This paper describes a procedure that makes it possible to design and fabricate (including sealing) microfluidic systems in an elastomeric materialpoly(dimethylsiloxane) (PDMS)in less than 24 h. A network of microfluidic channels (with width >20 μm) is designed in a CAD program. This design is converted into a transparency by a high-resolution printer; this transparency is used as a mask in photolithography to create a master in positive relief photoresist. PDMS cast against the master yields a polymeric replica containing a network of channels. The surface of this replica, and that of a flat slab of PDMS, are oxidized in an oxygen plasma. These oxidized surfaces seal tightly and irreversibly when brought into conformal contact. Oxidized PDMS also seals irreversibly to other materials used in microfluidic systems, such as glass, silicon, silicon oxide, and oxidized polystyrene; a number of substrates for devices are, therefore, practical options. Oxidation of the PDMS has the additional advantage that it ...

Rapid prototyping of microfluidic systems in poly(dimethylsiloxane)

Hydrophilic polymers are the center of research emphasis in nanotechnology because of their perceived “intelligence”. They can be used as thin films, scaffolds, or nanoparticles in a wide range of biomedical and biological applications. Here we highlight recent developments in engineering uncrosslinked and crosslinked hydrophilic polymers for these applications. Natural, biohybrid, and synthetic hydrophilic polymers and hydrogels are analyzed and their thermodynamic responses are discussed. In addition, examples of the use of hydrogels for various therapeutic applications are given. We show how such systems’ intelligent behavior can be used in sensors, microarrays, and imaging. Finally, we outline challenges for the future in integrating hydrogels into biomedical applications.

/pdf/hydrogels-in-biology-and-medicine-from-molecular-principles-3lowrzjjsl.pdf

Hydrogels in Biology and Medicine: From Molecular Principles to Bionanotechnology†

When considering new sensory technologies one should look to nature for guidance. Indeed, living organisms have developed the ultimate chemical sensors. Many insects can detect chemical signals with perfect specificity and incredible sensitivity. Mammalian olfaction is based on an array of less discriminating sensors and a memorized response pattern to identify a unique odor. It is important to recognize that the extraordinary sensory performance of biological systems does not originate from a single element. In actuality, their performance is derived from a completely interactive system wherein the receptor is served by analyte delivery and removal mechanisms, selectivity is derived from receptors, and sensitivity is the result of analyte-triggered biochemical cascades. Clearly, optimal artificial sensory sys-

Conjugated polymer-based chemical sensors.

Wearable sensor technologies are essential to the realization of personalized medicine through continuously monitoring an individual's state of health. Sampling human sweat, which is rich in physiological information, could enable non-invasive monitoring. Previously reported sweat-based and other non-invasive biosensors either can only monitor a single analyte at a time or lack on-site signal processing circuitry and sensor calibration mechanisms for accurate analysis of the physiological state. Given the complexity of sweat secretion, simultaneous and multiplexed screening of target biomarkers is critical and requires full system integration to ensure the accuracy of measurements. Here we present a mechanically flexible and fully integrated (that is, no external analysis is needed) sensor array for multiplexed in situ perspiration analysis, which simultaneously and selectively measures sweat metabolites (such as glucose and lactate) and electrolytes (such as sodium and potassium ions), as well as the skin temperature (to calibrate the response of the sensors). Our work bridges the technological gap between signal transduction, conditioning (amplification and filtering), processing and wireless transmission in wearable biosensors by merging plastic-based sensors that interface with the skin with silicon integrated circuits consolidated on a flexible circuit board for complex signal processing. This application could not have been realized using either of these technologies alone owing to their respective inherent limitations. The wearable system is used to measure the detailed sweat profile of human subjects engaged in prolonged indoor and outdoor physical activities, and to make a real-time assessment of the physiological state of the subjects. This platform enables a wide range of personalized diagnostic and physiological monitoring applications.

/pdf/fully-integrated-wearable-sensor-arrays-for-multiplexed-in-4nphg673vl.pdf

Fully integrated wearable sensor arrays for multiplexed in situ perspiration analysis

AACR Centennial Conference: Translational Cancer Medicine-- Nov 4-8, 2007; Singapore

PL02-05 

All cancers are due to abnormalities in DNA. The availability of the human genome sequence has led to the proposal that resequencing of cancer genomes will reveal the full complement of somatic mutations and hence all the cancer genes. To explore the nature of the information that will be derived from cancer genome sequencing we have sequenced the coding exons of the family of 518 protein kinases, ~1.3Mb DNA per cancer sample, in 210 cancers of diverse histological types. Despite the screen being directed toward the coding regions of a gene family that has previously been strongly implicated in oncogenesis, the results indicate that the majority of somatic mutations detected are “passengers”. There is considerable variation in the number and pattern of these mutations between individual cancers, indicating substantial diversity of processes of molecular evolution between cancers. The imprints of exogenous mutagenic exposures, mutagenic treatment regimes and DNA repair defects can all be seen in the distinctive mutational signatures of individual cancers. This systematic mutation screen and others have previously yielded a number of cancer genes that are frequently mutated in one or more cancer types and which are now anticancer drug targets (for example BRAF , PIK3CA , and EGFR ). However, detailed analyses of the data from our screen additionally suggest that there exist a large number of additional “driver” mutations which are distributed across a substantial number of genes. It therefore appears that cells may be able to utilise mutations in a large repertoire of potential cancer genes to acquire the neoplastic phenotype. However, many of these genes are employed only infrequently. These findings may have implications for future anticancer drug development.

Patterns of Somatic Mutation in Human Cancer Genomes

Bright luminescent, colloidal stable silica coated CdSe/ZnS nanocomposite by an in situ, one-pot surface functionalization

Sensitive, rapid and quantitative detection of substance P in serum samples using an integrated microfluidic immunochip.

Nanocrystalline CeO2 as Room Temperature Sensing Material for CO2 in Low Power Work Function Sensors

We report a simple, low-cost and lift-off free fabrication approach for periodic structures with adjustable nanometer gaps for interdigitated electrode arrays (IDAs). It combines an initial structure and two deposition process steps; first a dielectric layer is deposited, followed by a metal evaporation. The initial structure can be realized by lithography or any other structuring technique (e.g., nano imprint, hot embossing or injection molding). This method allows the fabrication of nanometer sized gaps and completely eliminates the need for a lift-off process. Different substrate materials like silicon, Pyrex or polymers can be used. The electrode gap is controlled primarily by sputter deposition of the initial structure, and thus, adjustable gaps in the nanometer range can be realized independently of the mask or stamp pattern. Electrochemical characterizations using redox cycling in ferrocenemethanol (FcMeOH) demonstrate signal amplification factors of more than 110 together with collection factors h...

Gerald Urban

Papers

Bright luminescent, colloidal stable silica coated CdSe/ZnS nanocomposite by an in situ, one-pot surface functionalization

Sensitive, rapid and quantitative detection of substance P in serum samples using an integrated microfluidic immunochip.

Nanocrystalline CeO2 as Room Temperature Sensing Material for CO2 in Low Power Work Function Sensors

Lift-Off Free Fabrication Approach for Periodic Structures with Tunable Nano Gaps for Interdigitated Electrode Arrays

Mg-MOF74 and Co-MOF74 as Sensing Layers for CO2 Detection