PDF Publication Title:
Text from PDF Page: 003
C.P. Sabino, et al. Journal of Photochemistry & Photobiology, B: Biology 212 (2020) 111999 The potential of viral spreading via contaminated surfaces depends on the ability of the virus to maintain infectivity in the environment, which in turn is influenced by several biological, physical, and chemical factors, including the type of virus, temperature, relative humidity, and type of surface [37]. Importantly, single-stranded nucleic acid (ssRNA and ssDNA) viruses were more susceptible to UV inactivation than viruses with double-stranded nucleic acid (dsRNA and dsDNA). Also, the UV dose necessary to achieve the same level of virus inactivation at 85% relative humidity (RH) was higher than that at 55% RH [37]. In a recent study, Fischer et al. showed that UV-C light can in- activate more than 99.9% of SARS-CoV-2 viral particles deposited over the filtering material of N95 masks and stainless steel surface [38]. As expected, inactivation kinetics over stainless steel was much faster (i.e., more than 99.9% for (0.33 J/cm2). However, after sufficient exposure (1.98 J/cm2) UV-C could promote germicidal efficacy levels that were similar to those promoted by ethanol, dry heat or vaporized hydrogen peroxide. Older studies have hypothesized that the necessary dose to inactivate 90% of viruses present in N95 filtering facepiece respirator (FFR) material would be about 30 times higher than over the surface of non-porous materials [39]. This was an interesting estimation, but we should keep in mind that UV-C emission spectrum and irradiance of different UV-C equipment as well as material composition are widely variable [40]. Therefore, such estimatives cannot be used as a robust procedure and experimental demonstrations must always be presented. Indeed, a recent in silico study demonstrated that for effective and fast decontamination one should consider the FFR shape besides the optical properties of the FFR model, which has to be determined at the UV-C specific wavelength [41]. Even though UV does not seem to affect the filtrating capacity of FFRs, it is important to note that high UV-C doses can lead to reduced tensile strength of its materials [42,43]. The combination of multiple light wavelengths has been explored for cosmetic, environmental (water disinfection) and clinical (microbial catheter disinfection) applications. However, the precise photo- biological mechanism of action and the experimental workflow to de- velop a marketable application is still missing [44,45]. It must be remarked that UV-C light at 254 nm is harmful to the eyes and skin and, therefore, it is recommended to use it in setups that avoid direct human exposure. Although, far-UV-C (207–222 nm) has been proposed as a disinfection technology that seems to be safer to human exposure [46]. This has been claimed because far-UV-C range is strongly absorbed by amino acid residues and, therefore, is further blocked by the acellular stratum corneum of the skin and the cornea of the eye, leading to lower levels of UV-C light reaching the cellular layers of eyes and skin. However, as far as our knowledge goes, robust studies showing the actual safety of far-UV-C towards animal tissues in short and long terms have not been strongly established and degrada- tion of proteins can also lead to serious eye and skin damages. Thus, we can only recommend UV-C application to inanimate objects. Ad- ditionally, far-UV-C technology is not broadly available in the market yet and the cost is far higher than common LP-Hg lamps. On the other hand, UV-C LED technology is limited to very compact applications. The shortest wavelengths available are around 255 nm, with the price per Watt being up to 1000 times higher than that of LP-Hg lamps, while displaying an energy efficiency (< 1%) far lower than that of LP-Hg lamps (25–40%) at 254 nm. 6. Photoantimicrobials and Photodynamic Therapy Visible light can exert antiviral effects via photodynamic mechan- isms that are initiated upon absorption of light by exogenous photo- sensitizer compounds, such as phenothiazinium salts, porphyrins, na- noparticles, and others [47–50]. The inactivation of microorganisms and viruses by visible light is based on the generation of lethal oxidant species via photosensitized oxidation reactions, which usually require three components: the chromophore, termed the photosensitizer (PS), light, and oxygen, even though some PS may also work through Fig. 1. Mechanisms of photosensitized oxidation reactions. The photosensitizer (PS) is a molecule capable of absorbing light depending on its specific ab- sorption spectra. Once excited, the PS is converted from the ground state 1PS to its singlet excited 1PS⁎ and triplet excited 3PS⁎ states. Via Type I (contact-de- pendent) reactions both 1PS⁎ and 3PS⁎ can react directly with O2 or biomole- cules, like carbohydrates, lipids, proteins, or nucleic acids, resulting in the formation of radicals capable of initiating redox chain reactions. Otherwise, 3PS⁎ can react with molecular oxygen (3O2), via the Type II (energy transfer) reaction, generating the reactive state of singlet oxygen (1O2). alternative reactions in the absence of oxygen [51]. After light ab- sorption, excited oxygen states are quickly formed, initially in the singlet, and subsequently in the triplet states (i.e., considering the photocycle of organic molecules). These species can release the ex- citation energy in the form of light emission (e.g., fluorescence and phosphorescence) or heat release (non-radiative decay). Since excited states are intrinsically more reactive than ground states, energy and electron transfer reactions can occur. There are two main mechanisms of photosensitized oxidation: Type I reactions depend on the encounter of the excited species with biological substrates. These reactions usually occur through electron or hydrogen abstraction, leading to radical chain reactions; Type II reactions rely on energy transfer reaction from the PS triplet state to molecular oxygen, generating singlet oxygen (1O2) (Fig. 1) [52]. Spacially, type I reactions require the PS to be within a subnanometer distance to the virus, whereas type II reactions allow singlet oxygen diffusion to more than 100 nm [51]. Light energy is thus converted into oxidation potential that can damage biomolecules. Antimicrobial photodynamic therapy (aPDT) is based on this process and it has been used to treat localized microbial infections caused by viruses, bacteria, fungi, and parasites [53]. Among the many pathogens that can be targeted by aPDT, viruses are perhaps the most vulnerable, as they depend on entering a host cell for survival and replication and can be inactivated by damaging the capsid or en- velope molecules (lipids, carbohydrates, proteins) or internal molecules (nucleic acids) (Fig. 1). Thus, many viruses can be treated via aPDT, including papillomavirus (HPV), hepatitis A virus (HAV), and herpes simplex virus (HSV) [54–56]. Additionally, the disinfection of biolo- gical fluids (plasma and blood products) by photoantimicrobials has been performed for decades and is a well-regarded technological ap- plication of these compounds. For instance, extracorporeal photo- inactivation of coronaviruses and other clinically relevant pathogens using methylene blue (MB)-mediated aPDT has been reported [57–62]. It is possible that photosensitized oxidation can neutralize SARS- CoV-2 and, consequently, play a role in mitigating the ongoing pan- demic; however, there is no data available on the photodynamic in- activation of this virus. Thus, here we sought to find and discuss sci- entific literature that could help predict whether COVID-19 is more or less susceptible to oxidant species generated during aPDT. While all types of viruses can be neutralized by aPDT, the in- activation efficiency depends on both the PS and the virus [63,64]. As a rule of the thumb, RNA-type phages are more easily photoinactivated than their DNA-type counterparts, suggesting that SARS-CoV-2, which is an enveloped RNA-type virus, can be easily neutralized by aPDT [64,65]. Guanine bases are the major targets for oxidation by 3PDF Image | A Light-based technologies for management of COVID-19 pandemic
PDF Search Title:
A Light-based technologies for management of COVID-19 pandemicOriginal File Name Searched:
light-based-covid-pandemic-management.pdfDIY PDF Search: Google It | Yahoo | Bing
Cruise Ship Reviews | Luxury Resort | Jet | Yacht | and Travel Tech More Info
Cruising Review Topics and Articles More Info
Software based on Filemaker for the travel industry More Info
The Burgenstock Resort: Reviews on CruisingReview website... More Info
Resort Reviews: World Class resorts... More Info
The Riffelalp Resort: Reviews on CruisingReview website... More Info
CONTACT TEL: 608-238-6001 Email: greg@cruisingreview.com (Standard Web Page)