Directly Linking Low-Angle Grain Boundary Misorientation to Device Functionality for GaAs Grown on Flexible Metal Substrates.

A new growth method to make highly oriented GaAs thin films on flexible metal substrates has been developed, enabling roll-to-roll manufacturing of flexible semiconductor devices. The grains are oriented in the <001> direction with <1° misorientations between them, and they have a comparable mobility to single-crystalline GaAs at high doping concentrations. At the moment, the role of low-angle grain boundaries (LAGBs) on device performance is unknown. A series of electron backscatter diffraction (EBSD) and cathodoluminesence (CL) studies reveal that increased doping concentrations decrease the grain size and increase the LAGB misorientation. Cross-sectional scanning transmission electron microscopy (STEM) reveals the complex dislocation structures within LAGBs. Most importantly, a correlative EBSD/electron beam-induced current (EBIC) experiment reveals that LAGBs are carrier recombination centers and that the magnitude of recombination is dependent on the degree of misorientation. The presented results directly link increased LAGB misorientation to degraded device performance, and therefore, strategies to reduce LAGB misorientations and densities would improve highly oriented semiconductor devices.

Generation of an in vitro 3D PDAC stroma rich spheroid model.

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a prominent desmoplastic/stromal reaction, which contributes to the poor clinical outcome of this disease. Therefore, greater understanding of the stroma development and tumor-stroma interactions is highly required. Pancreatic stellate cells (PSC) are myofibroblast-like cells located in exocrine areas of the pancreas, which as a result of inflammation produced by PDAC migrate and accumulate in the tumor mass, secreting extracellular matrix components and producing the dense PDAC stroma. Currently, only a few orthotopic or ectopic animal tumor models, where PDAC cells are injected into the pancreas or subcutaneous tissue layer, or genetically engineered animals offer tumors that encompass some stromal component. Herein, we report generation of a simple 3D PDAC in vitro micro-tumor model without an addition of external extracellular matrix, which encompasses a rich, dense and active stromal compartment. We have achieved this in vitro model by incorporating PSCs into 3D PDAC cell culture using a modified hanging drop method. It is now known that PSCs are the principal source of fibrosis in the stroma and interact closely with cancer cells to create a tumor facilitatory environment that stimulates local and distant tumor growth. The 3D micro-stroma models are highly reproducible with excellent uniformity, which can be used for PDAC-stroma interaction analysis and high throughput automated drug-screening assays. Additionally, the increased expression of collagenous regions means that molecular based perfusion and cytostaticity of gemcitabine is decreased in our Pancreatic adenocarcinoma stroma spheroids (PDAC-SS) model when compared to spheroids grown without PSCs. We believe this model will allow an improved knowledge of PDAC biology and has the potential to provide an insight into pathways that may be therapeutically targeted to inhibit PSC activation, thereby inhibiting the development of fibrosis in PDAC and interrupting PSC-PDAC cell interactions so as to inhibit cancer progression.

H2O2 Detection at Carbon Nanotubes and Nitrogen-Doped Carbon Nanotubes: Oxidation, Reduction, or Disproportionation?

The electrochemical behavior of hydrogen peroxide (H2O2) at carbon nanotubes (CNTs) and nitrogen-doped carbon nanotubes (N-CNTs) was investigated over a wide potential window. At CNTs, H2O2 will be oxidized or reduced at large overpotentials, with a large potential region between these two processes where electrochemical activity is negligible. At N-CNTs, the overpotential for both H2O2 oxidation and reduction is significantly reduced; however, the reduction current from H2O2, especially at low overpotentials, is attributed to increased oxygen reduction rather than the direct reduction of H2O2, due to a fast chemical disproportionation of H2O2 at the N-CNT surface. Additionally, N-CNTs do not display separation between observable oxidation and reduction currents from H2O2. Overall, the analytical sensitivity of N-CNTs to H2O2, either by oxidation or reduction, is considerably higher than CNTs, and obtained at significantly lower overpotentials. N-CNTs display an anodic sensitivity and limit of detection of 830 mA M(-1) cm(-2) and 0.5 µM at 0.05 V, and a cathodic sensitivity and limit of detection of 270 mA M(-1) cm(-2) and 10 µM at -0.25 V (V vs Hg/Hg2SO4). N-CNTs are also a superior platform for the creation of bioelectrodes from the spontaneous adsorption of enzyme, compared to CNTs. Glucose oxidase (GOx) was allowed to adsorb onto N-CNTs, producing a bioelectrode with a sensitivity and limit of detection to glucose of 80 mA M(-1) cm(-2) and 7 µM after only 30 s of adsorption time from a 81.3 µM GOx solution.

Electrochemical oxidation of dihydronicotinamide adenine dinucleotide at nitrogen-doped carbon nanotube electrodes.

Nitrogen-doped carbon nanotubes (N-CNTs) substantially lower the overpotential necessary for dihydronicotinamide adenine dinucleotide (NADH) oxidation compared to nondoped CNTs or traditional carbon electrodes such as glassy carbon (GC). We observe a 370 mV shift in the peak potential (Ep) from GC to CNTs and another 170 mV shift from CNTs to 7.4 atom % N-CNTs in a sodium phosphate buffer solution (pH 7.0) with 2.0 mM NADH (scan rate 10 mV/s). The sensitivity of 7.4 atom % N-CNTs to NADH was measured at 0.30 ± 0.04 A M(-1) cm(-2), with a limit of detection at 1.1 ± 0.3 µM and a linear range of 70 ± 10 µM poised at a low potential of -0.32 V (vs Hg/Hg2SO4). NADH fouling, known to occur to the electrode surface during NADH oxidation, was investigated by measuring both the change in Ep and the resulting loss of electrode sensitivity. NADH degradation, known to occur in phosphate buffer, was characterized by absorbance at 340 nm and correlated with the loss of NADH electroactivity. N-CNTs are further demonstrated to be an effective platform for dehydrogenase-based biosensing by allowing glucose dehydrogenase to spontaneously adsorb onto the N-CNT surface and measuring the resulting electrode's sensitivity to glucose. The glucose biosensor had a sensitivity of 0.032 ± 0.003 A M(-1) cm(-2), a limit of detection at 6 ± 1 µM, and a linear range of 440 ± 50 µM.