Interferometeric sensing of beta-galactosidase released by recombinant E-coli responding to an endocrine disruptor, tributyltin

A recombinant E. coli ACV1003 releasing beta -galactosidase by a SOS regulo n system when it is exposed to a DNA-damaging compound, has been used to de tect endocrine disruptors such as tributyltin (TBT) and triphenyltin (TPT). Maximum response ratio by E. coli ACV 1003 (recA::lacZ) - indicating the m aximum ratio of enzyme produced against an environmental toxicant to that p roduced in the absence of a toxicant - was estimated as 6.3 with 1.0 mug TB T ml(-1) at 37 degreesC, which was considerably higher than those with othe r strains. Extracellular beta -galactosidase activity was 51 unit ml(-1), w hich was 5% of that obtained by the conventional Miller's enzyme assay usin g solvents. Such a low enzyme activity can be rapidly determined, not by th e usual time-consuming and tedious enzyme assay, but by an alternative inte rferometric biosensor. Heavily-doped porous silicon to apply to an interfer ometer was fabricated by etching to produce a Fabry-Perot fringe pattern, w hich caused the change in the refractive index of the medium including beta -galactosidase. The change in the effective optical thickness versus beta -galactosidase activity showed a sigmoid increase up to the concentration o f 250 unit beta -galactosidase ml(-1).