The influence of hydrophobic surface to the manipulation of a reagent plug in a gas–liquid microsystem

• Experimental study of the manipulation of a reagent plug in two different substrates.
• Multiple experiments were realized to quantify the reagent loss difference.
• Multiple experiments were realized to quantify the plug position accuracy difference.
• Hydrophobic surface modification can be used to minimize the reagent loss of a reagent plug.
• The position controlling of a reagent plug is more repeatable in a hydrophobic PMMA microchannel.

Precise and reliable manipulation of a reagent plug in a microfluidic network is critical to the performance of a plug-based microfluidic device. This study is aimed to quantify the influence of different surface property to the position controlling of a reagent plug inside a microfluidic channel. Two sets of Poly(methyl methacrylate) (PMMA) microfluidic devices were micromilled and thermal bonded for experiments, the first set was the original PMMA substrate and the second set was the hydrophobic-coated PMMA substrate. The purpose of applying hydrophobic coating was to reduce the contact area and the thickness of the liquid deposition layer between the reagent plug and the microchannel walls. A 1 μl reagent plug was loaded in both microchannels and shuttled forward and backward repeatedly with a Labview-controlled pneumatic system. The experiment results revealed that: (1) the reagent loss in a hydrophobic PMMA microchannel was dramatically less, 6.87% in a hydrophobic PMMA microchannel while 26.5% in an original PMMA microchannel after 40 cycles; (2) the reduced mass and the thicker liquid deposition layer caused the moving distance and the position controlling instable in the original PMMA microchannel; (3) the position controlling of a reagent plug is more precise and repeatable in a hydrophobic PMMA microchannel.

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