Incubated protein reduction and digestion on an electrowetting-on-dielectric digital microfluidic chip for MALDI-MS

Localized heating of droplets on an electrowetting-on-dielectric (EWOD) chip has been implemented and shown to accelerate trypsin digestion reaction rates, sample drying, and matrix crystallization for matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS). Achieving this involved extending the functionality of previous EWOD droplet-based techniques by developing a multifunctional electrode with closed-loop temperature control, while minimizing overall system complexity and addressing challenges associated with rapid evaporation. For the EWOD chip design, we discuss the performance of multifunctional surface electrodes for actuation, localized Joule heating, and thermistic temperature sensing. Furthermore, a hydrophilic pattern is formed in the multifunctional electrode to control the location of an evaporating droplet on the electrode. To demonstrate the capabilities and limitations of this technique, we performed three experiments and measured the results using MALDI-MS: (i) insulin disulfide reductions in dithiothreitol (DTT) over a range of heater temperatures (22-70 °C) to show how reaction rates can be affected by thermal control, (ii) insulin disulfide reductions at 130 °C in dimethyl sulfoxide (DMSO) to demonstrate a reaction in a high boiling point solvent, and (iii) tryptic digestions of cytochrome c at 22 and 40 °C to show that heated droplets can yield reasonably higher peptide sequence coverage than unheated droplets. Although they do not decouple the effects of changing temperatures and concentrations, these experiments verified that thermal cycling by EWOD electrodes accelerates reaction rates in liquid droplets in air.     

Art students who cannot draw: Exploring the relations between drawing ability, visual memory, accuracy of copying, and dyslexia.

Some art students, despite being at art school, cannot draw very well, and would like to be able to draw well. It has been suggested that poor drawing may be a particular problem for students with dyslexia (and a high proportion of art school students is dyslexic). In Study 1 we studied 277 art students, using a questionnaire to assess self-perceived drawing ability and a range of background measures, including demography, education, a history of dyslexia, a self-administered spelling test, and personality and educational variables. In Study 2 we gave detailed drawing tests to a sample of 38 of the art students, stratified by self-rated drawing ability and spelling ability, and to 30 control participants. Students perceiving themselves as good at drawing did indeed draw better than self-perceived poor drawers, although the latter were still better than non-art student controls. In neither Study 1 nor Study 2 did skill at drawing relate to dyslexia or spelling ability, and neither did drawing ability relate to any of our wide range of background measures. However Study 2 did show that drawing ability was related both to ability at copying simple angles and proportions (using the “house” task of Cain, 1943), and also to visual memory (as suggested by Jones, 1922), poor drawers being less good at both immediate and delayed recall of the Rey-Osterrieth complex figure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Study of Non-linear Mechanical Behavior of Oil Palm Mesocarp Fibers

This work investigates the non-linear mechanical behavior of oil palm mesocarp fibers (OPMF) using tensile tests, microstructure observation, and finite element models. The micrograph images showed the fiber’s surface with partly embedded silica bodies, while the cross section contained cell wall structures. Viscoelastic behavior was observed when the fibers were relaxed over time after being stretched, whereas the stress--strain curves from the cyclic tests indicated permanent set (plastic strain) due to the fibers’ deformation. Finite element models were developed comprising single particles (2D and 3D) and 2D multi-particle geometries representing silica bodies embedded in a matrix representing the fiber. The modeling results suggested that silica bodies do not contribute much to the integrity of OPMF, highlighting the need to have a more complex model that considers cellular structures of the fibers and a constitutive relationship of cellulose, hemicelluloses, and lignin.     

Impedimetric thrombin aptasensor based on chemically modified graphenes

Highly sensitive biosensors are of high importance to the biomedical field. Graphene represents a promising transducing platform for construction of biosensors. Here for the first time we compare the biosensing performance of a wide set of graphenes prepared by different methods. In this work, we present a simple and label-free electrochemical impedimetric aptasensor for thrombin based on chemically modified graphene (CMG) platforms such as graphite oxide (GPO), graphene oxide (GO), thermally reduced graphene oxide (TR-GO) and electrochemically reduced graphene oxide (ER-GO). Disposable screen-printed electrodes were first modified with chemically modified graphene (CMG) materials and used to immobilize a DNA aptamer which is specific to thrombin. The basis of detection relies on the changes in impedance spectra of redox probe after the binding of thrombin to the aptamer. It was discovered that graphene oxide (GO) is the most suitable material to be used as compared to the other three CMG materials. Furthermore, the optimum concentration of aptamer to be immobilized onto the modified electrode surface was determined to be 10 μM and the linear detection range of thrombin was 10-50 nM. Lastly, the aptasensor was found to demonstrate selectivity for thrombin. Such simply fabricated graphene oxide aptasensor shows high promise for clinical diagnosis of biomarkers and point-of-care analysis.     

Single-electron capacitance spectroscopy of individual dopants in silicon

Motivated by recent transport experiments and proposed atomic-scale semiconductor devices, we present measurements that extend the reach of scanned-probe methods to discern the properties of individual dopants tens of nanometers below the surface of a silicon sample. Using a capacitance-based approach, we have both spatially resolved individual subsurface boron acceptors and detected spectroscopically single holes entering and leaving these minute systems of atoms. A resonance identified as the B+ state is shown to shift in energy from acceptor to acceptor. We examine this behavior with respect to nearest-neighbor distances. By directly measuring the quantum levels and testing the effect of dopant-dopant interactions, this method represents a valuable tool for the development of future atomic-scale semiconductor devices.     

Use of a chondroitin sulfate isomer as an effective and removable dispersant of single-walled carbon nanotubes

Three isomers of chondroitin sulfate (CS), i.e., CS-A, CS-B, and CS-C, are investigated as nanotube dispersants and are found to have vastly different abilities to disperse single-walled carbon nanotubes (SWNTs) in water due to their different intramolecular interactions. Only CS-A and CS-C effectively disperse SWNTs into small bundles or individual tubes while CS-B disperses SWNTs poorly. Computer simulation and circular dichrosim show that neat CS-A and CS-C have weak intramolecular hydrogen bonding and extended conformations in solution resulting in energetically more favorable interactions with nanotubes. CS-B has relatively strong intramolecular Coulombic interaction and more alpha-helical secondary structure in solution resulting in energetically less favorable interaction with the nanotubes. Atomic force microscopy images show helical wrappings of CS-A and CS-C around the SWNTs. Transmission electron microscopy corroborates the helical wrapping of CS-A. Different isomeric forms of a polymer can have vastly different dispersing power because of their different intramolecular interactions and conformations. The easy removability of CS-A from nanotubes is confirmed with X-ray photoelectron spectroscopy showing almost no detectable sulphur content after washing with water and by application of washed CS-A dispersed SWNTs in field-effect transistors.     

On the presence of Inulin and Oligofructose as natural ingredients in the western diet

The classic definitions of inulin and oligofructose are constructively criticized. It is observed that inulin cannot unequivocally be described as a polydisperse 1‐kestose‐based (GF_n) β(2 ? 1) linear fructan chain, but that inulin always contains small amounts of F_m and branched molecules. This review article describes the presence of inulin and oligofructose in common foodstuffs. Historical data on human consumption add an extra dimension.

Modern analytical techniques (HPLC, LGC, HPAEC‐PAD) are used to check the variety of data mentioned in the literature throughout the past century. Methods to determine inulin and oligofructose in natural foodstuffs (cereals, fruit, and vegetables) are optimized and used to determine the loss of inulin during storage and during preparation of the food.

These findings allow quantification of the amount of inulin and oligofructose in the average daily western diet. The daily per capita intake is estimated to range from 1 to 10 g, depending on geographic, demographic, and other related parameters (age, sex, season, etc.).

Inulin and oligofructose are not measured by classic methods of dietary fiber analysis and consequently are often not mentioned in food tables. Their significant contribution (1 to 10 g/d/per capita) to the dietary fiber fraction (recommended at 25 g/d/per capita) is not taken into account in any nutritional recommendations. In view of this, inulin and oligofructose deserve more attention, both in food composition tables and in diet or nutrition studies.     

Electronic structure and carrier transport at laminated polymer homojunctions

Soft contact lamination, whereby films prepared separately from solution are brought into contact to form a single device, was used here to form homojunctions comprising two identical layers of poly(3-hexylthiophene) (P3HT) or two layers of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1′-3}-thiadiazole)] (F8BT). Using ultraviolet photoemission spectroscopy (UPS), Kelvin Probe Force Microscopy (KPFM), and current–voltage (I–V) measurements, the electronic structure of, and carrier transport across, these homojunctions were investigated. UPS and KPFM show that lamination does not introduce any significant offset in the molecular levels across the interface. The I–V characteristics confirm this result by showing that transport across the film is largely unaffected by the presence of the laminated interface. This important result means that lamination could become a versatile tool for constructing multi-layer polymer devices.