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Abstract
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pH monitoring in micro volume samples is required for environmental and clinical analysis. Low cost, miniaturized and stable
metal oxide based pH sensors could be a suitable alternative to glass electrodes. In this study, a sensitive potentiometric
solid state pH sensor based on manganese oxide nanoparticles electrodeposited on graphenized pencil lead electrode (
MnO2/
GPLE) was reported. The prepared MnO2/
GPLE was carefully characterized by SEM, XRD and electrochemical techniques.
To miniaturize the prepared pH sensor, a stainless steel 304 needle was used as a reference electrode. Selectivity, response
time, stability and reproducibility of the miniaturized pH sensor were studied and compared with conventional glass pH
electrode. According to experimental results, a near-Nernstian slope of − 57.051 mV/pH and linearity over the pH range
of 1.5–12.5 were obtained for the developed MnO2/
GPLE pH sensor. The prepared sensor represented high ion selectivity
to mono-valence and multi-valence ions with −log KPot
A,B values around 6.49. A fast response time of 20 s in acidic medium
and 60 s in alkaline medium, long-term stability and reproducibility in 2 months, the simplicity of fabrication, low cost
and accuracy makes this sensor as a suitable choice for rapid pH recording in micro volume samples. The MnO2/
GPLE pH
sensor was successfully used for the pH monitoring of human tear, human blood, saliva, apple juice, lemon juice, milk, and
vinegar samples with satisfactory results.
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