Micromechanics of root development in soil

International audienc

Polyethylene imine-based receptor immobilization for label free bioassays

Polyethylene imine (PEI) based immobilization of antibodies is described and the concept is proved on the label free assay of C-Reactive Protein (CRP). This novel immobilization method is composed of a hyperbranched PEI layer which was deposited at a high pH (9.5) on the sensor surface. The free amino groups of PEI were derivatized with neutravidin by Biotin N-hydroxysuccinimide ester and the biotinylated anti-CRP antibody immobilized on this layer. Direct binding assay of recombinant CRP was successfully performed in the low μg/ml concentrations using a label free optical waveguide biosensor

Label-free optical monitoring of surface adhesion of extracellular vesicles by grating coupled interferometry

In this proof-of-principle study a label-free optical sensor is demonstrated to monitor the surface adhesion of extracellular vesicles secreted by live cells on to various extracellular matrix proteins

Smart soils track the formation of pH gradients across the rhizosphere

Aims Our understanding of the rhizosphere is limited by the lack of techniques for in situ live microscopy. Current techniques are either destructive or unsuitable for observing chemical changes within the pore space. To address this limitation, we have developed artificial substrates, termed smart soils, that enable the acquisition and 3D reconstruction of chemical sensors attached to soil particles. Methods The transparency of smart soils was achieved using polymer particles with refractive index matching that of water. The surface of the particles was modified both to retain water and act as a local sensor to report on pore space pH via fluorescence emissions. Multispectral signals were acquired from the particles using a light sheet microscope, and machine learning algorithms predicted the changes and spatial distribution in pH at the surface of the smart soil particles. Results The technique was able to predict pH live and in situ within ± 0.5 units of the true pH value. pH distribution could be reconstructed across a volume of several cubic centimetres around plant roots at 10 μm resolution. Using smart soils of different composition, we revealed how root exudation and pore structure create variability in chemical properties. Conclusion Smart soils captured the pH gradients forming around a growing plant root. Future developments of the technology could include the fine tuning of soil physicochemical properties, the addition of chemical sensors and improved data processing. Hence, this technology could play a critical role in advancing our understanding of complex rhizosphere processes

Dependence of cancer cell adhesion kinetics on integrin ligand surface density measured by a high-throughput label-free resonant waveguide grating biosensor

A novel high-throughput label-free resonant waveguide grating (RWG) imager biosensor, the Epic® BenchTop (BT), was utilized to determine the dependence of cell spreading kinetics on the average surface density (vRGD) of integrin ligand RGD-motifs. vRGD was tuned over four orders of magnitude by co-adsorbing the biologically inactive PLL-g-PEG and the RGD-functionalized PLL-g-PEG-RGD synthetic copolymers from their mixed solutions onto the sensor surface. Using highly adherent human cervical tumor (HeLa) cells as a model system, cell adhesion kinetic data of unprecedented quality were obtained. Spreading kinetics were fitted with the logistic equation to obtain the spreading rate constant (r) and the maximum biosensor response (Δλmax), which is assumed to be directly proportional to the maximum spread contact area (Amax). r was found to be independent of the surface density of integrin ligands. In contrast, Δλmax increased with increasing RGD surface density until saturation at high densities. Interpreting the latter behavior with a simple kinetic mass action model, a 2D dissociation constant of 1753 ± 243 μm−2 (corresponding to a 3D dissociation constant of ~30 μM) was obtained for the binding between RGD-specific integrins embedded in the cell membrane and PLL-g-PEG-RGD. All of these results were obtained completely noninvasively without using any labels

Investigation of thin polymer layers for biosensor applications

Novel biosensors made of polymers may offer advantages over conventional technology such as possibility of mass production and tunability of the material properties. With the ongoing work on the polymer photonic chip fabrication in our project, simple model samples were tested parallel for future immobilization and accessing conditions for applications in typical aqueous buffers. The model samples consist of a thin, high refractive index polyimide film on top of TEOS on Si wafer. These model samples were measured by in situ spectroscopic ellipsometry using different aqueous buffers. The experiments revealed a high drift in aqueous solutions; the drift in the ellipsometric parameters (delta, psi) can be evaluated and presented as changes in thickness and refractive index of the polyimide layer. The first molecular layer of immobilization is based on polyethyleneimine (PEI). The signal for the PEI adsorption was detected on a stable baseline, only after a long conditioning. The stability of polyimide films in aqueous buffer solutions should be improved toward the real biosensor application. Preliminary results are shown on the possibilities to protect the polyimide. Optical Waveguide Lightmode Spectroscopy (OWLS) has been used to demonstrate the shielding effect of the thin TiO2 adlayer in biosensor applications

Plant-environment microscopy tracks interactions of Bacillus subtilis with plant roots across the entire rhizosphere

Our understanding of plant–microbe interactions in soil is limited by the difficulty of observing processes at the microscopic scale throughout plants’ large volume of influence. Here, we present the development of three-dimensional live microscopy for resolving plant–microbe interactions across the environment of an entire seedling growing in a transparent soil in tailor-made mesocosms, maintaining physical conditions for the culture of both plants and microorganisms. A tailor-made, dual-illumination light sheet system acquired photons scattered from the plant while fluorescence emissions were simultaneously captured from transparent soil particles and labeled microorganisms, allowing the generation of quantitative data on samples ∼3,600 mm3 in size, with as good as 5 µm resolution at a rate of up to one scan every 30 min. The system tracked the movement of Bacillus subtilis populations in the rhizosphere of lettuce plants in real time, revealing previously unseen patterns of activity. Motile bacteria favored small pore spaces over the surface of soil particles, colonizing the root in a pulsatile manner. Migrations appeared to be directed toward the root cap, the point of “first contact,” before the subsequent colonization of mature epidermis cells. Our findings show that microscopes dedicated to live environmental studies present an invaluable tool to understand plant–microbe interactions

Birds in education: innovative learning methods for capacity building in nature conservation

The role of volunteer birdwatchers in bird censuses across the world is crucial to acquire data for science and conservation, and people with different skill specializations and motivations are engaged as citizen scientists. Bird species richness is positively related to life-satisfaction across Europe, while this association doesn’t exist in other wildlife groups. Therefore, birds seem to be particularly captivating for recruiting people to environmental monitoring and nature conservation efforts. The WildSkills EU Erasmus+ project identified a discrepancy at the European level between higher education training and the needs of the labour market in the field of environmental monitoring and nature conservation. To address this skills gap, a collaboration between professionals from European nongovernmental organizations and higher education institutions was set up to develop innovative and accessible distance learning. The project will use a virtual learning environment that combines the use of physical equipment and tools with webinars and livestream technologies, and periods of transnational mobility, to provide, assess, accredit, and support the acquisition of new knowledge. The Birds in Education course is part of the learning materials of the WildSkills EU project. This course will explore (1) the personal motivations for, and the implications to science and society, of our awareness of birds, (2) notions of bird conservation in the European context, (3) the basics of bird identification, (4) how to use birds as environmental education tools, and (5) digital tools for bird identification and citizen science. The course will be tested by higher education students from different backgrounds, aimed at developing skills for the nature conservation sector, and by professionals of the education sector. In the end, this course will contribute to capacity building and to citizen science and has the potential of increasing the public engagement in bird counts, which represents a growing need of many bird conservation organizations