Microfabricated Liquid Junction Ag/AgCl Reference Electrode and Its Application to a One-Chip Potentiometric Sensor

Abstract

A liquid-junction Ag/AgCl reference electrode was microfabricated. A silver thin-film pattern was covered with a polyimide protecting layer with a 50-µm-wide slit at the center of the pattern, and the AgCl layer was grown from there into the silver layer. A liquid junction was formed with a photocurable hydrophilic polymer. The electrolyte layer was formed by screen-printing a paste containing fine KCl powder. A silicone rubber passivation covered the entire area except for the pad and the end of the junction. The novel thin-film Ag/AgCl element could maintain its expected potential for longer than 30 h in a saturated KCl solution. The completed miniature liquidjunction reference electrode could maintain a stable potential level within (1 mV for longer than 100 h with the aid of a poly(vinylpyrrolidone) (PVP) matrix in the electrolyte layer. Fluctuation of the potential was less than 0.1 mV at each moment. Dependency on external KCl concentration and pH was shown to be insignificant. The miniature reference electrode was integrated with an iridium oxide pH indicator electrode. No significant difference was observed between the potential obtained with the miniature reference electrode and that obtained with a macroscopic commercial Ag/AgCl electrode, which confirmed that the miniature reference electrode was applicable to one-chip potentiometric sensors.

Multi-Parameter Improvement Method for (Micro-) Structural Properties of High Performance Ceramics

“…Its main task is to provide a conductive bridge between the two liquids, while simultaneously preventing the reference electrolyte to be polluted by substrate ions [4]. In the case of this study, the device in charge of maintaining such a junction is a small, cylindrical, porous piece of ceramics, Ddia= 1 mm in width, Ldia= 2 mm in length, referred to as diaphragm [5]- [7]. A schematic illustration of the type of pH-probes in question is shown in Figure 1 [1].…”

Fundamental relationships between 3D pore topology, electrolyte conduction and flow properties: Towards knowledge-based design of ceramic diaphragms for sensor applications

“…1b). More details about the principles of pH-probes and electrochemical processes at the electrodes can be obtained from literature [1][2][3][4][5].…”

Alternative strategy for manufacturing of all-solid-state reference electrodes for potentiometry

“…Many patents (Jayaweera et al, 1995;Shin et al, 2003;Sorensen and Zachau-Christiansen, 2004;Cha et al, 2005;Rodes, 2008) and articles (Suzuki et al, 1998(Suzuki et al, , 1999Tymecki et al, 2004;Guth et al, 2009;Rius-Ruiz et al, 2011;Valdés-Ramírez et al, 2011) reported innumerable strategies for construction of solid-state reference electrodes. Shin et al (2003) developed a reference electrode by depositing metal (Ag, Pt, Au or Cu) and insoluble salt (silver halide) in layers on a substrate using thick film.…”

“…Carbon nan-otubes were also used as a transducer from a polyacrylate membrane containing Ag/AgCl, Cl − system (Rius-Ruiz et al, 2011). Thin film technology has also been used for microfabrication of reference electrodes (Suzuki et al, 1999). Valdés-Ramírez et al (2011) electrodeposited silver and silver chloride on a graphite-epoxy electrode surface under adequate conditions of electrical potential and electrical current.…”