Biomedical subjects

Nathan H Mack

Publications and source records attributed to Nathan H Mack.

5 recordsLinked to original sources

PubMed2006

Quantitative multispectral biosensing and 1D imaging using quasi-3D plasmonic crystals.

We developed a class of quasi-3D plasmonic crystal that consists of multilayered, regular arrays of subwavelength metal nanostructures. The complex, highly sensitive structure of the optical transmission spectra of these crystals makes them especially well suited for sensing applications. Coupled with quantitative electrodynamics modeling of their optical response, they enable full multiwavelength spectroscopic detection of molecular binding events with sensitivities that correspond to small fractions of a monolayer. The high degree of spatial uniformity of the crystals, formed by a soft nanoimprint technique, provides the ability to image binding events over large areas with micrometer spatial resolution. These features, together with compact form factors, low-cost fabrication procedures, simple readout apparatus, and ability for direct integration into microfluidic networks and arrays, suggest promise for these devices in label-free bioanalytical detection systems.

Avidin↗

PubMed2006

Quantitative imaging of protein adsorption on patterned organic thin-film arrays using secondary electron emission.

Secondary electron emission is developed as a means to quantify and image protein binding to Au surfaces modified with patterned organic thin-film arrays. Alkane thiols were patterned via microcontact printing on gold, and their effects on the secondary electron (SE) yield of the surface, systematically quantified. We show that a self-assembled monolayer (SAM) of hexadecane thiol significantly increases the SE yield over the native gold surface, a yield that increases as a function of alkane chain length (C8-C16). This effect is linearly correlated with the surface potentials and wetting properties of these SAMs. Surface layers comprised of poly(ethylene glycol) (PEG) grafted polyacrylamide polymers behave differently, affecting the SE yield by attenuation according to the polymer thickness. These results demonstrate the relative contributions of factors related to the adsorbate molecular structures that serve to strongly mediate the SE yield, providing a foundation for exploiting them as a quantitative electron imaging probe. The latter capability is demonstrated using a model microfluidic assay in which a series of proteins was spatially addressed to a SAM-based pixel array. The gray scale contrasts seen with protein adsorption are directly correlated with both protein molecular weight and mass coverage. These methods are used in two model protein assay experiments: (1) the measurement of the concentration dependent adsorption isotherm for a model protein (fibrinogen); and (2) the selective recognition of a biotinylated protein layer by avidin. These results demonstrate a unique approach to imaging protein binding processes on surfaces with both high analytical and spatial sensitivity.

Acrylic Resins↗

PubMed2006

Origin of bulklike structure and bond length disorder of Pt37 and Pt6Ru31 clusters on carbon: comparison of theory and experiment.

We describe a theoretical analysis of the structures of self-organizing nanoparticles formed by Pt and Ru-Pt on carbon support. The calculations provide insights into the nature of these metal particle systems-ones of current interest for use as the electrocatalytic materials of direct oxidation fuel cells-and clarify complex behaviors noted in earlier experimental studies. With clusters deposited via metallo-organic Pt or PtRu(5) complexes, previous experiments [Nashner et al. J. Am. Chem. Soc. 1997, 119, 7760; Nashner et al. J. Am. Chem. Soc. 1998, 120, 8093; Frenkel et al. J. Phys. Chem. B 2001, 105, 12689] showed that the Pt and Pt-Ru based clusters are formed with fcc(111)-stacked cuboctahedral geometry and essentially bulklike metal-metal bond lengths, even for the smallest (few atom) nanoparticles for which the average coordination number is much smaller than that in the bulk, and that Pt in bimetallic [PtRu(5)] clusters segregates to the ambient surface of the supported nanoparticles. We explain these observations and characterize the cluster structures and bond length distributions using density functional theory calculations with graphite as a model for the support. The present study reveals the origin of the observed metal-metal bond length disorder, distinctively different for each system, and demonstrates the profound consequences that result from the cluster/carbon-support interactions and their key role in the structure and electronic properties of supported metallic nanoparticles.

Journal Article↗

PubMed2004

pH-dependent photophysical behavior of rhenium complexes containing hydroxypyridine ligands.

Data related to the pH-dependent photophysics of a class of rhenium complexes containing the hydroxypyridine ligand are presented. Data include ground-state pK(a) values, emission energies, and lifetimes. The complexes all have ground-state pK(a) values near 7.0 and exhibit a dramatic change in emission intensity near this pH. The lifetimes of these complexes, however, are constant over this pH range. A model is presented to account for the observed photophysical behavior. The pH-dependent emission properties of these species make them good candidates for luminescence-based pH probes, especially in the environmental and biomedical fields.

Hydrogen-Ion Concentration↗

PubMed2002

Multicomponent lifetime-based pH sensors utilizing constant-lifetime probes.

A multicomponent luminescent sensor system is described that uses probe species with constant lifetimes to generate an analyte-dependent change in the apparent sensor lifetime. This new sensing scheme not only allows for lifetime-based measurement techniques to be applied to sensors that employ static quenching interactions but also provides the ability to vary the sensitivity of the sensor system with simple changes in instrumental parameters. A model for the multicomponent sensor is presented, followed by data measured using a prototype pH sensor based on the model.

Biosensing Techniques↗