Ultraviolet Germicidal Irradiation for Disinfecting N95 Masks

Need of UV Disinfection

A sudden rise in the demand for N95 masks as PPE (Personal Protective Equipment), has been widely recognized among the general public during this COVID-19 pandemic. This unexpected demand has resulted in a limited supply of equipment. The need of the hour suggests disinfecting and reusing disposable N95 Filtering Facepiece Respirators (FFRs).

In this context, Ultraviolet Germicidal Irradiation (UVGI) is considered an effective adjunct. Though it is not a stand-alone technology, this could be a method for respiratory disinfection as it has corroborated effectiveness in inactivating an extensive group of pathogens including coronavirus.

Germicidal UV typically engages mercury-based lamps operating at 254nm, the energy at which strongly absorbed by nucleic acids, resulting in damaging RNA and DNA molecules in pathogens preventing their further growth and function.

Moreover, the irradiation level of UVGI inactivating those pathogens does not hamper the fit and filtration characteristics of N95 FFRs. As per the literature, in the range of 0.5-950J/cm2, FFR fit performance is at 90-100% passing rate after 3 cycles depending on model whereas exposures as low as 2-5mJ/cm2 are capable of inactivating coronaviruses on surfaces. Thus, though proven to be an efficient method, UVGI could be used to effectively disinfect disposable respirators for reuse but the maximum number of disinfection cycles will depend on the respirator model and the UVGI dose required to inactivate the pathogen.

Simulating the performance of your UV System:

The design method of UV systems needs some questions to be answered before starting the design:

  • How much irradiance do we need to kill bacteria?
  • How many UV sources do we need?
  • What power should they have?
  • Where should we place them?

Simulation tools like ANSYS SPEOS help designers to efficiently answer these questions.

Besides, the ray-tracing capabilities of the tool also help in calculating accurately radiometric distribution in UVGI Devices with different surface reflectivities and lamp configurations.

ANSYS SPEOS Simulation to calculate Irradiance over the surface of N95 Mask

Apart from Radiometric studies, Structural Integrity of the respirators is one of the major concerns & studies show a noticeable decrease in structural integrity at lower doses. In conclusion, there are so many works of literature which suggests UVGI can be used for respiratory disinfection, though the maximum number of disinfection cycle will be limited by the respirator model and UVGI doses.

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Confronting COVID-19 with Optics & Photonics

At the zenith of such a situation when the whole world is fighting against a pandemic COVID-19, a multidirectional approach for combating requires excessive attention. The quick detection of infected patients stands as a primary challenge due to variability in the symptoms. Though the field of Optics and Photonics provides various conventional molecular analysis instruments such as multiple spectrum cameras, multispectral optical spectrometers, and they still couldn’t achieve a potential detection method for the masses. Moreover, these methods are time-consuming, prone to error, and may lead to respiratory infections.

Recently, a method involving biosensor which uses thermal and optical effect for safe and reliable detection of COVID is to be seen in a picture. The Plasmonic biosensor used for detection combines Plasmonic Photothermal (PPT) and Localized Surface Plasmon Resonance (LSPR) on a tiny gold nanoisland chip kept on a glass substrate. Artificially produced DNA receptors that match specific RNA sequences of the SARS-CoV-2 virus are grafted onto the AuNI chips. Through Nucleic Acid Hybridization, sensitive detection of specific RNA sequences of the SARS virus is done. LSPR creates plasmonic near field by exciting the metallic nanostructure. The change in the refractive index is measured using an optical sensor helping in determining if the sample contains RNA strands of SARS. The LSPR response due to plasmonic sensing determines the concentration of sequences ranging from 1 pM to 1 nM. PPT helps in boosting the ambient temperature to secure the detection of only reliable matching of RNA strand and DNA receptor.

The sensing stability, sensitivity, and reliability of the device can be significantly enhanced by measuring the same at 2 different angles under 2 different wavelengths. The thermo-plasmonic heat is generated on the AuNI chips while being illuminated at their plasmonic resonance frequency for better sensing performance. The localized PPT heat can elevate the hybridization temperature during the process and facilitate the accurate discrimination of two similar gene sequences.
Though this technique is not yet efficient for a high frequented location, yet it embarks a step closer towards the modern techniques of simulations for such complicated processes.

ANSYS Lumerical Suite comes with all the tools which are required to simulate surface plasmon resonance(SPR) and photothermal heating in plasmonic nanostructures. It comes with a Finite difference time domain (FDTD) solver and heat transport solver for thermal simulation.

The picture below (fig 1) shows the simulation done for getting a source incidence angle that excites the SPR. The absorption in the Silver was measured to determine the angle with the strongest coupling.

Fig:1 Electric Field intensity vs Incident Angle
Source: Lumerical Knowledge Base
Simulation is done on plasmonic nano-structures to understand the effect of varying optical intensity on the performance
Source: Lumerical Knowledge Base

Want to explore how ANSYS solutions can help you in speeding your photonics research? Visit us at https://www.lumerical.com/

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