In general, the present invention provides microfluidic devices comprised of polymer coatings with triggerable analyte capture moieties. In some embodiments, a microfluidic device is provided, useful in electrophoresis, and is comprised of at least one separation channel with a surface, such as but not necessarily an inner surface, and having a polymer coating introduced onto the surface. The polymer coating is comprised of moieties capable of being triggered to immobilize analytes to the surface.