Porphyrin Polymers Bearing N,N'-Ethylene Crosslinkers as Photosensitizers against Bacteria

The appearance of microbes resistant to antibiotics requires the development of alternative therapies for the treatment of infectious diseases. In this work two polymers, PTPPF₁₆-EDA and PZnTPPF₁₆-EDA, were synthesized by the nucleophilic aromatic substitution of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin and its Zn(II) complex with ethylenediamine, respectively. In these structures, the tetrapyrrolic macrocycles were N,N'-ethylene crosslinked, which gives them greater mobility. The absorption spectra of the polymers showed a bathochromic shift of the Soret band of ~10 nm with respect to the monomers. This effect was also found in the red fluorescence emission peaks. Furthermore, both polymeric materials produced singlet molecular oxygen with high quantum yields. In addition, they were capable of generating superoxide anion radicals. Photodynamic inactivation sensitized by these polymers was tested in Staphylococcus aureus and Escherichia coli bacteria. A decrease in cell viability greater than 7 log (99.9999%) was observed in S. aureus incubated with 0.5 μM photosensitizer upon 30 min of irradiation. Under these conditions, a low inactivation of E. coli (0.5 log) was found. However, when the cells were treated with KI, the elimination of the Gram-negative bacteria was achieved. Therefore, these polymeric structures are interesting antimicrobial photosensitizing materials for the inactivation of pathogens.

Light-Induced Anti-Bacterial Effect Against Staphylococcus aureus of Porphyrin Covalently Bonded to a Polyethylene Terephthalate Surface

Antimicrobial photodynamic inactivation represents a promising and potentially greener alternative to conventional antimicrobials, and a solution for multidrug-resistant strains. The current study reports the development and characterization of tetra-substituted diazirine porphyrin covalently bonded to polyethylene terephthalate (PET) and its use as an antimicrobial surface. The diazirine moiety on the porphyrin was activated using a temperature of 120 °C, which initiated a C-H insertion mechanism that irreversibly functionalized the PET surface. Activation of the surface with white LED light in phosphate-buffered saline (PBS) led to singlet oxygen generation, which was detected via the degradation of 9,10-anthracenediylbis(methylene)dimalonic acid (ADMA) over time. The bactericidal effect of the ¹O₂-producing surface against Staphylococcus aureus was determined qualitatively and quantitatively. The growth of the pathogen beneath porphyrin-functionalized PET coupons was reduced; moreover, the PET coupons resulted in a 1.76-log reduction in cell counts after exposure to white LED light for 6 h. This is a promising material and platform for the development of safer antimicrobial surfaces, with applications in healthcare, food packaging, marine surfaces, and other surfaces in the environment.

Antimicrobial Photodynamic Coatings Reduce the Microbial Burden on Environmental Surfaces in Public Transportation—A Field Study in Buses

Millions of people use public transportation daily worldwide and frequently touch surfaces, thereby producing a reservoir of microorganisms on surfaces increasing the risk of transmission. Constant occupation makes sufficient cleaning difficult to achieve. Thus, an autonomous, permanent, antimicrobial coating (AMC) could keep down the microbial burden on such surfaces. A photodynamic AMC was applied to frequently touched surfaces in buses. The microbial burden (colony forming units, cfu) was determined weekly and compared to equivalent surfaces in buses without AMC (references). The microbial burden ranged from 0–209 cfu/cm² on references and from 0–54 cfu/cm² on AMC. The means were 13.4 ± 29.6 cfu/cm² on references and 4.5 ± 8.4 cfu/cm² on AMC (p < 0.001). The difference in microbial burden on AMC and references was almost constant throughout the study. Considering a hygiene benchmark of 5 cfu/cm², the data yield an absolute risk reduction of 22.6% and a relative risk reduction of 50.7%. In conclusion, photodynamic AMC kept down the microbial burden, reducing the risk of transmission of microorganisms. AMC permanently and autonomously contributes to hygienic conditions on surfaces in public transportation. Photodynamic AMC therefore are suitable for reducing the microbial load and closing hygiene gaps in public transportation.

Antimicrobial coatings for environmental surfaces in hospitals: a potential new pillar for prevention strategies in hygiene

Recent reports provide evidence that contaminated healthcare environments represent major sources for the acquisition and transmission of pathogens. Antimicrobial coatings (AMC) may permanently and autonomously reduce the contamination of such environmental surfaces complementing standard hygiene procedures. This review provides an overview of the current status of AMC and the demands to enable a rational application of AMC in health care settings. Firstly, a suitable laboratory test norm is required that adequately quantifies the efficacy of AMC. In particular, the frequently used wet testing (e.g. ISO 22196) must be replaced by testing under realistic, dry surface conditions. Secondly, field studies should be mandatory to provide evidence for antimicrobial efficacy under real-life conditions. The antimicrobial efficacy should be correlated to the rate of nosocomial transmission at least. Thirdly, the respective AMC technology should not add additional bacterial resistance development induced by the biocidal agents and co- or cross-resistance with antibiotic substances. Lastly, the biocidal substances used in AMC should be safe for humans and the environment. These measures should help to achieve a broader acceptance for AMC in healthcare settings and beyond. Technologies like the photodynamic approach already fulfil most of these AMC requirements.

Porphyrin-Schiff Base Conjugates Bearing Basic Amino Groups as Antimicrobial Phototherapeutic Agents

New porphyrin–Schiff base conjugates bearing one (6) and two (7) basic amino groups were synthesized by condensation between tetrapyrrolic macrocycle-containing amine functions and 4-(3-(N,N-dimethylamino)propoxy)benzaldehyde. This approach allowed us to easily obtain porphyrins substituted by positive charge precursor groups in aqueous media. These compounds showed the typical Soret and four Q absorption bands with red fluorescence emission (Φ_F ~ 0.12) in N,N-dimethylformamide. Porphyrins 6 and 7 photosensitized the generation of O₂(¹Δ_g) (Φ_Δ ~ 0.44) and the photo-oxidation of L-tryptophan. The decomposition of this amino acid was mainly mediated by a type II photoprocess. Moreover, the addition of KI strongly quenched the photodynamic action through a reaction with O₂(¹Δ_g) to produce iodine. The photodynamic inactivation capacity induced by porphyrins 6 and 7 was evaluated in Staphylococcus aureus, Escherichia coli, and Candida albicans. Furthermore, the photoinactivation of these microorganisms was improved using potentiation with iodide anions. These porphyrins containing basic aliphatic amino groups can be protonated in biological systems, which provides an amphiphilic character to the tetrapyrrolic macrocycle. This effect allows one to increase the interaction with the cell wall, thus improving photocytotoxic activity against microorganisms.

Antimicrobial Photodynamic Inactivation Using Topical and Superhydrophobic Sensitizer Techniques: A Perspective from Diffusion in Biofilms†

This review describes nanoparticle and dye diffusion in bacterial biofilms in the context of antimicrobial photodynamic inactivation (aPDI). aPDI requires the diffusion of a photosensitizer (Sens) into the biofilm and subsequent photoactivation of oxygen for the generation of reactive oxygen species (ROS) that inactivate microbes. Molecular diffusion in biofilms has been long investigated, whereas this review is intended to draw a logical link between diffusion in biofilms and ROS, a combination that leads to the current state of aPDI and superhydrophobic aPDI (SH-aPDI). This review should be of interest to photochemists, photobiologists and researchers in material and antimicrobial sciences as is ties together conventional aPDI with the emerging subject of SH-aPDI.

Penetration of Singlet Oxygen into Films with Oxygen Permeability Coefficient Close to that of Skin

Although its antiviral and antibacterial functions help prevent infection, singlet oxygen (¹ O₂ )-which is generated by the action of light on an endogenous photosensitizer-is cytotoxic. In the present study, we investigated the ability of ¹ O₂ -generated by the action of visible light on a photosensitizer-to penetrate skin. We used two polymer films with oxygen permeability coefficients similar to that of skin-i.e. cellulose acetate (CA) and ethyl cellulose (EC). Both films contained 1,3-diphenylisobenzofuran (DPBF), which was used as an ¹ O₂ probe. ¹ O₂ generated externally did not permeate the films by mere contact. Therefore, we conclude that the potential for ¹ O₂ to penetrate the skin is very low, and films that generate ¹ O₂ are safe and useful for preventing infections by contact. We also proved that ¹ O₂ can move between the layers of integrated polymer films when they are joined together.

Bactericidal efficiency of porphyrin systems

Photodynamic Inactivation is an innovative technique used to combat bacterial and viral infections which involves the use of photosensitizing agents along with light to generate cytotoxic reactive oxygen species able to kill bacteria and viruses. In the first section of this minireview, porphyrin-based fluorophores are shown to be remarkable dye candidates for PDI (photodynamic inactivation) applications. The second section is dedicated to the description of porphyrin-based antimicrobial materials and their potentialities for industrial applications such as in food packaging or antimicrobial medical devices and hygiene. Finally, the failings and perspectives of PDI are analyzed to demonstrate how the PDI technique could be an efficient and ecologically friendly antimicrobial technique.

A novel tricationic fullerene C60 as broad-spectrum antimicrobial photosensitizer: mechanisms of action and potentiation with potassium iodide

A novel amphiphilic photosensitizing agent based on a tricationic fullerene C₆₀ (DMC₆₀³⁺) was efficiently synthesized from its non-charged analogue MMC₆₀. These fullerenes presented strong UV absorptions, with a broad range of less intense absorption up to 710 nm. Both compounds showed low fluorescence emission and were able to photosensitize the production of reactive oxygen species. Furthermore, photodecomposition of L-tryptophan sensitized by both fullerenes indicated an involvement of type II pathway. DMC₆₀³⁺ was an effective agent to produce the photodynamic inactivation (PDI) of Staphylococcus aureus, Escherichia coli and Candida albicans. Mechanistic insight indicated that the photodynamic action sensitized by DMC₆₀³⁺ was mainly mediated by both photoprocesses in bacteria, while a greater preponderance of the type II pathway was found in C. albicans. In presence of potassium iodide, a potentiation of PDI was observed due to the formation of reactive iodine species. Therefore, the amphiphilic DMC₆₀³⁺ can be used as an effective potential broad-spectrum antimicrobial photosensitizer.

Staphylococcus aureus biofilm eradication by the synergistic effect exerted by PEG-coated silicon dots immobilized in silica films and light irradiation

Immobilization of PEG-covered silicon dots, PEGSiDs, on glass substrates was performed following a simple strategy involving particle embedding by a sol-gel process forming a silica film on glass slides. The obtained films, denoted as fSiO _x -PEGSiD, constitute a water-wettable, strongly supported, photoluminescent glass coating. The films showed high capacity for photosensitizing singlet oxygen (¹O₂) in the UVA when immersed in water. Staphylococcus aureus colonies formed on fSiO _x -PEGSiDs modified glasses revealed the inhibition of bacterial adhesion and bacterial growth leading to the formation of loosely-packed and smaller S. aureus colonies. Upon 350 nm light irradiation of the biofilmed fSiO _x -PEGSiDs -modified glasses, S. aureus growth was inhibited and bacteria killed reducing the number of living bacteria by three orders of magnitude. Eradication of attached bacteria was achieved by the synergistic effect exerted by a less adherent fSiO _x -PEGSiDs surface that inhibits biofilm formation and the ability of the surface to photosensitize ¹O₂ to kill bacteria.

A simple, inexpensive method for gas-phase singlet oxygen generation from sensitizer-impregnated filters: Potential application to bacteria/virus inactivation and pollutant degradation

Airborne infectious diseases such as the new Coronavirus 2019 (COVID-19) pose serious threat to human health. Indoor air pollution is a problem of global environmental concern as well. Singlet oxygen (¹O₂) is a reactive oxygen species that plays important role in bacteria/virus inactivation and pollutant degradation. In this study, we found that commercially available filters typically deployed in air purifier and air conditioning units, when impregnated with Rose Bengal (RB) as a ¹O₂ sensitizer, can be used for heterogeneous gas-phase generation of ¹O₂. It was confirmed that irradiation of the RB filter under oxygen gas stream produced ¹O₂, which was measured using furfuryl alcohol trapping method followed by HPLC analysis. It was also observed that the amount of ¹O₂ generated increases as the light intensity increased. Similarly, the sensitizer loading also positively influenced the ¹O₂ generation. The heterogeneous gas-phase generation of ¹O₂ can find potential applications in air purifier and air conditioning units for the purpose of bacteria/virus inactivation and/or pollutant degradation thereby improving indoor air quality.

Nanoscale integration of porphyrin in GroEL protein cage: Photophysical and photochemical investigation

In this paper, we introduce a new type of functional, supramolecular porphyrin conjugate created using the bacterial GroEL protein cage based on non-specific hydrophobic interaction. The synthesis, structure and property of the porphyrin conjugate were characterized by dynamic light scattering, UV-vis spectroscopy and fluorescence spectroscopy. We observed that the model zinc-tetraphenylporphyrin (Zn-TPP) with high hydrophobicity can be well-dispersed in aqueous solutions with the aid of GroEL open chamber, which is known to be a favorable nanocompartment for aggregation-prone molecules. The maximal encapsulation efficiency of Zn-TPP in GroEL was determined to be ~98%. It is further seen that the constructed double Zn-TPP-GroEL complex exhibited good photocatalytic activity in the model reactions of the production of singlet oxygen and the reduction of methyl viologen under illumination with visible light. Moreover, we found that GroEL can significantly improve the photostability of Zn-TPP molecules as a result of nanoscale assembly within its hydrophobic chamber. Hence enhanced water solubility and photostability of Zn-TPP, which are considered as the first two hurdles for the wide usage of porphyrins, were achieved simultaneously by the development of GroEL cage as a building block. Supramolecular nanostructures formed from porphyrins (or related molecules) and GroEL for photocatalysis would greatly simplify applications of such structures.

Imprinting Pentaphyrin on Conductive Electropolymerized Dipyrromethane Films: A New Strategy towards the Synthesis of Photokilling Materials

We report herein the synthesis and photoinduced bactericidal activity of two new polymeric materials, obtained by imprinting the photosensitizer 20-(4-carboxyphenyl)-2,13-dimethyl-3,12-diethyl-[22]pentaphyrin (PCox, 1) into suitable electropolymerized dipyrromethane films. 5-Phenyl-dipyrromethane (5-ph-DP) and 5-(4-pyridyl)dipyrromethane (5-py-DP) have been selected as the monomers for the synthesis of the materials in order to assess the correlation between the substituent in C5 and the capability in Pcox uptake. Both films have been tested in their photokilling ability toward Staphylococcus aureus by using a multi-LED blue lamp at a fluence rate of 40 W/m² . Poly-5-py-DP/PCox, with a PCox load of 10^-8  mol/cm² , achieved a 4-log reduction in microbial viability after 60 min of irradiation. The polymeric films proved to be stable over time and under oxidation conditions; in addition, no loss of photosensitizer was observed during the experiments, thus demonstrating that the bactericidal action was effectively brought by the ROS generated by PCox immobilized in the material. After use, the films were recharged with PCox, with almost complete recovery of their photodynamic efficiency.

Silver-decorated, light-activatable polymeric antimicrobials for combined chemo-photodynamic therapy of drug-resistant bacterial infection

In this article, we describe a silver-decorated, light-activatable polymeric antimicrobial with strong synergistic chemo-photodynamic effect to combat bacterial infections.

Novel nanomaterial-based antibacterial photodynamic therapies to combat oral bacterial biofilms and infectious diseases

Oral diseases such as tooth caries, periodontal diseases, endodontic infections, etc., are prevalent worldwide. The heavy burden of oral infectious diseases and their consequences on the patients' quality of life indicates a strong need for developing effective therapies. Advanced understandings of such oral diseases, e.g., inflammatory periodontal lesions, have raised the demand for antibacterial therapeutic strategies, because these diseases are caused by viruses and bacteria. The application of antimicrobial photodynamic therapy (aPDT) on oral infectious diseases has attracted tremendous interest in the past decade. However, aPDT had a minimal effect on the viability of organized biofilms due to the hydrophobic nature of the majority of the photosensitizers (PSs). Therefore, novel nanotechnologies were rapidly developed to target the delivery of hydrophobic PSs into microorganisms for the antimicrobial performance improvement of aPDT. This review focuses on the state-of-the-art of nanomaterials applications in aPDT against oral infectious diseases. The first part of this article focuses on the cutting-edge research on the synthesis, toxicity, and therapeutic effects of various forms of nanomaterials serving as PS carriers for aPDT applications. The second part discusses nanomaterials applications for aPDT in treatments of oral diseases. These novel bioactive nanomaterials have demonstrated great potential to serve as carriers for PSs to substantially enhance the PDT therapeutic effects. Furthermore, the novel aPDT applications not only have exciting therapeutic potential to inhibit bacterial plaque-initiated oral diseases, but also have a wide applicability to other biomedical and tissue engineering applications.

Comparison of light-induced formation of reactive oxygen species and the membrane destruction of two mesoporphyrin derivatives in liposomes

The photodynamic effect requires the simultaneous presence of light, photosensitizer (PS) and molecular oxygen. In this process, the photoinduced damage of cells is caused by reactive oxygen species (ROS). Besides DNA, the other target of ROS is the membranes, separating internal compartments in living cells. Hence, the ability of ROS formation of porphyrins as PSs, in liposomes as simple models of cellular membranes is of outstanding interest. Earlier we compared the binding parameters and locations of mesoporphyrin IX dihydrochloride (MPCl) and mesoporphyrin IX dimethyl ester (MPE), in small unilamellar vesicles (SUV) made from various saturated phosphatidylcholines. In this study, we used the same kinds of samples for comparing the ROS forming ability. Triiodide production from potassium iodide because of light-induced ROS in the presence of molybdate catalyst was applied, and the amount of product was quantitatively followed by optical spectrometry. Furthermore, we demonstrated and carefully studied SUVs disruption as direct evidence of membrane destruction by the methods of dynamic light scattering (DLS) and fluorescence correlation spectroscopy (FCS), applying unsaturated phosphatidylcholines as membrane components. Although the ROS forming ability is more pronounced in the case of MPCl, we found that the measured disruption was more effective in the samples containing MPE.

Novel photodynamic coating reduces the bioburden on near-patient surfaces thereby reducing the risk for onward pathogen transmission: a field study in two hospitals

BACKGROUND

Near-patient surfaces are recognized as a source for hospital-acquired infections. Such surfaces act as reservoirs for microbial contamination by which pathogens can be transmitted from colonized or infected patients to susceptible patients. Routine disinfection of surfaces only results in a temporal elimination of pathogens, and recontamination inevitably occurs shortly between disinfections.

AIM

A novel antimicrobial coating based on photodynamics was tested under laboratory conditions and subsequently in a field study in two hospitals under real-life conditions.

METHODS

Identical surfaces received a photodynamic or control coating. Bacterial counts [colony-forming units (cfu)/cm²) were assessed regularly for up to 6 months.

FINDINGS

The laboratory study revealed a mean reduction of several human pathogens of up to 4.0 ± 0.3 log₁₀. The field study in near-patient environments demonstrated mean bacterial values of 6.1 ± 24.7 cfu/cm² on all control coatings. Photodynamic coatings showed a significantly lower mean value of 1.9 ± 2.8 cfu/cm² (P<0.001). When considering benchmarks of 2.5 cfu/cm² or 5 cfu/cm², the relative risk for high bacterial counts on surfaces was reduced by 48% (odds ratio 0.38, P<0.001) or 67% (odds ratio 0.27, P<0.001), respectively.

CONCLUSION

Photodynamic coatings provide a significant and lasting reduction of bacterial counts on near-patient surfaces, particularly for high bacterial loads, in addition to routine hygiene. The promising results of this proof-of-concept study highlight the need for further studies to determine how this novel technology is correlated with the frequency of hospital-acquired infections.

Metal-Organic Framework-Templated Biomaterials: Recent Progress in Synthesis, Functionalization, and Applications

The integration of a porous crystalline framework with soft polymers to create novel biomaterials has tremendous potential yet remains very challenging to date. Metal-organic framework (MOF)-templated polymers (MTPs) have emerged as persistent modular materials that can be tailored for desired biofunctions. These represent a novel class of hierarchically structured assemblies that combine the advantages of MOFs (precisely controlled structure, enormous diversity in framework topology, and high porosity) with the intrinsic behaviors of polymers (soft texture, flexibility, biocompatibility, and improved stability under physiological conditions). Transformation of surface-anchored MOFs (SURMOFs) via orthogonal covalent cross-linking yields surface-anchored polymeric gels (SURGELs) that open up exciting new opportunities to create soft nanoporous materials. SURGELs overcome the main drawbacks of SURMOFs, such as their limited stability under physiological conditions and their potential to release toxic metal ions, a substantial problem for applications in life sciences. MOF (SURMOF)-templated polymerization processes control the synthesis on a molecular level. Additionally, the morphology of the original MOF crystal template is replicated in the final network polymers. The MOF-templated polymerization can be induced by light, a catalyst, or temperature using several types of reactions, including thiol-ene, metal-free alkyne-azide click reactions, and Glaser-Hay coupling. In the case of photoinduced reactions, the cross-linking process can be locally confined, allowing control of the macroscopic patterning of the resulting network polymer. The use of layer-by-layer (lbl) techniques in the SURMOF synthesis serves the purpose of precise, layer-selective incorporation of functionalities via the combination of the postsynthetic modification and heteroepitaxy strategies. Transforming the functionalized SURMOF into a SURGEL allows the fabrication of polymers with desired bioactive functions at the internal or external surfaces. This Account highlights our ongoing research and inspiring progress in transforming SURMOFs into persistent, modular nanoporous materials tailored with biofunctions. Using cell culture studies, we present various aspects of SURGEL materials, such as the ability to deliver bioactive molecules to adhering cells on SURGEL surfaces, applications to advanced drug delivery systems, the ability to tune cell adhesion via surface modification, and the development of porphyrin-based SURGEL thin films with antimicrobial properties. Then we critically examine the challenges and limitations of current systems and discuss future research directions and new approaches for advancing MOF-templated biocompatible materials, emphasizing the need to include responsive and adaptive functionalities into the system. We emphasize that the hierarchical structure, ranging from the molecular to the macroscopic scale, allows for optimization of the material properties across all length scales relevant for cell-material interactions.

Antibacterial photodynamic activity of carbon quantum dots/polydimethylsiloxane nanocomposites against Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae

Despite great efforts, the design of antibacterial surfaces is still a challenge. In this work, results of structural, mechanical, cytotoxic and antibacterial activities of hydrophobic carbon quantum dots/polydimethylsiloxane surfaces are presented. Antibacterial action of this surface is based on the generation of reactive oxygen species which cause bacteria damage by oxidative stress. At the same time, this surface was not cytotoxic towards the NIH/3T3 cells. Swelling-encapsulation-shrink method is applied for encapsulation of hydrophobic carbon quantum dots in medical grade silicone-polydimethylsiloxane. XPS and photoluminescence spectroscopy analyses confirm that hydrophobic carbon quantum dots have been encapsulated successfully into polydimethylsiloxane polymer matrix. Based on stress-strain test the improvement of mechanical properties of these nanocomposites is established. It is shown by electron paramagnetic resonance spectroscopy and luminescence method that nanocomposite generates singlet oxygen initiated by 470 nm blue light irradiation. Antibacterial testing shows the nanocomposite in the form of foil kills Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae and is very effective after only a 15 min irradiation.

A photodynamic antibacterial spray-coating based on the host–guest immobilization of the photosensitizer methylene blue

An efficient photodynamic antibacterial spray-coating is developed with a very low MB density and high singlet oxygen quantum yield.

Electron beam functionalized photodynamic polyethersulfone membranes - photophysical characterization and antimicrobial activity

Polymer membranes are powerful filtration tools in medicine and water treatment. Their efficiency and operational lifetime is limited by biofouling caused by microorganisms. This study describes the development of photodynamical active antimicrobial polymer membranes in a one-pot functionalization step using a well-known photosensitizer (PS). Commercially available polyethersulfone (PES) membranes for microfiltration were doped with the polycationic PS TMPyP using electron beam irradiation. These membranes were characterized in terms of binding stability and quantification of the PS and membrane morphology. Furthermore, the photodynamic ability was verified by time resolved singlet oxygen luminescence scans and successfully tested against the Gram-negative bacterium E. coli under low dose white light illumination resulting in the reduction in cell survival of 6 log10 units. Finally, in preliminarily experiments the photodynamic action against the Gram-positive bacteria M. luteus and the Gram-negative P. fluorescence and the mold C. cladosporioides was demonstrated. These promising results show the high photodynamic potential of electron beam functionalization of PES membranes with TMPyP. It preserves the photodynamic abilities of the immobilized PS resulting in efficient photodynamic inactivation of bacteria and mold on the membrane surface. The uprising worldwide spread of antibiotic resistant bacteria makes the development of new antibacterial strategies an inevitable challenge. The photodynamic inactivation of bacteria and its adaptation for antimicrobial surfaces, e.g. filtration membranes for water treatment, displays many advantages in terms of a wide application range, low mutagenic potential and environmental compatibility.

Carbon Quantum Dots Modified Polyurethane Nanocomposite as Effective Photocatalytic and Antibacterial Agents

Development of new types of antibacterial coatings or nanocomposites is of great importance due to widespread multidrug-resistant infections including bacterial infections. Herein, we investigated biocompatibility as well as structural, photocatalytic, and antibacterial properties of photoactive hydrophobic carbon quantum dots/polyurethane nanocomposite. The swell-encapsulation-shrink method was applied for production of these nanocomposites. Hydrophobic carbon quantum dots/polyurethane nanocomposites were found to be highly effective generator of singlet oxygen upon irradiation by low-power blue light. Analysis of conducted antibacterial tests on Staphyloccocus aureus and Escherichia coli showed 5-log bactericidal effect of these nanocomposites within 60 min of irradiation. Very powerful degradation of dye (rose bengal) was observed within 180 min of blue light irradiation of the nanocomposites. Biocompatibility studies revealed that nanocomposites were not cytotoxic against mouse embryonic fibroblast cell line, whereas they showed moderate cytotoxicity toward adenocarcinomic human epithelial cell line. Minor hemolytic effect of these nanocomposites toward red blood cells was revealed.

Superhydrophobic Photosensitizers: Airborne 1O2 Killing of an in Vitro Oral Biofilm at the Plastron Interface

Singlet oxygen is a potent agent for the selective killing of a wide range of harmful cells; however, current delivery methods pose significant obstacles to its widespread use as a treatment agent. Limitations include the need for photosensitizer proximity to tissue because of the short (3.5 μs) lifetime of singlet oxygen in contact with water; the strong optical absorption of the photosensitizer, which limits the penetration depth; and hypoxic environments that restrict the concentration of available oxygen. In this article, we describe a novel superhydrophobic singlet oxygen delivery device for the selective inactivation of bacterial biofilms. The device addresses the current limitations by: immobilizing photosensitizer molecules onto inert silica particles; embedding the photosensitizer-containing particles into the plastron (i.e. the fluid-free space within a superhydrophobic surface between the solid substrate and fluid layer); distributing the particles along an optically transparent substrate such that they can be uniformly illuminated; enabling the penetration of oxygen via the contiguous vapor space defined by the plastron; and stabilizing the superhydrophobic state while avoiding the direct contact of the sensitizer to biomaterials. In this way, singlet oxygen generated on the sensitizer-containing particles can diffuse across the plastron and kill bacteria even deep within the hypoxic periodontal pockets. For the first time, we demonstrate complete biofilm inactivation (>5 log killing) of Porphyromonas gingivalis, a bacterium implicated in periodontal disease using the superhydrophobic singlet oxygen delivery device. The biofilms were cultured on hydroxyapatite disks and exposed to active and control surfaces to assess the killing efficiency as monitored by colony counting and confocal microscopy. Two sensitizer particle types, a silicon phthalocyanine sol-gel and a chlorin e6 derivative covalently bound to fluorinated silica, were evaluated; the biofilm killing efficiency was found to correlate with the amount of singlet oxygen detected in separate trapping studies. Finally, we discuss the applications of such devices in the treatment of periodontitis.

Antibacterial and Barrier Properties of Gelatin Coated by Electrospun Polycaprolactone Ultrathin Fibers Containing Black Pepper Oleoresin of Interest in Active Food Biopackaging Applications

The present study evaluated the effect of using electrospun polycaprolactone (PCL) as a barrier coating and black pepper oleoresin (OR) as a natural extract on the morphology, thermal, mechanical, antimicrobial, oxygen, and water vapor barrier properties of solvent cast gelatin (GEL). The antimicrobial activity of the developed multilayer system obtained by the so-called electrospinning coating technique was also evaluated against Staphylococcus aureus strains for 10 days. The results showed that the multilayer system containing PCL and OR increased the thermal resistance, elongated the GEL film, and significantly diminished its permeance to water vapor. Active multilayer systems stored in hermetically closed bottles increased their antimicrobial activity after 10 days by inhibiting the growth of Staphylococcus aureus. This study demonstrates that addition of electrospun PCL ultrathin fibers and OR improved the properties of GEL films, which promoted its potential use in active food packaging applications.

Photodynamic inactivation of microorganisms sensitized by cationic BODIPY derivatives potentiated by potassium iodide

The photodynamic inactivation mediated by 1,3,5,7-tetramethyl-8-[4-(N,N,N-trimethylamino)phenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene 3 and 8-[4-(3-(N,N,N-trimethylamino)propoxy)phenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene 4 was investigated on Staphylococcus aureus, Escherichia coli and Candida albicans. In vitro experiments indicated that BODIPYs 3 and 4 were rapidly bound to microbial cells at short incubation periods. Also, fluorescence microscopy images showed green emission of BODIPYs bound to microbial cells. Photosensitized inactivation improved with an increase of the irradiation time. Similar photoinactivation activities were found for both BODIPYs in bacteria. The photoinactivation induced by these BODIPYs was effective for both bacteria. However, the Gram-positive bacterium was inactivated sooner and with a lower concentration of a photosensitizer than the Gram-negative bacterium. After 15 min irradiation, the complete eradication of S. aureus was obtained with 1 μM photosensitizer. A reduction of 4.5 log in the E. coli viability was found when using 5 μM photosensitizer and 30 min irradiation. Also, the last conditions produced a decrease of 4.5 log in C. albicans cells treated with BODIPY 3, while 4 was poorly effective. On the other hand, the effect of the addition of KI on photoinactivation at different irradiation periods and salt concentrations was investigated. A smaller effect was observed in S. aureus because the photosensitizers alone were already very effective. In E. coli, photokilling potentiation was mainly found at longer irradiation periods. Moreover, the photoinactivation of C. albicans mediated by these BODIPYs was increased in the presence of KI. In solution, an increase in the formation of the BODIPY triplet states was observed with the addition of the salt, due to the effect of external heavy atoms. The greater intersystem crossing together with the formation of reactive iodine species induced by BODIPYs may be contributing to enhance the inactivation of microorganisms. Therefore, these BODIPYs represent interesting photosensitizers to inactivate microorganisms. In particular, BODIPY 3 in combination with KI was highly effective as a broad spectrum antimicrobial photosensitizer.

High Antimicrobial Activity of Metal-Organic Framework-Templated Porphyrin Polymer Thin Films

Development of surface coatings with high antimicrobial activity is urgently required to fight bacteria and other microorganisms on technical and hygiene relevant surfaces. Control over structure and topology of the surface coatings, combined with the ability to include functional molecules within the structure, is crucial for optimizing their performance. Herein, we describe a novel strategy to synthesize structurally well-defined porphyrin polymer thin films via a template approach. In this approach, bisazido-functionalized porphyrin molecules are preorganized within a metal-organic framework (MOF) structure. Afterward, porphyrin units within the MOF are covalently connected via a secondary linker. Removal of the metal ions of the MOF results in water-stable porphyrin polymer thin films that demonstrate high antibacterial activity against pathogens via visible-light-promoted generation of reactive oxygen species. In addition, this approach offers the inherent possibility to incorporate guest molecules within the structures, to functionalize the surface with biomolecules, and to create hierarchically structured materials.

Covalently Attached Antimicrobial Surfaces Using BODIPY: Improving Efficiency and Effectiveness

The development of photoactivated antimicrobial surfaces that kill pathogens through the production of singlet oxygen has proved very effective in recent years, with applications in medical devices and hospital touch surfaces, to improve patient safety and well being. However, many of these surfaces require a swell-encapsulation-shrink strategy to incorporate the photoactive agents in a polymer matrix, and this is resource intensive, given that only the surface fraction of the agent is active against bacteria. Furthermore, there is a risk that the agent will leach from the polymer and thus raises issues of biocompatibility and patient safety. Here, we describe a more efficient method of fabricating a silicone material with a covalently attached monolayer of photoactivating agent that uses heavy-atom triplet sensitization for improved singlet oxygen generation and corresponding antimicrobial activity. We use boron-dipyrromethane with a reactive end group and incorporated Br atoms, covalently attached to poly(dimethylsiloxane). We demonstrate the efficacy of this material in producing singlet oxygen and killing Staphylococcus aureus and suggest how it might be easily modifiable for future antimicrobial surface development.

BODIPYs to the rescue: Potential applications in photodynamic inactivation

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives have been proposed in several potential biomedical applications. BODIPYs absorb strongly in blue-green region with high fluorescence emission, properties that convert them in effective fluorophores in the field of biological labeling. However, BODIPY structures can be conveniently modified by heavy atoms substitution to obtain photosensitizers with applications in photodynamic therapy. Also, external heavy atoms effect can be used to increase the photodynamic activity of these compounds. In recent years, BODIPYs have been proposed as phototherapeutic agents for the photodynamic inactivation of microorganisms. Therefore, BODIPY structures need to be optimized to produce an efficient photocytotoxic activity. In this way, amphiphilic cationic BODIPYs can selectively bind to microbial cells, inducing an effective photokilling of pathogenic microbial cells. This review summarizes the attributes of BODIPY derivatives for applications as antimicrobial photosensitizing agents.

Photodynamic inactivation of Escherichia coli - Correlation of singlet oxygen kinetics and phototoxicity

Photodynamic inactivation (PDI) of bacteria may play a major role in facing the challenge of the ever expanding antibiotic resistances. Here we report about the direct correlation of singlet oxygen luminescence kinetics and phototoxicity in E. coli cell suspension under PDI using the widely applied cationic photosensitizer TMPyP. Through direct access to the microenvironment, the time resolved investigation of singlet oxygen luminescence plays a key role in understanding the photosensitization mechanism and inactivation pathway. Using the homemade set-up for highly sensitive time resolved singlet oxygen luminescence detection, we show that the cationic TMPyP is localized predominantly outside the bacterial cells but in their immediate vicinity prior to photodynamic inactivation. Throughout following light exposure, a clear change in singlet oxygen kinetics indicates a redistribution of photosensitizer molecules to at least one additional microenvironment. We found the signal kinetics mirrored in cell viability measurements of equally treated samples from same overnight cultures conducted in parallel: A significant drop in cell viability of the illuminated samples and stationary viability of dark controls. Thus, for the system investigated in this work - a Gram-negative model bacteria and a well-known PS for its PDI - singlet oxygen kinetics correlates with phototoxicity. This finding suggests that it is well possible to evaluate PDI efficiency directly via time resolved singlet oxygen detection.

Dispersion of the Photosensitizer 5,10,15,20-Tetrakis(4-Sulfonatophenyl)-porphyrin by the Amphiphilic Polymer Poly(vinylpirrolidone) in Highly Porous Solid Materials Designed for Photodynamic Therapy

The ability of the amphiphilic and biocompatible poly(vinylpyrrolidone) to avoid self-aggregation of the photosensitizer 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin in aqueous solution in the presence of the biocompatible polycation chitosan, polymer that induces the dye self-aggregation, is shown. This is related to the tendency of the dye to undergo preferential solvation by the amphiphilic polymer. Importantly, the dispersant ability of this polymer is transferred to the solid state. Thus, aerogels made of the biocompatible polymers chitosan and chondroitin sulfate, and containing the photosensitizer dispersed by the amphiphilic polymer have been synthesized. Production of reactive oxygen species by the aerogel containing the amphiphilic polymer was faster than when the polymer was absent, correlating with the relative concentration of dyes dispersed as monomers. The aerogels presented here constitute low cost biocompatible materials bearing a conventional photosensitizer for photodynamic therapy, easy to produce, store, transport, and manage in clinical practice.

β-Formyl- and β-Vinylporphyrins: Magic Building Blocks for Novel Porphyrin Derivatives

Porphyrins bearing formyl or vinyl groups have been explored as starting materials to prepare new compounds with adequate features for different applications. In this review it is discussed mainly synthetic strategies based on the reaction of meso-tetraarylporphyrins bearing those groups at β-pyrrolic positions. The use of some of the obtained porphyrin derivatives for further transformations, namely via pericyclic reactions, is also highlighted.

Mannose-Functionalized Hyperbranched Polyglycerol Loaded with Zinc Porphyrin: Investigation of the Multivalency Effect in Antibacterial Photodynamic Therapy

The antibacterial photodynamic activity of hyperbranched polyglycerol (hPG) loaded with zinc porphyrin photosensitizers and mannose units was investigated. hPG, with a M_W of 19.5 kDa, was functionalized with about 15 molecules of the photosensitizer {5,10,15-tris(3-hydroxyphenyl)-20-[4-(prop-2-yn-1-ylamino)tetrafluorophenyl]porphyrinato}-zinc(II) by using copper(I)-catalyzed 1,3-dipolar cycloaddition (CuAAC). These nanoparticle conjugates were functionalized systematically with increasing loadings of mannose in the range of approximately 20 to 110 groups. With higher mannose loadings (ca. 58-110 groups) the water-insoluble zinc porphyrin photosensitizer could thus be transferred into a water-soluble form. Targeting of the conjugates was proven in binding studies to the mannose-specific lectin concanavalin A (Con A) by using surface plasmon resonance (SPR). The antibacterial phototoxicity of the conjugates on Staphylococcus aureus (as a typical Gram-positive germ) was investigated in phosphate-buffered saline (PBS). It was shown that conjugates with approximately 70-110 mannose units exhibit significant antibacterial activity, whereas conjugates with approximately 20-60 units did not induce bacterial killing at all. These results give an insight into the multivalency effect in combination with photodynamic therapy (PDT). On addition of serum to the bacterial cultures, a quenching of this antibacterial phototoxicity was observed. In fluorescence studies with the conjugates in the presence of increasing bovine serum albumin (BSA) concentrations, protein-conjugate associations could be identified as a plausible cause for this quenching.

Eosin-mediated synthesis of polymer coatings combining photodynamic inactivation and antimicrobial properties

Eosin-derived coatings exhibiting photodynamic bacterial inactivation and antibacterial properties.

Photosensitized singlet oxygen generation and detection: Recent advances and future perspectives in cancer photodynamic therapy

Photodynamic therapy (PDT) uses photosensitizers and visible light in combination with molecular oxygen to produce reactive oxygen species (ROS) that kill malignant cells by apoptosis and/or necrosis, shut down the tumor microvasculature and stimulate the host immune system. The excited singlet state of oxygen (¹ O₂ ) is recognized to be the main cytotoxic ROS generated during PDT for the majority of photosensitizers used clinically and for many investigational new agents, so that maximizing its production within tumor cells and tissues can improve the therapeutic response, and several emerging and novel approaches for this are summarized. Quantitative techniques for ¹ O₂ production measurement during photosensitization are also of immense importance of value for both preclinical research and future clinical practice. In this review, emerging strategies for enhanced photosensitized ¹ O₂ generation are introduced, while recent advances in direct detection and imaging of ¹ O₂ luminescence are summarized. In addition, the correlation between cumulative ¹ O₂ luminescence and PDT efficiency will be highlighted. Meanwhile, the validation of ¹ O₂ luminescence dosimetry for PDT application is also considered. This review concludes with a discussion on future demands of ¹ O₂ luminescence detection for PDT dosimetry, with particular emphasis on clinical translation. Eye-catching color image for graphical abstract.

Photoantimicrobials-are we afraid of the light?

Although conventional antimicrobial drugs have been viewed as miraculous cure-alls for the past 80 years, increasing antimicrobial drug resistance requires a major and rapid intervention. However, the development of novel but still conventional systemic antimicrobial agents, having only a single mode or site of action, will not alleviate the situation because it is probably only a matter of time until any such agents will also become ineffective. To continue to produce new agents based on this notion is unacceptable, and there is an increasing need for alternative approaches to the problem. By contrast, light-activated molecules called photoantimicrobials act locally via the in-situ production of highly reactive oxygen species, which simultaneously attack various biomolecular sites in the pathogenic target and therefore offer both multiple and variable sites of action. This non-specificity at the target circumvents conventional mechanisms of resistance and inhibits the development of resistance to the agents themselves. Photoantimicrobial therapy is safe and easy to implement and, unlike conventional agents, the activity spectrum of photoantimicrobials covers bacteria, fungi, viruses, and protozoa. However, clinical trials of these new, truly broad-spectrum, and minimally toxic agents have been few, and the funding for research and development is almost non-existent. Photoantimicrobials constitute one of the few ways forward through the morass of drug-resistant infectious disease and should be fully explored. In this Personal View, we raise awareness of the novel photoantimicrobial technologies that offer a viable alternative to conventional drugs in many relevant application fields, and could thus slow the pace of resistance development.