Interfacial Engineering of Pillararene‐Modified Ceria Nanoparticles for Regulable Enhanced Sonodynamic Therapy

Abstract

ABSTRACT

Sonodynamic therapy (SDT) has emerged as an advanced technology for treatment of malignant tumors. Many organic and inorganic sonosensitizers have been reported but they still have the respective limitations. Constructing the materials to integrate the superiorities of organic and inorganic sonosensitizers is expected to be a good method to enhance the efficiency of SDT. Herein, we report an intelligent sonosensitizer (TPA–OS⊂CP5@CeO_x), integrating the organic (TPA–OS) and inorganic sonosensitizers (CP5@CeO_x) via host–guest interaction. The modification of carboxyl‐pillar[5]arene (CP5) on CeO_x constructs the supramolecular interface by coupling of CP5 and oxygen vacancies. The band gap of CeO_x is reduced and the ratio of Ce⁴⁺/Ce³⁺ is increased to regulate tumor microenvironment. Thus, the SDT performance of CP5@CeO_x can be improved. Furthermore, the synergistic effect of TPA–OS with aggregation‐induced emission can further regulate and enhance the SDT efficiency. The cellular experiments demonstrate that TPA–OS⊂CP5@CeO_x exhibits the synergistic therapeutic effect in double organelle of lysosome and mitochondria. The in vivo experiments suggest TPA–OS⊂CP5@CeO_x has imaging‐guided enhanced SDT performance to achieve tumor inhibition. This study contributes to the construction of novel intelligent sonosensitizers, indicating that supramolecular interface engineering is promising to realize the customized treatments with minimal side effects.

Introduction

Malignant tumor is one of the major diseases that seriously threaten human health [1]. Currently, the most prevalent treatments encompass surgical intervention, chemotherapy, and radiotherapy. Despite their extensive utilization in clinical settings, these treatments still exhibit certain limitations such as grievous invasiveness and nonspecific targeting [2]. Photodynamic therapy and photothermal therapy have been extensively investigated due to the advantages of real-time in situ, high sensitivity, and minimal invasiveness [3–6]. However, they are still limited by the low penetration. Recently, sonodynamic therapy (SDT) has come to the vision as one of the promising methods for cancer therapy by activating sonosensitizers to generate radical oxygen species (ROS) under low-intensity ultrasound (US). SDT has the features of noninvasiveness, low side effects, as well as the high tissue penetration [7]. Since sonosensitizers play a crucial role in SDT, large amounts of sonosensitizers have also been reported, including organic sonosensitizers of porphyrins, chlorin e6, rose Bengal, and inorganic sonosensitizers of TiO₂, MnO₂, MoS₂, and so on. Organic sonosensitizers have more efficient therapeutic effects but suffer from poor solubility and chemical stability in blood circulation [8–10]. Though inorganic sonosensitizers have good stability and long-time tumor retention, they always exhibit lower efficiency [11–13].

Considering the respective properties of organic and inorganic sonosensitizers, various strategies have been developed to enhance the efficiency of SDT. For instance, organic sonosensitizers were encapsulated or self-assembled with typical inorganic materials to improve the stability in blood circulation [14–16]. The efficiency of inorganic sonosensitizers was enhanced by defect introduction, heterostructure fabrication, metal doping, and single-atom incorporation [17–20]. Since ROS generation is the most important factor for SDT, decreasing ROS scavenging and enhancing ROS production are two principal objectives to promote the SDT efficiency. Novel “intelligent” sonosensitizers with excellent SDT performance, that is, possessing the large ROS generation, properties of targeting, environmental responsiveness, and enzymatic properties, have been widely employed. One of the strategies is using the tumor microenvironment (TME) to achieve ROS regulation [21]. TME has the acidic environment, hypoxia, high concentration of glutathione (GSH) (10 × 10⁻³ M), and overproduction of H₂O₂ (100 × 10⁻⁶ M) [22], which would restrict the production of oxygen-dependent ROS and lead to tumor proliferation. The novel intelligent sonosensitizers can enhance the SDT efficacy by adapt to TME. For example, CeO_x nanoparticle is an N-type semiconductor with reversible conversion of states, which exhibits “enzyme” characteristic to regulate TME [23, 24]. Upon the valence change of Ce³⁺ and Ce⁴⁺, CeO_x nanoparticles have the activities of catalase (CAT) and superoxide dismutase, which can react with H₂O₂ to generate O₂ and to eliminate superoxide anions in biosystems, respectively [25–27]. Thus, CeO_x nanoparticle is expected to be a good candidate to construct intelligent sonosensitizer. The ROS generation of CeO_x nanoparticle triggered by US is really low due to the rapid electron–hole recombination and wide band gap. TME-regulated strategy still has its limitation due to the complex environment. The intelligent regulation achieved by the materials themselves is more conducive to precisely enhance and regulate SDT, which is still in its infancy.

Interfacial engineering strategy is commonly utilized to change physical and/or chemical properties of nanomaterials by inducing the redistribution of interfacial electrons [28]. Exploring the interface effect of the organic–inorganic hybrid materials is significant for catalysis, electronics, photovoltaics, and biomedical science. The modification of different organic ligands on the surface can largely influence their properties by producing rich high-valent metal active substances [29^–31]. Typically, pillar[n]arene, as a class of supramolecular macrocycles with symmetrical structures and electron-rich cavities [32], have been used as ideal organic ligands to construct intelligent materials by modifying on nanoparticles such as Au [33], Ag [34], CuS nanoparticles [35], Fe₃O₄ [36], upconversion [37], and mesoporous silica nanoparticles [38]. They are widely applied in molecular recognition, catalysis, drug delivery, nanotheranostics, and so on [39]. We envisage that the interfacial effect of modified-pillar[n]arenes will largely regulate the properties of inorganic materials due to the electron-rich and rigid cavities.

Herein, we design and construct an intelligent sonosensitizer, that is, TPA–OS⊂CP5@CeO_x, consisting of the organic and inorganic sonosensitizers via host–guest interaction (Figure 1). The supramolecular organic–inorganic interface of CP5@CeO_x is formed by modifying carboxyl-pillar[5]arene (CP5) on CeO_x. CP5 coupled with oxygen vacancies (V_O) of CeO_x can stabilize the vacancies by compensating the coordination number, which reduces the band gap of CeO_x and promotes the separation of electron–hole pairs. Thus, the efficiency of SDT can be enhanced. Additionally, the modified CP5 can accelerate the adsorption of H₂O and activate its oxidation to generate •OH with cytotoxicity. Furthermore, the CAT activity and GSH deletion of CeO_x are enhanced because the ratio of Ce⁴⁺/Ce³⁺ is increased after CP5 coupled with V_O, which can regulate the TME by relieving the tumor hypoxia and weakening the reducibility. Benefiting from the noncovalent interaction between TPA–OS and CP5, the acidic environment in lysosome can induce the release of TPA–OS to target mitochondria. TPA–OS with aggregation-induced emission (AIE) can be used as not only the near-infrared (NIR) imaging agent but also the organic sonosensitizer. Thus, TPA–OS⊂CP5@CeO_x exhibit the imaging-guided therapeutic effects in both lysosome and mitochondria. The SDT efficiency of TPA–OS⊂CP5@CeO_x can be regulated and enhanced by two approaches of synergistic effects from organic–inorganic sonosensitizers and double organelle activities. In this study, supramolecular interface engineering was used to efficiently regulate and enhance the SDT performance by adjusting the V_O and ratio of Ce³⁺/Ce⁴⁺, which paves a promising strategy to construct the organic–inorganic hybrid sonosensitizers with enhanced performance for tumor suppression.

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Results and Discussion

Synthesis and Characterization

An organic sonosensitizer with AIE feature was successfully synthesized and systematically characterized by ¹H NMR, ¹³C NMR, and mass spectrum (Figures S1–S10). CP5 was synthesized according to the previous literature (Figures S11 and S12). The detail in the synthetic route of TPA–OS⊂CP5@CeO_x is presented in Figure 2a. First, CeO_x nanoparticles were synthesized via a solvothermal approach in glycol. CP5 was modified on CeO_x via the approach of ligand exchange to prepare CP5@CeO_x. Subsequently, AIE-active TPA–OS was hybridized onto the surface of CP5@CeO_x via the host–guest interaction between CP5 and TPA–OS to construct supramolecular hybrid nanomaterials (TPA–OS⊂CP5@CeO_x). Moreover, the binding constant of TPA–OS⊂CP5 was determined to be (1.78 ± 0.5) × 10⁵ M⁻¹ by isothermal titration calorimetry (ITC), indicating the strong host–guest binding affinity between TPA–OS and CP5 (Figure S13).

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The morphologies of CeO_x, CP5@CeO_x, and TPA–OS⊂CP5@CeO_x were shown by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM) images (Figures 2b–d,f and S14–S17). TPA–OS⊂CP5@CeO_x possessed a uniform spherical morphology with the diameter of 85 nm and a narrow size distribution, which were in general consistent with that of CeO_x and CP5@CeO_x. Homogeneous distribution of Ce, O, and N in TPA–OS⊂CP5@CeO_x was observed by the element mapping results, indicating the successful anchoring of TPA–OS⊂CP5. TPA–OS⊂CP5@CeO_x showed an ordered fringe pattern with a lattice spacing of 0.32 nm, corresponding to the (1 1 1) plane of CeO_x (Figure 2f). The high-angle annular dark field aberration corrected scanning TEM (HAADF–STEM) image further confirmed the fine structure of TPA–OS⊂CP5@CeO_x (Figure 2g,h). Typically, Z-contrast analysis revealed the main interplanar spacing of area A and B in Figure 2g was about 3.2 Å (Figure S18). The corresponding crystal structure of CeO_x unit in TPA–OS⊂CP5@CeO_x through the [0 0 1] orientation was also observed as shown in the fast Fourier transform (FFT) image (Figure 2i). HRTEM lattice images (Figure S19) testified the existence of lattice distortion and surface strains. In addition, according to the corresponding strain mapping measured by geometric phase analysis (Figures 2e and S20), the degree of surface strain in CeO_x was increased after the modification of CP5. The results were demonstrated that the carboxylic acid rim of CP5 dissolved Ce on the surface, indicating the coordinated adsorption between CP5 and CeO_x surface [40]. As shown in the powder X-ray diffraction (PXRD) patterns (Figure 2j), except the main diffraction peaks of CeO_x, no other peaks were observed in CeO_x, CP5@CeO_x, and TPA–OS⊂CP5@CeO_x, indicating the introduction of CP5 and TPA–OS did not change the structural integrity of CeO_x. All of above characterization suggested that the modification of CP5 and encapsulation of TPA–OS had negligible influence on the phase, morphology, and exposed facet.

The modification of CP5 and encapsulation of TPA–OS was fully characterized. As shown in FT-IR spectra (Figure 2k), the peaks at 1502 and 1205 cm⁻¹ observed in CP5@CeO_x were ascribed to the benzene skeleton stretching of CP5, indicating the successful modification. The peak at 1733 cm⁻¹ corresponding to the C═O of CP5 completely disappeared because of the formation of carboxyl–Ce coordinated bonds in CP5@CeO_x. As shown in Raman spectra (Figure 2l), a major peak at 445 cm⁻¹ was observed in CeO_x, corresponding to the F_2g vibration pattern of Ce─O bond [41]. This peak underwent blue shift in CP5@CeO_x and TPA–OS⊂CP5@CeO_x, resulting from the enhanced Ce─O bond after coordination. Moreover, to further confirm the successful synthesis of material, the zeta potentials of CeO_x, CP5@CeO_x, and TPA–OS⊂CP5@CeO_x were measured to be 10.4, −30.7, and −18.7 mV (Figure 2m), respectively. Compared with CeO_x, the decreased zeta potential of CP5@CeO_x resulted from the modification of negative-charged CP5. The zeta potential of TPA–OS⊂CP5@CeO_x increased compared with CP5@CeO_x, indicating the encapsulation of positive-charged TPA–OS. According to the UV–Vis spectra (Figures S21 and S22), CP5 and CeO_x exhibited the characteristic absorbance peak at 295 and 300 nm, respectively. Typically, CP5@CeO_x showed a red shift of the absorbance at 350 nm [42], suggesting CP5 binding on the surface of CeO_x changed the state of Ce³⁺ into Ce⁴⁺. TPA–OS⊂CP5@CeO_x exhibited the similar absorbance at 350 nm as CP5@CeO_x due to the unchanged structural integrity. The absorbance at 475–500 nm was ascribed to the existence of TPA–OS. According to the thermogravimetric analysis (Figure S23), CeO_x showed a mass loss of 20.5%, attributing to the residual glycol molecules in the surface during the synthetic process. CP5@CeO_x showed a mass loss of 11.2%, while TPA–OS⊂CP5@CeO_x exhibited it of 17.5%. The results represented CP5@CeO_x had the maximum loading capacity of 6.3% of TPA–OS. Moreover, the weight percent of Ce in CeO_x, CP5@CeO_x, and TPA–OS⊂CP5@CeO_x were measured to be 9.2% by inductively coupled plasma optical emission spectrometry (ICP–OES) (Table S1), indicating the different mass loss were mainly from the modified CP5 and TPA–OS. The above experimental results suggested the successful coordination of CP5 on CeO_x and loading of TPA–OS via host–guest interaction. The morphologies and diameters of TPA–OS⊂CP5@CeO_x dispersed in phosphate-buffered saline (PBS) and fetal bovine serum did not change significantly for different times, indicating that the material exhibited good stability at room temperature (Figures S24 and S25).

X-ray photoelectron spectroscopy (XPS) for CeO_x, CP5@CeO_x, and TPA–OS⊂CP5@CeO_x was performed to evaluate the surface chemical elemental composition and valence state. The nanomaterials mainly consisted of Ce and O elements (Figure S26). N and S signals appeared in TPA–OS⊂CP5@CeO_x, suggesting the successful preparation of TPA–OS⊂CP5@CeO_x. As shown in the high-resolution XPS spectra of Ce 3d (Figure 3a), the peaks marked with v′ and u′ were of Ce³⁺, while the peaks of v, v″, v‴, and u, u″, u‴ belonged to Ce⁴⁺, indicating the coexists of Ce³⁺ and Ce⁴⁺ on the surface of materials [43]. The peaks v‴, v″, v′, and v were assigned to the spin splitting orbits of 3d_3/2, while the u‴, u″, u′, and u peaks were assigned to the spin splitting orbits of 3d_5/2. Typically, the ratio of Ce³⁺ and Ce⁴⁺ was estimated to be 0.43 for CP5@CeO_x and 0.76 for CeO_x. It demonstrated that the modification of CP5 on CeO_x increased Ce⁴⁺ on the surface of CeO_x, changing the ratio of Ce³⁺/Ce⁴⁺. Moreover, the spilled peaks of CP5@CeO_x existed at higher binding energies compared with CeO_x. The shift to higher binding energy was ascribed to the loss of electron [44], suggesting that the coordination of CP5 could induce the oxidation of Ce³⁺. According to O 1s spectra (Figure 3b), the peaks at 533.1, 531.5, and 528.9 eV were assigned to the hydroxyl groups, oxygen vacancies, and lattice oxygen of Ce⁴⁺, respectively [45]. Compared with the O 1s at 528.9 eV of CeO_x, the O 1s of CP5@CeO_x (529.5 eV) shifted to higher binding energy, indicating the excited transfer of charge carriers at the interface. To further confirm the valence states of Ce, Ce–M edge was measured by electron energy loss spectroscopy (STEM–EELS) (Figure 3c). In CP5@CeO_x and TPA–OS⊂CP5@CeO_x, M₄ edge possessed higher intensity compared with M₅ edge [46], indicating they had higher Ce⁴⁺ concentration than that CeO_x. The result was coincident with that of XPS analysis. The changed concentration of oxygen vacancy was further confirmed by electron paramagnetic resonance (EPR) (Figure S27). As conclusion, CP5 was adsorbed to the surface of CeO_x through coordinated interaction and the oxygen atom from CP5 reduced the concentration of oxygen vacancy on CeO_x surface, promoting the generation of hypervalent cerium active sites.

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CAT Activity and GSH Depletion

An increase in the surface Ce⁴⁺/Ce³⁺ ratio of the CP5@CeO_x can promote CAT-like activity. Simultaneously, Ce⁴⁺ can oxidize GSH to GSSG to weaken the reducibility of TME (Figure 3d). GSH maintains the redox balance of biological systems and prevents the ROS-induced damage. GSH depletion is a viable strategy to reduce the inhibition of oxidative stress and to improve the therapeutic effect of SDT. The GSH depletion was evaluated by using 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB) as the indicator. DTNB could react with GSH to form 2-nitro-5-thiobenzoate with the characteristic absorption peak at 412 nm. As shown in Figures 3e,f and S28, TPA–OS⊂CP5@CeO_x exhibited more efficient oxidation of GSH to glutathione (GSSG) in a time-dependent manner compared with CeO_x, because the coordination of CP5 increased the concentration of Ce⁴⁺. The depletion of GSH by TPA–OS⊂CP5@CeO_x was beneficial to maintain a high ROS level, which would enhance the sonodynamic efficiency. The CAT activity was studied by evaluating the amounts of O₂ generation. As shown in Figure 3g, since CAT activity of CeO_x nanoenzyme was mainly affected by the Ce⁴⁺ concentration, the amounts of O₂ was measured to reach 5.95 mg/L after 60 min in H₂O₂ when using TPA–OS⊂CP5@CeO_x and CP5@CeO_x, which was significantly higher than that achieved by CeO_x. According to the above results, the interfacial charge transfer would facilitate the CAT activity and GSH depletion.

Furthermore, the density functional theory (DFT) calculations were also used to clarify the interaction between CP5 and CeO_x. The interaction engineering models between CP5 and CeO_x were established (Figure S29). The negative binding energy of CP5 on the CeO_x surface indicated a spontaneous exothermic reaction of carboxyl–Ce coordinated adsorption and the formation of a tight contact interface in a supramolecular organic–inorganic hybrid material (Figure 3h). In addition, the electron transfer from CeO_x to CP5 after coordination is reflected by the differential charge density (DCD), which creates an internal electric field on the interface (Figure 3i).

Sonodynamic Performance

The efficiency of ROS generation is one of the important factors to evaluate the SDT performance. TPA–OS⊂CP5@CeO_x integrated the advantages of organic and inorganic sonosensitizers, rendering it potentially enhanced ROS generation and excellent sonodynamic performance. Thus, the ROS generation under US irradiation was first studied by EPR. No signal was detected by using 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMP) as a trapping agent, suggesting the nanomaterials could not produce ¹O₂ under US irradiation (Figure 4a). The characteristic peaks with an intensity ratio of 1:2:2:1 was observed by using 5, 5-dimethyl-1-pyrroline N-oxide (DMPO) as a trapping agent (Figure 4b), suggesting •OH was produced under US irradiation. Besides, TPA–OS⊂CP5@CeO_x exhibited the highest production of •OH, indicating its excellent SDT efficiency. To further quantify the ROS generation, the UV–Vis absorption spectra were measured by using 1,3-diphenylisobenzofuran (DPBF) as an indicator. As shown in Figures 4c and S30, TPA–OS⊂CP5@CeO_x exhibited the highest ROS generation compared with CP5@CeO_x, CeO_x, and individual TPA–OS, which was consistent with the EPR results. Moreover, TPA–OS⊂CP5@CeO_x produced larger amounts in acidic condition with pH value of 5.0. This was ascribed to the triggered delivery of TPA–OS from CP5@CeO_x in acidic condition, since the lowing pH would weaken the host–guest interaction of TPA–OS⊂CP5 [47]. All of the experimental results indicated that TPA–OS⊂CP5@CeO_x exhibited the best sonodynamic efficiency, benefiting from the integrated effects of the organic and inorganic sonosensitizer.

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The mechanism of enhanced ROS generation was also investigated. The solid diffuse reflectance UV–Vis absorption spectra were used to analyze the energy bands. CeO_x, CP5@CeO_x, and TPA–OS⊂CP5@CeO_x exhibited the absorption peaks at 300–450 nm (Figure S31), while the peak at 500–800 nm of TPA–OS⊂CP5@CeO_x was ascribed to the absorption of TPA–OS. Subsequently, the band gaps (E_g) of were estimated based on the plot of the Kubelka–Munk function versus the band gap energy. The band gap of CP5@CeO_x was 2.72 eV which was less than that (3.16 eV) of CeO_x. Valence bands (VB) of CP5@CeO_x and CeO_x were also evaluated to be 2.40 and 2.54 eV, respectively, by using VB–XPS curve (Figure S32). Accordingly, the HOMO–LUMO gaps of CP5, CeO_x, and CP5@CeO_x were further calculated (Figure 4d). In consequence, the energy of the band gap, VB, and conduction bands (CB) of CeO_x was effectively modulated by coordinated with CP5. In addition, the electron transfer from CeO_x to CP5 was accelerated upon being excited by US, forming holes at the interface of CeO_x. Further, we conducted in situ XPS experiments. The Ce 3d of CP5@CeO_x shifted to higher binding energy imply that the electrons in the CB of CeO_x will transfer to that of the CP5 irradiated by the visible light (Figure S33). All of the above results were consistent with the type II electron transfer mechanism. The significantly reduced band gap of CP5@CeO_x compared with CeO_x effectively lowered the energy barrier, which facilitated the separation of electron–hole pairs upon exciting by US. As confirmed by the density of states spectra (Figure S34), CP5@CeO_x and CeO_x had the lower band gap value compared with CeO_x at Fermi energy, indicating the coordination of CP5 increased its conductivity and further accelerated the electrons and holes transfer under US irradiation. Compared with CeO_x, the photocurrent of CP5@CeO_x (Figure S35) significantly increased, indicating the efficient charge separation and transfer at the interface of CP5@CeO_x. The electrochemical impedance spectroscopy showed that CP5@CeO_x exhibited decreased charge transfer resistance compared with CP5 (Figure S36), which also testified that the coordination of CP5 enhanced the rate of electron transfer. As evaluated by the photoluminescence (PL) spectra, the emission of CeO_x was reported to be 450–500 nm [48], while CP5@CeO_x showed the weaker PL intensity. The result suggested the modification of CP5 promoted the separation of electron–hole pairs (Figure S37). The surface photovoltages were determined by KPFM to characterize the behaviors of charge carriers at the interface [49–51], based on the illumination-induced changes of the surface potential. In these models, illumination was considered as an external stimulus, because the illumination-induced charge carriers at the surface/interface of catalysts was similar as that induced US irradiation. The KPFM images of CeO_x and CP5@CeO_x both exhibited different surface potentials under dark and light conditions (Figures 4f,g and S38). CP5@CeO_x possessed a stronger surface potential change of  +78.15 mV between dark and light conditions, significantly greater than that of CeO_x (Figures 4h and S39), indicating that the modified CP5 increased charge separation and transportation. All of the mechanism study revealed that the interfacial effect between CP5 and CeO_x promoted the separation of electron–hole pairs and transportation on the CP5@CeO_x surface. This improved the utilization rate of holes and produced hydroxyl radicals by oxidizing water, which would efficiently facilitate production of •OH under US irradiation.

The adsorption of H₂O molecules and •OH on CeO_x was critical to generate ROS [52]. To this end, we measured the adsorption energy of H₂O and •OH on CeO_x surface (Figure S40). Both of the surface adsorption energy of H₂O and •OH decreased after modifying CP5 (Figure S41). To further investigate the reaction energy barrier of H₂O oxidization to generate •OH with the aid of sonosensitizers, adsorption energy calculations were performed for all models (Figure 4e). The adsorption energy for •OH of CP5@CeO_x (−2.90 eV) was lower than that of CeO_x (−0.85 eV), demonstrating that CP5@CeO_x could effortlessly produce •OH than CeO_x. CP5@CeO_x had the lower energy barrier to form •OH, which further confirmed that coordination of CP5 would significantly accelerate the adsorption of H₂O and promote the generation of •OH.

Cellular Imaging and Therapeutics

Based on above systematic results of experiments and analyses, it can be concluded that the coordination of CP5 could not only enhance the sonodynamic efficiency by the interfacial effect, but also provide the opportunity to integrate with organic sonosensitizers via host–guest interaction. Thus, TPA–OS⊂CP5@CeO_x is deduced to simultaneously have excellent sonodynamic efficiency and bio-imaging. As evaluated by CCK8 assay, CeO_x, CP5@CeO_x, and TPA–OS⊂CP5@CeO_x exhibited negligible cytotoxicity toward HUVEC as normal cells and slight cytotoxicity toward HeLa cells (Figures 5a and S42), demonstrating the specific killing effect on cancer cells due to the chemodynamic effect of CeO_x. Besides, both of CP5@CeO_x and TPA–OS⊂CP5@CeO_x exhibited high biocompatibility. The cytotoxicity of HeLa cells incubated with the nanomaterials under US irradiation was also evaluated (Figure 5b). Compared with CeO_x, CP5@CeO_x and TPA–OS⊂CP5@CeO_x showed the most obvious cytotoxicity, indicating its best sonodynamic performance in cancer cells.

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According to the bio-TEM images (Figure 5c,d), TPA–OS⊂CP5@CeO_x in HeLa cells exhibited the double organelles targeting in both lysosomes and mitochondria after incubating for 1 and 6 h, respectively, which was further confirmed by the imaging of confocal laser scanning microscopy (CLSM). The ultimate mitochondria targeting was also clearly observed in the super-resolution CLSM images (Figure 5f). Based on the colocalization with Hoechst 33258, LysoTracker Green, and MitoTracker Green (Figure S43), it could be observed that TPA–OS⊂CP5@CeO_x entered lysosomes after incubating for 1 h, and then entered mitochondria at 6 h. The Pearson correlation coefficients toward lysosomes and mitochondria were estimated to be 0.93 and 0.91 (Figures S44 and S45), respectively, confirming TPA–OS⊂CP5@CeO_x had the high-bright fluorescent imaging and targeting abilities to double organelles. TPA–OS⊂CP5@CeO_x also exhibited pH-responsiveness due to the host–guest interaction (Figure S46), which was testified by adding Bafilomycin A1 (Baf-A1) to inhibit the acidity of lysosomes. No red fluorescence was observed in mitochondria after adding Baf-A1. Nevertheless, the red fluorescence was recovered after incubation in an acidic environment, indicating the TPA–OS was released to target mitochondria.

The accurate release process of TPA–OS was also verified by in situ imaging. Time series images for TPA–OS⊂CP5@CeO_x in HeLa cells were taken by using the LysoTracker Blue and MitoTracker Green probe (Figure S47 and Movies S1 and S2). It was observed that TPA–OS⊂CP5@CeO_x entered the lysosome after entering the cells and enriched mainly in lysosome at 1 h. Simultaneously, the host–guest interaction of TPA–OS⊂CP5 was weakened in the acidic lysosome, resulting in the escape of TPA–OS. TPA–OS molecules then targeted toward mitochondria at 2 h, while CP5@CeO_x remained in lysosome as a transport nanocarrier.

In order to investigate the therapeutic effects, different probes were used in HeLa cells (Figure 5e,g). First, the CAT activity was testified by using Ru(dpp)₃Cl₂ as an oxygen probe, whose red fluorescence could be quenched by O₂. The HeLa cells incubated with TPA–OS⊂CP5@CeO_x showed the weakest fluorescence compared with other groups, indicating the most O₂ generation of TPA–OS⊂CP5@CeO_x. The O₂ generation would alleviates the hypoxia in tumor cells. The depletion of GSH in HeLa cells was investigated by using Thiol Tracker violet (green) as a probe. The quenching of fluorescence after incubation of TPA–OS⊂CP5@CeO_x indicated the decrease of GSH level. In consequence, TPA–OS⊂CP5@CeO_x could generate O₂ to relieve the hypoxia in HeLa cells and reinforce intracellular oxidative stress due to the GSH depletion. Thus, TPA–OS⊂CP5@CeO_x exhibited good potentials for SDT in HeLa cells by regulate TME.

The ROS generation was evaluated by using a 2′,7′-dichlorodihydrofluorescein diacetate (DCFH-DA) as the probe. DCFH-DA without fluorescence can be oxidized by ROS to be 2′,7′-dichlorofluorescein with highly green fluorescence. The strong green fluorescence was observed in CLSM images, suggesting TPA–OS⊂CP5@CeO_x could largely producing ROS in HeLa cells under US irradiation. Moreover, the cell apoptosis was also estimated by using JC-1 as a fluorescent probe, which could detect the mitochondrial membrane potentials related to mitochondrial dysfunction. the cells treated with TPA–OS⊂CP5@CeO_x under US irradiation exhibited totally red fluorescence, indicating the decline of mitochondrial membrane potential and complete cell apoptosis (Figure S48). Moreover, TPA–OS⊂CP5@CeO_x also largely inhibited the proliferation of HeLa cells upon US irradiation, which was demonstrated by using Ki67 staining to detect the proliferation activity of tumor cells (Figure S49). In order to further study the sonodynamic therapeutic capacity of TPA–OS⊂CP5@CeO_x, Calcein-AM/propidium iodide (AM/PI) double staining method was used to distinguish the live and dead cells (Figure S50). As expected, strong red signals were observed when cells were treated with TPA–OS⊂CP5@CeO_x and irradiated with US. It was indicative of the efficient cytotoxicity of TPA–OS⊂CP5@CeO_x as the sonosensitizer upon US irradiation. Moreover, the flow cytometric apoptosis assay was conducted after staining with Annexin V-FITC and PI. The results indicated TPA–OS⊂CP5@CeO_x had the significantly higher apoptotic ratio than that of CP5@CeO_x and CeO_x under US irradiation due to its excellent SDT efficiency. All of above experimental results verified that TPA–OS⊂CP5@CeO_x possessed a high ability of ROS generation and enhanced efficiency of therapeutics for cancer cells under US irradiation, benefiting from the interfacial effect and the synergistic activities of organic–inorganic sonosensitizers.

In Vivo Imaging and Therapeutics

Since the nanomaterials exhibited impressive performance for imaging-guided SDT in HeLa cells, the in vivo imaging and tumoricidal performance were also investigated by injecting TPA–OS⊂CP5@CeO_x into HeLa breast cancer BALB/c-nu mice via tail vein (Figure 6a). First of all, the half-life of TPA–OS⊂CP5@CeO_x in blood circulation was determined to be 1.55 h by the pharmacokinetic profiles, indicating the stability of TPA–OS⊂CP5@CeO_x in bio-systems (Figure S51). Next, we studied the long-term toxicity of TPA–OS⊂CP5@CeO_x. As shown in Figure S52, this material exhibited low long-term biotoxicity in HUVEC cells without US irradiation. Based on the Ce levels measured by ICP–OES, a time-dependent biodistribution study was carried out (Figure S53). Significant retention of TPA–OS⊂CP5@CeO_x was mainly found in the liver and spleen of injected mice at 24 h post injection. However, the Ce levels in these organs rapidly decreased over time, indicating clearance of the nanoparticles. The blood routine indexes and liver and kidney function confirmed that TPA–OS⊂CP5@CeO_x exhibited negligible toxicity to the treated mice at this dose (Figure S54). In brief, the TPA–OS⊂CP5@CeO_x was highly biocompatible for in vivo therapeutic applications. As shown in Figure 6b, TPA–OS⊂CP5@CeO_x exhibited excellent capacity of in vivo NIR-I FLI and PAI, benefiting from the AIE-active TPA–OS and CeO_x, respectively. It was observed that the nanomaterials reached the maximum accumulation at the tumor site after 6 h injection. Both signals of NIR-I imaging and PA imaging were observed after 1 h injection and sustained for about 24 h, indicating that TPA–OS⊂CP5@CeO_x could efficiently accumulate in the tumor site through the blood circulation and achieve the double imaging of tumor to guide the precise tumor inhibition.

[IMAGE OMITTED. SEE PDF]

The antitumor efficacy was also studied on the HeLa tumor-bearing nude mice. The effect of tumor suppression was first observed in the photograph of tumors (Figure 6c) and the profile of relative tumor volumes (Figure 6d). For the groups of TPA–OS⊂CP5@CeO_x, CeO_x, and CP5@CeO_x, the tumors were partially eliminated without US irradiation, which was resulted from the chemodynamic effect of CeO_x. Nevertheless, the tumors were further inhibited for the groups of CeO_x and CP5@CeO_x upon US irradiation, attributed to the addition of sonodymanic effects. Compared with other groups, TPA–OS⊂CP5@CeO_x exhibited the maximum tumor inhibition. This was not only resulted from the combined chemodynamic and sonodynamic effects under the US irradiation, but also the results of synergistic effects of organic and inorganic sonosensitizers. The results of tumor inhibition were also confirmed by assessing the tumor weights after treatment (Figure 6e). Besides, the mice weights indicated that the nanomaterials had negligible systemic toxicity (Figure 6f). The content of Ce element in vital organs and tumors were analyzed by ICP–OES, demonstrated that the materials were mainly accumulated in the liver and tumors through metabolism and blood circulation (Figure 6g).

Subsequently, the histological and immunohistochemical studies were also conducted to further evaluate the side effects. After being treated with TPA–OS⊂CP5@CeO_x and US irradiation, the conspicuous karyopyknotic of tumor cells and sever cell apoptosis were observed on the tumor tissue slices staining by hematoxylin and eosin (H&E) and terminal-deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) immunofluorescence, respectively (Figure 6h). This revealed that TPA–OS⊂CP5@CeO_x had the effective destruction of tumors under US irradiation, due to the synergistic chemodynamic effects and enhanced ROS generation of combined organic–inorganic sonosensitizers. Additionally, no obvious inflammatory damage on the vital organs was observed via H&E staining (Figure S55), indicating that the nanomaterials exhibited excellent in vivo biocompatibility with negligible side effects. Thus, TPA–OS⊂CP5@CeO_x can serve as an imaging-guided nanotheranostics with enhanced sonodynamic and chemodynamic effects for long-acting cancer therapy.

Conclusion

A novel intelligent sonosensitizers with enhanced SDT performance, that is, TPA–OS⊂CP5@CeO_x, was successfully prepared. According to the experimental and theoretical results, the coordination of CP5 could reduce the band gap of CeO_x, promote the charge transfer, and accelerate the adsorption of H₂O molecules. Thus, the SDT efficiency of CP5@CeO_x was improved by large ROS generation under US and TME regulation. The combination of TPA–OS through host–guest interaction also achieved the enhancement of SDT due to the synergistic effects. Benefiting from the responsiveness of host–guest interaction, the therapeutic performance of organic–inorganic sonosensitizers was regulated and activated in both lysosomes and mitochondria. TPA–OS⊂CP5@CeO_x exhibited not only the double organelle-targeting in cells but also the excellent therapeutic effectiveness in FLI- and PAI-guided tumor suppression. This study paves a new way for the design and preparation of novel intelligent sonosensitizers with regulable performance and tailored therapeutic outcome.

Experimental Section

Preparation of CeO_x

CeO_x was prepared according to the previous literatures [53]. Briefly, Ce(NO₃)₃·6H₂O (434 mg, 1 mmol) was dissolved in H₂O (2 mL) and ethylene glycol (60 mL). After vigorous stirring at room temperature for 30 min, the mixed solution was transferred into an autoclave and heated at 180°C for 12 h. The mixture was then centrifuged to obtain a solid product.

Preparation of CP5@CeO_x

CP5@CeO_x was synthesized by ligand exchange. CeO_x (50 mg) synthesized before was dispersed in H₂O (5 mL). CP5 (141 mg) was dissolved in H₂O (5 mL). The solutions of CeO_x and CP5 was mixed and stirred at 25°C for 24 h. And then, the mixed solution was centrifuged to obtain a solid product, which was washed with H₂O and freeze-dried.

Preparation of TPA–OS⊂CP5@CeO_x

CP5@CeO_x (50 mg) was dispersed in H₂O (5 mL) and mixed with TPA–OS (4 mM, 5 mL). The solution was incubated for 24 h for sufficient interaction. Then, the solution was centrifugated and washed with H₂O. The solid sample was freeze-dried to obtain the final product.

pH-responsive Properties

The buffers with different pH values of 3.0, 5.0, 6.0, 7.4, and 8.5 were prepared based on citric acid, sodium acetate, and sodium hydrogen phosphate. The pH values were detected by a pH meter. The samples of TPA–OS, TPA–OS⊂CP5, and TPA–OS⊂CP5@CeO_x in different-pH buffers before/after centrifugation were prepared and their fluorescence intensities were measured.

Sonodynamic Performance

The sonodynamic performance was evaluated by the EPR test and DPBF indicator, respectively. The EPR test was using DMPO to capture the singlet oxygen. TPA–OS⊂CP5@CeO_x, CP5@CeO_x, and CeO_x (100 µg/mL) was dispersed in H₂O and sonicated for 2 min (0.8 W, 50% cycle power). Besides, DPBF (10 µL, 70 mM) was added to the system containing of TPA–OS⊂CP5@CeO_x (100 µg/mL), CeO_x, TPA–OS⊂CP5, CP5@CeO_x, and TPA–OS, respectively.

DFT Calculations

CP2K [54] based on a hybrid Gaussian plane wave was used for DFT calculation. The wave function was optimized by using the matrix orbital transformation method. The 1s electrons of H, 2s, 2p electrons of C, 2s, 2p electrons of O, 6s, 5s, 5p, 5d, 4f electrons of Ce, 2s, 2p, 3s electrons of Na were treated as valence, and the rest core electrons were represented by Goedecker–Teter–Hutter pseudopotentials [55, 56]. The Gaussian basis set was double-ζ with one set of polarization functions (DZVP) [57]. the plane wave cutoff was set to 350 Ry. Perdew–Burke–Ernzerhof function [58] was used to describe the electron exchange-correlation interactions. For structure optimization, Broyden–Fletcher Goldfarb–Shanno minimize was used to optimize the geometry. DFT + U method with U = 6 eV was used to describe the localized Ce 4f states. The maximum force was less than 0.02 eV/Å. The surface of CeO_x (1 1 1) was modeled by a 3 × 2 periodic. The supercell slab was separated by 27 Å of vacuum.

Cellular Uptake Assay

HeLa cells were cultured in separate confocal culture dishes. After incubation at 37°C for 24 h, TPA–OS⊂CP5@CeO_x (50 µg/mL) was added to the culture dishes. The HeLa cells with materials was further incubated for 1 and 6 h, respectively. Subsequently, the cells were contained with Hoechst 33258/LysoTracker Green or Hoechst 33258/MitoTracker Green for 30 min. Baf-A1 was added for inhibiting the lysosomal acidity. The irradiation of pH = 5 was used to trigger the release of AIEgens. After incubation and treatment, the cells were washed with PBS and imaged by CLSM to study the subcellular localization of materials.

In Situ Imaging

HeLa cells were cultured in separate confocal culture dishes. After incubation at 37°C for 24 h, the cells were contained with the LysoTracker Blue and MitoTracker Green for 30 min. Subsequently, TPA–OS⊂CP5@CeO_x (50 µg/mL) was added to the culture dishes. The culture dishes were immediately placed in a customized confocal cell culture incubator for continuous imaging (at 10-min intervals), with CO₂ gas supplied to maintain the viability of HeLa cells.

Cytotoxicity Assay

HeLa cells were incubated in 96-well plates (1 × 10⁴/pore) for 24 h. CeO_x, CP5@CeO_x, and TPA–OS⊂CP5@CeO_x at step-increased concentration were subsequently added and incubated for 12 h. The HeLa cells incubated with materials were washed with PBS for three times to remove un-uptaken materials and treated with US for 2 min (0.8 W, 50% cycle). CCK8 reagents were added for staining and the UV absorption at 450 nm was recorded. Finally, the cell survivals were calculated for each group (n = 3, mean ± s.d.). Moreover, the effect of TPA–OS⊂CP5@CeO_x on normal cells was also evaluated by using mouse fibroblast cell line HEVEC under the same experimental condition as HeLa cells.

Live-Dead Staining of Cells

HeLa cells were incubated at a density of 1 × 10⁴/pore on six-well plates. After 24 h of incubation, TPA–OS⊂CP5@CeO_x (100 µg/mL) was added and further incubated for 12 h. The materials remaining outside of cells were removed by washing with PBS. After that, the HeLa cells were treated with US for 2 min (0.8 W, 50% cycle) and incubated for another 24 h. After 15 min of staining with the dead-alive staining reagent, the cells were washed. The images were recorded under an inverted fluorescence microscope.

Animal and Tumor Models

BALB/c nu mice (4 weeks old) were purchased from Spelford (Beijing) Biotechnology Co., Ltd. Tumor models were inoculated by subcutaneously injecting HeLa cells (cell counts: 5.0 × 10⁶, 150 µL) into the hind legs of nude mice. The tumor volumes were recorded.

In Vivo Treatment

After the tumor volume reached nearly 150 mm³, thirty-five mice were randomly divided into seven groups (PBS, CeO_x, CP5@CeO_x, TPA–OS⊂CP5@CeO_x, CeO_x + US, CP5@CeO_x + US, TPA–OS⊂CP5@CeO_x + US) for in vivo antitumor experiments. 100 µL of PBS, CeO_x, CP5@CeO_x, and TPA–OS⊂CP5@CeO_x were injected of each tumor-bearing mouse through the tail vein respectively. After the materials reached the tumor sites, the mice in the US group were treated by an US therapeutic device (3 min, 1.5 W, 50% in cycle) every 3 days. Tumor volumes and body weights were recorded during the treatment. The mice were executed at the 15th day. The tumor tissues and major organs were collected for further analysis. Tumor volumes (V) were calculated by the following formula: V = W² × L/2 (W and L are the shortest and longest diameters of the tumors, respectively.).

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (projects 22221001, 22131007, and 22401119) and the 111 project (B20027), the Gansu provincial science and technology program (24ZD13GA015, 23ZDGA012, and 24JRRA435), and the Fundamental Research Funds for the Central Universities (lzujbky-2024-jdzx13).

Ethics Statement

All animal experiments were approved by Attitude of Animal Care Welfare Committee, Gansu University of Chinese Medicine, China (Approval number:SY2024-272).

Conflicts of Interest

The authors declare no conflicts of interests.

Data Availability Statement

All relevant data supporting the findings of this study are available in this paper and its Supporting Information. Synthetic procedures and characterization for all the compounds and all copies of nuclear magnetic resonance spectra are provided in the Supporting Information. All data are available from the corresponding author upon reasonable request.

References

H. Sung, J. Ferlay, R. L. Siegel, et al., “Global Cancer Statistics 2020: GLOBOCAN Estimates of Incidence and Mortality Worldwide for 36 Cancers in 185 Countries,” Ca: A Cancer Journal for Clinicians 71 (2021): 209–249.

J. J. Shi, P. W. Kantoff, R. Wooster, and O. C. Farokhzad, “Cancer Nanomedicine: Progress, Challenges and Opportunities,” Nature Reviews Cancer 17 (2017): 20–37.

H. Huang, Z. Y. Wang, L. Chen, H. Yu, and Y. Chen, “Catalytic Biomaterials and Nanomedicines With Exogenous and Endogenous Activations,” Advanced Healthcare Materials 12 (2023): 2201607.

R. He, Y. C. Wang, X. Y. Wang, et al., “Facile Synthesis of Pentacle Gold–Copper Alloy Nanocrystals and Their Plasmonic and Catalytic Properties,” Nature Communications 5 (2014): 4327.

J. Chen, S. K. Li, Z. Y. Wang, et al., “Synthesis of an AIEgen Functionalized Cucurbit[7]Uril for Subcellular Bioimaging and Synergistic Photodynamic Therapy and Supramolecular Chemotherapy,” Chemical Science 12 (2021): 7727–7734.

Z. Wang, Z. Yang, S. Li, et al., “Light‐Directed Microalgae Micromotor With Supramolecular Backpacks for Photodynamic Therapy,” Advanced Functional Materials 35 (2025): 2411070.

L. Wang, G. Z. Li, L. Cao, et al., “An Ultrasound‐driven Immune‐boosting Molecular Machine for Systemic Tumor Suppression,” Science Advances 7 (2021): eabj4796.

C. Zhang and K. Y. Pu, “Organic Sonodynamic Materials for Combination Cancer Immunotherapy,” Advanced Materials 35 (2023): 2303059.

X. Q. Qian, Y. Y. Zheng, and Y. Chen, “Micro/Nanoparticle‐Augmented Sonodynamic Therapy (SDT): Breaking the Depth Shallow of Photoactivation,” Advanced Materials 28 (2016): 8097–8129.

S. Liang, X. R. Deng, P. A. Ma, Z. Y. Cheng, and J. Lin, “Recent Advances in Nanomaterial‐Assisted Combinational Sonodynamic Cancer Therapy,” Advanced Materials 32 (2020): 2003214.

V. G. Deepagan, D. G. You, W. Um, et al., “Long‐Circulating Au‐TiO2 Nanocomposite as a Sonosensitizer for ROS‐Mediated Eradication of Cancer,” Nano Letters 16 (2016): 6257–6264.

L. H. Sun, P. Wang, J. X. Zhang, et al., “Design and Application of Inorganic Nanoparticles for Sonodynamic Cancer Therapy,” Biomaterials Science 9 (2021): 1945–1960.

C. H. Dong, H. Hu, L. P. Sun, and Y. Chen, “Inorganic Chemoreactive Nanosonosensitzers With Unique Physiochemical Properties and Structural Features for Versatile Sonodynamic Nanotherapies,” Biomedical Materials 16 (2021): 032006.

X. Pang, Q. C. Xiao, Y. Cheng, et al., “Bacteria‐Responsive Nanoliposomes as Smart Sonotheranostics for Multidrug Resistant Bacterial Infections,” ACS Nano 13 (2019): 2427–2438.

S. A. Liu, K. K. Dou, B. Liu, M. L. Pang, P. A. Ma, and J. Lin, “Construction of Multiform Hollow‐Structured Covalent Organic Frameworks via a Facile and Universal Strategy for Enhanced Sonodynamic Cancer Therapy,” Angewandte Chemie International Edition 62 (2023): e202301831.

Z. Gong, D. Hou, Y. Xu, et al., “Enhancing SDT Efficacy of Doxorubicin‐Loaded Sonosensitizer Micelles to Overcome Resistance of Cancer Therapy by Optimizing Acoustic Parameters,” Aggregate (2025): e70005, https://doi.org/10.1002/agt2.70005.

Y. J. Wang, F. Gong, Z. H. Han, et al., “Oxygen‐Deficient Molybdenum Oxide Nanosensitizers for Ultrasound‐Enhanced Cancer Metalloimmunotherapy,” Angewandte Chemie International Edition 62 (2023): e202215467.

Z. Yang, M. Yuan, B. Liu, et al., “Conferring BiVO4 Nanorods With Oxygen Vacancies to Realize Enhanced Sonodynamic Cancer Therapy,” Angewandte Chemie International Edition 61 (2022): e202209484.

Y. M. Zhao, J. H. Liu, M. T. He, et al., “Platinum–Titania Schottky Junction as Nanosonosensitizer, Glucose Scavenger, and Tumor Microenvironment‐Modulator for Promoted Cancer Treatment,” ACS Nano 16 (2022): 12118–12133.

G. Y. Feng, H. Huang, M. Zhang, et al., “Single Atom Iron‐Doped Graphic‐Phase C3 N4 Semiconductor Nanosheets for Augmented Sonodynamic Melanoma Therapy Synergy With Endowed Chemodynamic Effect,” Advanced Science 10 (2023): 2302579.

C. Gao, C. H. T. Kwong, Q. F. Wang, et al., “Conjugation of Macrophage‐Mimetic Microalgae and Liposome for Antitumor Sonodynamic Immunotherapy via Hypoxia Alleviation and Autophagy Inhibition,” ACS Nano 17 (2023): 4034–4049.

Y. Y. Wang, Y. C. Liu, H. W. Sun, and D. S. Guo, “Type I Photodynamic Therapy by Organic–inorganic Hybrid Materials: From Strategies to Applications,” Coordination Chemistry Reviews 395 (2019): 46–62.

Y. Zhang, S. Zhao, J. Feng, et al., “Unraveling the Physical Chemistry and Materials Science of CeO2‐Based Nanostructures,” Chem 7 (2021): 2022–2059.

C. F. Wang, J. Lei, C. Y. Mao, et al., “Defective S‐TiO2−x/CeO2 Heterojunction for Mutual Reinforcing Chemodynamic/Sonocatalytic Antibacterial Therapy and Sonoelectric/Ion‐Activated Bone Regeneration,” Advanced Functional Materials 33 (2023): 2306493.

C. Xu and X. G. Qu, “Cerium Oxide Nanoparticle: A Remarkably Versatile Rare Earth Nanomaterial for Biological Applications,” Npg Asia Materials 6 (2014): e90.

V. Baldim, F. Bedioui, N. Mignet, I. Margaill, and J. F. Berret, “The Enzyme‐Like Catalytic Activity of Cerium Oxide Nanoparticles and Its Dependency on Ce3+ Surface Area Concentration,” Nanoscale 10 (2018): 6971–6980.

C. Yao, W. X. Wang, P. Y. Wang, M. Y. Zhao, X. M. Li, and F. Zhang, “Near‐Infrared Upconversion Mesoporous Cerium Oxide Hollow Biophotocatalyst for Concurrent pH‐/H2O2‐Responsive O2‐Evolving Synergetic Cancer Therapy,” Advanced Materials 30 (2018): 1704833.

Y. P. Zhu, C. X. Guo, Y. Zheng, and S. Z. Qiao, “Surface and Interface Engineering of Noble‐Metal‐Free Electrocatalysts for Efficient Energy Conversion Processes,” Accounts of Chemical Research 50 (2017): 915–923.

Y. Peng, Q. M. Liu, B. Z. Lu, et al., “Organically Capped Iridium Nanoparticles as High‐Performance Bifunctional Electrocatalysts for Full Water Splitting in both Acidic and Alkaline Media: Impacts of Metal–Ligand Interfacial Interactions,” ACS Catalysis 11 (2021): 1179–1188.

Y. Song, S. Lee, Y. Ko, et al., “Charge‐Transfer Effects of Organic Ligands on Energy Storage Performance of Oxide Nanoparticle‐Based Electrodes,” Advanced Functional Materials 32 (2022): 2106438.

X. P. Liu, X. H. Wang, C. X. Mao, et al., “Ligand‐Hybridization Activates Lattice‐Hydroxyl‐Groups of NiCo(OH)X Nanowires for Efficient Electrosynthesis,” Angewandte Chemie International Edition 63 (2024): e202408109.

Z. T. Li, J. Yang, G. C. Yu, J. M. He, Z. Abliz, and F. H. Huang, “Water‐Soluble Pillar[7]Arene: Synthesis, pH‐Controlled Complexation With Paraquat, and Application in Constructing Supramolecular Vesicles,” Organic Letters 16 (2014): 2066–2069.

N. Song, Z. J. Zhang, P. Y. Liu, et al., “Pillar[5]Arene‐Modified Gold Nanorods as Nanocarriers for Multi‐Modal Imaging‐Guided Synergistic Photodynamic‐Photothermal Therapy,” Advanced Functional Materials 31 (2021): 2009924.

M. A. H. Muhammed, L. K. Cruz, A. H. Emwas, et al., “Pillar[5]Arene‐Stabilized Silver Nanoclusters: Extraordinary Stability and Luminescence Enhancement Induced by Host–Guest Interactions,” Angewandte Chemie International Edition 58 (2019): 15665–15670.

Q. L. Li, Y. Sun, L. Ren, et al., “Supramolecular Nanosystem Based on Pillararene‐Capped CuS Nanoparticles for Targeted Chemo‐Photothermal Therapy,” ACS Applied Materials & Interfaces 10 (2018): 29314–29324.

H. Zhang, J. R. Wu, X. Wang, et al., “One‐pot Solvothermal Synthesis of Carboxylatopillar[5]Arene‐modified Fe3O4 Magnetic Nanoparticles for Ultrafast Separation of Cationic Dyes,” Dyes Pigments 162 (2019): 512–516.

H. H. Li, R. Y. Wei, G. H. Yan, et al., “Smart Self‐Assembled Nanosystem Based on Water‐Soluble Pillararene and Rare‐Earth‐Doped Upconversion Nanoparticles for pH‐Responsive Drug Delivery,” ACS Applied Materials & Interfaces 10 (2018): 4910–4920.

X. Wang, L. L. Tan, X. Li, et al., “Smart Mesoporous Silica Nanoparticles Gated by Pillararene‐modified Gold Nanoparticles for on‐Demand Cargo Release,” Chemical Communications 52 (2016): 13775–13778.

G. C. Yu, K. C. Jie, and F. H. Huang, “Supramolecular Amphiphiles Based on Host–Guest Molecular Recognition Motifs,” Chemical Reviews 115 (2015): 7240–7303.

H. An, Y. Hu, N. Song, et al., “Two‐dimensional Heterostructures Built From Ultrathin CeO2 Nanosheet Surface‐coordinated and Confined Metal–organic Frameworks With Enhanced Stability and Catalytic Performance,” Chemical Science 13 (2022): 3035–3044.

K. K. Patra, Z. Liu, H. J. Lee, et al., “Boosting Electrochemical CO2 Reduction to Methane via Tuning Oxygen Vacancy Concentration and Surface Termination on a Copper/Ceria Catalyst,” ACS Catalysis 12 (2022): 10973–10983.

N. Yadav and S. Singh, “Polyoxometalate‐Mediated Vacancy‐Engineered Cerium Oxide Nanoparticles Exhibiting Controlled Biological Enzyme‐Mimicking Activities,” Inorganic Chemistry 60 (2021): 7475–7489.

B. A. Reddy, A. Khan, Y. Yamada, T. Kobayashi, S. Loridant, and J. C. Volta, “Surface Characterization of CeO2/SiO2 and V2O5/CeO2/SiO2 Catalysts by Raman, XPS, and Other Techniques,” Journal of Physical Chemistry B 106 (2002): 10964–10972.

Y. Lykhach, S. M. Kozlov, T. Skála, et al., “Counting Electrons on Supported Nanoparticles,” Nature Materials 15 (2016): 284–288.

S. C. Rood, O. Pastor‐Algaba, A. Tosca‐Princep, et al., “Synergistic Effect of Simultaneous Doping of Ceria Nanorods With Cu and Cr on CO Oxidation and NO Reduction,” Chemistry ‐ A European Journal 27 (2021): 2165–2174.

J. A. Fortner and E. C. Buck, “The Chemistry of the Light Rare‐earth Elements as Determined by Electron Energy Loss Spectroscopy,” Applied Physics Letters 68 (1996): 3817–3819.

L. Shao, Y. Pan, B. Hua, et al., “Constructing Adaptive Photosensitizers via Supramolecular Modification Based on Pillararene Host–Guest Interactions,” Angewandte Chemie International Edition 59 (2020): 11779–11783.

J. J. Kong, Z. W. Xiang, G. Y. Li, and T. C. An, “Introduce Oxygen Vacancies Into CeO2 Catalyst for Enhanced Coke Resistance During Photothermocatalytic Oxidation of Typical VOCs,” Applied Catalysis B: Environment and Energy 269 (2020): 118755.

R. T. Chen, F. T. Fan, T. Dittrich, and C. Li, “Imaging Photogenerated Charge Carriers on Surfaces and Interfaces of Photocatalysts With Surface Photovoltage Microscopy,” Chemical Society Reviews 47 (2018): 8238–8262.

X. F. Jia, Y. Lu, K. R. Du, et al., “Interfacial Mediation by Sn and S Vacancies of p ‐SnS/n ‐ZnIn2S4 for Enhancing Photocatalytic Hydrogen Evolution With New Scheme of Type‐I Heterojunction,” Advanced Functional Materials 33 (2023): 2304072.

S. Li, C. Gao, H. Yu, et al., “Vinylene‐Linked Donor‐π‐Acceptor Metal‐Covalent Organic Framework for Enhanced Photocatalytic CO2 Reduction,” Angewandte Chemie International Edition 63 (2024): e202409925.

B. F. Chen, Z. Y. Meng, P. Ouyang, et al., “S2‐ doping Inducing Self‐adapting Dual Anion Defects in ZnSn(OH)6 for Highly Efficient Photoactivity,” Applied Catalysis B: Environment and Energy 338 (2023): 123093.

S. M. Dong, Y. S. Dong, B. Liu, et al., “Guiding Transition Metal‐Doped Hollow Cerium Tandem Nanozymes With Elaborately Regulated Multi‐Enzymatic Activities for Intensive Chemodynamic Therapy,” Advanced Materials 34 (2022): 2107054.

J. VandeVondele, M. Krack, F. Mohamed, M. Parrinello, T. Chassaing, and J. Hutter, “Quickstep: Fast and Accurate Density Functional Calculations Using a Mixed Gaussian and Plane Waves Approach,” Computer Physics Communications 167 (2005): 103–128.

S. Goedecker, M. Teter, and J. Hutter, “Separable Dual‐Space Gaussian Pseudopotentials,” Physical Review B 54 (1996): 1703–1710.

C. Hartwigsen, S. Goedecker, and J. Hutter, “Relativistic Separable Dual‐Space Gaussian Pseudopotentials From H to Rn,” Physical Review B 58 (1998): 3641–3662.

J. VandeVondele and J. Hutter, “Gaussian Basis Sets for Accurate Calculations on Molecular Systems in Gas and Condensed Phases,” Journal of Chemical Physics 127 (2007): 114105.

J. P. Perdew, K. Burke, and M. Ernzerhof, “Generalized Gradient Approximation Made Simple,” Physical Review Letter 77 (1996): 3865–3868.