Measurement of protein concentration in solution has since long been of essential importance in biological laboratories. The most commonly used ways to determine protein concentrations are the Bradford, Lowry and BCA methods. These methods, however, have definite limitations speaking of sensitivity, dynamic range and - in the case of the Bradford and Lowry assay - compatibility with reducing agents.
When sample quantity is limited, protein quantification is often performed by measuring the absorbance at 280 nm using a microvolume spectrometer, which allows the quantification of total protein using as little as 1 µL of sample.
Even though a majority of biological and biochemical laboratories has at least at some point applied one of these methods, the detection and determination of some protein concentrations might not be satisfactory, if possible at all. Fluorescent labeling of proteins and subsequent detection of the label via fluorescence measurement has proven to be the method of choice in many types of assays.