Metabolizable Ultrathin Bi2Se3 Nanosheets in Imaging‐Guided Photothermal Therapy

Poly(vinylpyrrolidone)‐encapsulated Bi₂Se₃ nanosheets with a thickness of 1.7 nm and diameter of 31.4 nm are prepared by a solution method. Possessing an extinction coefficient of 11.5 L g^?1 cm^?1 at 808 nm, the ultrathin Bi₂Se₃ nanosheets boast a high photothermal conversion efficiency of 34.6% and excellent photoacoustic performance. After systemic administration, the Bi₂Se₃ nanosheets with the proper size and surface properties accumulate passively in tumors enabling efficient photoacoustic imaging of the entire tumors to facilitate photothermal cancer therapy. In vivo biodistribution studies reveal that they are expelled from the body efficiently after 30 d. The ultrathin Bi₂Se₃ nanosheets have large clinical potential as metabolizable near‐infrared‐triggered theranostic agents.     

Bifunctional Au@Bi2Se3 Core–Shell Nanoparticle for Synergetic Therapy by SERS‐Traceable AntagomiR Delivery and Photothermal Treatment

For the first time, topological insulator bismuth selenide nanoparticles (Bi₂Se₃ NP) are core–shelled with gold (Au@Bi₂Se₃) i) to represent considerably small‐sized (11 nm) plasmonic nanoparticles, enabling accurate bioimaging in the near‐infrared region; ii) to substantially improve Bi₂Se₃ biocompatibility, iii) water dispersibility, and iv) surface functionalization capability through straightforward gold–thiol interaction. The Au@Bi₂Se₃ is subsequently functionalized for v) effective targeting of SH‐SY5Y cancer cells, vi) disrupting the endosome/lysosome membrane, vii) traceable delivery of antagomiR‐152 and further synergetic oncomiR knockdown and photothermal therapy (PTT). Unprecedentedly, it is observed that the Au shell thickness has a significant impact on evoking the exotic plasmonic features of Bi₂Se₃. The Au@Bi₂Se₃ possesses a high photothermal conversion efficiency (35.5%) and a remarkable surface plasmonic effect (both properties are approximately twofold higher than those of 50 nm Au nanoparticles). In contrast to the siRNA/miRNA delivery methods, the antagomiR delivery is based on strand displacement, in which the antagomiR‐152 is displaced by oncomiR‐152 followed by a surface‐enhanced Raman spectroscopy signal drop. This enables both cancer cell diagnosis and in vitro real‐time monitoring of the antagomiR release. This selective PTT nanoparticle can also efficiently target solid tumors and undergo in vivo PTT, indicating its potential clinical applications.     

Chemical Patterning of High‐Mobility Semiconducting 2D Bi2O2Se Crystals for Integrated Optoelectronic Devices

Patterning of high‐mobility 2D semiconducting materials with unique layered structures and superb electronic properties offers great potential for batch fabrication and integration of next‐generation electronic and optoelectronic devices. Here, a facile approach is used to achieve accurate patterning of 2D high‐mobility semiconducting Bi₂O₂Se crystals using dilute H₂O₂ and protonic mixture acid as efficient etchants. The 2D Bi₂O₂Se crystal after chemical etching maintains a high Hall mobility of over 200 cm² V^?1 s^?1 at room temperature. Centimeter‐scale well‐ordered arrays of 2D Bi₂O₂Se with tailorable configurations are readily obtained. Furthermore, integrated photodetectors based on 2D Bi₂O₂Se arrays are fabricated, exhibiting excellent air stability and high photoresponsivity of ≈2000 A W^?1 at 532 nm. These results are one step towards the practical application of ultrathin 2D integrated digital and optoelectronic circuits.     

Layered MoS2 Hollow Spheres for Highly‐Efficient Photothermal Therapy of Rabbit Liver Orthotopic Transplantation Tumors

Combining photothermal therapy (PTT) with clinical technology to kill cancer via overcoming the low tumor targeting and poor therapy efficiency has great potential in basic and clinical researches. A brand‐new MoS₂ nanostructure is designed and fabricated, i.e., layered MoS₂ hollow spheres (LMHSs) with strong absorption in near‐infrared region (NIR) and high photothermal conversion efficiency via a simple and fast chemical aerosol flow method. Owing to curving layered hollow spherical structure, the as‐prepared LMHSs exhibit unique electronic properties comparing with MoS₂ nanosheets. In vitro and in vivo studies demonstrate their high photothermal ablation of cell and tumor elimination rate by single NIR light irradiation. Systematic acute toxicity study indicates that these LMHSs have negligible toxic effects to normal tissues and blood. Remarkably, minimally invasive interventional techniques are introduced to improve tumor targeting of PTT agents for the first time. To explore PTT efficiency on orthotopic transplantation tumors, New Zealand white rabbits with VX₂ tumor in liver are used as animal models. The effective elimination of tumors is successfully realized by PTT under the guidance of digital subtraction angiography, computed tomography, and thermal imaging, which provides a new way for tumor‐targeting delivery and cancer theranostic application.     

Dual Roles of Protein as a Template and a Sulfur Provider: A General Approach to Metal Sulfides for Efficient Photothermal Therapy of Cancer

Fabrication of clinically translatable nanoparticles (NPs) as photothermal therapy (PTT) agents against cancer is becoming increasingly desirable, but still challenging, especially in facile and controllable synthesis of biocompatible NPs with high photothermal efficiency. A new strategy which uses protein as both a template and a sulfur provider is proposed for facile, cost‐effective, and large‐scale construction of biocompatible metal sulfide NPs with controlled structure and high photothermal efficiency. Upon mixing proteins and metal ions under alkaline conditions, the metal ions can be rapidly coordinated via a biuret‐reaction like process. In the presence of alkali, the inert disulfide bonds of S‐rich proteins can be activated to react with metal ions and generate metal sulfide NPs under gentle conditions. As a template, the protein can confine and regulate the nucleation and growth of the metal sulfide NPs within the protein formed cavities. Thus, the obtained metal sulfides such as Ag₂S, Bi₂S₃, CdS, and CuS NPs are all with small size and coated with proteins, affording them biocompatible surfaces. As a model material, CuS NPs are evaluated as a PTT agent for cancer treatment. They exhibit high photothermal efficiency, high stability, water solubility, and good biocompatibility, making them an excellent PTT agent against tumors. This work paves a new avenue toward the synthesis of structure‐controlled and biocompatible metal sulfide NPs, which can find wide applications in biomedical fields.     

Salt-Assisted Low-Temperature Growth of 2D Bi2O2Se with Controlled Thickness for Electronics

Bi₂O₂Se is the most promising 2D material due to its semiconducting feature and high mobility, making it propitious channel material for high-performance electronics that demands highly crystalline Bi₂O₂Se at low-growth temperature. Here, a low-temperature salt-assisted chemical vapor deposition approach for growing single-domain Bi₂O₂Se on a millimeter scale with thicknesses of multilayer to monolayer is presented. Because of the advantage of thickness-dependent growth, systematical scrutiny of layer-dependent Raman spectroscopy of Bi₂O₂Se from monolayer to bulk is investigated, revealing a redshift of the A_1g mode at 162.4 cm⁻¹. Moreover, the long-term environmental stability of ≈2.4 nm thick Bi₂O₂Se is confirmed after exposing the sample for 1.5 years to air. The backgated field effect transistor (FET) based on a few-layered Bi₂O₂Se flake represents decent carrier mobility (≈287 cm² V⁻¹s⁻¹) and an ON/OFF ratio of up to 10⁷. This report indicates a technique to grow large-domain thickness controlled Bi₂O₂Se single crystals for electronics.     

Bolometric Effect in Bi2O2Se Photodetectors

Bi₂O₂Se is emerging as a photosensitive functional material for optoelectronics, and its photodetection mechanism is mostly considered to be a photoconductive regime in previous reports. Here, the bolometric effect is discovered in Bi₂O₂Se photodetectors. The coexistence of photoconductive effect and bolometric effect is generally observed in multiwavelength photoresponse measurements and then confirmed with microscale local heating experiments. The unique photoresponse of Bi₂O₂Se photodetectors may arise from a change of hot electrons during temperature rises instead of photoexcited holes and electrons. Direct proof of the bolometric effect is achieved by real‐time temperature tracking of Bi₂O₂Se photodetectors under time evolution after light excitation. Moreover, the Bi₂O₂Se bolometer shows a high temperature coefficient of resistance (?1.6% K^?1), high bolometric coefficient (?31 nA K^?1), and high bolometric responsivity (>320 A W^?1). These findings offer a new approach to develop bolometric photodetectors based on Bi₂O₂Se layered materials.     

Controlled Synthesis of Ag2Te@Ag2S Core–Shell Quantum Dots with Enhanced and Tunable Fluorescence in the Second Near‐Infrared Window

Fluorescence in the second near‐infrared window (NIR‐II, 900–1700 nm) has drawn great interest for bioimaging, owing to its high tissue penetration depth and high spatiotemporal resolution. NIR‐II fluorophores with high photoluminescence quantum yield (PLQY) and stability along with high biocompatibility are urgently pursued. In this work, a Ag‐rich Ag₂Te quantum dots (QDs) surface with sulfur source is successfully engineered to prepare a larger bandgap of Ag₂S shell to passivate the Ag₂Te core via a facile colloidal route, which greatly enhances the PLQY of Ag₂Te QDs and significantly improves the stability of Ag₂Te QDs. This strategy works well with different sized core Ag₂Te QDs so that the NIR‐II PL can be tuned in a wide range. In vivo imaging using the as‐prepared Ag₂Te@Ag₂S QDs presents much higher spatial resolution images of organs and vascular structures as compared with the same dose of Ag₂Te nanoprobes administrated, suggesting the success of the core–shell synthetic strategy and the potential biomedical applications of core–shell NIR‐II nanoprobes.     

Rational Design of Multifunctional Fe@γ‐Fe2O3@H‐TiO2 Nanocomposites with Enhanced Magnetic and Photoconversion Effects for Wide Applications: From Photocatalysis to Imaging‐Guided Photothermal Cancer Therapy

Titanium dioxide (TiO₂) has been widely investigated and used in many areas due to its high refractive index and ultraviolet light absorption, but the lack of absorption in the visible–near infrared (Vis–NIR) region limits its application. Herein, multifunctional Fe@γ‐Fe₂O₃@H‐TiO₂ nanocomposites (NCs) with multilayer‐structure are synthesized by one‐step hydrogen reduction, which show remarkably improved magnetic and photoconversion effects as a promising generalists for photocatalysis, bioimaging, and photothermal therapy (PTT). Hydrogenation is used to turn white TiO₂ in to hydrogenated TiO₂ (H‐TiO₂), thus improving the absorption in the Vis–NIR region. Based on the excellent solar‐driven photocatalytic activities of the H‐TiO₂ shell, the Fe@γ‐Fe₂O₃ magnetic core is introduced to make it convenient for separating and recovering the catalytic agents. More importantly, Fe@γ‐Fe₂O₃@H‐TiO₂ NCs show enhanced photothermal conversion efficiency due to more circuit loops for electron transitions between H‐TiO₂ and γ‐Fe₂O₃, and the electronic structures of Fe@γ‐Fe₂O₃@H‐TiO₂ NCs are calculated using the Vienna ab initio simulation package based on the density functional theory to account for the results. The reported core–shell NCs can serve as an NIR‐responsive photothermal agent for magnetic‐targeted photothermal therapy and as a multimodal imaging probe for cancer including infrared photothermal imaging, magnetic resonance imaging, and photoacoustic imaging.     

Epitaxial Growth of Ternary Topological Insulator Bi2Te2Se 2D Crystals on Mica

Nanostructures of ternary topological insulator (TI) Bi₂Te₂Se are, in principle, advantageous to the manifestation of topologically nontrivial surface states, due to significantly enhanced surface‐to‐volume ratio compared with its bulk crystals counterparts. Herein, the synthesis of 2D Bi₂Te₂Se crystals on mica via the van der Waals epitaxy method is explored and systematically the growth behaviors during the synthesis process are investigated. Accordingly, 2D Bi₂Te₂Se crystals with domain size up to 50 µm large and thickness down to 2 nm are obtained. A pronounced weak antilocalization effect is clearly observed in the 2D Bi₂Te₂Se crystals at 2 K. The method for epitaxial growth of 2D ternary Bi₂Te₂Se crystals may inspire materials engineering toward enhanced manifestation of the subtle surface states of TIs and thereby facilitate their potential applications in next‐generation spintronics.     

NIR‐Responsive Polycationic Gatekeeper‐Cloaked Hetero‐Nanoparticles for Multimodal Imaging‐Guided Triple‐Combination Therapy of Cancer

Responsive multifunctional organic/inorganic nanohybrids are promising for effective and precise imaging‐guided therapy of cancer. In this work, a near‐infrared (NIR)‐triggered multifunctional nanoplatform comprising Au nanorods (Au NRs), mesoporous silica, quantum dots (QDs), and two‐armed ethanolamine‐modified poly(glycidyl methacrylate) with cyclodextrin cores (denoted as CD‐PGEA) has been successfully fabricated for multimodal imaging‐guided triple‐combination treatment of cancer. A hierarchical hetero‐structure is first constructed via integration of Au NRs with QDs through a mesoporous silica intermediate layer. The X‐ray opacity and photoacoustic (PA) property of Au NRs are utilized for tomography (CT) and PA imaging, and the imaging sensitivity is further enhanced by the fluorescent QDs. The mesoporous feature of silica allows the loading of a typical antitumor drug, doxorubicin (DOX), which are sealed by the polycationic gatekeepers, low toxic hydroxyl‐rich CD‐PGEA/pDNA complexes, realizing the co‐delivery of drug and gene. The photothermal effect of Au NRs is utilized for photothermal therapy (PTT). More interestingly, such photothermal effect also induces a cascade of NIR‐triggered release of DOX through the facilitated detachment of CD‐PGEA gatekeepers for controlled chemotherapy. The resultant chemotherapy and gene therapy for glioma tumors are complementary for the efficiency of PTT. This work presents a novel responsive multifunctional imaging‐guided therapy platform, which combines fluorescent/PA/CT imaging and gene/chemo/photothermal therapy into one nanostructure.     

Unveiling the Fine Structural Distortion of Atomically Thin Bi2O2Se by Third-Harmonic Generation

Bismuth oxyselenide (Bi₂O₂Se), a new type of 2D material, has recently attracted increased attention due to its robust bandgap, stability under ambient conditions, and ultrahigh electron mobility. In such complex oxides, fine structural distortion tends to play a decisive role in determining the unique physical properties, such as the ferrorotational order, ferroelectricity, and magnetoelasticity. Therefore, an in-depth investigation of the fine structural symmetry of Bi₂O₂Se is necessary to exploit its potential applications. However, conventional techniques are either time consuming or requiring tedious sample treatment. Herein, a noninvasive and high-throughput approach is reported for characterizing the fine structural distortion in 2D centrosymmetric Bi₂O₂Se by polarization-dependent third-harmonic generation (THG). Unprecedentedly, the divergence between the experimental results and the theoretical prediction of the perpendicular component of polarization-dependent THG indicates a fine structural distortion, namely, a <1.4° rotation of the oxygen square in the tetragonal (Bi₂O₂) layers. This rotation breaks the intrinsic mirror symmetry of 2D Bi₂O₂Se, eventually reducing the symmetry from the D_4h to the C_4h point group. The results demonstrate that THG is highly sensitive to even fine symmetry variations, thereby showing its potential to uncover hidden phase transitions and interacting polarized sublattices in novel 2D material systems.     

Poly(Vinylpyrollidone)‐ and Selenocysteine‐Modified Bi2Se3 Nanoparticles Enhance Radiotherapy Efficacy in Tumors and Promote Radioprotection in Normal Tissues

The development of a new generation of nanoscaled radiosensitizers that can not only enhance radiosensitization of tumor tissues, but also increase radioresistance of healthy tissue is highly desirable, but remains a great challenge. Here, this paper reports a new versatile theranostics based on poly(vinylpyrollidone)‐ and selenocysteine‐modified Bi₂Se₃ nanoparicles (PVP‐Bi₂Se₃@Sec NPs) for simultaneously enhancing radiotherapeutic effects and reducing the side‐effects of radiation. The as‐prepared nanoparticles exhibit significantly enhanced free‐radical generation upon X‐ray radiation, and remarkable photothermal effects under 808 nm NIR laser irradiation because of their strong X‐ray attenuation ability and high NIR absorption capability. Moreover, these PVP‐Bi₂Se₃@Sec NPs are biodegradable. In vivo, part of selenium can be released from NPs and enter the blood circulation system, which can enhance the immune function and reduce the side‐effects of radiation in the whole body. As a consequence, improved superoxide dismutase and glutathione peroxidase activities, promoted secretion of cytokines, increased number of white blood cell, and reduced marrow DNA suppression are found after radiation treatment in vivo. Moreover, there is no significant in vitro and in vivo toxicity of PVP‐Bi₂Se₃@Sec NPs during the treatment, which demonstrates that PVP‐Bi₂Se₃@Sec NPs have good biocompatibility.     

Charge Transfer Modulation in Vanadium-Doped WS2/Bi2O2Se Heterostructures

The field of photovoltaics is revolutionized in recent years by the development of two–dimensional (2D) type-II heterostructures. These heterostructures are made up of two different materials with different electronic properties, which allows for the capture of a broader spectrum of solar energy than traditional photovoltaic devices. In this study, the potential of vanadium (V)-doped WS₂ is investigated, hereafter labeled V-WS₂, in combination with air-stable Bi₂O₂Se for use in high-performance photovoltaic devices. Various techniques are used to confirm the charge transfer of these heterostructures, including photoluminescence (PL) and Raman spectroscopy, along with Kelvin probe force microscopy (KPFM). The results show that the PL is quenched by 40%, 95%, and 97% for WS₂/Bi₂O₂Se, 0.4 at.% V-WS₂/Bi₂O₂Se, and 2 at.% V-WS₂/Bi₂O₂Se, respectively, indicating a superior charge transfer in V-WS₂/Bi₂O₂Se compared to pristine WS₂/Bi₂O₂Se. The exciton binding energies for WS₂/Bi₂O₂Se, 0.4 at.% V-WS₂/Bi₂O₂Se and 2 at.% V-WS₂/Bi₂O₂Se heterostructures are estimated to be ≈130, 100, and 80 meV, respectively, which is much lower than that for monolayer WS₂. These findings confirm that by incorporating V-doped WS₂, charge transfer in WS₂/Bi₂O₂Se heterostructures can be tuned, providing a novel light-harvesting technique for the development of the next generation of photovoltaic devices based on V-doped transition metal dichalcogenides (TMDCs)/Bi₂O₂Se.     

Molecular Beam Epitaxy and Electronic Structure of Atomically Thin Oxyselenide Films

Atomically thin oxychalcogenides have been attracting intensive attention for their fascinating fundamental properties and application prospects. Bi₂O₂Se, a representative of layered oxychalcogenides, has emerged as an air‐stable high‐mobility 2D semiconductor that holds great promise for next‐generation electronics. The preparation and device fabrication of high‐quality Bi₂O₂Se crystals down to a few atomic layers remains a great challenge at present. Here, molecular beam epitaxy (MBE) of atomically thin Bi₂O₂Se films down to monolayer on SrTiO₃ (001) substrate is achieved by co‐evaporating Bi and Se precursors in oxygen atmosphere. The interfacial atomic arrangements of MBE‐grown Bi₂O₂Se/SrTiO₃ are unambiguously revealed, showing an atomically sharp interface and atom‐to‐atom alignment. Importantly, the electronic band structures of one‐unit‐cell (1‐UC) thick Bi₂O₂Se films are observed by angle‐resolved photoemission spectroscopy (ARPES), showing low effective mass of ≈0.15 m₀ and bandgap of ≈0.8 eV. These results may be constructive to the synthesis of other 2D oxychalcogenides and investigation of novel physical properties.     

Manganese Dioxide Coated WS2@Fe3O4/sSiO2 Nanocomposites for pH‐Responsive MR Imaging and Oxygen‐Elevated Synergetic Therapy

Recently, the development of multifunctional theranostic nanoplatforms to realize tumor‐specific imaging and enhanced cancer therapy via responding or modulating the tumor microenvironment (TME) has attracted tremendous interests in the field of nanomedicine. Herein, tungsten disulfide (WS₂) nanoflakes with their surface adsorbed with iron oxide nanoparticles (IONPs) via self‐assembly are coated with silica and then subsequently with manganese dioxide (MnO₂), on to which polyethylene glycol (PEG) is attached. The obtained WS₂‐IO/S@MO‐PEG appears to be highly sensitive to pH, enabling tumor pH‐responsive magnetic resonance imaging with IONPs as the pH‐inert T2 contrast probe and MnO₂ as the pH‐sensitive T1 contrast probe. Meanwhile, synergistic combination tumor therapy is realized with such WS₂‐IO/S@MO‐PEG, by utilizing the strong near‐infrared light and X‐ray absorbance of WS₂ for photothermal therapy (PTT) and enhanced cancer radiotherapy (RT), respectively, as well as the ability of MnO₂ to decompose tumor endogenous H₂O₂ and relieve tumor hypoxia to further overcome hypoxia‐associated radiotherapy resistance. The combination of PTT and RT with WS₂‐IO/S@MO‐PEG results in a remarkable synergistic effect to destruct tumors. This work highlights the promise of developing multifunction nanocomposites for TME‐specific imaging and TME modulation, aiming at precision cancer synergistic treatment.     

Ultrasensitive 2D Bi2O2Se Phototransistors on Silicon Substrates

2D materials are considered as intriguing building blocks for next‐generation optoelectronic devices. However, their photoresponse performance still needs to be improved for practical applications. Here, ultrasensitive 2D phototransistors are reported employing chemical vapor deposition (CVD)‐grown 2D Bi₂O₂Se transferred onto silicon substrates with a noncorrosive transfer method. The as‐transferred Bi₂O₂Se preserves high quality in contrast to the serious quality degradation in hydrofluoric‐acid‐assisted transfer. The phototransistors show a responsivity of 3.5 × 10⁴ A W^?1, a photoconductive gain of more than 10⁴, and a time response in the order of sub‐millisecond. With back gating of the silicon substrate, the dark current can be reduced to several pA. This yields an ultrahigh sensitivity with a specific detectivity of 9.0 × 10¹³ Jones, which is one of the highest values among 2D material photodetectors and two orders of magnitude higher than that of other CVD‐grown 2D materials. The high performance of the phototransistor shown here together with the developed unique transfer technique are promising for the development of novel 2D‐material‐based optoelectronic applications as well as integrating with state‐of‐the‐art silicon photonic and electronic technologies.     

First Demonstration of Gold Nanorods‐Mediated Photodynamic Therapeutic Destruction of Tumors via Near Infra‐Red Light Activation

Previously, a large volume of papers reports that gold nanorods (Au NRs) are able to effectively kill cancer cells upon high laser doses (usually 808 nm, 1–48 W/cm²) irradiation, leading to hyperthermia‐induced destruction of cancer cells, i.e, photothermal therapy (PTT) effects. Combination of Au NRs‐mediated PTT and organic photosensitizers‐mediated photodynamic therapy (PDT) were also reported to achieve synergistic PTT and PDT effects on killing cancer cells. Herein, we demonstrate for the first time that Au NRs alone can sensitize formation of singlet oxygen (¹O₂) and exert dramatic PDT effects on complete destrcution of tumors in mice under very low LED/laser doses of single photon NIR (915 nm, <130 mW/cm²) light excitation. By changing the NIR light excitation wavelengths, Au NRs‐mediated phototherapeutic effects can be switched from PDT to PTT or combination of both. Both PDT and PTT effects were confirmed by measurements of reactive oxygen species (ROS) and heat shock protein (HSP 70), singlet oxygen sensor green (SOSG) sensing, and sodium azide quenching in cellular experiments. In vivo mice experiments further show that the PDT effect via irradiation of Au NRs by 915 nm can destruct the B16F0 melanoma tumor in mice far more effectively than doxorubicin (a clinically used anti‐cancer drug) as well as the PTT effect (via irradiation of Au NRs by 780 nm light). In addition, we show that Au NRs can emit single photon‐induced fluorescence to illustrate their in vivo locations/distribution.     

Novel Mn3[Co(CN)6]2@SiO2@Ag Core–Shell Nanocube: Enhanced Two‐Photon Fluorescence and Magnetic Resonance Dual‐Modal Imaging‐Guided Photothermal and Chemo‐therapy

The versatile Mn₃[Co(CN)₆]₂@SiO₂@Ag core–shell NCs are prepared by a simple coprecipitation method. Ag nanoparticles with an average diameter of 12 nm deposited on the surface of Mn₃[Co(CN)₆]₂@SiO₂ through S–Ag bonding are fabricated in ethanol solution by reducing silver nitrate (AgNO₃) with NaBH₄. The NCs possess T₁–T₂ dual‐modal magnetic resonance imaging ability. The inner Prussian blue analogs (PBAs) Mn₃[Co(CN)₆]₂ exhibit bright two‐photon fluorescence (TPF) imaging when excited at 730 nm. Moreover, the TPF imaging intensity displays 1.85‐fold enhancement after loading of Ag nanoparticles. Besides, the sample also has multicolor fluorescence imaging ability under 403, 488, and 543 nm single photon excitation. The as‐synthesized Mn₃[Co(CN)₆]₂@SiO₂@Ag NCs show a DOX loading capacity of 600 mg g⁻¹ and exhibit an excellent ability of near‐infrared (NIR)‐responsive drug release and photothermal therapy (PTT) which is induced from the relative high absorbance in NIR region. The combined chemotherapy and PTT against cancer cells in vitro test shows high therapeutic efficiency. The multimodal treatment and imaging could lead to this material a potential multifunctional system for biomedical diagnosis and therapy.     

Theranostic 2D Tantalum Carbide (MXene)

The large‐dimensional and rigid ceramic bulks fabricated by high‐temperature solid‐phase reaction and sintering have never been considered for possibly entering and circulating within the blood vessels for biomedical applications, especially on combating cancer. Here, it is reported for the first time that MAX ceramic biomaterials exhibit unique functionalities for dual‐mode photoacoustic/computed tomography imaging and are highly effective for in vivo photothermal ablation of tumors upon being exfoliated into ultrathin nanosheets within atomic thickness (MXene). As a paradigm, 2D ultrathin tantalum carbide nanosheets (Ta₄C₃ MXenes) with nanosized lateral sizes are successfully synthesized based on a two‐step liquid exfoliation strategy of MAX phase Ta₄AlC₃ by combined hydrofluoric acid (HF) etching and probe sonication. The structural, electronic, and surface characteristics of the as‐exfoliated nanosheets are revealed by various characterizations combined with first‐principles calculations via density functional theory. Especially, the superior photothermal‐conversion performance (efficiency η of 44.7%) and in vitro/in vivo photothermal ablation of tumor by biocompatible soybean phospholipid‐modified Ta₄C₃ nanosheets are systematically revealed and demonstrated. Based on the large family members of MXenes, this work may offer a paradigm that MXenes can achieve the specific biomedical applications (here, theranostic) providing that their compositions and nanostructures are carefully tuned and optimized to meet the strict requirements of biomedicine.