Disclosed herein is a method and apparatus of immobilizing a biocatalyst on a microfluidic biochip for conducting reactions in the presence of electroosmotic flow. The biochip includes a polymer on its microfluidic flow surfaces, wherein the polymer includes a first substituent selected from ionic groups of the same polarity or precursors thereof, a second substituent that is a hydrophobic group, and a third substituent comprising an immobilized biocatalyst-or precursor thereof. The biochip can be used to conduct multiple sequential biocatalyzed reactions in the presence of electroosmotic flow.