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    Fabrication and fluidic characterization of silicon micropillar array electrospray ionization chip

    Year: 2008

    Journal: Sensors and Actuators B: Chemical, Volume 132, Issue 2, 16 June 2008, Pages 380-387, 20111221

    Authors: Lauri Sainiemi, Teemu Nissilä, Ville Jokinen, Tiina Sikanen, Tapio Kotiaho, Risto Kostiainen, Raimo A. Ketola, and Sami Franssila

    Organizations: Micro and Nanosciences Laboratory, Helsinki University of Technology, Helsinki, Finland, Division of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland, Drug Discovery and Development Technology Center, University of Helsinki, Helsinki, Finland, Protein Chemistry Unit, Institute of Biomedicine, Biomedicum Helsinki, University of Helsinki, Helsinki, Finland, Laboratory of Analytical Chemistry, University of Helsinki, Helsinki, Finland

    A silicon electrospray ionization (ESI) chip for the mass spectrometric analysis is designed, fabricated, and characterized. The chip has three parts: a liquid sample introduction spot, a flow channel, and a sharp electrospray ionization tip. A regular micropillar array is micromachined inside the whole channel. The chip has no lid, which makes the sample application and chip fabrication easier. A two photomask level fabrication process utilizes nested masks of silicon dioxide and aluminum oxide. A combination of anisotropic and isotropic plasma etching steps allows formation of a truly three-dimensional electrospray ionization tip without double-sided lithography. The filling properties of the lidless micropillar channel are studied. Because of the capillary forces facilitated by the micropillar array, the sample applied onto the sample introduction spot spontaneously fills the whole flow channel including the electrospray ionization tip, without external pumping. Besides reliable self-filling, the chip offers stable electrospraying and high sensitivity chemical analysis when coupled to a mass spectrometer (MS).