Electrochemical impedance spectroscopy of the interaction of STMpep9 with CDK2-expressing cell lysate. (a) EIS φ(ω) data for a gold surface functionalized with STMpep9 (orange circles) and following exposure to CDK2-expressing yeast lysate (blue circles). (b) As (a) but following exposure of STMpep9 to a CDK-free yeast lysate. (c) Data from (a) and (b) plotted as the phase shift (Δφ(ω)) for independent electrodes functionalized with STMpep9 and exposed to either a CDK2-expressing yeast lysate (blue line) or a CDK2-free lysate (orange line). The black line represents the Δφ(ω) of an STM-functionalized gold electrode following exposure to CDK2-expressing yeast lysate. A phase shift is only detectable upon exposure of STMpep9 to CDK2, indicating that yeast proteins neither interact nonspecifically with the peptide aptamers nor specifically or nonspecifically with the electrode surface.