# Peroxidase-Like Metal-Based Nanozymes: Synthesis, Catalytic Properties, and Analytical Application
## 3 Results and Discussion
### Characterization of the Most Effective Cu/Ce\({}^{5}\)-Modified Electrode  
The Cu/Ce\({}^{5}\)-NZ with the highest PO-like activity was studied in detail. The Cu/Ce\({}^{5}\)/GE demonstrated the highest PO-like activity, compared with other NZs and with natural PO (Figure S2, Tables 3 and 4). The highest current response (\(I_{max}\)) on the tested analyte at substrate saturation of the Cu/Ce\({}^{5}\)/GE was 157-fold higher, and its sensitivity was 5.4-fold higher, than that of the PO/GE (Table 3). It is worth mentioning that Cu/Ce\({}^{5}\) has PO-like ability but lacks oxidase (lactase)-like properties. This conclusion was reached from the results of colorimetric tests using \(o\)-dianisidine in the presence of H\({}_{2}\)O\({}_{2}\) as a substrate for PO, and with \(o\)-dianisidine only as a substrate for oxidase (see Section 2.4). The Cu/Ce\({}^{5}\) specificity to H\({}_{2}\)O\({}_{2}\) is the important valuable characteristic for applying it as a selective PO-mimetic element in sensors and oxidase-based biosensors. Figure 3 shows the effect of quantity on the NZ immobilized on the GE surface, based on the amperometric signal as a response to H\({}_{2}\)O\({}_{2}\) addition. Table 4 presents comparative analytical characteristics of the recently developed metallic NZ-based sensors for H\({}_{2}\)O\({}_{2}\) analysis, including the results described here.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Electrode** & **PO Mimetic** & **Potential, mV** & \
\begin{tabular}{c} **Sensitivity,** \\ **A M\({}^{-1}\) m\({}^{-2}\)** \\ \end{tabular} &
\begin{tabular}{c} **Linear Range,** \\ **uM** \\ \end{tabular} & **Ref.** \\ \hline \({}^{1}\) GCE & Cu\({}_{2}\)O/PANI/rGhO & \(-200\) & 394 & 0.8–12,780 & [45] \\ GCE & Fe\({}_{3}\)O\({}_{4}\)/3D GNCs & \(-200\) & 2742 & 0.8–330 & [46] \\ GCE & Ni–Fe PBA-4 HNCs & \(-50\) & 361 & 0.1–20,000 & [47] \\  & PB/BG & \(-50\) & 2852 & 4–830 & [48] \\  & AuNPs-PB/BG & 11,243 & 9.2–8100 & [48] \\ \({}^{2}\) DBD & PB & 2100 & & \\ DBD & Ni-FePBA & \(-50\) & 1500 & 0.5–1000 & [11] \\ GE & PB/NZ & 4500 & & \\ GCE & MnPBA & 1472 & 3–8610 & [49] \\ GCE & rGhO/Pt-Ag & \(-50\) & 6996 & 5–1500 & [50] \\ GCE & Ni-PB & \(-50\) & 3500 & 0.1–1000 & [51] \\  & Ni-FePBA & 1130 & 2–1000 & [52] \\ Graphite paste & Cu-FePBA & \(-50\) & 2030 & 0.5–1000 & [52] \\ \({}^{3}\) GE & PtRu & \(-50\) & 194 & 17–25,000 & [41] \\  & gCuHCF & 1620 & 16–4100 & \\ GE & gFeHCF & \(-50\) & 1090 & 116–14,300 & [42] \\  & PO & 352 & 15–20,000 & \\ GCE & Ni-FePBA & 0 & 18,000 & up to 100 & [53] \\ GCE & PNAANI–PB & 0 & 5073 & 1–1000 & [54] \\ GCE & PB & 50 & 6000 & 0.1–100 & [55] \\ GCE & Fe/rGhO-Pt & 100 & 3400 & 7.5–4270 & [56] \\ GCE & PB & 180 & 10,000/20,000 & 1–5000 & [57] \\  & Cu/Ce\({}^{5}\) & 1890 & 1.5–20,000 & \\  & Au/Cu & \(-50\) & 793 & 17–15,000 & \\ GE & Fe/Ce & - & 1372 & up to 1000 & This paper \\ \hline \hline \end{tabular} \({}^{1}\) GCE—glassy carbon electrode; \({}^{2}\) DBD—diamond boron-doped; \({}^{3}\) GE—graphite electrode; \({}^{4}\) HNCs—hollow nanocubes.  
\end{table}
Table 4: The main operational characteristics of the recently described H\({}_{2}\)O\({}_{2}\)-sensitive metallic NZ-based sensors working at low potentials.