DNA-directed assembly of gold nanoparticles into precise two- and three-dimensional patterns has enabled bold advances in probing their optical properties such as the local enhancement in their surface plasmon resonance. DNA nanostructures synthesized using the principles of DNA origami have been programmed to contain unique capture sites for positioning metal nanoparticles in diverse geometries for applications in biosensing, therapy, and miniature electronics. However, to enable scalability beyond simple 2-3 nanoparticle architectures, it is important to understand the requirement for orthogonal capture sequences for attaching more than a single gold nanoparticle on a DNA nanostructure. In this work, we sought to assemble an angular gold nanorod-nanosphere-nanorod pattern on a DNA origami triangle with multiple capture sites utilizing a common capture sequence. Results indicate that gold nanospheres preferentially bound to all the capture sites on the DNA origami triangle and prevented attachment of gold nanorods. This suggests that requirement for orthogonal capture sites is correlated with the physical properties of the individual nanoparticle such as shape and size.
A non-mechanical refractive laser beam steering device has been developed to provide continuous, two-dimensional steering of infrared beams. The technology implements a dielectric slab waveguide architecture with a liquid crystal (LC) cladding. With voltage control, the birefringence of the LC can be leveraged to tune the effective index of the waveguide under an electrode. With a clever prism electrode design a beam coupled into the waveguide can be deflected continuously in two dimensions as it is coupled out into free space. The optical interaction with LC in this beamsteerer is unique from typical LC applications: only the thin layer of LC (100s of nm) near the alignment interface interacts with the beam’s evanescent field. Whereas most LC interactions take place over short path lengths (microns) in the bulk of the material, here we can interrogate the behavior of LC near the alignment interface over long path lengths (centimeters). In this work the beamsteerer is leveraged as a tool to study the behavior of LC near the alignment layer in contrast to the bulk material. We find that scattering is substantially decreased near the alignment interface due to the influence of the surface anchoring energy to suppress thermal fluctuations. By tracking the position of the deflected beam with a high speed camera, we measure response times of the LC near the interface in off-to-on switching (~ms) and on-to-off switching (~100ms). Combined, this work will provide a path for improved alignment techniques, greater optical throughput, and faster response times in this unique approach to non-mechanical beamsteering.
The main principle of photodynamic therapy (PDT) is to kill malignant cells by generation of reactive oxygen species (ROS). PDT appeared highly effective when ROS can be produced in subcellular location such as plasma membrane. The plasma membrane maintains the structural integrity of the cell and regulates multiple important cellular processes, such as endocytosis, trafficking, and apoptotic pathways, could be one of the best points to kill the cancer cells. Previously, we have developed a plasma membrane-targeted liquid crystal nanoparticle (LCNP) formulation that can be loaded with dyes or drugs. Here we highlight the utility of this LCNP for membrane targeted delivery and imaging for a photosensitizer (PS) for PDT applications.
Beam steering is a crucial technology for a number of applications, including chemical sensing/mapping and light detection and ranging (LIDAR). Traditional beam steering approaches rely on mechanical movement, such as the realignment of mirrors in gimbal mounts. The mechanical approach to steering has several drawbacks, including large size, weight and power usage (SWAP), and frequent mechanical failures. Recently, alternative non-mechanical approaches have been proposed and developed, but these technologies do not meet the demanding requirements for many beam steering applications. Here, we highlight the development efforts into a particular non-mechanical beam steering (NMBS) approach, refractive waveguides, for application in the MWIR. These waveguides are based on an Ulrich-coupled slab waveguide with a liquid crystal (LC) top cladding; by selectively applying an electric field across the liquid crystal through a prismatic electrode, steering is achieved by creating refraction at prismatic interfaces as light propagates through the device. For applications in the MWIR, we describe a versatile waveguide architecture based on chalcogenide glasses that have a wide range of refractive indices, transmission windows, and dispersion properties. We have further developed robust shadow-masking methods to taper the subcladding layers in the coupling region. We have demonstrated devices with >10° of steering in the MWIR and a number of advantageous properties for beam steering applications, including low-power operation, compact size, and fast point-to-point steering.
The mid-wave infrared (MWIR) portion of the electromagnetic spectrum is critically important for a variety of applications such as LIDAR and chemical sensing. Concerning the latter, the MWIR is often referred to as the “molecular fingerprint” region owing to the fact that many molecules display distinctive vibrational absorptions in this region, making it useful for gas detection. To date, steering MWIR radiation typically required the use of mechanical devices such as gimbals, which are bulky, slow, power-hungry, and subject to mechanical failure. We present the first non-mechanical beam steerer capable of continuous angular tuning in the MWIR. These devices, based on refractive, electro-optic waveguides, provide angular steering in two dimensions without relying on moving parts. Previous work has demonstrated non-mechanical beam steering (NMBS) in the short-wave infrared (SWIR) and near infrared (NIR) using a waveguide in which a portion of the propagating light is evanescently coupled to a liquid crystal (LC) layer in which the refractive index is voltage-tuned. We have extended this NMBS technology into the MWIR by employing chalcogenide glass waveguides and LC materials that exhibit high MWIR transparency. As a result, we have observed continuous, 2D MWIR steering for the first time with a magnitude of 2.74° in-plane and 0.3° out-of-plane.
In addition to maintaining the structural integrity of the cell, the plasma membrane regulates multiple important cellular processes, such as endocytosis and trafficking, apoptotic pathways and drug transport. The modulation or tracking of such cellular processes by means of controlled delivery of drugs or imaging agents via nanoscale delivery systems is very attractive. Nanoparticle-mediated delivery systems that mediate long-term residence (e.g., days) and controlled release of the cargoes in the plasma membrane while simultaneously not interfering with regular cellular physiology would be ideal for this purpose. Our laboratory has developed a plasma membrane-targeted liquid crystal nanoparticle (LCNP) formulation that can be loaded with dyes or drugs which can be slowly released from the particle over time. Here we highlight the utility of these nanopreparations for membrane delivery and imaging.
The demonstration of fine control over nanomaterials within biological systems, particularly in live cells, is integral for
the successful implementation of nanoparticles (NPs) in biomedical applications. Here, we show the ability to
differentially label the endocytic pathway of mammalian cells in a spatiotemporal manner utilizing fluorescent
nanocolloids (NCs) doped with a perylene-based dye. EDC-based conjugation of green- and red-emitting NCs to the
iron transport protein transferrin resulted in stable bioconjugates that were efficiently endocytosed by HEK 293T/17
cells. The staggered delivery of the bioconjugates allowed for the time-resolved, differential labeling of distinct
vesicular compartments along the endocytic pathway in a nontoxic manner. We further demonstrated the ability of the
NCs to be impregnated with the anticancer therapeutic, doxorubicin. Delivery of the drug-doped nanoconjugates
resulted in the intracellular release and nuclear accumulation of doxorubicin in a time- and dose-dependent manner. We
discuss our results in the context of the utility of such materials for NP-mediated drug delivery applications.
In this paper, we present electro-chromatic switching of a cholesteric gel, which exhibits a shift in the reflection band with the application of an electric field, but preserves the intensity of the reflected light. The reflecting color of the cholesteric gel was controlled by the strength of an electric field. When optimized to reflect visible light the reflecting color of the gel reversibly shifts to shorter wavelengths with increasing voltage. The reflection intensity remains the same over a range of voltage and begins to decrease with further application of the electric field, eventually leading to homeotropic alignment. We have systematically investigated the mechanism of the switching by studying the optical spectra and measuring the dielectric constant of a cholesteric gel as a function of voltage. Using a simple model that includes tilting and untwisting of a helical structure, we show that uniform electro-chromatic switching is mostly initiated by a helix tilting mechanism, whereas decrease in the intensity of reflection is mainly caused by helical untwisting.
Novel liquid crystalline elastomers with properties that mimic the action of a muscle have been developed. Uniaxial contraction of free standing film of the material can be achieved by heating the film through the nematic to isotropic phase transition. Thermoelastic response shows strain changes through the nematic-isotropic phase transition of about 30-35%. Retractive force of nearly 450 kPa was measured in the isotropic phase. Static workloop studies show that the visco-elastic losses in these materials to be very small.
Smectic-A liquid crystals exhibiting a large electroclinic effect are important for applications in view of their analog gray scale capability. In most of these materials, large electroclinic tilt angles are accompanied by buckling effects due to layer compression. This layer buckling is easily observed in an optical microscope as periodic stripes and drastically reduces the high contrast ratio necessary for optical devices. We have performed optical and x-ray scattering studies on a chiral, organosiloxane smectic-A liquid crystal. It is found that while the optical tilt angle exhibits a large dependence on the field, reaching values of about 31 degrees (for 5 V/micrometer applied field), the layer spacing shows only a very weak field-dependence, suggesting that the molecules have a nonzero tilt even with no applied field, and that the primary effect of the field is to induce long range order in the direction of the molecular tilt. This important result -- large field-induced optical tilt without a layer shrinkage -- has led to the development of materials with 256 gray -- large field-induced optical tilt without a layer shrinkage -- has led to the development of materials with 256 gray levels.
Chiral smectic A electroclinic liquid crystalline materials are prime candidates for electrooptic applications because of their gray scale capability and fast dynamic response. The evolution of this technology greatly depends on the development of chiral smectic A materials with large induced tilt angles, field-independent fast switching times and a broad operating temperature range. We report in this paper the physical properties of a series of liquid crystal materials. Features of this series of materials are broad smectic A phase range and large induced tilt angles. Such large electroclinic coefficients make these materials good candidates of the development of silicon based reflective displays. Comparison of the electrooptic performance of the materials in SmA mesophase will be discussed.
A photo-dimerized monolayer (PDML) has been recently developed by us for liquid crystal alignment. Electro-optic properties of a single pixel prototype device with the PDML alignment layer have been measured. Data on the contrast, threshold voltage and slope of the response curve are presented which demonstrate the efficacy of the PDML layer for LCD applications. In addition, the polar anchoring energy was measured for PDML layers differing in the chemical composition. The ability to tune this anchoring energy through chemical modification is demonstrated. It is shown that the anchoring strength is comparable to that obtained for liquid crystal cells using the mechanically rubbed polyimide alignment layer.
A non-rubbing process suitable for active matrix LCDs based on a photo-dimerized monolayer (PDML) has been developed. The PDML yields defect free alignment of nematic liquid crystal molecules. The electro-optic characteristics of LCDs fabricated using the photo-dimerized layers are shown to be comparable to those of a rubbed polyimide alignment layer.
Chiral smectic A liquid crystals with large electroclinic coefficients and fast response times have been developed. The capability of achieving the optimum tilt angle of 22.5 degrees for applied fields less than 3V/micrometer, opens up the possibility developing silicon based high-resolution reflective displays without compromising on resolution and speed.
Liquid crystal (LC) materials possessing the chiral smectic A phase have been designed to yield high induced tilt angels and low response times. The primary objective of our work is to design materials that can provide the optimum tilt angle of 22.5 degrees for applied voltages less than 5V/micrometers , making them CMOS compatible Optical response measurement to illustrate the feasibility of obtaining 256 gray levels are presented. The gray scale capability of the material is visually demonstrated using a 1 X 64 array driven by a dc balanced circuit.
The pyroelectric properties of three chiral smectic liquid crystalline materials have been investigated. The magnitude of the pyroelectric coefficient for in two of these compounds is very high exceeding 200 nC/cm2K. A mixture containing one of these compounds exhibits a high pyroelectric coefficient over a temperature range that is attractive for thermal (or IR) sensing applications. The relevant figure of merit of these materials as elements for IR sensors is discussed in comparison to those that are currently used in sensing devices.
The synthesis and properties of a novel ferroelectric cyclic siloxane oligomer are reported. The properties of the oligomer are compared with those of a linear siloxane polymer and its unattached side group consisting of the same mesogenic moiety as in the cyclic siloxane oligomer. The ferroelectric and electroclinic response times as well as the tilt angles of the cyclic material are found to be similar to those of the monomer while the spontaneous polarization is comparable to that of the linear siloxane polymer. These studies constitute the first detailed comparison of the ferroelectric properties of a cyclic siloxane oligomer and a linear siloxane polymer.
The electric field induced tilt angles and the corresponding optical transmission properties are presented for two homologs and a mixture which exhibit a strong electroclinic effect at ambient temperatures. Tilt angles as large as 15 degree(s) are reported. The relationship between the molecular tilt angle and the transmission properties are emphasized.
We have synthesized many ferroelectric side-chain liquid crystalline polymers exhibiting the Smectic C* phase over a wide temperature range extending to sub-ambient temperatures. The tuning of the mesophase temperature has been achieved by incorporating two different mesogens as side groups attached to the siloxane backbone. These copolymers exhibit large values of spontaneous polarization which varies linearly through out the Smectic C* phase. The pyroelectric coefficient and dielectric constants of these materials have been measured. The potential of these ferroelectric liquid crystals as pyroelectric detector materials will be examined.
Electro-optic properties of new liquid crystalline polymers exhibiting a ferroelectric phase over a wide range of temperature are reported. The materials exhibit bistable electro-optic switching in the smectic C* phase and a pronounced linear electroclinic effect in the smectic A phase. The response times are very fast, of the order of 100 microseconds.
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