A langasite SH SAW 0157:H7 E. coli Sensor

Abstract

The toxigenic O157:H7 Escherichia coli (E. coli) bacterium has been connected with hemorrhagic colitis band hemolytic uremic syndrome, which may be characterized by diarrhea, kidney failure, and death. On average O157:H7 causes 73,000 illnesses, 2,100 hospitalizations, and 60 deaths annually in the United States alone. Current methods for the detection and identification of pathogenic E. coli typically involve tedious laboratory analyses which are often implemented only after symptomatic illness has been identified. Sensors capable of detecting bacteria rapidly in the field are needed to provide early warning of the presence of dangerous microbes such as these in food and water supplies, with the goal of limiting the exposure of human and animal populations. A biosensor using langasite (LGS) shear horizontal surface acoustic wave (SH SAW) delay lines meets the needs for required sensitivity, temperature stability, compatibility with biochemicaly derived recognition receptors, and low attenuation in liquid environments. Previous work by the authors indicated that SH SAW delay lines fabricated along LGS Euler angles (0o, 22o, 90o) produce measurable transmission coefficient phase ( ∠ S21) variations in liquid phase testing as macromolecular protein assemblies were attached to the delay path. These early results suggested the application of these devices in bacterial detection. A test setup utilizing a small-volume fluid injection system, highly-stable Peltier temperature control, and high-frequency phase measurement was used to validate biosensor performance. LGS SH SAW delay lines were fabricated and derivatized with a rabbit polyclonal IgG antibody which selectively binds to E. coli O157:H7. To quantify the effect of nonspecific binding due to interfering bacteria, anti-trinitrophenol (anti-TNP) receptor layer was also used. A nontoxigenic test strain of E. coli O157:H7 was grown, fixed with formaldehyde, stained with SYTO 13 cell- permeant nucleic acid stain, suspended in phosphate buffered saline, and applied to the antibody-conjugated sensing surfaces. Fluorescence microscopy indicated selective binding of E. coli to the antibody receptor layer greater than 30 times non-selective binding. In bacteria tests, ∠ S21 variations of approximately 14o due to selective bacterial binding, and variations of around 2o on the non-selective control layer were measured. These tests were repeated 3 times proving the utility of the LGS SH-SAW E. coli sensor.