The metal oxides have been
widely studied for pH sensing application including water quality, engine oil
oxidation detection, Coca-Cola, base water, lemon, wine, vinegar, milk,
seawater and hard clam (meretrix lusoria) cultivated solutions, glucose
concentration, total cholesterol concentration and biosensor applications. Recently various metal oxides such as RuO2, IrO2,
PtO2, RhO2, TiO2, SnO2, Ta2O5
and PdO have been investigated for use as pH sensing electrodes. Their
attractive features include insolubility, stability, mechanical strength,
electro-catalyst and manufacturing technology. Compared with other metal oxides, ruthenium oxide exhibits
unique properties including thermal stability, excellent corrosion resistance,
low hysteresis high sensitivity, and low resistivity.
Following are a few researchers specifically on metal
oxides for various application:
Y. H. Liaoet al 5 have used RuO2
thin film as pH sensor array used in real-time measurements. The
sensing layer is a hydrogen ion selective electrodes (ISE) for pH array
sensors. The pH sensitivity of the RuO2 sensing membrane for
the developed ISE.
J. Chou 9 has designed reactively
sputtered ruthenium oxide (RuOx) and ruthenium nitride(RuN)as a sensing
membrane deposited on silicon substrate for pH sensing applications.
Moreover, to increase the sensing range of the pH sensor.
Tsai al 10 have studied the pH sensing characteristics and hysteresis
effect of the R.F. Sputtered tin oxide (SnO2) electrode.
C. Chouet al. 11 have carried out long-term monitoring of sea water
using solid-state TiO2: Ru sensing electrodes for hard clam cultivation.
In this study, a co-sputtering system was used to fabricate the TiO2: Ru
sensing film deposited on a p-type silicon substrate.
also reported that an increase in the thickness of the ruthenium oxide layer
increases response time and decreases in drift rate. In addition, it was
observed that the pronounced redox cross-sensitivity of ruthenium oxide is a
limiting factor in situations where the concentration of dissolved oxygen is
not constant or cannot be directly measured. Hence, an ideal
thin film sensor should overlook the above limitations.