Micromechanics of root development in soil

International audienc

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

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

SAMPLE SIZES REQUIRED FOR PREDICTING ALBUMEN QUALITY IN STORED EGGS FROM EIGHT COMMERCIAL STOCKS

Over a period of 48 wk, eggs were sampled from the eight commercial strains in a layer evaluation test. Half the eggs were oiled as laid. All eggs, except those broken on day 1, were washed and graded 4 days after lay. Samples of eggs were broken at 1, 5, 12, 19 and 26 days after lay for Haugh unit determination. The number of eggs required to assure the mean Haugh unit value in the sample, within ±2.5 Haugh units of the mean of the population, 90% of the time, was computed. This sample size varied with age of the layer, from 19 to 52 for eggs of layers of brown-shelled eggs and from 16 to 32 for eggs from layers of white-shelled eggs. Days in storage and oiling had comparatively little effect on these sample sizes. The Haugh unit losses varied with length of storage, age of birds and oiling from 1.8 to 22.1. The implications of these losses upon the maintenance of Canada’s egg-grading standards are discussed. </jats:p

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

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

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

Whole plant-environment microscopy reveals how Bacillus subtilis utilises the soil pore space to colonise plant roots

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 3D 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 scattering signals from the plant whilst fluorescence signals were captured from transparent soil particles and labelled microorganisms, allowing the generation of quantitative data on samples approximately 3600 mm3 in size with as good as 5 μm resolution at a rate of up to one scan every 30 minutes. 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 favoured small pore spaces over the surface of soil particles, colonising the root in a pulsatile manner. Migrations appeared to be directed towards the root cap, the point “first contact”, before subsequent colonisation of mature epidermis cells. Our findings show that microscopes dedicated to live environmental studies present an invaluable tool to understand plant-microbe interactions