Engineering Highly Interconnected Neuronal Networks on Nanowire Scaffolds.

Identifying the specific role of physical guidance cues in the growth of neurons is crucial for understanding the fundamental biology of brain development and for designing scaffolds for tissue engineering. Here, we investigate the structural significance of nanoscale topographies as physical cues for neurite outgrowth and circuit formation by growing neurons on semiconductor nanowires. We monitored neurite growth using optical and scanning electron microscopy and evaluated the spontaneous neuronal network activity using functional calcium imaging. We show, for the first time, that an isotropic arrangement of indium phosphide (InP) nanowires can serve as physical cues for guiding neurite growth and aid in forming a network with neighboring neurons. Most importantly, we confirm that multiple neurons, with neurites guided by the topography of the InP nanowire scaffolds, exhibit synchronized calcium activity, implying intercellular communications via synaptic connections. Our study imparts new fundamental insights on the role of nanotopographical cues in the formation of functional neuronal circuits in the brain and will therefore advance the development of neuroprosthetic scaffolds.

Nonlinear Generation of Vector Beams From AlGaAs Nanoantennas.

The quest for nanoscale light sources with designer radiation patterns and polarization has motivated the development of nanoantennas that interact strongly with the incoming light and are able to transform its frequency, radiation, and polarization patterns. Here, we demonstrate dielectric AlGaAs nanoantennas for efficient second harmonic generation, enabling the control of both directionality and polarization of nonlinear emission. This is enabled by specialized III-V semiconductor nanofabrication of high-quality AlGaAs nanostructures embedded in optically transparent low-index material, thus allowing for simultaneous forward and backward nonlinear emission. We show that the nanodisk AlGaAs antennas can emit second harmonic in preferential direction with a backward-to-forward ratio of up to five and can also generate complex vector polarization beams, including beams with radial polarization.

Enhanced luminescence from GaN nanopillar arrays fabricated using a top-down process.

We report the fabrication of GaN nanopillar arrays with good structural uniformity using the top-down approach. The photoluminescence intensity from the nanopillar arrays is enhanced compared to the epilayer. We use finite difference time domain simulations to show that the enhancement in photoluminescence intensity from the nanopillar arrays is a result of anti-reflection properties of the arrays that result in enhanced light absorption and increase light extraction efficiency compared to the epilayer. The measured quantum efficiency of the nanopillars is comparable to that of an epitaxially grown GaN epilayer.

Structure-based design, synthesis and biological evaluation of ß-glucuronidase inhibitors.

Using structure-based virtual screening approach, a coumarin derivative (1) was identified as ß-glucuronidase inhibitor. A focused library of coumarin derivatives was synthesized by eco-benign version of chemical reaction, and all synthetic compounds were characterized by using spectroscopy. These compounds were found to be inhibitor of ß-glucuronidase with IC50 values in a micromolar range. All synthetic compounds exhibited interesting inhibitory activity against ß-glucuronidase, however, their potency varied substantially from IC50 = 9.9-352.6 µM. Of twenty-one compounds, four exhibited a better inhibitory profile than the initial hit 1. Interestingly, compounds 1e, 1k, 1n and 1p exhibited more potency than the standard inhibitor with IC50 values 34.2, 21.4, 11.7, and 9.9 µM, respectively. We further studied their dose responses and also checked our results by using detergent Triton ×-100. We found that our results are true and not affected by detergent.

Evaluation of bisindole as potent ß-glucuronidase inhibitors: synthesis and in silico based studies.

Bisindole analogs 1-17 were synthesized and evaluated for their in vitro ß-glucuronidase inhibitory potential. Out of seventeen compounds, the analog 1 (IC50=1.62±0.04 µM), 6 (IC50=1.86±0.05 µM), 10 (IC50=2.80±0.29 µM), 9 (IC50=3.10±0.28 µM), 14 (IC50=4.30±0.08 µM), 2 (IC50=18.40±0.09 µM), 19 (IC50=19.90±1.05 µM), 4 (IC50=20.90±0.62 µM), 7 (IC50=21.50±0.77 µM), and 3 (IC50=22.30±0.02 µM) showed superior ß-glucuronidase inhibitory activity than the standard (d-saccharic acid 1,4-lactone, IC50=48.40±1.25 µM). In addition, molecular docking studies were performed to investigate the binding interactions of bisindole derivatives with the enzyme. This study has identified a new class of potent ß-glucouronidase inhibitors.

Evaluation of the thiazole Schiff bases as ß-glucuronidase inhibitors and their in silico studies.

Twenty eight (28) derivatives 2-29 were synthesized and four analogs were found to exhibit single-digit IC(50) values as ß-glucuronidase inhibitors. Molecular modeling indicates that three factors: substituent R, lone pair on the nitrogen of azomethine part, and the interactions made by the main skeleton of the molecule, determined the enzyme inhibitory potential of these compounds. The planar conformation of the molecules allows them to fit deep inside the pocket while blocking the entry of other physiological substrates seems to play an important role in their activity.

Synthesis and ß-glucuronidase inhibitory potential of benzimidazole derivatives.

Benzimidazole derivatives 1-24 have been synthesized and their in vitro ß-glucuronidase inhibitory activitiy was evaluated. Compounds 15 (IC50=6.33+/-0.40 µM), 7 (IC50=22.0+/-0.33 µM), 2 (IC50=23.1+/-1.78 µM), 17 (IC50=23.9+/-1.46 µM), and 3 (IC50=33.8+/-1.61 µM) showed more potent ß-glucuronidase inhibitory activity than the standard (D-saccharic acid 1,4 lactone, IC50=48.4+/-1.25 µM). This study has identified a new series of potential ß-glucuronidase inhibitors. A structure-activity relationship has also been studied.

Junction-type photonic crystal waveguides for notch- and pass-band filtering.

Evolution of the mode gap and the associated transmission mini stop-band (MSB) as a function of photonic crystal (PhC) waveguide width is theoretically and experimentally investigated. The change of line-defect width is identified to be the most appropriate way since it offers a wide MSB wavelength tuning range. A high transmission narrow-band filter is experimentally demonstrated in a junction-type waveguide composed of two PhC waveguides with slightly different widths. The full width at half maximum is 5.6 nm; the peak transmission is attenuated by only ~5 dB and is ~20 dB above the MSBs. Additionally, temperature tuning of the filter were also performed. The results show red-shift of the transmission peak and the MSB edges with a gradient of dλ/dT = 0.1 nm/°C. It is proposed that the transmission MSBs in such junction-type cascaded PhC waveguides can be used to obtain different types of filters.

High optical quality InP-based nanopillars fabricated by a top-down approach.

Dense and uniform arrays of InP-based nanopillars were fabricated by dry etching using self-assembly of colloidal silica particles for masking. The pillars, both single and arrays, fabricated from epitaxially grown InP and InP/GaInAsP/InP quantum well structures show excellent photoluminescence (PL) even at room temperature. The measured PL line widths are comparable to the as-grown wafer indicating high quality fabricated pillars. A stamping technique enables transfer with arbitrary densities of the nanopillars freed from the substrate by selectively etching a sacrificial InGaAs layer.