The role of the light source in antimicrobial photodynamic therapy

Antimicrobial photodynamic therapy (APDT) is a promising approach to fight the growing problem of antimicrobial resistance that threatens health care, food security and agriculture. APDT uses light to excite a light-activated chemical (photosensitiser), leading to the generation of reactive oxygen species (ROS). Many APDT studies confirm its efficacy in vitro and in vivo against bacteria, fungi, viruses and parasites. However, the development of the field is focused on exploring potential targets and developing new photosensitisers. The role of light, a crucial element for ROS production, has been neglected. What are the main parameters essential for effective photosensitiser activation? Does an optimal light radiant exposure exist? And finally, which light source is best? Many reports have described the promising antibacterial effects of APDT in vitro, however, its application in vivo, especially in clinical settings remains very limited. The restricted availability may partially be due to a lack of standard conditions or protocols, arising from the diversity of selected photosensitising agents (PS), variable testing conditions including light sources used for PS activation and methods of measuring anti-bacterial activity and their effectiveness in treating bacterial infections. We thus sought to systematically review and examine the evidence from existing studies on APDT associated with the light source used. We show how the reduction of pathogens depends on the light source applied, radiant exposure and irradiance of light used, and type of pathogen, and so critically appraise the current state of development of APDT and areas to be addressed in future studies. We anticipate that further standardisation of the experimental conditions will help the field advance, and suggest key optical and biological parameters that should be reported in all APDT studies. More in vivo and clinical studies are needed and are expected to be facilitated by advances in light sources, leading to APDT becoming a sustainable, alternative therapeutic option for bacterial and other microbial infections in the future.

Possibilities to estimate the personal UV radiation exposure from ambient UV radiation measurements

People are exposed to solar ultraviolet radiation (UVR) throughout their entire lives. Exposure to UVR is vital but also poses serious risks. The quantification of human UVR exposure is a complex issue. Personal UVR exposure is related to ambient UVR as well as to a variety of factors such as the orientation of the exposed anatomical site with respect to the sun and the duration of exposure. This is mainly determined by personal behaviour. A variety of efforts have been made in the past to measure or model the personal UVR exposure of people and often personal UVR exposure has been expressed as the percentage of ambient UVR. On the other hand, ambient UVR is being monitored at a variety of places and measurements are available even online. This suggests that both the knowledge of personal UVR exposure and measurements of ambient UVR is required. In this paper, a summary on the different methods, which use ambient UVR measurements to estimate personal UVR exposure of people, as well as a few examples, are given. Advantages and disadvantages will be discussed as well as possibilities and limitations. This also includes an overview of appropriate terminology, units and basic statistic parameters to describe personal UVR exposure.

Multi-anthracene containing fluorescent probe for spectrofluorimetric iron determination in environmental water samples

An anthracene-based fluorescence (FL) system was synthesized via a general synthetic procedure. Fourier transform infrared spectroscopy (FTIR), MALDI-MS, and nuclear magnetic resonance spectroscopy (¹³C and ¹H NMR) were carried out to characterize the multi-anthracene containing probe. The photophysical properties of the probe were illustrated via 3D-FL analysis and excitation-emission matrix (EEM) measurements. Density-functional theory (DFT) was applied to optimize the structure of the prepared probe and investigate its molecular interactions with Fe³⁺. The FL proficiency of the probe was appraised by spectroscopic measurements like Ultraviolet-Visible (UV-Vis) and FL spectroscopies. The simple and highly sensitive probe was able to diagnose ferric ions' low concentrations and detection limit reached upto 0.223 µM with linear working range between 0.22 and 92.00 µM for Fe³⁺ ions. The efficacy of this fluorescent probe was confirmed by testing for iron determination in environmental samples. Various fluorophores or ionophores could be applied for achieving novel probes by the proposed procedures and for diagnosing diverse metal ions.

Personal ultraviolet Radiation exposure in a cohort of Chinese mother and child pairs: the Chinese families and children study

BACKGROUND

Few studies in China have examined personal ultraviolet radiation (UVR) exposure using polysulfone dosimetry.

METHODS

In this study, 93 mother and adolescent child pairs (N = 186) from two locations in China, one rural (higher latitude) and one urban (lower latitude), completed 3 days of personal UVR dosimetry and a sun/clothing diary, as part of a larger pilot study.

RESULTS

The average daily ambient UVR in each location as measured by dosimetry was 20.24 Minimal Erythemal Doses (MED) in the rural location and 20.53 MED in the urban location. Rural mothers had more average daily time outdoors than urban mothers (5.5 h, compared with 1.5 h, in urban mothers) and a much higher daily average personal UVR exposure (4.50 MED, compared with 0.78 MED in urban mothers). Amongst adolescents, rural males had the highest average daily personal UVR exposure, followed by rural females, urban females and urban males (average 2.16, 1.05, 0.81, and 0.48 MED, respectively).

CONCLUSIONS

Although based on small numbers, our findings show the importance of geographic location, age, work/school responsibilities, and sex of the adolescents in determining personal UVR exposure in China. These results suggest that latitude of residence may not be a good proxy for personal UVR exposure in all circumstances.

An Anthracene Excimer Fluorescence Probe on Mesoporous Silica for Dual Functions of Detection and Adsorption of Mercury (II) and Copper (II) with Biological In Vivo Applications

Dual functional activity by the same organic-inorganic hybrid material toward selective metal ion detection and its adsorption has drawn more attraction in the field of sensing. However, most of the hybrid materials in the literature are either for sensing studies or adsorption studies. In this manuscript, a fluorescent active hybrid material SiO₂ @PBATPA is synthesized by covalent coupling of anthracene-based chelating ligand N,N'-(propane-1,3-diyl) bis(N-(anthracen-9-ylmethyl)-2-((3-(triethoxysilyl)propyl) amino) acetamide) (PBATPA) within the mesopores of newly synthesized cubic mesoporous silica. The synthetic strategy is designed to form an exclusively intramolecular excimer on a solid surface, which is then used as a sensory tool for selective detection of metal ions through fluorescence quenching by the destruction of excimer upon metal ion binding. The dual functions of sensing and adsorption studies show selectivity toward Hg²⁺ and Cu²⁺ among various metal ions with detection limits of 37 and 6 ppb, respectively, and adsorption capacities of 482 and 246 mg g^-1 , respectively. This material can be used as a sensory cum adsorbent material in real food samples and living organisms such as the brine shrimp Artemia salina without any toxic effects from the material.

Effect of fiber insertion depth on antibacterial efficacy of photodynamic therapy against Enterococcus faecalis in rootcanals

OBJECTIVES

This in vitro study evaluated the effect of fiber insertion depth on antimicrobial efficacy of antimicrobial photodynamic therapy (aPDT) using a photosensitizer (PS; toluidine blue) and a red light-emitting diode (LED) in root canals infected with Enterococcus faecalis.

MATERIALS AND METHODS

Single-rooted extracted teeth were prepared with nickel-titanium-instruments, sterilized, contaminated with E. faecalis, and incubated for 72 h. Roots were randomly divided into four experimental groups: PS only, LED only, aPDT with LED in the apical third, aPDT with LED in the coronal third, as well as into infection and sterile controls (each n = 10). Samples were taken by collecting standardized dentine shavings from the root canal walls. After serial dilution and culturing on blood agar, colony-forming units (CFU) were counted.

RESULTS

Both aPDT groups showed a CFU reduction of 1-2 log₁₀ steps compared with the infection control, whereas the effect of fiber insertion depth was negligible (<0.5 log₁₀ steps). CFU reduction of approximately 0.5 log₁₀ steps for PS alone was detected compared with the infection control, but PS alone was less effective than both aPDT groups. No antibacterial effect was detected for LED alone.

CONCLUSIONS

aPDT reduced E. faecalis within the root canal, whereas fiber insertion depth had a negligible influence on antimicrobial effectiveness of aPDT.

CLINICAL RELEVANCE

The insertion depth of the light-emitting diode may not influence the antibacterial efficacy of photodynamic therapy against E. faecalis in straight root canals.