A novel colorimetric oxygen sensor: dye redox chemistry in a thin polymer film

A simple, reversible, colorimetric, thin film sensor for oxygen, based on the redox chemistry of 2,6-dichloroindophenol (2,6-DCIP) in the presence of fructose and base in a thin ethyl cellulose polymer film, has been developed. The sensor film is colourless in the absence of oxygen, but gives a strong blue colouration in the presence of oxygen at approximately 30 Torr and above. At oxygen pressures in the range 0–50 Torr, the absorbance of the film shows reasonable linearity with the partial pressure of oxygen. Sensor response has been studied as a function of plasticiser type, and fructose and base concentration. Of the three plasticisers examined: castor oil, and Santicizers™ 278 and 141, films made using castor oil are most stable in terms of changes in response characteristics with time. Sensor response is rapid, with the equilibrium response reached within 20 s of a change in oxygen partial pressure. The sensor equilibrium response to oxygen is stable over many air/nitrogen cycles, but there is an increase in response time upon prolonged cycling.