Iridium oxide based coaxial pH ultramicroelectrode

In this communication, a coaxial pH microelectrode consisting of a working electrode made of IrOx and a Ag/AgCl reference electrode has been developed. The outer wall of the glass capillary with a tip diameter of 5 pm was sputtered with Au and then IrOx film was electrodeposited on the Au layer, while the inside of the capillary was a Ag/AgCl wire which can serve as a reference electrode. This electrode presented a linear response in the pH range from 2.0 to 12.0 with a sensitivity of 58.73 +/- 0.41 mV/pH. In selectivity tests, several alkaline cations such as Na+ and K+ didn't interfere with the performance of the electrode. Furthermore, the ultramicroelectrode exhibited rapid response times ranging from 0.5 s to 5 s depending on the solution pH. The excellent performance and ultramicro-size of this pH sensor make it very promising for in situ/in vivo pH measurements. (C) 2013 Elsevier B.V. All rights reserved.