Localized immobilization of proteins onto microstructures within a preassembled microfluidic device

We describe herein a method for the site-specific immobilization of proteins on a three-dimensional polydimethylsiloxane (PDMS) microstructure, i.e., an array of microposts, within the channel of a microfluidic device. The protein-adhesive sites in the preassembled device are protected by a layer of heparin, an antibiofouling agent. To ready a device for experimentation, electrical pulses from microelectrodes within the channel spatiotemporally generate hypobromous acid that quickly removes the heparin, exposing protein-adhesive surface. To prove that, for assays performed within microfluidic channels of identical dimensions, their relative sensitivities can be increased if the inner channel surface areas are increased by the presence of PDMS microstructures, a glutathione peroxidase (GPX) sandwich immunoassay was performed within a microfluidic channel that had a region without and a region with a microstructure. Even though both regions had the same two-dimensional areas, the added dimension of the PDMS microstructure significantly increased the sensitivity of the GPX assay. Finally, irregularly shaped, protein-adsorptive regions occur upon electrochemical treatment when there is fluid-flow even in the absence of moving liquid. We found that the shape of protein-adsorptive regions can be completely controlled, even in the presence of fluid-flow, when the protein-adsorptive regions are delineated by regions of poly(ethylene glycol)dimethacrylate.