Probing single molecule interactions by AFM using bio-functionalized dendritips

A new strategy for AFM (atomic force microscopy) tip functionalization based on the use of aldehyde-phosphorus dendrimers for the immobilization of biomolecules such as proteins (e.g. antibodies) is presented. Firstly functionalized with amino groups, the tips are reacted with dendrimers leading to dendrimer-activated tips (so-called dendritips). Free aldehyde functions on the dendrimer are therefore available to react with amino-functions present on every protein and many biomolecules. Using biofunctionalized-dendritip, single molecule force interactions between glutathione-S-transferase (GST) and its cognate antibody immobilized on dendritips (67 ± 11 pN for single interaction) were probed by AFM spectroscopy. The specificity of our measurements was demonstrated by performing blocking tests resulting in the loss of interactions.