A polydimethylsiloxane electrophoresis microchip with a thickness controllable insulating layer for capacitatively coupled contactless conductivity detection

A polydimethylsiloxane (PDMS) electrophoresis microchip with a thickness-controllable insulating layer for capacitatively coupled contactless conductivity detection is presented. A PDMS film is spin-coated on a glass slide with Pt microelectrodes to be the insulating layer, and then permanently bonded with a PDMS channel plate to make the whole microchip. The thickness of PDMS films can be precisely controlled down to submicrometers. With a microchip with a 0.6 μm-thick PDMS insulating layer, a superior limit of detection (LOD) of 0.07 μM for Na+ was obtained. For comparison, another two microchips with the same design but different insulating layer thicknesses (15 μm and 50 μm) were tested, and LODs were 1 μM and 3 μM respectively, which are almost two orders of magnitude higher. Moreover, the microchip detector also exhibited excellent linearity, reproducibilities and separation efficiencies.

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► The thickness of the insulating layer on the microchip can be precisely controlled down to submicrometers.
► With the new contactless conductivity microchip detector, a superior limit of detection (< 100 nM for inorganic ions) was obtained.
► The microchip detector exhibited excellent linearity, reproducibilities and separation efficiencies.
► The microchip detector holds great promise for a wide range of analytical applications.