Photodynamic Eradication of Pseudomonas aeruginosa with Ru-Photosensitizers Encapsulated in Enzyme Degradable Nanocarriers

The development of new approaches for the treatment of the increasingly antibiotic-resistant pathogen Pseudomonas aeruginosa was targeted by enhancing the effect of local antimicrobial photodynamic therapy (aPDT) using poly(ethylene glycol)-block-poly(lactic acid) (PEG114-block-PLAx) nanocarriers that were loaded with a ruthenium-based photosensitizer (PS). The action of tris(1,10-phenanthroline) ruthenium (II) bis(hexafluorophosphate) (RuPhen3) encapsulated in PEG114-block-PLAx micelles and vesicles was shown to result in an appreciable aPDT inactivation efficiency against planktonic Pseudomonas aeruginosa. In particular, the encapsulation of the PS, its release, and the efficiency of singlet oxygen (1O2) generation upon irradiation with blue light were studied spectroscopically. The antimicrobial effect was analyzed with two strains of Pseudomonas aeruginosa. Compared with PS-loaded micelles, formulations of the PS-loaded vesicles showed 10 times enhanced activity with a strong photodynamic inactivation effect of at least a 4.7 log reduction against both a Pseudomonas aeruginosa lab strain and a clinical isolate collected from the lung of a cystic fibrosis (CF) patient. This work lays the foundation for the targeted eradication of Pseudomonas aeruginosa using aPDT in various medical application areas.

Antimicrobial Photodynamic Therapy: Latest Developments with a Focus on Combinatory Strategies

Antimicrobial photodynamic therapy (aPDT) has become a fundamental tool in modern therapeutics, notably due to the expanding versatility of photosensitizers (PSs) and the numerous possibilities to combine aPDT with other antimicrobial treatments to combat localized infections. After revisiting the basic principles of aPDT, this review first highlights the current state of the art of curative or preventive aPDT applications with relevant clinical trials. In addition, the most recent developments in photochemistry and photophysics as well as advanced carrier systems in the context of aPDT are provided, with a focus on the latest generations of efficient and versatile PSs and the progress towards hybrid-multicomponent systems. In particular, deeper insight into combinatory aPDT approaches is afforded, involving non-radiative or other light-based modalities. Selected aPDT perspectives are outlined, pointing out new strategies to target and treat microorganisms. Finally, the review works out the evolution of the conceptually simple PDT methodology towards a much more sophisticated, integrated, and innovative technology as an important element of potent antimicrobial strategies.

Probing of local polarity in poly(methyl methacrylate) with the charge transfer transition in Nile red

The permittivity of polymers and its spatial distribution play a crucial role in the behavior of thin films, such as those used, e.g., as sensor coatings. In an attempt to develop a conclusive approach to determine these quantities, the polarity of the model polymer poly(methyl methacrylate) (PMMA) in 600 nm thin films on a glass support was probed by the energy of the charge transfer transition in the oxazine dye Nile red (NR) at 25 °C. The absorption and fluorescence spectra of NR were observed to shift to the red with increasing solvent polarity, because of the intramolecular charge transfer character of the optical transition. New types of solvatochromic plots of emission frequency against absorption frequency and vice versa afforded the Onsager radius-free estimation of the ground and excited states dipole moment ratio. With this approach the values of these dipole moments of 11.97 D and 18.30–19.16 D, respectively, were obtained for NR. An effective local dielectric constant of 5.9–8.3 for PMMA thin films was calculated from the solvatochromic plot and the fluorescence maximum of NR observed in the PMMA films. The fluorescence band of NR in the rigid PMMA films shifted to the red by 130 cm⁻¹ with increasing excitation wavelength from 470 to 540 nm, while in a series of liquids the position of the emission maximum of NR remained constant within same range of the excitation wavelength. It is concluded that the fluorescence spectrum of NR in PMMA undergoes inhomogeneous broadening due to different surroundings of NR molecules in the ground state and slow sub-glass transition (T_g) relaxations in PMMA.

Fluorescence lifetime-based sensing of polymersome leakage

Assays to analyze the degradation, lysis and leakage of vesicles are commonly utilized in biology and physical chemistry. Here we show the fluorescence lifetime-based sensing of the leakage of stimuli responsive PEG₁₁₄-b-PLA₁₆₇ block copolymer vesicles. The time-resolved technique differentiates between the fluorophore molecules in the solvated state at high concentrations, and in the wall material and in the solvated state at low concentrations. The vesicle leakage occurs after an incubation period, which was detected by the change of the time correlated single photon counting decays.

Detailed Study of BSA Adsorption on Micro- and Nanocrystalline Diamond/β-SiC Composite Gradient Films by Time-Resolved Fluorescence Microscopy

The adsorption of bovine serum albumin (BSA) on micro- and nanocrystalline diamond/β-SiC composite films synthesized using the hot filament chemical vapor deposition (HFCVD) technique has been investigated by confocal fluorescence lifetime imaging microscopy. BSA labeled with fluorescein isothiocyanate (FITC) was employed as a probe. The BSA^FITC conjugate was found to preferentially adsorb on both O-/OH-terminated microcrystalline and nanocrystalline diamond compared to the OH-terminated β-SiC, resulting in an increasing amount of BSA adsorbed to the gradient surfaces with an increasing diamond/β-SiC ratio. The different strength of adsorption (>30 times for diamond with a grain size of 570 nm) coincides with different surface energy parameters and differing conformational changes upon adsorption. Fluorescence data of the adsorbed BSA^FITC on the gradient film with different diamond coverage show a four-exponential decay with decay times of 3.71, 2.54, 0.66, and 0.13 ns for a grain size of 570 nm. The different decay times are attributed to the fluorescence of thiourea fluorescein residuals of linked FITC distributed in BSA with different dye-dye and dye-surface distances. The longest decay time was found to correlate linearly with the diamond grain size. The fluorescence of BSA^FITC undergoes external dynamic fluorescence quenching on the diamond surface by H- and/or sp²-defects and/or by amorphous carbon or graphite phases. An acceleration of the internal fluorescence concentration quenching in BSA^FITC because of structural changes of albumin due to adsorption, is concluded to be a secondary contributor. These results suggest that the micro- and nanocrystalline diamond/β-SiC composite gradient films can be utilized to spatially control protein adsorption and diamond crystallite size, which facilitates systematic studies at these interesting (bio)interfaces.

Recent advances in hybrid measurement methods based on atomic force microscopy and surface sensitive measurement techniques

This review summaries the recent progress of the combination of optical and non-optical surface sensitive techniques with the atomic force microscopy.