Fig. 2

Engineering the architecture and coordination environment of the Cu–DHN nanozyme via L-Cysteine (Cys) modulation. a Synthesis scheme of Cu–DHN, illustrating the role of L-Cys as a coordination terminator and size regulator. The zoomed-in region illustrates the intermolecular hydrogen bonding between L-Cys molecules. This scheme was created with BioRender.com. b Hydrodynamic size distribution profiles (n = 3), and c TEM images of Cu–DHN with varying Cu:DHN:Cys feed molar ratios, revealing a non-monotonic size trend. d Variation profiles of hydrodynamic size for different M-DHN (M = Fe, Mn, Co) nanoparticles (n = 3) demonstrating the generalizability of Cys-mediated size control. e Fourier transform infrared (FT-IR) spectra confirming the involvement of phenolic –OH and thiol –SH groups; f normalized Cu K-edge XANES spectra, g Fourier transforms of k³-weighted Cu K-edge EXAFS spectra, and h high-resolution Cu 2p XPS spectra of Cu–DHN with varying Cu:DHN:Cys molar ratios, collectively evidencing the evolution of a mixed (O, S)-coordination shell and a rising Cu⁺/Cu²⁺ ratio with increasing Cys content. i HR-TEM image and corresponding SAED pattern, and j elemental distribution mapping and corresponding line-scan profile of Cu–DHN at a Cu:DHN:Cys molar ratio of 0.6:1:0.2. k XRD patterns, and l Brunauer–Emmett–Teller (BET) N₂ adsorption–desorption isotherms demonstrating the pore structure evolution of Cu–DHN with varying Cu:DHN:Cys molar ratios, confirming the progressive surface passivation that defines the core–shell pore structure. Data are represented as mean ± SD