Cationic Oligo(thiophene ethynylene) with Broad-Spectrum and High Antibacterial Efficiency under White Light and Specific Biocidal Activity against S. aureus in Dark

Cholesterol vs Ergosterol: Influence on the Dynamic and Structural Properties of the Cobalt-Based Metallosomal Bilayer Membrane

Sterol derivatives are a crucial part of liposomes, as their concentration and nature can induce significant alternations in their characteristic features. For natural liposomal-based (phospholipid-based) studies, the bulk literature is already present depicting the role of the concentration or nature of different sterol derivatives in modulation of membrane properties. However, the studies aiming at evaluating the effect of sterol derivatives on synthetic liposomal assemblies are limited to cholesterol (Chl), and a comparative effect with other sterol derivatives, such as ergosterol (Erg), has never been studied. To fill this research gap, through this work, we intend to provide insights into the concentration-dependent effect of two sterol derivatives (Chl and Erg) on a synthetic liposomal assembly (i.e., metallosomes) prepared via thin film hydration route using a double-tailed metallosurfactant fabricated by modifying cetylpyridinium chloride with cobalt (Co) (i.e., Co:CPC II). The morphological evaluations with cryogenic-transmission electron microscopy (cryo-TEM), atomic force microscopy (AFM), and field emission-scanning electron microscopy (FE-SEM) indicated that metallosomes retained their spherical morphology irrespective of the nature and concentration of sterol derivatives. However, the size, ζ-potential, and lamellar width values were significantly modified with the incorporation of sterol derivatives in a concentration-dependent manner. In-depth studies affirmed that the extent of modulation of the bilayer in terms of hydrophobicity, fluidity, and rigidity was more severe with Chl than Erg. Such differences in the membrane properties lead to their contrasting behavior in the delivery of the broad-spectrum active compound "curcumin". From entrapment to in vitro behavior, the metallosomes demonstrated dissimilar behavior as even though Erg-modified metallosomes (at higher concentrations of Erg) exhibited low entrapment efficiency, they still could easily release >80% of the entrapped drug. In vitro studies conducted with Staphylococcus aureus bacterial cultures further revealed an interesting pattern of activity as the incorporation of Chl reduced the toxicity of the self-assembly, whereas their Erg-modified counterparts yielded slightly augmented toxicity toward these bacterial cells. Furthermore, Chl- and Erg-modified assemblies also exhibited contrasting behavior in their interaction studies with bacterial DNA.

Near-infrared light triggered upconversion nanocomposites with multifunction of enhanced antimicrobial photodynamic therapy and gas therapy for inflammation regulation

Antibacterial photodynamic therapy (aPDT) is highly effective in killing bacteria, while the problem of hypoxia and limited light penetration in deep tissue has not been properly solved. In addition, few aPDT works take into account the regulation of inflammation, which is an important regulatory process after antimicrobial therapy and the final purpose of treatment. In this work, to address the above isssues, we have designed a multi-functional composite UCNPs-Ce6-Mn(CO)5Br@Silane (referred to as UCM@Si), which consists of several key components: Up-conversion nanoparticles (UCNPs: NaErF4:Tm3+@NaYF4:Yb3+), Chlorin e6 (Ce6) and Manganese pentacarbonyl bromide (Mn(CO)5Br). When exposed to near-infrared (NIR) light (980 nm), the UCNPs can emit strong red light at 655 nm which further trigger the aPDT of Ce6. The generated reactive oxygen (ROS) subsequently break the metal carbonyl bond of Mn(CO)5Br, leading to the production of carbon monoxide (CO) molecules as well as manganese ions (Mn2+), which further decomposes hydrogen peroxide (H2O2) in the microenvironment to oxygen (O2). Therefore, this simple nanocomposite not only provides substantial self-oxygen replenishment for enhanced aPDT, but also facilitates effective inflammation regulation via CO across a wide range of deep infections. This approach leverages the unique properties of these materials to combat bacterial infections by simultaneously killing bacteria, regulating inflammation, and enhancing the oxygen levels in the affected microenvironment. This O2 and CO gas based aPDT treatment system offers a promising approach to comprehensively address microbial-induced infectious diseases, particularly deep infections, holding the potential clinical applications.

Visible light-promoted anti-biofouling performance of cellulose acetate membrane for reverse osmosis desalination

Sea water desalination is regarded as a major solution that could alleviate the water scarcity problem. Reverse osmosis (RO) is typically employed to recover fresh water from sea and brackish water via economical means. RO membrane fouling remains a critical issue restricting their widespread application. In this work, a tertiary thiophenal quaternary ammonium salt-based antibacterial agent was covalently reacted with cellulose acetate (CA) to obtain contact-active antibacterial quaternized CA-RO membrane (QCA-RO). The membrane was characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, water contact angle testing, and X-ray diffraction spectroscopy. The obtained QCA-RO membrane displayed good antibacterial activity against Pseudomonas aeruginosa and Staphylococcus aureus and had bactericidal rates of 99 % in the presence of visible light. Results showed that embedding the quaternary ammonium salt did not cause any significant changes to the morphology, mechanical performance, and thermal stability of the RO membrane. The method described in this work not only produces QCA-RO membranes with good anti-biofilm performance but also presents great potential in seawater desalination.

A telluroviologen-anchored tetraphenylporphyrin as sonosensitizer for periodontitis sonodynamic therapy

Periodontitis is a chronic disease caused by bacteria (e.g. Porphyromonas gingivalis, P.gingivalis) that currently lacks effective non-invasive treatment options. Sonodynamic therapy (SDT) is an emerging non-invasive antimicrobial therapeutic strategy. Since ultrasonic tooth cleaning is widely used in dental treatments, SDT has significant potential for the facile implementation of treat periodontitis. However, hypoxia in periodontitis severely limits the effectiveness of traditional sonosensitizers. To address this issue, we have developed a new sonosensitizer termed as TPP-TeV, which combines the traditional sonosensitizer tetraphenylporphyrin (TPP) with a new photosensitizer telluroviologen (TeV). Under ultrasound radiation, TPP-TeV can produce numerous cationic free radicals (TPP-TeV•), which subsequently generate ROS free radicals (O2•-, •OH) efficiently via electron transfer mechanism, resulting in the effective killing of anaerobic P.gingivalis both in vivo and in vitro. As a result, the dental environment is improved, and the inhibition rate of alveolar bone loss reaches 80 %. The introduction of tellurium into the viologen molecule induces changes in its reduction potential, resulting in increased rigidity of the molecule. This modification systematically reduces the biotoxicity of our novel sonosensitizer by 75 % at 50 μM based on bacterial experiments. These promising findings could potentially establish new options for sonodynamic therapy (SDT) in periodontitis clinical treatments.

A Visible Light-Induced and ROS-Dependent Method for the Rapid Formation of a MOF Composite Membrane with Antibacterial Properties

The diverse application potential of metal-organic framework (MOF) materials are currently limited by their challenging and complicated preparation processes. In this study, we successfully developed a novel strategy for the rapid synthesis of a sustainable MOF composite membrane under neutral conditions with improved physicochemical and antibacterial properties. Our reaction pipeline comprised visible light that induced the production of reactive oxygen species (ROS) from ZIF-8 particles, which facilitated the rapid oxidative polymerization of dopamine to polydopamine. The physicochemical properties of the composite membrane were assessed using imaging methods, including scanning and transmission electron microscopy, X-ray photoelectron spectrometry, and nitrogen adsorption/desorption; its antibacterial effects against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa were measured using optical densitometry. The bactericidal potency of the synthesized membrane was >99% against all tested strains under the conditions of simulated sunlight. Moreover, the composite membrane retained its structural integrity and antibacterial effect after multiple cycles of use and recovery, showcasing remarkable stability. Overall, this study displays a ROS-mediated method for the rapid preparation of sustainable MOF composite membranes under neutral conditions with optimal physicochemical characteristics, antibacterial properties, and performance. Our study provides insights into the use of membrane materials as design platforms for a range of diverse practical applications.

An unexpected strategy to alleviate hypoxia limitation of photodynamic therapy by biotinylation of photosensitizers

The most common working mechanism of photodynamic therapy is based on high-toxicity singlet oxygen, which is called Type II photodynamic therapy. But it is highly dependent on oxygen consumption. Recently, Type I photodynamic therapy has been found to have better hypoxia tolerance to ease this restriction. However, few strategies are available on the design of Type I photosensitizers. We herein report an unexpected strategy to alleviate the limitation of traditional photodynamic therapy by biotinylation of three photosensitizers (two fluorescein-based photosensitizers and the commercially available Protoporphyrin). The three biotiylated photosensitizers named as compound 1, 2 and 3, exhibit impressive ability in generating both superoxide anion radicals and singlet oxygen. Moreover, compound 1 can be activated upon low-power white light irradiation with stronger ability of anion radicals generation than the other two. The excellent combinational Type I / Type II photodynamic therapy performance has been demonstrated with the photosensitizers 1. This work presents a universal protocol to provide tumor-targeting ability and enhance or trigger the generation of anion radicals by biotinylation of Type II photosensitizers against tumor hypoxia.

Type I photodynamic therapy (PDT) sensitizers show good hypoxia tolerance but only few strategies are available for the design of purely organic Type I photosensitizers (PS). Here, the authors use biotinylation as design strategy to obtain PS-Biotin sensitizers with high efficiency for the generation of superoxide anion radicals and singlet oxygen.

Water-soluble thienoviologen derivatives for imaging bacteria and antimicrobial photodynamic therapy

A series of water-soluble cationic thienoviologen derivative photosensitizers (nTPy-Rs) for photodynamic therapy (PDT) is reported. Cationic pyridine groups were introduced into the thiophene framework to enhance solubility and bacteria-binding ability, which effectively improved bacteriological imaging and antibacterial activity. The optoelectronic properties of nTPy-Rs were regulated by adjusting the number of thiophene groups, and the differences in antibacterial activity due to the functional scaffolds were compared. The results showed that nTPy-Rs could generate reactive oxygen species (ROS, including macroscopic free radicals), efficiently inhibit bacterial growth, and achieve the minimum inhibitory concentration (MIC) to the ng mL^-1 level. Remarkably, 2TPyC6, containing two thiophene groups and modified by alkyl side chains, showed the best bacteriostatic performance, with the MIC of 20 ng mL^-1 and 4.5 ng mL^-1 for E. coli and S. aureus, respectively, which are the lowest photosensitizer concentrations used in PDT to date. The low cell cytotoxicity and excellent antibacterial performance give nTPy-Rs great potential as PDT agents in vivo.

Thiophene-containing compounds with antimicrobial activity

Thiophene, as a member of the group of five-membered heterocycles containing one heteroatom, is one of the simplest heterocyclic systems. Many synthetic strategies allow the accurate positioning of various functionalities onto the thiophene ring. This review provides a comprehensive, systematic and detailed account of the developments in the field of antimicrobial compounds featuring at least one thiophene ring in their structure, over the last decade.

Eumelanin-Inspired Antimicrobial with Biocidal Activity against Methicillin-Resistant Staphylococcus aureus

The reliance on antibiotics and antimicrobials to treat bacterial infectious diseases is threatened by the emergence of antibiotic resistance and multi-drug-resistant organisms, thus having the potential to greatly impact human health. Thus, the discovery and development of antimicrobials capable of acting on antibiotic-resistant bacteria is a major area of significance in scientific research. Herein, we present the development of a eumelanin-inspired antimicrobial capable of killing methicillin-resistant Staphylococcus aureus (MRSA). By ligating quaternary ammonium-functionalized "arms" to a eumelanin-inspired indole with intrinsic antimicrobial activity, an antimicrobial agent with enhanced activity was prepared. This resulting antimicrobial, EIPE-1, had a minimum inhibitory concentration of 16 μg/mL (17.1 μM) against a clinical isolate of MRSA obtained from an adult cystic fibrosis patient. The biocidal activity occurred within 30 min of exposure and resulted in changes to the bacterial cell surface as visualized with a scanning electron microscope. Taken together, these studies demonstrate that EIPE-1 is effective at killing MRSA.

Recent Strategies to Develop Innovative Photosensitizers for Enhanced Photodynamic Therapy

This review presents a robust strategy to design photosensitizers (PSs) for various species. Photodynamic therapy (PDT) is a photochemical-based treatment approach that involves the use of light combined with a light-activated chemical, referred to as a PS. Attractively, PDT is one of the alternatives to conventional cancer treatment due to its noninvasive nature, high cure rates, and low side effects. PSs play an important factor in photoinduced reactive oxygen species (ROS) generation. Although the concept of photosensitizer-based photodynamic therapy has been widely adopted for clinical trials and bioimaging, until now, to our surprise, there has been no relevant review article on rational designs of organic PSs for PDT. Furthermore, most of published review articles in PDT focused on nanomaterials and nanotechnology based on traditional PSs. Therefore, this review aimed at reporting recent strategies to develop innovative organic photosensitizers for enhanced photodynamic therapy, with each example described in detail instead of providing only a general overview, as is typically done in previous reviews of PDT, to provide intuitive, vivid, and specific insights to the readers.

Comparison and Mechanism Study of Antibacterial Activity of Cationic and Neutral Oligo-Thiophene-Ethynylene

Photodynamic therapy (PDT) is a potential approach to resolve antibiotic resistance, and phenylene/thiophene-ethynylene oligomers have been widely studied as effective antibacterial reagents. Oligomers with thiophene moieties usually exhibit good antibacterial activity under light irradiation and dark conditions. In the previous study, we verified that neutral oligo-p-phenylene-ethynylenes (OPEs) exhibit better antibacterial activity than the corresponding cationic ones; however, whether this regular pattern also operates in other kinds of oligomers such as oligo-thiophene-ethynylene (OTE) is unknown. Also, the antibacterial activity comparison of OTEs bearing cyclic and acyclic amino groups will offer useful information to further understand the role of amino groups in the antibacterial process and guide the antibacterial reagent design as amino groups affect the antibacterial activity a lot. We synthesized four OTEs bearing neutral or cationic, cyclic, or acyclic amino groups and studied their antibacterial activity in detail. The experimental results indicated that the OTEs exhibited better antibacterial activity than the OPEs, the neutral OTEs exhibited better antibacterial activity in most cases, and OTEs bearing cyclic amino groups exhibited better antibacterial activity than those bearing acyclic ones in most cases. This study provides useful guidelines for further antibacterial reagent design and investigations.

New Approach in the Application of Conjugated Polymers: The Light-Activated Source of Versatile Singlet Oxygen Molecule

For many years, the research on conjugated polymers (CPs) has been mainly focused on their application in organic electronics. Recent works, however, show that due to the unique optical and photophysical properties of CPs, such as high absorption in UV–Vis or even near-infrared (NIR) region and efficient intra-/intermolecular energy transfer, which can be relatively easily optimized, CPs can be considered as an effective light-activated source of versatile and highly reactive singlet oxygen for medical or catalytic use. The aim of this short review is to present the novel possibilities that lie dormant in those exceptional polymers with the extended system of π-conjugated bonds.

On-Demand Antimicrobial Agent Release from Functionalized Conjugated Oligomer-Hyaluronic Acid Nanoparticles for Tackling Antimicrobial Resistance

Controllable drug release is promising for fighting against antimicrobial resistance, which is a critical threat to human health worldwide. Herein, new hyaluronidase-responsive conjugated oligo(thiophene ethynylene) (OTE)-covalently modified hyaluronic acid (OTE-HA) nanoparticles for on-demand release of antimicrobial agents are reported. The synthesis of amphiphilic OTE-HA was carried out by esterification reaction. The resulting macromolecules were self-assembled in water to form nanoparticles, in which the hydrophobic OTE section, as bactericides, formed "cores" and the hydrophilic hyaluronic acid (HA) formed "shells". The OTE-HA nanoparticles avoid bactericide premature leakage and effectively block the dark cytotoxicity of the OTE section, possessing excellent biocompatibility. Using methicillin-resistant Staphylococcus aureus (MRSA) as an example, hyaluronidase, largely secreted by MRSA, can in situ trigger the release of OTE via hydrolyzing OTE-HA nanoparticles into fragments, even disaccharides linked with OTE. Importantly, the OTE section could effectively break cell membranes, leading to bacterial death. The half-maximal inhibitory concentration of the nanoparticles against MRSA is 3.3 μg/mL. The great antibacterial activity of OTE-HA nanoparticles against Gram-positive bacteria Streptococcus pneumoniae further confirms the controllable bactericide delivery mechanism. OTE-HA nanoparticles coated on a surface can also effectively inhibit the growth of bacteria, which holds a remarkable promise in biomedical applications. Therefore, this work provides a favorable strategy of on-demand and in situ drug release for sterilization and defeating antimicrobial resistance.

Hybrids of Upconversion Nanoparticles and Silver Nanoclusters Ensure Superior Bactericidal Capability via Combined Sterilization

It is highly desired to develop new antibacterial agents with superior bactericidal efficiency for minimizing the damage to biological cells. We developed a combined antibacterial nanohybrid exhibiting a superb bactericidal effect and excellent biocompatibility by integrating upconversion nanoparticles (UCNPs) with silver nanoclusters (AgNCs). UCNPs and methylene blue (MB) molecules were encapsulated with silica microspheres via microemulsion, with MB as the photosensitizer. Silver ions (Ag⁺) were reduced by amino groups on the surface of silica spheres, wherein silver nanoclusters (AgNCs) were formed in situ to produce the nanohybrid, UCNPs@SiO₂(MB)@AgNCs. UCNPs emit visible light at 655 nm under excitation by near-infrared radiation (NIR, 980 nm). MB absorbs the emission from UCNPs to generate toxic singlet oxygen (¹O₂), which leads to the apoptosis of bacteria cells. Meanwhile, silver ions released from AgNCs destroy the bacteria membrane structure. Upon NIR irradiation at 980 nm for 10 min, 8.33 μg mL^-1 nanohybrid results in a 100% killing rate for both Gram-positive S. aureus (+) and Gram-negative E. coli (-).

Cationic π-Conjugated Polyelectrolyte Shows Antimicrobial Activity by Causing Lipid Loss and Lowering Elastic Modulus of Bacteria

Cationic, π-conjugated oligo-/polyelectrolytes (CCOEs/CCPEs) have shown great potential as antimicrobial materials to fight against antibiotic resistance. In this work, we treated wild-type and ampicillin-resistant (amp-resistant) Escherichia coli (E. coli) with a promising cationic, π-conjugated polyelectrolyte (P1) with a phenylene-based backbone and investigated the resulting morphological, mechanical, and compositional changes of the outer membrane of bacteria in great detail. The cationic quaternary amine groups of P1 led to electrostatic interactions with negatively charged moieties within the outer membrane of bacteria. Using atomic force microscopy (AFM), high-resolution transmission electron microscopy (TEM), we showed that due to this treatment, the bacterial outer membrane became rougher, decreased in stiffness/elastic modulus (AFM nanoindentation), formed blebs, and released vesicles near the cells. These evidences, in addition to increased staining of the P1-treated cell membrane by lipophilic dye Nile Red (confocal laser scanning microscopy (CLSM)), suggested loosening/disruption of packing of the outer cell envelope and release and exposure of lipid-based components. Lipidomics and fatty acid analysis confirmed a significant loss of phosphate-based outer membrane lipids and fatty acids, some of which are critically needed to maintain cell wall integrity and mechanical strength. Lipidomics and UV-vis analysis also confirmed that the extracellular vesicles released upon treatment (AFM) are composed of lipids and cationic P1. Such surface alterations (vesicle/bleb formation) and release of lipids/fatty acids upon treatment were effective enough to inhibit further growth of E. coli cells without completely disintegrating the cells and have been known as a defense mechanism of the cells against cationic antimicrobial agents.

Enhanced photodynamic inactivation for Gram-negative bacteria by branched polyethylenimine-containing nanoparticles under visible light irradiation

Antibiotic pollution has been a serious global public health concern in recent years, photodynamic inactivation is one of the most promising and innovative methods for antibacterial applications that avoids antibiotic abuse and minimizes risks of antibiotic resistance. However, limited by the weak interaction between the photosensitizers and Gram-negative bacteria, the effect of photodynamic inactivation cannot be fully exerted. Herein, photosensitizer chlorin e6-loaded polyethyleneimine-based micelle was constructed. The synergy of electrostatic and hydrophobic interactions between the nanoparticles and the bacterial surface promoted the anchoring of nanoparticles onto the bacteria, resulting in enhanced photoinactivation activities on Gram-negative bacteria. As expected, an eminent antibacterial effect was also observed on the Gram-positive bacteria Staphylococcus aureus. The cellular uptake results showed that photosensitizer was firmly anchored to the bacterial cell surface of Escherichia coli or Staphylococcus aureus by the introduction of branched polyethylenimine-containing nanoparticles. The light-triggered generation of reactive oxygen species, mainly singlet oxygen, from the membrane-bound nanoparticles caused irreversible damage to the bacterial outer membrane, achieving enhanced bactericidal efficiency than free photosensitizer. The study would provide an efficient and promising antimicrobial alternative to prevent overuse of antibiotics and have enormous potential for human healthcare and the environment remediation.

Fluorescein-Metal Hybrid Surfactant Conjugates as a Smart Material for Antimicrobial Photodynamic Therapy against Staphylococcus aureus

Photodynamic therapy (PDT) has been extensively used as an effective alternative for the treatment of bacterial infection using photosensitizers (PSs) in the presence of appropriate light. However, the limitation in the effectiveness of PDT is because of the low yield of singlet oxygen from existing PSs because of their low solubility. Thus, we have developed a platform to enhance the solubility and the photodynamic activity of PSs against bacterial cells using metallosurfactants. Herein, we have used manganese metal-containing single- (MnC I) and double-chain metallosurfactants (MnC II) which show an interplay of electrostatic/hydrophobic interactions with fluorescein (FL) dye (as a PS) and when used in the presence of light enhances the PDT. These interactions play a significant role in enhancing the singlet oxygen generation efficiency of FL. MnC I and MnC II have shown good antimicrobial activity against Gram-positive Staphylococcus aureus (S. aureus) bacteria. More interestingly, these metallosurfactants when combined with FL significantly enhanced the affectivity against S. aureus, wherein 100% killing was achieved. As compared to experiments performed in the dark, the metallosurfactant, by enhancing the solubility of FL, increases the formation of singlet oxygen upon light irradiation and thus increases cell death. Therefore, the synergistic effect of FL (light toxicity) and metallosurfactants (dark toxicity) defined excellent reduction in the colony formation of bacteria. These results were corroborated through field-emission scanning electron microscopy and optical microscopy, where the rupturing of the cell wall of bacterial cells was observed during this therapy. Moreover, the binding of metallosurfactants to the genomic DNA of S. aureus was also evaluated by gel retardation analysis and UV-visible spectroscopy. The outcomes from this study will deliver formulations for PDT which can be used in clinical medical applications and cancer therapy in the future.

Exploring BODIPY Derivatives as Singlet Oxygen Photosensitizers for PDT

This minireview is devoted to honoring the memory of Dr. Thomas Dougherty, a pioneer of modern photodynamic therapy (PDT). It compiles the most important inputs made by our research group since 2012 in the development of new photosensitizers based on BODIPY chromophore which, thanks to the rich BODIPY chemistry, allows a finely tuned design of the photophysical properties of this family of dyes to serve as efficient photosensitizers for the generation of singlet oxygen. These two factors, photophysical tuning and workable chemistry, have turned BODIPY chromophore as one of the most promising dyes for the development of improved photosensitizers for PDT. In this line, this minireview is mainly related to the establishment of chemical methods and structural designs for enabling efficient singlet oxygen generation in BODIPYs. The approaches include the incorporation of heavy atoms, such as halogens (iodine or bromine) in different number and positions on the BODIPY scaffold, and also transition metal atoms, by their complexation with Ir(III) center, for instance. On the other hand, low-toxicity approaches, without involving heavy metals, have been developed by preparing several orthogonal BODIPY dimers with different substitution patterns. The advantages and drawbacks of all these diverse molecular designs based on BODIPY structural framework are described.

Evaluating the Photodynamic Biocidal Activity and Investigating the Mechanism of Thiazolium Cyanine Dyes

In order to develop ideal photosensitizers for photodynamic therapy (PDT), a thiazolium group was introduced in cyanine dyes to possess the advantages of intense absorption in the visible region and anti-microbial activity. We evaluated the anti-bacterial activity of the three thiazolium cyanine dyes against Staphylococcus aureus (Gram-positive bacteria) and Escherichia coli (Gram-negative bacteria) in vitro. This is the first time that such kinds of cyanine dyes are applied in the photodynamic antibiotic area. Cyanines display excellent anti-bacterial activity to S. aureus and E. coli exposed to white light irradiation, and the corresponding light-induced biocidal efficacy of cyanines increased with irradiation time and concentration. At the same time, there was no observation of dark anti-bacterial abilities. Especially, cyanines show low cell cytotoxicity and excellent biocompatibility. These results suggest that thiazolium cyanine could work as a photosensitizer in PDT with great promise and broad applications for killing bacteria. Mechanistic studies suggest that the reactive oxygen species (ROS) is the vital factor for combating bacteria exposure to white light conditions, whereas it is not the only determining factor of the biocidal activity. The interaction of the cyanine to the cell membrane also plays a critical role in killing bacteria, which has exhibited a synergic effect of electrostatic and hydrophobic interactions. It influences the cell uptake and the membrane perturbation activity of the cyanines, which indirectly affects the biocidal activity.

Enhanced Energy Transfer in a Donor-Acceptor Photosensitizer Triggers Efficient Photodynamic Therapy

Photosensitizers (PSs) play a vital role in photodynamic therapy (PDT) for combating bacterial resistance and treating tumor. In this study, we report new donor-acceptor porphyrin PSs with a cationic conjugated oligomer (OPV) as a donor unit and porphyrin (TPP) as an acceptor unit by covalent linkage and achieved a fluorescence resonance energy transfer efficiency of 99% owing to their strong spectral overlap and short distance. The ¹O₂ yield of porphyrin derivatives is 121% (rose bengal as the standard reference) by virtue of OPVs' excellent light-harvesting ability and high fluorescence resonance energy transfer efficiency, greatly exceeding those of oligomer and porphyrin derivatives reported in the literature. Additionally, the cationic donors significantly improved the water solubility, decreased the aggregation of porphyrin, and promoted the adherence of the PSs to cell membranes through electrostatic interactions. As a result, the D-A porphyrin PSs exhibit dramatic PDT treatment efficiency. The half-inhibitory concentration is as low as 33 and 88 nM for methicillin-resistant Staphylococcus aureus and Escherichia coli, respectively. Therefore, this study provides a new strategy to construct PSs with high ¹O₂ yield and an excellent treatment effect at a low dose of PSs, which is promising for application in PDT used to treat cancer and microbial infections.

Core-Shell Gold Nanorod@Layered Double Hydroxide Nanomaterial with Highly Efficient Photothermal Conversion and Its Application in Antibacterial and Tumor Therapy

Photothermal conversion efficiency (η) of gold nanorods (GNRs) can be tuned by enlarging the aspect ratio and forming the core-shell structure. Herein, an easy synthesis method is developed to construct the core-shell GNR@LDH nanostructure with GNRs and layered double hydroxides (LDHs). The interaction between Au and LDHs results some electron deficiency on the surface of Au and the more electrons induce more thermal energy conversion. The η value of GNR@LDH can reach up to 60% under the 808 nm laser irradiation, which is a significant enhanced conversion efficiency compared with the reported GNR-based photothermal therapy materials. CTAB (cetyltrimethyl ammonium bromide) can be replaced totally during the synthesis process, and GNRs maintain a good dispersion in LDHs. This core-shell composite GNR@LDH can be applied in photothermal, antibacterial, tumor therapy and biological imaging with low dosage and nontoxicity.

An on-site bacterial detection strategy based on broad-spectrum antibacterial ε-polylysine functionalized magnetic nanoparticles combined with a portable fluorometer

A sensitive on-site bacterial detection strategy is presented that integrates the broad-spectrum capturing feature of ε-polylysine-functionalized magnetic nanoparticles with an in-house built portable fluorometer. Based on the electrostatic interaction, the functionalized magnetic nanoparticles (ε-PL-MNPs) were prepared for Gram-positive and Gram-negative bacterial separation and subsequent viable release. ε-PL-MNPs show a broad reactivity towards bacteria with the high capture efficiency from real-world sample media. They also enable controlled viable bacterial release with pH adjustment. Detection of bacteria is based on a combination of broad-spectrum capture with colorimetric and fluorimetric immunoassays. A portable fluorometer is built to enhance the applicability for sensitive on-site detection. A limit of detection of 98 CFU·mL^-1 is achieved that is comparable to that of a known spectrofluorometric method for E. coli DH5α. Graphical abstract Schematic presentation of bacterial capture using cationic polymer functionalized magnetic nanoparticles and general fluorometric immunoassay with portable fluorometer. The limit of detection is 98 CFU·mL^-1 for E. coli DH5α.

Water-dispersible glycosylated poly(2,5'-thienylene)porphyrin-based nanoparticles for antibacterial photodynamic therapy

Here we report the preparation of water-dispersible glycosylated poly(2,5'-thienylene)porphyrin based nanoparticles by a nanoprecipitation method and demonstrate the application of these nanoparticles in antibacterial photodynamic therapy. The diameter of the nanoparticles is in the range of 50-80 nm and the resulting nanoparticles are stable in water without precipitation at least for a month. They have high singlet oxygen efficiency and display light-triggered biocidal activity against both Gram negative bacteria (Escherichia coli, E. coli) and Gram positive bacteria (Bacillus subtilis, B. subtilis). Upon white light irradiation for 10 min with a flux of 22 mW cm-2 of the E. coli suspension incubated with NPs (18 μg mL-1), a killing efficiency of 99% is achieved, whereas in the dark the effect is recorded as only around 8%.

Rejuvenated Photodynamic Therapy for Bacterial Infections

The emergence of multidrug resistant bacterial strains has hastened the exploration of advanced microbicides and antibacterial techniques. Photodynamic antibacterial therapy (PDAT), an old-fashioned technique, has been rejuvenated to combat "superbugs" and biofilm-associated infections owing to its excellent characteristics of noninvasiveness and broad antibacterial spectrum. More importantly, bacteria are less likely to produce drug resistance to PDAT because it does not require specific targeting interaction between photosensitizers (PSs) and bacteria. This review mainly focuses on recent developments and future prospects of PDAT. The mechanisms of PDAT against bacteria and biofilms are briefly introduced. In addition to classical macrocyclic PSs, several innovative PSs, including non-self-quenching PSs, conjugated polymer-based PSs, and nano-PSs, are summarized in detail. Numerous multifunctional PDAT systems such as in situ light-activated PDAT, stimuli-responsive PDAT, oxygen self-enriching enhanced PDAT, and PDAT-based multimodal therapy are highlighted to overcome the inherent defects of PDAT in vivo (e.g., limited penetration depth of light and hypoxic environment of infectious sites).

Amino Acid-Modified Conjugated Oligomer Self-Assembly Hydrogel for Efficient Capture and Specific Killing of Antibiotic-Resistant Bacteria

Bacterial infection is one of main causes that threaten global human health. Especially, antibiotic-resistant bacteria like methicillin-resistant Staphylococcus aureus (MRSA) lead to high mortality rate and more expensive treatment cost. Here, a novel amino-acid-modified conjugated oligomer OTE-d-Phe was synthesized by modifying the side chain of conjugated oligo(thiophene ethynylene) with d-phenylalanine. By mixing 9-fluorenylmethyloxycarbonyl-l-phenylalanin (Fmoc-l-Phe) with OTE-d-Phe, a new and biocompatible low-molecular weight hydrogel (HG-2) was prepared through self-assembly. In solution, HG-2 can effectively capture bacteria spontaneously, such as Escherichia coli and MRSA. Most importantly, the hydrogel has specific and strong antibacterial activity against MRSA over methicillin-susceptible S. aureus, Staphylococcus epidermidis, and E. coli. Interestingly, when the hydrogel was put on a model surface, a piece of cloth, it also is able to selectively kill MRSA with low cell cytotoxicity. The antibacterial mechanism was investigated, and it demonstrated that the HG-2 interacts with and physically breaks the cell wall and membrane, which leads to MRSA death. Therefore, this new conjugated oligomer-based hydrogel provides promising applications in disinfection and therapy of MRSA in hospital and in community.

Precisely Defined Conjugated Oligoelectrolytes for Biosensing and Therapeutics

Conjugated oligoelectrolytes (COEs) are a relatively new class of synthetic organic molecules with, as of yet, untapped potential for use in organic optoelectronic devices and bioelectronic systems. COEs also offer a novel molecular approach to biosensing, bioimaging, and disease therapy. Substantial progress has been made in the past decade at the intersection of chemistry, materials science, and the biological sciences developing COEs and their polymer analogues, namely, conjugated polyelectrolytes (CPEs), into synthetic systems with biological and biomedical utility. CPEs have traditionally attracted more attention in arenas of sensing, imaging, and therapy. However, the precisely defined molecular structures and interactions of COEs offer potential key advantages over CPEs, including higher reliability and fluorescence quantum efficiency, larger diversity of subcellular targeting strategies, and improved selectivity to biomolecules. Here, the unique-and sometimes overlooked-properties of COEs are discussed and the noticeable progress in their use for biological sensing, imaging, and therapy is reviewed.

Sequence and Dispersity Are Determinants of Photodynamic Antibacterial Activity Exerted by Peptidomimetic Oligo(thiophene)s

A library of functionalized oligo(thiophene)s with precisely controlled chain length, regioregularity, sequence, and pendant moieties in the side chains was prepared by iterative convergent/divergent organometallic couplings. The cationic and facially amphiphilic structures were designed to mimic the salient physiochemical features of host defense peptides (HDPs) while concurrently exerting a photodynamic mechanism of antibacterial activity. In the dark, the oligothiophenes exert broad-spectrum and rapid bactericidal activity in the micromolar regime, which is the typical range of HDP activity. Under visible light, the antibacterial potency is enhanced by orders of magnitude, leading to potency in the nanomolar concentration range, whereas the toxicity to red blood cells (RBCs) is almost unaffected by the same visible light exposure. We attribute the potent and selective antibacterial activity to a dual mechanism of action that involves bacterial cell binding, combined with reactive oxygen species production in the bound state. Comonomer sequence and chain length dispersity play important roles in dictating the observed biological activities. The most promising candidate compound from a set of screening experiments showed antibacterial activity that is 3 orders of magnitude more potent against bacteria relative to toxicity against RBCs. Importantly, this compound did not induce resistance upon 21 subinhibitory passages, whereas the activity of ciprofloxacin was reduced 32× in the same condition. Cytotoxicity against HeLa cells in vitro is orders of magnitude weaker than antibacterial activity under visible light illumination. Thus, we have established a new class of HDP-mimetic antibacterial compounds with nanomolar activity and cell type selectivity of greater than 1300-fold. These and related compounds may be highly promising candidates in the urgent search for new topical photodynamic antibacterial formulations.

Design of smart targeted and responsive drug delivery systems with enhanced antibacterial properties

The use of antibiotics has been an epoch-making invention in the past few decades for the treatment of infectious diseases. However, the intravenous injection of antibiotics lacking responsiveness and targeting properties has led to low drug utilization and high cytotoxicity. More importantly, it has also caused the development and spread of drug-resistant bacteria due to repeated medication and increased dosage. The differences in the microenvironments of the bacterial infection sites and normal tissues, such as lower pH, high expression of some special enzymes, hydrogen peroxide and released toxins, etc., are usually used for targeted and controlled drug delivery. In addition, bacterial surface charges, antigens and the surface structures of bacterial cell walls are all different from normal tissue cells. Based on the special bacterial infection microenvironments and bacteria surface properties, a series of drug delivery systems has been constructed for highly efficient drug release. This review summarizes the recent progress in targeted and responsive drug delivery systems for enhanced antibacterial properties.

Red Fluorescence Conjugated Polymer with Broad Spectrum Antimicrobial Activity for Treatment of Bacterial Infections In Vivo

To address the problem of bacterial resistance, a practical strategy for broad spectrum antimicrobial based on conjugated polymers was proposed in the work. Three red fluorescence conjugated polymers (P1, P2, and P3) bearing quaternary ammonium groups with different length of side chains were designed and synthesized. By virtue of inserting capacity of the longer side chain, conjugated polymer (P3) displayed well broad spectrum antimicrobial activity toward Gram-negative and Gram-positive bacteria and fungi under a white light density of 25 mW cm^-2 and short time (15 min) by aid of dark toxicity and light toxicity, derived from the quaternary ammonium groups and reactive oxygen species produced by the backbone, respectively. Notably, for ampicillin-resistant Escherichia coli TOP10, P3 could kill the bacteria 100% at a very low concentration of 5 μM upon light irradiation. Furthermore, wound healing tests indicated that the polymer could be expediently employed for wound disinfection in vivo without any tissue damaging. The contribution of the work not only provides an efficient and broad spectrum antimicrobial material but also offers a multimodal antimicrobial strategy to fight against bacterial infections in vivo.

Polyhedral Oligomeric Silsesquioxane (POSS)-Based Cationic Conjugated Oligoelectrolyte/Porphyrin for Efficient Energy Transfer and Multiamplified Antimicrobial Activity

Cationic quaternary ammonium (QA) groups and reactive oxygen species as two main approaches for antibacterial study have been intensively studied. Herein, we report a multifunctional antimicrobial agent (porphyrin-POSS-OPVE, PPO), which combines bacterial membrane intercalation, high density of local QA groups, efficient energy transfer, significantly reduced aggregation, and high water solubility into one single molecule. The light-harvesting PPO contains multiple donor-absorbing arms (oligo( p-phenylenevinylene) electrolytes, OPVEs) on its globular periphery and a central porphyrin acceptor in the core by using three-dimensional nanocages (polyhedral oligomeric silsesquioxanes, POSSs) as bridges. The antiaggregation ability of POSS and the highly efficient energy transfer from multiple OPVE arms to porphyrin could greatly amplify singlet oxygen generation in PPO. Particularly, OPVEs with QA terminal chains were able to intercalate into Escherichia coli membranes, which facilitated ¹O₂ diffusion and bacterial cell membrane disintegration by QA groups. The increased local cationic QA charges in OPVE arms can also enhance the biocidal activity of PPO. Benefiting from these satisfactory features, PPO exhibits multiamplified antibacterial efficacy under a very low concentration level and white light dose (400-700 nm, 6 mW·cm^-2, 5 min, 1.8 J·cm^-2) to Escherichia coli (8 μM) and Staphylococcus aureus (500 nM). Therefore, PPO shows great potential for photodynamic antimicrobial chemotherapy at a much lower irradiation light dose and photosensitizer concentration level compared to previous reports.

Rise of Conjugated Poly-ynes and Poly(Metalla-ynes): From Design Through Synthesis to Structure-Property Relationships and Applications

Conjugated poly-ynes and poly(metalla-ynes) constitute an important class of new materials with potential application in various domains of science. The key factors responsible for the diverse usage of these materials is their intriguing and tunable chemical and photophysical properties. This review highlights fascinating advances made in the field of conjugated organic poly-ynes and poly(metalla-ynes) incorporating group 4-11 metals. This includes several important aspects of conjugated poly-ynes viz. synthetic protocols, bonding, electronic structure, nature of luminescence, structure-property relationships, diverse applications, and concluding remarks. Furthermore, we delineated the future directions and challenges in this particular area of research.

Flower-like Surface of Three-Metal-Component Layered Double Hydroxide Composites for Improved Antibacterial Activity of Lysozyme

Microbes play an important function in our lives, while some pathogenic bacteria are responsible for many infectious diseases, food safety, and ecological pollution. Layered double hydroxide (LDH) is a kind of natural two-dimensional material and has been applied in many fields. Lysozyme is a green natural antibacterial agent, while the antimicrobial activity of lysozyme is not as good as antibiotics. We use a different ratio of cations to tune the morphology of LDH covered with lysozyme to enhance the antibacterial ability of lysozyme. We synthesize MgAl-LDH, ZnAl-LDH, and ZnMgAl-LDH covered with lysozyme, characterize the structure and morphology, test the antibacterial in culture media, and evaluate the biotoxicity in vitro and in vivo. The flower-like structure of ZnMgAl-LDH has a rough surface, covered with lysozyme with a perfect ring, and presents good antibaterial properties and promotes wound healing of mice. The bloom flower structure of ZnMgAl-LDH can enhance the loading rate of lysozyme; meanwhile, the rougher surface can adhere more bacteria, so lyso@ZnMgAl-LDH presents better antibacterial activity than the binary LDHs.

Self-Assembled Rose Bengal-Exopolysaccharide Nanoparticles for Improved Photodynamic Inactivation of Bacteria by Enhancing Singlet Oxygen Generation Directly in the Solution

It is of great value to develop new antibacterial photodynamic therapy (PDT) strategies to improve antibacterial PDT efficacy of noncationic photosensitizers without introducing cytotoxicity, which is a great challenge for current leading efforts on antimicrobial PDT based on cell surface engineering. In this research, the hydrophobic and anionic photosensitizer rose bengal (RB) was chemically conjugated with bacterial exopolysaccharide (EPS) to generate an amphiphilic and negatively charged compound EPS-RB that could self-assemble into nanoparticles (NPs) in solution. These EPS-RB NPs possessed an increased singlet oxygen generation property in solution. As a result, EPS-RB exhibited improved photoinactivation for both Gram-negative and Gram-positive bacteria, leading to a record low RB working concentration, 8 μM or 500 nM for Escherichia coli or Staphylococcus aureus, respectively. Upon light irradiation, more EPS-RB bound to the cell surface and penetrated into bacteria than RB, with EPS-RB staying around the cell surface of the most irradiated E. coli while entering all irradiated S. aureus. Both scanning electron microscopy and fluorescence confocal imaging results show that the cell membrane of E. coli was damaged heavily but not S. aureus. All of these observations indicate that both the enhanced singlet oxygen production of EPS-RB NPs in solution and their consequently increased membrane binding and cellular penetration into the bacteria through the damaged cell membrane contribute to their significantly improved bacterial photoinactivation efficiency. In addition, EPS-RB has low cytotoxicity and negligible hemolytic activity, showing great biocompatibility. Therefore, the construction of EPS-RB provides a new strategy for the PDT effectiveness improvement of the separated cell/sensitizer systems and thus the design of next-generation antimicrobial agents.

Antibacterial activity of cationic polymers: side-chain or main-chain type?

Imidazolium (Im), quaternary ammonium (Qa), and 1,4-diazabicyclo[2.2.2]octane-1,4-diium (DABCO-diium) cation-based small molecule cationic compounds and their corresponding side-chain/main-chain cationic polymers were synthesized.

Cholesterol-Assisted Bacterial Cell Surface Engineering for Photodynamic Inactivation of Gram-Positive and Gram-Negative Bacteria

Antibacterial photodynamic therapy (PDT), which enables effective killing of regular and multidrug-resistant (MDR) bacteria, is a promising treatment modality for bacterial infection. However, because most photosensitizer (PS) molecules fail to strongly interact with the surface of Gram-negative bacteria, this technique is suitable for treating only Gram-positive bacterial infection, which largely hampers its practical applications. Herein, we reveal for the first time that cholesterol could significantly facilitate the hydrophobic binding of PSs to the bacterial surface, achieving the hydrophobic interaction-based bacterial cell surface engineering that could effectively photoinactivate both Gram-negative and Gram-positive bacteria. An amphiphilic polymer composed of a polyethylene glycol (PEG) segment terminated with protoporphyrin IX (PpIX, an anionic PS) and cholesterol was constructed (abbreviated Chol-PEG-PpIX), which could self-assemble into micelle-like nanoparticles (NPs) in aqueous solution. When encountering the Gram-negative Escherichia coli cells, the Chol-PEG-PpIX NPs would disassemble and the PpIX moieties could effectively bind to the bacterial surface with the help of the cholesterol moieties, resulting in the significantly enhanced fluorescence emission of the bacterial surface. Under white light irradiation, the light-triggered singlet oxygen (¹O₂) generation of the membrane-bound PpIX could not only severely damage the outer membrane but also facilitate the entry of external Chol-PEG-PpIX into the bacteria, achieving >99.99% bactericidal efficiency. Besides, as expected, the Chol-PEG-PpIX NPs also exhibited excellent antibacterial performance against the Gram-positive Staphylococcus aureus. We also verified that this nanoagent possesses negligible dark cytotoxicity toward mammalian cells and good hemocompatibility. To the best of our knowledge, this study demonstrates for the first time the feasibility of constructing a fully hydrophobic interaction-based and outer membrane-anchored antibacterial PDT nanoagent.

Zinc Ion Coordinated Poly(Ionic Liquid) Antimicrobial Membranes for Wound Healing

Herein, a series of quaternary ammonium (Qa) or imidazolium (Im) cation-based poly(ionic liquid) (PIL) membranes and their corresponding zinc ion coordinated PIL membranes were synthesized. The effects of chemical structure, including organic cations, alkyl side chain of substitution, and zinc atoms on the antimicrobial activities against Escherichia coli, Staphylococcus aureus, and Candida albicans were investigated. The Zn-containing PIL membranes show higher antibacterial activities compared to those of pristine PIL membranes due to the synergistic attributes of both organic cations (Qa or Im) and zinc atoms. A wound healing test using methicillin-resistant S. aureus infected mouse as the model further demonstrated that zinc ion coordinated PIL membranes were antibacterially active, biologically safe, and may have potential application as an antimicrobial wound dressing in a clinical setting.

Metal-Containing Poly(ionic liquid) Membranes for Antibacterial Applications

Imidazolium-type metal-containing ionic liquid (IL) monomers and their corresponding poly(ionic liquid) (PIL) membranes coordinated with CuCl₂ (PILM-Cu), FeCl₃ (PILM-Fe), or ZnCl₂ (PILM-Zn) were synthesized. The effect of metal ions on the antimicrobial activities against both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) was investigated. Compared with pristine PILM-Br membrane, PILM-Cu, PILM-Fe, and PILM-Zn membranes exhibit enhanced antibacterial activities due to the attributes of both imidazolium cations and metal-containing anions. Furthermore, all of the metal-containing PIL membranes present low hemolysis toward human red blood cell and high long-term antibacterial stability, even after immersion in water for 90 days, demonstrating clinical feasibility in topical applications.