B. Pignataro et al., Specific adhesion of vesicles monitored by scanning force microscopy and quartz crystal microbalance, BIOPHYS J, 78(1), 2000, pp. 487-498
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.