Radio Frequency Tank Circuit for Probing Planar Lipid Bilayers

We present first results from a hybrid coplanar waveguide microfluidic tank circuit for monitoring lipid bilayer formation and fluctuations of integrated proteins. The coplanar waveguide is a radio frequency resonator operating at ~250 MHz. Changes within the integrated microfluidic chamber, such as vesicle bursting and subsequent nanopore formation alter the reflected signal, and can be detected with nanosecond resolution. We show experimental evidence of such alterations when the microfluidic channel is filled with giant unilamellar vesicles (GUVs). Subsequent settling and bursting of the GUVs form planar lipid bilayers, yielding a detectable change in the resonant frequency of the device. Results from finite element simulations of our device correlate well with our experimental evidence. These simulations also indicate that nanopore formation within the bilayer is easily detectable. The simulated structure allows for incorporation of microfluidics as well as simultaneous RF and DC recordings. The technique holds promise for high throughput drug screening applications and could also be used as an in-plane probe for various other applications. It opens up possibilities of exploring ion channels and other nano scale pores in a whole new frequency band allowing for operating at bandwidths well above the traditional DC methods.

Direct Transfer of GaAs Microtube Arrays onto Transparent Substrates for Imaging Neuron Outgrowth

We introduce a direct method for transferring arrays of GaAs microtubes from an opaque substrate to a transparent glass substrate in a controlled manner. This enables us to build a platform for optical readout of the microtubes’ interaction with overgrown cellular networks. We achieve this by applying a double layer of polydimethylsiloxane (PDMS). The first PDMS layer serves as a smooth and mechanically compliant transparent substrate. The second, adhesive layer contains a mixture of PDMS and n-hexane, which creates a layer thickness smaller than the tube diameter. This will prevent the tubes from sinking into the substrate. The microtubes themselves are made of GaAs heterostructures. The direct bandgap of the material allows for the integration of embedded optical device components into the tube wall. The microtubes have diameters on the same scale as typical mouse cortical axons, being on average 1 μm. The axons can be grown through the tubes, hence maximally enhancing the capacitive coupling of the signal source (axon) and the electrode (tube). Although the tube material is toxic to cells, we are able to overcome this by a parylene-coating step.