Biofunctionalization and self-interaction chromatography in PDMS microchannels

Abstract

In this paper we present an experimental protocol for protein immobilization on polydimethylsiloxane (PDMS) polymer surfaces and the subsequent application of a chromatographic PDMS microfluidic chip to measure protein–protein interactions. The PDMS surface modification steps are quantitatively and qualitatively experimentally analyzed using an array of techniques (water contact angle measurement, fluorescence spectroscopy and X-ray photoelectron spectroscopy). The protocol involves PDMS acidic surface activation using a potassium disulfite/potassium peroxidisulfate/acrylic acid mixture, followed by amination with 3-aminopropyl diethoxymethylsilane, followed by glutaraldehyde grafting and subsequent covalent protein binding. The applicability of such a miniaturized PDMS-based microfluidic system has been exemplified by measuring protein–protein interactions in a fast and accurate fashion for three model proteins, namely: hen egg white lysozyme, bovine ribonuclease-A and α-chymotrypsinogen. The protein interaction results align well with existing literature data using different materials and techniques. As the fabrication process for PDMS-based microstructures is relatively cheap, quick and requires limited lab expertise/access to specialized equipments, we consider that the implementation of such a flexible, easy to fabricate, PDMS-based microfluidic system for estimating protein interactions an important step toward quickly mapping protein phase behavior and measuring protein (self/cross) interactions in complex biological systems.