Current advancements in thefield of magnetron sputtered thin film for pH sensing have been investigated.
Variousmetal oxides have been studied for Ph sensing applications. We have discussedthe potential of various metal oxide based pH sensing electrodes, andhighlighted the unique properties of ruthenium oxide and tin oxide electrodesfor various sensing applications, such as high sensitivity, good potentialstability, wide temperature range, fast response and outstanding corrosionresistance. Furthermore, variousapplications of magnetron sputtered pH sensors have been discussed, includingfluid quality analysis, glucose and cholesterol concentration monitoring andbio-sensing. Here, the effects of conditioning-pH, RuO2, SnO2 materialthickness and oxidising/reducing agents on the sensitivity and hysteresis ofRuO2, SnO2 pHsensitive working electrodes was investigated. It was shown that to obtain pHsensor that exhibits 0.01 units of precision it is necessary to use anelectrode with at least 300 nm thickens of RuO2 and SnO2.Whilst 50 nm thickness can be used to achieve a precision of 0.
05 pH units. Investigation of the redoxinterference of these electrodes demonstrates that the pH sensitivity of RuO2electrodes decreases due to the loss of active hydroxyl sites, caused byoxidisation of RuIII. Whilst, the E0 value changesdepending on the proportion of RuIII to RuIV present inthe material. This provides a concise explanation for the sensitivity,hysteresis, drift and ageing effects observed for these types of electrodes andhighlights the need protect them from redox interference, to increase theirapplication and use. In this project, the effect of Ar/O2 gasratio on the performance of RF sputtered RuO2 and SnO2 thin-filmpH sensors have been experimentally investigated.
Several 300nm thin film RuO2and SnO2 sensing electrodes, prepared by varying Ar/O2 gasratio from 10/0 to 7/3 during RF sputtering, have been developed and theirsensitivity, response time, stability, reversibility and hysteresis propertiesfor pH sensing have been investigated. Experimental investigations have shownthat an Ar/O2 gas ratio of 9/1 results in a RuO2 and SnO2thin-film of excellent pH sensing properties, namely high sensitivity, lowhysteresis and faster response, using a conventional RuO2 and SnO2sputtering target. The optimized pH sensor structure has demonstrated asuper-Nernstian response of 57.66 mV/pH, good stability and reversibility.
Thedeveloped pH sensor can further be miniaturized as a lab-on-a-chip device andhas application in biological analyses, water quality monitoring, chemical andenvironmental monitoring and in vivo clinical tests.