Surface charge and hydrophilicity of microchannels are very important for lab-on-a-chips devices. A facile way for in-channel tuning of both hydrophilicity and surface charge of microchannels of cyclic olefin copolymer chips with photochemical grafting was verified. Six acrylic monomers with anionic, neutral and cationic functional groups, respectively, were selected to implement different surface charges. Influence of experimental conditions, such as UV intensity, irradiation time, monomer concentration and reaction temperature, were investigated based on the contact angles of pure water on the modified surfaces. Surface charges of the modified channels were confirmed with streaming potential measurement. The modified microchannels were used in the electrophoretic separation of four fluorescein isothiocyanate labeled amino acids. The results indicated that photochemical grafting could be used to introduce hydrophilic layer of predefined surface charge onto the channel surface within 60 s and good electrophoretic separation could be obtained inside the modified channels, which implied that the method could be used for tailoring the surface of microchannels of lab-on-a-chip devices. (c) 2012 Elsevier B.V. All rights reserved.