Bioluminescent whole cell optical fiber sensor to genotoxicants: system optimization

An Escherichia coli strain, genetically modified to emit a luminescent signal in the presence of genotoxic agents, was alginate-immobilized onto an exposed core of a fiber-optic. The performance of this whole-cell optical fiber sensor system was examined as a function of several parameters, including gel probe matrix volume, bacterial cell density, numerical aperture of the fiber core and working temperature. An optimal response to a model genotoxicant, mitomycin C, was achieved with six alginate/bacterial adlayers on a 1 cm exposed fiber-optic core. Total alginate volume per tip was about 100 μl, containing a bacterial suspension of around 1.5–3.0×107 cells. When the core diameter was etched down to 270 μm, photon detection efficiency significantly increased, although to a lesser extent than that expected from theoretical calculations. Further reduction in core diameter led to a reduced performance. Activity at 37°C was superior to that at 26°C. Under these optimized conditions, optrode response was mitomycin C dose-dependent for at least 6 h, with a lower detection threshold of 25 μg/l.