Blue light is an emerging technology used for the decontamination of food contact surfaces and products. It is based on the activation of photosensitizers by light, determining the release of reactive oxygen species (ROS). ROS causes damage to bacterial cells leading to cell death. Several types of microbes may be treated, such as bacteria, yeasts, moulds and viruses, in planktonic or biofilm form. Blue light technology is affected by several factors: light parameters (i.e., irradiance, dose, wavelength), microbial parameters (i.e., pH, temperature, initial inoculum, grade of biofilm maturation) and surface parameters (i.e., material, roughness, and optical properties). In addition, it may be used alone or coupled with other technologies. The use of blue light shows several advantages, such as safety for food operators, and a lower release of chemicals in the environment. Moreover, it seems unlikely for bacteria to develop resistance to the blue light application. 

An Overview of the Application of Blue Light-Emitting Diodes as a Non-Thermic Green Technology for Microbial Inactivation in the Food Sector

A photoactivatable antimicrobial polymeric surface based on a porphycene derivate was efficiently prepared and evaluated to kill pathogenic microorganisms. The development of this self-sterilizing material consisted in the electrochemical polymerization of a peripherally tetra-substituted porphycene bearing benzyl-carbazole groups (Pc-Cbz). The latter were used as electropolymerizable centers, while the porphycene core triggered the photodynamic action. The electrodeposited photodynamic films (P-Pc-Cbz) were obtained in a reproducible and controllable manner. Electrochemistry studies combined with spectroscopic measurements demonstrated that the porphycene core remains unaffected after the electrodeposition process. Moreover, it retains its spectroscopic and photodynamic properties within the polymeric matrix. The photoactive layers were photostable and able to produce reactive oxygen species (ROS) by both photodynamic mechanisms. Also, the antimicrobial efficiency of P-Pc-Cbz was evaluated against two antibiotic-resistant strains (methicillin-resistant Staphylococcus aureus and Escherichia coli), exhibiting an antimicrobial action higher than 99.998% over these Gram-positive and Gram-negative bacteria. This work represents the first electropolymerization of a porphycene derivative and the first porphycene-based photobiocidal surface. P-Pc-Cbz shows great potential as an efficient self-sterilizing coating activated by visible light. 

Light-Activated Antibacterial Polymeric Surface Based on Porphycene

Light-Activated Antibacterial Ethylcellulose Electrospun Nanofibrous Mats Containing Fluorinated Zn(II) Porphyrin

The World Health Organization has reported that antimicrobial resistance is one of the top 10 health threats that humanity faces today. Due to this, alternative therapies to the common antimicrobials are being explored and among these is photodynamic antimicrobial chemotherapy, where a combination of light, a photosensitizer and reactive oxygen species can be used to target microbial cells. In this research, free base, tin (IV) and indium (III) tetramethoxyporphyrins photosensitizers are adsorbed onto inorganic titanium dioxide nanofibers in an effort to create reusable fibers that are effective against Staphylococcus aureus. The photodynamic antimicrobial chemotherapy studies indicate that the metalloporphyrin adsorbed nanofibers exhibit good photodynamic antimicrobial activity against Staphylococcus aureus where the Cl2Sn(IV) tetramethoxyporphyrin dyed TiO2 exhibited 100% bacterial inhibition after a 30 min irradiation period. 

The application of Sn(IV)Cl2 and In(III)Cl porphyrin-dyed TiO2 nanofibers in photodynamic antimicrobial chemotherapy for bacterial inactivation in water.

The increase in bacteria resistant to antibiotics in clinical use has led to the establishment of new treatments for infections. One of the proposed therapies includes photodynamic inactivation (PDI) of microorganisms. In this context, two novel polymeric conjugates, PEI-TPPF10 and PEI-TPPF20, were synthesized by the aromatic nucleophilic substitution reaction between polyethylenimine (PEI) and 5,15-di(4-N,N-dimethylaminophenyl)-10,20-di(pentafluorophenyl)porphyrin (TPPF10) or 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TPPF20), respectively. The structures of these polymers were characterized by FTIR. UV–visible absorption and fluorescence studies indicated that the porphyrin units maintain their spectroscopic characteristics in the conjugates. The polymeric materials were able to produce singlet molecular oxygen and superoxide anion radical in solution. Furthermore, they were effective photosensitizers to photooxidize L-tryptophan and produce iodine in presence of iodide anions. The ability of these conjugates to photoinactivate bacteria was tested against Staphylococcus aureus and Escherichia coli. A reduction of 7 log (>99.9999 %) in cell survival was found after an irradiation with white light (90 mW/cm2) of 5 min (27 J/cm2) and 15 min (81 J/cm2), respectively. In these conjugates, the remaining amino groups are precursors of positive charges in the biological medium, favoring the interaction with microbial cells, which improves the photokilling activity. The results indicate that both conjugates are promising photosensitizing polymeric materials for the eradication of pathogens. 

Porphyrin-polyethylenimine conjugates as photodynamic polymers to eliminate Staphylococcus aureus and Escherichia coli

• Differently substituted meso -aromatic groups influenced the supramolecular assembly of porphyrins, finally driving the surface morphology of PVC-based composites obtained by their incorporation. • The correlation among molecular structure, aggregation, topographies, and antibacterial activity of the materials was investigated. • The key role of composite microstructure towards bactericidal activity was evidenced. • The prepared composites proved resistant under operative conditions, fully reusable, and prone to high scale application in water disinfection. Four porphyrins, namely: 5,10,15,20-tetrakis(4-methylphenyl)-21H,23H-porphine (4MeP, 1 ), 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine (4OMeP, 2 ), 5,10,15,20-tetra-4-pyridinyl-21H,23H-porphine (4PyP, 3 ), and 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphine (4NH 2 P, 4 ) have been selected to prepare polyvinyl chloride/octyl adipate composites having antibacterial photodynamic properties. The four porphyrins were assumed suitable to elucidate the role of non-covalent interactions, established through the peripheral groups of the macrocycles, in tuning the final antibacterial performances of the composites. A correlation between photosensitizer structures/self-aggregation/surface morphologies and antimicrobial activity of the materials was established. Among the materials tested, the most efficient in terms of photokilling activity and cost-benefits was selected to assess physicochemical stability, the number of reuse turnover, and the reliable shelf-life. These bioactive composites proved to be well promising for effective and sustainable applications in water disinfection, while the facile scale up of the synthesis and the transferability of the approach to a large dimension of contaminated water was verified. 

New antimicrobial PVC composites. Porphyrins self-aggregation in tuning surface morphologies and photodynamic inactivation towards sustainable water disinfection

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New antimicrobial PVC composites. Porphyrins self-aggregation in tuning surface morphologies and photodynamic inactivation towards sustainable water disinfection