UVC Light Sources Research Articles

Photocatalysis Using UV-A and UV-C Light Sources for Advanced Oxidation of Anti-Cancer Drugs Spiked in Laboratory-Grade Water and Synthetic Urine

The presence of anti-cancer drugs in European surface waters appeals for the development of novel treatment processes. In this work, light emitting diodes (LEDs) that emit light at 255 nm (UV-C) an...

Evaluation of the sterilization effect of a new mercury-free UVC light source

Evaluation of the sterilization effect of a new mercury-free UVC light source

Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases

Airborne-mediated microbial diseases such as influenza and tuberculosis represent major public health challenges. A direct approach to prevent airborne transmission is inactivation of airborne pathogens, and the airborne antimicrobial potential of UVC ultraviolet light has long been established; however, its widespread use in public settings is limited because conventional UVC light sources are both carcinogenic and cataractogenic. By contrast, we have previously shown that far-UVC light (207–222 nm) efficiently inactivates bacteria without harm to exposed mammalian skin. This is because, due to its strong absorbance in biological materials, far-UVC light cannot penetrate even the outer (non living) layers of human skin or eye; however, because bacteria and viruses are of micrometer or smaller dimensions, far-UVC can penetrate and inactivate them. We show for the first time that far-UVC efficiently inactivates airborne aerosolized viruses, with a very low dose of 2 mJ/cm2 of 222-nm light inactivating >95% of aerosolized H1N1 influenza virus. Continuous very low dose-rate far-UVC light in indoor public locations is a promising, safe and inexpensive tool to reduce the spread of airborne-mediated microbial diseases.

Effect of LaF3: Ag fluorescent nanoparticles on photodynamic efficiency and cytotoxicity of Protoporphyrin IX photosensitizer

LaF3: Ag nanoparticles (NPs) were synthesized by the co-precipitation method. The produced NPs were characterized by X-ray diffraction (XRD) pattern, scanning electron microscope (SEM), dynamic light scattering (DLS) and Fourier transform infrared spectroscopy (FTIR). The emission spectrum of LaF3:Ag NPs is mostly overlapped with the absorption band of protoporphyrin IX (PpIX) and their conjugation was confirmed by studying fluorescence resonance energy transfer (FRET) from LaF3:Ag donor to protoporphyrin IX acceptor. The energy transfers from LaF3:Ag NPs to photosensitizer molecules is very efficient. So, the produced LaF3:Ag NPs can be recommended as light source for photodynamic therapy (PDT). The thiol group of cysteine was bound to LaF3:Ag NPs in order to conjugate LaF3:Ag NPs and protoporphyrin IX. UVC light source was used to excite fluorescent LaF3:Ag NPs. The reactive oxygen species (ROS) produced by photosensitizer was identified using special fluorescent probes (anthracene, methylene blue and methyl orange) as detectors.

Stratosphere Conditions Inactivate Bacterial Endospores from a Mars Spacecraft Assembly Facility.

Every spacecraft sent to Mars is allowed to land viable microbial bioburden, including hardy endospore-forming bacteria resistant to environmental extremes. Earth's stratosphere is severely cold, dry, irradiated, and oligotrophic; it can be used as a stand-in location for predicting how stowaway microbes might respond to the martian surface. We launched E-MIST, a high-altitude NASA balloon payload on 10 October 2015 carrying known quantities of viable Bacillus pumilus SAFR-032 (4.07 × 107 spores per sample), a radiation-tolerant strain collected from a spacecraft assembly facility. The payload spent 8 h at ∼31 km above sea level, exposing bacterial spores to the stratosphere. We found that within 120 and 240 min, spore viability was significantly reduced by 2 and 4 orders of magnitude, respectively. By 480 min, <0.001% of spores carried to the stratosphere remained viable. Our balloon flight results predict that most terrestrial bacteria would be inactivated within the first sol on Mars if contaminated spacecraft surfaces receive direct sunlight. Unfortunately, an instrument malfunction prevented the acquisition of UV light measurements during our balloon mission. To make up for the absence of radiometer data, we calculated a stratosphere UV model and conducted ground tests with a 271.1 nm UVC light source (0.5 W/m2), observing a similarly rapid inactivation rate when using a lower number of contaminants (640 spores per sample). The starting concentration of spores and microconfiguration on hardware surfaces appeared to influence survivability outcomes in both experiments. With the relatively few spores that survived the stratosphere, we performed a resequencing analysis and identified three single nucleotide polymorphisms compared to unexposed controls. It is therefore plausible that bacteria enduring radiation-rich environments (e.g., Earth's upper atmosphere, interplanetary space, or the surface of Mars) may be pushed in evolutionarily consequential directions. Key Words: Planetary protection—Stratosphere—Balloon—Mars analog environment—E-MIST payload—Bacillus pumilus SAFR-032. Astrobiology 17, 337–350.

On the photodegradation of azithromycin, erythromycin and tylosin and their transformation products – A kinetic study

In this study, the photo-induced degradation of azithromycin (Azi), erythromycin (Ery) and tylosin (Tyl) was investigated. The three macrolides are regularly found in different kinds of water, and are thus considered a potential environmental risk. In search of efficient ways for elimination, the compounds were systematically irradiated with a polychromatic UVC light source emitting 185, 254 and discretely further up to 580nm. Due to their specific structural features, the macrolides possess different optical absorption characteristics leading to photodegradation pathways with dissimilar kinetic properties. Hence, the photodegradation products and their kinetics were analyzed using high-performance liquid chromatography (HPLC) coupled to high-resolution time-of-flight mass spectrometry. Among the degradants, i.e. the products formed during UV irradiation, both sugar moieties and lactone macrocycles were observed. Applying a first order kinetic model, the half-life of Azi was determined as 1.0−3.7min, that of Ery as 1.0−14.2min depending on the reaction conditions. The two compounds possess much lower absorption cross-sections than Tyl, in particular at 254nm. Their half-lives appeared at least three times higher than that of Tyl that has t1/2 of 0.2−1.0min. Based on quantum efficiency considerations, it was assumed that the degradation of Ery and Azi was mainly due to hydroxyl radical formation, which originated from water irradiation below 200nm, whereas Tyl experienced predominantly photo induced degradation. The photodegradants of Azi exhibited half-lives of over 200min, whereas most of the photo-products of Ery and Tyl showed half-lives of less than 10min. Photodegradation processes were investigated at pH 3, pH 7 and pH 9 and in the presence of hydrogen peroxide. Both the educts and the photo-products were degraded more rapidly under neutral and acid conditions.

Preliminary Results on Deoxynivalenol Degradation in Maize by UVA and UVC Irradiation

Summary The aim of this work was to investigate the possibility of using UV irradiation for degradation of deoxynivalenol (DON) in naturally contaminated maize samples. The study was carried out by varying the distance of the contaminated maize from the UVA (368 nm) and UVC (254 nm) light source and duration of exposure of contaminated maize to UV irradiation. Two control samples of maize were used for the irradiation procedure, at DON levels of 1.902 mg/kg and 5.334 mg/kg. The samples were exposed to both UVA and UVC light at two different distances from UV lamp (15 and 30 cm) during three exposure intervals (30, 60 and 120 minutes). After irradiation DON content was determinated so the reduction levels could be quantified. Generally, the results showed reduced DON content in treated samples, but they were not consistent. The most probable reason for this was a very uneven DON distribution in naturally contaminated samples. For this reason, further research must be performed and should include irradiation of artificially inoculated samples with consistent DON distribution, the amount of irradiated sample needs to be enlarged and the higher number of replicates should be analyzed. As an additional improvement, an increase in frequency of sample mixing during the irradiation procedure needs to be done.

Reprint of: Photostability of wool fabrics coated with pure and modified TiO2 colloids

The surface of wool fabrics was coated with TiO2 and TiO2-based nanocomposite colloids and the impact of this coating on the photostability of wool was investigated. TiO2 along with TiO2/Metal and TiO2/Metal/SiO2 sols were synthesized through a low-temperature sol–gel method and applied to fabrics. Composite colloids were synthesized through integrating the silica and three noble metals of silver (Ag), gold (Au) and platinum (Pt) into the synthesis process of sols. Four different molar ratios of Metal to TiO2 (0.01%, 0.1%, 0.5% and 1%) were used to elucidate the role of metal type and amount on the obtained features. Photostability and UV protection features of fabrics were evaluated through measuring the photo-induced chemiluminescence (PICL), photoyellowing rate and ultraviolet protection factor (UPF) of fabrics. PICL and photoyellowing tests were carried out under UVA and UVC light sources, respectively. PICL profiles demonstrated that the presence of pure and modified TiO2 nanoparticles on fabrics reduced the intensity of PICL peak indicating a lower amount of polymer free radicals in coated wool, compared to that of pristine fabric. Moreover, a higher PICL peak intensity as well as photoyellowing rate was observed on fabrics coated with modified colloids in comparison with pure TiO2. The surface morphology of fabrics was further characterized using FESEM images.

Photostability of wool fabrics coated with pure and modified TiO2 colloids

The surface of wool fabrics was coated with TiO2 and TiO2-based nanocomposite colloids and the impact of this coating on the photostability of wool was investigated. TiO2 along with TiO2/Metal and TiO2/Metal/SiO2 sols were synthesized through a low-temperature sol–gel method and applied to fabrics. Composite colloids were synthesized through integrating the silica and three noble metals of silver (Ag), gold (Au) and platinum (Pt) into the synthesis process of sols. Four different molar ratios of Metal to TiO2 (0.01%, 0.1%, 0.5% and 1%) were used to elucidate the role of metal type and amount on the obtained features. Photostability and UV protection features of fabrics were evaluated through measuring the photo-induced chemiluminescence (PICL), photoyellowing rate and ultraviolet protection factor (UPF) of fabrics. PICL and photoyellowing tests were carried out under UVA and UVC light sources, respectively. PICL profiles demonstrated that the presence of pure and modified TiO2 nanoparticles on fabrics reduced the intensity of PICL peak indicating a lower amount of polymer free radicals in coated wool, compared to that of pristine fabric. Moreover, a higher PICL peak intensity as well as photoyellowing rate was observed on fabrics coated with modified colloids in comparison with pure TiO2. The surface morphology of fabrics was further characterized using FESEM images.

UV-C LEDs for Sterilization Applications

HexaTech has developed a proprietary, patented process for manufacturing bulk aluminum nitride (AlN) crystals and semiconductor wafers. HexaTech is leveraging this unique capability to develop and commercialize high-performance, long-lifetime Ultra Violet Light Emitting Diodes (UV-C LEDs) for disinfection applications (particularly clean water) and high-voltage, high-efficiency power semiconductors for power conversion applications (particularly smart grid). Deep-ultraviolet light with wavelength in the range of 250 to 280nm (UV-C) has been used to sterilize liquids, air and surfaces for over a century. UV-C light is absorbed by and damages the DNA of harmful bacteria, either outright killing the bacteria or preventing their ability to replicate. Traditionally, high voltage mercury tubes have been used to generate such UV light. While mercury tubes have enabled UV-C use bulk disinfection applications such as drinking water and waste water, they have proven impractical in point-of-use applications where small size, elimination of harmful mercury, and high reliability under intermittent use conditions are required. The solution is to generate UV-C light using LEDs. In spite of numerous efforts, the power output and reliability of UV-C LEDs is still not sufficient for their adoption as practical and reliable UV-C light sources. Traditionally, AlGaN-based UV-C LEDs have been fabricated on sapphire substrates. Because of huge number of defects caused by the lattice mismatch between the AlGaN active layers and the sapphire substrate, these sapphire-based UV-C LEDs show performance and reliability of limited interest to sterilization system manufacturers. HexaTech's AlN crystal growth and wafer processing technology results in single crystal wafers with extremely high quality. HexaTech and its development partners have fabricated UV-C LEDs that have shown performance dramatically superior to other devices in the market in terms of output power, power density and lifetime. In this presentation, we will discuss the market requirements for UV-C LEDs, the challenges of UV-C device fabrication, package and test, and the solutions that are being pursued.

Kinetics of water disinfection using UV-C radiation

The current work is concerned with the development of a kinetic model for UV disinfection process at 254nm. The micro-organism was Escherichia coli (E. coli). The inactivation of E. coli active cells, suspended in sterile double-distilled water, free-of solids, nutrient and any trace of broth, was carried out in a bench-scale annular photoreactor, designed specifically for developing kinetic studies. The UV-C light source used was a tubular low pressure Philips lamp, model TUV-36W. The reactor model was based on the conservation principles. The radiation field was modelled according to the radial incidence model. The incident radiation energy at the photoreactor optical entrance was measured by homogeneous potassium ferrioxalte actinometry (1.4×10−9Einsteincm−2s−1). The Naperian absorption coefficient of the E. coli active cells was obtained (1.05×10−8cm2MPN−1). The kinetic model proposed was a simple phenomenological equation relating the reaction rate to both the concentration of microbial active cells and the radiation energy absorbed by these cells. A term related to the rate of growth of microbial cells was added to the kinetic model. The experimental runs were carried out for conditions where the initial concentration of E. coli active cells varied from 2.0×104MPNcm−3 to 2.0×106MPNcm−3, pH7 and temperature 25°C. Disinfection efficacies of 4.3-Log and 6.3-Log were achieved for both conditions and the respective required UV doses were 23.4mWcm−2 and 31.2mWscm−2. The kinetic model fitted the data well (to 95%). The kinetic parameters, n and K, were estimated in 0.5 and 2.9×10−2s−1(cm3Einstein−1)0.5, respectively.

Parametric optimization of individual and hybridized AOPs of Fe 2+/H 2O 2 and UV/S 2O 82− for rapid dye destruction in aqueous media

The aim of the study was to assess and optimize the UV/S 2O 8 2− (activated persulfate ion), Fe 2+/H 2O 2 (Fenton), UV/Fe 2+/H 2O 2 (photo-Fenton), and their hybridized processes for discoloration, degradation and mineralization of an azo dye, Direct Red 16, as a model pollutant, in aqueous media. A special air bubbling photo-reactor, with a perfect photon utilizing of an only 6 W, UV-C light source, was employed and a promising hybridized homogeneous AOP, as: UV/S 2O 8 2−/Fe 2+/H 2O 2, under initial natural pH of 6.0, was introduced. This process exhibits a rapid discoloration (100% in 30 min), as well as aromatic rings degradation (more than 86% in 40 min) and mineralization (more than 50% in 60 min) of DR16 with 30 mg/L initial concentration at 25 °C. The optimum parameters of initial pH, initial reagents dosage and temperature were reported for each process. The ferrous ion catalyst concentration was much less than its standard limit. Different processes kinetic relationships were introduced in a power law model and as a function of dye concentration and temperature. Moreover, synergism impact of UV light on the catalytic center of Fenton process was proved based on a kinetic analysis.

Artificial neural networks developed for prediction of dye decolorization efficiency with UV/K 2S 2O 8 process

The present work has focused on modeling the decolorization of C.I. Direct Red 16 (DR16) using UV/K 2S 2O 8 process. The experiments were conducted in an air bubbled batch photo-reactor with three liters capacity, and equipped with a UV-C light source of only 6 W, placed horizontally in its center. An artificial neural network (ANN) model was developed to model and predict the behavior of the process. Five important operational parameters and decolorization efficiency were introduced as the inputs and outputs of the network. Six three-layered ANNs with different component functions and also one four-layered ANN were constructed. A developed three-layered ANN provides the best results, using BFGS quasi-Newton backpropagation learning algorithm (trainbfg), “tansig” and “purelin” as transfer functions in hidden and output layers. Also, application of 9 neurons in the hidden layer and 400 iterations for the network calibration caused to satisfy network training while overfitting was prevented. For the four-layered ANN the 5-4 mode of the 9 neurons repartition is the best among all the possibilities. The K-fold cross-validation method, employed for the performance evaluation, showed high correlation coefficient (0.9968) and low mean square error (2.56 × 10 −4) for testing data. Sensitivity analysis indicated order of operational parameters relative importance on the reaction as: time > [DR16] 0 > [S 2O 8] 0 > pH ≈ temperature.

Photodegradation Kinetics of Toluene in Indoor Air at Different Humidities Using UVA, UVC and UVLED Light Sources in the Presence of Silver Titanium Dioxide

This study investigated the photo-decomposition kinetics of toluene in indoor air pollution by ultraviolet light using ultraviolet light emitting diodes (UVLEDs) instead of the more traditional ultraviolet lamp emitting at 254 nm (UVC) or 365 nm (UVA). The study was conducted at different humidities (RHs) and energy efficiencies of the lamps. Experiments were conducted over a range of residence times between 20 and 450 min, relative RHs of 0—50% and toluene concentrations between 20 and 350 ppm. Photo-catalytic decomposition of toluene at various initial concentrations and moisture contents were elucidated according to the Langmuir—Hinshelwood model. The reaction kinetics of the three light sources over 0.5 g of silver titanium oxide (Ag/TiO2) are proposed. A comparison of the simulation results with the experimental data was also made, indicating good agreement. The magnitudes of average energy effectiveness (Ee) under various RHs at the same degradation efficiency (η) were in the order of UVLED (6.7 × 10-4 mg · kW-1 · h-1) &gt;UVC (1.1 × 10-4 mg · kW-1 · h-1) &gt;UVA (9 × 10 -5 mg · kW-1 · h-1). The UVLED uses a lot less energy in comparison with traditional UV lamps. Thus, this study shows the feasible and potential use of UVLED for photocatalysis in the indoor environment with the advantage of energy conservation and greater security.

Abstract 1314: Real-time imaging of individual cancer cell nuclear-cytoplasmic dynamics of UV-induced apoptosis of cancer cells in the brain

Abstract We have developed a novel in vivo mouse model to image cancer cell nuclear-cytoplasmic dynamics in the brain in real-time and to visualize UV-C light killing of these cells. We used dual-color fluorescent cancer cells that express green fluorescent protein (GFP) linked to histone H2B in the nucleus and retroviral red fluorescent protein (RFP) in the cytoplasm. In order to visualize metastatic single cancer cell nuclear-cytoplasmic dynamics in the brain, dual-color Lewis Lung carcinoma (LLC) cells were injected into the right internal carotid artery of nude mice. A craniectomy open window was made over the right parietal bone. Metastatic dual-color LLC cells were irradiated with a 3.6-watt hand held UV-C light source for 60 seconds. The cells were then observed over 24 hours at 3 hour intervals through the open craniectomy window. The cancer cells were observed in the brain with the Olympus OV100 Small Animal Imaging System under high magnification. Metastatic dual-color LLC cells were visualized at the subcellular level in the brain enabling apoptosis to be imaged by nuclear morphology. UV-C light induced apoptosis of the dual-color LLC cells in the brain. Aggregation of chromatin at the nuclear membrane and fragmented nuclei of the cancer cell were followed in real time in the brain. More than 90% of the cancer cells irradiated with UV-C light died and disappeared without overt toxicity of the host. The novel mouse model used here will enable a deeper understanding of cancer cell dynamics in the brain. UV-C light may be a powerful tool for treatment of cancer cells expressing fluorescent reporters which now can be effected in vivo (Proc. Natl. Acad. Sci. USA, 1-6, 14514-14517, 2009 and Molecular Cancer Therapeutics 8, 3001-3008, 2009). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1314.

Disinfection of Pseudomonas aeruginosa biofilm contaminated tube lumens with ultraviolet C light emitting diodes

Bacterial biofilms on long-term catheters are a major source of infection. Exposure to ultraviolet C (UVC – 265 nm) light was shown in an earlier study to reduce the number of bacteria substantially on ex vivo treated urinary patient catheters. Very large doses (long treatment times) should, however, be applied to obtain 99.9% disinfection rates. The major reason was that besides cells the mature biofilm contained absorbing and scattering particulates, which made the biofilm opaque. The potential of UVC light emitting diodes (LED) for disinfection purposes in catheter-like tubes contaminated with biofilm was investigated. It was shown that UVC light propagation was possible through both Teflon and catheter tubes (silicone). The disinfection efficiency of the diodes was demonstrated on tubes contaminated artificially with a Pseudomonas aeruginosa biofilm. The tubes were connected to a flow system and biofilms were produced during a 3 day period. Tubes in lengths of 10 (Teflon, silicone) and 20 cm (Teflon) were contaminated. Tubes for control and for UVC treatment were contaminated in parallel. Biofilms were sampled from the total inner surface of the tubes. Colony counts on the control samples were in the range of 5 × 105–1.3 × 109 CFU ml−1, with disinfection rates in the range 96–100%. The applied UVC doses corresponded to treatment times between 15 and 300 min. Disinfection (100%) was obtained in 10 cm Teflon tubes exposed for 30 min (detection limit <5 CFU ml−1). The same result was obtained for a 20 cm Teflon tube exposed for 300 min. The disinfection rate was 96% for the 20 cm tube if the dose was reduced to 30 min. A disinfection rate of 99.99% was observed for a 10 cm peritoneal dialysis catheter tube (silicone) exposed for 300 min. Differences between the tubes were dependent on the differences in length and the type of the material. The UVC light was transmitted six times more efficiently in Teflon than in silicone tubes of equal length (10 cm). The germicidal effect to obtain a 99.99% killing rate for the biofilm (∼78 J m−2) is comparable to that for the planktonic bacterium. It is concluded that there is potential for LED UVC light sources if they are used for disinfection of thin biofilms.

Dissection of the high velocity air control (HVAC) system serving the in vitro fertilization (IVF) laboratory: the impact of ultraviolet-c band (UVC) irradiation on clinical pregnancy rates (CPR)

Successful preimplantation embryogenesis (pe) is critically dependent upon the culture environment and changing organic chemistry of the ambient air (aa) provided by the IVF laboratory. The HVAC system serving the IVF laboratory plays a key role in controlling aa quality. Its design and maintenance is critical as it can serve as both the source of and perfect conduit for the spread of embryotoxic bioaersols and microorganisms. Placement of UVC light sources within the HVAC system will kill pathogens threatening the aa.

Estimation of ventricular overload using a magnetocardiogram and its use for pre- and postoperative evaluation

The aim of the study was to assess and optimize the UV/S2O82− (activated persulfate ion), Fe2+/H2O2 (Fenton), UV/Fe2+/H2O2 (photo-Fenton), and their hybridized processes for discoloration, degradation and mineralization of an azo dye, Direct Red 16, as a model pollutant, in aqueous media. A special air bubbling photo-reactor, with a perfect photon utilizing of an only 6 W, UV-C light source, was employed and a promising hybridized homogeneous AOP, as: UV/S2O82−/Fe2+/H2O2, under initial natural pH of 6.0, was introduced. This process exhibits a rapid discoloration (100% in 30 min), as well as aromatic rings degradation (more than 86% in 40 min) and mineralization (more than 50% in 60 min) of DR16 with 30 mg/L initial concentration at 25 °C. The optimum parameters of initial pH, initial reagents dosage and temperature were reported for each process. The ferrous ion catalyst concentration was much less than its standard limit. Different processes kinetic relationships were introduced in a power law model and as a function of dye concentration and temperature. Moreover, synergism impact of UV light on the catalytic center of Fenton process was proved based on a kinetic analysis.