[Show abstract][Hide abstract] ABSTRACT: This work examines charge transport (CT) through self-assembled monolayers (SAMs) of oligoglycines having an N-terminal cysteine group that anchors the molecule to a gold substrate, and demonstrate that CT is rapid (relative to SAMs of n-alkanethiolates). Comparisons of rates of charge transport-using junctions with the structure AuTS/SAM//Ga2O3/EGaIn (across these SAMs of oligoglycines, and across SAMs of a number of structurally and electronically related molecules) established that rates of charge tunneling along SAMs of oligoglycines are comparable to that along SAMs of oligophenyl groups (of comparable length). The mechanism of tunneling in oligoglycines is compatible with superexchange, and involves interactions among high-energy occupied orbitals in multiple, consecutive amide bonds, which may by separated by one to three methylene groups. This mechanistic conclusion is supported by density functional theory (DFT).
[Show abstract][Hide abstract] ABSTRACT: This paper addresses a growing need in clinical diagnostics for parallel, multiplex analysis of biomarkers from small biological samples. It describes a new procedure for assembling arrays of ssDNA and proteins on paper. This method starts with the synthesis of DNA oligonucleotides covalently linked to paper, and proceeds to assemble microzones of DNA-conjugated paper into arrays capable of simultaneously capturing DNA, DNA-conjugated protein antigens, and DNA-conjugated antibodies. The synthesis of ssDNA oligonucleotides on paper is convenient and effective, with 32% of the oligonucleotides cleaved and eluted from the paper substrate being full-length by HPLC for a 32-mer. These ssDNA arrays can be used to detect fluorophore-linked DNA oligonucleotides in solution, and as the basis for DNA-directed assembly of arrays of DNA-conjugated capture antibodies on paper, detect protein antigens by sandwich ELISAs. Paper-anchored ssDNA arrays with different sequences can be used to assemble paper-based devices capable of detecting DNA and antibodies in the same device, and enable simple microfluidic paper-based devices.
[Show abstract][Hide abstract] ABSTRACT: This work describes the adaptive use of conventional stainless steel pins-used in unmodified form or coated with carbon paste-as working, counter, and quasi-reference electrodes in electrochemical devices fabricated using cotton thread or embossed omniphobic R(F) paper to contain the electrolyte and sample. For some applications, these pin electrodes may be easier to modify and use than printed electrodes, and their position and orientation can be changed as needed. Electroanalytical devices capable of multiplex analysis (thread-based arrays or 96-well plates) were easily fabricated using pins as electrodes in either thread or omniphobic R(F) paper.
Lab on a Chip 11/2015; DOI:10.1039/C5LC00867K · 6.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Soft, pneumatic actuators that buckle when interior pressure is less than exterior provide a new mechanism of actuation. Upon application of negative pneumatic pressure, elastic beam elements in these actuators undergo reversible, cooperative collapse, and generate a rotational motion. These actuators are inexpensive to fabricate, lightweight, easy to control, and safe to operate. They can be used in devices that manipulate objects, locomote, or interact cooperatively with humans, as described by G. M. Whitesides and co-workers on page 6323.
[Show abstract][Hide abstract] ABSTRACT: It is well known that 3D in vitro cell cultures provide a much better model than 2D cell cultures for understanding the in vivo microenvironment of cells. However, significant technical challenges in handling and analyzing 3D cell cultures remain, which currently limits their widespread application. Herein we demonstrate the application of wholly synthetic thermo-responsive block copolymer worms in sheet-based 3D cell culture. These worms form a soft, free-standing gel reversibly at 20-37 °C, which can be rapidly converted into a free-flowing dispersion of spheres on cooling to 5 °C. Functionalization of the worms with disulfide groups was found to be essential for ensuring sufficient mechanical stability of these hydrogels to enable long-term cell culture. These disulfide groups are conveniently introduced via statistical copolymerization of a disulfide-based dimethacrylate under conditions that favour intramolecular cyclization and subsequent thiol/disulfide exchange leads to the formation of reversible covalent bonds between adjacent worms within the gel. This new approach enables cells to be embedded within micrometer-thick slabs of gel with good viability, permits cell culture for at least 12 days, and facilitates recovery of viable cells from the gel simply by incubating the culture in buffer at 37 °C (thus avoiding the enzymatic degradation required for cell harvesting when using commercial protein-based gels such as Matrigel).
[Show abstract][Hide abstract] ABSTRACT: Soft, pneumatic actuators that buckle when interior pressure is less than exterior provide a new mechanism of actuation. Upon application of negative pneumatic pressure, elastic beam elements in these actuators undergo reversible, cooperative collapse, and generate a rotational motion. These actuators are inexpensive to fabricate, lightweight, easy to control, and safe to operate. They can be used in devices that manipulate objects, locomote, or interact cooperatively with humans.
[Show description][Hide description] DESCRIPTION: This paper describes the design and fabrication
of ion-sensing electrochemical paper-based analytical devices
(EPADs) in which a miniaturized paper reference electrode is
integrated with a small ion-selective paper electrode (ISPE) for
potentiometric measurements. Ion-sensing EPADs use printed
wax barriers to define electrochemical sample and reference
[Show abstract][Hide abstract] ABSTRACT: Clinical tests based on primer-initiated amplification of specific nucleic acid sequences achieve high levels of sensitivity and specificity. Despite these desirable characteristics, these tests have not reached their full potential because their complexity and expense limit their usefulness to centralized laboratories. This paper describes a device that integrates sample preparation and Loop-mediated Isothermal Amplification (LAMP) with endpoint detection using a handheld UV source and camera phone. The prototype device integrates paper microfluidics (to enable fluid handling) and a multi-layer structure - or a "paper machine" - that allows a central patterned paper strip to slide in and out of fluidic path, and thus to allow introduction of sample, wash buffers, amplification master mix, and detection reagents with minimal pipetting, in a hand-held, disposable device intended for point-of-care use in resource-limited environments. This device creates a dynamic seal that prevents evaporation during incubation at 65 °C for 1 hour. This interval is sufficient to allow a LAMP reaction for the Escherichia coli malB gene to proceed with an analytical sensitivity of 1 double-stranded DNA target copy. Starting with human plasma spiked with whole, live E. coli cells, this paper demonstrates full integration of sample preparation with LAMP amplification and endpoint detection with a limit of detection of 5 cells. Further, it shows that the method used to prepare sample enables concentration of DNA from sample volumes commonly available from fingerstick blood draw.
[Show abstract][Hide abstract] ABSTRACT: This paper describes a method of isolating small, highly accurate density-standard beads and characterizing their densities using accurate and experimentally traceable techniques. Density standards have a variety of applications, including the characterization of density gradients, which are used to separate objects in a variety of fields. Glass density-standard beads can be very accurate (± 0.0002 g cm-3), but are too large (3-7 mm in diameter) for many applications. When smaller density standards are needed, commercial polymer microspheres are often used. These microspheres have standard deviations in density ranging from 0.006 to 0.021 g cm-3; these distributions in density make these microspheres impractical for applications demanding small steps in density. In this paper, commercial microspheres are fractionated using aqueous multiphase systems (AMPS)-aqueous mixture of polymers and salts that spontaneously separate into phases having molecularly sharp steps in density-to isolate microspheres having much narrower distributions in density (standard deviations from 0.0003 to 0.0008 g cm-3) than the original microspheres. By reducing the heterogeneity in densities, this method reduces the uncertainty in the density of any specific bead and, therefore, improves the accuracy within the limits of the calibration standards used to characterize the distributions in density.
[Show abstract][Hide abstract] ABSTRACT: Combining aqueous multiphase systems (AMPS) and magnetic levitation (MagLev) provides a method to produce hybrid gradients in apparent density. AMPS-solutions of different polymers, salts, or surfactants that spontaneously separate into immiscible but predominantly aqueous phases-offer thermodynamically stable steps in density that can be tuned by the concentration of solutes. MagLev-the levitation of diamagnetic objects in a paramagnetic fluid within a magnetic field gradient-can be arranged to provide a near-linear gradient in effective density where the height of a levitating object above the surface of the magnet corresponds to its density; the strength of the gradient in effective density can be tuned by the choice of paramagnetic salt and its concentrations, and by the strength and gradient in the magnetic field. Including paramagnetic salts (e.g., MnSO4 or MnCl2) in AMPS, and placing them in a magnetic field gradient, enables their use as media for MagLev. The potential to create large steps in density with AMPS allows separations of objects across a range of densities. The gradients produced by MagLev provide resolution over a continuous range of densities. By combining these approaches, mixtures of objects with large differences in density can be separated and analyzed simultaneously. Using MagLev to add an effective gradient in density also enables tuning the range of densities captured at an interface of an AMPS by simply changing the position of the container in the magnetic field. Further, by creating AMPS in which phases have different concentrations of paramagnetic ions, the phases can provide different resolutions in density. These results suggest that combining steps in density with gradients in density can enable new classes of separations based on density.
[Show abstract][Hide abstract] ABSTRACT: Die universitäre Forschung an Point-of-Care-Diagnostik für die globale Gesundheit verzeichnet ein stetes Wachstum, allerdings verlassen viele Testsysteme niemals das Labor. Prozesse, die die diagnostische Technologie vom Labor ins Feld überführen – Prozesse, mit deren Hilfe Betrieb und Leistungsvermögen unter realistischen Bedingungen evaluiert werden sollen –, sind komplizierter, als sie scheinen mögen. Zwei Fallstudien illustrieren diesen Prozess: die Entwicklung eines papierbasierten Testsystems zur Messung der Leberfunktion sowie die eines Testsystems zur Identifikation von Sichelzellanämie, das auf wässrigen, mehrphasigen Systemen sowie Unterschieden in der Dichte normaler und sichelförmiger Zellen beruht. Aus den Details der Entwicklung dieser beiden Testsysteme lassen sich allgemeingültige Strategien zum Aufbau von Kooperationen, zum Herstellen von Prototypen, zur Validierung, zum Design von Studien und zur Evaluation von Point-of-Care-Diagnostik ableiten. Die aus diesen Erfahrungen gezogenen (verfahrens)technischen Lehren können Wissenschaftlern nutzen, die diagnostische Tests für Entwicklungsländer und – allgemeiner – Technologien für den Einsatz bei begrenzten Ressourcen entwerfen.
[Show abstract][Hide abstract] ABSTRACT: Charge transport through junctions consisting of insulating molecular units is a quantum phenomenon that cannot be described adequately by classical circuit laws. This paper explores tunneling current densities in self-assembled monolayer (SAM)-based junctions with the structure AgTS/O2C‒R1‒R2‒H//Ga2O3/EGaIn, where AgTS is template-stripped silver, and EGaIn is the eutectic alloy of gallium and indium; R1 and R2 refer to two classes of insulating molecular units-(CH2)n and (C6H4)m-that are connected in series and have different tunneling decay constants in the Simmons equation. These junctions can be analyzed as a form of series tunneling junctions based on the observation that permuting the order of R1 and R2 in the junction does not alter the overall rate of charge transport. By using the Ag/O2C interface, this system decouples the HOMO (which is localized on the carboxylate group) from strong interactions with the R1 and R2 units. The differences in rates of tunneling are thus determined by the electronic structure of the groups R1 and R2; these differences are not influenced by the order of R1 and R2 in the SAM. In an electrical potential model that rationalizes this observation, R1 and R2 contribute independently to the height of the barrier. This model explicitly assumes that contributions to rates of tunneling from the AgTS/O2C and H//Ga2O3 interfaces are constant across the series examined. The current density of these series tunneling junctions can be described by J(V) = J0(V)exp(-β1d1 - β2d2), where J(V) is the current density (A/cm2) at applied voltage V, and βi and di are the parameters describing the attenuation of the tunneling current through a rectangular tunneling barrier, with width d and a height related to the attenuation factor β.
Journal of the American Chemical Society 04/2015; 137(18). DOI:10.1021/jacs.5b00448 · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Die Badische Anilin- & Sodafabrik – die BASF – wurde am 6. April 1865 von Friedrich Engelhorn in Mannheim gegründet und wird damit in diesem Jahr 150 Jahre alt. Das vorliegende Heft bietet anlässlich dieses besonderen Firmenjubiläums eine Sammlung von Aufsätzen und Essays, die sich mit Beiträgen der Chemie zu den Themen Energie, Ernährung und städtisches Leben befassen. Woher wird die Energie in Zukunft kommen, die wir brauchen? Wie können genug Nahrung und sauberes Wasser für alle Menschen bereit gestellt werden? Wie werden die Städte der Zukunft aussehen? Passend dazu sind auf dem Titelbild einige Highlights aus der breiten Produktpalette der BASF herausgestellt: Kathodenmaterialien für Lithium-Ionen-Batterien (oben), Membranen für sauberes Wasser (unten) sowie Xemium®, ein neuer fungizider Wirkstoff. Dieses Heft begleitet drei BASF-Jubiläumssymposien in Ludwigshafen (9./10. März), Chicago (23./24. Juni) und Shanghai (10./11. November), bei denen Autoren dieses Heftes vortragen. Es wird eingeleitet von einem Essay von A. Kreimeyer et al. auf S. 3220 ff. über die Geschichte und aktuelle Position der Forschung der BASF, worauf ein Essay von G. M. Whitesides auf S. 3238 ff. folgt, in dem er zu einem Umdenken in der chemischen Forschung aufruft. Alle zwanzig Essays und Aufsätze dieses Heftes demonstrieren die enorme Bedeutung chemischer Forschung – sie muss und wird zur Hebung des durchschnittlichen Lebensstandards einer wachsenden Weltbevölkerung beitragen. Die Redaktion der Angewandten Chemie gratuliert der BASF zu ihrem Jubiläum.
[Show abstract][Hide abstract] ABSTRACT: This paper describes the influence of substitution of fluorine for hydrogen on the rate of charge transport through junctions of the form AgTSO2C(CH2)n(CF2)mT//Ga2O3/EGaIn, where T is methyl (CH3) or trifluoromethyl (CF3). Alkanoate-based self-assembled monolayers (SAMs) having perfluorinated groups (RF) show current densities that are lower (by factors of 20-30) than those of the homologous hydrocarbons (RH), while the attenuation factors of the simplified Simmons equation for methylene (β =1.05 ± 0.02 nCH2-1) and difluoromethylene (β =1.15 ± 0.02 nCF2-1) are similar. A comparative study focusing on the terminal fluorine substituents in SAMs of omega-tolyl and -phenyl alkanoates suggests that the C-F//Ga2O3 interface is responsible for the lower tunneling currents for CF3. The decrease in the rate of charge transport in SAMs with RF groups (relative to homologous RH groups) is plausibly due to an increase in the height of the tunneling barrier at the T//Ga2O3 interface, and/or to weak van der Waals interactions at that interface.
Journal of the American Chemical Society 03/2015; 137(11). DOI:10.1021/jacs.5b00137 · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Badische Anilin- & Sodafabrik BASF, was founded on April 6th, 1865 by Friedrich Engelhorn in Mannheim, Germany, and is thus 150 years old this year. To celebrate the firm's special anniversary, this Issue offers a collection of Reviews and Essays covering the contributions made by chemistry in the areas of energy, nutrition, and city life. Where will the energy that we need come from in the future? How can enough food and clean water for every single person be provided? What will the city of the future look like? Appropriately the Cover Picture presents some highlights from the broad pallet of products produced by BASF: cathode materials for lithium-ion batteries (top), membranes for clean water (bottom), along with Xemium®, a new active ingredient and next-generation fungicide. This Issue accompanies three BASF anniversary symposia in Ludwigshafen (9th/10th March), Chicago (23rd/24th June), and Shanghai (10th/11th November), at which authors in this Issue are lecturing. It is introduced by an Essay by A. Kreimeyer et al. on page 3178 ff. about the history of and the current direction of research at BASF, and followed by an Essay by G. M. Whitesides on page 3196 ff., in which he calls for a rethink in chemical research. All twenty Essays and Reviews in this Issue demonstrate the huge importance of chemical research—it must, and will, contribute to raising the average quality of life of a growing world population. Angewandte Chemie congratulates BASF on its anniversary.
[Show abstract][Hide abstract] ABSTRACT: This paper uses the binding pocket of human carbonic anhydrase II (HCAII, EC 184.108.40.206) as a tool to examine the properties of Hofmeister anions that determine (i) where, and how strongly, they associate with concavities on the surfaces of proteins and (ii) how, upon binding, they alter the structure of water within those concavities. Results from X-ray crystallography and isothermal titration calorimetry show that most anions associate with the binding pocket of HCAII by forming inner-sphere ion pairs with the Zn2+ cofactor. In these ion pairs, the free energy of anion-Zn2+ association is inversely proportional to the free energetic cost of anion dehydration; this relationship is consistent with the mechanism of ion pair formation suggested by the "Law of Matching Water Affinities." Iodide and bromide anions also associate with a hydrophobic declivity in the wall of the binding pocket. Molecular dynamics simulations suggest that anions, upon associating with Zn2+, trigger rearrangements of water that extend up to 8 Å away from their surfaces. These findings expand the range of interactions previously thought to occur between ions and proteins by suggesting that (i) weakly hydrated anions can bind complementarily shaped hydrophobic declivities, and that (ii) ion-induced rearrangements of water within protein concavities can (in contrast with similar rearrangements in bulk water) extend well beyond the first hydration shells of the ions that trigger them. This study paints a picture of Hofmeister anions as a set of structurally varied ligands that differ in size, shape, and affinity for water and, thus, in their ability to bind to--and to alter the hydration structure of--polar, nonpolar, and topographically complex concavities on protein surfaces.
Journal of the American Chemical Society 03/2015; 137(11). DOI:10.1021/jacs.5b00187 · 12.11 Impact Factor