Poly(dimethylsiloxane) Surface Modification by Plasma Treatment for DNA Hybridization Applications

In this work, the surface modification of poly(dimethylsiloxane) (PDMS) was carried out by using a 2-step plasma modification with Ar followed by acrylic acid (AAc). The optimal conditions were found to be 0.5 min with Ar at 0.7 mbar; and 5 min with AAc at 0.2 mbar. The water contact angle (WCA) of the native PDMS decreased from 110 degrees to 30 degrees after modification, then stabilized to values between 50 degrees to 60 degrees after 1 day exposure to air. The stability of the modified PDMS was further improved by Soxhlet-extracting the PDMS with hexane prior to plasma treatment. Atomic force microscopy (AFM) showed significant changes in surface morphology after the 2-step plasma modification. X-ray photoelectron (XPS) spectroscopy further confirmed the successful modification of the PDMS surface with PAAc, by exhibiting C1s peaks at 285.9 eV, 287.4 eV and 289.9 eV, originating from C-O, C=O and O-C=O moieties, respectively. Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy of the poly(acrylic acid) (PAAc) modified PDMS surface showed a distinctive peak at 1715 cm(-1), attributed to the presence of COOH groups from the PAAc. The carboxyl peak on the spectra of the PAAc modified PDMS was quite stable even after storage at room temperature in phosphate buffer saline (PBS) and N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) buffer for 17 h. 5'-amino-terminated oligonucleotides were covalently attached to the PAAc modified PDMS surface via carbodiimide coupling. Subsequently, fluorescently tagged complementary oligonucleotides were successfully hybridized to this surface, as determined by fluorescence microscopy.