When worlds collide: interactions at the interface between biological systems and synthetic cationic conjugated polyelectrolytes and oligomers

An Effective Approach to the Disinfection of Pathogens: Cationic Conjugated Polyelectrolytes and Oligomers

The synthetic cationic conjugated polyelectrolytes and oligomers have demonstrated great effectiveness and versatility as antimicrobial materials. They have the ability to eliminate or render inactive various pathogens, including viruses like SARS-CoV-2, bacteria, and fungi. These pathogens can be rapidly eradicated when the polyelectrolytes and oligomers are applied as sprays, wipes, or coatings on solid surfaces. Inactivation of the pathogens occurs through two distinct processes: a non-light-activated process similar to Quats, and a more efficient and faster process that is triggered by light. These materials possess fluorescence and photosensitizing properties, enabling prolonged protection when coated on surfaces. The level of fluorescence exhibited by samples applied to nonfluorescent surfaces serves as an indicator of the coating's integrity and viability, making it easily detectable. Importantly, these materials demonstrate low toxicity towards mammalian cells and human skin, allowing for their safe use. While they can serve as durable coatings for pathogen protection, extended exposure to visible or ultraviolet light leads to their photochemical degradation. Our research also suggests that these materials act against pathogens through nonspecific mechanisms, minimizing the likelihood of pathogens developing resistance and rendering the materials ineffective.

Multifunctional Fluorescent Main-Chain Charged Polyelectrolytes Synthesized by Cascade C-H Activation/Annulation Polymerizations

Fluorescent polyelectrolytes have attracted enormous attention as functional polymer materials. In contrast with the widely studied conjugated polyelectrolytes with ionic groups in side chains, fluorescent main-chain charged polyelectrolytes (MCCPs) have rarely been explored due to the large synthetic difficulty. Herein, we develop a facile and atom-economical N-heterocyclic carbene-directed cascade C-H activation/annulation polymerization strategy that can transform readily available imidazolium substrates and internal diynes into multifunctional fluorescent MCCPs with complex structures and high molecular weights (absolute Mn up to 135 600) in nearly quantitative yields. The presence of multisubstituted polycyclic N-heteroaromatic cations in polymer backbones endow the obtained MCCPs with excellent solution processability, high thermal stability, and dual-state efficient fluorescence in both solution and aggregate states. Benefiting from the strong electron-withdrawing capability of the cationic heterocycles in main chains, multicolored aggregate-state fluorescence can be readily achieved by modifying the substituents around the cationic ring-fused core. Taking advantage of the good photosensitivity of the fluorescent MCCP thin films, multiscale and high-resolution fluorescent photopatterns with different colors can be facilely prepared with potential applications in optical display devices and anticounterfeiting systems. Moreover, the strong electrostatic interactions of these cationic MCCPs with anionic polyelectrolytes enable them to form multicolored fluorescent interfacial polyelectrolyte complexation microfibers with directly visualized internal structures. Such flexible microfibers can be further made into diversified forms of fiber-based macroscopic patterns or painting.

Cascade C-H-Activated Polyannulations toward Ring-Fused Heteroaromatic Polymers for Intracellular pH Mapping and Cancer Cell Killing

The development of straightforward and efficient synthetic methods toward ring-fused heteroaromatic polymers with attractive functionalities has great significance in both chemistry and materials science. Herein, we develop a facile cascade C-H-activated polyannulation route that can in situ generate multiple ring-fused aza-heteroaromatic polymers from readily available monomers in an atom-economical manner. A series of complex polybenzimidazole derivatives with high absolute molecular weights of up to 24 000 are efficiently produced in high yields within 2 h. Benefiting from their unique imidazole-containing ring-fused structures with multiple aryl pendants, the obtained polymers show excellent thermal and morphological stability, good solution processability, high refractive index, small chromic dispersion, as well as remarkable acid-base-responsive fluorescence. Taking advantage of the ratiometric fluorescence response of the triphenylamine-substituted heteroaromatic polymer to pH variations, we successfully apply it as a sensitive fluorescence probe for the mapping and quantitative analysis of intracellular pH in live cells. Furthermore, through the simple N-methylation reaction of the ring-fused polybenzimidazoles, diverse azonia-containing polyelectrolytes are readily produced, which can efficiently kill cancer cells via the synergistic effects of dark toxicity and phototoxicity.

Rapid and Effective Inactivation of SARS-CoV-2 with a Cationic Conjugated Oligomer with Visible Light: Studies of Antiviral Activity in Solutions and on Supports

This paper presents results of a study of a new cationic oligomer that contains end groups and a chromophore affording inactivation of SARS-CoV-2 by visible light irradiation in solution or as a solid coating on paper wipes and glass fiber filtration substrates. A key finding of this study is that the cationic oligomer with a central thiophene ring and imidazolium charged groups gives outstanding performance in both the killing of E. coli bacterial cells and inactivation of the virus at very short times. Our introduction of cationic N-methyl imidazolium groups enhances the light activation process for both E. coli and SARS-CoV-2 but dampens the killing of the bacteria and eliminates the inactivation of the virus in the dark. For the studies with this oligomer in solution at a concentration of 1 μg/mL and E. coli, we obtain 3 log killing of the bacteria with 10 min of irradiation with LuzChem cool white lights (mimicking indoor illumination). With the oligomer in solution at a concentration of 10 μg/mL, we observe 4 log inactivation (99.99%) in 5 min of irradiation and total inactivation after 10 min. The oligomer is quite active against E. coli on oligomer-coated paper wipes and glass fiber filter supports. The SARS-CoV-2 is also inactivated by oligomer-coated glass fiber filter papers. This study indicates that these oligomer-coated materials may be very useful as wipes and filtration materials.

Aggregation-Induced Emission-Active Poly(phenyleneethynylene)s for Fluorescence and Raman Dual-Modal Imaging and Drug-Resistant Bacteria Killing

Poly(phenyleneethynylene) (PPE) is a widely used functional conjugated polymer with applications ranging from organic optoelectronics and fluorescence sensors to optical imaging and theranostics. However, the fluorescence efficiency of PPE in aggregate states is generally not as good as their solution states, which greatly compromises their performance in fluorescence-related applications. Herein, a series of PPE derivatives with typical aggregation-induced emission (AIE) properties is designed and synthesized. In these PPEs, the diethylamino-substituted tetraphenylethene units function as the long-wavelength AIE source and the alkyl side chains serve as the functionalization site. The obtained AIE-active PPEs with large π-conjugation show strong aggregate-state fluorescence, interesting self-assembly behaviors, inherently enhanced alkyne vibrations in the Raman-silent region of cells, and efficient antibacterial activities. The PPE nanoparticles with good cellular uptake capability can clearly and sensitively visualize the tumor region and residual tumors via their fluorescence and Raman signals, respectively, to benefit the precise tumor resection surgery. After post-functionalization, the obtained PPE-based polyelectrolyte can preferentially image bacteria over mammalian cells and possesses efficient photodynamic killing capability against Gram-positive and drug-resistant bacteria. This work provides a feasible design strategy for developing functional conjugated polymers with multimodal imaging capability as well as photodynamic antimicrobial ability.

Understanding the Photochemical Properties of Polythiophene Polyelectrolyte Soft Aggregates with Sodium Dodecyl Sulfate for Antimicrobial Activity

The threat of antibiotic-resistant bacteria is an ever-increasing problem in public health. In this report, we examine the photochemical properties with a proof-of-principle biocidal assay for a novel series of regio-regular imidazolium derivative poly-(3-hexylthiophene)/sodium dodecyl sulfate (P3HT-Im/SDS) materials from ultrafast sub-ps dynamics to μs generation of reactive oxygen species (ROS) and 30 min biocidal reactivity with Escherichia coli (E. coli). This broad series encompassing pure P3HT-Im to cationic, neutral, and anionic P3HT-Im/SDS materials are all interrogated by a variety of techniques to characterize the physical material structure, electronic structure, and antimicrobial activity. Our results show that SDS complexation with P3HT-Im results in aggregate materials with reduced ROS generation and light-induced anti-microbial activity. However, our characterization reveals that the presence of non-aggregated or lightly SDS-covered polymer segments is still capable of ROS generation. Full encapsulation of the P3HT-Im polymer completely deactivates the light killing pathway. High SDS concentrations, near and above critical micelle concentration, further deactivate all anti-microbial activity (light and dark) even though the P3HT-Im regains its electronic properties to generate ROS.

A Portrait of the OPE as a Biological Agent

Oligophenylene ethynylenes, known as OPEs, are a sequence of aromatic rings linked by triple bonds, the properties of which can be modulated by varying the length of the rigid main chain or/and the nature and position of the substituents on the aromatic units. They are luminescent molecules with high quantum yields and can be designed to enter a cell and act as antimicrobial and antiviral compounds, as biocompatible fluorescent probes directed towards target organelles in living cells, as labelling agents, as selective sensors for the detection of fibrillar and prefibrillar amyloid in the proteic field and in a fluorescence turn-on system for the detection of saccharides, as photosensitizers in photodynamic therapy (due to their capacity to highly induce toxicity after light activation), and as drug delivery systems. The antibacterial properties of OPEs have been the most studied against very popular and resistant pathogens, and in this paper the achievements of these studies are reviewed, together with almost all the other roles held by such oligomers. In the recent decade, their antifungal and antiviral effects have attracted the attention of researchers who believe OPEs to be possible biocides of the future. The review describes, for instance, the preliminary results obtained with OPEs against severe acute respiratory syndrome coronavirus 2, the virus responsible for the COVID-19 pandemic.

Different Surface Interactions between Fluorescent Conjugated Polymers and Biological Targets

Fluorescent conjugated polymers (CPs) have attracted considerable interest in biosensing owing to their high fluorescence, tunable bandgap, and good biocompatibility. Aiming at acquiring the desired optical responses of CPs for bioapplications, it is essential that the CPs bind to biological targets with high efficacy and affinity. However, the efficient binding of CPs is largely driven by their effective interaction with target surfaces. In this Review, we will focus on the different surface interactions that pervade between CPs and biological targets. The multiple surface interactions can lead to changes in spatial conformation and distribution of CPs, which manifest alterable optical properties of CPs based on accumulation of target-directed CPs, Förster resonance energy transfer mechanism, and metal-enhanced fluorescence mechanism. Then, we display diverse bioapplications applying CPs-based surface interactions, such as cell imaging, imaging-guided detection, and photodynamic therapy. Finally, the challenges and future developments to control the efficient attachment of CPs to biological targets are discussed. We expect that the understanding of surface interactions between CPs and biological targets benefits the CPs-based system design and expands their applications in biological detections and therapies.

New Hybrid Copper Nanoparticles/Conjugated Polyelectrolyte Composite with Antibacterial Activity

In the search for new materials to fight against antibiotic-resistant bacteria, a hybrid composite from metallic copper nanoparticles (CuNPs) and a novel cationic π-conjugated polyelectrolyte (CPE) were designed, synthesized, and characterized. The CuNPs were prepared by chemical reduction in the presence of CPE, which acts as a stabilizing agent. Spectroscopic analysis and electron microscopy showed the distinctive band of the metallic CuNP surface plasmon and their random distribution on the CPE laminar surface, respectively. Theoretical calculations on CuNP/CPE deposits suggest that the interaction between both materials occurs through polyelectrolyte side chains, with a small contribution of its backbone electron density. The CuNP/CPE composite showed antibacterial activity against Gram-positive (Staphylococcus aureus and Enterococcus faecalis) and Gram-negative (Escherichia coli and Salmonella enteritidis) bacteria, mainly attributed to the CuNPs’ effect and, to a lesser extent, to the cationic CPE.

Highly Effective Inactivation of SARS-CoV-2 by Conjugated Polymers and Oligomers

In the present study, we examined the inactivation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by synthetic conjugated polymers and oligomers developed in our laboratories as antimicrobials for bacteria, fungi, and nonenveloped viruses. The results show highly effective light-induced inactivation with several of these oligomers and polymers including irradiation with near-UV and visible light. In the best case, one oligomer induced a 5-log reduction in pfu/mL within 10 min. In general, the oligomers are more active than the polymers; however, the polymers are active with longer wavelength visible irradiation. Although not studied quantitatively, the results show that in the presence of the agents at concentrations similar to those used in the light studies, there is essentially no dark inactivation of the virus. Because three of the five materials/compounds examined are quaternary ammonium derivatives, this study indicates that conventional quaternary ammonium antimicrobials may not be active against SARS-CoV-2. Our results suggest several applications involving the incorporation of these materials in wipes, sprays, masks, and clothing and other personal protection equipment that can be useful in preventing infections and the spreading of this deadly virus and future outbreaks from similar viruses.

Highly Effective Inactivation of SARS-CoV-2 by Conjugated Polymers and Oligomers

The current Covid-19 Pandemic caused by the highly contagious SARS-CoV-2 virus has proven extremely difficult to prevent or control. Currently there are few treatment options and very few long-lasting disinfectants available to prevent the spread. While masks and protective clothing and social distancing may offer some protection, their use has not always halted or slowed the spread. Several vaccines are currently undergoing testing; however there is still a critical need to provide new methods for inactivating the virus before it can spread and infect humans. In the present study we examined the inactivation of SARS-CoV-2 by synthetic conjugated polymers and oligomers developed in our laboratories as antimicrobials for bacteria, fungi and non-enveloped viruses. Our results show that we can obtain highly effective light induced inactivation with several of these oligomers and polymers including irradiation with near-UV and visible light. With both the oligomers and polymers, we can reach several logs of inactivation with relatively short irradiation times. Our results suggest several applications involving the incorporation of these materials in wipes, sprays, masks and clothing and other Personal Protection Equipment (PPE) that can be useful in preventing infections and the spreading of this deadly virus and future outbreaks from similar viruses.

Conformationally tuned antibacterial oligomers target the peptidoglycan of Gram-positive bacteria

The recent rise of antibiotic resistance amongst Staphylococcus aureus (S. aureus) populations has made treating Staph-based infections a global medical challenge. Therapies that specifically target the peptidoglycan layer of S. aureus have emerged as new treatment avenues, towards which bacteria are less likely to develop resistance. While the majority of antibacterial polymers/oligomers have the ability to disrupt bacterial membranes, the design parameters for the enhanced disruption of peptidoglycan outer layer of Gram-positive bacteria remain unclear. Here, the design of oligomeric structures with favorable conformational characteristics for improved disruption of the peptidoglycan outer layer of Gram-positive bacteria is reported. Molecular dynamics simulations were employed to inform the structure design and composition of cationic oligomers displaying collapsed and expanded conformations. The most promising diblock and triblock cationic oligomers were synthesized by photo-induced atom transfer radical polymerization (photo ATRP). Following synthesis, the diblock and triblock oligomers displayed average antibacterial activity of ~99% and ~98% for S. aureus and methicillin-resistant S. aureus (MRSA), respectively, at the highest concentrations tested. Importantly, triblock oligomers with extended conformations showed significantly higher disruption of the peptidoglycan outer layer of S. aureus compared to diblock oligomers with more collapsed conformation, as evidenced by a number of characterization techniques including scanning electron, confocal and atomic force microscopy. This work provides new insight into the structure/property relationship of antibacterial materials and advances the design of functional materials for combating the rise of drug-resistant bacteria.

Quantitative Determination of Dark and Light-Activated Antimicrobial Activity of Poly(Phenylene Ethynylene), Polythiophene, and Oligo(Phenylene Ethynylene) Electrolytes

Much recent effort has been directed toward the development of novel antimicrobial materials able to defeat new and antibiotic resistant pathogens. In this report, we study the efficacy of cationic poly(phenylene ethynylene), polythiophene, and oligo(phenylene ethynylene) electrolytes against laboratory strains of Pseudomonas aeruginosa, Staphylococcus aureus and Staphylococcus epidermidis. The focus of the study is to quantitatively evaluate the speed and extent of dark and light-activated antimicrobial activity. Using cell plating with serial dilutions, we determined that planktonic bacteria suspensions exposed to the antimicrobials (at 10 μg/mL) result in several log kills at 10 min both in the dark and under UV irradiation (360 nm) for all eight synthetic antimicrobials. However, there are significant differences in the ease of killing the different pathogens. In most trials, there is significantly greater killing under light-irradiation, indicating these materials may be used as versatile disinfectants.

Application of Nanoscale Zwitterionic Polyelectrolytes Brush with High Stability and Quantum Yield in Aqueous Solution for Cell Imaging

Cationic and zwitterionic polyelectrolytes are synthesized through atom transfer radical polymerization (ATRP), comprising a polyfluorene backbone with a small fraction of 2,1,3-benzothiadiazole and poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) side chains. Due to higher charge density generated from grafted side chains, two polymers show higher water solubility and higher quantum yield. In comparison with cationic polyelectrolytes, zwitterionic polyelectrolytes are stable over a broad pH range from 1 to 13, even in 1 M NaCl solution. The absence of FRET between zwitterionic polymers and dye-labeled ssDNA indicates their ultralow nonspecific adsorption, while cationic polymer shows much stronger nonspecific interactions. The MTT assay of zwitterionic polymers exhibits their minimal cytotoxicity and potential in long-term clinical application. Most importantly, zwitterionic polymer could be efficiently taken up by cells, whereas cationic polymer stains the surface of cell due to membrane disruption generated from positive charges. The results illustrate that conjugated zwitterionic polymer could serve as a novel type of highly efficient ultralow fouling material with low cytotoxicity for labelling cell or potential biomedical applications.

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%.

Tuning the Potential of Electron Extraction from Microbes with Ferrocene-Containing Conjugated Oligoelectrolytes

Synthetic systems that facilitate electron transport across cellular membranes are of interest in bio-electrochemical technologies such as bio-electrosynthesis, waste water remediation, and microbial fuel cells. The design of second generation redox-active conjugated oligoelectrolytes (COEs) bearing terminal cationic groups and a π-delocalized core capped by two ferrocene units is reported. The two COEs, DVFBO and F₄ -DVFBO, have similar membrane affinity, but fluorination of the core results in a higher oxidation potential (422 ± 5 mV compared to 365 ± 4 mV vs Ag/AgCl for the neutral precursors in chloroform). Concentration-dependent aggregation is suggested by zeta potential measurements and confirmed by cryogenic transmission electron microscopy. When the working electrode potential (E_CA ) is poised below the oxidation potential of the COEs (E_CA = 200 mV) in three-electrode electrochemical cells containing Shewanella oneidensis MR-1, addition of DVFBO and F₄ -DVFBO produces negligible biocurrent enhancement over controls. At E_CA = 365 mV, DVFBO increases steady-state biocurrent by 67 ± 12% relative to controls, while the increase with F₄ -DVFBO is 30 ± 5%. Cyclic voltammetry supports that DVFBO increases catalytic biocurrent and that F₄ -DVFBO has less impact, consistent with their oxidation potentials. Overall, electron transfer from microbial species is modulated via tailoring of the COE redox properties.

A Retrospective: 10 Years of Oligo(phenylene-ethynylene) Electrolytes: Demystifying Nanomaterials

In this retrospective, we first reviewed the synthesis of the oligo(phenylene-ethynylene) electrolytes (OPEs) we created in the past 10 years. Since the general antimicrobial activity of these OPEs had been reported in our previous account in Langmuir, we are focusing only on the unusual spectroscopic and photophysical properties of these OPEs and their complexes with anionic scaffolds and detergents in this Feature Article. We applied classical all-atom MD simulations to study the hydrogen bonding environment in the water surrounding the OPEs with and without detergents present. Our finding is that OPEs could form a unit cluster or unit aggregate with a few oppositely charged detergent molecules, indicating that the photostability and photoreactivity of these OPEs might be considerably altered with important consequences to their activity as antimicrobials and fluorescence-based sensors. Thus, in the following sections, we showed that OPE complexes with detergents exhibit enhanced light-activated biocidal activity compared to either OPE or detergent individually. We also found that similar complexes between certain OPEs and biolipids could be used to construct sensors for the enzyme activity. Finally, the OPEs could covalently bind to microsphere surfaces to make a bactericidal surface, which is simpler and more ordered than the surface grafted from microspheres with polyelectrolytes. In the Conclusions and Prospects section, we briefly summarize the properties of OPEs developed so far and future areas for investigation.

Salt-induced thermochromism of a conjugated polyelectrolyte

We report here the photophysical properties of a water-soluble polythiophene with cationic side-chains in PBS buffer solution.

Biomimetic Light-Harvesting Antenna Based on the Self-Assembly of Conjugated Polyelectrolytes Embedded within Lipid Membranes

Here we report a biomimetic light-harvesting antenna based on negatively charged poly(phenylene ethynylene) conjugated polyelectrolytes assembled within a positively charged lipid membrane scaffold constructed by the lipid 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP). Light harvested by the polymers was transferred via through-space mechanisms to a lipophilic energy acceptor (the cyanine dye DiI) whose effective molar absorption was enhanced by up to 18-fold due to the antenna effect. Absorption amplification of DiI was found to be due primarily to direct energy transfer from polymers. The efficiency of homoenergy transfer among polymers was next probed by the membrane embedding fullerene derivative phenyl-C₆₁-butryic acid methyl ester (PCBM) acting as an electron acceptor. PCBM was able to quench the emission of up to five polymers, consistent with a modest amount of homotransfer. The ability of the membrane to accommodate a high density of polymer donors without self-quenching was crucial to the success of electronic energy harvesting achieved. This work highlights the potential of lipid membranes as a platform to organize light-harvesting molecules on the nanoscale toward achieving efficient energy transfer to a target chromophore/trap.

Antifungal Properties of Cationic Phenylene Ethynylenes and Their Impact on β-Glucan Exposure

Candida species are the cause of many bloodstream infections through contamination of indwelling medical devices. These infections account for a 40% mortality rate, posing a significant risk to immunocompromised patients. Traditional treatments against Candida infections include amphotericin B and various azole treatments. Unfortunately, these treatments are associated with high toxicity, and resistant strains have become more prevalent. As a new frontier, light-activated phenylene ethynylenes have shown promising biocidal activity against Gram-positive and -negative bacterial pathogens, as well as the environmental yeast Saccharomyces cerevisiae In this study, we monitored the viability of Candida species after treatment with a cationic conjugated polymer [poly(p-phenylene ethynylene); PPE] or oligomer ["end-only" oligo(p-phenylene ethynylene); EO-OPE] by flow cytometry in order to explore the antifungal properties of these compounds. The oligomer was found to disrupt Candida albicans yeast membrane integrity independent of light activation, while PPE is able to do so only in the presence of light, allowing for some control as to the manner in which cytotoxic effects are induced. The contrast in killing efficacy between the two compounds is likely related to their size difference and their intrinsic abilities to penetrate the fungal cell wall. Unlike EO-OPE-DABCO (where DABCO is quaternized diazabicyclo[2,2,2]octane), PPE-DABCO displayed a strong propensity to associate with soluble β-glucan, which is expected to inhibit its ability to access and perturb the inner cell membrane of Candida yeast. Furthermore, treatment with PPE-DABCO unmasked Candida albicans β-glucan and increased phagocytosis by Dectin-1-expressing HEK-293 cells. In summary, cationic phenylene ethynylenes show promising biocidal activity against pathogenic Candida yeast cells while also exhibiting immunostimulatory effects.

Recent Advances in Conjugated Polymer Materials for Disease Diagnosis

The extraordinary optical amplification and light-harvesting properties of conjugated polymers impart sensing systems with higher sensitivity, which meets the primary demands of early cancer diagnosis. Recent advances in the detection of DNA methylation and mutation with polyfluorene derivatives based fluorescence resonance energy transfer (FRET) as a means to modulate fluorescent responses attest to the great promise of conjugated polymers as powerful tools for the clinical diagnosis of diseases. To facilitate the ever-changing needs of diagnosis, the development of detection approaches and FRET signal analysis are highlighted in this review. Due to their exceptional brightness, excellent photostability, and low or absent toxicity, conjugated polymers are verified as superior materials for in-vivo imaging, and provide feasibility for future clinical molecular-imaging applications. The integration of conjugated polymers with clinical research has shown profound effects on diagnosis for the early detection of disease-related biomarkers, as well as in-vivo imaging, which leads to a multidisciplinary scientific field with perspectives in both basic research and application issues.

Synthesis and application of a novel poly-l-phenylalanine electroactive macromonomer as matrix for the biosensing of ‘Abused Drug’ model

The synthesis and biosensing application of a novel poly-l-phenylalanine-bearing electroactive macromonomer has been carried out.

Self-Sterilizing, Self-Cleaning Mixed Polymeric Multifunctional Antimicrobial Surfaces

Mitigation of bacterial adhesion and subsequent biofilm formation is quickly becoming a strategy for the prevention of hospital-acquired infections. We demonstrate a basic strategy for surface modification that combines the ability to control attachment by microbes with the ability to inactivate microbes. The surface consists of two active materials: poly(p-phenylene ethynylene)-based polymers, which can inactivate a wide range of microbes and pathogens, and poly(N-isopropylacrylamide)-based polymers, which can switch between an hydrophobic "capture" state and a hydrophilic "release" state. The combination of these materials creates a surface that can both bind microbes in a switchable way and kill surface-bound microbes efficiently. Considerable earlier work with cationic poly(p-phenylene ethynylene) polyelectrolytes has demonstrated and characterized their antimicrobial properties, including the ability to efficiently destroy or deactivate Gram-negative and Gram-positive bacteria, fungi, and viruses. Similarly, much work has shown (1) that surface-polymerized films of poly(N-isopropylacrylamide) are able to switch their surface thermodynamic properties from a swollen, relatively hydrophilic state at low temperature to a condensed, relatively hydrophobic state at higher temperature, and (2) that this switch can control the binding and/or release of microbes to poly(N-isopropylacrylamide) surfaces. The active surfaces described herein were fabricated by first creating a film of biocidal poly(p-phenylene ethynylene) using layer-by-layer methods, and then conferring switchable adhesion by growing poly(N-isopropylacrylamide) through the poly(p-phenylene ethynylene) layer, using surface-attached polymerization initiators. The resulting multifunctional, complex films were then characterized both physically and functionally. We demonstrate that such films kill and subsequently induce widespread release of Gram-negative and Gram-positive bacteria.

Exploiting Conjugated Polyelectrolyte Photophysics toward Monitoring Real-Time Lipid Membrane-Surface Interaction Dynamics at the Single-Particle Level

Herein we report the real-time observation of the interaction dynamics between cationic liposomes flowing in solution and a surface-immobilized charged scaffolding formed by the deposition of conjugated polyanion poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene (MPS-PPV) onto 100-nm-diameter SiO2 nanoparticles (NPs). Contact of the freely floating liposomes with the polymer-coated surfaces led to the formation of supported lipid bilayers (SLBs). The interaction of the incoming liposomes with MPS-PPV adsorbed on individual SiO2 nanoparticles promoted the deaggregation of the polymer conformation and led to large emission intensity enhancements. Single-particle total internal reflection fluorescence microscopy studies exploited this phenomenon as a way to monitor the deformation dynamics of liposomes on surface-immobilized NPs. The MPS-PPV emission enhancement (up to 25-fold) reflected on the extent of membrane contact with the surface of the NP and was correlated with the size of the incoming liposome. The time required for the MPS-PPV emission to reach a maximum (ranging from 400 to 1000 ms) revealed the dynamics of membrane deformation and was also correlated with the liposome size. Cryo-TEM experiments complemented these results by yielding a structural view of the process. Immediately following the mixing of liposomes and NPs the majority of NPs had one or more adsorbed liposomes, yet the presence of a fully formed SLB was rare. Prolonged incubation of liposomes and NPs showed completely formed SLBs on all of the NPs, confirming that the liposomes eventually ruptured to form SLBs. We foresee that the single-particle studies we report herein may be readily extended to study membrane dynamics of other lipids including cellular membranes in live cell studies and to monitor the formation of polymer-cushioned SLBs.

Oligo(p-phenylene ethynylene) Electrolytes: A Novel Molecular Scaffold for Optical Tracking of Amyloids

Finding new optical probes to detect and track amyloid protein aggregates is key to understanding and defeating the myriad of neurodegenerative and other diseases associated with these misfolded proteins. Herein we report that a series of fluorescent, soluble oligo(p-phenylene ethynylene)s (OPEs) are able to detect amyloids in vitro by massive binding-activated superluminescence, with low micromolar affinity and high selectivity for the amyloid conformer. The OPEs track the kinetics of amyloid fibril formation from native hen egg white lysozyme (HEWL) similarly to thioflavin T (ThT), and the dependence of binding affinity on OPE length supports the theory of a linear binding groove. We hypothesize, based on spectral properties, induced circular dichroism, and previous work in analogous systems, that the fluorescence turn-on mechanism is a combination of the reduction of static solvent-mediated quenching at the ethyl ester end groups of the phenylene ethynylene fluorophore and the formation of chiral J-type aggregates templated on the amyloid fibril surface.

Assessing the Sporicidal Activity of Oligo-p-phenylene Ethynylenes and Their Role as Bacillus Germinants

A wide range of oligo-p-phenylene ethynylenes has been shown to exhibit good biocidal activity against both Gram-negative and Gram-positive bacteria. While cell death may occur in the dark, these biocidal compounds are far more effective in the light as a result of their ability to sensitize the production of cell-damaging reactive oxygen species. In these studies, the interactions of a specific cationic oligo-p-phenylene ethynylene with spore-forming Bacillus atrophaeus and Bacillus anthracis Sterne have been investigated. Flow cytometry assays are used to rapidly monitor cell death as well as spore germination. This compound effectively killed Bacillus anthracis Sterne vegetative cells (over 4 log reduction), presumably by severe perturbations of the bacterial cell wall and cytoplasmic membrane, while also acting as an effective spore germinant in the dark. While 2 log reduction of B. anthracis Sterne spores was observed, it is hypothesized that further killing could be achieved through enhanced germination.

Antimicrobial and bacteria-releasing multifunctional surfaces: oligo (p-phenylene-ethynylene)/poly (N-isopropylacrylamide) films deposited by RIR-MAPLE

Antimicrobial oligo (p-phenylene-ethynylene) (OPE) films have previously been demonstrated to show effective ultraviolet A (UVA) light-induced biocidal activity; however, a serious problem arises from the accumulation of dead bacteria and debris on the films that limits their effectiveness and application. In this work, we address this challenge by incorporating thermally-responsive poly (N-isopropylacrylamide) (PNIPAAm), which provides on-demand bacteria-releasing functionality. Multifunctional surfaces comprising blended films of OPE and PNIPAAm were deposited on substrates by resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) using a sequential co-deposition mode. In this way, RIR-MAPLE enabled the deposition of multifunctional films with surface properties and film functionality that can be tailored, precisely and systematically, by controlling the chemical composition of the deposited film. The surface properties of these films were characterized by UV-visible (UV-vis) absorbance spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and water contact angle measurements. The interactions between bacteria and the deposited films were tested using two model bacteria: Escherichia coli K12 (Gram-negative) and Staphylococcus epidermidis (Gram-positive). The antimicrobial and bacteria-release properties of the blended films were controlled by varying the OPE/PNIPAAm ratio in the RIR-MAPLE emulsion target, providing an easy way to optimize the multifunctional surface. The OPE/PNIPAAm blended films with optimized composition killed a majority of attached E. coli bacteria at 37 °C and under UVA exposure, and the dead bacteria were then removed from the films simply by rinsing with water at 25 °C.

Pendant ionic groups of conjugated oligoelectrolytes govern their ability to intercalate into microbial membranes

The ionic groups of lipid membrane intercalating conjugated oligoelectrolytes affect their interaction with E. coli and application in microbial fuel cells.

Interaction of anionic phenylene ethynylene polymers with lipids: from membrane embedding to liposome fusion

Here we report spectroscopic studies on the interaction of negatively charged, amphiphilic polyphenylene ethynylene (PPE) polymers with liposomes prepared either from negative, positive or zwitterionic lipids. Emission spectra of PPEs of 7 and 49 average repeat units bearing carboxylate terminated side chains showed that the polymer embeds within positively charged lipids where it exists as free chains. No interaction was observed between PPEs and negatively charged lipids. Here the polymer remained aggregated giving rise to broad emission spectra characteristic of the aggregate species. In zwitterionic lipids, we observed that the majority of the polymer remained aggregated yet a small fraction readily embedded within the membrane. Titration experiments revealed that saturation of zwitterionic lipids with polymer typically occurred at a polymer repeat unit to lipid mole ratio close to 0.05. No further membrane embedding was observed above that point. For liposomes prepared from positively charged lipids, saturation was observed at a PPE repeat unit to lipid mole ratio of ∼0.1 and liposome precipitation was observed above this point. FRET studies showed that precipitation was preceded by lipid mixing and liposome fusion induced by the PPEs. This behavior was prominent for the longer polymer and negligible for the shorter polymer at a repeat unit to lipid mole ratio of 0.05. We postulate that fusion is the consequence of membrane destabilization whereby the longer polymer gives rise to more extensive membrane deformation than the shorter polymer.

Synergism between airborne singlet oxygen and a trisubstituted olefin sulfonate for the inactivation of bacteria

The reactivity of a trisubstituted alkene surfactant (8-methylnon-7-ene-1 sulfonate, 1) to airborne singlet oxygen in a solution containing E. coli was examined. Surfactant 1 was prepared by a Strecker-type reaction of 9-bromo-2-methylnon-2-ene with sodium sulfite. Submicellar concentrations of 1 were used that reacted with singlet oxygen by an "ene" reaction to yield two hydroperoxides (7-hydroperoxy-8-methylnon-8-ene-1 sulfonate and (E)-8-hydroperoxy-8-methylnon-6-ene-1 sulfonate) in a 4:1 ratio. Exchanging the H2O solution for D2O where the lifetime of solution-phase singlet oxygen increases by 20-fold led to an ∼2-fold increase in the yield of hydroperoxides pointing to surface activity of singlet oxygen with the surfactant in a partially solvated state. In this airborne singlet oxygen reaction, E. coli inactivation was monitored in the presence and absence of 1 and by a LIVE/DEAD cell permeabilization assay. It was shown that the surfactant has low dark toxicity with respect to the bacteria, but in the presence of airborne singlet oxygen, it produces a synergistic enhancement of the bacterial inactivation. How the ene-derived surfactant hydroperoxides can provoke (1)O2 toxicity and be of general utility is discussed.

Synthesis, characterization, and biological affinity of a near-infrared-emitting conjugated oligoelectrolyte

A near-IR-emitting conjugated oligoelectrolyte (COE), ZCOE, was synthesized, and its photophysical features were characterized. The biological affinity of ZCOE is compared to that of an established lipid-membrane-intercalating COE, DSSN+, which has blue-shifted optical properties making it compatible for tracking preferential sites of accumulation. ZCOE exhibits diffuse staining of E. coli cells, whereas it displays internal staining of select yeast cells which also show propidium iodide staining, indicating ZCOE is a “dead” stain for this organism. Staining of mammalian cells reveals complete internalization of ZCOE through endocytosis, as supported by colocalization with LysoTracker and late endosome markers. In all cases DSSN+ persists in the outer membranes, most likely due to its chemical structure more closely resembling a lipid bilayer.

PHACOS, a functionalized bacterial polyester with bactericidal activity against methicillin-resistant Staphylococcus aureus

Biomaterial-associated infections represent a significant clinical problem, and treatment of these microbial infections is becoming troublesome due to the increasing number of antibiotic-resistant strains. Here, we report a naturally functionalized bacterial polyhydroxyalkanoate (PHACOS) with antibacterial properties. We demonstrate that PHACOS selectively and efficiently inhibits the growth of methicillin-resistant Staphylococcus aureus (MRSA) both in vitro and in vivo. This ability has been ascribed to the functionalized side chains containing thioester groups. Significantly less (3.2-fold) biofilm formation of S. aureus was detected on PHACOS compared to biofilms formed on control poly(3-hydroxyoctanoate-co-hydroxyhexanoate) and poly(ethylene terephthalate), but no differences were observed in bacterial adhesion among these polymers. PHACOS elicited minimal cytotoxic and inflammatory effects on murine macrophages and supported normal fibroblast adhesion. In vivo fluorescence imaging demonstrated minimal inflammation and excellent antibacterial activity for PHACOS compared to controls in an in vivo model of implant-associated infection. Additionally, reductions in neutrophils and macrophages in the vicinity of sterile PHACOS compared to sterile PHO implant were observed by immunohistochemistry. Moreover, a similar percentage of inflammatory cells was found in the tissue surrounding sterile PHACOS and S. aureus pre-colonized PHACOS implants, and these levels were significantly lower than S. aureus pre-colonized control polymers. These findings support a contact active surface mode of antibacterial action for PHACOS and establish this functionalized polyhydroxyalkanoate as an infection-resistant biomaterial.