We present a new method for calibrating an optical-tweezer setup that is based on Bayesian inference1. This method employs an algorithm previously used to analyze the confined trajectories of receptors within lipid rafts2,3. The main advantages of this method are that it does not require input parameters and is insensitive to systematic errors like the drift of the setup. Additionally, it exploits a much larger amount of the information stored in the recorded bead trajectory than standard calibration approaches. The additional information can be used to detect deviations from the perfect harmonic potential or detect environmental influences on the bead. The algorithm infers the diffusion coefficient and the potential felt by a trapped bead, and only requires the bead trajectory as input. We demonstrate that this method outperforms the equipartition method and the power-spectrum method in input information required (bead radius and trajectory length) and in output accuracy. Furthermore, by inferring a higher order potential our method can reveal deviations from the assumed second-order potential. More generally, this method can also be used for magnetic-tweezer calibration.
We demonstrated the direct and noninvasive imaging of functional neurons,1 as well as auricular heart muscle
electrical activity2 by Ionic Contrast Terahertz (ICT) near-field microscopy. This technique provides quantitative
measurements of ionic concentrations in both the intracellular and extracellular compartments and opens
the way to direct noninvasive imaging of neurons during electrical, toxin, or thermal stresses. Furthermore,
neuronal activity results from both a precise control of transient variations in ionic conductances and a much
less studied water exchange between the extracellular matrix and the intraaxonal compartment. The developed
ICT technique associated with a full three-dimensional simulation of the axon-aperture near-field system allows
a precise measurement of the axon geometry and therefore the direct visualization of neuron swelling induced by
temperature change or neurotoxin poisoning. This technique should then provide grounds for the development
of advanced functional neuroimaging methods based on diffusion anisotropy of water molecules.
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