Enhanced antimicrobial efficacy and energy efficiency of low irradiance 405-nm light for bacterial decontamination.

Due to its increased safety over ultraviolet light, there is interest in the development of antimicrobial violet-blue light technologies for infection control applications. To ensure compatibility with exposed materials and tissue, the light irradiances and dose regimes used must be suitable for the target application. This study investigates the antimicrobial dose responses and germicidal efficiency of 405 nm violet-blue light when applied at a range of irradiance levels, for inactivation of surface-seeded and suspended bacteria. Bacteria were seeded onto agar surfaces (101-108 CFUplate-1) or suspended in PBS (103-109 CFUmL-1) and exposed to increasing doses of 405-nm light (≤ 288 Jcm-2) using various irradiances (0.5-150 mWcm-2), with susceptibility at equivalent light doses compared. Bacterial reductions ≥ 96% were demonstrated in all cases for lower irradiance (≤ 5 mWcm-2) exposures. Comparisons indicated, on a per unit dose basis, that significantly lower doses were required for significant reductions of all species when exposed at lower irradiances: 3-30 Jcm-2/0.5 mWcm-2 compared to 9-75 Jcm-2/50 mWcm-2 for low cell density (102 CFUplate-1) surface exposures and 22.5 Jcm-2/5 mWcm-2 compared to 67.5 Jcm-2/150 mWcm-2 for low density (103 CFUmL-1) liquid exposures (P ≤ 0.05). Similar patterns were observed at higher densities, excluding S. aureus exposed at 109 CFUmL-1, suggesting bacterial density at predictable levels has minimal influence on decontamination efficacy. This study provides fundamental evidence of the greater energy efficacy of 405-nm light for inactivation of clinically-significant pathogens when lower irradiances are employed, further supporting its relevance for practical decontamination applications.

Investigating the Mechanisms Underlying the Low Irradiance-Tolerance of the Economically Important Seaweed Species Pyropia haitanensis.

Pyropia haitanensis, one of the most economically and ecologically important seaweed species, is often exposed to persistent or transient low irradiance (LI), resulting in limited yield and quality. However, the mechanisms mediating P. haitanensis responses to LI are largely unknown. In this study, LI-tolerant (LIT) and LI-sensitive (LIS) P. haitanensis strains were compared regarding their physiological and transcriptomic changes induced by 1 and 4 days of LI (5 µmol photons/m2·s). The results indicated that the inhibition of photomorphogenesis and decreases in photosynthesis and photosynthetic carbon fixation as the duration of LI increased are the key reasons for retarded blade growth under LI conditions. A potential self-amplifying loop involving calcium signaling, phosphatidylinositol signaling, reactive oxygen species signaling, and MAPK signaling may be triggered in blades in response to LI stress. These signaling pathways might activate various downstream responses, including improving light energy use, maintaining cell membrane stability, mitigating oxidative damage, to resist LI stress. Additionally, the LIT strain maintained transcriptional homeostasis better than the LIS strain under LI stress. Specifically, photosynthesis and energy production were relatively stable in the LIT strain, which may help to explain why the LIT strain was more tolerant to LI stress than the LIS strain. The findings of this study provide the basis for future investigations on the precise mechanisms underlying the LI stress tolerance of P. haitanensis.

Universal Emission Characteristics of Upconverting Nanoparticles Revealed by Single-Particle Spectroscopy.

Upconverting nanoparticles (UCNPs) have been extensively investigated for nanophotonics and biomedical applications. However, establishing a unified view of their emission characteristics to elucidate the underlying photophysics and expand the application fields of these materials is a great challenge due to their sophisticated internal energy transfer and lack of standardized single-particle spectroscopy (SPS) platform. Here, we present an SPS technique called multiband single-particle irradiance-dependent imaging (multiband SPIDI). We demonstrate that the emission characteristics of Yb3+,Tm3+-doped UCNPs are universal for three emission bands over a wide range of irradiance and dependent on the Tm3+ doping concentration, indicating that the number of emitted photons of each band is proportional to the number of activator ions and is dependent on the number of absorbed photons and the activator interionic distance. We also suggest a cooperative energy transfer upconversion (CETU) mechanism for transition to a higher-energy state through photon accumulation. For a single UCNP, the emission at 800 nm is detectable at an ultralow irradiance of 4.9 W cm-2; moreover, that at 450 nm is measurable at 98 W cm-2, based on the optimal concentration. These findings based on the multiband SPIDI platform can provide insights into the interionic energy transfer by studying irradiance-dependent steady-state dynamics to achieve brighter UCNPs and their broader applications.

Pulse rate and blood pressure changes during low-irradiance PDT compared with conventional PDT in the treatment of facial actinic keratoses: A retrospective study.

BACKGROUND: Conventional photodynamic therapy (c-PDT) is a highly effective treatment for actinic keratoses. Besides pain as the main side effect, blood pressure (BP) increases and hypertensive crises may occur during treatment. Reducing the irradiation intensity while keeping the total dose constant (low-irradiance PDT) can achieve a clinically relevant reduction in pain. This study aimed to evaluate the influence of li-PDT on the BP and pulse (PR) during therapy and the incidence of post-interventional hypertension compared with c-PDT. METHODS: We retrospectively analyzed the treatment data of 79 patients (39 c-PDT and 40 li-PDT). BP and PR measurements were performed in all patients before PDT, at mid-exposure, and immediately after PDT. In addition, the pain was assessed by using the visual analog scale. RESULTS: Patients treated with li-PDT reported significantly lower pain than those receiving c-PDT (p < .0005). Additionally, they showed less systolic (SBP) and diastolic (DBP) BP increase (∆SBP: p < .0005, ∆DBP: p = .015) and overall lower absolute BP values (SBP: p < .0005, DBP: p = .008) compared with c-PDT. They were also significantly less likely to develop post-interventional hypertension (p = .037) or higher stages of arterial hypertension. Regarding PR, there was no difference in absolute values between both groups, but the increase from onset to half irradiation duration was significantly higher in c-PDT (p = .013). CONCLUSIONS: Li-PDT is an excellent option to reduce the elevation of arterial BP and decrease the incidence of post-interventional hypertension and hypertensive crisis. This finding has considerable relevance, especially with the risk profile of many PDT patients in mind (advanced age and cardiovascular history).

The Effect of Low Irradiance on Leaf Nitrogen Allocation and Mesophyll Conductance to CO2 in Seedlings of Four Tree Species in Subtropical China.

Low light intensity can lead to a decrease in photosynthetic capacity. However, could N-fixing species with higher leaf N contents mitigate the effects of low light? Here, we exposed seedlings of Dalbergia odorifera and Erythrophleum fordii (N-fixing trees), and Castanopsis hystrix and Betula alnoides (non-N-fixing trees) to three irradiance treatments (100%, 40%, and 10% sunlight) to investigate the effects of low irradiance on leaf structure, leaf N allocation strategy, and photosynthetic physiological parameters in the seedlings. Low irradiance decreased the leaf mass per unit area, leaf N content per unit area (Narea), maximum carboxylation rate (Vcmax), maximum electron transport rate (Jmax), light compensation point, and light saturation point, and increased the N allocation proportion of light-harvesting components in all species. The studied tree seedlings changed their leaf structures, leaf N allocation strategy, and photosynthetic physiological parameters to adapt to low-light environments. N-fixing plants had a higher photosynthesis rate, Narea, Vcmax, and Jmax than non-N-fixing species under low irradiance and had a greater advantage in maintaining their photosynthetic rate under low-radiation conditions, such as under an understory canopy, in a forest gap, or when mixed with other species.

Municipal wastewater treatment by purple phototropic bacteria at low infrared irradiances using a photo-anaerobic membrane bioreactor.

Light energy is one of the major costs for phototrophic systems. This study evaluated the photoreactor efficiency of purple phototropic bacteria anaerobic membrane bioreactor (PAnMBR) at low irradiance for the treatment of municipal wastewater. Infrared irradiance levels of 3.0 and 1.4 W/m2 produced by an infrared (IR) lamp emitting in the 800-900 nm wavelength range were investigated, with the ultimate goal of optimizing the irradiance energy demand. Experimental and modeling results demonstrated the ability of PPB to grow and treat raw municipal wastewater at the applied low irradiances, with effluent quality below target limits of TCOD˂50 mg/L, TN˂10 mg/L, and TP˂1 mg/L. While Monod kinetic parameters, km and Y, were determined to be lower than previous high-energy studies (1.9 mgCOD/mgVSS-d and 0.38 mgVSS/mgCOD, respectively), the photobioreactor performance were consistently maintained, indicating that energy cost associated with IR illumination can be reduced by up to 97%. To determine whether the treatment process could approach energy neutrality, subsequent anaerobic digestion experiments of the residual PPB biomass proved a potential for biogas recovery of up to 240 NmLCH4/gVSSadded, and a moderate biomass biodegradability of 41%. As a result, the net energy consumption of the process was estimated at 0.5 kWh/m3 of treated municipal wastewater, considering an energy demand for illumination of 0.67 kWh/m3 and an energy recovery attributed to the anaerobic digestion of 0.17 kWh/m3 from the excess PPB biomass wasted from PAnMBR.

Low irradiance compared with conventional photodynamic therapy in the treatment of actinic keratoses.

BACKGROUND: Photodynamic therapy (PDT) is an effective therapy treating photodamaged areas with multiple actinic keratoses (AK). Still pain during therapy is one of the most challenging obstacles for patients. This retrospective study compares pain and efficacy intra-individual in patients using conventional PDT (c-PDT) compared to a low irradiance PDT protocol (li-PDT) with a reduced irradiance to 25% of c-PDT. METHODS: Thirty-one patients were enrolled into this retrospective analysis treated with li-PDT and c-PDT on comparable fields of actinic damage on the forehead or the cheek. Pain was scored by the patients using a VAS. Moreover, number and time to therapy interruptions were documented. For effectiveness number and grade of AK were counted before and 4 weeks after PDT. RESULTS: Maintaining a total light dose of 37 J/cm2 , a decrease in irradiation in li-PDT patients resulted in significant less pain (VAS score 2.8 vs 7.6) and fewer therapy interruptions compared to treatment with c- PDT (P < 0.0005). No significant difference in treatment outcome was found (P = 0.068). CONCLUSION: Our data shows that li-PDT can reduce pain with at least comparable clinical outcome compared to c-PDT. Therefore, it is an effective and well-tolerated treatment for patients with multiple AK.

Efficacy and safety of continuous low-irradiance photodynamic therapy in the treatment of chest wall progression of breast cancer.

BACKGROUND: Photodynamic therapy (PDT) is a binary therapy using a drug and high-energy light source. PDT is approved for several premalignant and malignant conditions. Recent in-vitro and animal data suggest that enhanced tumor-specific cytotoxicity can be achieved with far less collateral damage to normal surrounding tissues if PDT is administered continuously at a lower dose rate for extended periods of time. Based on these promising preclinical data, we conducted a Phase I clinical trial of continuous low-irradiance photodynamic therapy (CLIPT) using 630 nm laser energy and intravenously administered porforin sodium as the photosensitizer. We determined the maximum tolerated dose (MTD) of CLIPT on skin and tumor response in subjects with cutaneous and subcutaneous metastatic nodules who had failed radiation and surgery. METHODS: Patients with cutaneous and/or subcutaneous metastatic nodules that had failed radiation and surgery were offered enrollment into the trial. The initial study design planned for sequential cohorts of six subjects to be treated at increasing laser intensity, starting at 100 J/cm(2) administered continuously over 24 h (10(-2) dose rate compared with standard PDT). Dose-limiting toxicity was defined as partial or full-thickness necrosis of the surrounding tumor-free, previously irradiated skin. The MTD was defined as the highest laser energy at which ≤33% of subjects experienced the dose-limiting toxicity. Subjects received intravenous porfirmer sodium 0.8 mg/kg 48 h before commencing CLIPT. Response rates and quality of life measures were assessed. RESULTS: Nine subjects were enrolled with chest wall progression of breast cancer following mastectomy. All had failed prior surgery and electron-beam radiation therapy. The initial two subjects were treated at 100 J/cm(2) and developed partial thickness skin necrosis. Dose reduction was therefore instituted, and the next cohort was treated at 50 J/cm(2). None of the subsequent seven subjects suffered partial or full thickness necrosis, thus establishing the MTD at 50 J/cm(2) over 24 h (0.5 mW irradiance). Six of the nine subjects (67%) had either a complete or partial clinical response. Of note, two subjects had significant regression of tumor nodules distant from the treatment field. Of the eight subjects whose terminal deoxynucleotidyl transferase dUTP nick end labeling assay results were available, 8 (100%) demonstrated histologic response to treatment as evidenced by either tumor apoptosis or regression. Quality of life measures were improved following treatment-particularly bleeding and pain from the tumor nodules. CONCLUSIONS: The MTD of CLIPT was established at 50 J/cm(2) administered continuously over 24 h. These preliminary data suggest CLIPT may be an effective, low-morbidity therapeutic modality in the treatment of cutaneous and subcutaneous metastases of breast cancer following mastectomy. Further evaluation in a larger cohort is warranted to better assess efficacy and optimize the intervention.

Salinity manipulation as an effective method for enhanced starch production in the marine microalga Tetraselmis subcordiformis.

Microalgal starch is considered a promising feedstock for bioethanol production. The biomass and starch accumulation in the marine microalga Tetraselmis subcordiformis were characterized under different salinities in response to nitrogen repletion (+N) or depletion (-N) at high irradiance (HI) or low irradiance (LI). Under favorable nutritional conditions (HI+N), biomass accumulation was seldom affected under 20% normal salinity, though starch accumulation were somewhat reduced. Increased salinity impaired overall biomass and starch accumulation, though it led to a temporary starch accumulation at initial cultivation phase. Under nitrogen deprivation, decreased salinity strengthened biomass and starch accumulation regardless of irradiance. The highest starch content of 58.2% dry weight and starch productivity of 0.62 g L(-1) d(-1) were obtained under HI-N with 20% normal salinity. Decreased salinity combined with -N generated moderate stress to facilitate starch accumulation. Salinity manipulation can be effectively applied for enhanced starch production in marine microalgae.

Effects of irradiance on non-structural carbohydrates, growth, and hypoglycemic activity of Rhynchelytrum repens (Willd.) C.E. Hubb. (Poaceae)

Irradiance is a crucial factor in plant development. Different radiant energy levels cause different responses related to plant growth and the production and distribution of dry matter. Considering the relationship between light availability and metabolism of carbohydrates and derived compounds, the aim of this work was to assess the effects of irradiance on non-structural carbohydrate contents and composition, as well as on the hypoglycemiant activity of Rhynchelytrum repens, a pantropical grass species popularly used for diabetes treatment. Plants of R. repens growing under natural irradiance (NI) showed increased content of total soluble carbohydrate (TSC), higher fluctuations in starch content (SC) and higher number of tillers. The flowering process of these plants was preceded by an increase in sucrose. However, their water content was low when compared to that of plants cultivated under low irradiance (LI). The ratio root/aerial organs and SC showed no significant differences in plants grown under LI, although TSC increased and a lower number of tillers were observed during the experimental period. In both conditions, sucrose was the ubiquitous sugar and seemed to be involved in the flowering process. A reduction in the blood sugar level was observed through the intra-peritoneal (IP) administration of the precipitate of aqueous extracts obtained from plants growing in both conditions of light; the supernatant fraction showed no hypoglycemic effect.

A irradiância é um fator crucial em reações vitais para o crescimento e desenvolvimento das plantas. A utilização da energia radiante pelos vegetais afeta diferentes respostas em relação ao padrão de desenvolvimento e à produção de matéria seca e sua conseqüente distribuição. Tendo em vista a intrínseca relação entre disponibilidade de luz, acúmulo de biomassa e metabolismo de carboidratos e compostos relacionados, os objetivos deste trabalho foram avaliar o efeito da irradiância sobre o conteúdo e a composição dos carboidratos não-estruturais, sobre o desenvolvimento e sobre a atividade hipoglicemiante de Rhynchelytrum repens, uma gramínea pantropical de origem africana utilizada popularmente no tratamento de diabetes. O cultivo a pleno sol (PS) estimulou aumento no conteúdo de carboidratos solúveis totais (CST), no perfilhamento das plantas e nas flutuações do conteúdo de amido (CA). O florescimento dessas plantas foi precedido por um aumento de CST, especialmente de sacarose. Foi observado também menor conteúdo de água nas plantas sob PS quando comparado com as plantas cultivadas sob irradiância reduzida (IR). Nesta última condição, o CA e a razão raiz/parte aérea não sofreram alterações significativas, porém houve aumento no conteúdo de CST ao longo do período experimental, menor grau de perfilhamento e formação de raízes adventícias aéreas. Em ambas as condições de luminosidade, a sacarose foi o açúcar mais abundante e com maiores variações. Esse açúcar parece estar envolvido nos processos de florescimento da espécie. Uma redução no nível de glicose plasmática foi observada a partir da administração do precipitado do extrato aquoso de R. repens obtido de plantas cultivadas em PS e IR, não havendo diferença significativa entre os tratamentos. A fração sobrenadante não apresentou efeito hipoglicemiante.