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On the diffusion length of singlet oxygen in cells and tissues

Influenza A viruses can be transmitted indirectly by surviving on the surface of an object. Photodynamic inactivation (PDI) is a promising approach for disinfection of pathogens.

PDI was generated using Hypocrellin A (HA) and red light emitting diode (625–635 nm, 280 W/m²). Effects of the HA-mediated PDI on influenza viruses H1N1 and H3N2 were evaluated by the reduction of viral titers compared to virus control. After selection of the HA concentrations and illumination times, the applicability of PDI was assessed on surgical masks. Reactive oxygen species (ROS) were determined using a 2′-7′-dichlorodihydrofluorescein diacetate fluorescence probe.

In solution, 10 μM HA inactivated up to 5.11 ± 0.19 log₁₀ TCID₅₀ of H1N1 and 4.89 ± 0.38 log₁₀ TCID₅₀ of H3N2 by illumination for 5 and 30 min, respectively. When surgical masks were contaminated by virus before HA addition, PDI inactivated 99.99% (4.33 ± 0.34 log reduction) of H1N1 and 99.40% (2.22 ± 0.39 log reduction) of H3N2 under the selected condition. When the masks were pretreated with HA before virus addition, PDI decontaminated 99.92% (3.11 ± 0.19 log reduction) of H1N1 and 98.71% (1.89 ± 0.20 log reduction) of H3N2 virus. The fluorescence intensity of 2′,7′-dichlorofluorescein in photoactivated HA was significantly higher than the cell control (P > 0.05), indicating that HA efficiently generated ROS.

HA-mediated PDI is effective for the disinfection of influenza viruses H1N1 and H3N2. The approach could be an alternative to decontaminating influenza A viruses on the surfaces of objects.

The vital roles of synergetic carbon structure and iron species in periodate (PI)-based oxidation reaction remains unclear. In this study, multiple active species were identified as Fe(IV), ¹O₂, •O₂⁻, and IO₃• in the magnetic ferrite-modified biochar (MFBC)/PI process. The MFBC/PI system maintained stable degradation efficiency under wide pH ranges and the presence of various interfering anions. A unique continuous cycle experiment verifies the contribution of iron leaching-precipitation equilibrium and redox equilibrium to the degradation efficiency of PI/MFBC system. Moreover, except carbonyl functional groups (CO) on biochar could activate PI, the interacted biochar-Fe provides an active site dispersion and fast electron transfer. The attack sites and degradation pathways on DDA were determined with DFT, P and S atoms on diphenylamine dithiophosphoric acid (DDA) were suggested to be the most active sites in MFBC/PI systems. Overall, this work investigated the mechanism of PI activation by the synergistic metal–carbon at the solid–liquid interface of heterogeneous catalysts, would provide a new perspective into the catalytic activation of PI by iron-carbon composites.

Anticancer photodynamic therapy (PDT) in recent years has gained attention among therapists due to its low systemic toxicity and non-invasive nature. Today, one of the big trends in the development of photosensitizers for photodynamic therapy is a construction of advanced multifunctional molecules, which can overcome known problems for conventional drugs. In this paper, we made an attempt to create bimodal conjugates consisting of a meso-tetraphenylporphyrin (photosensitizer) and E-combretastatin A-4 (chemotherapeutic drug), which under light irradiation could: 1) participate in photodynamic treatment by ROS generation; 2) participate in chemotherapy by liberation of low-toxic E-combretastatin A-4 followed by its photoisomerization into more cytotoxic Z-combretastatin A-4. We believe, that such conjugates should demonstrate a low dark toxicity and significant light-induced antitumor properties due to step-by-step transformation of E-combretastatin A-4 into Z-combretastatin A-4. Thus, we describe the design, synthesis, photophysical and TDDFT computational studies for the new class of porphyrin/combretastatin A-4 conjugates.

The deadly viruses, which are spreading worldwide at an alarming rate, are a major challenge for the life sciences. More efficient and cost-effective methods with fewer side effects can provide a good alternative to traditional drug-based methods. Currently, physical phenomena such as light in the form of photodynamic action are increasingly being used to inactivate viruses. Photodynamic inactivation (PDI) uses a photosensitizer (PS), light, and oxygen to generate reactive oxygen species (ROS) to inactivate microorganisms. This article reviews the use of existing PSs, as one of the essential anti-viral agents, and introduces new materials and strategies combined with PDI. Physiochemical properties of PSs and their role in interaction with virus components are discussed. Furthermore, the effectiveness of optical sensitizers with radiation methods to inactivate viruses is highlighted.

Protoporphyrin IX (PpIX) is a molecule produced in the mitochondria following the administration of its approved precursor, aminolevulinic acid (ALA). Strong light absorber at different wavelengths in the visible range, PpIX is extensively used as a photosensitizer (PS) for Photodynamic Therapy (PDT). PpIX is also an ideal molecular probe for the quantification of the tissue oxygen partial pressure (pO₂), as its delayed fluorescence (DF) is quenched by oxygen, creating a direct relationship between the DF lifetime and the pO₂. A limitation of both techniques is the ignorance of the PpIX concentration in tissues when the pO₂ is measured or during PDT.

In this study, the prompt (PF) and delayed fluorescence of PpIX dissolved in DiMethylFormamide (DMF) were acquired, in absence of oxygen, at different PpIX concentrations.

Measurements of the PpIX emission for different excitation energies and temperatures, as well as spectral considerations led to the conclusion that E-type (thermal) DF was the dominant DF mechanism at low PpIX excited states concentrations (density of absorbed energy Hε[PpIX] < 1 μJ. cm⁻³, H:excitation radiant exposure per pulse, ε: molar extinction coefficient at excitation wavelength) while P-type (Triplet Triplet Annihilation) DF took place at higher excited states concentrations (Hε[PpIX] > 10 μJ. cm⁻³). The gradual development of a strong, red-shifted structureless DF peak at 670 nm, invisible in the PF and absorption spectra, strongly points towards the first observation of PpIX excimer DF (EDF). It appears that, similarly to other aromatic molecules, PpIX excimers can be formed either by the encounter of two molecules in the first excited triplet state T₁, or by the reaction of an excited singlet S₁ with a triplet T₁. Excimer DF could be beneficially used to determine the local concentration of PpIX, as the initial DF intensity ratio I₀⁶⁷⁰/I₀⁶³⁰ is linearly correlated with the local PpIX concentration, and thus rises up to the challenge of PpIX based pO₂ measurement and PDT. This work could also pave the way for a fine comprehension of the production, diffusion and catabolization of PpIX in biological tissues.