The air-drying of Escherichia coli reporters in natural polymers and incorporation into simple bioassays

Abstract

Microbial biosensor systems (MBS) are useful for analyte detection owing to their low cost, sensitivity, and selectivity for bioavailable analytes. Due to typically poor shelf-life and sensitivity to external conditions, there are few reports of MBS technology applied to simple analytical devices. The effectiveness of air-drying MBS in natural polymers was investigated as a novel preservation technique. Two colorimetric Escherichia coli MBS, a tetracycline-inducible reporter and an arsenate-inducible reporter, were dried on various substrates yielding novel MBS platforms. In proof-of-concept experiments performed in 96-well microplates, both systems demonstrated responsivity after air-drying in low concentrations of pullulan. However, the MBS were unresponsive following brief storage of 1 week. To improve the preservation of MBS, sensing strips were created by air-drying concentrated acacia gum-based MBS suspensions onto paper. Cells dried on these strips demonstrated responsivity upon solubilization in various tube-based assays. MBS sensing strip responsivity was demonstrated following storage for 6 weeks at 4 °C. Tetracycline-responsive sensing strips also performed well in assays using spiked lake water samples. Air-drying in natural polymers was an effective MBS preservation technique, and allowed for the creation of “mix and read” style assays which were simple, equipment-free and ready-to-use.