Quasi-stable nematic liquid crystal director reorientation under the influence of focused Gaussian laser beam and electric fields

For liquid crystals with positive dielectric anisotropy a torque is generated in the liquid crystal to align the highest polarizability with the electric field, in order to get an equilibrium with minimal energy density in the system. Director reorientation due to the laser beam and electric fields We report on the generation of quasi-stable domains (Fig. 1) in nematic liquid crystal due to the combined influence of optical and electric fields. The generated domains are an order of magnitude larger than the size of the optical field profile due to a leverage mechanism. To achieve the formation of quasi-stable domains with opposite tilting with respect to the rest of the cell, the optical field needs to be applied first. The final reorientation strongly depends on the starting conditions and properties of this optical field. It reverses the pre-tilt and an additional application of the voltage amplifies it dramatically. The resulting reorientation of the director due to the joint influence of the focused Gaussian laser light and the electric field leads to an unusual refractive index profile which itself causes lensing effects. Our experiments confirm the concept of competitive switching when simultaneously electrical and optical torques are present in a nematic liquid crysta

Sizing nanomaterials in bio-fluids by cFRAP enables protein aggregation measurements and diagnosis of bio-barrier permeability

Sizing nanomaterials in complex biological fluids, such as blood, remains a great challenge in spite of its importance for a wide range of biomedical applications. In drug delivery, for instance, it is essential that aggregation of protein-based drugs is avoided as it may alter their efficacy or elicit immune responses. Similarly it is of interest to determine which size of molecules can pass through biological barriers in vivo to diagnose pathologies, such as sepsis. Here, we report on continuous fluorescence recovery after photobleaching (cFRAP) as a analytical method enabling size distribution measurements of nanomaterials (1-100 nm) in undiluted biological fluids. We demonstrate that cFRAP allows to measure protein aggregation in human serum and to determine the permeability of intestinal and vascular barriers in vivo. cFRAP is a new analytical technique that paves the way towards exciting new applications that benefit from nanomaterial sizing in bio-fluids

Technical implementations of light sheet microscopy

Fluorescence-based microscopy is among the most successful methods in biological studies. It played a critical role in the visualization of subcellular structures and in the analysis of complex cellular processes, and it is nowadays commonly employed in genetic and drug screenings. Among the fluorescence-based microscopy techniques, light sheet fluorescence microscopy (LSFM) has shown a quite interesting set of benefits. The technique combines the speed of epi-fluorescence acquisition with the optical sectioning capability typical of confocal microscopes. Its unique configuration allows the excitation of only a thin plane of the sample, thus fast, high resolution imaging deep inside tissues is nowadays achievable. The low peak intensity with which the sample is illuminated diminishes phototoxic effects and decreases photobleaching of fluorophores, ensuring data collection for days with minimal adverse consequences on the sample. It is no surprise that LSFM applications have raised in just few years and the technique has been applied to study a wide variety of samples, from whole organism, to tissues, to cell clusters, and single cells. As a consequence, in recent years numerous set-ups have been developed, each one optimized for the type of sample in use and the requirements of the question at hand. Hereby, we aim to review the most advanced LSFM implementations to assist new LSFM users in the choice of the LSFM set-up that suits their needs best. We also focus on new commercial microscopes and do-it-yourself strategies; likewise we review recent designs that allow a swift integration of LSFM on existing microscopes