Performance and energy efficiency of low irradiance antimicrobial violet-blue light for environmental decontamination applications

Student thesis: Doctoral Thesis


Healthcare associated infections are one of the most frequent adverse events to occur during healthcare delivery, affecting 7-15% of patients with an estimated mortality of 10%. The healthcare environment plays a significant role in the transmission of pathogens which can instigate such infections. Environmental decontamination technologies which use UV-light or chemicals can be employed to control infection-inducing pathogen spread, but are limited to episodic use in vacant rooms due to safety restrictions. Antimicrobial 405-nm violet-blue visible light has emerged as an alternative technology, due to its inherent safety at low irradiance levels, enabling its use for continuous decontamination of air and exposed surfaces within occupied settings. The research of this PhD generated new information pertaining to low irradiance 405-nm light and its efficacy for environmental decontamination. Initial experiments investigated the broad-spectrum bactericidal efficacy of 405-nm light at exposure levels typically employed for decontamination in occupied settings (≤0.5 mW cm-2), with results indicating successful inactivation of surface-seeded nosocomial bacteria within practical exposure times. Bactericidal efficacy was then evaluated under exposure conditions emulating realistic clinical deployment – namely, exposure to a range of possible illuminating irradiances; desiccated on clinical surfaces; associated with biological substrates; and presented as biofilms – with results indicating significant inactivation in all instances using irradiances ≥0.005 mW cm-2. Subsequent experiments established an enhancement in the germicidal efficiency of 405-nm light, on a per-unit-dose basis, when employed using low irradiances, analogous to levels employed for environmental decontamination, in comparison to higher irradiances; highlighting the energy efficiency of such lighting systems. Further testing demonstrated the ability of low irradiance 405-nm light to inactivate a SARS-CoV-2 surrogate in both minimal and biologically-relevant media, with reductions significantly enhanced in the latter, likely due to the presence of photosensitive components; overall indicating its ability to control transmission of SARS-CoV-2, and potentially other respiratory viruses, within occupied environments. This research significantly advances fundamental knowledge of the germicidal efficiency of low irradiance 405-nm light, furthering clinical delivery of this novel environmental decontamination technology which holds potential to reduce healthcare associated infection acquisition and thus address current challenges associated with infection prevention and control within healthcare settings.
Date of Award4 Jun 2024
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorMichelle Maclean (Supervisor) & Scott MacGregor (Supervisor)

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