UV graft polymerization of polyacrylamide hydrogel plugs in microfluidic channels

It has been recently demonstrated that single-stranded DNA, modified on the 5' end with an acrylic acid functionality, can be incorporated into a polyacrylamide hydrogel matrix. These types of DNA-containing gels have recently been spatially immobilized in plastic microfluidic channels by photopolymerization, creating selective DNA three-dimensional capture elements. The DNA oligomers retain activity and are able to bind complementary target strands as they migrate through the gel plug under electrophoretic conditions. One problem that has compromised the performance of the DNA hydrogels is gel plug breakdown under continuous electrophoretic operation. When gel plugs fail, the gel delaminates from the microchannel wall and electroosmotic flow occurs between the plug and the microchannel wall. Past measurements have shown that the lifetime of the polyacrylamide gel plugs rarely exceeds 25 min under continuous use. Here we report a method to increase the stability of the polyacrylamide gel plugs by the introduction of polymerization attachment points to the polymeric microchannel surfaces prior to gel plug formation. Ultraviolet/ozone (UV/O-3) treatment is used to oxidize both top poly(methyl methacrylate) (PMMA) and bottom poly(carbonate) (PC) surfaces. A methacrylate functionality, which can cross-link with the polyacrylamide gel, is introduced by reacting the oxidized surfaces with 3-methacryloxypropyltrimethoxysilane. Polyacrylamide is then T TV grafted onto the chemically modified model surfaces. Contact angle measurements and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra confirm polyacrylamide grafting on PC and PMMA surfaces. The success of graft polymerization within the microchannel devices is also corroborated by scanning electron microscopy of delaminated devices and timed performance measurements under electrophoretic conditions that demonstrate an increase in the lifetime of the gel plugs by 2.5 times on average.