Encapsulated Hydrogels by E-beam Lithography and Their Use in Enzyme Cascade Reactions

Electron beam (e-beam) lithography was employed to prepare one protein immobilized hydrogel encapsulated inside another by first fabricating protein-reactive hydrogels of orthogonal reactivity and subsequently conjugating the biomolecules. Exposure of thin films of eight arm star poly(ethylene glycol) (PEG) functionalized with biotin (Biotin-PEG), alkyne (Alkyne-PEG) or aminooxy (AO-PEG) end-groups to e-beam radiation resulted in cross-linked hydrogels with the respective functionality. It was determined via confocal microscopy that a nominal size exclusion effect exists for streptavidin immobilized on Biotin-PEG hydrogels of feature sizes ranging from 5 to 40 μm. AO-PEG was subsequently patterned as an encapsulated core inside a contiguous outer shell of Biotin-PEG. Similarly, Alkyne-PEG was patterned as a core inside an AO-PEG shell. The hydrogel reactive end-groups were conjugated to dyes or proteins of complementary reactivity, and the three-dimensional (3-D) spatial orientation was determined for both configurations using confocal microscopy. The enzyme glucose oxidase (GOX) was immobilized in the core of the encapsulated Alkyne-PEG core/ AO-PEG shell architecture, and horseradish peroxidase (HRP) was conjugated to the shell periphery. Bioactivity for the HRP-GOX enzyme pair was observed in this encapsulated configuration by demonstrating that the enzyme pair was capable of enzyme cascade reactions.