Microengineered membranes coated with titanium with a pore size of 500 nm have also been used [166] as a scaffold for a functional monolipid layer obtained by the coalescence and spreading of corresponding lipid vesicles on the membrane surface.

Micro- and nanoengineered membranes can further be used as a scaffold for the construction of functional 2D nanoarchitectures to probe, for example, selective molecular transport and controlled release properties of biomedical molecules. See Figure 63.

Cornell et al. [167] have elaborated tethered supported lipid bilayers into devices that will sense both large and small analytes. The impedance of the bilayers depends upon the density of open gramicidin channels. In one manifestation, an analyte (such as a protein) with two antigenic sites binds to antibodies at the membrane surface disrupting a preexisting channel with the disadvantage that the response is a diminution of a large preexisting signal. In a second manifestation, channels are opened when an analyte, which can in this case be a small molecule, releases half channels from an immune complex in the upper leaflet of the bilayer so that they can find half channels in the lower leaflet. Another promising approach is stochastic sensing with engineered pores [168]. Stochastic sensing is based on the detection of individual binding events between analyte molecules and a single pore. The read-out is the single-channel electrical current. The frequency of the binding events is determined by the concentration of the analyte. The nature of the binding events (e.g., the magnitude and duration of the associated signal) is determined by the properties of the analyte. The ability to identify an analyte by its characteristic signature is a distinctive feature of stochastic sensing. Engineered versions of a-hemolysin were first used to detect and quantify divalent metal ions.

Figure 63. Support structure 1 with a nanoengineered scaffold 2 for a functional membrane layer 3.

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