# Deposition of Cell Culture Coatings Using a Cold Plasma Deposition Method
## 3 Results
### Characterization of the Plasma Discharge
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Ferrocyanide**} & \multicolumn{2}{c}{**Ferrocene**} & \multicolumn{2}{c}{**Ruthenium**} \\  & & \multicolumn{2}{c}{**Methanol**} & \multicolumn{2}{c}{**Hexamine**} \\ \hline
**Electrode** & \(\mathbf{k^{e}/s-1}\) & **Current Normalization Factor** & \(\mathbf{k^{e}/s-1}\) & **Current Normalization Factor** & \(\mathbf{k^{e}/s-1}\) & **Current Normalization Factor** \\ \hline Bare Gold & \(1.60\pm 0.12\times 10^{-4}\) & 1.00 & \(1.23\pm 0.05\times 10^{-2}\) & 1.00 & \(9.21\pm 0.6\times 10^{-3}\) & 1.00 \\ \hline Plasma Deposited Collagen & \(4.12\pm 0.32\times 10^{-4}\) & 0.82 & \(1.15\pm 0.04\times 10^{-2}\) & 0.51 & \(7.35\pm 0.55\times 10^{-3}\) & 0.58 \\ \hline Wet Chemical Deposited Collagen & \(8.10\pm 0.60\times 10^{-6}\) & 0.80 & \(1.06\pm 0.05\times 10^{-2}\) & 0.70 & \(9.12\pm 0.7\times 10^{-3}\) & 1.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Dependence of the standard heterogeneous electron transfer rate constants, \(\mathbf{k^{e}}\), and apparent fractional area, area normalized to that of the bare electrode, on the method of collagen deposition and the identity of the electroactive probe in solution. Figure 11 illustrates voltammograms obtained at electrodes functionalized with the plasma deposited collagen film. The k\({}^{o^{\prime}}\) values for ferrocene methanol and ruthenium hexamine are within 20% of those found at the bare electrode. This result suggests that the plasma deposited collagen film does not present a significant barrier to electron transfer. However, the normalization factors are both less than unity, 0.51 and 0.58, respectively. Given that the film is negatively charged and at the charges are 0/1+ and 2+/3+ for ferrocene and ruthenium hexamine, respectively, it seems unlikely that the interfacial concentration would be lower than that found at a bare electrode. Thus, it appears that the area available for electron transfer at the plasma deposited collagen film is approximately 50-60% of the corresponding bare electrode. For ferrocyanide, the rate of electron transfer is actually higher at the plasma deposited layer, 4.12 \(\pm\) 0.32 \(\times\) 10\({}^{-4}\) s\({}^{-1}\), compared to either the bare, 1.60 \(\pm\) 0.12 \(\times\) 10\({}^{-4}\) s\({}^{-1}\), or wet chemical collagen film, 8.10 \(\pm\) 10\({}^{-6}\) s\({}^{-1}\), suggesting that the plasma deposited collagen film increases the rate of heterogeneous electron transfer perhaps by changing the reorganization energy due to changes in solvation. These effects will be more pronounced for ferrocyanide given that it undergoes an inner sphere electron transfer reaction whereas the other two probes are outer sphere. The normalization factor for the plasma deposited collagen film, 0.82, is indistinguishable from that found for the wet chemical films, 0.80. The combined results indicate that employing this plasma deposition process produced collagen films that show generally similar properties to those produced using conventional wet chemical processes in terms of their overall charge and porosity. However, the electron transfer properties of the plasma deposited films are superior to those of the wet chemical films for the negatively charged, inner sphere couple, [Fe(CN)\({}_{6}\)]\({}^{4-3-}\), where the electron transfer rate is enhanced by a factor of approximately 2.6 compared to the bare electrode. Figure 10: Cyclic voltammetry of 1 mM (**a**) ferri/ferro cyanide, (**b**) ferrocene methanol, and (**c**) ruthenium hexamine, in 0.1 M LiClO4 at a gold-coated silicon wafer electrode functionalized with a rat tail collagen film deposited using a wet chemical method. Scan rates varied from 500 to 10 mV/s. The open circles are the best fits to a semi-infinite linear diffusion-controlled model in which the adjustable variables are the standard heterogeneous electron transfer rate constant, k\({}^{o^{\prime}}\), and the fractional area (values in Table 2).