## 3 Results and Discussion
### Potentiodynamic Deposition  
Even if the galvanodynamic approach optimized in this study proved capable of successfully depositing and in situ co-crosslinking GOD and BSA on the electrode surface, further approaches were investigated and studied. As previously pointed out, the concurrent and deleterious processes of water discharge and dioxygen bubbling are catalyzed by platinum oxide formation: since this last process is merely controlled by the potential of the deposition electrode under suitable chemical conditions, a potentiodynamic technique, wherein the potential is under the control of the EPD process, should increase the selectivity of the electrophoretic deposition towards gas evolution, increasing the efficiency of the overall EPD/co-crosslinking process; in fact, the galvanodynamic approach investigated herein, even if optimized, did not permit the true control of the potential reached by the deposition electrode since, as Figures 3 and 4 show, its value increased, even if only slightly, during the current sequence application. Since the preliminary potentiostatic experiments (see Section 3.2) failed to reach the goal of the present research, a potentiodynamic electrophoretic deposition technique was developed and investigated for protein deposition: here, a pulsed potential sequence (see Scheme 2) was applied at the deposition electrode while varying the potential step values \(E_{i}\) and \(E_{f}\) and the pulse duty cycle by \(t_{1}\) and \(t_{2}\). Figure 5: Resonance frequency changes at the deposition electrode during the application of the galvanodynamic current pulse sequence optimized in this study. Arrows labeled _start_ and _stop_ represent the timing of current pulse application at the electrode. (**a**): only phosphate buffer solution (pH 7, 1.0 M); (**b**,**c**): GOD 0.5% \(w/v\), BSA 1% \(w/v\), and GLU 2.5% \(v/v\) in phosphate buffer solution (pH 7, 1.0 M); (**b**,**c**) differing exclusively in the deposition time. Apart from \(t_{1}\) and \(t_{2}\) optimization, the selection of \(E_{\rm i}\) and \(E_{\rm f}\) was of paramount importance for removing any Pt oxide formed during the electrophoretic pulse step and minimizing oxide formation, respectively; accordingly, several electrochemical experiments were preliminarily conducted for this purpose. In this respect, Figure S2 shows typical cyclic voltammograms of the deposition Pt electrode as a function of scan rate in the media used for EPD/co-crosslinking deposition. Clearly evident are (a) the oxidation of the adsorbed dihydrogen and the subsequent Pt oxide formation due to Pt electrooxidation during the anodic scan (shown from left to right by the lower curves in both panels) and (b) Pt oxide stripping due to Pt electroreduction and the subsequent water reduction generating dihydrogen evolution during the reversal cathodic scan (right to left, the upper curves in both panels). As can be seen, the stripping peak, corresponding to the removal of Pt oxide from the electrode, shifts toward cathodic values, increasing the scan rate, but it was not lower than \(-0.1\) V vs. Ag/AgCl, even for the fastest scan rate; accordingly, \(E_{\rm i}\) was set at this potential value to assure the complete removal of the Pt oxide on the surface of the deposition electrode. Figure S2 also shows that the Pt oxide was formed in the range \(0.2\div 1\) V vs. Ag/AgCl and shifted toward more positive values, increasing the scan rate. Due to this significant dependence on the scan rate, double potential step experiments (see Figure 6) were performed; particularly, chronoamperometric curves were acquired after the application of a single potential step of potential starting from \(E_{\rm f}\) (Pt oxide formation) in the range of \(0.1\div 2\) V vs. Ag/AgCl to \(E_{\rm i}\) (oxide stripping) set at \(-0.1\) V; in this case, \(t_{2}\) was \(1\) s, and \(t_{1}\) was \(5\) s. These experiments were preferred over simple cyclic voltammograms since the conditions were more akin to the potential pulse sequence under study.