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Biomedical subjects

P E Sheehan

Publications and source records attributed to P E Sheehan.

9 recordsLinked to original sources
PubMed2003

A simple pen-spotting method for arraying biomolecules on solid substrates.

We describe a simple, relatively inexpensive method for depositing biomolecules on a solid substrate using Rapidograph drafting pens. The pens can be used without modification to accurately deposit spots between approximately 100 and 600 microm in diameter. When mounted on a suitable microtranslation stage, the pens can be used to easily deposit tens of spots aligned with underlying substrate features such as microfabricated sensors. The pens are particularly convenient because pre-mixed solutions can be stored in the pens for multiple uses. We demonstrate the use of this approach to deposit DNA probes on a microsensor array.

Adsorption↗
PubMed2002

Thiol diffusion and the role of humidity in "Dip Pen Nanolithography".

The radii of octadecanethiol spots deposited by an atomic force microscope tip onto a gold surface were studied as a function of contact time and humidity. The deposition is well described by two-dimensional diffusion from an annular source of constant concentration, with a surface diffusion coefficient of 8400 nm(2) s(-1), independent of humidity. Facile transfer is observed even after near continuous deposition for more than 24 h in a dry N2 environment, indicating that a water meniscus is not required.

Biosensing Techniques↗
PubMed2001

Estimated effects of temperature on secondary organic aerosol concentrations.

The temperature-dependence of secondary organic aerosol (SOA) concentrations is explored using an absorptive-partitioning model under a variety of simplified atmospheric conditions. Experimentally determined partitioning parameters for high yield aromatics are used. Variation of vapor pressures with temperature is assumed to be the main source of temperature effects. Known semivolatile products are used to define a modeling range of vaporization enthalpy of 10-25 kcal/mol-1. The effect of diurnal temperature variations on model predictions for various assumed vaporization enthalpies, precursor emission rates, and primary organic concentrations is explored. Results show that temperature is likely to have a significant influence on SOA partitioning and resulting SOA concentrations. A 10 degrees C decrease in temperature is estimated to increase SOA yields by 20-150%, depending on the assumed vaporization enthalpy. In model simulations, high daytime temperatures tend to reduce SOA concentrations by 16-24%, while cooler nighttime temperatures lead to a 22-34% increase, compared to constant temperature conditions. Results suggest that currently available constant temperature partitioning coefficients do not adequately represent atmospheric SOA partitioning behavior. Air quality models neglecting the temperature dependence of partitioning are expected to underpredict peak SOA concentrations as well as mistime their occurrence.

Aerosols↗
PubMed2000

The BARC biosensor applied to the detection of biological warfare agents.

The Bead ARray Counter (BARC) is a multi-analyte biosensor that uses DNA hybridization, magnetic microbeads, and giant magnetoresistive (GMR) sensors to detect and identify biological warfare agents. The current prototype is a table-top instrument consisting of a microfabricated chip (solid substrate) with an array of GMR sensors, a chip carrier board with electronics for lock-in detection, a fluidics cell and cartridge, and an electromagnet. DNA probes are patterned onto the solid substrate chip directly above the GMR sensors, and sample analyte containing complementary DNA hybridizes with the probes on the surface. Labeled, micron-sized magnetic beads are then injected that specifically bind to the sample DNA. A magnetic field is applied, removing any beads that are not specifically bound to the surface. The beads remaining on the surface are detected by the GMR sensors, and the intensity and location of the signal indicate the concentration and identity of pathogens present in the sample. The current BARC chip contains a 64-element sensor array, however, with recent advances in magnetoresistive technology, chips with millions of these GMR sensors will soon be commercially available, allowing simultaneous detection of thousands of analytes. Because each GMR sensor is capable of detecting a single magnetic bead, in theory, the BARC biosensor should be able to detect the presence of a single analyte molecule.

Biological Warfare↗
PubMed1998

A biosensor based on magnetoresistance technology.

We are developing a biosensor that will measure, at the level of single molecules, the forces that bind DNA-DNA, antibody-antigen, or ligand-receptor pairs together. The Bead Array Counter (BARC) will use these interaction forces to hold magnetic microbeads to a solid substrate. Microfabricated magnetoresistive transducers on the substrate will indicate whether or not the beads are removed when pulled by magnetic forces. By adapting magnetoresistive computer memory technology, it may be possible to fabricate millions of transducers on a chip and detect or screen thousands of analytes. The multi-analyte capability of this portable sensor would be ideal for on-site testing, while the potential to directly gauge intermolecular interaction strengths suggests drug discovery applications.

Biosensing Techniques↗
PubMed1995

Purchasing: a necessary partnership.

According to a recent survey published in Hospital Purchasing News, a Mcknight Medical Communications publication, the average hospital in the United States spent $16.7 million, not including equipment purchases, in 1994. This represents an increase of 41.6 percent over the amount spent in 1990, $11.8 million. The hospital's objective of having year-end revenues exceed expenses largely depends on the ability to purchase materiel at the best price, not necessarily the lowest cost. This goal can be achieved by partnering with suppliers and customers (hospital administrative and surgical staff, as well as patients) through open communication and trust. Reducing costs by a percent on the dollar could return $167,000 to the average hospital. Partnering can assist in achieving these savings!

Commerce↗