## 4 Conclusions  
Novel L-arginine-selective amperometric biosensors (ABSs) based on mushroom-derived L-arginine oxidase and metal-based nanozymes as 'artificial peroxididases' are described. Substitution of PO with PO-like mimetics in a biosensing layer improved the electrochemical properties of the electrodes and the detection of Arg in wider ranges of linear responses.  
The nCeCu, nNiPtPd, and gCuHCF, as the most effective PO mimetics, can be used as H\({}_{2}\)O\({}_{2}\)-sensitive platforms for the development of ArgO-based ABSs. These ABSs exhibit very high sensitivities and broad linear ranges to Arg when tested on real samples of pharmaceuticals and juices.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**NZ As H\({}_{2}\)O\({}_{2}\)-Sensor** & \multicolumn{2}{c}{**nCeCu**} & \multicolumn{2}{c}{**nNiPtPd**} \\ \hline Sample & C, mM & \({}^{1}\) CV, \% & C, mM & CV, \% \\ Pharmaceutical “Tivortine” & 198.7 \(\pm\) 6.22 & 3.1 & 199.5 \(\pm\) 2.12 & 1.06 \\ Commercial apple-pear juice & 7.1 \(\pm\) 0.08 & 1.1 & 7.4 \(\pm\) 0.5 & 6.8 \\ Freshly prepared apple juice & 4.99 \(\pm\) 0.001 & 0.02 & \({}^{2}\) ND & - \\ Commercial grape-apple juice & 8.71 \(\pm\) 0.43 & 4.9 & ND & - \\ Commercial multifruit juice & 6.14 \(\pm\) 0.25 & 4.1 & ND & - \\ Wine, red, dry & 3.26 \(\pm\) 0.09 & 2.8 & ND & - \\ \hline \hline \end{tabular} \({}^{1}\) CV, %—coefficient of variation, values are expressed as mean \(\pm\) SD, \({}^{2}\) ND—not determined.  
\end{table}
Table 3: Results of Arg determination (C) in the real samples using different ArgO-NZ-based biosensors.  
Figure 7: Graphical SAT method for Arg assay in the real sample of “Tivortin” using AgO/nCeCu/GE (**a**) and ArgO/nNiPtPd/GE (**b**). A, B—parameters for the linear regression; N—dilution factor; R—correlation coefficient.  
Thus, the developed mono-enzyme nanozymes-based ABSs may be used in analytical practice for fast and simple assay of Arg in beverages, pharmaceutical preparations, and other goods. An extremely high sensitivity of the proposed ArgO/nCeCu-based ABS makes it promising in clinical diagnostics for Arg determination in blood and other biological liquids.  
Conceptualization, G.G.; Methodology, G.G., N.S. and O.D.; Investigation, N.S., O.D. and L.D.; Resources, M.G. and M.N.; Data curation, G.G. and M.G.; Writing--original draft preparation, N.S., O.D. and G.G.; Writing--review and editing, G.G., M.G. and M.N.; Supervision, G.G. and M.G.; Project administration, G.G.; Funding acquisition, M.G. and M.N. All authors have read and agreed to the published version of the manuscript.  
This research was partially funded by NAS of Ukraine (The program \"Smart sensor devices of a new generation based on modern materials and technologies\"; grant \"New dual casein kinase 2 inhibitors and histone deacetylase targeted tumor chemotherapy\" for research laboratories/groups of young scientists in priority areas of science and technology in 2021-2022), by National Research Foundation of Ukraine (project 2020.02/0100 \"Development of new nanozymes as catalytic elements for enzymatic kits and chemo/biosensors\"), by the Ministry of Education and Science of Ukraine (Ukrainian-Lithuanian R&D, project 0120U103398), and by the Research Authority of the Ariel University, Israel.  
Not applicable.  
The data are presented in this study, in Appendix A and are available on request from the corresponding authors.  
We acknowledge the engineer [PERSON] for his help with SEM-XRM experiments (Institute of Cell Biology, Lviv, Ukraine).  
The authors declare no conflict of interest.