Ultraviolet photolithographic development of polyphosphazene hydrogel microstructures for potential use in microarray biosensors

Polyphosphazenes that bear both methoxyethoxyethoxy and cinnamyl side groups were synthesized and evaluated for use as hydrogels incorporated into micrometer-scale biosensor arrays. Polymers with the general formula [NPR _xR′ _y] _n where R = OCH ₂CH ₂OCH ₂CH ₂OCH ₃ and R′ = OCH=CHCH ₂Ph (x = y = 1; x = 2, y = 0) were synthesized. The polymers were cross-linked to form hydrogels by exposure to ultraviolet radiation (λ = 320-480 nm) in the presence of a photoinitiator. Hydrogel microstructures in the size range 50-500 μm were fabricated using standard photolithographic techniques. The resolution and dimensions of these microstructures were examined by optical microscopy, scanning electron microscopy, and profilometry. The resultant three-dimensional hydrogel microstructures were used to encapsulate enzymes for biosensor applications. The enzymatic activity of encapsulated horseradish peroxidase (HRP) was examined as a model system. The HRP catalyzed reaction between H ₂O ₂ and Amplex Red to produce a fluorescent product, resorufin, was confirmed by fluorescence microscopy.