Self-Patterned Gold-Electroplated Multicapillary Gas Separation Columns With MPG Stationary Phases

Gas chromatography (GC) is a powerful analytical method to accurately and reliably identify the constituents of a complex mixture. There are numerous efforts to miniaturize GC system, in general, and separation columns, in particular, for rapid, dependable, and portable on-site analysis. This paper reports the development of two diverse self-patterned gold electrodeposition fabrication techniques for high-aspect-ratio microfluidic channels including multicapillary GC columns. First approach involves geometry-dependent tuned electroplating conditions to self-pattern gold along the vertical sidewalls without any deposition on horizontal top and bottom surfaces, while the second method provides highly conformal gold deposition inside the 3-D microchannels. Both reported approaches do not require a postdeposition patterning step while affording at the same time excellent bonding and stationary phase coating yields. The ability of thiol to self-assemble on gold surface is also utilized to form monolayer-protected gold (MPG) surfaces and is used as a stationary phase for micro GC. To evaluate the chromatographic performance of both schemes, 250-μm -deep 30-μm-wide 25-cm-long microfabricated multicapillary columns (μMCCs) with 16 channels are functionalized by self-assembly of octadecanethiol (C₁₈H₃₇ SH) to form the MPG surface. With about 7300-plate/m theoretical plates, these columns demonstrate the highest reported separation efficiency on 16-channel μMCCs and are capable of separating complex gas mixtures containing compounds with wide range of boiling points.