Measurement of light
Solutions are often analyzed in the biotechnology lab by measuring how the solutes interact with light. A spectrophotometer measures the amount of light that is absorbed by a solution at a specific wavelength or over a range of wavelengths. If you know a wavelength at which a specific substance absorbs light, you can calculate the amount of that substance in a solution from the measured absorbance of that solution at that wavelength.
A. VIS spectrophotometer –A visible (VIS) spectrophotometermeasures absorbance of light in the visible region of the spectrum (wavelength of about 400-700 nm). A small vessel called a cuvette, which is generally plastic or glass and which usually has an internal diameter of 1.0 cm, is filled with the solution and placed in the spectrophotometer for measurements.
B. UV/VIS spectrophotometer –An ultraviolet/visible (UV/VIS)spectrophotometer can also measure absorbance of light in the ultraviolet region of the spectrum (about 100-400nm). These spectrophotemeters require a halogen light bulb that emits ultraviolet light and require special cuvettes that don‘t absorb UV light.
C. Scanning spectrophotometer –A scanning spectrophotometer canmeasure the absorbance of a solution over a range of wavelengths, creating an absorbance spectrum that can be used to identify substances in a solution.
D. NanoDrop spectrophotometer –A NanoDrop spectrophotometer isa brand of scanning UV/VIS spectrophotometer that allows the user to measure the absorbance of a very small sample of liquid (1-2 uL). This instrument makes it easy to quickly evaluate the quality and quantity of nucleic acids or proteins in a small sample prep.
E. Microplate reader –A microplate reader is a spectrophotometerthat can measure the absorbance in the individual wells of a plate. Usually the plates are 96 wells, but other formats are available, such as 48 wells and 384 wells. This allows the user to prepare and read many small samples at once, saving time and money. Microplate readers may also be capable of reading fluorescence and chemiluminescence, which are two types of light emission that are frequently used in biological research.
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