|MadSci Network: Biochemistry|
Glucose solutions are essentially transparent to visible light (400 – 700 nm wavelength, blue to red light respectively). Therefore visible light absorption can not be used to directly to detect and measure glucose. Because of this, most assays for glucose have consisted of carrying out some chemical reaction, where glucose is one of the reactants, which ultimately produces a colored product. This is the method used by many 1st generation glucose meters used by diabetics today to measure their blood glucose levels. For example, many use a test strip containing the enzyme glucose oxidase. A sample of blood is applied to the strip, the glucose oxidase oxidizes the glucose to glucuronic acid and hydrogen peroxide. The hydrogen peroxide then oxidizes another compound, producing a colored dye that is measured by the absorbance of visible light. These devices are relatively simple to use and accurate, but of course require the drawing of a small sample of blood.
While itself glucose doesn’t absorb visible wavelengths of light, it does absorb near infrared radiation (strongly at the 9.25 mm wavelength, weakly at 8.45 mm)). This is of interest because human tissues, which are mostly water, have a “transmission window” for radiation between 6 and 12 mm in wavelength. Thus one should theoretically be able to detect and quantify glucose non-invasively by looking at the absorbance of near infrared light. Indeed some devices are under development (e.g. by companies such as CME Teletrix, InLight Solutions , and Sensys Medical) that use this property of glucose. However, these devices are at present far form ready for routine use.
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