Visualization of the Mesoscopic Biofilm Structure by Means of Optical Coherence Tomography
Helmholtz Wasser Allianz
The structure of biofilms is quite complex and can be analyzed and discribed at different scales. At the microscale (µm-range) constituents within the biofilm matrix are identified and visualized. The investigation of this scale is well established. The standard tool to explore the microscale of biofilms is confocal laser scanning microscopy (CLSM). Typically, CLSM image stack dimensions are 230×230×10-300µm3. Thus, CLSM image stacks represent a kind of a „snapshot“ of the biofilm structure. Representative volumes can only be observed at the mesoscale (mm-range). For this purpose optical coherence tomography (OCT) is a well suited imaging modality.
OCT is an interferometric method that has been introduced in biofilm research in 2006. Briefly, the sample is „excited“ with infrared light of λ=930±80nm. This light is scattered and reflected by the sample (e.g. biofilm). The resulting interference pattern is analyzed and visualized. A depth profile is named A-scan. A series of A-scans equals an optical section in xz-direction (B-scan). Consecutive acquired B-scans represent a volume dataset named C-scan.
The principle of measurement is simple and allows for the detection of particulate materials only. A distinguishing between organics and inorganics is not possible. But voids are identified, which makes OCT a powerful tool to correlate the biofilm structure with mass transport and transfer phenomena.
The Chair of Water Chemistry and Water Technology owns a spectral domain OCT (Thorlabs, Dachau, Germany), which acquires C-scans of up to 10×10×2.853mm3 at up to 500×500×1024 voxels. Thereby, representative biofilm volumes are visualized at high resolution and high speed since such a C-scan is acquired below one minute.
The object of this research is to apply OCT for the non-invasive and in situ visualization of the biofilm structure at the mesoscale, which further can be quantified and correlated to the cultivation conditions. Thus, a deeper understanding of mass transport and transfer processes will be derived.