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Double‐layer capacitance of pH‐sensitive self‐assembled thiol layers on gold determined by electrical impedance spectroscopy in a microfluidic channel
Author(s) -
Kleppisius Anne,
Kick Alfred,
Mertig Michael
Publication year - 2017
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201600921
Subject(s) - capacitance , dielectric spectroscopy , electrode , electrolyte , microfluidics , analytical chemistry (journal) , double layer capacitance , layer (electronics) , materials science , chemistry , conductivity , electrochemistry , nanotechnology , chromatography
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 mm 2 . 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.