| Abstract
| - A new concept of protein sensing at the air−water interface is introduced, based on amphiphilicreceptor molecules embedded in a lipid monolayer. The process begins with incorporation of a small amount(0.13 equiv) of one or two different calix[4]arenes, adorned with charged functional groups at their upperrims, into a stearic acid monolayer. These doped monolayers are subsequently shown to attract peptidesand proteins from the aqueous subphase. Depending on the host structure, the monolayers can be madeselective for basic or acidic proteins. A working model is proposed, which explains the large observed p/Ashifts with reincorporation of excess receptor molecules into the lipid monolayer after complex formationwith the oppositely charged protein. This requires a self-assembly of multiple calixarene units over theprotein surface, which bind the protein in a cooperative fashion. Oppositely charged calixarene derivativesdo not form molecular capsules inside the monolayer, but rather remain separate inside the lipid layer,adopting a perpendicular orientation. They combine their hydrogen bond donor and acceptor capacities,and thus markedly enhance the sensitivity of the sensor system toward proteins, pushing the detectionlimits to 10 pM concentrations. The response pattern obtained from various receptor units inside themonolayer toward the same protein creates a fingerprint for this protein, which can hence be selectivelydetected at nanomolar concentrations (pattern recognition).
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