A new and easy-to-use method that allows for mold-free and rapid prototyping of microfluidic devices, comprising channels, access holes, and surface-modified patterns, is presented. The innovative method is based on direct photolithographic patterning of an off-stoichiometry thiol-ene (OSTE) polymer formulation, tailor-made for photolithography, which offers unprecedented spatial resolution and allows for efficient, robust and reliable, room temperature surface modification and glue-free, covalent room temperature bonding. This mold-free process does not require clean room equipment and therefore allows for rapid, i.e., less than one hour, design-fabricate-test cycles, using a material suited for larger-scale production. The excellent photolithographic properties of this new OSTE formulation allow patterning with unprecedented, for thiol-ene polymer systems, resolution in hundreds of micrometers thick layers, 200 mu m thick in this work. Moreover, we demonstrated robust, covalent and spatially controlled modification of the microchannel surfaces with an initial contact angle of 76A degrees by patterning hydrophobic/hydrophilic areas with contact angles of 102A degrees and 43A degrees, respectively.