Colloid biology - Develop and analyse microbial interactions

The open online course on "Methods to develop and analyse microbial cell-surface and surface-colloid interactions" consists of 9 chapters where you can learn about different approaches and its importance to develop novel analytical techniques. It is given by European experts in several fields.

Novel techniques for bio-colloid characterization: Bio-colloids are attracting increasing attention from the scientific community due to their potential for developing novel applications. Fluorescence microscopy has been one of the standard and commonly used techniques for characterization of bio-colloids. But in recent years, new technologies became available, and they are now widely used to characterize bio-colloids. Among these techniques are Raman microscopy, atomic force microscopy (AFM), interferometric microscopy and radio-labeling.

Objectives: Objectives of this course are to provide insights into novel techniques applicable for bio-colloid and bacterial-surface interfaces. The emphasis lies on novel label-free techniques and radio-labeling which allows characterization of deep samples.

Raman microscopy is a part of vibrations spectroscopy techniques, in which vibrations of atoms are used as molecular fingerprints of molecules revealing the composition of microbial cells in a label-free manner. Scattering is the key process in this technique, but due to non-resonance nature of the process, the scattering is weak. Besides, fluorescence, a much stronger process can overshadow that weak Raman scattering. That is why different approaches are used for facilitating and enhancing it. For example, choosing the wavelength of the excitation laser in the near-infrared spectral range would reduce the contribution of fluorescence to the scattering. Besides, nanoparticles have been used for chemical or electromagnetic enhancement of the signal through surface enhanced Raman scattering (SERS). All these developments led to the label-free Raman characterization of bacterial cells, where even different phenotypes of bacteria were also distinguished. Another complementary technique is atomic force microscopy (AFM), which allows to study nanotopography and mechanical properties of the samples. Applied to bio-colloids and bacterial cells, AFM has been used to determine the height of bacteria, which in principle can be also determined by alternative methods. But a special niche application of AFM is on studying mechanical properties and interactions of bacteria with surfaces. The uniqueness of AFM as a novel technique has led to uncovering new insights and strength of bacterial cell-surface interaction.

As mentioned above, there are other and new techniques which enable determination of the height profiles and topography of the samples. For transparent samples, interferometric or digital holographic microscopy can be used, in which the phase difference of light propagated through the sample and near-by located substrate is calculated and translated into the height of the sample. What is peculiar about such interferometric microscopy approach is that variations at the nanoscale can be also detected by light, whose wavelength is much higher than those features. Besides, such topography determination is carried out quickly and efficiently. Various companies offer microscopes with interferometric microscopy. In addition to these light- or surface- interacting techniques, radio-labelling represents an interesting and powerful alternative for imaging. As the name suggests, in this case labels (radio-labelling) are applied to the sample. But unlike microscopy techniques with fluorescence labeling, radio-labeling allows for much deeper penetration, which enables one to investigate substantially thick samples.

In short, new approaches and techniques have been recently developed to study bio-colloids and bacteria-surface interaction. Raman microscopy, AFM, interferometric microscopy and radio-labeling are available in fluorescence microscopy approaches. These techniques have already produced an enormous impact on visualizing, uncovering interactions, and discovering new mechanisms in the area of bio-colloids and bacteria-surface interactions resulting in more effective ways of cell culturing.

SURFBIO project has recieved funding under the European Union's Horizon 2020 Research & Innovation programme under grant agreement Nº 952379.