indicators. Thereafter, (R)-dihydrolipoic acid (R-DHLA)-stabilized gold nanoclusters (AuNCs) without (R-DHLA-AuNCs) and with cerium modification (R-DHLA-AuNCs-Ce) were employed for treatment of the RA rat model in vitro and in vivo. R-DHLA-AuNCs-Ce exhibited extraordinary reactive oxygen species-scavenging and anti-inflammation effects by regulating macrophage polarization, which was found to be more effective than methotrexate. The inflammation response of the joint microenvironment was also reduced with an exciting efficiency. By complex analysis of the pro-inflammatory cytokines and activity period indicators in vivo and in vitro, we concluded that macrophage-mediated inflammation exacerbated autoimmunity, which fully relieved the symptoms after administration of R-DHLA-AuNCs-Ce to RA rats.

The effect of different energy portions on the 2D/3D stability swapping for 13-atom metal clusters

The complexity of Cu₁₃, Ag₁₃, and Au₁₃ coinage-metal clusters was investigated through their energy contributions via a density functional theory study, considering improvements in the PBE functional, such as van der Waals (vdW) corrections, spin-orbit coupling (SOC), Hubbard term (+U), and their combinations. Investigating two-dimensional (planar 2D) and three-dimensional (distorted 3D, CUB - cuboctahedral, and ICO - icosahedral) configurations, we found that vdW corrections are dominant in modulating the stability swapping between 2D and ICO (3D) for Ag₁₃ (Au₁₃), whereas for Cu₁₃ its role is increasing the relative stability between 2D (least stable) and 3D (most stable), setting ICO as the reference. Among the energy portions that constitute the relative total energy, the dimensionality difference correlates with the magnitude of the relative dispersion energy (large for 2D/ICO and small for 3D/ICO) as the causal factor responsible for an eventual stability swapping. For instance, empirical vdW corrections may favor Ag₁₃ as ICO, while semi empirical ones tend to swap the stability by favoring 2D. The same tendency is observed for Au₁₃, except when SOC is included, which enlarges the stability of 3D over 2D. Energy decomposition analysis combined with the natural orbitals for the chemical valence approach confirmed the correlations between the dimensionality difference and the magnitude of the relative dispersion energies. Our structural analysis protocol was able to capture the local distortion effects (or even their absence) through the quantification of the Hausdorff chirality measure. Here, ICO, CUB, and 2D are achiral configurations for all coinage-metal clusters, whereas Cu₁₃ as 3D presents a slight chirality when vdW correction based on many body dispersion is used, at the same time Ag₁₃ as 3D turned out to be chiral for all calculation protocols as evidence of the role of the chemical composition.

Designing Coordination Polymers as Multi-drug-self-delivery System for Tuberculosis and Cancer Therapy: in vitro Viability and in vivo Toxicity Assessment

A proof of the concept for designing multi-drug-delivery system suitable for self-drug-delivery is disclosed. Simple coordination chemistry was employed to anchor two kinds of drugs namely isoniazid (IZ – anti-tuberculosis),...

Assessment of the van der Waals, Hubbard U parameter and spin-orbit coupling corrections on the 2D/3D structures from metal gold congeners clusters

The coinage-metal clusters possess a natural complexity in their theoretical treatment that may be accompanied by inherent shortcomings in the methodological approach. Herein, we performed a scalar-relativistic density functional theory study, considering Perdew, Burke, and Ernzerhof (PBE) with (empirical and semi empirical) van der Waals (vdW), spin-orbit coupling (SOC), +U (Hubbard term), and their combinations, to treat the Cu 13 , Ag 13 , and Au 13 clusters in different structural motifs. The energetic scenario is given by the confirmation of the 3D lowest energy configurations for Cu 13 and Ag 13 within all approaches, while for Au 13 there is a 2D/3D competition, depending on the applied correction. The 2D geometry is 0.43 eV more stable with plain PBE than the 3D one, the SOC, +U, and/or vdW inclusion decreases the overestimated stability of the planar configurations, where the most surprising result is found by the D3 and D3BJ vdW corrections, for which the 3D configuration is 0.29 and 0.11 eV, respectively, more stable than the 2D geometry (with even higher values when SOC and/or +U are added). The D3 dispersion correction represents 7.9% (4.4%) of the total binding energy for the 3D (2D) configuration, (not) being enough to change the sd hybridization and the position of the occupied d -states. Our predictions are in agreement with experimental results and in line with the best results obtained for bulk systems, as well as with hybrid functionals within D3 corrections. The properties description undergoes small corrections with the different approaches, where general trends are maintained, that is, the average bond length is smaller (larger) for lower (higher)-coordinated structures, since a same number of electrons are shared by a smaller (larger) number of bonds, consequently, the bonds are stronger (weaker) and shorter (longer) and the sd hybridization index is larger (smaller). Thus, Au has a distinct behavior in relation to its lighter congeners, with a complex potential energy surface, where in addition to the relevant relativistic effects, correlation and dispersion effects must also be considered.

Assembly of Carbon Dots into Frameworks with Enhanced Stability and Antibacterial Activity

Carbon dots (CDs) have been widely used as antimicrobials due to their active surface, but some CDs suffer instability. Therefore, the relative applications such as the antibacterial activity may not be reliable for long-term use. Herein, we synthesize CDs with blue fluorescence by a hydrothermal process. Thereafter, polyethylenimine was applied for the assembly of CDs into CDs-based frameworks (CDFs). The CDFs exhibited quenched fluorescence but showed more stable properties based on the scanning electron microscope and zeta potential investigations. Both CDs and CDFs show antibacterial activity toward Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus), but CDFs exhibited better antibacterial performance, and S. aureus could be completely inhibited with the minimum inhibitory concentration of 30 μg/mL. This reveals CDFs magnify both the stability and antibacterial activity, which would be more promising for practical applications.

Transition metal oxide and chalcogenide-based nanomaterials for antibacterial activities: an overview

A new battle line is drawn where antibiotic misuse and mismanagement have made treatment of bacterial infection a thorny issue. It is highly desirable to develop active antibacterial materials for bacterial control and destruction without drug resistance. A large amount of effort has been devoted to transition metal oxide and chalcogenide (TMO&C) nanomaterials as possible candidates owing to their unconventional physiochemical, electronic and optical properties and feasibility of functional architecture assembly. This review expounds multiple TMO&C-based strategies to combat pathogens, opening up new possibilities for the design of simple, yet highly effective systems that are crucial for antimicrobial treatment. A special emphasis is placed on the multiple mechanisms of these nanoagents, including mechanical rupture, photocatalytic/photothermal activity, Fenton-type reaction, nanozyme-assisted effect, released metal ions and the synergistic action of TMO&C in combination with other antibacterial agents. The applications of TMO&C nanomaterials mostly in air/water purification and wound healing along with their bactericidal activities and mechanisms are also described. Finally, the contemporary challenges and trends in the development of TMO&C-based antibacterial strategies are proposed.