Yichen Zhao

Single-Walled Carbon Nanotubes Inhibit the Cytochrome P450 Enzyme, CYP3A4

We report a detailed computational and experimental study of the interaction of single-walled carbon nanotubes (SWCNTs) with the drug-metabolizing cytochrome P450 enzyme, CYP3A4. Dose-dependent inhibition of CYP3A4-mediated conversion of the model compound, testosterone, to its major metabolite, 6β-hydroxy testosterone was noted. Evidence for a direct interaction between SWCNTs and CYP3A4 was also provided. The inhibition of enzyme activity was alleviated when SWCNTs were pre-coated with bovine serum albumin. Furthermore, covalent functionalization of SWCNTs with polyethylene glycol (PEG) chains mitigated the inhibition of CYP3A4 enzymatic activity. Molecular dynamics simulations suggested that inhibition of the catalytic activity of CYP3A4 is mainly due to blocking of the exit channel for substrates/products through a complex binding mechanism. This work suggests that SWCNTs could interfere with metabolism of drugs and other xenobiotics and provides a molecular mechanism for this toxicity. Our study also suggests means to reduce this toxicity, eg., by surface modification.

Synthesis of tetrahedral quasi-type-II CdSe-CdS core-shell quantum dots

Synthesis of colloidal nanocrystals of II-VI semiconductor materials has been refined in recent decades and their size dependent optoelectronic properties have been well established. Here we report a facile synthesis of CdSe-CdS core-shell heterostructures using a two-step hot injection process. Red-shifts in absorption and photoluminescence spectra show that the obtained quantum dots have quasi-type-II alignment of energy levels. The obtained nanocrystals have a heterostructure with a large and highly faceted tetrahedral CdS shell grown epitaxially over a spherical CdSe core. The obtained morphology as well as high resolution electron microscopy confirms that the tetrahedral shell have a zinc blende crystal structure. A phenomenological mechanism for the growth and morphology of the nanocrystals is discussed.

Electric field induced optical anisotropy of P3HT nanofibers in a liquid solution

The nanofiber morphology of regioregular Poly-3- hexylthiophene (P3HT) is a 1D crystalline structure organized by π - π stacking of the backbone chains. In this study, we report the impact of elect ...

Direct determination of spatial localization of carriers in CdSe-CdS quantum dots

Colloidal quantum dots (QDs) have gained significant attention due to their tunable band gap, simple solution processability, ease of scale-up, and low cost. By carefully choosing the materials, core-shell heterostructure QDs (HQDs) can be further synthesized with a controlled spatial spread of wave functions of the excited electrons and holes for various applications. Many investigations have been done to understand the exciton dynamics by optical characterizations. However, these spectroscopic data demonstrate that the spatial separation of the excitons cannot distinguish the distribution of excited electrons and holes. In this work, we report a simple and direct method to determine the localized holes and delocalized electrons in HQDs. The quasi-type-II CdSe-CdS coreshell QDs were synthesized via a thermolysis method. Poly(3-hexylthiophene) (P3HT) nanofiber and ZnO nanorods were selected as hole and electron conductor materials, respectively, and were combined with HQDs to form two different nanocomposites. Photoelectrical properties were evaluated under different environments via a quick and facile characterization method, confirming that the electrons in the HQDs were freely accessible at the surface of the nanocrystal, while the holes were confined within the CdSe core.

Relaxation is the key to longer life: suppressed degradation of P3HT films on conductive substrates

Here we show the dependence of the degree of degradation of poly-3-hexylthiophene (P3HT) films on the conductivity of the supporting substrate. P3HT is widely used for organic solar cells and electronic devices because it allows simple, low cost fabrication and has potential for the fabrication of flexible devices. However, P3HT is known to have a relatively low photostability, and investigating the photodegradation mechanism is an active research field. We find that P3HT films on conductive substrates show significantly retarded degradation and retain their chemical and morphological features when compared to similar films on glass substrates. This ‘substrate effect’ in retarding the degradation of P3HT films is evident even upon prolonged exposure to air for up to five months.

Direct birefringence and transmission modulation via dynamic alignment of P3HT nanofibers in an advanced opto-fluidic component

Poly-3-hexylthiophene (P3HT) nanofibers are semiconducting high-aspect ratio nanostructures with anisotropic absorption and birefringence properties found at different regions of the optical spectr ...

Improving Uv Radiation Absorption by Copper Oxide NPs/PMMA Nanocomposites for Electrical Switching Applications

Nanocomposites based on the radiation absorbing polymer (PNCs) are of interest for a variety of applications including circuit breakers, UV-shielding windows, contact lenses, and glasses among others. Such PNCs can be made by incorporating suitable radiation absorbing nanoparticles into a polymeric matrix by in situ polymerization. In this study, spherical nanoparticles (5–6 nm) of oleic acid (OA) surface modified cupric oxide (CuO) are synthesized and used to improve the ultra-violet (UV) radiation absorption property of a polymer matrix, i.e., polymethylmethacrylate (PMMA). The synthesis of spherical CuO nanoparticles, surface modification using OA, dispersion of CuO nanoparticles with different concentrations in PMMA, and UV radiation absorption property of the resultant PNC are investigated. Two different PNCs are produced using OA modified CuO nanoparticles with different concentrations. As synthesized CuO nanoparticles and OA modified CuO nanoparticles are examined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR) techniques. The UV absorption edges are evaluated from the UV-Vis absorption spectra by using UV-Visible absorption spectroscopy. The results show that the UV radiation absorption of the PNC with higher concentration of CuO nanoparticles is improved compared with PMMA and the absorption edge moved towards longer wavelengths i.e., from 271 to 281 nm. These PNCs are successful in arc interruption process by absorbing a broad range of radiation emitted from high-energy copper arcs produced in the circuit breakers.

Wafer-scale epitaxial graphene on SiC for sensing applications

The epitaxial graphene-on-silicon carbide (SiC-G) has advantages of high quality and large area coverage owing to a natural interface between graphene and SiC substrate with dimension up to 100 mm. It enables cost effective and reliable solutions for bridging the graphene-based sensors/devices from lab to industrial applications and commercialization. In this work, the structural, optical and electrical properties of wafer-scale graphene grown on 2’’ 4H semi-insulating (SI) SiC utilizing sublimation process were systemically investigated with focus on evaluation of the graphene’s uniformity across the wafer. As proof of concept, two types of glucose sensors based on SiC-G/Nafion/Glucose-oxidase (GOx) and SiC-G/Nafion/Chitosan/GOx were fabricated and their electrochemical properties were characterized by cyclic voltammetry (CV) measurements. In addition, a few similar glucose sensors based on graphene by chemical synthesis using modified Hummer’s method were also fabricated for comparison.

Evaluation of Zinc Oxide Nano-Microtetrapods for Biomolecule Sensing Applications

Zinc oxide tetrapods (ZnO-Ts) were synthesized by flame transport synthesis using Zn microparticles. This work herein reports a systematical study on the structural, optical and electrochemical properties of the ZnO-Ts. The morphology of the ZnO-Ts was confirmed by scanning electron microscopy (SEM) as joint structures of four nano-microstructured legs, of which the diameter of each leg is 0.7-2.2 μm in average from the tip to the stem. The ZnO-Ts were dispersed in glucose solution to study the luminescence as well as photocatalytic activity in a mimicked biological environment. The photoluminescence (PL) intensity in the ultraviolet (UV) region quenches with linear dependence to increased glucose concentration up to 4 mM. The ZnO-Ts were also attached with glucose oxidase (GOx) and over coated with a thin film of Nafion to form active layers for electrochemical glucose sensing. The attachment of GOx and coating of Nafion were confirmed by infrared spectroscopy (FT-IR). Furthermore, the current response of the active layers based on ZnO-Ts was investigated by cyclic voltammetry (CV) in various glucose concentrations. Stable current response of glucose was detected with linear dependence to glucose concentration up to 12 mM, which confirms the potential of ZnO-Ts for biomolecule sensing applications.