An optical micro-instrumentation system for measurement of fluorescent proteins in whole-cell biosensors

One well-developed paradigm for biosensing uses living microorganisms as sensors for environmental stimuli. In this paradigm, engineered cells contain plasmid or chromosomal sequences that link stress-inducible promoters to the production of fluorescent reporter proteins. We are developing such a sensor system with an aim for portability. This work describes the development and performance of a compact optical system designed for low-power detection of fluorescent reporter proteins in microliter-scale cell suspensions. Light-emitting diodes (LEDs) and silicon photodetectors (PDs) were configured to measure red fluorescence, green fluorescence, and cell biomass pseudo-simultaneously in 100 mul samples. The optical detectors were calibrated using E. coli cells that expressed red and green fluorescent proteins (dsRed2 and gfp-asv, Clontech) either constitutively or through chemical induction. We show that sufficient sensitivity for certain whole-cell biosensor applications is achievable in low-volume samples, despite the simplicity and low-cost nature of the detector system. The prototype optical detector occupies approximately 1.8 cmtimes2.2 cmtimes3.0 cm