Surface Plasmon Resonance (SPR) has become a widely accepted technique for real-time detection of interactions
between receptor molecules and ligands. Antibody may serve as receptor and can be attached to the gold surface of the
SPR device, while candidate analyte fluids contact the detecting antibody. Minute, but detectable, changes in refractive
indices (RI) indicate that analyte has bound to the antibody.
A decade ago, an inexpensive, robust, miniature and fully integrated SPR chip, called SPREETA, was developed.
University of Washington (UW) researchers subsequently developed a portable, temperature-regulated instrument, called
SPIRIT, to simultaneously use eight of these three-channel SPREETA chips. A SPIRIT prototype instrument was tested
in the field, coupled to a remote reporting system on a surrogate unmanned aerial vehicle (UAV). Two target protein
analytes were released sequentially as aerosols with low analyte concentration during each of three flights and were
successfully detected and verified.
Laboratory experimentation with a more advanced SPIRIT instrument demonstrated detection of very low levels of
several select biological agents that might be employed by bioterrorists. Agent detection under field-like conditions is
more challenging, especially as analyte concentrations are reduced and complex matricies are introduced. Two different
sample preconditioning protocols have been developed for select agents in complex matrices. Use of these
preconditioning techniques has allowed laboratory detection in spiked heavy mud of Francisella tularensis at 103
CFU/ml, Bacillus anthracis spores at 103 CFU/ml, Staphylococcal enterotoxin B (SEB) at 1 ng/ml, and Vaccinia virus (a
smallpox simulant) at 105 PFU/ml. Ongoing experiments are aimed at simultaneous detection of multiple agents in
spiked heavy mud, using a multiplex preconditioning protocol.
On March 14, 2003 an experimental aircraft fitted with surface plasmon resonance (SPR) biosensors connected to an air sampling system performed a 90-minute flight over Renton, Washington, demonstrating the first-ever use of SPR sensors for airborne biodetection. In this paper, we describe the instrumentation constructed for this purpose, the experiment conducted, and the results obtained. Instrumentation was based on Texas Instruments’ Spreeta SPR sensors combined with sample collection and fluidic apparatus designed for airborne sensing. Detection targets were two innocuous proteins ovalbumin and horseradish peroxidase. We describe future enhancements necessary to apply this technology on an unmanned airborne vehicle.