Search Results (24)

This study is the first to investigate the performance of ultraviolet germicidal irradiation (UVGI) in underfloor air distribution (UFAD) systems. A simplified mathematical model is developed to predict airborne pathogen transport and inactivation by upper room UVGI in UFAD spaces. The proposed model is substantiated for the SARS-CoV-2 virus as a simulated pathogen through a comprehensive computational fluid dynamics methodology validated against published experimental data of upper room UVGI and UFAD flows. Simulations show an 11% decrease in viral concentration within the upper irradiated zone when a 15 W louvered germicidal lamp is utilized. Finally, a case study on Mycobacterium tuberculosis (M. tuberculosis) bacteria is carried out using the validated simplified model to optimize the use of return air and UVGI implementation, ensuring acceptable indoor air quality and enhanced energy efficiency. Results reveal that the UFAD-UVGI system may consume up to 13.6% less energy while keeping the occupants at acceptable levels of M. tuberculosis concentration and UV irradiance when operated with 26% return air and a UVGI output of 72 W. Full article

This paper addresses the upconversion of blue light to ultraviolet-C (UVC) with Pr³⁺-activated materials for antibacterial applications of UVC. It discusses the processes through which UV radiation provides biocidal effects on microorganisms, along with the most popular UVC sources employed in these processes. We describe the electronic and optical properties of the Pr³⁺ ion, emphasizing the conditions the host material must meet to obtain broad and intense emission in the UVC from parity-allowed transitions from the 4f5d levels and provide a list of materials that fulfill these conditions. This paper also delineates lanthanide-based upconversion, focusing on Pr³⁺ blue to UVC upconversion via the ³P₀ and ¹D₂ intermediate states, and suggests routes for improving the quantum efficiency of the process. We review literature related to the use of upconversion materials in antimicrobial photodynamic treatments and for the blue to UVC upconversion germicidal effects. Further, we propose the spectral overlap between the UVC emission of Pr³⁺ materials and the germicidal effectiveness curve as a criterion for assessing the potential of these materials in antimicrobial applications. Finally, this paper briefly assesses the toxicity of materials commonly used in the preparation of upconversion materials. Full article

UV-C LEDs, which offer short-wavelength characteristics and serve as an alternative to traditional UV mercury lamps, represent a new light source for applications in space decontamination and surface disinfection. This paper presents the design and development of a UV-C LED lamp driver circuit configured to operate with a DC-input voltage source for sterilization and germicidal purposes. The primary circuit integrates a modified buck converter with a flyback converter, resulting in an innovative single-stage, single-switch DC-DC power converter. Additionally, the proposed electronic driver recovers energy stored in the transformer’s leakage inductors, enhancing overall circuit efficiency. A prototype driver circuit with a 3.3 W power rating (10 V/330 mA) is developed for a UV-C LED lamp intended for sterilization and germicidal applications with a DC-input voltage source. The experimental results from the prototype circuit, tested at an 18 V DC input, confirm the functionality of the proposed electronic driver for UV-C LED sterilization and germicidal lighting. Additionally, the circuit achieves efficiency exceeding 91%. Full article

The prevalence of airborne pathogens in indoor environments presents significant health risks due to prolonged human occupancy. This review addresses diverse air purification systems to combat airborne pathogens and the factors influencing their efficacy. Indoor aerosols, including bioaerosols, harbor biological contaminants from respiratory emissions, highlighting the need for efficient air disinfection strategies. The COVID-19 pandemic has emphasized the dangers of airborne transmission, highlighting the importance of comprehending how pathogens spread indoors. Various pathogens, from viruses like SARS-CoV-2 to bacteria like Mycobacterium (My) tuberculosis, exploit unique respiratory microenvironments for transmission, necessitating targeted air purification solutions. Air disinfection methods encompass strategies to reduce aerosol concentration and inactivate viable bioaerosols. Techniques like ultraviolet germicidal irradiation (UVGI), photocatalytic oxidation (PCO), filters, and unipolar ion emission are explored for their specific roles in mitigating airborne pathogens. This review examines air purification systems, detailing their operational principles, advantages, and limitations. Moreover, it elucidates key factors influencing system performance. In conclusion, this review aims to provide practical knowledge to professionals involved in indoor air quality management, enabling informed decisions for deploying efficient air purification strategies to safeguard public health in indoor environments. Full article

Far-ultraviolet C light, with a wavelength of 200–230 nm, has demonstrated broad-spectrum germicidal efficacy. However, due to increased interest in its use as an alternative antimicrobial, further knowledge about its fundamental bactericidal efficacy is required. This study had two objectives. Firstly, it investigated experimentally the Far-UVC dose–response of common bacteria suspended at various cell densities in transparent buffer, ensuring no influence from photosensitive suspending media. Increasing doses of Far-UVC were delivered to Enterococcus faecium, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus in PBS at 10¹, 10², 10³, 10⁵ and 10⁷ CFU·mL⁻¹, with surviving colony-forming units enumerated (n ≥ 3). Secondly, through a systematised literature review, this work sought to explore the impact of genus/species, Gram type, cell form, cell density and irradiance on dose–response. The screening of 483 publications was performed with 25 included in the study. Data for 30 species were collated, analysed and compared with the experimental results. Overall, Gram-positive species showed greater resilience to Far-UVC than Gram-negative; some inter-species and inter-genera differences in resilience were identified; endospores were more resilient than vegetative cells; the results suggested that inactivation efficiency may decrease as cell density increases; and no significant correlation was identified between irradiance and bactericidal dose effect. In conclusion, this study has shown Far-UVC light to be an effective decontamination tool against a vast range of bacterial vegetative cells and endospores. Full article

Germicidal lamps that primarily emit 254 nm ultraviolet (UV) radiation have been effectively utilized for surface sterilization, but they cannot be used on human skin and eyes due to their harmful and genotoxic activity. Recent reports have shown that far UV-C light (207–222 nm) can efficiently kill pathogens with potentially no harm to exposed human tissues. However, these methods still require additional filtering and/or further protective equipment. In this study, we demonstrate a filter-free, harmless, and single-wavelength far UV-C 207 nm germicidal light source that can be used to inactivate different respiratory viruses. It can be exploited as a safe and effective disinfection tool for various airborne viruses. We successfully developed a single-wavelength far UV-C source that produces an exact wavelength of 207 nm. We examined its safety on human skin and corneal cell lines, as well as its effects on inactivating different airborne viruses, such as coronavirus, adenovirus, and vaccinia virus. We expect that our far UV-C lamps can be safely and conveniently used to reduce COVID-19 infections and protect both our living spaces and hospitals from the threat of contamination by possible new or mutant viruses. Full article

The COVID-19 pandemic has brought renewed urgency to air disinfection. Upper room germicidal ultraviolet light (GUV) disinfects room air very efficiently. Its effect on practical outcomes in public settings remains unclear, but history may provide some insights. An interrupted time series model was fitted to a newly discovered dataset of attendance records from a preschool between 1941 to 1949, where GUV was installed in December 1945. GUV was associated with a sizable reduction in child absenteeism due to respiratory illnesses of any cause. Odds ratios for the effect ranged from 0.5 to 0.77, depending on the season. In all but high summer, model-predicted absenteeism rates were reduced by between a third and a half by GUV. Wider use of upper room germicidal UV systems in schools and preschools may be worthwhile, to reduce absenteeism due to respiratory illness and the educational, social, and economic consequences that ensue. Full article

Difenoconazole is a triazole germicide that is usually applied to prevent fungal diseases on crops with high efficiency and safety. Jujube is a spiny Rhamnaceous plant that originated in China more than 4000 years ago and is extensively cultivated in northern China nowadays. To evaluate the safety of difenoconazole in jujube, supervised field trials were carried out in six provinces of China, and the final residue and dissipation behavior of difenoconazole on jujube were determined by gas chromatography (GC). The results showed that when addition levels were 0.02, 0.2, and 2 mg·kg⁻¹, average recoveries of the aforementioned method for difenoconazole in jujube can be put into the range of 73–108%, and relative standard deviation (RSD) was 3–9%. The limit of quantitation (LOQ) for this method was 0.02 mg·kg⁻¹. In the final residue test, difenoconazole was sprayed to deal with the jujube at 100 and 150 mg·kg⁻¹ doses twice or three times, respectively, while the dissipation test was applied only once at a 150 mg·kg⁻¹ dose. Final residue testing results have revealed that when jujube samples were harvested and tested at 7, 14, and 21 days post-application, difenoconazole residues in samples were 0.11–1.59, 0.05–0.77, 0.04–0.63 mg·kg⁻¹, respectively. The dissipation testing results showed that the digestion process of difenoconazole in jujube tends to be a gradual reduction process and the dynamic regularity of the residue dissipation proves consistent with the first-order dynamics reaction equation. The half-life (t_1/2) for difenoconazole residue dissipation in Qingdao and Yuncheng was 13.1 days and 16.5 days, respectively. The risk quotient (RQ) was 84.9% lower than 100%, showing that dietary intake risk to difenoconazole was acceptable and the maximum residue limit (MRL) of difenoconazole on jujube is recommended to be 2 mg·kg⁻¹. Full article

Shortage of personal protective equipment (PPE) is often projected in response to public health emergencies such as infection outbreaks and pandemics. Respiratory protective devices (RPDs), namely medical face masks and respirators, are considered the last defense for the front-line healthcare workers. Cleaning, decontamination and reuse of the disposable RPDs have been accepted by local health authorities during the pandemic period. To contribute to the mitigation of RPD shortage and ensure the safe adoption of decontamination protocols, this review discusses the regulated testing standards and the most commonly studied decontamination methods in the literature. The reuse of RPDs must fulfill three criteria: remove the microbial thread, maintain original function and structural integrity (including fitting tests) and leave no harmful residuals. Decontamination methods such as ultraviolet germicidal irradiation, moist heat and vaporized hydrogen peroxide appeared to be the most promising methods in balancing the above-mentioned criteria. However, the effectiveness of decontamination methods varies depending on the RPDs’ models, materials and design. Therefore, the adoption of protocols needs to be evidence-based with full validation in the local institutes. Additionally, new technology such as antimicrobial treated PPE that can reduce the risks of fomite during donning and doffing process with an extended lifespan should be encouraged. Overall, good training and guidance for appropriate reuse of RPDs are fundamental to ensure their efficiency in protecting front-line healthcare workers. Full article

The current coronavirus pandemic has increased worldwide consumption of individual protective devices. Single-use surgical masks are one of the most used devices to prevent the transmission of the COVID-19 virus. Nevertheless, the improper management of such protective equipment threatens our environment with a new form of plastic pollution. With the intention of contributing to a responsible policy of recycling, in the present work, five decontamination methods for used surgical masks that can be easily replicated with common household equipment are described. The decontamination procedures were hot water at 40 °C and 80 °C; autoclave; microwave at 750 W; and ultraviolet germicidal irradiation. After each decontamination procedure, the bacterial load reduction of Staphylococcus aureus ATCC 6538 was recorded to verify the effectiveness of these methods and, moreover, bacterial filtration efficiency and breathability tests were performed to evaluate mask performances. The best results were obtained with the immersion in 80 °C water and the microwave-assisted sterilization. Both methods achieved a high degree of mask decontamination without altering the filtration efficiency and breathability, in accordance with the quality standard. The proposed decontamination methods represent a useful approach to reduce the environmental impact of this new waste material. Moreover, these procedures can be easily reproduced with common household equipment to increase the recycling efforts. Full article

The study focused on increasing the efficiency of germicidal UV radiation by using highly diffuse reflective materials such as PTFE in irradiated cavities of UV air purifiers. In a conventional cylindrically symmetric cavity with a linear amalgam mercury lamp as UV-radiation source on the axis UV-radiation, flux directed from the lamp to the walls dropped from the axis to the periphery. To increase the UV irradiation, the walls are often made mirror-reflective, but the radiation flux distribution remained radially symmetric with a maximum on the source emitting surface in this case as well. When most of the emitted light is returned to the source after one reflection, the conditions of its operation are disturbed. If the walls are made of highly diffuse reflective materials, the radiation flux density inside the cavity increases on average, and its distribution becomes uniform and highly symmetric. Thus, the effect of amplification of the radiation flux due to the highly diffuse reflectivity of the walls increases with radius and reaches a maximum at the wall. Experiments were performed to demonstrate increasing amplification of germicidal UV radiation flux with a diffuse reflection coefficient in cylindrical cavities with walls of PTFE and ePTFE. The irradiation of the cavity wall was observed to increase up to 20 times at the resonant mercury line of 253.7 nm and up to 40 times at some non-resonant lines of the visible range due to highly diffuse reflectivity of the cavity walls. The flux amplification effect was limited by the diffuse reflectivity value of the walls and absorption coefficient of the radiation emitting surface. A formula for calculating the radiation flux amplification factor in a diffusely reflecting cylindrically symmetric cavity was derived for the case of Lambertian source and reflector, including wall reflectivity and source surface absorption coefficients. The effects of heating and cooling of the mercury lamp amalgam directly affected the amplification, and symmetrization of germicidal irradiation was observed and is discussed in the paper. Numerical calculations were performed by the ray tracing method. The calculated model was verified by comparing the numerical results with those of both the approximate theoretical consideration and experiments. The promising use of diffusely reflecting cylindrical cavities for UV air purifiers is discussed. Designs of air inlet and outlet ports that allow effective locking of germicidal radiation inside the UV air purifiers were considered. The results of this work may be of interest for further developments in the UV disinfection technique. Full article

Background: The contamination of ambulances with pathogenic agents represents a potential threat for the public health, not only for common pathogens but also for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The aim of this project was to exploits the germicidal effect of the UVC radiation at 254 nm to sanitize the patient’s compartment of ambulances with an advanced UltraViolet SANitizing System (UV-SAN) and assess its relevance for avoiding the spread of COVID-19 and other drug resistant pathogens. Methods: The system is equipped with UVC lamps that are activated when the ambulance compartment is empty and sanitize the environment in less than 15 min. An Ozone sensor continuously monitors the gas concentration, ensuring it does not exceed threshold value harmful for patients and operators’ health. The system is relying on GNSS data and a satellite communication link, which allow to monitor and record traceability (when, where and what) of all the sanitation operations performed. This information is real-time monitored from a dedicated web-application. Results: UVC irradiation efficiently reduced SARS-CoV-2 virus titer (>99.99%), on inanimate surfaces such as plastic, stainless steel or rubber, with doses ranging from 5.5 to 24.8 mJ/cm² and the UV-SAN system is effective against multi drug resistant (MDR) bacteria up to >99.99%, after 10 to 30 min of irradiation. Conclusions: UV-SAN can provide rapid, efficient and sustainable sanitization procedures of ambulances. Full article

“Wear a mask. Save lives” is the slogan of WHO and all the government agencies over the world to the public. One of the most adopted prevention measures that can limit the spread of the airborne virus in the form of respiratory viral diseases, including the new strain of COVID-19, is wearing a proper mask. If the mask surface is heated to 65 to 70 °C, it could help potentially diminish any viruses or bacteria accumulated. The FAR-Ultraviolet -C (FAR-UV-C) dose for the influenza limit to 254 nm light is ~3 mJ/cm²/hour exposure is not harmful to the human skin and eyes. Here, we propose an intelligent mask served by FAR-UV-C and conducting a yarn-based heater that could potentially be activated in a controlled manner to kill the virus. The effective irradiation intensity for skin application would be under 0.1 µW/cm². The exposure risk of UV-C is technically prevented by fabricating multi-layered fabrics with multiple functionalities. Along with experimental validation on bacterial filtration efficiency (BFE), tinker cad simulation for circuit design, and comsol multiphysics for temperature profile study, we probed Moisture Management Test (MMT) in addition with cytotoxicity risk by MTT Assay for survivability to ensure safer application potential. This novel proposed design with the germicidal combination of heating and FAR-UV-C models, described here, is promising in retaliating and combating any airborne viruses. Full article

In the preparation and response to the COVID-19 pandemic, a sufficient supply of personal protective equipment (PPE), particularly the face mask, is essential. Shortage of PPE due to growing demand leaves health workers at significant risk as they fight this pandemic on the frontline. As a mitigation measure to overcome potential mask shortages, these masks could be decontaminated and prepared for reuse. This review explored past scientific research on various methods of decontamination of the N95-type respirators and their efficiency against the SARS-CoV-2 virus. Ultraviolet germicidal irradiation (UVGI) and hydrogen peroxide vapor (HPV) show great potential as an effective decontamination system. In addition, UVGI and HPV exhibit excellent effectiveness against the SARS-CoV-2 virus on the N95 respirator surfaces. Full article

Cryptococcal cells can manifest skin infections in immunocompromised persons. While it may be easy to diagnose cryptococcal infection, treatment often fails due to the ineffectiveness of current antifungal agents. To this end, the present study explored the repurposing of primaquine (PQ), as a photosensitizer. PDT was carried out using a germicidal ultraviolet (UV) lamp, which has a radiation output of approximately 625 µW/cm² at a distance of 20 cm. When compared to the non-treated cells, the metabolic activity of cryptococcal cells was significantly (p < 0.05) limited. The photolytic products of PQ were observed to alter the ultrastructure of treated cells. The latter was not incidental, as the same cells were also documented to lose their selective permeability. Importantly, PDT also improved the efficiency of macrophages to kill internalized cryptococcal cells (p ≤ 0.05) when compared to non-treated macrophages. Equally importantly, PDT was not detrimental to macrophages, as their metabolic activity was not significantly (p > 0.05) limited, even when exposed to 20× the MIC (determined for cryptococcal cells) and an exposure time that was 4× longer. Taken together, the results suggest PQ has the potential to control the growth of cryptococcal cells and limit their survival inside the macrophage. Full article