Speaker
Description
Bacteria and other microorganisms form biofilms upon and within materials, affecting their physical and chemical properties, such as pore-scale clogging, mineral precipitation, or gas production. Upon the surface, biofilms can be studied by electron and optical microscopy. However, within opaque materials, other techniques such as micro-computed tomography (µCT) are necessary. Unfortunately, biofilms consist of water and other light materials, making them nearly indistinguishable from water. Contrast-Enhancing Staining Agents (CESAs) can improve visualization, but existing CESAs mainly stain the water phase, can precipitate, are toxic, or are time-consuming. In our research, five CESAs: Mono-WD POM, Hf-WD 1:2 POM, isotonic Lugol, Hexabrix® and CA4+ were evaluated for their ability to enhance the contrast of biofilms with conventional lab-based µCT. Two CESAs, Hf-WD 1:2 POM and isotonic Lugol, effectively increased the attenuation and contrast of the biofilm. It enabled the visualization of biofilms that could otherwise not be (fully) visualized. It included cyanobacterial biofilms colonizing sandstone [1] and biofilms of heterotrophic bacteria colonizing the pores of sand filters [2] (Fig. 1). Isotonic Lugol produced stronger attenuation but may induce shrinkage, whereas Hf-WD 1:2 POM could potentially induce swelling. Furthermore, spectral CT at TESCAN XRE was applied to further confirm the uptake of iodine (for biofilms stained with isotonic Lugol) and tungsten and hafnium (for biofilms stained with Hf-WD 1:2 POM) and to enhance further discrimination between the phases. While iodine signals correlated clearly with biofilm presence, tungsten and hafnium detection were less consistent. Future research should focus on the CESA-biofilm interaction and apply these CESAs within the industrial and research fields. Initial experiments have already been conducted in the scope of the BugControl project at Utrecht University and within the EXCITE Transnational Access at Ghent University.
