Nanozyme-Triggered Cascade Reactions from Cup-Shaped Nanomotors Promote Active Cellular Targeting

Abstract

Self-propelled nanomotors have shown enormous potential in biomedical applications. Herein, we report on a nanozyme-powered cup-shaped nanomotor for active cellular targeting and synergistic photodynamic/thermal therapy under near-infrared (NIR) laser irradiation. The nanomotor is constructed by the asymmetric decoration of platinum nanoparticles (PtNPs) at the bottom of gold nanocups (GNCs). PtNPs with robust peroxidase- (POD-) like activity are employed not only as propelling elements for nanomotors but also as continuous O₂ generators to promote photodynamic therapy via catalyzing endogenous H₂O₂ decomposition. Owing to the Janus structure, asymmetric propulsion force is generated to trigger the short-ranged directional diffusion, facilitating broader diffusion areas and more efficient cellular searching and uptake. This cascade strategy combines key capabilities, i.e., endogenous substrate-based self-propulsion, active cellular targeting, and enhanced dual-modal therapy, in one multifunctional nanomotor, which is crucial in advancing self-propelled nanomotors towards eventual therapeutic agents.

Figure 1

Schematic illustration of the nanozyme-powered GNCs-Pt-ICG/Tf nanomotor for enhanced dual-modal phototherapy upon NIR laser irradiation via a cascaded strategy consisting of the catalytic and photodynamic reactions.

Figure 2

The preparation and characterization of GNCs-Pt. (a) Schematic representation of the preparation of GNCs-Pt. (b) UV-vis spectra of GNCs (red) and GNCs-Pt (green). Dark-field optical microscopic (c), SEM (d), and TEM (e) images of GNCs-Pt. (f) HAADF-STEM images and corresponding elemental maps of GNCs-Pt. (g) Size distribution of GNCs (red, 149 ± 16 nm) and GNCs-Pt (green, 154 ± 11 nm) determined by SEM images (based on 150 particles). Data are represented as mean ± SD. (h) Single-particle scattering spectra of GNCs (red) and GNCs-Pt (green). The gray line is the fitted curve based on Gaussian function. (i) The polarization-dependent scattering response (green circles) from a single GNC-Pt as a function of the angle relative to the optical axis of the polarizer. (j) Zeta potential of hexadecyl trimethyl ammonium bromide (CTAB) stabilized PbS NPs (blue, 48.9 ± 1.1 mV), GNCs (red, 35.8 ± 0.1 mV), and GNCs-Pt (green, 55.4 ± 0.3 mV). Inset: schematic diagrams of corresponding nanomaterials.

Figure 3

The POD-like activity of GNCs-Pt. (a) Schematic illustration of the POD-like activity of GNCs-Pt with TMB as the substrate. (b) Optical images of the oxTMB produced under different catalytic conditions for 30 min. (I) TMB + H₂O₂, (II) GNCs - Pt + H₂O₂ + TMB, (III) GNCs - Pt +TMB, (IV) GNCs + H₂O₂ + TMB, (V) GNCs + TMB. (c) The TMB oxidation reactions in GNCs or GNCs-Pt solutions with and without H₂O₂ (1%) in the disodium hydrogen phosphate-citric acid buffer (0.1 M, pH 3.0). [GNCs‐Pt] = 0.27 mg/mL, [GNCs] = 0.27 mg/mL, [TMB] = 1.0 mM. (d) and (e) Effects of the concentrations of GNCs-Pt and H₂O₂ on the POD-like activity.

Figure 4

Enhanced diffusion of GNCs-Pt in long term with different H₂O₂ concentrations (0, 1, 2, 3, 5, and 10%). (a) Illustration of the self-electrophoresis of a GNC-Pt via catalyzing the decomposition of H₂O₂. A gradient of electric charge density will be generated across the GNC-Pt as reaction proceeds. Electroosmotic flow induced by the charge imbalance will then drive GNCs-Pt to move in the direction opposite to that of the fluid flow (red arrow). (b) Trajectories (for 10 s), (c) instantaneous velocity, and (d) EA-TA-MSD of GNCs-Pt at different H₂O₂ concentrations. (e) Dependence of D_e of GNCs-Pt with different H₂O₂ concentrations. (f) The distributions of D_e of GNCs-Pt with different H₂O₂ concentrations. The dashed lines are the fitted curve based on Gaussian function.

Figure 5

The temporal heterogeneity of diffusion behaviors of GNCs-Pt in the absence or presence of H₂O₂ (10%). (a) Trajectories of GNCs-Pt with the color-coded speed during 10 s. The color bar from purple to deep red represents the speed from 0 to 20 μm/s. (b) The distributions of diffusion modes including subdiffusion, Brownian motion (BW), and superdiffusion. (c) The distributions of D_e of GNCs-Pt by a moving time-window method (1 s).

Figure 6

The ROS generation and photothermal properties of GNCs-Pt-ICG/Tf. (a) Schematic illustration of the mechanism of GNCs-Pt-ICG/Tf for synergistic PDT/PTT upon NIR laser irradiation via a cascade reaction. (b)–(d) The ROS generation ability of GNCs-Pt-ICG/Tf with SOSG as an indicator. (b) GNCs-Pt-ICG/Tf in the presence of H₂O₂ (1%) with and without 808 nm laser. (c) GNCs-Pt-ICG/Tf in the absence of H₂O₂ with and without 808 nm laser. (d) GNCs-Pt-ICG/Tf and free ICG in different conditions. [nanomaterials] = 270 μg/mL; [ICG] = 9.05 μM; laser: 808 nm, 2 W/cm². (e)–(g) Photothermal properties of GNCs-Pt-ICG/Tf and GNCs-ICG/Tf. (e) Temperature evaluation of GNCs-Pt-ICG/Tf, GNCs-ICG/Tf, PBS, and deionized water with 808 nm laser irradiation for different times. (f) A plot of −lnθ versus time obtained from the cooling period for 15 min. (g) The photostability of GNCs-Pt-ICG/Tf and GNCs-ICG/Tf in PBS with 808 nm laser on and off for five cycles. [nanomaterials] = 137 μg/mL; PBS: 10 mM, pH = 7.4; laser: 808 nm, 2 W/cm².

Figure 7

Cytotoxicity and antitumor efficacy of GNCs-Pt-ICG/Tf in vitro. (a) HepG2 cell viability incubated with GNCs-Pt-ICG/Tf of various concentrations (0, 1, 5, 10, 25, and 50 μg/mL) for 24 h. Error bars represent the mean ± SD (n = 5). (b) The effects of PtNPs and Tf/ICG modification on the cellular uptake efficiency of GNCs-Pt-ICG/Tf. Inset: schematic diagrams of the corresponding nanomaterials. (c) The cellular uptake capability of (i) GNCs-Pt-ICG/Tf, (ii) GNCs-Pt-ICG, (iii) GNCs-ICG/Tf, and (iv) GNCs-ICG for HepG2 cells and (v) GNCs-Pt-ICG/Tf and (vi) GNCs-Pt-ICG for NCTC1469 cells, respectively. Confocal laser scanning microscopy (CLSM) images (d) and corresponding cell mortality (e) of HepG2 cells treated with (I) culture medium, (II) GNCs-Pt-ICG/Tf+laser, (III) GNCs-Pt-ICG/Tf (in dark), (IV) GNCs-Pt-Tf+laser, (V) free ICG+laser, and (VI) GNCs-ICG/Tf+laser, respectively. Scale bar: 50 μm. (f) CLSM images of HepG2 cells cocultured with GNCs-Pt-ICG/Tf at the edge of laser irradiation. Scale bar: 100 μm. [nanomaterials] = 50 μg/mL; [ICG] = 1.68 μM; Laser: 808 nm, 2 W/cm².