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.     

Bright Aggregation‐Induced‐Emission Dots for Targeted Synergetic NIR‐II Fluorescence and NIR‐I Photoacoustic Imaging of Orthotopic Brain Tumors

Precise diagnostics are of significant importance to the optimal treatment outcomes of patients bearing brain tumors. NIR‐II fluorescence imaging holds great promise for brain‐tumor diagnostics with deep penetration and high sensitivity. This requires the development of organic NIR‐II fluorescent agents with high quantum yield (QY), which is difficult to achieve. Herein, the design and synthesis of a new NIR‐II fluorescent molecule with aggregation‐induced‐emission (AIE) characteristics is reported for orthotopic brain‐tumor imaging. Encapsulation of the molecule in a polymer matrix yields AIE dots showing a very high QY of 6.2% with a large absorptivity of 10.2 L g^?1 cm^?1 at 740 nm and an emission maximum near 1000 nm. Further decoration of the AIE dots with c‐RGD yields targeted AIE dots, which afford specific and selective tumor uptake, with a high signal/background ratio of 4.4 and resolution up to 38 µm. The large NIR absorptivity of the AIE dots facilitates NIR‐I photoacoustic imaging with intrinsically deeper penetration than NIR‐II fluorescence imaging and, more importantly, precise tumor‐depth detection through intact scalp and skull. This research demonstrates the promise of NIR‐II AIE molecules and their dots in dual NIR‐II fluorescence and NIR‐I photoacoustic imaging for precise brain cancer diagnostics.     

Miniature Hollow Gold Nanorods with Enhanced Effect for In Vivo Photoacoustic Imaging in the NIR‐II Window

The miniaturization of gold nanorods exhibits a bright prospect for intravital photoacoustic imaging (PAI) and the hollow structure possesses a better plasmonic property. Herein, miniature hollow gold nanorods (M‐AuHNRs) (≈46 nm in length) possessing strong plasmonic absorbance in the second near‐infrared (NIR‐II) window (1000–1350 nm) are developed, which are considered as the most suitable range for the intravital PAI. The as‐prepared M‐AuHNRs exhibit 3.5 times stronger photoacoustic signal intensity than the large hollow Au nanorods (≈105 nm in length) at 0.2 optical density under 1064 nm laser irradiation. The in vivo biodistribution measurement shows that the accumulation in tumor of miniature nanorods is twofold as high as that of the large counterpart. After modifying with a tumor‐targeting molecule and fluorochrome, in living tumor‐bearing mice, the M‐AuHNRs group gives a high fluorescence intensity in tumors, which is 3.6‐fold that of the large ones with the same functionalization. Moreover, in the intravital PAI of living tumor‐bearing mice, the M‐AuHNRs generate longer‐lasting and stronger photoacoustic signal than the large counterpart in the NIR‐II window. Overall, this study presents the fabrication of M‐AuHNRs as a promising contrast agent for intravital PAI.     

Facile Aqueous‐Phase Synthesis of Biocompatible and Fluorescent Ag2S Nanoclusters for Bioimaging: Tunable Photoluminescence from Red to Near Infrared

Low toxicity and fluorescent nanomaterials have many advantages in biological imaging. Herein, a novel and facile aqueous‐phase approach to prepare biocompatible and fluorescent Ag₂S nanoclusters (NCs) is designed and investigated. The resultant Ag₂S NCs show tunable luminescence from the visible red (624 nm) to the near infrared (NIR; 724 nm) corresponding to the increasing size of the NCs. The key for preparing tunable fluorescent Ag₂S NCs is the proper choice of capping reagent, glutathione (GSH), and the novel sulfur‐hydrazine hydrate complex as the S^2? source. As a naturally occurring and readily available tripeptide, GSH functions as an important scaffold to prevent NCs from growing large nanoparticles. Additionally, GSH is a small biomolecule with several functional groups, including carboxyl and amino groups, which suggests the resultant Ag₂S NCs are well‐dispersed in aqueous solution. These advantages make the as‐prepared Ag₂S NCs potentially applicable to biological labeling as well. For example, the resultant Ag₂S NCs are used as a probe for MC3T3‐EI cellular imaging.     

Hierarchically Nanostructured Hybrid Platform for Tumor Delineation and Image‐Guided Surgery via NIR‐II Fluorescence and PET Bimodal Imaging

Bimodal imaging with fluorescence in the second near infrared window (NIR‐II) and positron emission tomography (PET) has important significance for tumor diagnosis and management because of complementary advantages. It remains challenging to develop NIR‐II/PET bimodal probes with high fluorescent brightness. Herein, bioinspired nanomaterials (melanin dot, mesoporous silica nanoparticle, and supported lipid bilayer), NIR‐II dye CH‐4T, and PET radionuclide ⁶⁴Cu are integrated into a hybrid NIR‐II/PET bimodal nanoprobe. The resultant nanoprobe exhibits attractive properties such as highly uniform tunable size, effective payload encapsulation, high stability, dispersibility, and biocompatibility. Interestingly, the incorporation of CH‐4T into the nanoparticle leads to 4.27‐fold fluorescence enhancement, resulting in brighter NIR‐II imaging for phantoms in vitro and in situ. Benefiting from the fluorescence enhancement, NIR‐II imaging with the nanoprobe is carried out to precisely delineate and resect tumors. Additionally, the nanoprobe is successfully applied in tumor PET imaging, showing the accumulation of the nanoprobe in a tumor with a clear contrast from 2 to 24 h postinjection. Overall, this hierarchically nanostructured platform is able to dramatically enhance fluorescent brightness of NIR‐II dye, detect tumors with NIR‐II/PET imaging, and guide intraoperative resection. The NIR‐II/PET bimodal nanoprobe has high potential for sensitive preoperative tumor diagnosis and precise intraoperative image‐guided surgery.     

S‐Doped Carbon Fibers Uniformly Embedded with Ultrasmall TiO2 for Na+/Li+ Storage with High Capacity and Long‐Time Stability

Building a rechargeable battery with high capacity, high energy density, and long lifetime contributes to the development of novel energy storage devices in the future. Although carbon materials are very attractive anode materials for lithium‐ion batteries (LIBs), they present several deficiencies when used in sodium‐ion batteries (SIBs). The choice of an appropriate structural design and heteroatom doping are critical steps to improve the capacity and stability. Here, carbon‐based nanofibers are produced by sulfur doping and via the introduction of ultrasmall TiO₂ nanoparticles into the carbon fibers (CNF‐S@TiO₂). It is discovered that the introduction of TiO₂ into carbon nanofibers can significantly improve the specific surface area and microporous volume for carbon materials. The TiO₂ content is controlled to obtain CNF‐S@TiO₂‐5 to use as the anode material for SIBs/LIBs with enhanced electrochemical performance in Na⁺/Li⁺ storage. During the charge/discharge process, the S‐doping and the incorporation of TiO₂ nanoparticles into carbon fibers promote the insertion/extraction of the ions and enhance the capacity and cycle life. The capacity of CNF‐S@TiO₂‐5 can be maintained at ≈300 mAh g^?1 over 600 cycles at 2 A g^?1 in SIBs. Moreover, the capacity retention of such devices is 94%, showing high capacity and good stability.     

Plasma‐Induced Amorphous Shell and Deep Cation‐Site S Doping Endow TiO2 with Extraordinary Sodium Storage Performance

Structural design and modification are effective approaches to regulate the physicochemical properties of TiO₂, which play an important role in achieving advanced materials. Herein, a plasma‐assisted method is reported to synthesize a surface‐defect‐rich and deep‐cation‐site‐rich S doped rutile TiO₂ (R‐TiO_2–x‐S) as an advanced anode for the Na ion battery. An amorphous shell (≈3 nm) is induced by the Ar/H₂ plasma, which brings about the subsequent high S doping concentration (≈4.68 at%) and deep doping depth. Experimental results and density functional theory calculations demonstrate greatly facilitated ion diffusion, improved electronic conductivity, and an increased mobility rate of holes for R‐TiO_2?x‐S, which result in superior rate capability (264.8 and 128.5 mAh g^?1 at 50 and 10 000 mA g^?1, respectively) and excellent cycling stability (almost 100% retention over 6500 cycles). Such improvements signify that plasma treatment offers an innovative and general approach toward designing advanced battery materials.     

Incorporating Nitrogen‐Doped Graphene Quantum Dots and Ni3S2 Nanosheets: A Synergistic Electrocatalyst with Highly Enhanced Activity for Overall Water Splitting

A noble‐metal‐free electrocatalyst is fabricated via in situ formation of nanocomposite of nitrogen‐doped graphene quantum dots (NGQDs) and Ni₃S₂ nanosheets on the Ni foam (Ni₃S₂‐NGQDs/NF). The resultant Ni₃S₂‐NGQDs/NF can serve as an active, binder‐free, and self‐supported catalytic electrode for direct water splitting, which delivers a current density of 10 mA cm^?2 at an overpotential of 216 mV for oxygen evolution reaction and 218 mV for hydrogen evolution reaction in alkaline media. This bifunctional electrocatalyst enables the construction of an alkali electrolyzer with a low cell voltage of 1.58 V versus reversible hydrogen electrode (RHE) at 10 mA cm^?2. The experimental results and theoretical calculations demonstrate that the synergistic effects of the constructed active interfaces are the key factor for excellent performance. The nanocomposite of NGQDs and Ni₃S₂ nanosheets can be promising water splitting electrocatalyst for large‐scale hydrogen generation or other energy storage and conversion applications.     

Synthesis of Large‐Size 1T′ ReS2xSe2(1−x) Alloy Monolayer with Tunable Bandgap and Carrier Type

Chemical vapor deposition growth of 1T′ ReS_2x Se_{2(1?x )} alloy monolayers is reported for the first time. The composition and the corresponding bandgap of the alloy can be continuously tuned from ReSe₂ (1.32 eV) to ReS₂ (1.62 eV) by precisely controlling the growth conditions. Atomic‐resolution scanning transmission electron microscopy reveals an interesting local atomic distribution in ReS_2x Se_{2(1?x )} alloy, where S and Se atoms are selectively occupied at different X sites in each Re‐X₆ octahedral unit cell with perfect matching between their atomic radius and space size of each X site. This structure is much attractive as it can induce the generation of highly desired localized electronic states in the 2D surface. The carrier type, threshold voltage, and carrier mobility of the alloy‐based field effect transistors can be systematically modulated by tuning the alloy composition. Especially, for the first time the fully tunable conductivity of ReS_2x Se_{2(1?x )} alloys from n‐type to bipolar and p‐type is realized. Owing to the 1T′ structure of ReS_2x Se_{2(1?x )} alloys, they exhibit strong anisotropic optical, electrical, and photoelectric properties. The controllable growth of monolayer ReS_2x Se_{2(1?x )} alloy with tunable bandgaps and electrical properties as well as superior anisotropic feature provides the feasibility for designing multifunctional 2D optoelectronic devices.     

Strong and Tunable Electrical Anisotropy in Type‐II Weyl Semimetal Candidate WP2 with Broken Inversion Symmetry

A transition metal diphosphide, WP₂, is a candidate for type‐II Weyl semimetals (WSMs) in which spatial inversion symmetry is broken and Lorentz invariance is violated. As one of the prerequisites for the presence of the WSM state in WP₂, spatial inversion symmetry breaking in this compound has rarely been investigated. Furthermore, the anisotropy of the WP₂ electrical properties and whether its electrical anisotropy can be tuned remain elusive. Angle‐resolved polarized Raman spectroscopy, electrical transport, optical spectroscopy, and first‐principle studies of WP₂ are reported. The energies of the observed Raman‐active phonons and the angle dependences of the detected phonon intensities are consistent with results obtained by first‐principle calculations and analysis of the proposed crystal symmetry without spatial inversion, showing that spatial inversion symmetry is broken in WP₂. Moreover, the measured ratio (R_c /R_a ) between the crystalline c‐axis and a‐axis electrical resistivities exhibits a weak dependence on temperature (T) in the temperature range from 100 to 250 K, but increases abruptly at T ≤ 100 K, and then reaches the value of ≈8.0 at T = 10 K, which is by far the strongest in‐plane electrical resistivity anisotropy among the reported type‐II WSM candidates with comparable carrier concentrations. Optical spectroscopy study, together with the first‐principle calculations on the electronic band structure, reveals that the abrupt enhancement of the electrical resistivity anisotropy at T ≤ 100 K mainly arises from a sharp increase in the scattering rate anisotropy at low temperatures. More interestingly, the R_c /R_a of WP₂ at T = 10 K can be tuned from 8.0 to 10.6 as the magnetic field increases from 0 to 9 T. The so‐far‐strongest and magnetic‐field‐tunable electrical resistivity anisotropy found in WP₂ can serve as a degree of freedom for tuning the electrical properties of type‐II WSMs, which paves the way for the development of novel electronic applications based on type‐II WSMs.     

2D Ca3Sn2S7 Chalcogenide Perovskite: A Graphene‐Like Semiconductor with Direct Bandgap 0.5 eV and Ultrahigh Carrier Mobility 6.7 × 104 cm2 V−1 s−1

Graphene, a star 2D material, has attracted much attention because of its unique properties including linear electronic dispersion, massless carriers, and ultrahigh carrier mobility (10⁴–10⁵ cm² V^?1 s^?1). However, its zero bandgap greatly impedes its application in the semiconductor industry. Opening the zero bandgap has become an unresolved worldwide problem. Here, a novel and stable 2D Ruddlesden–Popper‐type layered chalcogenide perovskite semiconductor Ca₃Sn₂S₇ is found based on first‐principles GW calculations, which exhibits excellent electronic, optical, and transport properties, as well as soft and isotropic mechanical characteristics. Surprisingly, it has a graphene‐like linear electronic dispersion, small carrier effective mass (0.04 m₀), ultrahigh room‐temperature carrier mobility (6.7 × 10⁴ cm² V^?1 s^?1), Fermi velocity (3 × 10⁵ m s^?1), and optical absorption coefficient (10⁵ cm^?1). Particularly, it has a direct quasi‐particle bandgap of 0.5 eV, which realizes the dream of opening the graphene bandgap in a new way. These results guarantee its application in infrared optoelectronic and high‐speed electronic devices.