To validate its internal chemical bonding information and more precisely confirm the existence of the partially mimicked cofactor of the peroxidase enzyme (e.g., Fe-N sites), XPS analysis with manual deconvolution was conducted (Figure -D, . Through the survey mode, 4 core elements with designated orbital (C 1s, N 1s, O1s, and Fe 2p) are specifically targeted for internal deconvoluted peaks, providing information on the chemical bonding in the OA nanozyme. From the survey with elemental quantification, the peak position of the target elements and the estimated atomic ratio were obtained (C 1s: N 1s: O 1s: Fe 2p = 55.86: 3.17 : 40.60: 0.37, respectively) (Figure ). The C 1s range (around 278 eV-287 eV, binding energy) was first targeted for chemical bonding analysis as it is associated with the core organic materials and located in the lower range of the binding energy. Among several peaks, 282. 4eV peaks are perceptible, corresponding to the C 1s peak , and 284.8 eV indicates the saturated carbon derived from PEG . From N 1s (394 eV-407 eV, binding energy), several peaks were observed: 369.3 eV indicates the Fe-N bond formed by the chelation through iron ion and the nitrogen from the alanine's coordination . The 395.8 eV corresponds to the nitrogen-metal-oxygen bond; in the case of OA, nitrogen-metal-oxygen is equivalent to nitrogen-iron-oxygen, as iron ion is the only metallic element used in OA nanozyme fabrication . These two bonds reinforce the existence of the Fe-N site, which can act as an active site to mimic POD activity. The 403.1 eV peak demonstrates the presence of oxidized N , resulting from the coordination activity or other consequences. From O 1s (524eV -532eV, binding energy), fewer internal peaks were observed compared to the previous organic compound-based nanozyme due to the lack of a hydroxyl group on the particle stabilizing polymer to promote initial chelation. Besides, a 528.3 eV peak was observed, corresponding to the O 2-ions oxidation state . From the Fe 2p (710 eV -738 eV, binding energy), several peaks were observed: 707.3 eV demonstrates the Fe 2p 3/2 peak (30), 709.