Characterization of pH microelectrodes

In 1909, Danish biochemist Soren Sorenson first introduced the pH concept. pH is defined by the negative logarithm of the hydrogen ion activity  

A schematic diagram of a typical pH electrode system is shown in Fig. 10.1. The cell potential, i.e. the electromotive force, is measured between a pH electrode and a reference electrode in a test solution. The pH electrode responds to the activity or concentration of hydrogen ions in the solution. The reference electrode has a very stable half-cell potential. The most commonly used reference electrodes for potentiometry are the silver/silver chloride electrodes (Ag/AgCl) and the saturated calomel electrodes (SCE). 

The properties of a pH electrode are characterized by parameters like linear response slope, response time, sensitivity, selectivity, reproducibility/accuracy, stability and biocompatibility. Most of these properties are related to each other, and an optimization process of sensor properties often leads to a compromised result. For the development of pH sensors for in-vivo measurements or implantable applications, both reproducibility and biocompatibility are crucial. Recommendations about using ion-selective electrodes for blood electrolyte analysis have been made by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) [37]. lUPAC working party on pH has published lUPAC s recommendations on the definition, standards, and procedures 

Electrochemical Sensors, Biosensors and Their Biomedical Applications 

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Takmakov P, Zachek MK, Keithley RB, Bucher ES, McCarty GS, Wightman RM. Characterization of local pH changes in brain using fast-scan cyclic voltammetry with carbon microelectrodes. Anal Chem 2010 82 9892—900. 

Imokawa, T., WUhams, K.-J., Denuault, G., Fabrication and characterization of nanostructured Pd hydride pH microelectrodes. Anal Ghent 2006, 78, 265-271. 

Makos MA, Omiatek DM, Ewing AG, Heien ML (2010) Development and characterization of a voltammetric carbon-fiber microelectrode pH sensor. Langmuir 26(12) 10386-10391. doi 10.1021Aal00134r... 

The Fc label was introduced as an amide using Fc-OBt, an active ester that readily reacts with available amino groups. One construct had the Fc group at the 5 terminus of the DNA, whereas the other had the Fc at the 3 terminus. The DNA constructs were purified by RP-HPLC and characterized by MALDI-TOF MS and UV-vis spectroscopy. Typical UV-vis spectra for Fc-labeled ds-DNA and Fc-labeled ss-DNA are shown in Figure 8. After hybridization of the Fc-labeled DNA strand to its complementary strand in 20 mM Tris buffer (pH 8.7) for 24 h at room temperature, the Fc-labeled ds-DNA was exposed to gold microelectrodes of 50 om... 

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