Conjugated polyelectrolyte-grafted silica microspheres

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.

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.

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.

Structure of Rigid Polymers Confined to Nanoparticles: Molecular Dynamics Simulations Insight

Nanoparticles (NPs) grafted with organic layers form hybrids able to retain their unique properties through integration into the mesoscopic scale. The organic layer structure and response often determine the functionality of the hybrids on the mesoscopic length scale. Using molecular dynamics (MD) simulations, we probe the conformation of luminescent rigid polymers, dialkyl poly(p-phenylene ethynylene)s (PPE), end-grafted onto a silica nanoparticle in different solvents as the molecular weights and polymer coverages are varied. We find that, in contrast to NP-grafted flexible polymers, the chains are fully extended independent of the solvent. In toluene and decane, which are good solvents, the grafted PPEs chains assume a similar conformation to that observed in dilute solutions. In water, which is a poor solvent for the PPEs, the polymer chains form one large cluster but remain extended. The radial distribution of the chains around the core of the nanoparticle is homogeneous in good solvents, whereas in poor solvents clusters are formed independent of molecular weights and coverages. The clustering is distinctively different from the response of grafted flexible and semiflexible polymers.

Nanohybrid conjugated polyelectrolytes: highly photostable and ultrabright nanoparticles

We present a general and straightforward one-step approach to enhance the photophysical properties of conjugated polyelectrolytes. Upon complexation with an amphiphilic polymer (polyvinylpyrrolidone), an anionic conjugated polyelectrolyte (poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene]) was prepared into small nanoparticles with exceptional photostability and brightness. The polymer fluorescence intensity was enhanced by 23 -fold and could be easily tuned by changing the order of addition. Single molecule experiments revealed a complete suppression of blinking. In addition, after only losing 18% of the original intensity, a remarkable amount of photons were emitted per particle (∼10(9), on average). This number is many folds greater than popular organic fluorescent dyes. We believe that an intimate contact between the two polymers is shielding the conjugated polyelectrolyte from the destructive photooxidation. The prepared nanohybrid particles will prove instrumental in single particle based fluorescent assays and can serve as a probe for the current state-of-the-art bioimaging fluorescence techniques.

‘Switch-on’ DNA sensor based on poly (p-phenylene vinylenes) bound tentacle probes

The development of highly sensitive and selective DNA sensors has fuelled applications in a wide range of fields including medical diagnostics, forensics, biodefense, food contamination and environment monitoring. We demonstrate a novel superquenching based DNA sensor with “switch-on” readout using poly(p-phenylenevinylene) (PPV) coated magnetic beads (PPV-MagSi) and quencher functionalized tentacle probes (TP). The sensor design utilizes signal amplification properties of PPV and cooperativity of TPs to monitor hybridization of target oligonucleotides (ONs). The switch-on sensor exhibits excellent sensitivity and selectively discriminates mismatches in the target DNA sequence. Two novel anionic PPVs – poly (6,6′-((2-methyl-5-((E)-4-((E)-prop-1-en-1-yl)styryl)-1,4-phenylene)-bis(oxy) dihexanoic acid) (PMDH) and poly (6,6′-((2-((E)-2,5-bis(2-methoxyethoxy)-4-((E)-prop-1-en-1-yl)styryl)-5-methyl-1,4-phenylene)-bis-(oxy)) di-hexanoic acid) (PDMonoG) were tested and compared against each other as part of the sensor design. The employed hairpin TPs possess further advantages of avoiding labelling of target ON, increased selectivity and sensitivity; faster assay time, and capability of magnetically controlled deployment and separation of PPV-MagSi beads.

Highly functionalisable polythiophene phenylenes

The synthesis and properties of novel conducting polymer monomers, and their polymers, based on poly(thiophene phenylenes) (PThP) is described.

Facile preparation of polydiacetylene-based uniform porous fluorescent microspheres for potential immunoassay applications

Fluorescent microspheres are prepared by loading PDA onto the substrate microspheresviaa self-assembled vesicle precursor pathway.

Synthesis, optical properties and explosive sensing performances of a series of novel π-conjugated aromatic end-capped oligothiophenes

Four novel terthiophene (3T) derivatives, have been synthesized by employing Grignard coupling reaction via end-capping of naphthyl (NA) or pyrenyl (Py) unit to the one or two ends of 3T. It has been shown that both increasing electron donating strength and extending conjugation are effective approaches to improve the photochemical stability of the oligothiophene. Fluorescence studies demonstrated that the emission of the 3T derivatives is sensitive to the presence of some important nitro-containing explosives in their ethanol solution, in particular, 2,4,6-trinitrophenol (PA) and 3,5-dinitro-2,6-bispicrylamino pyridine (PYX). As an example, the detection limits of 4 to PA and PYX were determined to be 6.21 × 10(-7)mol/L and 8.95 × 10(-7)mol/L, respectively. Based on the discovery, a colorimetric detection method has been developed. The sensitive and selective response of the modified 3T to the explosives have been tentatively attributed to the adsorptive affinity of the compounds to the explosives, and to the higher probability of the electron transfer from the electron-rich 3T derivatives to the electron-poor nitro-containing explosives. No doubt, present study broadens the family of fluorophores which may be employed for the development of fluorescent sensors.

Conjugated-polyelectrolyte-grafted cotton fibers act as "micro flypaper" for the removal and destruction of bacteria

We demonstrate herein a method for chemically modifying cotton fibers and cotton-containing fabric with a light-activated, cationic phenylene-ethynylene (PPE-DABCO) conjugated polyelectrolyte biocide. When challenged with Pseudomonas aeruginosa and Bacillus atropheaus vegetative cells from liquid suspension, light-activated PPE-DABCO effects 1.2 and 8 log, respectively, losses in viability of the exposed bacteria. These results suggest that conjugated polyelectrolytes retain their activity when grafted to fabrics, showing promise for use in settings where antimicrobial textiles are needed.

Rapid evaluation of the antibacterial activity of arylene-ethynylene compounds

A series of oligo(arylene-ethynylene) (1-3 repeat units) compounds functionalized with quaternary ammonium groups was screened for their antibacterial activity in the dark and with activation by long-wavelength (365 nm) UV irradiation. Several of these compounds have effective bactericidal activity (>99.9% killing) at concentrations between 0.01 and 10 μg/mL. Our approach uses flow cytometry to rapidly screen and evaluate the susceptibility of bacterial populations. The rapidity, high information content, and accuracy of this approach make it an extremely valuable method for the study of antibacterial compounds.

Light and dark-activated biocidal activity of conjugated polyelectrolytes

This Spotlight on Applications provides an overview of a research program that has focused on the development and mechanistic study of cationic conjugated polyelectrolytes (CPEs) that function as light- and dark-active biocidal agents. Investigation has centered on poly-(phenylene ethynylene) (PPE) type conjugated polymers that are functionalized with cationic quaternary ammonium solubilizing groups. These polymers are found to interact strongly with Gram-positive and Gram-negative bacteria, and upon illumination with near-UV and visible light act to rapidly kill the bacteria. Mechanistic studies suggest that the cationic PPE-type polymers efficiently sensitize singlet oxygen ((1)O(2)), and this cytotoxic agent is responsible for initiating the sequence of events that lead to light-activated bacterial killing. Specific CPEs also exhibit dark-active antimicrobial activity, and this is believed to arise due to interactions between the cationic/lipophilic polymers and the negatively charged outer membrane characteristic of Gram-negative bacteria. Specific results are shown where a cationic CPE with a degree of polymerization of 49 exhibits pronounced light-activated killing of E. coli when present in the cell suspension at a concentration of 1 μg mL(-1).

Synthesis, self-assembly, and photophysical properties of cationic oligo(p-phenyleneethynylene)s

Three series of cationic oligo p-phenyleneethynylenes (OPEs) have been synthesized to study their structure-property relationships and gain insights into the transition from molecular to macromolecular properties. The absorbance maxima and molar extinction coefficients in all three sets increase with increasing number of repeat units; however, the increase in λ(max) between the oligomers having 2 and 3 repeat units is very small, and the oligomer having 3 repeat units shows virtually the same spectra as a p-phenyleneethynylene polymer having 49 repeat units. A computational study of the oligomers using density functional theory calculations indicates that while the simplest oligomers (OPE-1) are fully conjugated, the larger oligomers are nonplanar and the limiting "segment chromophore" may be confined to a near-planar segment extending over three or four phenyl rings. Several of the OPEs self-assemble on anionic "scaffolds", with pronounced changes in absorption and fluorescence. Both experimental and computational results suggest that the planarization of discrete conjugated segments along the phenylene-ethynylene backbone is predominantly responsible for the photophysical characteristics of the assemblies formed from the larger oligomers. The striking differences in fluorescence between methanol and water are attributed to reversible nucleophilic attack of structured interfacial water on the excited singlet state.

Silica hybrid particles with nanometre polymer shells and their influence on the toughening of polypropylene

Colloidal silica particles were synthesized by the sol-gel process and then modified with 3-methacryloxypropyltrimethoxysilane (γ-MPS) to induce vinyl groups on the surface of the silica particles. By means of in situ emulsion copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA), a series of core-shell silica hybrid particles with nanometre poly(MMA-co-BA) shells were fabricated, which were subsequently compounded with isotactic polypropylene (PP) in the molten state. Upon increasing the feed silica : monomer ratio from 1 : 1 to 4 : 1, the poly(MMA-co-BA) shell thickness on the silica core decreased from 50 nm to 10 nm. Owing to the existence of the nanometre poly(MMA-co-BA) shells, the silica hybrid particles were monodispersed in the PP matrix, causing homogeneous debonding at the PP/silica interface, followed by plastic void expansion and matrix shear yielding during impact fracture. These deformation mechanisms greatly toughened the PP-silica composites. A critical shell thickness of poly(MMA-co-BA) was needed to achieve optimal mechanical properties. That is, when the polymer shell thickness was 15 nm, compared to pure PP, the impact toughness of the PP-silica composite was more than doubled with little degradation of tensile strength.

Nanoscale control over phase separation in conjugated polymer blends using mesoporous silica spheres

A method of preparing blended conjugated polymer microparticles using mesoporous silica spheres is described. Poly(3,4-ethylenedioxythiophene) (PEDOT) was blended with poly(furfuryl alcohol) (PFA) by a sequential infiltration-polymerization approach. The materials were evaluated by both scanning and transmission electron microscopy and are shown to retain the overall spherical structure of the silica template. The filling of the mesopores and the polymer distribution within individual particles were determined by a combination of energy-dispersive X-ray microanalysis, X-ray photoelectron spectroscopy, and nitrogen adsorption. The results suggest that when PEDOT is added to the silica host, followed by PFA, the phase separation of the two immiscible polymers is constrained by the dimensions of the silica mesopores, ensuring nanoscale contact between the two phases. The silica template can be removed by etching with 25% hydrofluoric acid, leaving behind a blended polymer microparticle. The etched microparticles exhibit macroporous morphologies different from that of pure PEDOT particles prepared by a similar route. The blended microparticles also appear to undergo limited phase separation; no evidence for distinct polymer domains was observed. Conductivity measurements indicate that the blended particles are above the percolation threshold and support the conclusion that the phase domains are extremely small. Importantly, when PFA is added to the host first, followed by PEDOT, there is a striking difference to the final composition and morphology of the particles. This reversal of the blending order results in a more amorphous, phase-separated material. These results demonstrate the preparation of conjugated polymer blends with engineered nanoscale phase separation and may allow for future improvements in organic device architecture and performance.

Light and dark biocidal activity of cationic poly(arylene ethynylene) conjugated polyelectrolytes

In this paper we report a study of cationic poly(arylene ethynylene) conjugated polyelectrolytes. The objective of the study was to compare the behavior of a polymer where a thiophene has replaced a phenyl ring in poly(phenylene ethynylene) polycations (PPE) previously investigated. Properties of solution phase and physisorbed suspensions of the polymer on microspheres were investigated. The photophysical properties of the polymer are evaluated and used to understand the striking differences in biocidal activity compared to the PPE polymers previously examined. The principal findings are that the thiophene polymer has remarkable dark biocidal activity against Pseudomonas aeruginosa strain PAO1 but very little light-activated activity. The low light-activated biocidal activity of the thiophene polymer is attributed to a highly aggregated state of the polymer in aqueous solutions and on microspheres as a physisorbed coating. This results in low triplet yields and a very poor sensitization of singlet oxygen and other reactive oxygen intermediates. The highly effective dark biocidal activity of the thiophene-containing polymers is attributed to its high lipophilicity and the presence of accessible quaternary ammonium groups. The difference in behavior among the polymers compared provides insights into the mechanism of the dark process and indicates that aggregation of polymer can reduce light activated biocidal activity by suppressing singlet oxygen generation.

Synthesis, self-assembly, and photophysical behavior of oligo phenylene ethynylenes: from molecular to supramolecular properties

A pair of cationic phenylene ethynylene oligomers (OPEs) have been synthesized, and their optical properties have been studied in solution with and without added scaffold materials, including carboxymethylcellulose, carboxymethylamylose, and Laponite. The OPEs are strongly fluorescent in methanol solution, but in water, the fluorescence yield is suppressed. The addition of scaffolds to aqueous solutions of OPEs leads to a red shift in the absorption and in most cases a significant increase in the fluorescence quantum yield. The effects most likely arise because of template-induced formation of linear J-dimers or possibly because of planarization, which give rise to an effective increase in the conjugation length of OPEs.

Light-induced biocidal action of conjugated polyelectrolytes supported on colloids

A series of water soluble, cationic conjugated polyelectrolytes (CPEs) with backbones based on a poly(phenylene ethynylene) repeat unit structure and tetraakylammonium side groups exhibit a profound light-induced biocidal effect. The present study examines the biocidal activity of the CPEs, correlating this activity with the photophysical properties of the polymers. The photophysical properties of the CPEs are studied in solution, and the results demonstrate that direct excitation produces a triplet excited-state in moderate yield, and the triplet is shown to be effective at sensitizing the production of singlet oxygen. Using the polymers in a format where they are physisorbed or covalently grafted to the surface of colloidal silica particles (5 and 30 microm diameter), we demonstrate that they exhibit light-activated biocidal activity, effectively killing Cobetia marina and Pseudomonas aeruginosa. The light-induced biocidal activity is also correlated with a requirement for oxygen suggesting that interfacial generation of singlet oxygen is the crucial step in the light-induced biocidal activity.

Conjugated polyelectrolyte supported bead based assays for phospholipase A2 activity

A fluorescence based assay for human serum-derived phospholipase activity has been developed in which cationic conjugated polyelectrolytes are supported on silica microspheres. The polymer-coated beads are overcoated with an anionic phospholipid (1,2-dimyristoyl-sn-glycero-3-[phospho- rac-(1-glycerol)) (DMPG) to provide "lipobeads" that serve as a sensor for PLA2. The lipid serves a dual role as a substrate for PLA2 and an agent to attenuate quenching of the polymer fluorescence by the external electron transfer quencher 9,10-anthraquinone-2,6-disulfonic acid (AQS). In this case quenching of the polymer fluorescence by AQS increases as the PLA2 digests the lipid. The lipid can also be used itself as a quencher and substrate by employing a small amount of energy transfer quencher substituted lipid in the DMPG. In this case the fluorescence of the polymer is quenched when the lipid layer is intact; as the enzyme digests the lipid, the fluorescence of the polymer is restored. The sensing of PLA2 activity has been studied both by monitoring fluorescence changes in a multiwell plate reader and by flow cytometry. The assay exhibits good sensitivity with EC50 values in the nanomolar range.