Hydrogen Peroxide Enhances the Antibacterial Effect of Methylene Blue‐based Photodynamic Therapy on Biofilm‐forming Bacteria

Recently, increased attention has been focused on endoscopic disinfection after outbreaks of drug‐resistant infections associated with gastrointestinal endoscopy. The aims of this study were to investigate the bactericidal efficacy of methylene blue (MB)‐based photodynamic therapy (PDT) on Pseudomonas aeruginosa (P. aeruginosa), which is the major cause of drug‐resistant postendoscopy outbreak, and to assess the synergistic effects of hydrogen peroxide addition to MB‐based PDT on biofilms. In planktonic state of P. aeruginosa, the maximum decrease was 3 log₁₀ and 5.5 log₁₀ at 20 and 30 J cm^?2, respectively, following MB‐based PDT. However, the maximum reduction of colony forming unit (CFU) was decreased by 2.5 log₁₀ and 3 log₁₀ irradiation on biofilms. The biofilm formation was significantly inhibited upon irradiation with MB‐based PDT. When the biofilm state of P. aeruginosa was treated with MB‐based PDT with hydrogen peroxide, the CFU was significantly decreased by 6 log₁₀ after 20 J cm^?2, by 7 log₁₀ after 30 J cm^?2 irradiation, suggesting significantly higher efficacy than MB‐based PDT alone. The implementation of the combination of hydrogen peroxide with MB‐based PDT through working channels might be appropriate for preventing early colonization and biofilm formation in the endoscope and postendoscopy outbreak.     

On the Synergism of Biogenic Gold Nanoparticles and Hydroxyaluminum Phthalocyanines in the Photoeradication of Staphylococcus aureus

Due to the unusual properties of gold nanoparticles, these structures are widely used in medicine and biology. This paper describes for the first time the synthesis of colloidal gold nanoparticles by the cell-free filtrate obtained from the Coriolus versicolor biomass and the use of these biogenic nanostructures to increase the photosensitizing efficiency of di- (AlPcS₂) and tetrasulfonated (AlPcS₄) hydroxyaluminum phthalocyanines in antibacterial photodynamic therapy. The obtained monodisperse particles were extremely stable, and this remarkable stability was due to the presence of phosphoprotein as a capping agent. The studied gold nanoparticles had a spherical shape, were uniformly distributed, and were characterized by a single plasmon band at wavelength of 514–517 nm. Almost 60% of the gold particles were found to be in the range of 13 to 15 nm. In accordance with the regulations of the American Microbiological Society, indicating that any antimicrobial technique must kill at least 3 log CFU (99.9%) to be accepted as “antimicrobial”, this mortality of Staphylococcus aureus was shown to be achieved in the presence of AlPcS₄ + AuNPs mixture and 4.8 J cm⁻² light dose compared to AlPcS₄ alone, which required a light dose of 24 J cm⁻². The best effect of increasing the effectiveness of combating this pathogen was observed in the case of AlPcS₂ + AuNPs as a photosensitizing mixture. The light dose of 24 J cm⁻² caused a lethal effect of the studied coccus in the planktonic culture.     

Photodynamic Inactivation of Bacterial and Yeast Biofilms With a Cationic Porphyrin

The efficiency of 5,10,15,20‐tetrakis(1‐methylpyridinium‐4‐yl)porphyrin tetra‐iodide (Tetra‐Py⁺‐Me) in the photodynamic inactivation of single‐species biofilms of Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans and mixed biofilms of S. aureus and C. albicans was evaluated. The effect on the extracellular matrix of P. aeruginosa was also assessed. Irradiation with white light up to an energy dose of 64.8 J cm^?2 in the presence of 20 μm of Tetra‐Py⁺‐Me caused significant inactivation in all single‐species biofilms (3–6 log reductions), although the susceptibility was attenuated in relation to planktonic cells. In mixed biofilms, the inactivation of S. aureus was as efficient as in single‐species biofilms but the susceptibility of C. albicans decreased. In P. aeruginosa biofilms, a reduction of 81% in the polysaccharide content of the matrix was observed after treatment with a 20 μm PS concentration and a total light dose of 64.8 J cm^?2. The results show that the Tetra‐Py⁺‐Me causes significant inactivation of the microorganisms, either in biofilms or in the planktonic form, and demonstrate that polysaccharides of the biofilm matrix may be a primary target of photodynamic damage.     

Effectiveness of the Photoactive Dye Methylene Blue versus Caspofungin on the Candida parapsilosis Biofilm in vitro and ex vivo

This research studied the effectiveness of the photoactive compound methylene blue (MB) activated with red LED light (576–672 nm) compared to that of caspofungin (CAS) on 1 Candida albicans and 3 Candida parapsilosis strains. Results were evaluated in terms of SMIC₅₀ for CAS or in PDI (photodynamic inactivation)‐SMIC₅₀ for MB (minimal inhibitory concentration inhibiting sessile biofilm to 50% in comparison to the control without CAS or after irradiation in comparison to the control without MB). While all strains were susceptible to CAS in planktonic form, the SMIC₅₀ was determined to be >16 μg mL^?1 when CAS was added to a 24 h biofilm. However, PDI‐MIC_50s (1.67 mW cm^?2, fluence 15 J cm^?2) were 0.0075–0.03 mmol L^?1. For biofilm, PDI‐SMIC_50s were in the range from 0.7 to 1.35 mmol L^?1. MB concentration of 1 mmol L^?1 prevented a biofilm being formed ex vivo on mouse tongues after irradiation regardless of the application time, in contrast to CAS, which was only effective at a concentration of 16 μg mL^?1 when it was added at the beginning of biofilm formation. PDI seems to be a promising method for the prevention of microbial biofilms that do not respond significantly to conventional drugs.     

Xanthene Dyes and Green LED for the Inactivation of Foodborne Pathogens in Planktonic and Biofilm States

This study evaluated the rose bengal‐ and erythrosine‐mediated photoinactivation against Salmonella Typhimurium and Staphylococcus aureus planktonic and sessile cells using green LED as a light source. The free‐living or 2‐day‐old biofilm cells were treated with different concentrations of the photosensitizing agents and subjected to irradiation. Only 5 min photosensitization with rose bengal at 25 nmol L^?1 and 75 μmol L^?1 completely eliminated S. aureus and S. Typhimurium planktonic cells, respectively. Erythrosine at 500 nmol L^?1 and 5 min of light exposure also reduced S. aureus planktonic cells to undetectable levels. Eradication of S. aureus biofilms was achieved when 500 μmol L^?1 of erythrosine or 250 μmol L^?1 of rose bengal was combined with 30 min of irradiation. Scanning electron microscopy allowed the observation of morphological changes in planktonic cells and disruption of the biofilm architecture after photodynamic treatment. The overall data demonstrate that rose bengal and erythrosine activated by green LED may be a targeted strategy for controlling foodborne pathogens in both planktonic and sessile states.     

Efflux Pump Inhibitor Potentiates Antimicrobial Photodynamic Inactivation of Enterococcus faecalis Biofilm

Microbial biofilm architecture contains numerous protective features, including extracellular polymeric material that render biofilms impermeable to conventional antimicrobial agents. This study evaluated the efficacy of antimicrobial photodynamic inactivation (aPDI) of Enterococcus faecalis biofilms. The ability of a cationic, phenothiazinium photosensitizer, methylene blue (MB) and an anionic, xanthene photosensitizer, rose bengal (RB) to inactivate biofilms of E. faecalis (OG1RF and FA 2-2) and disrupt the biofilm structure was evaluated. Bacterial cells were tested as planktonic suspensions, intact biofilms and biofilm-derived suspensions obtained by the mechanical disruption of biofilms. The role of a specific microbial efflux pump inhibitor (EPI), verapamil hydrochloride in the MB-mediated aPDI of E. faecalis biofilms was also investigated. The results showed that E. faecalis biofilms exhibited significantly higher resistance to aPDI when compared with E. faecalis in suspension (P < 0.001). aPDI with cationic MB produced superior inactivation of E. faecalis strains in a biofilm along with significant destruction of biofilm structure when compared with anionic RB (P < 0.05). The ability to inactivate biofilm bacteria was further enhanced when the EPI was used with MB (P < 0.001). These experiments demonstrated the advantage of a cationic phenothiazinium photosensitizer combined with an EPI to inactivate biofilm bacteria and disrupt biofilm structure.     

Assessment of Dentifrices Against Candida Biofilm

The invasion of opportunistic pleiomorphic Candida albicans into oral cavity environment leads to development and progression of its resistance to both naturally occurring antifungal peptides in human saliva as well as commercially available antifungal therapies. As a result of this, the usage and popularity of natural medicine and dentifrices had increased significantly in the last decade. In the present investigation, we have assessed the action of locally available dentifrices against C. albicans biofilm. Disk diffusion test showed maximum zone of inhibition (20?mm) by herbal dentifrice (D-5) as compared to other dentifrices when incubated at 37?°C and 48?h. Assessment of dentifrice D-5 for its effectiveness against C. albicans was further shown in MIC₉₀ (3.12?mg?mL^?1) and SMIC₉₀ (6.2?mg?mL^?1) values for planktonic and sessile cells (biofilm forming), respectively. Our data depicted 80% reduction in the cell surface hydrophobicity when 6.2?mg?mL^?1 of herbal dentifrice D-5 was used against 48-h grown Candida biofilm at 37?°C. Visualization of herbal dentifrice D-5-treated C. albicans biofilm under SEM revealed drastic reduction in the dense network of yeast, hyphae, and pseudohyphae enclosed in its ECM as compared to its control biofilm. The data were further supported by CLSM analysis which depicted C. albicans architecture disruption by herbal dentifrices. From the above data, it is inferred that these studies would provide researchers and medical practitioners with better insight into the antifungal effect of natural herbal dentifrices.     

Photodynamic Inactivation of Planktonic Cultures and Biofilms of Candida albicans Mediated by Aluminum‐Chloride‐Phthalocyanine Entrapped in Nanoemulsions

New drug delivery systems, such as nanoemulsions (NE), have been developed to allow the use of hydrophobic drugs on the antimicrobial photodynamic therapy. This study evaluated the photodynamic potential of aluminum‐chloride‐phthalocyanine (ClAlPc) entrapped in cationic and anionic NE to inactivate Candida albicans planktonic cultures and biofilm compared with free ClAlPc. Fungal suspensions were treated with different delivery systems containing ClAlPc and light emitting diode. For planktonic suspensions, colonies were counted and cell metabolism was evaluated by XTT assay. Flow cytometry evaluated cell membrane damage. For biofilms, the metabolic activity was evaluated by XTT and ClAlPc distribution through biofilms was analyzed by confocal laser scanning microscopy (CLSM). Fungal viability was dependent on the delivery system, superficial charge and light dose. Free ClAlPc caused photokilling of the yeast when combined with 100 J cm^?2. Cationic NE‐ClAlPc reduced significantly both colony counts and cell metabolism (P < 0.05). In addition, cationic NE‐ClAlPc and free ClAlPc caused significant damage to the cell membrane (P < 0.05). For the biofilms, cationic NE‐ClAlPc reduced cell metabolism by 70%. Anionic NE‐ClAlPc did not present antifungal activity. CLSM showed different accumulation on biofilms between the delivery systems. Although NE system showed a lower activity for planktonic culture, cationic NE‐ClAlPc showed better results for Candida biofilms.     

Killing Bacterial Spores with Blue Light: When Innate Resistance Meets the Power of Light

This article is a highlight of the study by Maclean et al. in this issue of Photochemistry and Photobiology describing the sporicidal effects 405 nm visible light alone on endospores of the Clostridium and Bacillus genera. 1.73 kJ cm^?2 was capable of reducing endospore colony‐forming units by up to 4‐log₁₀. These findings have never been previously demonstrated and may be incorporated into decontamination methods that span medical, military and food preparatory applications.     

Delivery of Methylene Blue and meso-tetra (N-methyl-4-pyridyl) porphine tetra tosylate from cross-linked poly(vinyl alcohol) hydrogels: A potential means of photodynamic therapy of infected wounds

Poly(vinyl alcohol)–borate complexes were evaluated as a potentially novel drug delivery platform suitable for in vivo use in photodynamic antimicrobial chemotherapy (PACT) of wound infections. An optimised formulation (8.0% w/w PVA, 2.0% w/w borax) was loaded with 1.0 mg ml⁻¹ of the photosensitisers Methylene Blue (MB) and meso-tetra (N-methyl-4-pyridyl) porphine tetra tosylate (TMP). Both drugs were released to yield receiver compartment concentrations (>5.0 μg ml⁻¹) found to be phototoxic to both planktonic and biofilm-grown methicillin-resistant Staphylococcus aureus (MRSA), a common cause of wound infections in hospitals. Newborn calf serum, used to simulate the conditions prevalent in an exuding wound, did not adversely affect the properties of the hydrogels and had no significant effect on the rate of TMP-mediated photodynamic kill of MRSA, despite appreciably reducing the fluence rate of incident light. However, MB-mediated photodynamic kill of MRSA was significantly reduced in the presence of calf serum and when the clinical isolate was grown in a biofilm. Results support the contention that delivery of MB or TMP using gel-type vehicles as part of PACT could make a contribution to the photodynamic eradication of MRSA from infected wounds.     

Photodynamic Action Mechanism Mediated by Zinc(II) 2,9,16,23‐Tetrakis[4‐(N‐methylpyridyloxy)]phthalocyanine in Candida albicans Cells

The photoreaction type I/type II pathways mediated by zinc(II) 2,9,16,23‐tetrakis[4‐(N‐methylpyridyloxy)]phthalocyanine (ZnPPc⁴⁺) was studied in Candida albicans cells. This photosensitizer was strongly bound to C. albicans cells at short times. After 30 min irradiation, 5 μM ZnPPc⁴⁺ produced ~5 log decrease in cell viability. Different probes were used to detect reactive oxygen species (ROS) in cell suspensions (~10⁶ CFU mL^?1). Singlet molecular oxygen, O₂(¹Δ_g), was observed by the reaction with 9,10‐dimethylanthracene (DMA) and tetrasodium 2,2‐(anthracene‐9,10‐diyl)bis(methylmalonate) (ABMM), whereas the nitro blue tetrazolium (NBT) method was used to sense superoxide anion radical (). Moreover, the effects produced by an anoxic atmosphere and cell suspensions in D₂O, as well as the addition of sodium azide and mannitol as ROS trapping were evaluated in the PDI of C. albicans. These investigation indicates that O₂(¹Δ_g) is generated in the cells, although a minor extension other radical species can also be involved in the PDI of C. albicans mediated by ZnPPc⁴⁺.     

Influence of biomass and gold salt concentration on nanoparticle synthesis by the tropical marine yeast Yarrowia lipolytica NCIM 3589

Cell-associated gold nanoparticles and nanoplates were produced when varying number of Yarrowia lipolytica cells were incubated with different concentrations of chloroauric acid (HAuCl₄) at pH 4.5. With 10⁹ cells ml⁻¹ and 0.5 or 1.0 mM of the gold salt, the reaction mixtures developed a purple or golden red colour, respectively, and gold nanoparticles were synthesized. Nanoparticles of varying sizes were produced when 10¹⁰ cells ml⁻¹ were incubated with 0.5, 1.0 or 2.0 mM chloroauric acid salt. With 3.0, 4.0 or 5.0 mM HAuCl₄, nanoplates were also observed. With 10¹¹ cells ml⁻¹ nanoparticles were synthesized with almost all the gold salt concentrations. The cell-associated particles were released outside when nanoparticle-loaded cells were incubated at low temperature (20 °C) for 48 h. With increasing salt concentrations and a fixed number of cells, the size of the nanoparticles progressively increased. On the other hand, with increasing cell numbers and a constant gold salt concentration, the size of nanoparticles decreased. These results indicate that by varying the number of cells and the gold salt concentration, a variety of nanoparticles and nanoplates can be synthesized. Fourier transform infrared (FTIR) spectroscopy revealed the possible involvement of carboxyl, hydroxyl and amide groups on the cell surfaces in nanoparticle synthesis.     

Combined Magnetic Resonance Imaging and Photodynamic Therapy Using Polyfunctionalised Nanoparticles Bearing Robust Gadolinium Surface Units

A robust dithiocarbamate tether allows novel gadolinium units based on DOTAGA (q=1) to be attached to the surface of gold nanoparticles (2.6–4.1 nm diameter) along with functional units offering biocompatibility, targeting and photodynamic therapy. A dramatic increase in relaxivity (r₁) per Gd unit from 5.01 mm ⁻¹ s⁻¹ in unbound form to 31.68 mm ⁻¹ s⁻¹ (10 MHz, 37 °C) is observed when immobilised on the surface due to restricted rotation and enhanced rigidity of the Gd complex on the nanoparticle surface. The single-step synthetic route provides a straightforward and versatile way of preparing multifunctional gold nanoparticles, including examples with conjugated zinc–tetraphenylporphyrin photosensitizers. The lack of toxicity of these materials (MTT assays) is transformed on irradiation of HeLa cells for 30 minutes (PDT), leading to 75 % cell death. In addition to passive targeting, the inclusion of units capable of actively targeting overexpressed folate receptors illustrates the potential of these assemblies as targeted theranostic agents.     

Why is Rose Bengal More Phototoxic to Fibroblasts In Vitro Than In Vivo?

Photosensitized protein cross‐linking has been recently developed to seal wounds and strengthen tissue. Although the photosensitizing dye, Rose Bengal (RB), is phototoxic to cultured cells, cytotoxicity does not accompany RB‐photosensitized tissue repair in vivo. We investigated whether the environment surrounding cells in tissue or the high irradiances used for photo–cross‐linking inhibited RB phototoxicity. Fibroblasts (FB) grown within collagen gels to mimic a tissue environment and monolayer cultured FB were treated with RB (0.01–1 mm ) and the high 532 nm laser irradiances used in vivo for tissue repair (0.10–0.50 W cm^?2). Monolayer FB were substantially more sensitive to RB photosensitization: the LD₅₀ was >200‐fold lower than that in collagen gels. Collagen gel protection was associated with increased Akt phosphorylation, a prosurvival pathway. RB phototoxicity in collagen gels was 25‐fold greater at low (0.030 W cm^?2) that at high (0.50 W cm^?2) irradiances. Oxygen depletion at high irradiance only partially accounted for the irradiance dependence of phototoxicity as replacing air with nitrogen only increased the LD₅₀ by four‐fold in monolayers. These results indicate that the lack of RB phototoxicity during in vivo tissue repair results from upregulation of prosurvival pathways in tissue cells, oxygen depletion and irradiance‐dependent RB photochemistry.     

In Vitro Photodynamic Inactivation Effects of Ru(II) Complexes on Clinical Methicillin‐resistant Staphylococcus aureus Planktonic and Biofilm Cultures

Photosensitizers (PSs) combined with light are able to generate antimicrobial effects. Ru(II) complexes have been recognized as a novel class of PSs. In this study, we investigated the effectiveness of photodynamic inactivation (PDI) mediated by three Ru(II) polypyridine complexes, 1–3, against four isolates of clinical methicillin‐resistant Staphylococcus aureus (MRSA‐1, MRSA‐2, MRSA‐3 and MRSA‐4). In PDI of a planktonic culture of MRSA‐1, compound 3 showed the highest efficacy, likely owing to its advantageous light absorption, ¹O₂ quantum yield and bacterial cellular binding. The PDI efficacy of 3 was further evaluated against all other strains and MRSA‐1 biofilms. At appropriate PS concentrations, viability reduction of 100% or 96.83% was observed in planktonic or biofilm forms of MRSA, respectively. The mechanisms of action were investigated using negative staining transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). It was demonstrated that PDI of planktonic bacteria was achieved primarily through damage to the cell envelope. Biofilms were eliminated through both the destruction of their structure and inactivation of the individual bacterial cells. In conclusion, Ru(II) complexes, especially 3, are potential candidates for the effective photodynamic control of MRSA infections.     

Proanthocyanin-Capped Biogenic TiO2 Nanoparticles with Enhanced Penetration,Antibacterial and ROS Mediated Inhibition of Bacteria Proliferation and Biofilm Formation: A Comparative Approach

Biofunctionalized TiO₂ nanoparticles with a size range of 18.42±1.3 nm were synthesized in a single-step approach employing Grape seed extract (GSE) proanthocyanin (PAC) polyphenols. The effect of PACs rich GSE corona was examined with respect to 1) the stability and dispersity of as-synthesized GSE-TiO₂-NPs, 2) their antiproliferative and antibiofilm efficacy, and 3) their propensity for internalization and reactive oxygen species (ROS) generation in urinary tract infections (UTIs) causing Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus saprophyticus strains. State-of-the-art techniques were used to validate GSE-TiO₂-NPs formation. Comparative Fourier transformed infrared (FTIR) spectral analysis demonstrated that PACs linked functional -OH groups likely play a central role in Ti⁴⁺ reduction and nucleation to GSE-TiO₂-NPs, while forming a thin, soft corona around nascent NPs to attribute significantly enhanced stability and dispersity. Transmission electron microscopic (TEM) and inductively coupled plasma mass-spectroscopy (ICP-MS) analyses confirmed there was significantly (p<0.05) enhanced intracellular uptake of GSE-TiO₂-NPs in both Gram-negative and -positive test uropathogens as compared to bare TiO₂-NPs. Correspondingly, compared to bare NPs, GSE-TiO₂-NPs induced intracellular ROS formation that corresponded well with dose-dependent inhibitory patterns of cell proliferation and biofilm formation in both the tested strains. Overall, this study demonstrates that -OH rich PACs of GSE corona on biogenic TiO₂-NPs maximized the functional stability, dispersity and propensity of penetration into planktonic cells and biofilm matrices. Such unique merits warrant the use of GSE-TiO₂-NPs as a novel, functionally stable and efficient antibacterial nano-formulation to combat the menace of UTIs in clinical settings.     

PHOTODYNAMIC ACTION OF HEMATOPORPHYRIN ON YEAST CELLS—A KINETIC APPROACH

Abstract— By a technique which combines rapid mixing of cells and hematoporphyrin (HP) with a short duration of illumination, the photodynamic inactivation of yeast cells was investigated, particularly, in seeking for the information of the location of HP at the time of action. The fluence-survival curves obtained under the conditions where the reaction mixture was kept in the dark for Is, 60s and even 35 min before illumination were indistinguishable from each other, indicating no interaction between cells and sensitizers took place in about 30 min in such a way that the photodynamic efficiency could be modified. It is unlikely that HP acted intracellularly, since the protective effect of N^?₃ was observed at concentrations as low as 0.5 mM. Furthermore, the rate constant k_p related to the protective effect of NJ, was estimated to be 1 × 10⁸M^?1 s^?1 under the assumption that ¹O₂ was the active intermediate and had a lifetime of 2 μs under the present conditions. This value of k_p is rather close to that of k_q, the quenching rate constant of N^?₃ for ¹O₂, of which the accepted value is 2 × 10⁸M^?1s^?1 in the homogeneous aqueous system. This information, together with the absence of uptake of HP by cells and a well response of survival upon illumination to the D₂O fraction of the reaction mixture, provide strong bases for the argument that direct interaction of HP with yeast cells is of minor importance in the photodynamic processes, and the photodynamic action is largely mediated by an intermediate (¹0₂) generated in bulk medium.     

Preparation and Visible-Light Photocatalytic Activity of FeTPP-Cr-TiO2 Microspheres

Tetraphenyl-porphyrin iron (FeTPP) was chosen to sensitize Cr doped TiO₂ (Cr-TiO₂) nanoparticles, a novel multimodified photocatalyst FeTPP-Cr-TiO₂ with excellent visiblelight photocatalytic activity was successfully synthesized. The FeTPP-Cr-TiO₂ microspheres were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electronic microscopy, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectra and N₂ adsorption-desorption isotherms. The photocatalytic activity of FeTPP-Cr-TiO₂ was evaluated by degradations of methylene blue in aqueous solution under irradiation with Xe lamp (150 W). The results showed that the FeTPP-Cr-TiO₂ multimodified photocatalyst was anatase phase with high specific surface area (74.7 m²/g), and exhibited higher photocatalytic degradation efficiency than Cr-TiO₂ and FeTPP-TiO₂. The photocatalytic degradations of three quinolone antibiotics (lomefloxacin, norfloxacin, and ofloxacin) were further estimated for the feasibility of practical application of catalyst in wastewater treatment. It is desirable that photodegradation of antibiotics with FeTPP-Cr-TiO₂ achieved pretty high degradation rates and all followed the pseudo first-order reaction model, and the rate constants k of 3.02×10^-2, 2.81×10^-2, and 3.86×10^-2 min^-1 and the half-lifes t_1/2 of 22.9, 24.6, and 17.9 min were achieved respectively.     

A collaborative CeO2@metal-organic framework nanosystem to endow scaffolds with photodynamic antibacterial effect

Antibacterial photodynamic therapy had attracted considerable attention in implant-associated infections treatment due to its high selectivity and no resistance. Actually, bacteria readily formed protective biofilm to cover themselves and impede the permeation of photosensitizers, severely impairing the therapeutic effect. Herein, a collaborative nanosystem was constructed by in-situ growing cerium oxide (CeO₂) nanoparticles on porphyrinic metal-organic framework PCN-224, and then mixed with poly-l-lactic acid (PLLA) powder to fabricate CeO₂@PCN-224/PLLA scaffold. In the nanosystem, CeO₂ was expected to disrupt the biofilm integrity by releasing Ce⁴⁺, exposing bacteria. Subsequently, PCN-224 could grab this opportunity to kill the bacteria by generating reactive oxygen species (ROS) under light irradiation, thereby achieving the desired antibacterial effect. Crystal violet staining and agarose gel electrophoresis results demonstrated that the bacterial biofilm was effectively eliminated by cleaving the extracellular DNA chains. Coomassie brilliant blue and acridine orange staining revealed that the generated ROS effectively killed bacteria by destroying their cell membrane, causing DNA hydrolysis and protein leakage. Furthermore, ROS could also weaken the antioxidant capacity of bacteria by consuming their glutathione, further accelerating bacterial death. As a consequence, the scaffolds presented a robust antibacterial rate of 97% against S. aureus. Collectively, this work provides a promising strategy for efficient implant-related infection treatment.     

Determination of 131mXe and 133mXe in the presence of 133gXe via combined beta-spectroscopy and delayed coincidence

The International Monitoring System for the Comprehensive Nuclear-Test-Ban Treaty will include measurements of Xe fission products. Pacific Northwest National Laboratory has developed an automated system for separating Xe from air which detects Xe fission products using a beta-gamma counting system for ^131mXe, ^133mXe, ^133gXe, and ^135gXe. Betas and conversion electrons are detected in a plastic scintillation cell containing the Xe sample. Gamma and X-rays are detected in a NaI(Tl) scintillation detector which surrounds the plastic scintillator sample cell. Two-dimensional pulse-height spectra of gamma-energy versus beta-energy are obtained. The plastic scintillator spectrum in coincidence with the 31-keV X-rays from ^131mXe. ^133mXe, and ^133gXe is a complex mixture of conversion electrons and betas. A new technique to simultaneously measure the delayed coincidence (T _1/2 = 6.27 ns) between beta-particles from ^133gXe and conversion electrons depopulating the 81-keV state in 133 Cs is being developed. This technique allows separation of the ^133gXe beta spectrum from the conversion electrons due to ^131mXe and ^133mXe and uniquely quantifies all three nuclides.