laser - induced phase - separation polymerization of a porous acrylate polymer is used for in - situ fabrication of dialysis membranes inside glass microchannels . a shaped 355 nm laser beam is used to produce a porous polymer membrane with a thickness of about 15 μm , which bonds to the glass microchannel and form a semi - permeable membrane . differential permeation through a membrane formed with pentaerythritol triacrylate was observed and quantified by comparing the response of the membrane to fluorescein and fluorescently tagging 200 nm latex microspheres . differential permeation was observed and quantified by comparing the response to rhodamine 560 and lactalbumin protein in a membrane formed with spe - methylene bisacrylamide . the porous membranes illustrate the capability for the present technique to integrate sample cleanup into chip - based analysis systems .