Author(s):

Landenberger, Benjamin; Yatish & Rohrbach, Alexander

Abstract:

“In modern 3D microscopy, holding and orienting arbitrary biological objects with optical forces instead of using coverslips and gel cylinders is still a vision. Although optical trapping forces are strong enough and related photodamage is acceptable, the precise (re-) orientation of large specimen with multiple optical traps is difficult, since they grab blindly at the object and often slip off. Here, we present an approach to localize and track regions with increased refractive index using several holographic optical traps with a single camera in an off-focus position. We estimate the 3D grabbing positions around several trapping foci in parallel through analysis of the beam deformations, which are continuously measured by defocused camera images of cellular structures inside cell clusters. Although non-blind optical trapping is still a vision, this is an important step towards fully computer-controlled orientation and feature-optimized laser scanning of sub-mm sized biological specimen for future 3D light microscopy.”

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Author(s):

Zamboni, Riccardo; Imbrock, Jörg & Denz, Cornelia

Abstract:

“The precise spatio-temporal manipulation of droplets is fundamental for many lab-on-a-chip systems with applications in biology, healthcare and chemistry. Different approaches have been investigated, including thermal, chemical and electrical methodologies. Among this latter, electrophoresis (EP) and dielectrophoresis (DEP) play a key role, since they are highly compatible with microfluidic systems and provide sufficiently strong forces to control up to microliter volume aqueous droplets. However, EP and DEP techniques typically require the presence of metallic electrodes to create the desired electric fields, making these approaches less flexible and efficient than those exploiting pure optical techniques. Iron-doped lithium niobate (LiNbO₃:Fe) allows for the generation of strong electric field modulation due to an inhomogenous illumination, thanks to its photovoltaic properties. These photoinduced fields interact as EP and DEP forces with microdroplets, while guaranteeing the flexibility provided by optical field-based modulation. Indeed, the combination with well-known techniques to control and modulate light fields can be exploited to generate virtual electrodes on the material, achieving reliable as well as flexible devices for water droplets control. In our approach, the photoinduced fields generated by the complex illumination of LiNbO₃:Fe are exploited to control motion and trajectory of water droplets inside microfluidic channel. Moreover, the crystal is integrated in standard droplet microfluidic polymeric device, substituting the usual glass substrate and, thus without hindering the portability. This feature combined with the control of positions of aqueous droplets represents a key tool for several applications of customized lab-on-a-chip systems, highlighting the capabilities of LinbO₃:Fe-based virtual electrodes.”

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Author(s):

Tamás Fekete, Mária Mészáros, Zsolt Szegletes, Gaszton Vizsnyiczai, László Zimányi, Mária A. Deli, Szilvia Veszelka*, and Lóránd Kelemen

Abstract:

“Targeting nanoparticles as drug delivery platforms is crucial to facilitate their cellular entry. Docking of nanoparticles by targeting ligands on cell membranes is the first step for the initiation of cellular uptake. As a model system, we studied brain microvascular endothelial cells, which form the anatomical basis of the blood–brain barrier, and the tripeptide glutathione, one of the most effective targeting ligands of nanoparticles to cross the blood–brain barrier. To investigate this initial docking step between glutathione and the membrane of living brain endothelial cells, we applied our recently developed innovative optical method. We present a microtool, with a task-specific geometry used as a probe, actuated by multifocus optical tweezers to characterize the adhesion probability and strength of glutathione-coated surfaces to the cell membrane of endothelial cells. The binding probability of the glutathione-coated surface and the adhesion force between the microtool and cell membrane was measured in a novel arrangement: cells were cultured on a vertical polymer wall and the mechanical forces were generated laterally and at the same time, perpendicularly to the plasma membrane. The adhesion force values were also determined with more conventional atomic force microscopy (AFM) measurements using functionalized colloidal probes. The optical trapping-based method was found to be suitable to measure very low adhesion forces (≤ 20 pN) without a high level of noise, which is characteristic for AFM measurements in this range. The holographic optical tweezers-directed functionalized microtools may help characterize the adhesion step of nanoparticles initiating transcytosis and select ligands to target nanoparticles.”

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