Planar fluorescence sensors for two-dimensional measurements of H2S distributions and dynamics in sedimentary deposits

Planar fluorescence sensors have been developed for measuring two-dimensional hydrogen sulfide (H2S) distributions in marine sediments by using pyronin Y (PY) as a novel H2S indicator. Sensing foils were prepared by non-covalently immobilizing PY in ethyl cellulose polymer membranes on transparent polyester sheets, and coating them with gas permeable silicone. Fluorescence from the sensors emitted at 567nm (excitation at 554nm) is inversely correlated to H2S concentration in solution. Two primary sensor modifications, M1 and M2, were used. The M1 sensor shows an excellent linear response versus H2S in the range of non-detectable (nd) to 3150 mu mol/l with a detection limit of 40 mu mol/l H2S (3 sigma ), and it can be utilized for high concentration H2S measurement. The M2 sensor has a dynamic working dynamic range of nd-125 mu mol/l H2S with a detection limit of 4 mu mol/l (3 sigma ) and can be used to detect low level H2S in samples. The response time (t90) and recovery time (R90) of the M1 sensor are ~60 and 30s, respectively, and for the M2, ~15s. These fluorosensors are only sensitive to H2S rather than ionic sulfide and bisulfide species, and their performance is independent of temperature and other dissolved gases such as oxygen, CO2, NH3 and N2. No interferences from major ions and trace elements in sediment porewater were observed due to the protection of the fluorophore by the silicone membrane. The sensors are simple, stable, and semi-reversible (reversible for M2) for extended periods, and have been successfully used to measure 2-dimensional H2S distributions and dynamics in sulfidic salt marsh sediments with a theoretical pixel resolution of ~5050 mu m. Complex heterogeneous H2S distributions in marine sediments and previously undocumented time-dependent biogeochemical reaction dynamics associated with both inhabited and abandoned biogenic structures were readily revealed.