Brett D. Martin

Reduction of Non-Specific Protein Adsorption Using Poly(ethylene) Glycol (PEG) Modified Polyacrylate Hydrogels In Immunoassays for Staphylococcal Enterotoxin B Detection

Three PEG molecules (PEG-methacrylate, -diacrylate and -dimethacrylate) were incorporated into galactose-based polyacrylate hydrogels and their relative abilities to reduce non-specific protein adsorption in immunoassays were determined. Highly crosslinked hydrogels containing amine-terminated functionalities were formed and used to covalently attach antibodies specific for staphylococcal enterotoxin B (SEB). Patterned arrays of immobilized antibodies in the PEG-modified hydrogels were created with a PDMS template containing micro-channels for use in sandwich immunoassays to detect SEB. Different concentrations of the toxin were applied to the hydrogel arrays, followed with a Cy3-labeled tracer antibody specific for the two toxins. Fluorescence laser scanning confocal microscopy of the tracer molecules provided both qualitative and quantitative measurements on the detection sensitivity and the reduction in non-specific binding as a result of PEG incorporation. Results showed the PEG-modified hydrogel significantly reduced non-specific protein binding with a detection limit for SEB of 1 ng/mL. Fluorescence signals showed a 10-fold decrease in the non-specific binding and a 6-fold increase in specific binding of SEB.

Use of Low‐Temperature Thermal Alkylation to Eliminate Ink Migration in Microcontact Printed Patterns

We demonstrate aqueous hydrogel-based microcontact printing of amine ligands into solvent-templated nanocavities of chloromethylphenyl-based siloxane or thin polymer films. Migration of pyridine ligands within films following printing, which can compromise pattern fidelity, is eliminated by heat treatment of the substrate. Gentle heating (e.g., 50 degrees C, 5 min) leads to the efficient alkylation of mobile pyridine adsorbate by the C-Cl bonds of the film, covalently tethering the adsorbate to the surface as a pyridinium salt. Subsequent binding of a Pd-based colloid to surface pyridinium (and remaining strongly bound and immobile pyridine ligand) sites permits selective electroless metal deposition and fabrication of patterned metal films.

Diffusion and transfer of antibody proteins from a sugar-based hydrogel

Diffusion of antibody protein from hydrogel films and hydrogel encapsulated in a microcapillary was studied. Thin hydrogel films were formed by crosslinking 6-acryloyl-B-O-methylgalactoside withN,N’-methylene-bis-acrylamide and the diffusive transport of monoclonal antimouse IgG-FITC into and out of the hydrated films was measured. Diffusion coefficients in 2 and 4% crosslinked hydrogel films were measured. The measured diffusion constants determined for IgG in both the 2 and 4% hydrogel films were comparable to the free diffusion of IgG in bulk water (Dmean ∼ 10-7cm2/s). In addition, 2% crosslinked hydrogels were prepared in a capillary tube and the transport of antimouse IgG-FITC into and out of the hydrated hydrogel was measured. Kinetic analysis indicated that the protein transport through the capillary hydrogel was faster than would be expected for a simple diffusion process. Finally, by utilizing the diffusion of antibody from the capillary hydrogel, transfer of antibody to a silica surface was demonstrated. A capillary hydrogel loaded with antimouse IgG-FITC was used to transfer the protein to a silica surface forming a 30-μm spot of antibody, which was imaged using fluorescence microscopy. These results may lead to the development of a nonlithographic method of patterning antibodies on surfaces for use in integrated microimmunosensors.

Generation of fluorescent silver nanoscale particles in reverse micelles using gamma irradiation

Reverse micelles (RMs) containing aqueous solutions of Ag(+) ions in their core produce fluorescent Ag species, upon exposure to gamma irradiation. A two-phase liquid system is used for RM formation. The RMs can be employed in novel gamma radiation detectors with appearance of fluorescence indicating that radiation was once present.

Photo-enhanced hydrolysis of bis(4-nitrophenyl) phosphate using Cu(II) bipyridine-capped plasmonic nanoparticles

We show that the hydrolysis of bis(4-nitrophenyl) phosphate by a Cu(II) bipyridine complex was enhanced by 1000-fold when covalently attached to 10 nm gold nanoparticles (AuNP) and irradiated with a 120 mW green laser at 532 nm when compared to an unsupported vinyl-substituted Cu bipyridine analog. The catalytic reaction was monitored by UV-vis spectroscopy in 20 mM MOPS buffer at pH 8 and at room temperature by observing the growth of the product, 4-nitrophenolate, at 405 nm. Initial rate data was analyzed using a Michaelis–Menten formalism. Control experiments suggested that the photo-enhanced hydrolysis reaction required that the Cu metal center be attached to the AuNPs via a thiolated bpy ligand. At higher laser power, the initial rate data deviated from the Michaelis–Menten formalism. Possible mechanisms are discussed.

Directional photoinduced electron transfer in paraquat silicate thin films containing entrapped ruthenium(II)-tris(bathophenanthroline-disulfonate)

We have demonstrated directional photoinduced electron transfer in paraquat silicate thin films containing entrapped ruthenium(II)-tris(bathophenanthroline-disulfonate (RuBPS). The films were made by electrochemically-induced hydrolysis of a silane analogue of paraquat with ruthenium(II)-tris(bathophenanthroline-disulfonate as its ion pair.