Programmable chemical gradient patterns by soft grayscale lithography

A method for fabricating chemical gradients on planar and nonplanar substrates using grayscale lithography is reported. Compliant grayscale amplitude masks are fabricated using a vacuum-assisted microfluidic filling protocol that employs dilutions of a carbon-black-containing polydimethylsiloxane emulsion (bPDMS) within traditional clear PDMS (cPDMS) to create planar, fully self-supporting mask elements. The mask is then placed over a surface functionalized with a hydrophobic coumarin-based photocleavable monolayer, which exposes a polar group upon irradiation. The mask serves to modulate the intensity of incident UV light, thereby controlling the density of molecules cleaved. The resulting molecular-level grayscale patterns are characterized by condensation microscopy and imaging mode time-of-flight secondary-ion mass spectrometry (ToF-SIMS). Due to the inherent flexibility of this technique, the photofuse as well as the gradient patterns can be designed for a wide range of applications; in this paper two proof-of-concept demonstrations are shown. The first utilizes the ability to control the resulting contact angle of the surface for the fabrication of a passive pressure-sensitive microfluidic gating system. The second is a model surface modification process that utilizes the functional groups deprotected during the photocleavage to pattern the deposition of moieties with complementary chemistry. The spatial layout, resolution, and concentration of these covalently linked molecules follow the gradient pattern created by the grayscale mask during exposure. The programmable chemical gradient fabrication scheme presented in this work allows explicit engineering of both surface properties that dictate nonspecific interactions (surface energy, charge, etc.) and functional chemistry necessary for covalent bonding.     

An experimental comparison of ER and UML class diagrams for data modelling

We present the results of three sets of controlled experiments aimed at analysing whether UML class diagrams are more comprehensible than ER diagrams during data models maintenance. In particular, we considered the support given by the two notations in the comprehension and interpretation of data models, comprehension of the change to perform to meet a change request, and detection of defects contained in a data model. The experiments involved university students with different levels of ability and experience. The results demonstrate that using UML class diagrams subjects achieved better comprehension levels. With regard to the support given by the two notations during maintenance activities the results demonstrate that the two notations give the same support, while in general UML class diagrams provide a better support with respect to ER diagrams during verification activities.     

Cover Picture: Fabrication of Stable Metallic Patterns Embedded in Poly(dimethylsiloxane) and Model Applications in Non‐Planar Electronic and Lab‐on‐a‐Chip Device Patterning (Adv. Funct. Mater. 4/2005)

A composite image is shown that highlights examples of device architectures that either incorporate or exploit polymer‐embedded metallic microstructures. In work reported by Nuzzo and co‐workers on p. 557, new applications of soft lithography, in conjunction with advanced forms of multilayer metallization, are used to construct these exceptionally durable structures. They are suitable for use in non‐planar lithographic patterning, and as device components finding applications ranging from microelectronics to Lab‐on‐a‐Chip analytical systems. This article describes the fabrication of durable metallic patterns that are embedded in poly(dimethylsiloxane) (PDMS) and demonstrates their use in several representative applications. The method involves the transfer and subsequent embedding of micrometer‐scale gold (and other thin‐film material) patterns into PDMS via adhesion chemistries mediated by silane coupling agents. We demonstrate the process as a suitable method for patterning stable functional metallization structures on PDMS, ones with limiting feature sizes less than 5 μm, and their subsequent utilization as structures suitable for use in applications ranging from soft‐lithographic patterning, non‐planar electronics, and microfluidic (lab‐on‐a‐chip, LOC) analytical systems. We demonstrate specifically that metal patterns embedded in both planar and spherically curved PDMS substrates can be used as compliant contact photomasks for conventional photolithographic processes. The non‐planar photomask fabricated with this technique has the same surface shape as the substrate, and thus facilitates the registration of structures in multilevel devices. This quality was specifically tested in a model demonstration in which an array of one hundred metal oxide semiconductor field‐effect transistor (MOSFET) devices was fabricated on a spherically curved Si single‐crystalline lens. The most significant opportunities for the processes reported here, however, appear to reside in applications in analytical chemistry that exploit devices fabricated using the methods of soft lithography. Toward this end, we demonstrate durably bonded metal patterns on PDMS that are appropriate for use in microfluidic, microanalytical, and microelectromechanical systems. We describe a multilayer metal‐electrode fabrication scheme (multilaminate metal–insulator–metal (MIM) structures that substantially enhance performance and stability) and use it to enable the construction of PDMS LOC devices using electrochemical detection. A polymer‐based microelectrochemical analytical system, one incorporating an electrode array for cyclic voltammetry and a microfluidic system for the electrophoretic separation of dopamine and catechol with amperometric detection, is demonstrated.     

Migrating legacy video lectures to multimedia learning objects

Video lectures are an old distance learning approach that offers only basic interaction and retrieval features to the user. Thus, to follow the new learning paradigms, we need to re‐engineer the e‐learning processes while preserving the investments made in the past. In this paper we present an approach for migrating video lectures to multimedia learning objects. Two essential problems are tackled: the detection of slide transitions and the generation of the learning objects. To this aim, the video of the lecture is scanned to detect the slide changes, while the learning object metadata and the slide pictures are extracted from the presentation document. A tool named VLMigrator (video lecture migrator) has been developed to support the migration of video lectures and the restructuring of their contents in terms of learning objects. Both the migration strategy and the tool have been experimented in a case study. Copyright © 2008 John Wiley & Sons, Ltd.     

A CMOS Ultra-Wideband Receiver for Low Data-Rate Communication

A low-power impulse-radio ultra-wideband receiver is demonstrated for low data-rate applications. A topology selection study demonstrates that the quadrature analog correlation is a good receiver architecture choice when energy consumption must be minimized. The receiver operates in the 3.1-5 GHz band of the UWB FCC spectrum mask on channels of 500 MHz bandwidth. The pulse correlation operation is done in the analog domain in order to reduce the ADC sampling speed down to the pulse repetition rate, thereby reducing the power consumption. The receiver comprises a low-noise amplifier with full on-chip matching network, an RF local oscillator generation, two quadrature mixers, two analog baseband chains followed by two ADCs, and a clock generation network. The receiver is implemented in 0.18 mum CMOS technology and achieves 16 mA power consumption at 20 Mpulses/s pulse repetition rate.     

Cover Picture: Photolithographic Route to the Fabrication of Micro/Nanowires of III–V Semiconductors (Adv. Funct. Mater. 1/2005)

The cover shows a patterned assembly of GaAs nanowires with their ends tethered to a bulk single‐crystal wafer as described on p. 30 by Rogers and co‐workers. These wires, which have triangular cross‐sections, were fabricated via a top–down process that combines photolithography and anisotropic chemical etching. Nano/microwires of semiconducting materials (e.g., GaAs and InP) with triangular cross‐sections can be fabricated by “top–down” approaches that combine lithography of high‐quality bulk wafers (using either traditional photolithography or phase‐shift optical lithography) with anisotropic chemical etching. This method gives good control over the lateral dimensions, lengths, and morphologies of free‐standing wires. The behaviors of many different resist layers and etching chemistries are presented. It is shown how wire arrays with highly ordered alignments can be transfer printed onto plastic substrates. This “top–down” approach provides a simple, effective, and versatile way of generating high‐quality single‐crystalline wires of various compound semiconductors. The resultant wires and wire arrays have potential applications in electronics, optics, optoelectronics, and sensing.     

Surface Composition and Morphology of Particles Dried Individually and by Spray Drying

This study investigates how the morphology of spray-dried particles is related to the formulation and properties of the components in the formulation. Further, the scale effects in comparisons of levitation-dried single particles and spray-dried particles in a lab-scale spray dryer have been addressed. The Drying Kinetics Analyzer^TM generates single particles from a levitated drop under simulated spray-drying conditions. A set of surface-active polymers (bovine serum albumin, hydroxypropyl methyl cellulose, and triblock co-polymer Poloxamer), in combination with lactose, were analyzed for their dynamic surface properties in solution, and their effect on particle morphology and surface composition were determined by low-vacuum SEM and XPS analyses. The morphology obtained in spray drying was reproduced in the single-particle drying. The surface compositions were also similar, but higher levels of surface-active materials were found at the surface of the single particles as compared to the spray-dried particles. Further, the adsorption rate of surface-active compounds at the drop surface estimated by dynamic surface tension was found to be an important parameter to estimate the surface composition at different drying scales. The particle morphology was primarily determined by the surface rheological properties of the feed solution and, to a lesser extent, by the surface composition.     

Fabrication of patterned multicomponent protein gradients and gradient arrays using microfluidic depletion

We demonstrate that depletion effects in the fluids used to fill a poly(dimethylsiloxane) microfluidic device can be used in conjunction with its design rules to generate patterned protein gradients. The linear portions of these structures can be designed to present gradients of bound protein coverage-varying from near-saturation to effectively zero-over distances ranging from a few hundred micrometers to more than 1 cm by design. Such patterns can be developed in a simple, single-channel form as well as in a multichannel gradient array of more complex design. The patterning protocols also support the use of multiple protein sources, and we demonstrate an assembly process mediated by a protein that inhibits adsorption to generate a gradient array in pixel form. We describe examples of multiple protein gradient patterns along with simple immunoassays to illustrate the scope of the methodology, the activity of the patterned proteins, and their recognition in gradient form on a surface. These gradients should prove useful to studies in biosensor and bioassay development and as substrates for cell culture to study growth and motility.