Fibre-optic bacterial biosensors and their application for the analysis of bioavailable Hg and As in soils and sediments from Aznalcollar mining area in Spain

Fibre-optic biosensors for Hg and As were developed by attaching alginate-immobilised recombinant luminescent Hg- and As-sensor bacteria onto optical fibres. The optimised biosensors (consisting of seven layers of fibre-attached bacteria pre-grown till mid-logarithmic growth phase) enabled quantification of environmentally relevant concentrations of the target analytes: 2.6 μg l−1 of Hg(II) and 141 μg l−1 of As(V) or 18 μg l−1 of As(III). The highest viability and sensitivity for target analyte was obtained when fibre tips were stored in CaCl2 solution at −80 °C.Applicability of the fibre-optic biosensors in parallel to the respective non-immobilised sensors was assessed on 10 natural soil and sediment samples from Aznalcollar mining area (Spain). On the average 0.2% of the total Hg and 0.87% of the total As proved bioavailable to fibre-attached bacteria. Interestingly, about 20-fold more Hg and 4-fold more As was available to non-immobilised sensor bacteria indicating the importance of direct cell contact (possible only for non-immobilised cells) for enhanced bioavailability of these metals in solid samples.