# Ru(terpy)-Based Conducting Polymer in Electrochemical Biosensing of Epinephrine
## 3 Results and Discussion
### Comparison between the Au/pRuTt/Tyr and GC/pRuTt/Tyr Biosensors  
The analogue GC/pRuTt/Tyr was prepared, and its performances were compared to Au/pRuTt/Tyr (Table 2).  
In particular, LoD values appear higher in the case of the GC-based biosensor, but comparable to (or better than) analogue devices reported in literature (Table 3).  
The recovery test results performed on 25.0 \(\upmu\)mol dm\({}^{-3}\) of EP solutions are comparable to Au/pRuTt/Tyr biosensor (Table 4). According to the decrease in recovery as the EP concentration increased, which was observed at the Au/pRuTt/Tyr device, as well as to the less satisfactory performances of the GC-based biosensor, recovery in 100 \(\upmu\)mol dm\({}^{-3}\) EP solutions is lower than 100%.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Biosensor** & **Linearity** & **LoD** & **LoQ** & & & & **Sensitivity** \\  & **[umol dm\({}^{-3}\)]** & **[umol dm\({}^{-3}\)]** & **[umol dm\({}^{-3}\)]** & **R\({}^{2}\)** & **Slope** & **Intercept** & **[A \(\upmu\)mol\({}^{-1}\) dm\({}^{-3}\) cm\({}^{-2}\)]** \\ \hline Au/pRuTt/Tyr & 1 \(\div\) 100 & 0.47 & 0.71 & 0.998 & 1.18 \(\times\) 10\({}^{-9}\) & 2.94 \(\times\) 10\({}^{-9}\) & 3.70 \(\times\) 10\({}^{-8}\) \\ GC/pRuTt/Tyr & 3.7 \(\div\) 250 & 2.45 & 3.73 & 0.997 & 1.35 \(\times\) 10\({}^{-8}\) & 1.78 \(\times\) 10\({}^{-8}\) & 1.93 \(\times\) 10\({}^{-7}\) \\ \hline \end{tabular}
\end{table}
Table 2: Analytical parameters of the calibration curves for EP determination at the Au/pRuTt/Tyr and glassy carbon (GC)/pRuTt/Tyr biosensors.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**(Bio)sensor** & **Technique** &
\begin{tabular}{c} **Linear Range** \\ **[mol dm\({}^{-3}\)]** \\ \end{tabular} & **LoD** & **Ref.** \\ \hline GCE/GQDs/Lac & CV & 1 \(\div\) 120 \(\times\) 10\({}^{-6}\) & 0.083 & [16] \\ CPE/PtNPs in BMILPF\({}_{6}\)/Lac & SWV & 9.99\(\cdot\)10\({}^{-7}\)\(\div\) 2.13 \(\times\) 10\({}^{-4}\) & 0.29 & [26] \\ CPE/MWCNT/Nafion/Tyr & DPV & 5.0 \(\div\) 500 \(\times\) 10\({}^{-6}\) & 0.3 & [22] \\ GCE/SWCNT/Tyr & CA & 10 \(\div\) 110 \(\times\) 10\({}^{-6}\) & 2.54 & [24] \\ Nanostructured Au electrode & LSV and DPV & 10 \(\div\) 150/60 \(\div\) 600 \(\times\) 10\({}^{-6}\) & 2.8/7.3 & [27] \\ MnO2/GCE/Nafion & CV and DPV & 0.03 \(\div\) 10/1 \(\div\) 100 \(\times\) 10\({}^{-6}\) & 0.005 & [28] \\ CPE/MWCNT & DPV & 0.05 \(\div\) 1/1 \(\div\) 10\(\times\) 10\({}^{-5}\) & 0.029 & [29] \\ MWCNT/EPPCE & SWV & 0.5 \(\div\) 100 \(\times\) 10\({}^{-9}\) & 0.15 \(\times\) 10\({}^{-3}\) & [30] \\ Au/pRuTt/Tyr & DPV/CA & 1 \(\div\) 100 \(\times\) 10\({}^{-6}\)/1 \(\div\) 100 \(\times\) 10\({}^{-6}\) & 0.67/0.47 & This work \\ GC/pRuTt/Tyr & DPV & 3.7 \(\div\) 250 \(\times\) 10\({}^{-6}\) & 2.45 & This work \\ \hline \end{tabular}
\end{table}
Table 3: Comparison of amperometric biosensors for determination of EP.  
The effect of interference by AA, UA, Trp, and L-cys (Figure 7) at GC-biosensors can be compared to the Au-based arrangement. In particular, at the EP:interferent ratio 1:1, the only interference in the GC-based biosensor seems to be L-cys, which causes an underestimation of 14%. Moreover, with increasing concentrations of interferents, the GC arrangement demonstrates a lower effect than that of the Au. In particular, an over- or underestimation from 0% to \(-\)20% and from +9% to \(-\)52% was observed for the EP:interferent 1:5 and 1:10 ratios, respectively, for the GC-biosensor, with ranges of +7% \(\div-\)49% and +7% \(\div-\)66% for the Au-biosensor in the same conditions.