Nematic liquid crystal environment enables directional propulsion of spherical droplets representing aqueous dispersion of bacterial microswimmers[1]. Here we explore how the dynamics of active droplets can be controlled by patterning the nematic environment with singular and nonsingular director field. We use the plasmonic metamasks technique to pattern the director the form of non-singular disclinations. We demonstrate that interactions of the active droplet with the director gradients of the environment can be used to control propagation direction, speed, and locations of traps that stop propulsion.

1. Rajabi, M., Baza, H., Turiv, T. & Lavrentovich, O. D. Directional self-locomotion of active droplets enabled by nematic environment. Nat. Phys., doi:https://doi.org/10.1038/s41567-020-01055-5 (2020).

An increasing demand for fast and efficient random-access pointing has led to more investigation on beam steering approaches. This capability is crucial for LiDAR, remote sensing and many other emerging applications.

Electro-Optical devices have advantages over mechanical approach that include a lower cost, faster steering rates, and a random-access beam pointing capability. We have designed, fabricated, Optimized, and characterized a recently proposed non-mechanical beam steering device based on the Pancharatnam-Berry phase. The architecture of our proposed device employs a linear array of phase control elements (PCEs) which are comprised of a fringe field switching electrode structure, are able to locally control the orientation of the liquid crystal director into a cycloidal pattern to deflect transmitted light. Efficiency data verifies a high beam steering efficiency for the proposed device.

A liquid crystal elastomer (LCE) combines a rubber-like elasticity with an orientational order, which makes the material sensitive to external cues such as temperature and light. Recently, Liu et al. [1] demonstrated that LCE coatings change their profile in response to an in-plane AC electric field. The response is attributed to the realignments of the molecular dipoles by the field and the ensuing volumetric expansion of the material [1,2]. We explore experimentally how the temperature, frequency and amplitude of the AC field affect the surface profile of the LCE coatings and demonstrate the existence of two resonance frequencies at which the response is maximized.

References:

[1] Danqing Liu, Nicholas B. Tito, and Dirk J. Broer, Protruding organic surfaces triggered by in-plane electric fields, Nature Communications 8, 1526 (2017).
[2] Guido L. A. Kusters, Inge P. Verheul, Nicholas B. Tito, Paul van der Schoot, and Cornelis Storm, Dynamical Landau–de Gennes theory for electrically-responsive liquid crystal networks, Phys. Rev. E 102, 042703 (2020).

The isolation and characterization of circulating tumor cells (CTCs) has great potential for non-invasive biopsy. In this study, a surface-enhanced Raman spectroscopy (SERS) method was developed using magnetic nanoparticles and a solid SERS-active substrate integrated with an external field-assisted microfluidic device to efficiently isolate CTCs from blood samples. A new SERS substrate was used, developed by physically modifying the surface with a femtosecond laser, sputtering the active SERS layer and chemically modifying the surface with anti-EpCAM antibodies. Magnetic nanoparticles (Fe2O3) were coated with SERS active metal and then modified with para-mercaptobenzoic acid (p-MBA), which acts simultaneously as a Raman reporter and a linker with anti-EpCAM antibodies. The sensitive immune recognition of tumor cells is aided by the introduction of a controlled external magnetic field into the microfluidic chip. The integration of the SERS-active platform and p-MBA labeled immuno-Ag@Fe2O3 nanostructures with the microfluidic device ensures lower demand for samples and analytes, precise operation, increases the reproducibility of spectral responses and enables miniaturization and portability of the presented approach. We used four target tumor cell lines with relatively large (human prostate metastatic adenocarcinoma cells (LNCaP)), medium (adenocarcinomic human alveolar basal epithelial cells (A549)), weak (human prostate tumor line (PC3)) and no expression of EpCAM (tumor cells) cervical cancer (HeLa)) to estimate the detection limits on the basis of constructed calibration curves blood samples from lung cancer patients were used to validate the developed method.[1]

1. M. Czaplicka, K. Niciński, A. Nowicka, T. Szymborski i A. Kamińska, Cancers, 2020, 12 (3315), 1-21.

The coupling between molecular conformation and chirality is a cornerstone in the construction of supramolecular helical structures of small molecules across various length scales. Inspired by biological systems, conformational preselection and control in artificial helical molecules, polymers, and aggregates has guided various applications in optics, photonics, and chiral sorting among others, which are frequently based on an inherent chirality amplification through processes such as templating and self-assembly. The so-called B4 nano- or microfilament phase formed by some bent-shaped molecules [1-5] is an exemplary case for such chirality amplification across length scales, best illustrated by the formation of distinct nano- or microscopic chiral morphologies controlled by molecular conformation. Introduction of one or more chiral centers in the aliphatic side chains led to the discovery of homochiral helical nanofilament, helical microfilament, and heliconical-layered nanocylinder morphologies. Herein, we demonstrate how a priori calculations of the molecular conformation affected by chiral side chains are used to design bent-shaped molecules that self-assemble into chiral nano- and microfilament as well as nanocylinder conglomerates despite the homochiral nature of the molecules. Furthermore, relocation of the chiral center leads to formation of helical as well as flat nanoribbons. Self-consistent data sets from polarized optical as well as scanning and transmission electron microscopy, thin film and solution circular dichroism spectropolarimetry, and synchrotron-based X-ray diffraction experiments support the progressive and predictable change in morphology controlled by structural changes in the chiral side chains. The formation of these morphologies is discussed in light of the diminishing effects of molecular chirality as the chain length increases or as the chiral center is moved away from the core-chain juncture. The type of phase (B1-columnar or B4) and morphology of the nano- or microfilaments generated can further be controlled by sample treatment conditions such as by the cooling rate from the isotropic melt or by the presence of an organic solvent in the ensuing colloidal dispersions. We show that these nanoscale morphologies can then organize into a wealth of two- and three-dimensional shapes and structures ranging from flower blossoms to fiber mats formed by intersecting flat nanoribbons.

References:

[1] L. Li, M. Salamonczyk, A. Jakli, T. Hegmann, Small 2016, 12, 3944.
[2] L. Li, M. Salamonczyk, S. Shadpour, C. Zhu, A. Jakli, T. Hegmann, Nat Commun 2018, 9, 714.
[3] S. Shadpour, A. Nemati, N. J. Boyd, L. Li, M. E. Prévôt, S. L. Wakerlin, J. P. Vanegas, M. Salamończyk, E. Hegmann, C. Zhu, M. R. Wilson, A. I. Jákli, T. Hegmann, Materials Horizons 2019, 6, 959.
[4] S. Shadpour, A. Nemati, J. Liu, T. Hegmann, ACS Appl Mater Interfaces 2020, 12, 13456.
[5] S. Shadpour, A. Nemati, M. Salamonczyk, M. E. Prevot, J. Liu, N. J. Boyd, M. R. Wilson, C. Zhu, E. Hegmann, A. I. Jakli, T. Hegmann, Small 2020, 16, e1905591.