A method for photopatterning multiple enzymes on porous polymer monoliths within microfluidic devices has been developed and used to perform spatially separated multienzymatic reactions. To reduce nonspecific adsorption of enzymes on the monolith, its pore surface was modified by grafting poly(ethylene glycol), followed by surface photoactivation and enzyme immobilization in the presence of a nonionic surfactant. Characterization of bound horseradish peroxidase (HRP) was carried out using a reaction in which the steady-state profiles of the fluorescent reaction product could be measured in situ and then analyzed using a plug-flow bioreactor model to determine the observed maximum reaction rate and Michaelis constant. The Michaelis constant of 1.9 micro mol/L agrees with previously published values. Mass-transfer limitations were evident at relatively low flow rates but were absent at higher flow rates. Sequential multienzymatic reactions were demonstrated using the patternwise assembly of two- and three-enzyme systems. Glucose oxidase (GOX) and HRP were patterned in separate regions of a single channel, and product formation was analyzed as a function of flow direction. Significant product formation occurred only in the GOX to HRP direction. A three-enzyme sequential reaction was performed using invertase, GOX, and HRP. All possible arrangements of the three enzymes were tested, but significant product formation was only observed when the enzymes were in the correct sequential order. Photopatterning enzymes on polymer monoliths provides a simple technique for preparing spatially localized multiple-enzyme microreactors capable of directional synthesis.

Surface-modified macroporous polymer monoliths that resist the adsorption of proteins have been prepared using both single-and two-step photografting of hydrophilic monomers. The adsorption of protein was measured using a fluorescence assay based on bovine serum albumin labeled with fluorescein. Acrylamide, 2-hydroxyethyl methacrylate, vinyl pyrrolidinone, and poly(ethylene glycol) methacrylate (PEGMA) monomers were grafted and evaluated for their ability to prevent protein adsorption. Photografted layers of PEGMA reduced protein adsorption to less than 2% relative to unmodified surfaces. The sequential two-step photografting process consisted in (i) the formation of covalently bound surface photoinitiator sites followed by (ii) surface-localized graft polymerization. Monomer concentration and irradiation time during photografting were found to be the most important parameters for optimization of the two-step process. For simultaneous single-step photografting, the solvent and the presence of photoinitiator were the key variables. Initiator-free single-step photografting was less efficient than the two-step technique, yet resulted in similar prevention of protein adsorption after grafting for an extended period of time. The utility of photografting as a simple, patternable modification technique was demonstrated by first creating a hydrophilic surface within the monolith that was subsequently patterned with a layer of reactive 2-vinyl-4,4-dimethylazlactone polymer chains followed by the immobilization of green fluorescent protein.

UV-initiated grafting of plastic tubes and microfluidic chips with ethylene diacrylate followed by the preparation of porous polymer monoliths has been studied. The first step affords a thin grafted layer of polymer with a multiplicity of pendent double bonds that are then used in the second step for covalent attachment of the monolith to the wall. As clearly seen on scanning electron micrographs, this procedure prevents the formation of voids at the monolith-channel interface a problem that has always plagued approaches involving bulk polymerization in nontreated channels due to the shrinkage of the monolith during the polymerization process and its lack of compatibility with the material of the device. Irradiation with UV light through a photomask allows precise patterning specifying both the area subjected to surface modification and the location of the monolith within specific areas of the device.

Articles you may be interested inGas diffusion electrode setup for catalyst testing in concentrated phosphoric acid at elevated temperatures Rev. Sci. Instrum. 86, 024102 (2015); 10.1063/1.4908169Submillisecond post-exposure bake of chemically amplified resists by C O 2 laser spike annealing Effects of photoacid generator incorporation into the polymer main chain on 193 nm chemically amplified resist behavior and lithographic performance In a chemically amplified resist absorbed photons generate stable catalyst molecules instead of directly switching resist solubility via photochemical reaction. This allows for much lower exposure doses to be used in imaging. Some catalyst mobility is necessary to achieve amplification since the catalyst must move from reaction site to reaction site, but a mobile catalyst can blur the deposited aerial image. Catalyst molecules that are free to move in exposed regions are also free to move into adjacent unexposed regions. Understanding acid catalyst diffusion in photoresist resins is complicated by the constantly changing chemical environment the diffusing catalyst experiences as the resist undergoes chemical reactions. The diffusing catalyst promotes chemical reactions which change the properties of its surrounding resin. In addition, it is possible a transient material state is generated by volatile reaction byproducts and their desorption from the film. In most photoresist systems it is impossible to separate reaction and diffusion effects. This work describes studies of acid diffusion in polymers that are close structural analogs to reactive photoresist resins but do not react with the diffusing acidic catalyst. The purpose of this study into nonreactive polymer is to gain insight into the more complex, reactive systems. In addition, experiments with polymeric photoacid generators are reported. These materials provide added insight into acid transport in photoresist materials.