The Effects of Luminescent CdSe Quantum Dot-Functionalized Antimicrobial Peptides Nanoparticles on Antibacterial Activity and Molecular Mechanism

Antibacterial Photodynamic Therapy of the Metallosurfactant-Fluorescein Conjugate under Visible Light Illumination

Antibacterial photodynamic therapy (APDT) has received increased attention as a treatment for multidrug-resistant bacterial infections caused by antibiotic abuse. However, photosensitizers used in APDT have disadvantages such as water insolubility, self-aggregation, and photobleaching. To address these limitations, metal complexes have been explored. However, the use of such complexes tends to confine their antibacterial effectiveness specific bacterial strains. In this study, we report iron (Fe)- and copper (Cu)-based metallosurfactants as unique moieties for antibacterial photodynamic therapy (PDT) under the illumination of visible light. Briefly, our formulated Fe and Cu metallosurfactants, when combined with a fluorescein photosensitizer, exhibit nearly 100% antibacterial efficacy. This high efficiency is primarily attributed to the enhanced generation of singlet oxygen using FL in the presence of metallosurfactants when targeting bacteria such as Escherichia coli and Staphylococcus aureus under laser light. In vitro experiments further confirmed the superior antimicrobial activity of these metallosurfactants against a diverse range of microbial cultures, encompassing Gram-negative and Gram-positive bacteria as well as fungi. This performance outpaces conventional surfactants like cetyltrimethylammonium chloride and cetylpyridinium chloride. The compelling results from MTT assays and flow cytometry endorsed the substantial enhancement in antimicrobial properties achieved through Fe and Cu doping, all without the need for additional secondary agents. Notably, this synergistic antibacterial approach using metallosurfactants in PDT holds significant promise for the elimination of various bacteria in vivo, with the added advantage of mitigating the emergence of multidrug resistance.

Multi-step strategies for synergistic treatment of urinary tract infections based on D-xylose-decorated antimicrobial peptide carbon dots

Urinary tract infections (UTIs) caused by Uropathogenic Escherichia coli (UPEC), often reoccur due to the formation of intracellular bacterial colonies (IBCs) and antibiotic resistance. Given the significance of YadC for UPEC infection in our previous study, we developed D-xylose-decorated ɛ-poly-L-lysine (εPL)-based carbon dots (D-xyl@εPLCDs) that can be traced, and employed multi-step approaches to elucidate the functional roles of D-xyl@εPLCDs in UPEC infection. Compared to undecorated particles, D-xyl@εPLCDs demonstrate YadC-dependent bacterial targeting and exhibit enhanced bactericidal activities both intracellularly and extracellularly. Moreover, pre-treatment of D-xyl@εPLCDs before infection blocked the subsequent adhesion and invasion of UPEC to bladder epithelial cells 5637. Increase of ROS production and innate immune responses were observed in bladder epithelial cells 5637 treated with D-xyl@εPLCDs. In addition, treatment of D-xyl@εPLCDs post-infection facilitated clearance of UPEC in the bladders of the UTI mouse model, and reduced ultimate number of neutrophils, macrophages and inflammatory responses raised by invaded bacteria. Collectively, we presented a comprehensive evaluating system to show that D-xyl@εPLCDs exhibits superior bactericidal effects against UPEC, making them a promising candidate for drug development in clinical UTI therapeutics.

Study of Laser-Induced Multi-Exciton Generation and Dynamics by Multi-Photon Absorption in CdSe Quantum Dots

Multi-exciton generation by multi-photon absorption under low-energy photons can be thought a reasonable method to reduce the risk of optical damage, especially in photoelectric quantum dot (QD) devices. The lifetime of the multi-exciton state plays a key role in the utilization of photon-induced carriers, which depends on the dynamics of the exciton generation process in materials. In this paper, the exciton generation dynamics of the photon absorption under low-frequency light in CdSe QDs are successfully detected and studied by the temporal resolution transient absorption (TA) spectroscopy method. Since the cooling time of hot excitons extends while the rate of auger recombination is accelerated when incident energy is increased, the filling time of defect states is irregular, and exciton generation experiences a transition from single-photon absorption to multi-photon absorption. This result shows how to change the excitation. Optical parameters can prolong the lifetime of excitons, thus fully extracting excitons and improving the photoelectric conversion efficiency of QD optoelectronic devices, which provides theoretical and experimental support for the development of QD optoelectronic devices.

Improving the biocompatibility and antibacterial efficacy of silver nanoparticles functionalized with (LLRR)3 antimicrobial peptide

The selection of effective antibiotics is becoming increasingly limited due to the emergence of bacterial resistance. Designing and developing nanoscale antibacterials is a strategy for effectively addressing the antibiotic crisis. In this work, AgNPs@AMP nanoparticles were synthesized to take advantage of the synergistic antibacterial activity of the (LLRR)3 antimicrobial peptide (AMP) and silver nanoparticles (AgNPs). Based on morphological structure characterization and biocompatibility analysis, the inhibitory properties of AgNPs@AMP on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were evaluated. The results demonstrated that AMP and AgNPs were physically bound to form AgNPs@AMP nanoparticles, which had better solution stability, improved nanomaterial properties, and overcame the hemolytic activity of AMP and the cytotoxicity of AgNPs. The inhibitory activity of AgNPs@AMP against E. coli and S. aureus was significantly higher than that of AMP and AgNPs. It was capable of disrupting the morphology and internal structure of cells, damaging the cell membrane, and inhibiting the activity of enzymes related to the material-energy metabolism of the tricarboxylic acid cycle. Compared to AMP and AgNPs, AgNPs@AMP were found to effectively inhibit the infection of mouse wounds and promote their healing. Therefore, AMP-modified AgNPs can enhance their biocompatibility and antibacterial activity, and they can be further developed as a potential antimicrobial agent.

Silver Nanoparticles Modified with Polygonatum sibiricum Polysaccharide Improve Biocompatibility and Infected Wound Bacteriostasis

Silver nanoparticles (AgNPs) exhibit strong antibacterial activity and do not easily induce drug resistance; however, the poor stability and biocompatibility in solution limit their widespread application. In this study, AgNPs were modified with Polygonatum sibiricum Polysaccharide (PSP) to synthesize PSP@AgNPs with good stability, biocompatibility, and antibacterial activity. When PSP@AgNP synthesis was performed under a reaction time of 70 min, a reaction temperature of 35 °C, and an AgNO₃-to-PSP volume ratio of 1:1, the synthesized PSP@AgNPs were more regular and uniform than AgNPs, and their particle size was around 10 nm. PSP@AgNPs exhibited lower cytotoxicity and hemolysis, and stronger bacteriostatic activity. PSP@AgNPs damage the integrity and internal structure of cells, resulting in the leakage of intracellular nucleic acids and proteins. The rate of cell membrane damage in Escherichia coli and Staphylococcus aureus treated with PSP@AgNPs increased by 38.52% and 43.75%, respectively, compared with that of AgNPs. PSP@AgNPs inhibit the activities of key enzymes related to antioxidant, energy and substance metabolism in cells. The inhibitory effects on the activities of superoxide dismutase (SOD), catalase (CAT), adenosine triphosphate enzyme (ATPase), malate dehydrogenase (MDH), and succinate dehydrogenase (SDH) in E. coli and S. aureus cells were significantly higher than those of AgNPs. In addition, compared with AgNPs, PSP@AgNPs promote faster healing of infected wounds. Therefore, PSP@AgNPs represent potential antibacterial agents against wound infections.

Metal selenide nanomaterials for biomedical applications

Metal selenide nanomaterials have received enormous attention as they possess diverse compositions, microstructures, and properties. The combination of selenium with various metallic elements gives the metal selenide nanomaterials distinctive optoelectronic and magnetic properties, such as strong near-infrared absorption, excellent imaging properties, good stability, and long in vivo circulation. This makes metal selenide nanomaterials advantageous and promising for biomedical applications. This paper summarizes the research progress in the last five years in the controlled synthesis of metal selenide nanomaterials in different dimensions and with different compositions and structures. Then we discuss how surface modification and functionalization strategies are well-suited for biomedical fields, including tumor therapy, biosensing, and antibacterial biological applications. The future trends and issues of metal selenide nanomaterials in the biomedical field are also discussed.

Size- and surface functionalization-driven molecular interaction of CdSe quantum dots with jack bean urease: multispectroscopic, thermodynamic, and AFM approach

Quantum dots (QDs) with distinctive optical properties have been extensively researched and developed for usage in solar cells, imaging, drug delivery, cellular targeting, etc. But the inevitable production of QDs can lead to their unavoidable release and increased environmental concentration. Depending on morphological and surface properties, QDs at the nano-bio interface considerably impact the activity and structure of bio-molecules. The present study investigates the interaction of metalloenzyme jack bean urease (JBU) and bi-sized CdSe QDs (2.43 nm and 3.63 nm), surface-functionalized to mercaptopropionic acid (MPA) (-COOH), L-cysteine (CYS), L-glutathione (GSH), N-acetyl L-cysteine (NAC) (-COOH, -NH₂), and cysteamine hydrochloride (CYST) (-NH₂) to assess any alterations in JBU's binding, microenvironment, structure, exciton lifetime, and activity. JBU catalyzes the hydrolysis of urea to produce ammonia and carbon dioxide; any changes in its properties could threaten the survival of several microbes and plants. Spectroscopy techniques such as UV-Vis, fluorescence, circular dichroism, synchronous, time-resolved fluorescence, atomic force microscopy, and JBU activity assay were studied. Results suggested highly spontaneous and energy-favored interactions, which involved static quenching and hydrophobic forces of varied magnitude, dependent on QDs properties. The size, surface modifications, and dosage of QDs significantly impacted the secondary structure and activity of JBUs. Even though the larger sizes of the relevant modifications demonstrated stronger binding, the smaller sizes had the greatest impact on α-helicity and activity. CYST-capped QDs with an average number of the binding site (n) = 1, reduced α-helicity by 16% and activity by 22-30% at 7 nM concentration. In contrast, MPA-capped QDs with n < 1 had the least effect on α-helical structure and activity. The smaller GSH-capped QDs increased the activity by 9%, via partially restoring JBU's α-helical content. The study thus thoroughly analyzed the impact of varied-size and surface-functionalized QDs on the structure and function of JBU, which can be exploited further for several biomedical applications.

New Insights into the Cellular Toxicity of Carbon Quantum Dots to Escherichia coli

In this study, the cytotoxicity and toxic mechanism of carbon quantum dots (CQDs) to E. coli were evaluated in vitro. The synthetic CQDs were extremely small in size (~2.08 nm) and displayed strong fluorescence. The results demonstrated that CQDs showed good biocompatibility with E. coli within a short culture time. However, when the exposure time exceeded 24 h, the toxicity of CQDs became apparent, and the contents of reactive oxygen species, lactate dehydrogenase, and the crystal violet absorption rate increased significantly. To further explore the cytotoxic mechanism, approaches including confocal laser scanning microscopy, scanning electron microscopy, and biological transmission electron microscopy combined with zeta potential tests, osmotic pressure measurement, and comet assays were performed. On the one hand, the CQDs altered the surface charges of cells and induced lipid peroxidation by adhesion on the surface of E. coli, leading to an increase in the permeability of the cell wall. On the other hand, when the concentration of CQDs reached 200 µg/mL, the osmotic pressure of the extracellular environment was significantly reduced. These are the main factors that lead to cell edema and death. Finally, the comet assays confirmed that CQDs could induce DNA damage, which could inhibit the proliferation of E. coli.

Biofilm Microenvironment-Mediated MoS2 Nanoplatform with Its Photothermal/Photodynamic Synergistic Antibacterial Molecular Mechanism and Wound Healing Study

Drug-resistant bacterial infections pose a serious threat to human public health. Biofilm formation is one of the main factors contributing to the development of bacterial resistance, characterized by a hypoxic and microacidic microenvironment. Traditional antibiotic treatments have been ineffective against multidrug-resistant (MDR) bacteria. Novel monotherapies have had little success. On the basis of the photothermal effect, molybdenum disulfide (MoS₂) nanoparticles were used to link quaternized polyethylenimine (QPEI), dihydroporphyrin e6 (Ce6), and Panax notoginseng saponins (PNS) in a zeolitic imidazolate framework-8 (ZIF-8). A multifunctional nanoplatform (MQCP@ZIF-8) was constructed with dual response to pH and near-infrared light (NIR), which resulted in synergistic photothermal and photodynamic antibacterial effects. The nanoplatform exhibited a photothermal conversion efficiency of 56%. It inhibited MDR Escherichia coli (E. coli) and MDR Staphylococcus aureus (S. aureus) by more than 95% and effectively promoted wound healing in mice infected with MDR S. aureus. The nanoplatform induced the death of MDR bacteria by promoting biofilm ablation, disrupting bacterial cell membranes and intracellular DNA, and interfering with intracellular material and energy metabolism. In this study, a multifunctional nanoplatform with good antibacterial effect was developed. The molecular mechanisms of MDR bacteria were also elucidated for possible clinical application.

Combination Strategies of Different Antimicrobials: An Efficient and Alternative Tool for Pathogen Inactivation

Despite the discovery and development of an array of antimicrobial agents, multidrug resistance poses a major threat to public health and progressively increases mortality. Recently, several studies have focused on developing promising solutions to overcome these problems. This has led to the development of effective alternative methods of controlling antibiotic-resistant pathogens. The use of antimicrobial agents in combination can produce synergistic effects if each drug invades a different target or signaling pathway with a different mechanism of action. Therefore, drug combinations can achieve a higher probability and selectivity of therapeutic responses than single drugs. In this systematic review, we discuss the combined effects of different antimicrobial agents, such as plant extracts, essential oils, and nanomaterials. Furthermore, we review their synergistic interactions and antimicrobial activities with the mechanism of action, toxicity, and future directions of different antimicrobial agents in combination. Upon combination at an optimum synergistic ratio, two or more drugs can have a significantly enhanced therapeutic effect at lower concentrations. Hence, using drug combinations could be a new, simple, and effective alternative to solve the problem of antibiotic resistance and reduce susceptibility.

Synthesis of a Two-Dimensional Molybdenum Disulfide Nanosheet and Ultrasensitive Trapping of Staphylococcus Aureus for Enhanced Photothermal and Antibacterial Wound-Healing Therapy

Photothermal therapy has been widely used in the treatment of bacterial infections. However, the short photothermal effective radius of conventional nano-photothermal agents makes it difficult to achieve effective photothermal antibacterial activity. Therefore, improving composite targeting can significantly inhibit bacterial growth. We inhibited the growth of Staphylococcus aureus (S. aureus) by using an extremely low concentration of vancomycin (Van) and applied photothermal therapy with molybdenum disulfide (MoS₂). This simple method used chitosan (CS) to synthesize fluorescein 5(6)-isothiocyanate (FITC)-labeled and Van-loaded MoS₂-nanosheet hydrogels (MoS₂-Van-FITC@CS). After modifying the surface, an extremely low concentration of Van could inhibit bacterial growth by trapping bacteria synergistically with the photothermal effects of MoS₂, while FITC labeled bacteria and chitosan hydrogels promoted wound healing. The results showed that MoS₂-Van-FITC@CS nanosheets had a thickness of approximately 30 nm, indicating the successful synthesis of the nanosheets. The vitro antibacterial results showed that MoS₂-Van-FITC with near-infrared irradiation significantly inhibited S. aureus growth, reaching an inhibition rate of 94.5% at nanoparticle concentrations of up to 100 µg/mL. Furthermore, MoS₂-Van-FITC@CS could exert a healing effect on wounds in mice. Our results demonstrate that MoS₂-Van-FITC@CS is biocompatible and can be used as a wound-healing agent.

Industrial application of antimicrobial peptides based on their biological activity and structure-activity relationship

Last several years, a rapid increase in drug resistance to traditional antibiotics has driven the emergence and development of antimicrobial peptides (AMPs). AMPs have also gained considerable attention from scientists due to their high potency in combatting infectious pathogens. A subset of analogues and their derivatives with specific targets have been successfully designed based on natural peptide patterns. In this review, scientific knowledge on the mechanisms of action related to biological activity and structure-activity relationship (SAR) of AMPs are summarized, and the biological applications in several important fields are critically discussed. SAR shows that the positive charge, secondary structure, special amino acid residues, hydrophobicity, and helicity of AMPs are closely related to their biological activities. The combination of nanotechnology, bioinformatics, and genetic engineering can accelerate to achieve the application of AMPs as effective, safe, economical, and nonresistant antimicrobial agents in medicine, the food and feed industries, and agriculture in coming years. Given the intense interest in AMPs, further investigations are needed in the future to evaluate the specific structure and function that make their use favorable in several industries. This review may provide a comprehensive reference for future studies on chemical modifications, mechanistic exploration, and applications of AMPs.