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1 April 2020 Aqueous photochemistry for the fabrication of grating sensors in hydrogels
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A photofunctionalisable hydrogel based on copolymers of a nitroveratryl chloroformate derivative with acrylamide has been developed that permits the uncaging of amine groups on exposure to patterns of light at 405 nm using a watersoluble thioxanthone sensitizer. Hydrogel films of 3, 35 and 100 μm thickness were fabricated to use as leaky waveguide and grating sensors. The smallest feature sizes produced in 35 and 100 μm thick films were 21.6 and 43.2 μm respectively, limited by the depth of field of the digital projector. It was found that essentially complete deprotection could be obtained in ~2 minutes. The two thicker hydrogel films were used to create amplitude and phase gratings, while the thinnest film was used as a leaky waveguide to investigate the porosity of the films and monitor immobilization of protein using a PEG linker. The amplitude grating formed by reacting the uncaged amines with fluorescein isothiocyanate was shown to act as a pH sensor with resolution 0.0325 pH units. Protein immobilization using glutaraldehyde as a linker to create a phase grating was attempted, which gave a strong signal with glutaraldehyde but no subsequent signal with BSA. Investigation with a thin film acting as a leaky waveguide showed that glutaraldehyde significantly reduces the porosity of the film to high molecular mass species. Finally, leaky waveguiding was used to monitor protein immobilization using an amine-reactive PEG linker, showing that selective immobilization occurred in the exposed regions of the film without affecting the sensitivity of the film to bulk index changes.
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Anil Kumar Pal, Nicholas J. Goddard, and Ruchi Gupta "Aqueous photochemistry for the fabrication of grating sensors in hydrogels", Proc. SPIE 11367, Photosensitive Materials and their Applications, 1136702 (1 April 2020);

Diffraction gratings


Refractive index




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