Specific adhesion of vesicles monitored by scanning force microscopy and quartz crystal microbalance

The specific adhesion of unilamellar vesicles with an average diameter of 1 00 nm on functionalized surfaces mediated by molecular recognition was inve stigated in detail. Two complementary techniques, scanning force microscopy (SFM) and quartz crystal microbalance (QCM) were used to study adhesion of liposomes consisting of 1,2-dipalmitoyl-snglycero-3-phosphocholine and var ying concentrations of N-((6-biotinoyl)amino)hexanoyl)-1,2-dihexadecanoyl-s n-glycero-3-phosphoethanolamine (biotin-X-DHPE), Monitoring the adhesion of the receptor-doped vesicles to avidin-coated gold surfaces by QCM (f(o) = 5 MHz) revealed an increased shift in resonance frequency with increasing b iotin concentration up to 10 mol% biotin-X-DHPE. To address the question of how the morphology of the liposomes changes upon adhesion and how that con tributes to the resonator's frequency response, we performed a detailed ana lysis of the liposome morphology by SFM, We found that, with increasing bio tin-concentration, the height of the liposomes decreases considerably up to the point where vesicle rupture occurs. Thus, we conclude that the unexpec ted high frequency shifts of the quartz crystal (>500 Hz) can be attributed to a firm attachment of the spread bilayers, in which the number of contac ts is responsible for the signal. These findings are compared with one of o ur recent studies on cell adhesion monitored by QCM.