Doctoral defence: Ott Rebane “In situ non-contact sensing of microbiological contamination by fluorescence spectroscopy”

On 29 August at 14:00 Ott Rebane will defend his doctoral thesis “In situ non-contact sensing of microbiological contamination by fluorescence spectroscopy” for obtaining the degree of Doctor of Philosophy (in Physics).

Supervisors:
Professor Marco Kirm, University of Tartu
Dr. Sergey Babichenko, LDI Innovation OÜ

Opponents:
Dr. Ilpo Kulmala, VTT (Finland)
Professor Janis Spigulis, University of Latvia (Latvia)

Summary
In the course of the current industrial PhD program several novel photonic sensors and their applications were developed, ranging from a lidar to spectrofluorometers and fluorometers. The main goal of these devices is to monitor and control microbiological pathogens on surfaces. The lidar was designed for remote detection and classification of pathogens on field hospital surfaces, while the spectrofluorometers enable close-range reagentless detection of pathogens with fibre-optic cable and the multi-spectral fluorometer enables handheld quick estimation of surface cleanliness. A completely novel photonic sensor solution to the monitoring of hydrogen peroxide vapour decontamination procedures was developed in the course of the PhD program as well. This approach uses the fluorescence of commonly used biological decontamination indicators, such as bacterial spores, to estimate the efficiency of an ongoing H₂O₂ vapour decontamination procedure in real time. The fluorescence intensity fall-off effect discovered in this work is found to be extremely sensitive to H₂O₂ vapour concentration, so that the practical application in the form of a commercial product for monitoring VHP decontamination procedures is a completely viable option. The discovered effect was studied further by comparing the fluorescence emission spectra, the time-resolved spectra, the effect of UV radiation and the scanning electron micrographs of H₂O₂-vapour-killed pathogens (bacterial spores) on one side to similarly prepared but still viable pathogens on the other side. The results of the work prove that fluorescence can be used to distinguish classes of pathogens on various background materials. The results also indicate that denaturation of key proteins as well as oxidation of the inner parts of the proteins are both considered causes of death for pathogens during the highly efficient decontamination with hydrogen peroxide vapour. At the same time, the scanning electron microscopy images indicated that the mechanical damage caused by oxidation is not the main cause of pathogen death. Finally found how UV dose affects measurement results and has to be taken into account in the design of such photonic devices.