## 3 Results and Discussion  
### Amperometric Characteristics of the PO-Like NZs/GE  
In our previous works, different types of PO-like NZs were described: a chemically synthesized NZs [46] and a 'green' synthesized one [47]. The most effective electroactive NZs, nCeCu, and gCuHCF, were chosen for further study. These and the newly obtained promising artificial PO, nNiPtPd, were characterized by Scanning electron microscopy (SEM) coupled with X-ray microanalysis (SEM-XRM) and were used here as potential platforms for construction of Arg-sensitive ArgO-based ABSs. SEM provided information on the size, distribution, and shape of the tested sample. Figures 13-13 present the overall morphology of the formed hybrid particles, namely, nCeCu, nNiPtPd, and gCuHCF, respectively. The XRM images of the synthesized NZs showed the characteristic peaks for metals of the composites. The amperometric characteristics of the nCeCu/GE and nNiPtPd/GE as effective chemosensors for H\({}_{2}\)O\({}_{2}\) determination were studied (Figures 1 and 2, respectively). The cyclic voltammograms (CV) for the nCeCu/GE (Figure 1a) and for the nNiPtPd/GE (Figure 2a) demonstrated that cathodic reduction peaks contributed from H\({}_{2}\)O\({}_{2}\) decomposition arose at potentials of approximately \(-50\) mV and \(-200\) mV, respectively (vs. Ag/AgCl). The chronamperometric dependences and calibration graphs for H\({}_{2}\)O\({}_{2}\) determination are shown in Figures 1 and 2b-d, respectively. As a control, unmodified GE was tested, and no signal was detected upon H\({}_{2}\)O\({}_{2}\) addition (data not shown). Figure 1: Amperometric characteristics of nCeCu/GE: (**a**) Cyclic voltammograms as current responses upon addition of H\({}_{2}\)O\({}_{2}\) up to concentrations: (1) 0 mM (black), (2) 2.5 mM (red); (3) 5.0 mM (blue); (4) 10 mM (green); (**b**,**c**) chronamperometric response and dependence of amperometric signal on concentration of H\({}_{2}\)O\({}_{2}\), respectively; (**d**) calibration graph for H\({}_{2}\)O\({}_{2}\) determination. Conditions: Ag/AgCl (reference electrode) in 50 mM phosphate buffer, pH 7.0; scan rate 50 mV\(\cdot\)s\({}^{-1}\) (**a**); working potential \(-\)50 mV (**b–d**). A and B are parameters of a linear regression: Y = A + BX, and R is a correlation coefficient. The analytical characteristics of the developed amperometric NZ-based chemosensors for H\({}_{2}\)O\({}_{2}\) are summarized in Table 1. It is worth mentioning that the apparent value of the Michaelis-Menten constant (\(K_{M}\)\({}^{app}\)) represents the analyte concentration yielding an amperometric response equal to half of its maximum value (\(I_{max}\)). Sensitivity of an amperometric electrode is usually calculated from the linearity graph as a ratio of slope (B) to the active surface area of the working electrode. Sensitivity data are expressed in standard SI units, A\(\cdot\)M\({}^{-1}\cdot\)m\({}^{-2}\). This parameter, contrary to Imax, does not depend on the electrode area; it characterizes the specific activity of the electrode. The limit of detection (LOD) of a (bio)sensor is the triplicated standard deviation value of blank samples divided by the slope of the calibration graph. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**PO-like NZ**} & **Sensitivity,** & **Linear Range,** & **LOD, \(\mu\)M** & **\(I_{max}\), \(\mu\)A** & \(K_{M}\)\({}^{app}\), \(mM\)** & **Reference** \\  & **A\(\cdot\)M\({}^{-1}\cdot\)m\({}^{-2}\)** & **Up to, mM** & & **LOD, \(\mu\)M** & **\(I_{max}\), \(\mu\)A** & \(K_{M}\)\({}^{app}\), \(mM\)** & **Reference** \\ \hline nCeCu & 2164 \(\pm\) 70 & 1.5 & 0.5 & 172.6 \(\pm\) 1.1 & 9.0 \(\pm\) 0.05 & Current work \\ nNiPtPd & 13250 \(\pm\) 150 & 1.0 & 5 & 374 \(\pm\) 20 & 2.6 \(\pm\) 0.24 & Current work \\ gCuHCF & 1620 & 0.8 & 10 & 138.0 \(\pm\) 8.5 & 31.0 \(\pm\) 4.4 & [47] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Analytical characteristics of the PO-like NZ/GE as a chemosensor for H\({}_{2}\)O\({}_{2}\).