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(a) Top view of the CPW defined on a borosilicate glass slide with size . The conductor layers are covered with . Glued on top of the CPW is a polycarbonate microfluidic chamber. The inlets of the chamber and the channel where fluid is in contact with the CPW are indicated. The dimensions of the CPW were chosen in order to match its impedance to the inputs of the network analyzer. The impedance was calculated from the distributed capacitances of the waveguide, for which estimates for the effective permittivity of its surroundings (air, water, polycarbonate) were used. These effective values were obtained for the static case from numerical calculations with a self-written Laplace solver. Outside the channel area, the width of the center conductor is and the distance of the ground lines is . Below the channel, the width of the inner conductor is reduced to . The CPW is contacted with microwave probes (indicated by black spots) and transmission is measured from Port 1 to 2. (b) Cross section of the chamber at the position indicated by the dashed line in (a). The cross section area of the channel is .
(a) Negative imaginary part of the dielectric function of water and methanol in the frequency range covered by the experiments. (b) Linear dependence of the absolute value of from part (c) of this figure at and at on the methanol fraction. (c) The transmission of the waveguide changes significantly when the chamber is loaded with solutions with increasing methanol fraction. From all signals, the transmission of the waveguide in the presence of pure PBS buffer has been subtracted.
Signal change due to the formation of a DOPC bilayer. The reference signal is obtained with pure PBS buffer solution. To form the bilayer, lipid vesicles in PBS are injected into the perfusion chamber. A clear signal change is observed a few minutes after introduction of the vesicle suspension. This signal slightly increases over a period of several hours. Extensive subsequent rinsing with buffer solution does not change the signal significantly, indicating that most of the change in HF transmission is caused by the formation of a supported lipid bilayer membrane.
Transmission of the CPW with DOPC membrane after addition of alamethicin (Alm). The reference signal is obtained before the addition of alamethicin.
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