Direct-write laser micromachining and universal surface modification of PMMA for device development

The use of direct-write laser micromachining on poly(methyl methacrylate) (PMMA) to fabricate microfluidic chip has the potential for fast prototyping and production. However, the advantage has been diminished by the rugged surface and the limited surface chemistry modification available. To overcome this problem, we have developed a flexible and economic pipeline including PMMA micromachining, surface smoothness improvement, and a universal surface modification for introduction of various functional groups. The micromachining is accomplished by a commercial laser scriber, to which a user designed computer drawing is sent directly for grooving. The typical trench width is 140 μm while the aspect ratio up to more than 7 is easily achieved. Smooth surface is obtained after a one-step thermal annealing treatment after machining. The chemical modification is performed by a simple reduction reaction followed by the widely used organosilane chemistry to introduce diverse functional groups such as perfluoroalkyl (CnF2n+2), amino (NH2), and sulfhydryl (SH) for surface passivation or further biomolecule immobilization. The surface smoothness after thermal annealing has been examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM) to be comparable to pristine surface. The surface chemistry modification has been confirmed by attenuated total reflectance–Fourier transform infrared spectroscopy (ATR–FTIR) and X-ray photoelectron spectroscopy (XPS). The whole procedure provides a very efficient micromachining platform to fabricate PMMA microfluidic chip for both prototyping and production.