Photoinactivation Of Bacteria Research Articles

Construction of Ag/CdZnS QDs nanocomposite for enhanced visible light photoinactivation of Staphylococcus aureus

With increasing use of antibiotics, the development of antibiotic-resistant pathogens poses a serious threat to human health and the environment. Photocatalytic inactivation of these harmful pathogens is one of the novel and non-antibiotic treatments. The study fabricated Ag NPs decorated CdZnS QDs via a facile and biological co-precipitation method using L. camara plant extract as a green alternative to treat the toxic chemicals. The fabricated Ag/CdZnS QDs (NCs) were prepared for the efficient treatment of antibiotic-resistant pathogens as they raise a major global concern. The fabricated NCs were characterized with various characterization techniques to verify its physicochemical properties. The fabricated NCs have shown excellent photo-sterilization performance of 97 % against S. aureus. The excellent activity was attributed to the decoration of Ag NPs on CdZnS QDs as it helped in shortening band gap, improved visible light absorption ability, increased active sites, and boosted photogenerated electron/hole pairs stability. Radical trapping experiment and ESR analysis indicated the involvement of •OH and h+ in the photoinactivation of bacteria. The photo sterilization reaction of NCs was carried out under different environmental conditions, including light and dark conditions and different pH conditions. The experiment was carried out in sewage-treated water in order to test the real-time application, and the fabricated NCs achieved excellent 95.9 % photo-inactivation of S. aureus cells in sewage treated water and the Chemical Oxygen Demand (COD) of the system was increased after photo inactivation treatment. The fabricated NCs have also shown excellent reusable efficiency of 95% after six runs and the photostability and anti-corrosive nature of NCs were confirmed. The study provides an insight for the employment of photocatalysis for the sterilization of pathogens in real time aquatic environment across the globe.

Asymmetrical zinc phthalocyanine conjugated to various nanomaterials for applications in phototransformation of organic pollutants and photoinactivation of bacteria

Zinc phthalocyanine (ZnPc) complexes are linked to metallic nanoparticles covalently via amide and ester bonds. The photocatalytic activity of the conjugates of ZnPc complexes with NiWO4, Ag2WO4, CoWO4 and Ag-Fe3O4 nanoparticles are evaluated for photodegradation of methylene blue, tetracycline, and dibenzothiophene. The photocatalytic efficiencies of the prepared phthalocyanine complexes increased in the presence of nanoparticles. This work also reports on the photodynamic antimicrobial chemotherapy activity of these materials against Staphylococcus aureus (S. aureus) bacteria. The results indicate that Ag2WO4 based nanoconjugates exhibit high antimicrobial activity with higher log reduction compared to NiWO4, CoWO4 and Ag-Fe3O4 based materials.

Synthesis of platinum decorated copper oxide doped layer graphite carbon nitrite: An efficient photocatalyst for disintegration of bacteria and decomposition of dye

Platinum decorated copper oxide doped layer graphite carbon nitrite (Pt/CuO@g-C 3 N 4 ) was synthesized by green hydrothermal method. Amylopectin was employed as a source of reduction and stabilization. Aforementioned nanomaterial is made up of a layer graphite carbon nitrite nanosheet with CuO nanofibers and Pt embedded in a cluster of nanofibers. Methylene blue (MB) degradation, free radical stabilization, and photo inactivation of bacteria were all targets for the synthesized photocatalyst. For instance, the developed composites exhibited the remarkable photocatalytic activity to degrade 90% MB in about 20 minutes, under visible light irradiation. Moreover, the synthesized nanomaterials were also tested against bacteria Staphylococcus aureus and Escherichia coli (S. aureus & E. coli ) both in the presence and absence of visible light irradiation. The light-treated platinum adorned copper oxide doped layer graphite carbon nitrite has inhibitory diameter 13 and 18 mm for E. coli and S. aureus respectively though in dark was 7 and 10 mm respectively. The effects of various factors on the photoinhibition potency of the said nanomaterial were also investigated. Furthermore, the nanomaterial exhibits a high resistance to 2,2-diphenyl-1-picrylhydrazyl (DPPH) stabilization. • Preparation of Platinum decorated Copper Oxide doped Layer Graphite Carbon Nitrite by simple, non-toxic way • Antibacterial activity examination • Examination of MB degradation • DPPH scavenging activity examination

Antimicrobial and Photoantimicrobial Activities of Chitosan/CNPPV Nanocomposites.

Multidrug-resistant bacteria represent a global health and economic burden that urgently calls for new technologies to combat bacterial antimicrobial resistance. Here, we developed novel nanocomposites (NCPs) based on chitosan that display different degrees of acetylation (DAs), and conjugated polymer cyano-substituted poly(p-phenylene vinylene) (CNPPV) as an alternative approach to inactivate Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria. Chitosan’s structure was confirmed through FT-Raman spectroscopy. Bactericidal and photobactericidal activities of NCPs were tested under dark and blue-light irradiation conditions, respectively. Hydrodynamic size and aqueous stability were determined by DLS, zeta potential (ZP) and time-domain NMR. TEM micrographs of NCPs were obtained, and their capacity of generating reactive oxygen species (ROS) under blue illumination was also characterized. Meaningful variations on ZP and relaxation time T2 confirmed successful physical attachment of chitosan/CNPPV. All NCPs exhibited a similar and shrunken spherical shape according to TEM. A lower DA is responsible for driving higher bactericidal performance alongside the synergistic effect from CNPPV, lower nanosized distribution profile and higher positive charged surface. ROS production was proportionally found in NCPs with and without CNPPV by decreasing the DA, leading to a remarkable photobactericidal effect under blue-light irradiation. Overall, our findings indicate that chitosan/CNPPV NCPs may constitute a valuable asset for the development of innovative strategies for inactivation and/or photoinactivation of bacteria.

Preparation and characterization of curcumin and pomegranate peel extract chitosan/gelatin-based Films and their photoinactivation of bacteria

The development of photoantimicrobial films for food and medical devices decontamination is a continuous challenge. In this work, chitosan/gelatin-based films containing curcumin and pomegranate peel extract in different concentrations (0.5–5.0 mg photosensitizer g−1 solution) were prepared and characterized by ultraviolet–visible spectroscopy, fluorescence spectroscopy, infrared spectroscopy and scanning electron microscope; their structural morphology (thickness and moisture content, solubility and swelling degree, and opacity) was also analyzed. The photobleaching results (up to 90%) demonstrated a potential application of the films in antimicrobial photodynamic therapy (aPDT). In the antimicrobial tests, the films displayed a significant photoantimicrobial effect reducing Staphylococcus aureus up to 4 log units, using a light source at 450 and 525 nm (50 J cm−2) for curcumin and pomegranate peel extract films, respectively. The results of this work open way for future development of photoantimicrobial films based on natural polymers, containing photosensitizers, for medical devices (e.g.: endotracheal tubes and catheters) and food packaging.

Meso-substituted cationic 3- and 4-N-Pyridylporphyrins and their Zn(II) derivatives for antibacterial photodynamic therapy

Photodynamic inactivation of microorganisms known as antibacterial photodynamic therapy (APDT) is one of the most promising and innovative approaches for the destruction of pathogenic microorganisms. Among the photosensitizers (PSs), compounds based on cationic porphyrins/metalloporphyrins are most successfully used to inactivate microorganisms. Series of meso-substituted cationic pyridylporphyrins and metalloporphyrins with various peripheral groups in the third and fourth positions of the pyrrole ring have been synthesized in Armenia. The aim of this work was to determine and test the most effective cationic porphyrins and metalloporphyrins with high photoactivity against Gram negative and Gram positive microorganisms. It was shown that the synthesized cationic pyridylporphyrins/metalloporphyrins exhibit a high degree of phototoxicity towards both types of bacteria, including the methicillin-resistant S. aureus strain. Zinc complexes of porphyrins are more phototoxic than metal-free porphyrin analogs. The effectiveness of these Zn–metalloporphyrins on bacteria is consistent with the level of singlet oxygen generation. It was found that the high antibacterial activity of the studied cationic porphyrins/metalloporphyrins depends on four factors: the presence in the porphyrin macrocycle of a positive charge (+4), a central metal atom (Zn[Formula: see text] and hydrophobic peripheral functional groups as well as high values of quantum yields of singlet oxygen. The results indicate that meso-substituted cationic pyridylporphyrins/metalloporphyrins can find wider application in photoinactivation of bacteria than anionic or neutral PSs usually used in APDT.

Controlling morphology evolution of titanium oxide–gold nanourchin for photocatalytic degradation of dyes and photoinactivation of bacteria in the infected wound

We report a one-pot, room-temperature, morphology-controlled synthesis of titanium oxide (TiOx)–gold nanocomposites (TiOx–Au NCs) using HAuCl4 and TiCl3 as precursors, and catechin as reducing agent. TiOx–Au NCs have a range of morphologies from star-like to urchin-like shape depending on the concentration of TiCl3 in the reaction mixture. The urchin-shaped TiOx–Au NCs exhibited excellent photocatalytic activity toward dye degradation due to strong light absorption, plasmon-induced excitation, high conductivity of the gold, and reduced hole-electron pair recombination. TiOx–Au NCs have the advantage of a wide range of light absorption and surface plasmon absorption-mediated excitation due to their abundant gold spikes, which enabled the degradation of dyes over 97% in 60 min, using a xenon lamp as a light source. In addition, TiOx–Au NCs are highly efficient for the photoinactivation of Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA), and Candida albicans through the photodynamic generation of reactive oxygen species (ROS) and damage to the bacterial membrane. The catechin derivatives on the NCs effectively promoted curing MRSA infected wounds in rats through inducing collagen synthesis, migration of keratinocytes, and neovascularization.

Type-II heterojunction constructed by Ag2S-coupled ZnO microspheres with visible light-responsive antibacterial activity

ZnO nanorods-assembled microspheres were photosensitized with a layer of low bandgap Ag2S nanoparticles on the branched nanorods to get a type-II core/shell heterojunction (ZnO@Ag2S). The heterojunction with unique band configuration exhibited better visible light-responsive antibacterial activity than pure ZnO, which is attributed to the inhibition of photocarrier recombination and efficient charge separation and transfer. Scavenger test confirmed that the photoinactivation of bacteria was directed by the combined assistance of O2− radicals and photogenerated holes. The growth of Gram-negative bacteria was more effectively restrained by ZnO@Ag2S than that of Gram-positive bacteria and fungi because of structural difference of cell walls.

Boron-dipyrromethene derivatives bearing N-alkyl phthalimide and amine substituents of potential application in the photoinactivation of bacteria

Novel boron-dipyrromethene derivatives with N-alkyl phthalimide and amine substituents, including iodinated derivative, were synthesized and characterized using UV–Vis spectrophotometry, mass spectrometry (HRMS) and NMR spectroscopy. Non-iodinated analogs revealed high emission properties with fluorescence quantum yields (ΦF) between 0.48 and 0.58. But singlet oxygen generation quantum yields (ΦΔ) were low with values in the range of 0.01–0.06. Iodinated derivative revealed a strong heavy atom effect resulted in the red-shifted absorption and emission bands, fluorescence quenching with ΦF values of about 0.02, but increased singlet oxygen generation abilities with excellent ΦΔ values of 0.97 and 0.85 in methanol and ethanol, respectively. In vitro photodynamic inactivation activity was evaluated on Gram-positive cocci of Staphylococcus aureus and Gram-negative rods of Escherichia coli. Novel BODIPY derivatives showed promising inactivation efficiency on S. aureus, with the highest activity for iodinated derivative, which reduced the number of bacteria by 3.6 logs10 at low 0.5 μM concentration. However, none of the tested derivatives showed a satisfactory ability to eradicate E. coli. Only non-iodinated derivative with amine substituent, at high concentrations, showed some significant activity with log10 reduction values of 2.0 and 1.1 at 500 and 50 μM, respectively. Nevertheless, the presented approach enabled to obtain novel BODIPY derivatives with promising photoinactivation activity and properties such as fluorescence and singlet oxygen generation efficacy, easy to modify by the heavy atom substitution. Also, peripheral phthalimide or amine groups can be used for further structural modifications.

Photoinactivation of bacteria by hypocrellin-grafted bacterial cellulose

With the aim of developing self-disinfecting materials to prevent pathogen transmission from surfaces to new hosts, here we report a simple and eco-friendly way to prepare photodynamic bacterial cellulose (BC) onto which the naturally-occurring photosensitizer hypocrellin (Hc) has been covalently appended. The resultant hypocrellin-grafted BC membrane (Hc-BC) was characterized by both physical (SEM, TGA, XRD) and spectroscopic (IR, diffuse reflectance UV–visible) methods, and the photosensitizer loading was found to be 155 nmol Hc/mg membrane. Indirect cytotoxicity tests employing mouse skin fibroblast (L929) cells showed no changes in cell viability, demonstrating that the Hc-BC membrane lacked any leachable components (e.g., unreacted coupling agent or hypocrellin) that could be cytotoxic to mammalian cells. The photodynamic antibacterial activity of Hc-BC was evaluated against gram-positive S. aureus (ATCC-6538) and gram-negative E. coli strain 8099. Our results demonstrated a 99.5 + % (2.7 log units) reduction in S. aureus upon illumination (Xe lamp, 65 ± 5 mW/cm2, 420–780 nm; 30 min), however, no statistically significant inactivation of E. coli was observed. Potentiation with potassium iodide was found to increase the antibacterial efficacy of Hc-BC against S. aureus to 99.997% (4.8 log units) at 10 mM KI, while E. coli was inactivated by 99.1% (2 log units) at 100 mM KI, with the increase in inactivation being attributable to short-lived reactive iodide radicals that are the major biocidal agents in the potentiation of Hc-BC by KI. Taken together, our findings demonstrated that hypocrellin-grafted bacterial cellulose is a sustainable material from which potent photodynamic antibacterial materials may be derived.

Application of Porphyrins in Antibacterial Photodynamic Therapy.

Antibiotics are commonly used to control, treat, or prevent bacterial infections, however bacterial resistance to all known classes of traditional antibiotics has greatly increased in the past years especially in hospitals rendering certain therapies ineffective. To limit this emerging public health problem, there is a need to develop non-incursive, non-toxic, and new antimicrobial techniques that act more effectively and quicker than the current antibiotics. One of these effective techniques is antibacterial photodynamic therapy (aPDT). This review focuses on the application of porphyrins in the photo-inactivation of bacteria. Mechanisms of bacterial resistance and some of the current ‘greener’ methods of synthesis of meso-phenyl porphyrins are discussed. In addition, significance and limitations of aPDT are also discussed. Furthermore, we also elaborate on the current clinical applications and the future perspectives and directions of this non-antibiotic therapeutic strategy in combating infectious diseases.

405 nm and 450 nm Photoinactivation of Saccharomyces cerevisiae.

Photoinactivation of bacteria with visible light has been reported in numerous studies. Radiation around 405 nm is absorbed by endogenous porphyrins and generates reactive oxygen species that destroy bacteria from within. Blue light in the spectral range of 450–470 nm also exhibits an antibacterial effect, but it is weaker than 405 nm radiation, and the photosensitizers involved have not been clarified yet, even though flavins and porphyrins are possible candidates.There are significantly fewer photoinactivation studies on fungi. To test if visible light can inactivate fungi and to elucidate the mechanisms involved, the model organism Saccharomyces cerevisiae (DSM no. 70449) was irradiated with violet (405 nm) and blue (450 nm) light. The mean irradiation doses required for a one log reduction of colony forming units for this strain were 182 J/cm2 and 526 J/cm2 for 405 nm and 450 nm irradiation, respectively. To investigate the cell damaging mechanisms, trypan blue staining was performed. However, even strongly irradiated cultures hardly showed any stained S. cerevisiae cells, indicating an intact cell membrane and thus arguing against the previously suspected mechanism of cell membrane damage during photoinactivation with visible light at least for the investigated strain. The results are compatible with photoinactivated Saccharomyces cerevisiae cells being in a viable but nonculturable state.To identify potential fungal photosensitizers, the absorption and fluorescence of Saccharomyces cerevisiae cell lysates were determined. The spectral absorption and fluorescence results are in favor of protoporphyrin IX as the most important photosensitizer at 405 nm radiation. For 450 nm irradiation, riboflavin and other flavins may be the main photosensitizer candidates, since porphyrins do not play a prominent role at this wavelength. No evidence of the involvement of other photosensitizers was found in the spectral data of this strain.

Additive effect of heparin on the photoinactivation of Escherichia coli using tricationic P-porphyrins

Polycationic porphyrins have received substantial attention in developing singlet oxygen-sensitizers for biological use such as in the photoinactivation of bacteria and photodynamic therapy (PDT) of tumor cells because they have strong binding affinities for DNA and proteins. However, these strong cellular interactions can retard elimination of the drug after PDT. Therefore, the studies on the interactions of porphyrins with other molecules present much interest, in order to modulate the sensitizers’ activity or even remove them from the human body after PDT. Here, we studied the additive effect of heparin on the photoinactivation by polycationic porphyrins using Escherichia coli as a model cell. Tricationic P-porphyrin sensitizers substituted with an N-alkylpyridinium group (alkyl = pentyl (1a), hexyl (1b), and heptyl (1c)) or N-hexylammonium (1d) as the axial ligand were used. Additionally, dicationic Sb-porphyrin substituted with an N-hexylpyridinium group (1e) was prepared. We studied the additive effect of heparin on the photoinactivation of E. coli by 1a–1e. The bactericidal activities were evaluated using the half-life (T1/2 in min) of E. coli and the minimum effective concentrations ([P]) of the porphyrin sensitizers. In the absence of heparin, the [P] values were determined to be 0.4–0.5 μM for 1a−1c and 2.0 μM for 1d−1e. The bactericidal activity of 1a−1c was completely retarded by the addition of heparin (1.0 μM). However, the addition of heparin (1.0 μM) could not completely retard the bactericidal activity of 1d−1e whose [P] values were relatively large. It is suggested that tricationic 1a−1c adsorbed onto the anionic heparin through electrostatic interactions. The adsorption of 1 on heparin disturbs the uptake of 1 into E. coli cells. Thus, the addition of heparin was found to be a useful method for retarding photoinactivation.

An effective and potentially safe blood disinfection protocol using tetrapyrrolic photosensitizers.

Conventional disinfection techniques, considered safe for plasma, are usually associated with collateral damages on concentrated platelets and erythrocytes. Alternative methods are required and antimicrobial photodynamic therapy (aPDT) seems promising. In this study the effectiveness of two photosensitizers (PS), a porphyrin and a phthalocyanine, to disinfect blood products was evaluated. The cationic porphyrin was more effective in the photoinactivation of bacteria. Also, no significant osmotic stress was found for samples treated with PS at 5.0 µM in isotonic conditions after antimicrobial photodynamic therapy. Effective reduction of Gram-positive bacteria at 5.0 µM of PS provided promising indications toward its safe use to disinfect blood samples. For Gram-negative bacteria, lower PS concentrations, between 5.0 and 10 µM, must be tested.

Zinc(II)-Tetradentate-Coordinated Probe with Aggregation-Induced Emission Characteristics for Selective Imaging and Photoinactivation of Bacteria.

The emergence of drug-resistant bacterial pathogens highlights an urgent need for new therapeutic options. Photodynamic therapy (PDT) has emerged as a potential alternative to antibiotics to kill bacteria, which has been used in clinical settings. PDT employs photosensitizers (PSs), light, and oxygen to kill bacteria by generating highly reactive oxygen species (ROS). PDT can target both external and internal structures of bacteria, which does not really require the PSs to enter bacteria. Therefore, bacteria can hardly develop resistance to PDT. However, most of the PSs reported so far are hydrophobic and tend to form aggregates when they interact with bacteria. The aggregation could cause fluorescence quenching and reduce ROS generation, which generally compromises the effects of both imaging and therapy. In this contribution, we report on a Zn(II)-tetradentate-coordinated red-emissive probe with aggregation-induced emission characterization. The probe could selectively image bacteria over mammalian cells. Moreover, the probe shows potent phototoxicity to both Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Bacillus subtilis).

Photoinactivation of bacteria by endogenous photosensitizers and exposure to visible light of different wavelengths - a review on existing data.

Visible light has strong disinfectant properties, a fact that is not well known in comparison to the antibacterial properties of UV light. This review compiles the published data on bacterial inactivation caused by visible light and endogenous photosensitizers. It evaluates more than 50 published studies containing information on about 40 different bacterial species irradiated within the spectral range from 380 to 780 nm. In the available data a high variability of photoinactivation sensitivity is observed, which may be caused by undefined illumination conditions. Under aerobic conditions almost all bacteria except spores should be reduced by at least three log-levels with a dose of about 500 Jcm-2 of 405 nm irradiation, including both Gram-positive as well as Gram-negative microorganisms. Irradiation of 470 nm is also appropriate for photoinactivating all bacteria species investigated so far but compared to 405 nm illumination it is less effective by a factor between 2 and 5. The spectral dependence of the observed photoinactivation sensitivities gives reason to the assumption that a so far unknown photosensitizer may be involved at 470 nm photoinactivation.

467 - Application of Porphyrins in Antibacterial Photodynamic Therapy

Antibiotics are commonly used to control, treat or prevent bacterial infections, however bacterial resistance to all known classes of traditional antibiotics has significantly increased in the last decades especially in hospitals rendering certain therapies ineffective. To limit this emerging public health problem there is a need to develop non-invasive, non-toxic and novel antimicrobial strategies that act more efficiently and faster than the current antibiotics, to which pathogens will not easily develop resistance. One of these methods is Antibacterial Photodynamic Therapy (aPDT). This review focuses on the application of porphyrins in the photo-inactivation of bacteria. Mechanisms of bacterial resistance and some of the current ‘greener’ methods of synthesis of meso-phenyl porphyrins are discussed. In addition, significance and limitations of aPDT are also discussed. Furthermore, we also elaborate on the current clinical applications and the future perspectives and directions of this non-antibiotic therapeutic strategy in combating infectious diseases.

In situ sol-gel synthesis of anatase TiO 2 -MWCNTs nanocomposites and their photocatalytic applications

Abstract Visible light photoactive titania-multiwalled carbon nanotubes (TiO 2 -MWCNTs) nanocomposites were synthesized by in situ sol-gel method, in this TiO 2 nanoparticles were decorated on the surface of MWCNTs. The XRD analysis shows good crystalline nature of synthesized nanocomposite. UV–vis DRS study confirms the red shift of nanocmposites with respect to the increasing content of MWCNTs. The photocatalytic activity has investigated by degradation of methyl orange dye under ultraviolet as well as sunlight irradiation and photo-inactivation of Bacillus subtilis under visible light irradiation. The MWCNTs exist in the nanocomposite was able to absorb a high amount of photon energy in the sunlight, driving effectively photochemical degradation reactions. In the photodegradation of methyl orange dye under sunlight as well as photo-inactivation of Bacillus substilis under visible light, significant enhancement in the degradation/inactivation reaction rate was observed with the TiO 2 -MWCNTs (0.5 wt.%), nanocomposite as compared to TiO 2 NPs. The COD study confirms the environmentally benign nature of photodegraded dye solution. This work provides new insight for the fabrication of sunlight/visible active TiO 2 -MWCNTs nanocomposite photocatalyst for degradation of organic compounds and photo-inactivation of bacteria.

Visible light photo catalytic inactivation of bacteria and photo degradation of methylene blue with Ag/TiO2 nanocomposite prepared by a novel method

Water purification is one of the worldwide problem and most of the conventional methods are associated with a number of drawbacks. Therefore it is the need of the day to develop new methods and materials to overcome the problem of water purification. In this research work we present a simple and green approach to synthesize silver decorated titanium dioxide (Ag/TiO2) nanocomposite with an efficient photo catalytic activities. Phytochemicals of the Cestrum nocturnum leaf extract were used to synthesize silver nanoparticles (AgNPs), Titanium dioxide (TiO2) and Ag/TiO2 nanocomposite. To confirm the formation, crystal structure, particle size and shape of green synthesized nanoparticles and nanocomposite, they were characterized by UV–visible spectroscopy (UV–vis), X-ray diffraction spectroscopy (XRD), high resolution transmission electron microscopy (HRTEM), Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The AgNPs, TiO2 and Ag/TiO2 were evaluated for photo degradation of methylene blue (MB) and photo inhibition of Bacteria. The bio-synthesized Ag/TiO2 nanocomposite was observed to have strong catalytic activities for photo reduction of MB and photo inactivation of bacteria as compared to bare AgNPs and TiO2. In the presence of Ag/TiO2, 90% of MB was degraded only in 40min of irradiation. Alternatively the bare AgNPs and TiO2 degraded less than 30% and 80% respectively of MB even in more than 100min of irradiation. Similarly the Ag/TiO2 has very strong photo inhibition efficiency towards Escherichia coli and Pseudomonas aeruginosa. The zone of inhibition of irradiated Ag/TiO2 nanocomposites against E. coli and P. aeruginosa was 19mm and 17mm respectively which was two times higher than in dark. These promising photocatalytic activities of nanocomposite may be due to the highly decorated AgNPs over the surface of TiO2.

Efficient photo-oxidation of phenol and photo-inactivation of bacteria by cationic tetrakis(trimethylanilinium)porphyrins

Photo-oxidation of phenol in aqueous alkaline and neutral buffer solutions by irradiation with visible light in the presence of 5,10,15,20-tetrakis(4-N,N,N-trimethylanilinium)porphyrin (TAPP) and its zinc metal ion (ZnTAPP) photo-sensitizers is described. The inhibitory effect of these molecules on the growth of Gram-positive bacteria Bacillus subtilis and Bacillus strophaeus and the Gram-negative strain Pseudomonas aeruginosa has also been examined. Furthermore, to determine the relationship between inhibition and attachment, the degree of binding of these photo-sensitizers to these bacteria was determined. The results show that TAPP is more effective than ZnTAPP in the photo-oxidation of phenol and photo-inactivation of the bacteria. In addition, the degree of binding of TAPP to these bacteria was more than that of ZnTAPP.