Physiochemical and electrochemical characterization of SpyDirect‐based nanobody functionalized Au electrode. A) High‐resolution XPS spectra for Au 4f, C 1s, and N 1s of the gold surface after immobilization of cysteine‐terminated spyTag‐peptide and the VHH72‐spyCatcher. The VHH72‐spyCatcher buffer contained BSA. B) Cyclic voltammogram, C) Bode plot (solid lines and dotted lines correspond to the magnitude and the phase of the impedance, respectively), D) Nyquist plot of the gold electrode before and after the subsequent functionalization with cysteine‐terminated spyTag peptide, and the VHH72‐spyCatcher. Inset to D is the equivalent circuit model used to fit the impedance spectra. E) The R
ct and C
dl of the electrode. The measurements were done in 10 mm [Fe(CN)6]3−/4− in 10 mm PBS, pH 7.4.