Abstract |
Acoustic biosensors are analytical devices that use ultrasound waves to extract information
about a molecule of interest. More specically, Quartz Crystal Microbalance with Dissipation
monitoring (QCM-D) has been used to follow interactions between attached molecules and
solid surfaces. Thus QCM-D has been able to probe viscoelastic properties of films formed
by biomolecules at the interface between solid surfaces and liquid. In order to monitor these
reactions the surface chemistry must be carefully designed.
For the quantitative and qualitative interpretation of QCM-D data, we used a discretemolecule
binding theory combined with designed surfaces to follow molecular hydrodynamic
properties of molecules. The model suggests that the acoustic ratio ΔD/Δf is related to the
intrinsic viscosity [η], a measure of the hydrodynamic properties of bound biomolecules.
Two different surfaces were used in order to immobilize (a) DNA molecules of various lengths
and (b) C terminal constructs of a coiled-coil protein involved in endosomal trafficking. In
both cases, Supported Lipid Bilayers (SLB) were first formed, following the binding of discrete
molecules that maintain their native structure.
For the immobilization of DNA molecules we used the biotin-streptavidin interaction that
has been widely exploited for nucleic acid detection using QCM-D monitoring. In previous
work biotinylated DNA molecules were immobilized at surfaces covered with neutravidin. In
this report we try to elucidate the "linker effect" to evaluate the effect of different linking
strategies between the sensor surface and DNA molecules. For this reason we tested the
biotin-streptavidin system on Supported Lipid Bilayers (SLBs). The results suggest that the
"linker" between sensor surface and target DNA, affects significantly the acoustic measurements.
For the specific immobilization of Early endosomal antigen 1 (EEA1) constructs, SLBs containing
Phosphatidylinositol 3-phosphate (PI3P) lipids were prepared. In order to apply the
discrete molecule approach we used different protein concentration on those surfaces. This
particular SLB lipid composition allowed the stable immobilization of protein constructs and
preliminary acoustic measurements were evaluated.
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