[Phys. Status Solidi A] Double-layer capacitance ofpH-sensitive self-assembled thiollayers on gold d
The determination of the double-layer capacitance of planar interdigitated gold electrodes in a microfluidic channel by electrical impedance spectroscopy is presented. A simple and miniaturized two-electrode setup is used to investigate electrodes coated with pH-sensitive self-assembled thiol layers of 4-mercaptopyridine (4-MP) or 4-mercaptobenzoic acid (4-MBA). The total sensing area is about 0.25 mm2. Surface modifications and pH have a pronounced influence on the double-layer capacitance of the electrodes. The interfacial capacitance rises significantly at pH < 3 on the 4-MP and at pH > 10 on the 4-MBA layer. This effect is related to surface protonation or deprotonation of the pyridine or carboxylic moieties, respectively. It is shown that this double-layer capacitance is widely independent from the electrolyte concentration. Such electrodes can be used as pH indicators in microfluidic channels, additionally allowing the determination of the electrolyte conductivity. This kind of sensor is supposed to be used in lab-on-a-chip systems for fast readout of local chemical and physical process parameters.
Anne Kleppisius, Alfred Kick, Michael Mertig First published: 9 March 2017 DOI: 10.1002/pssa.201600921