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.
Specificity is provided by placing a thin biofilm on the sensor surface. For example, by placing an
antibody to fluoroscein 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 (150,000 daltons). To analyze a sample, 0.5 g 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 mg/kg). For this verification test, the lowest reported interval was 0 to 0.3 mg/kg.
For more information: Texas Instruments, contact Jerry Elkind,
elkind@ti.com, 972-995-1214