Synergistic ROS Generation via Core-Shell Nanostructures with Increased Lattice Microstrain Combined with Single-Atom Catalysis for Enhanced Tumor Suppression

Abstract

This study emphasizes the innovative application of FePt and Cu core-shell nanostructures with increased lattice microstrain, coupled with Au single-atom catalysis, in significantly enhancing ^•OH generation for catalytic tumor therapy. The combination of core-shell with increased lattice microstrain and single-atom structures introduces an unexpected boost in hydroxyl radical (^•OH) production, representing a pivotal advancement in strategies for enhancing reactive oxygen species. The creation of a core-shell structure, FePt@Cu, showcases a synergistic effect in ^•OH generation that surpasses the combined effects of FePt and Cu individually. Incorporating atomic Au with FePt@Cu/Au further enhances ^•OH production. Both FePt@Cu and FePt@Cu/Au structures boost the O₂ → H₂O₂ → ^•OH reaction pathway and catalyze Fenton-like reactions. This enhancement is underpinned by DFT theoretical calculations revealing a reduced O₂ adsorption energy and energy barrier, facilitated by lattice mismatch and the unique catalytic activity of single-atom Au. Notably, the FePt@Cu/Au structure demonstrates remarkable efficacy in tumor suppression and exhibits biodegradable properties, allowing for rapid excretion from the body. This dual attribute underscores its potential as a highly effective and safe cancer therapeutic agent.

Keywords: Fenton-like reaction; chemodynamic therapy; core−shell effect; single-atom catalyst; strain effect.

Figure 1

Characterization of nanoparticles. (a) TEM images of FePt nanocubes. (b) HR-TEM image of FePt nanocubes. (c) TEM image of FePt@Cu nanocubes. (d) TEM images of FePt@Cu/Au nanocubes. (e) HRTEM image of FePt@Cu/Au, the lattice space correlates to the Cu(111) phase and the blue circle indicates FePt nanocube. (f) TEM image of compared Cu nanocubes. (g) XRD results of FePt, Cu, Cu₂O, FePt@Cu, and FePt@Cu/Au. (h) Pt L₃_edge XANES spectra of FePt@Cu/Au, FePt@Cu and Pt foil. (i) Cu K_edge XANES spectra of FePt@Cu/Au, Cu nanoparticles, Cu foil, and cuprous oxides. (j) Au L₃_edge XANES spectra of FePt@ Cu/Au and Au foil.

Figure 2

Synergetic self-supply of H₂O₂ and ^•OH generation from FePt@Au/Cu. (a) HAADF-STEM image showing the single-atom property of FePt@Cu/Au nanocube. (b) FT-EXAFS spectra of Au L₃_edge for FePt@Cu/Au and Au foil. (c) FT-EXAFS spectra of Cu K_edge for FePt@Cu/Au and Cu foils. All data were obtained in triplicate. (d) Quantification of H₂O₂ generation using H₂O₂ kits. (e) H₂O₂ generation efficiency at different concentrations under normal and anaerobic conditions. (f) ^•OH efficiency at different pH levels (5 and 7) detected by TPA fluorescence intensity. (g) The 1:2:2:1 amplitude with quartet ESR signals of DMPO–OH associated with ^•OH from FePt, Cu, FePt@Cu, and FePt@Cu/Au nanocubes. (h) HRTEM image of the edge of FePt@Cu nanocube; blue dots represent surface alignment, indicating a rough surface. (i) HRTEM image of the edge of Cu nanocube; blue dots represent surface alignment, indicating a smooth surface. (j) BET results showing the surface area of core–shell FePt@Cu and Cu nanocubes. (k) Voigt fit by XRD; the slope indicates the strain of the crystal (the p-values calculated by one-way ANOVA: *p < 0.05, **p < 0.01, ns: no significance).

Figure 3

DFT calculations. (a) O₂ adsorption energy, strain %, lattice length, and model of pure Cu(111) and FePt@Cu(111) surfaces. (b) Calculated potential energy profile of H₂O₂ production on pure Cu(111) surface. (c) Calculated potential energy profile of H₂O₂ production on FePt@Cu(111) surface. (d) Calculated potential energy profile of H₂O₂ production on FePt@Cu/Au(111) surface.

Figure 4

Stability and self-decomposition behavior in FePt@Cu/Au and FePt@ Cu/Au@SA under different conditions (H₂O, PBS at pH = 7 and 5). (a) TEM images reveal that the FePt@Cu/Au nanocubes started to decompose immediately in PBS. (b) ICP quantized results indicate that over 85% of elements (Cu, Pt, and Fe) were dissolved after 1-day storage in PBS (pH 7). (c, d) The XPS spectrum of FePt@Cu/Au nanocubes given Cu⁰ and Cu²⁺ signals under PBS condition (pH 7) as a function of day (2p_3/2 assigned as 932 eV for Cu⁰ and assigned as 934 eV for Cu²⁺). (e) TEM image of the FePt@Cu/Au@SA nanocubes. (f, g) Quantitative analysis of H₂O₂ and ^•OH generation in FePt@Cu/Au@SA nanocubes. The suppression of H₂O₂ and ^•OH orignates from the SA modification. All data were obtained in triplicate (the p-values calculated by one-way ANOVA: *p < 0.05, **p < 0.01, ns: no significance).

Figure 5

In vitro studies of SA coating nanocubes. (a) Cytotoxicity analysis of HepG2 cancer cells treated with Cu@SA, FePt@Cu@SA, and FePt@Cu/Au@SA nanocubes for 24 h incubation. (b) Flow cytometry analysis of HepG2 cancer cells treated with different nanocubes. (c) Live (green color) and dead cells (red color) stained with fluorescent green dye (Calein-AM) and red dye (propidium iodide), respectively, for cancer cells treated with different nanocubes. (d) Cu⁺ release stained by CopperGreen dye treated with different nanocubes showing green color as Cu⁺ releasing. (e) H₂O₂ generation stained by hydrogen peroxide assay kit treated with different nanocubes showing green color as H₂O₂ generated. (f) ^•OH generation stained by APF dye treated with different nanocubes showing green color as ^•OH generated.

Figure 6

Antitumor efficacy of FePt@Cu/Au@SA in orthotopic hepatocellular carcinoma model (n = 4). (a) Biodistribution determined by Cu concentration collected from FePt@Cu/Au@SA nanocubes through intravenous injection. (b) Monitoring the orthotopic tumor growth of HepG2-Red-FLuc cells in NOD-SCID mice treated with PBS, FePt@SA, Cu@SA, FePt@Cu@SA, and FePt@Cu/Au@SA using the IVIS system. (c) Evaluation of IVIS bioluminescence of livers with hepatocellular carcinoma in each treatment group after sacrificing the mice. (d) Assessment of the morphology of hepatocellular carcinoma in each treated mouse through hematoxylin and eosin staining (Scale bar, 1 mm). The tumor area is highlighted by the yellow circle with T labeling. (e) Investigation of the expression of phospho-histone H2A.X (Ser139) and (f) cleaved caspase-3 (Asp175) within hepatocellular carcinoma from mice in each treatment group using IHC staining (Scale bar, 100 μm). The p-value was calculated by one-way ANOVA (*p < 0.05, **p < 0.01, ***p < 0.001).