title: High-resolution, high-throughput, positive-tone patterning of poly(ethylene glycol) by helium beam exposure through stencil masks.
abstract: In this work, a collimated helium beam was used to activate a thiol-poly(ethylene glycol) (SH-PEG) monolayer on gold to selectively capture proteins in the exposed regions. Protein patterns were formed at high throughput by exposing a stencil mask placed in proximity to the PEG-coated surface to a broad beam of helium particles, followed by incubation in a protein solution. Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) spectra showed that SH-PEG molecules remain attached to gold after exposure to beam doses of 1.5-60 µC/cm(2) and incubation in PBS buffer for one hour, as evidenced by the presence of characteristic ether and methoxy peaks at 1120 cm(-1) and 2870 cm(-1), respectively. X-ray Photoelectron Spectroscopy (XPS) spectra showed that increasing beam doses destroy ether (C-O) bonds in PEG molecules as evidenced by the decrease in carbon C1s peak at 286.6 eV and increased alkyl (C-C) signal at 284.6 eV. XPS spectra also demonstrated protein capture on beam-exposed PEG regions through the appearance of a nitrogen N1s peak at 400 eV and carbon C1s peak at 288 eV binding energies, while the unexposed PEG areas remained protein-free. The characteristic activities of avidin and horseradish peroxidase were preserved after attachment on beam-exposed regions. Protein patterns created using a 35 µm mesh mask were visualized by localized formation of insoluble diformazan precipitates by alkaline phosphatase conversion of its substrate bromochloroindoyl phosphate-nitroblue tetrazolium (BCIP-NBT) and by avidin binding of biotinylated antibodies conjugated on 100 nm gold nanoparticles (AuNP). Patterns created using a mask with smaller 300 nm openings were detected by specific binding of 40 nm AuNP probes and by localized HRP-mediated deposition of silver nanoparticles. Corresponding BSA-passivated negative controls showed very few bound AuNP probes and little to no enzymatic formation of diformazan precipitates or silver nanoparticles.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas, United States of America.
authors.forename: Eliedonna E
authors.initials: EE
authors.lastname: Cacao
authors.forename: Azeem
authors.initials: A
authors.lastname: Nasrullah
authors.forename: Tim
authors.initials: T
authors.lastname: Sherlock
authors.forename: Steven
authors.initials: S
authors.lastname: Kemper
authors.forename: Katerina
authors.initials: K
authors.lastname: Kourentzi
authors.forename: Paul
authors.initials: P
authors.lastname: Ruchhoeft
authors.forename: Gila E
authors.initials: GE
authors.lastname: Stein
authors.forename: Richard C
authors.initials: RC
authors.lastname: Willson
mesh_terms: D001360:Avidin / Q000737:chemistry; D001391:Azo Compounds / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry; D011232:Chemical Precipitation; D006046:Gold / Q000737:chemistry; D006371:Helium; D006735:Horseradish Peroxidase / Q000737:chemistry; D055767:Immobilized Proteins / Q000737:chemistry; D053768:Metal Nanoparticles / Q000737:chemistry; D058626:Plasma Gases; D011092:Polyethylene Glycols / Q000737:chemistry*; D012834:Silver / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties
chemical_list: D001391:Azo Compounds; D001426:Bacterial Proteins; D055767:Immobilized Proteins; D058626:Plasma Gases; C058865:Strep-avidin conjugated horseradish peroxidase; C033302:diformazan dye; D001360:Avidin; D006371:Helium; D012834:Silver; D011092:Polyethylene Glycols; D006046:Gold; D006735:Horseradish Peroxidase