Quartz crystal microbalance (QCM) monitoring of grafting of a biotin-functionalized polymer onto an avidin monolayer

th century and have been widely used as resonators in various equipment, mainly communication devices. However, they have only started to be considered as analytical devices after the discovery by Sauerbrey 1 that there is a linear relationship between deposited mass and the frequency response 2 . Quartz Crystal Microbalances have been used to monitor the thicknesses of thin rigid films in vacuuo and air. In the 1980's different groups found that QCM could also operated in liquid environment 3 . Such discovery laid the basis of a wide range of applications and QCM are now increasingly being used in life science 4 as biochemical sensors and in chemistry to study attachment of polymers 5 , dendrimers 6 or smaller molecules 7 on gold surfaces. Transition Metal Mediated Living radical polymerization (TMM-LRP) 8 is a versatile technique that allows the synthesis of functionalized monodisperse polymers of well defined architectures. This technique is suitable for the synthesis of macromolecules that can be attached to a surface and which grafting can be monitored by QCM. A well chosen terminal function group provides the anchoring point and narrow molecular weight distribution ensures the regularity of the brushes and facilitates the calculation of the grafting density. Avidin and streptavidin are proteins composed of four subunits and have been studied in detail 9 . Each of their subunits can bind biotin with the strongest non covalent binding constant known so far. In the recent years the avidin-biotin system has been used in proteomics 10 , drug delivery 11 , pretargeting startegy 12 , surface engineering 13 and polymer science 14 .