SPR is real-time, label-free measurements of binding kinetics and affinity. This has distinct advantage over radioactive or fluorescent labelling methods, in terms of: 1) ligand-analyte binding kinetics, that can be probed without the costly and time-consuming labeling process that may interfere with molecular binding interactions; 2) binding rates and affinity can be measured directly and 3) low affinity interactions in high protein concentrations for can be characterized with less reagent consumption than other equilibrium measurement techniques; 4) Label-free detection of molecular interactions presents an attractive alternative. This is particularly true for protein targets where labels can compromise protein function. Label-free methods are also desirable because they are typically compatible with real-time detection, enabling the determination of rates of association. The success of SPR biosensors was indicated by the growing number of commercially available instruments. Since Biacore AB (originally Pharmacia Biosensor AB) launched the first commercial SPR biosensor on market in 1990, there have been many more competing SPR instruments including IASys (Affinity Sensors), SPR-670 (Nippon Laser Electronics), IBIS (IBIS Technology BV), TISPR (Texas Instruments), etc.