Spreeta is an integrated, miniaturized sensor platform which employs surface plasmon resonance (SPR) to detect changes in refractive index within a few thousand angstroms of the active gold surface. Specificty is provided by placing a thin biofihn on the sensor surface. For example, by placing an antibody to fluorescein on the sensor surface, the binding of fluorosceinated proteins, seen as a local increase in refractive index, is simply performed. SPR has been used in this way to study biomolecular binding events for more than a decade, but Spreeta is the first miniaturized SPR platform. TNT detection is most efficiently performed by methods other than direct binding. This is because on a molecule-for-molecule basis, small molecules are much less effective than large molecules at changing refractive index; thus, any direct SPR assay can detect large molecules at a lower concentration than it can detect small molecules. For this reason, Texas Instruments has developed a robust inhibition assay in which the presence of two TNT molecules (228 daltons) effectively inhibits the binding of one antibody molecule (I 50,000 daltons). To analyze a sample, 0.5g of soil is extracted in an aqueous solution. The assay starts with a conjugate of trinitrobenzene (TNB) and bovine serum albumin on the gold sensing surface. Assays are then performed by exposing that sensing surface to an anti-TNT antibody solution which may or may not contain free TNT. When free TNT is present, it binds to anti-TNT antibodies in solution and thereby keeps them from binding to the surface-bound TNT analog. This inhibited binding is compared to a reference run where the antibody solution did not contain free TNT. Results from this assay are reported as interval data (i.e., the concentration of TNT is between 0.3 and 0.9 rng/kg). The lowest reporting interval was 0 to 0.3 mg/kg.

Cover title. "August 2001." "EPA 600-R-01-064."