Biofilm-Sensitive Photodynamic Nanoparticles for Enhanced Penetration and Antibacterial Efficiency

Efficient antimicrobials are urgently needed for the treatment of bacterial biofilms due to their resistance to traditional drugs. Photodynamic therapy (PDT) is a new strategy that has been used to combat bacteria and biofilms. Cationic photosensitizers, particularly cationic photodynamic nanoagents, are usually chosen to enhance photodynamic antimicrobial activity. However, positively charged nanoparticles (NPs) are beneficial to cellular internalization, which causes increased cell cytotoxicity. Herein, a pH-sensitive photodynamic nanosystem is designed. Rose Bengal (RB) polydopamine (PDA) NPs are decorated in a layer-by-layer fashion with polymyxin B (PMB) and gluconic acid (GA) to generate functionally adaptive NPs (RB@PMB@GA NPs). RB@PMB@GA NPs remain negative at physiological pH and exhibit good biocompatibility. When RB@PMB@GA NPs are exposed to an acidic infectious environment, the surface charge of the NPs is, in turn, positively charged as a result of pH-sensitive electrostatic interactions. This surface charge conversion allows the RB@PMB@GA to effectively bind to the surfaces of bacteria and enhance photoinactivation efficiency against gram-negative bacteria. Most importantly, RB@PMB@GA NPs exhibit good biofilm penetration and eradication under acidic conditions. Furthermore, RB@PMB@GA NPs efficiently eliminate biofilm infections in vivo. This study provides a promising strategy for safely treating biofilm-associated infections in vivo.     

Enhanced Antibacterial Activity of Nanocrystalline ZnO Due to Increased ROS‐Mediated Cell Injury

An innovative study aimed at understanding the influence of the particle size of ZnO (from the microscale down to the nanoscale) on its antibacterial effect is reported herein. The antibacterial activity of ZnO has been found to be due to a reaction of the ZnO surface with water. Electron‐spin resonance measurements reveal that aqueous suspensions of small nanoparticles of ZnO produce increased levels of reactive oxygen species, namely hydroxyl radicals. Interestingly, a remarkable enhancement of the oxidative stress, beyond the level yielded by the ZnO itself, is detected following the antibacterial treatment. Likewise, an exposure of bacteria to the small ZnO nanoparticles results in an increased cellular internalization of the nanoparticles and bacterial cell damage. An examination of the antibacterial effect is performed on two bacterial species: Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive). The nanocrystalline particles of ZnO are synthesized using ultrasonic irradiation, and the particle sizes are controlled using different solvents during the sonication process. Taken as a whole, it is apparent that the unique properties (i.e., small size and corresponding large specific surface area) of small nanometer‐scale ZnO particles impose several effects that govern its antibacterial action. These effects are size dependent and do not exist in the range of microscale particles.     

Sunlight-Sensitive Plasmonic Nanostructured Composites as Photocatalytic Coating with Antibacterial Properties

Infections caused by microorganisms are a global public health problem that continually demands new antimicrobial strategies. The generation of reactive oxygen species (ROS) by photocatalytic materials is an attractive approach to combat microbes. Along these lines, titanium dioxide (TiO₂) constitutes an outstanding light-driven ROS generator. However, the wide bandgap of this semiconductor limits its use to the ultraviolet range of the spectral region. Herein, nanostructured materials composed of TiO₂ nanoparticles and plasmonic gold nanorods (AuNRs) are presented for the photoinactivation of bacteria by means of sunlight irradiation, aiming to extend the photocatalytic action of the nanocomposite to the visible and near-infrared ranges. It is shown that, upon simulated sunlight irradiation, the different composites as coating films show photodegradation of rhodamine B, ROS production, photocatalytic inactivation of protein function in bacterial biofilms, and strong antimicrobial activity. This approach involving AuNRs/TiO₂ photocatalytic composites may pave the way for the fabrication of visible light-responsive surfaces with antimicrobial activity.     

非水溶胶-凝胶法制备纳米二氧化钛及其抑菌性能研究

以四氯化钛为钛源,叔丁醇为溶剂,采用非水溶胶-凝胶法制备了TiO2纳米颗粒,利用红外光谱(FT-IR)、X-射线衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)等技术手段对其进行了结构表征.基于定量菌落计数法考查了TiO2纳米颗粒对大肠杆菌和枯草杆菌的抑菌特性.结果表明,通过该方法合成的TiO2纳米颗粒粒径小,对这两种细菌的抑菌率都在93％以上,具有良好的抑菌效果.同时,简要分析了纳米TiO2抑菌机理,并对TiO2光催化材料的未来发展趋势进行了展望.     

Assembly of Au Plasmonic Photothermal Agent and Iron Oxide Nanoparticles on Ultrathin Black Phosphorus for Targeted Photothermal and Photodynamic Cancer Therapy

Photodynamic therapy (PDT), as a minimally invasive and high‐efficiency anticancer approach, has received extensive research attention recently. Despite plenty of effort devoted to exploring various types of photodynamic agents with strong near‐infrared (NIR) absorbance for PDT and many encouraging progresses achieved in the area, effective and safe photodynamic photosensitizers with good biodegradability and biocompatibility are still highly expected. In this work, a novel nanocomposite has been developed by assembly of iron oxide (Fe₃O₄) nanoparticles (NPs) and Au nanoparticles on black phosphorus sheets (BPs@Au@Fe₃O₄), which shows a broad light absorption band and a photodegradable character. In vitro and in vivo assay indicates that BPs@Au@Fe₃O₄ nanoparticles are highly biocompatible and exhibit excellent tumor inhibition efficacy owing to a synergistic photothermal and photodynamic therapy mediated by a low‐power NIR laser. Importantly, BPs@Au@Fe₃O₄ can anticipatorily suppress tumor growth by visualized synergistic therapy with the help of magnetic resonance imaging (MRI). This work presents the first combination application of the photodynamic and photothermal effect deriving from black phosphorus nanosheets and plasmonic photothermal effect from Au nanoparticles together with MRI from Fe₃O₄ NPs, which may open the new utilization of black phosphorus nanosheets in biomedicine, optoelectronic devices, and photocatalysis.     

光动力抗菌纳米制剂研究进展

新兴的光动力抗菌疗法是一种无创激发式治疗手段,主要利用近红外光作为光源,激活富集在病灶部位的光敏剂并产生活性氧自由基,最终实现对目标病菌的杀伤。近年来,随着生物材料与纳米医学技术的发展,小分子光敏剂纳米功能化后其生物兼容性和生物安全性得到优化,量子产率和病灶部位富集率显著提升,在抗菌治疗方面有很大的临床应用前景。本文结合小分子光敏剂纳米化策略方法实例,综述了纳米技术在光动力抗菌疗法的应用和发展。     

Photothermal Modulation of Depression-Related Ion Channel Function through Conjugated Polymer Nanoparticles

Considering recent breakthroughs in the field of optogenetics, a powerful tool is established in the present study to modulate the activities of target neurons through the application of light-based methods. Near-infrared (NIR) light enables the penetration of deep-tissue. As a result, it can be used to modulate the functions of proteins/cells. Herein, it is aimed to develop a NIR light-sensitive drug delivery system to spatially and temporally control the activation of the loaded drug at the stimulation sites through its release from a nanoparticle sensitive to NIR. Owing to their excellent photothermal effect under NIR irradiation, the nanoparticles are found to penetrate the blood-brain barrier effectively, ultimately reaching neurons. Furthermore, by loading fasudil, a selective activator of the Kv7.4 potassium channel, into the precisely designed and synthesized NIR light-sensitive nanoparticles, the firing frequency of dopaminergic neurons in the ventral tegmental area is found to be remarkably reduced upon NIR light irradiation. Such findings shed light on a new concept that can be used for developing more selective drug therapies for the treatment of diseases, such as major depression.     

Significant Enhancement of Photothermal and Photoacoustic Efficiencies for Semiconducting Polymer Nanoparticles through Simply Molecular Engineering

Semiconducting polymer nanoparticles (SP NPs) are employed as efficient nanoagents for “all‐in‐one” theranostic nanoplatforms with dual photoacoustic imaging (PAI) and photothermal therapy (PTT) functions based on their photothermal conversion effect. However, the mechanisms of tuning the PTT efficiency are still elusive, though several SP NPs with high photothermal efficiency are reported. Herein, two donor–acceptor (D–A) SP NPs PTIGSVS and PIIGSVS with the same donor unit but different acceptor units are designed and synthesized. Through tuning the acceptor unit, PTIGSVS shows more planar backbone structure, stronger D–A strength, redshifted absorption, enhanced extinction efficient, weakened emission properties, and more efficient nonradiative decay in comparison to the polymeric analogue PIIGSVS . Thus, PTIGSVS NPs present much higher photothermal conversion efficiencies (74%) than PIIGSVS NPs (11%), resulting in significantly enhanced in vitro and in vivo PAI and PTT performance. This contribution demonstrates that PTIGSVS NPs are superior PA/PTT agents for effective cancer theranostic and shed light on understanding the relationship between molecular structures and photothermal effect of CPs.     

A Zn‐Doped CuO Nanocomposite Shows Enhanced Antibiofilm and Antibacterial Activities Against Streptococcus Mutans Compared to Nanosized CuO

Zinc‐doped copper oxide and copper oxide nanoparticles (NPs) are synthesized and deposited on artificial teeth by sonic irradiation, and the ability of these coatings to restrict biofilm formation by Streptococcus mutans is examined. The CuO and Zn:CuO NP‐coated teeth show significant reductions in biofilm formation of 70% and 88%, respectively, compared to uncoated teeth. The mechanism of the Zn:CuO nanoparticles is investigated, revealing that the nanoparticles attach to and penetrate the bacteria and generate intracellular reactive oxygen species (ROS) that enhance lipid peroxidation and cause cell death. Conversely, the CuO or ZnO NPs do not show this behavior and could not generate intracellular ROS. These results highlight the superior efficacy of Zn:CuO nanocomposites over CuO and ZnO NPs and the role of ROS in their antimicrobial effect.     

Copper Clusters: An Effective Antibacterial for Eradicating Multidrug-Resistant Bacterial Infection In Vitro and In Vivo

Infections caused by multidrug-resistant (MDR) bacteria pose a threat to human health worldwide, making new effective antibacterial agents urgently desired. To date, it is still a great challenge to develop new antibiotics for MDR bacteria with clear antibacterial mechanisms. Herein, a novel alternative antibacterial copper clusters (CuCs) molecule is precisely synthesized utilizing an artificially designed theanine peptide. The prepared CuCs exhibit excellent broad-spectrum antibacterial activity in vitro, including gram-positive bacteria (methicillin-resistant Staphylococcus aureus [MRSA], Staphylococcus aureus, and Staphylococcus epidermidis) and gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa). The robust antibacterial effect is due to its ability to not only destroy the bacterial wall structure, but also regulate the ratio of GSH/GSSG by inhibiting the activity of glutathione reductase, thus causing the outbreak of reactive oxygen species and ultimately leading to bacterial death. In addition, in vivo studies demonstrate that CuCs can significantly rescue skin wound infections and sepsis in mice caused by MRSA, and has the same therapeutic efficacy as mupirocin ointment and first-line clinically anchored anti-MRSA drug vancomycin. Moreover, CuCs exhibit extremely low cytotoxicity to normal mammalian cells compared to silver and platinum clusters. With further development and optimization, CuCs has great potential as a new class of antibacterial agents to fight antibiotic-resistant pathogens.     

High-Efficiency Reactive Oxygen Species Generation by Multiphase and TiO6 Distortion-Mediated Superior Piezocatalysis in Perovskite Ferroelectrics

Piezocatalysis, governed by piezo-potential within piezoelectrics, has gained prominence for reactive oxygen species (ROS) generation, which is significant to environmental and biological applications. However, designing piezocatalysts with excellent piezocatalytic performance in a wide temperature and efficient charge carrier separation ability is still challenging. Herein, eco-friendly BaTiO₃ (BT)-based perovskite ferroelectrics with tailored multiphase coexistence in a wide temperature range are constructed to boost higher piezoelectricity and large piezo-potential, which is attributed to decreased polarization anisotropy by flat Gibbs energy profile. Elevated piezo-potential in designed BT-based piezocatalyst guarantees high-efficient generation rate of •OH (200 µmol g⁻¹ h⁻¹) and •O₂⁻ (40 µmol g⁻¹ h⁻¹) by ultrasound stimulation, which is 3.5 times more than that of pure BT. Besides, piezocatalytic capacity to degrade dye wastewater shows a rate constant of 0.0182 min⁻¹ and gives an antibacterial rate of 95% within 30 min for eliminating E. coli. Theoretical simulations validate that the local distortion of TiO₆ octahedra also contributes to piezocatalytic performance by inducing electron–hole pairs separation in real space, and better response to slight structural deformation. This work is important to design high-performance piezocatalysts with high-efficiency ROS generation for sewage treatment and sonodynamic therapy.     

Dendritic Fe3O4@Poly(dopamine)@PAMAM Nanocomposite as Controllable NO‐Releasing Material: A Synergistic Photothermal and NO Antibacterial Study

Nowadays, antibiotic abuse increases the emergence of multidrug‐resistant bacterial strains, which is the major reason for the failure of conventional antibiotic therapies. Therefore, developing novel antibacterial materials or therapies is an urgent demand. In the present study, photothermal and NO‐releasing properties are integrated into a single nanocomposite to realize more efficient bactericidal effects. To this end, polydopamine (PDA) coated iron oxide nanocomposite (Fe₃O₄@PDA) is used as a photoconversion agent and the core, first three generation dendritic poly(amidoamine) (PAMAM‐G3) is grafted on the surface of Fe₃O₄@PDA, and subsequently NO is loaded with the formation of NONOate. The resultant Fe₃O₄@PDA@PAMAM@NONOate displays controllable NO release property under intermittent 808 nm laser irradiation and excellent bacteria‐separation efficiency. Moreover, excellent synergistic photothermal and NO antibacterial effects are observed against both Gram‐negative Escherichia coli and Gram‐positive Staphylococcus aureus, where bacterial viability and biofilm are significantly reduced. An antibacterial mechanism study reveals that the materials first adsorb onto the bacterial membrane, then cause damage to the membrane by the increased local temperature and the released NO under laser irradiation conditions, finally leak the intracellular components like DNA and induce bacteria death. The work provides a novel way for designing of antibacterial materials with higher efficiency.     

pH Switchable Nanoplatform for In Vivo Persistent Luminescence Imaging and Precise Photothermal Therapy of Bacterial Infection

Photothermal therapy (PTT) is one of the most promising approaches to combat multidrug‐resistant bacteria with less potential to induce resistance and systemic toxicity. However, uncontrollable distribution of photothermal agents leads to lethal temperatures for normal cells, and failure to offer timely and effective antibacterial stewardship. A pH switchable nanoplatform for persistent luminescence imaging‐guided precise PTT to selectively destroy only pathological cells while protecting nearby normal cells in bacterial infected microenvironment is shown. The PLNP@PANI‐GCS is fabricated by grafting polyaniline (PANI) and glycol chitosan (GCS) onto the surface of persistent luminescence nanoparticles (PLNPs). It takes advantage of the long persistent luminescence of PLNPs to realize autofluorescence‐free imaging, the pH‐dependent light–heat conversion property of PANI to get a stronger photothermal effect at pH 6.5 than pH 7.4, and the pH environment responsive surface charge transition of GCS. Consequently, PLNP@PANI‐GCS enables effective response to bacterial‐infected acid region and electrostatic bonding to bacteria in vivo, ensuring the spatial accuracy of near‐infrared light irradiation and specific heating directly to bacteria. In vivo imaging‐guided PTT to bacterial infection abscess shows effective treatment. PLNP@PANI‐GCS has great potential in treating multidrug‐resistant bacterial infection with low possibility of developing microbial drug resistance and little harm to normal cells.     

NIR‐Laser‐Controlled Hydrogen‐Releasing PdH Nanohydride for Synergistic Hydrogen‐Photothermal Antibacterial and Wound‐Healing Therapies

For decades, hydrogen (H₂) gas has been recognized as an excellent antioxidant molecule that holds promise in treating many diseases like Alzheimer's, stroke, cancer, and so on. For the first time, active hydrogen is demonstrated to be highly efficient in antibacterial, antibiofilm, and wound‐healing applications, in particular when used in combination with the photothermal effect. As a proof of concept, a biocompatible hydrogen‐releasing PdH nanohydride, displaying on‐demand controlled active hydrogen release property under near‐infrared laser irradiation, is fabricated by incorporating H₂ into Pd nanocubes. The obtained PdH nanohydride combines both merits of bioactive hydrogen and photothermal effect of Pd, exhibiting excellent in vitro and in vivo antibacterial activities due to its synergistic hydrogen‐photothermal therapeutic effect. Interestingly, combinational hydrogen‐photothermal treatment is also proved to be an excellent therapeutic methodology in healing rats' wound with serious bacterial infection. Moreover, an in‐depth antibacterial mechanism study reveals that two potential pathways are involved in the synergistic hydrogen‐photothermal antibacterial effect. One is to upregulate bacterial metabolism relevant genes like dmpI, narJ, and nark, which subsequently encode more expression of oxidative metabolic enzymes to generate substantial reactive oxygen species to induce DNA damage and another is to cause severe bacterial membrane damage to release intracellular compounds like DNA.     

Leaf-Structure-Inspired Through-Hole Electrode with Boosted Mass Transfer and Photothermal Effect for Oxygen Evolution Reactions

The sluggish kinetics of oxygen evolution reaction (OER) remains a bottleneck for the electrocatalytic water splitting. In addition to improving the intrinsic activity of electrocatalysts, the electrode structure and external environment also have a significant influence on catalytic performance. Inspired by photosynthesis in plant leaves, a photothermal conversion strategy is proposed via the decoration of photothermal responsive MoS₂/FeCoNiS-nanotube (MoS₂/FeCoNiS-NT) on designed through-hole porous nickel foam (PNF), defined as MoS₂/FeCoNiS-NT@PNF, to boost OER performance. The PNF facilitated bubble transport in OER by mimicking stomata structure of the leaf, and simultaneously, the MoS₂/FeCoNiS-NT increases light absorption and photothermal conversion by simulating the leaf epidermis. Benefiting from bionic structure and functional design, the MoS₂/FeCoNiS-NT@PNF electrode exhibits highly effective oxygen-evolving ability and excellent photothermal conversion capacity (surface temperature: 25 °C → 52.3 °C, AM1.5G), which increases the intrinsic activity of electrocatalysts. With the assistance of optimized electrode structure and the photothermal effect, the MoS₂/FeCoNiS-NT@PNF electrode exhibits a low overpotential of 214 mV to achieve 50 mA cm⁻². This research reveals that tuning the electrode structure can promote light absorption in the electrolyte in favor of OER performance, which can serve as an inspiration for the development of high-performance catalytic electrodes.     

Zwitterion Functionalized Graphene Oxide/Polyacrylamide/Polyacrylic Acid Hydrogels with Photothermal Conversion and Antibacterial Properties for Highly Efficient Uranium Extraction from Seawater

In this study, graphene oxide (GO) and polyacrylamide/polyacrylic acid (PAM/PAA) are used to prepare hydrogels with photothermal conversion properties for highly efficient uranium extraction from seawater. Zwitterionic 2-methacryloyloxy ethyl phosphorylcholine (MPC) is introduced in the PAM/PAA/GO hydrogel to obtain PAM/PAA/GO/MPC (PAGM), exhibiting good antibacterial properties. PAGM demonstrates efficient and specific adsorption of uranium (VI) (U(VI)). Under light conditions, the adsorption capacity of PAGM reaches 196.12 mg g⁻¹ (pH = 8, t = 600 min, C₀ = 99.8 mg L⁻¹, m/v = 0.5 g L⁻¹). The adsorption capacity is only 160.29 mg g⁻¹ under dark conditions (pH = 8, t = 600 min, C₀ = 99.8 mg L⁻¹, m/v = 0.5 g L⁻¹). The adsorption capacity of light is 22.5% higher than that of dark. The adsorption process is fitted using the Langmuir and pseudo-second-order models. Furthermore, PAGM exhibits good repeatability and stability after five adsorption–desorption cycles. PAGM exhibits a U(VI) adsorption capacity of 6.1 mg g⁻¹ after storage for one month in natural seawater. The X-ray photoelectron spectroscopy (XPS) results demonstrate that the coordination of the amino, carboxyl, and hydroxyl groups with U(VI) is the primary mechanism of U(VI) adsorption. The mechanism is confirmed through detailed density functional theory calculations. PAGM demonstrates durability, high efficiency, photothermal conversion properties, and antibacterial properties. Thus, it is a promising candidate for uranium extraction from seawater.     

Construction of Nanozyme‐Hydrogel for Enhanced Capture and Elimination of Bacteria

The widespread multidrug resistance resulting from the abuse of antibiotics motivates researchers to explore alternative methods to treat bacterial infections. Recently, the emergence of nanozymes has provided a potential approach to combat bacteria. Such nanozymes can mimic the functions of natural enzymes to induce the production of highly toxic reactive oxygen species (ROS) as an antibacterial. However, the lack of effective interaction between nanozymes and bacteria, and the intrinsic short lifetime and diffusion distance of ROS greatly compromise their bactericidal activity. Furthermore, the dead bacteria left in the infected area can give rise to unexpected tissue inflammation. Herein, for the first time, a nanozyme‐hydrogel is constructed to realize reinforced antibacterials. The nanozyme‐hydrogel with the traits of positive charge and macropore can capture and restrict bacteria in the range of ROS destruction. Significantly, by combining the near‐infrared photothermal property of nanozymes, the nanozyme‐hydrogel can achieve a synergistic bactericidal effect. More importantly, the nanozyme‐hydrogel can eliminate bacteria and reduce the risk of inflammation. In consequence, the current work manifests an original strategy to improve the antibacterial performance of nanozymes, concurrently promote wound healing.     

PEGylated Polypyrrole Nanoparticles Conjugating Gadolinium Chelates for Dual‐Modal MRI/Photoacoustic Imaging Guided Photothermal Therapy of Cancer

Polypyrrole nanoparticles conjugating gadolinium chelates were successfully fabricated for dual‐modal magnetic resonance imaging (MRI) and photoacoustic imaging guided photothermal therapy of cancer, from a mixture of pyrrole and pyrrole‐1‐propanoic acid through a facile one‐step aqueous dispersion polymerization, followed by covalent attachment of gadolinium chelate, using polyethylene glycol as a linker. The obtained PEGylated poly­pyrrole nanoparticles conjugating gadolinium chelates (Gd‐PEG‐PPy NPs), sized around around 70 nm, exhibited a high T₁ relaxivity coefficient of 10.61 L mm ^?1 s^?1, more than twice as high as that of the relating free Gd³⁺ complex (4.2 L mm ^–1 s^?1). After 24 h intravenous injection of Gd‐PEG‐PPy NPs, the tumor sites exhibited obvious enhancement in both T₁‐weighted MRI intensity and photoacoustic signal compared with that before injection, indicating the efficient accumulation of Gd‐PEG‐PPy NPs due to the introduction of the PEG layer onto the particle surface. In addition, tumor growth could be effectively inhibited after treatment with Gd‐PEG‐PPy NPs in combination with near‐infrared laser irradiation. The passive targeting and high MRI/photo­acoustic contrast capability of Gd‐PEG‐PPy NPs are quite favorable for precise cancer diagnosing and locating the tumor site to guide the external laser irradiation for photothermal ablation of tumors without damaging the surrounding healthy tissues. Therefore, Gd‐PEG‐PPy NPs may assist in better monitoring the therapeutic process, and contribute to developing more effective “personalized medicine,” showing great potential for cancer diagnosis and therapy.     

Synergistic Antimicrobial and Antibiofilm Nanoparticles Assembled from Naturally Occurring Building Blocks

Bacterial infections represent one of the serious human healthcare threats, and ≈80% of bacterial infections are related to biofilm. So far, there are extensive investigations on the development of robust biomaterials toward the elimination of biofilms and synergistic antibacterial applications. Despite the progress made, concerns have always been raised regarding the sophisticated synthesis and pre-modification of hybrid materials, complicated purification and high-cost work. In this study, a series of robust and integrative nanoparticles (NPs) assembled from two types of natural building blocks (natural polyphenols and tobramycin antibiotics) is successfully fabricated via a one-pot integration approach, which can efficiently destruct the biofilm structure and kill bacteria via enhanced antibiotic infiltration. Notably, natural polyphenols and tobramycin can release from the formed NPs in an on-demand manner in the bacterial-induced environment. The former ones can inhibit quorum sensing within bacteria through competitive combination with autoinducer-2 (AI-2) to remove the existing biofilm, and the latter antibiotics exert high antibacterial activity both in vitro and in vivo. This study provides new inspirations toward robust and synergistic antimicrobial and antibiofilm nanomaterials via the facile integration of naturally occurring molecules.     

Templateless Synthesis of Polygonal Gold Nanoparticles: An Unsupported and Reusable Catalyst with Superior Activity

We report the synthesis of polygonal gold nanoparticles (GNPs) by an in situ reduction technique using ferric ammonium citrate as reducing agent in absence of any surfactant or polymeric template. Transmission electron microscopic analysis and selected area electron diffraction patterns confirmed the formation of well‐crystalline polygonal GNPs grown preferentially along the (111) direction, which is consistent with the results of X‐ray diffractometry analysis. The results of control experiments of HAuCl₄ with tri‐ammonium citrate in presence of different externally added metal ions like Fe³⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Al³⁺ suggested the ion‐induced growth mechanism in the formation of polygonal GNPs. The purified polygonal GNPs were then successfully used as catalyst in the borohydride reduction of three isomeric nitrophenols and also in the aerobic oxidation of different D ‐hexoses (e.g., D ‐glucose, D ‐mannose, D ‐fructose). The catalytic activity of these polygonal GNPs is higher by a factor of 300–1000, depending on the GNP's sample type, in nitrophenol reduction compared to that of spherical GNPs. Similar activity enhancement was also observed in the aerobic oxidation of different D ‐hexoses. These polygonal GNPs catalyst are very stable and could be reused several times in the borohydride reduction of nitrophenols without much losing in their virgin catalytic activity.