Spreeta is an electro-optical device utilizing surface plasmon resonance to detect small changes in refractive index of liquids. The Spreeta device was developed by Texas Instruments, Inc. in the 1990s. Device design incorporates a light-emitting diode (LED) illuminating a thin metal film (usually gold) in the Kretchmann geometry (needed to excite surface plasmons). The reflected light is detected by a

photodiode A photodiode is a light-sensitive semiconductor diode. It produces current when it absorbs photons. The package of a photodiode allows light (or infrared or ultraviolet radiation, or X-rays) to reach the sensitive part of the device. The packag ...

linear array Linearity is the property of a mathematical relationship (''function'') that can be graphically represented as a straight line. Linearity is closely related to '' proportionality''. Examples in physics include rectilinear motion, the linear re ...

(which translates angle of reflection to pixel position) and the resonance (a dip in the reflectivity at a specific

angle of incidence Angle of incidence is a measure of deviation of something from "straight on" and may refer to: * Angle of incidence (aerodynamics), angle between a wing chord and the longitudinal axis, as distinct from angle of attack In fluid dynamics, ang ...

) denotes the refractive index on the outer surface of the metal film. Applications include real-time measurement of binding of antigens to antibodies attached to the sensor surface, monitoring changes in oil quality, and measuring sugar content in drinks (

Brix Degrees Brix (symbol °Bx) is a measure of the dissolved solids in a liquid, and is commonly used to measure dissolved sugar content of an aqueous solution. One degree Brix is 1 gram of sucrose in 100 grams of solution and represents the strength ...

level). The term "Spreeta" is an anglic derivative of SPR-ITA, which combines SPR (for Surface Plasmon Resonance) with "ita" (a Spanish suffix meaning "small"). File:Spreeta Diagram and Sensors(1).jpg, The top image shows an optical diagram of the sensor (in cross-section). The lower-left image is the original integrated sensor. The lower-right image is a smaller version of the sensor with less sensitivity but more amiable to system integration.

References

* U.S. Patent Number 5912456 - Filed Mar 19, 1997 - Texas Instruments Incorporated * Sensors Texas Instruments hardware Plasmonics {{electronics-stub