Microplasma arrays: a new approach for maskless and localized patterning of materials surfaces

Endre J. Szili, Sameer A. Al-Bataineh, Paul Ruschitzka, Gilles Desmet, Craig Priest, Hans J. Griesser, Nicolas H. Voelcker, Frances J. Harding, David A. Steele, Robert D. Short
2012 RSC Advances  
S3 EXPERIMENTAL DETAILS Substrate preparation. A 5% (w/v) of polystyrene (Goodfellow Cambridge Ltd.) was prepared in toluene. The solution was spin-coated onto polished silicon wafer pieces. The spin-coated samples were soft-baked at 50C for 5 min to facilitate the removal of residual toluene. Commercial microscope glass slides were functionalized with 3-aminopropyl triethoxysilane (APTES, Sigma) to enhance protein adsorption onto the glass surface. The slides were incubated with an undiluted
more » ... with an undiluted solution of APTES at 25C for 45 min, rinsed in isopropanol, dried under nitrogen and then soft-baked at 120C for 5 min. Surface passivation. Bovine serum albumin (BSA) passivated polystyrene and APTES functionalized glass slides were made by incubating a 1% (w/v) solution of BSA (Sigma) in phosphate buffered saline (PBS, pH 7.4, Sigma) over the surfaces at 25C for 4 h. The surfaces were washed in Milli-Q water and dried under nitrogen. Similarly, a 1% (w/v) solution of fluorescein conjugated BSA (Invitrogen) was incubated over the sample at 25C for 4 h for fluorescence measurements. Microplasma array treatment. A detailed description of the microplasma array fabrication and operation is provided elsewhere. 1 Briefly, the device consists of a dielectric barrier (SU8-50 photoresist, MicroChem Corp., USA) sandwiched between two gold electrodes. A 7 x 7 array of 250 µm diameter cavities with a depth of 55 nm and a separation distance (edge-toedge) of 500 µm was patterned into the top gold layer using standard photolithography. Plasma generation was carried out using a custom-built electrical system. A power supply consisted of an oscillator (Agient Technologies, DS06034A), an audio amplifier (AMPRO, XA1400) and a step-up transformer (Southern Electronic Services) powered the microplasma array using sinusoidal AC excitation. The microplasma array was operated at 1 kV peak-peak and 10 kHz in an atmospheric pressure (760 Torr) of helium. The microplasma array was mounted upside down on the top flange inside a custom-built microplasma reactor. Substrates were placed face-up on an insulated sample stage for surface treatment with the microplasma array. The chamber was initially pumped down to a base pressure < 5 x 10 -2 Torr to remove background air. For treatment, the chamber was filled with high purity helium (99.99%, BOC). A computerized stage was used to precisely control the distance between substrate and microplasma array. Electronic Supplementary Material (ESI) for RSC Advances This journal is S6 Dulbecco's phosphate buffered saline with calcium and magnesium (D-PBS+ Ca 2+ / Mg 2+ , 0.9 mM CaCl 2 , 2.67 mM KCl, 1.47 mM KH 2 PO 4 , 0.50 mM MgCl 2 -6H 2 O, 138 mM NaCl, 8.10 mM Na 2 HPO 4 ). Cells were fixed with 3.7% formaldehyde solution for 10 minutes, then stained with 2 μg/ml Hoechst 33342 (Sigma) in culture media for 10 minutes. Samples were finally washed with D-PBS+ Ca 2+ /Mg 2+ and mounted in Fluoro-Gel/Tris buffer (ProSciTech) for analysis. Mounted samples were observed on an Eclipse50i fluorescence microscope (Nikon) with a DS-U2 digital camera (Nikon). CellTracker Orange CMRA was observed through excitation filter 540-557 nm and emission filter 605-625 nm and Hoechst 33342 through excitation filter 340-380 nm and emission filter 435-485 nm. All images were processed and analyzed by NIS-Elements BR 3.0 software. Fabrication of glass microfluidic chips. Glass microfluidic chips were prepared using a combination of UV-photolithography and deep-reactive ion etching (DRIE). Pyrex TM plates were spin-coated (2000 rpm) with SU8-10 photoresist and baked on hotplates for 2 min and 5 min at 65˚C and 95˚C, respectively. The sample was then exposed (180 mJ/cm 2 , 360 nm) through a chrome-glass photomask patterned with the microchannel design, and postexposure baked for 1 min and 3 min at 65˚C and 95˚C, respectively. The pattern was developed in the photoresist in SU8 developer solution for 3 min, was rinsed in isopropanol, and hard-baked for 1 min and 5 min at 95˚C and 150˚C, respectively. DRIE (ULVAC NLD570) was carried out using fluorocarbon plasma (C 4 F 8 ) at an etch rate (in Pyrex TM glass) of ~ 0.3 m/min. The final etch depth was 18 m. Integration of the electrodes into the glass microchip was carried out using molten gallium metal according to the methodology given elsewhere. 2 Protein patterning in microfluidic chips. The microchannel wall was first functionalized with 3-aminopropyl triethoxysilane (APTES) by incubation with 100 mM 3-aminopropyl triethoxysilane (APTES), prepared in toluene at 25C for 1 h. The microchannel was rinsed in toluene and then dried under nitrogen. The microchannel was then passivated by incubating with 1% (w/v) BSA prepared in PBS at 25C for 4 h. The microchannel was then flushed with Milli-Q water and dried under nitrogen. Microplasma array treatment was performed at 5 kV peak-peak and 10 kHz in a helium flow of 5 ml/min. A solution of 20 µg/ml Alexa Fluor  568 conjugated streptavidin protein (in PBS) was incubated in the microchannel at 25C for 12 h. The microchannel was flushed with PBS-T, then Milli-Q Electronic Supplementary Material (ESI) for RSC Advances This journal is
doi:10.1039/c2ra21504g fatcat:tcpkwrczwvahppvndz6wcffeem