Reversible and oriented immobilization of ferrocene-modified proteins

Adopting supramolecular chemistry for immobilization of proteins is an attractive strategy that entails reversibility and responsiveness to stimuli. The reversible and oriented immobilization and micropatterning of ferrocene-tagged yellow fluorescent proteins (Fc-YFPs) onto ß-cyclodextrin (ßCD) molecular printboards was characterized using surface plasmon resonance (SPR) spectroscopy and fluorescence microscopy in combination with electrochemistry. The proteins were assembled on the surface through the specific supramolecular host–guest interaction between ßCD and ferrocene. Application of a dynamic covalent disulfide lock between two YFP proteins resulted in a switch from monovalent to divalent ferrocene interactions with the ßCD surface, yielding a more stable protein immobilization. The SPR titration data for the protein immobilization were fitted to a 1:1 Langmuir-type model, yielding KLM = 2.5 × 105 M–1 and Ki,s = 1.2 × 103 M–1, which compares favorably to the intrinsic binding constant presented in the literature for the monovalent interaction of ferrocene with ßCD self-assembled monolayers. In addition, the SPR binding experiments were qualitatively simulated, confirming the binding of Fc-YFP in both divalent and monovalent fashion to the ßCD monolayers. The Fc-YFPs could be patterned on ßCD surfaces in uniform monolayers, as revealed using fluorescence microscopy and atomic force microscopy measurements. Both fluorescence microscopy imaging and SPR measurements were carried out with the in situ capability to perform cyclic voltammetry and chronoamperometry. These studies emphasize the repetitive desorption and adsorption of the ferrocene-tagged proteins from the ßCD surface upon electrochemical oxidation and reduction, respectively.