Detection of oxygen is important to many industrial processes, especially where an absence of oxygen, or the accurate control of its concentration, is essential. One area of particular interest [1–4] is in the monitoring of headspace gas within food packages, since oxygen is responsible for a variety of food-spoiling processes, including promotion of microbial growth, lipid oxidation, and protein decomposition and discolouration. Importantly, in order to extend shelf-life, many food packages utilise modified atmosphere packaging (MAP), whereby the package is flushed with the inert gas N2 , and/or the active gas CO2 , in order to reduce the O2 concentration from ambient 21% to ∼0.5–2%. Furthermore, oxygen scavenging techniques [1] are often employed, lowering the oxygen content to about 0.01% and subsequently sustaining it at this level.