Amperometric micro pH measurements in oxygenated saliva

Abstract

An amperometric micro pH sensor has been developed based on the chemical oxidation of carbon fibre surfaces (diameter of 9 μm and length of ca. 1 mm) to enhance the population of surface quinone groups for the measurement of salivary pH. The pH analysis utilises the electrochemically reversible two-electron, two-proton behaviour of surface quinone groups on the micro-wire electrodes. A Nernstian response is observed across the pH range 2-8 which is the pH range of many biological fluids. We highlight the measurement of pH in small volumes of biological fluids without the need for oxygen removal and specifically the micro pH electrode is examined by measuring the pH of commercial synthetic saliva and authentic human saliva samples. The results correspond well with those obtained by using commercial glass pH electrodes on large volume samples.

Recent Advances in Optical, Electrochemical and Field Effect pH Sensors

“…The sensor showed a sensitivity of approximately 58 mv/pH in a range from 1 to 12 pH units with a reproducibility of 0.83%. Chaisiwamongkhol et al reported a sensor based on porous graphitic carbon fibers functionalized with quinone groups [81]. This sensor had a superNernstian sensitivity of 65 mV/pH in the pH range 2 to 8 by performing scans on a potential range from −0.2 to 0.8 V. When tested in a real saliva sample, the performances were comparable with those of a glass electrode.…”

Electrocatalysis via Intrinsic Surface Quinones Mediating Electron Transfer to and from Carbon Electrodes

“…Voltammograms obtained in other solutions containing variable concentrations of Fe 3+ can be found in SI section 6. For the clean carbon surface the voltammetric response of the electrode exhibits a relatively large capacitative charging current and at a pH of 0.69, a broad surface bound feature corresponding to the redox chemistry of surface quinone groups (at ca.0.38 V vs SCE) 9 . From this voltammetric peak the surface coverage of catechol on a clean carbon electrode was calculated to be (4.33 ± 0.66) × 10 -11 mol cm -2 as ascertained from the integration of the quinone/catechol peak observed in blank solution.…”

“…Of the many groups shown, the quinones have excited particular interest since as isolated molecules they are electroactive in both aqueous and non-aqueous solutions. This, in the case of intrinsic surface species, has been exploited, for example, in the development of carbon based pH sensors where voltammetric signals due to the two electron, two proton reduction of quinones are used to indicate the pH of aqueous solutions [9][10] .…”

Electrochemical Determination of the Steroid Tibolone and Its Metabolites in Saliva Samples

“…Recently, competitive advantages of electrochemical methods have been successfully explored for analysis of drugs and other compounds in saliva samples. [13,[24][25][26][27][28][29][30][31][32] Boron-doped diamond (BDD) has become an important material applied in electrochemistry and electroanalysis. [33][34][35] In fact, its properties are different from other commonly used carbonaceous electrodes, such as favorable electron-transfer kinetics, a wide potential range in aqueous solution (oxygen evolution at~2.0 V), low and stable background current, high corrosion resistance, good resistance to adsorption of molecules and stability in successive measurements.…”

“…According to our knowledge, no electrochemical studies were reported before for the determination of TIB or its metabolites. Recently, competitive advantages of electrochemical methods have been successfully explored for analysis of drugs and other compounds in saliva samples [13,24–32] …”