## 3 Results and Discussion
### Potentiodynamic Deposition
Unlike the previous EQCM experiments (see Figure 5), after the application of the optimized potential pulse sequence at the deposition electrode, the frequency change abruptly varied in less than 1 min, reaching a plateau in less than 5 min: this feature suggested quick protein deposition of the layer, which, after a few minutes, quickly stopped growing, as confirmed via a visual inspection. Even if the growth rate was much greater (roughly \(10^{-6}\) g/min) than that observed for the galvanodynamic deposition technique, the amount of the deposit formed at the plateau was significantly lower, estimated to be about 3.3 ug, with the deposit requiring less than 5 min to be formed. While a fast growth rate is surely desirable, unfortunately, it seems the growth of the proteic layer cannot be changed so that higher amounts are obtained. The reasons for this undesirable behavior are unknown: a severe ohmic drop due to the presence of a compact proteic layer, significantly reducing the electrical field around the electrode, may be tentatively suggested; even if a similar deposit is expected when employing the galvanodynamic approach, on the contrary, there, the increase in potential, as previously evidenced in this technique, should maintain an adequate electrical field to continue promoting satisfactory electrophoresis of proteins towards the electrode. Finally, a further frequency change was observed after stopping the potential pulse application (see Figure 8), wherein the growth of the deposit somewhat continued even in the absence of any electrophoretic movement of the proteins. Anyway, this last frequency change, which was significantly lower, exhibited a slower rate and reached a plateau after a few minutes. Notably, this peculiar feature disappeared completely if the potential pulse sequence application was protracted for more than 30 min, even if a plateau had  
Figure 8: Resonance frequency change at the deposition electrode during the application of the potentiodynamic current pulse sequence optimized in this study. Arrows labeled _start_ and _stop_ represent the timing of potential pulse application at the electrode. already been reached a while ago. This last piece of evidence suggested the chemical (as opposed to electrophoretic) nature of this frequency change: it is probable that the co-crosslinking kinetics were less intense than the electrophoretic kinetics, so the frequency change observed after the stop time in Figure 8 was due to residual co-crosslinking still acting after the end of the electrophoretic movement of the proteins. This feature was not evident in the galvanodynamic deposition approaches since the EPD growth was slower and the co-crosslinking was not limiting. Even if the potentiodynamic approach apparently permitted the quick formation of a proteic deposit of a well-defined mass and thickness, which cannot induce further growth, the preliminary experiments showed that thicker deposits can be grown by varying some electrical parameters, like \(E_{\text{f}}\), instead of increasing the deposition time. In this context, further experiments are ongoing in our laboratory.