Sensors and technologies for in situ dissolved methane measurements and their evaluation using Technology Readiness Levels

Dissolved methane measurements rely on the time-consuming collection of discrete water samples followed by gas-chromatography analysis. To date, this approach has proved useful for broad interpretation of environmental processes. However, it limits comprehension of environmental processes that are highly variable in space and or time. This has led to increased interest in in situ dissolved methane sensors to augment data from point sampling. So far, three sensing strategies have been explored using: 1) gas-phase measurements after gas extraction through semi-permeable silicon membranes; 2) measurements using biosensors; and, 3) optical measurements (e.g., surface-plasmon resonance and surface-enhanced Raman spectroscopy). Optical measurements may represent the future for in situ dissolved methane sensing. We review and evaluate different in situ methane sensors and technologies using Technology Readiness Levels.