Microfabrication of a multilayer nano-ESI focusing electrode based on SU-8 material

A new ion-focusing electrode based on SU-8 polymer is developed in a nano-electrospray ionization (nano-ESI) system to improve the ion transmission efficiency from a spray emitter tip into the counter electrode at atmospheric pressure. The novel SU-8 structure with a three-stepped microhole was fabricated by utilizing micro-electro-mechanical systems (MEMS) technology including three-step UV photolithography and single development. The SU-8 structure was peeled away from the substrate and coated with a metal layer on both side surfaces. Finally, the novel SU-8 electrode was characterized in the nano-ESI system and a 10-fold increase in the electrospray (ES) ion current was observed for an emitter tip voltage of 2600 V, an electrode voltage of 600 V and a distance of 11 mm between the capillary tip and the SU-8 multilayer focusing electrode.

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► A new ion focusing electrode based on SU-8 photoresist material was proposed.
► The SU-8 structure with the three-stepped inner hole was fabricated utilizing MEMS.
► The SU-8 electrode was characterized in the nESI system.
► A tenfold increase in the electrosprayed ion current was observed.