Emerging metal ion-coordinated black phosphorus nanosheets and black phosphorus quantum dots with excellent stabilities

Reaction Chemistry at Discrete Organometallic Fragments on Black Phosphorus

Black phosphorus (bP) is a two-dimensional van der Waals material unique in its potential to serve as a support for single-site catalysts due to its similarity to molecular phosphines, ligands quintessential in homogeneous catalysis. However, there is a scarcity of synthetic methods to install single metal centers on the bP lattice. Here, we demonstrate the functionalization of bP nanosheets with molecular Re and Mo complexes. A suite of characterization techniques, including infrared, X-ray photoelectron and X-ray absorption spectroscopy as well as scanning transmission electron microscopy corroborate that the functionalized nanosheets contain a high density of discrete metal centers directly bound to the bP surface. Moreover, the supported metal centers are chemically accessible and can undergo ligand exchange transformations without detaching from the surface. The steric and electronic properties of bP as a ligand are estimated with respect to molecular phosphines. Sterically, bP resembles tri(tolyl)phosphine when monodentate to a metal center, and bis(diphenylphosphino)propane when bidentate, whereas electronically bP is a σ-donor as strong as a trialkyl phosphine. This work is foundational in elucidating the nature of black phosphorus as a ligand and underscores the viability of using bP as a basis for single-site catalysts.

Hyaluronic acid-based injectable nanocomposite hydrogels with photo-thermal antibacterial properties for infected chronic diabetic wound healing

A hydrogel wound dressing with a single functionality fails to meet the requirements for successful clinical treatment of chronic diabetic wounds that generally possess complicated microenvironments. A multifunctional hydrogel is thus highly desirable for improved clinical treatment. For this purpose, we reported herein construction of an injectable nanocomposite hydrogel with self-healing and photo-thermal properties as an antibacterial adhesive via dynamic Michael addition reaction and electrostatic interactions among three building moieties, i.e., catechol and thiol-modified hyaluronic acid (HA-CA and HA-SH), poly(hexamethylene guanidine) (PHMG), and black phosphorus nanosheets (BPs). An optimized hydrogel formulation eliminated over 99.99 % of bacteria (E. coli and S. aureus) and exhibited a free radical scavenging capability >70 % as well as photo-thermal properties in addition to viscoelastic characteristics, degradation properties in vitro, good adhesion and self-adaptation capacity. Wound healing experiments in vivo further confirmed the better performance of the developed hydrogels than that of a commercially available dressing (Tegaderm™) in promoting the healing of infected chronic wounds by preventing wound infection, decreasing inflammation, supporting collagen deposition, facilitating angiogenesis, and improving granulation tissues formation in the wound sites. Overall, the HA-based injectable composite hydrogels developed herein represent promising multifunctional wound dressings for infected diabetic wound repair.

Exosomes incorporated with black phosphorus quantum dots attenuate retinal angiogenesis via disrupting glucose metabolism

Black phosphorus quantum dots (BPQDs) have shown potential in tumor therapy, however, their anti-angiogenic functions have not been studied. Although BPQDs are easily degraded to non-toxic phosphrous, the reported toxicity, poor stability, and non-selectivity largely limit their further application in medicine. In this study, a vascular targeting, biocompatible, and cell metabolism-disrupting nanoplatform is engineered by incorporating BPQDs into exosomes modified with the Arg-Gly-Asp (RGD) peptide (BPQDs@RGD-EXO nanospheres, BREs). BREs inhibit endothelial cells (ECs) proliferation, migration, tube formation, and sprouting in vitro. The anti-angiogenic role of BREs in vivo is evaluated using mouse retinal vascular development model and oxygen-induced retinopathy model. Combined RNA-seq and metabolomic analysis reveal that BREs disrupt glucose metabolism, which is further confirmed by evaluating metabolites, ATP production and the c-MYC/Hexokinase 2 pathway. These BREs are promising anti-angiogenic platforms for the treatment of pathological retinal angiogenesis with minimal side effects.

Cotton swabs decorated with Ag@BPQD for the fluorescence determination of 3-aminosalicylic and 5-aminosalicylic acid

Novel and portable cotton swab-based fluorometry was constructed for the first time for 3-aminosalicylic acid (3-ASA) and 5-aminosalicylic acid (5-ASA) detection. It was carried out by fluorescence enhancement on silver (Ag)-doped black phosphorus quantum dots (Ag@BPQD). Ag@BPQD were prepared from AgNO₃ and bulk black phosphorus in N, N-dimethylformamide (DMF) solution by solvothermal decomposition after mechanical exfoliation. Ag@BPQD show blue fluorescence with a quantum yield (QY) of 2.43%. In the presence of Ag@BPQD, 3-ASA exhibited bright blue fluorescence (λ_ex = 328 nm, λ_em = 448 nm). The fluorescence of 5-ASA was also enhanced significantly and exhibited bright green emission (λ_ex = 328 nm, λ_em = 484 nm). The linear range of 3-ASA is 0-90 μM with a detection limit (LOD) of 0.10 μM, relative standard deviation (RSD) ≤ 2.04%, and a recovery range of 98.0-104.3%. The linear range of 5-ASA is 0-120 μM with a LOD of 0.12 μM, RSD ≤ 1.34%, and a recovery range of 98.0-101.3%. When 3-ASA and 5-ASA were mixed in different ratios, the fluorescence showed different colors. The possible mechanism of the interaction between 3-ASA (or 5-ASA) and Ag@BPQD may be ascribed to the generation of excited-state intramolecular proton transfer. To realize convenient detection of 3-ASA and 5-ASA, a Ag@BPQD portable sensing method using cotton swabs were built. The proposed approach provides the detection of 3-ASA and 5-ASA in environmental and biological samples with high efficiency, accuracy and portability.

Metal-Doped Boron Quantum Dots for Versatile Detection of Lactate and Fluorescence Bioimaging

To improve the stability and fluorescence (FL) of monoelemental boron nanomaterials, this work put forward a metal-coordination strategy to explore emerging metal-doped boron quantum dots, Co@BQDs. Through theoretical calculations, B-Co bonding as predicted can suppress the B-O reaction and protect the electronic structures of exfoliated two-dimensional (2D) boron from oxidation and decomposition upon exposure to oxygen. In experimental studies, Co²⁺ was added into a dispersion liquid of bulk boron and subjected to probe sonication to promote Co²⁺ adsorption on the surface of exfoliated 2D boron, followed by Co²⁺ coordination with exposed boron atoms. Solvothermal treatment of exfoliated 2D boron resulted in the generation of Co²⁺-doped 0D boron Co@BQDs. Experimental results confirm that Co@BQDs have higher colloidal and FL stability than BQDs as a reference. B-Co bonding formation to suppress the B-O reaction ensures the high stability of exfoliated boron structures. A dispersion liquid of Co@BQDs with stable and bright FL was used for visual FL imaging of solutions and solid substrates. Based on enzymatic and cascade oxidation-induced FL quenching of Co@BQDs, a novel FL bio-probe of lactate was explored. This bio-probe, with a broad detection range of 0.01-10 mM and a low detection limit of 3.1 μM, enables FL sensing of lactate in biosamples and shows high detection recoveries of 98.0-102.8%. Moreover, this bio-probe realized versatile FL imaging and visual detection of lactate in liquid/solid-phase systems. These results demonstrate great prospects of Co@BQDs as emerging and efficient imaging reagents for long-term tracking and bioimaging applications.

Monoelemental two-dimensional boron nanomaterials beyond theoretical simulations: From experimental preparation, functionalized modification to practical applications

During the past decade, there is an explosive growth of theoretical and computational studies on 2D boron-based nanomaterials. In terms of extensive predictions from theoretical simulations, borophene, boron nanosheets and 2D boron derivatives show excellent structural, electronic, photonic and nonlinear optical characteristics, and potential applications in a wide range of fields. In recent years, previous studies have reported the successful experimental preparations, superior properties, multi-functionalized modifications of various 2D boron and its derivatives, which show many practical applications in significant fields. To further promote the ever-increasing experimental studies, this present review systematically summarizes recent progress on experimental preparation methods, functionalized modification strategies and practical applications of 2D boron-based nanomaterials and multifunctional derivatives. Firstly, this review summarizes the experimental preparation methods, including molecular beam epitaxy, chemical vapor deposition, liquid-phase exfoliation, chemical reaction, and other auxiliary methods. Then, various strategies for functionalized modification are introduced overall, focusing on borophene derivatives, boron-based nanosheets, atom-introduced, chemically-functionalized borophene and boron nanosheets, borophene or boron nanosheet-based heterostructures, and other functionalized 2D boron nanomaterials. Subsequently, various potential applications are discussed in detail, involving energy storage, catalysis conversion, photonics, optoelectronics, sensors, bio-imaging, biomedicine therapy, and adsorption. We comment the state-of-the-art related studies concisely, and also discuss the current status, probable challenges and perspectives rationally. This review is timely, comprehensive, in-depth and highly attractive for scientists from multiple disciplines and scientific fields, and can facilitate further development of advanced functional low-dimensional nanomaterials and multi-functionalized systems toward high-performance practical applications in significant fields.

Ten Years Progress of Electrical Detection of Heavy Metal Ions (HMIs) Using Various Field-Effect Transistor (FET) Nanosensors: A Review

Heavy metal pollution remains a major concern for the public today, in line with the growing population and global industrialization. Heavy metal ion (HMI) is a threat to human and environmental safety, even at low concentrations, thus rapid and continuous HMI monitoring is essential. Among the sensors available for HMI detection, the field-effect transistor (FET) sensor demonstrates promising potential for fast and real-time detection. The aim of this review is to provide a condensed overview of the contribution of certain semiconductor substrates in the development of chemical and biosensor FETs for HMI detection in the past decade. A brief introduction of the FET sensor along with its construction and configuration is presented in the first part of this review. Subsequently, the FET sensor deployment issue and FET intrinsic limitation screening effect are also discussed, and the solutions to overcome these shortcomings are summarized. Later, we summarize the strategies for HMIs' electrical detection, mechanisms, and sensing performance on nanomaterial semiconductor FET transducers, including silicon, carbon nanotubes, graphene, AlGaN/GaN, transition metal dichalcogenides (TMD), black phosphorus, organic and inorganic semiconductor. Finally, concerns and suggestions regarding detection in the real samples using FET sensors are highlighted in the conclusion.

Conjugated polymer coating enabled light-resistant black phosphorus with enhanced stability

As an advanced two-dimensional (2D) material with unique properties, black phosphorus (BP) has attracted great attention in a variety of fields. One of the main obstacles for the practical application of BP is the poor ambient stability of few-layer BP, especially under light irradiation. In this study, a light-absorbing conjugated polymer is functionalized on the surface of BP during the exfoliation process, yielding BP nanosheets with light-resistance. The obtained BP/polymer nanosheets demonstrate enhanced stability compared to pure BP under sunlight. Systematic characterization reveals that the crystal structure and electronic characteristics of BP are well retained after 30 days of sun exposure. This convenient and efficient conjugated polymer passivation provides a novel light-prohibited method to improve the stability of BP for future applications.

Recent advances in black phosphorus-based electrochemical sensors: A review

Since the discovery of liquid-phase-exfoliated black phosphorus (BP) as a field-effect transistor in 2014, BP, with its 2D layered structure, has attracted significant attention, owing to its anisotropic electroconductivity, tunable direct bandgap, extraordinary surface activity, moderate switching ratio, high hole mobility, good biocompatibility, and biodegradability. Several pioneering research efforts have explored the application of BP in different types of electrochemical sensors. This review summarizes the latest synthesis methods, protection strategies, and electrochemical sensing applications of BP and its derivatives. The typical synthesis methods for BP-based crystals, nanosheets, and quantum dots are discussed in detail; the degradation of BP under ambient conditions is introduced; and state-of-the-art protection methodologies for enhancing BP stability are explored. Various electrochemical sensing applications, including chemically modified electrodes, electrochemiluminescence sensors, enzyme electrodes, electrochemical aptasensors, electrochemical immunosensors, and ion-selective electrodes are discussed in detail, along with the mechanisms of BP functionalization, sensing strategies, and sensing properties. Finally, the major challenges in this field are outlined and future research avenues for BP-based electrochemical sensors are highlighted.