Solution-Processable Route for Large-Area Uniform 2D Semiconductor Nanofilms

The semiconductor thin film engineering technique plays a key role in the development of advanced electronics. Printing uniform nanofilms on freeform surfaces with high efficiency and low cost is significant for actual industrialization in electronics. Herein, a high-throughput colloidal printing (HTCP) strategy is reported for fabricating large-area and uniform semiconductor nanofilms on freeform surfaces. High-throughput and uniform printing rely on the balance of atomization and evaporation, as well as the introduced thermal Marangoni flows of colloidal dispersion, that suppresses outward capillary flows. Colloidal printing with in situ heating enables the fast fabrication of large-area semiconductor nanofilms on freeform surfaces, such as SiO2/Si, Al2O3, quartz glass, poly(ethylene terephthalate) (PET), Al foil, plastic tube, and Ni foam, expanding their technological applications where substrates are essential. The printed SnS2 nanofilms are integrated into thin-film semiconductor gas sensors with one of the fastest responses (8 s) while maintaining the highest sensitivity (Rg/Ra = 21) (toward 10 ppm NO2), as well as an ultralow limit of detection (LOD) of 46 ppt. The ability to print uniform semiconductor nanofilms on freeform surfaces with high-throughput promises the development of next-generation electronics with low cost and high efficiency.

Deep-Learning-Assisted Discriminative Detection of Vitamin B12 and Vitamin B9 by Fluorescent MoSe2 Quantum Dots

A facile and environmentally mindful approach for the synthesis of MoSe2 QDs was developed via the hydrothermal method from bulk MoSe2. In this, the exfoliation of MoSe2 was enhanced with the aid of an intercalation agent (KOH), which could reduce the exfoliation time and increase the exfoliation efficiency to form MoSe2 QDs. We found that MoSe2 QDs display blue emission that is suitable for different applications. This fluorescence property of MoSe2 QDs was harnessed to fabricate a dual-modal sensor for the detection of both vitamin B12 (VB12) and vitamin B9 (VB9), employing fluorescence quenching. We performed a detailed study on the fluorescence quenching mechanism of both analytes. The predominant quenching mechanism for VB12 is via Förster resonance energy transfer. In contrast, the recognition of VB9 primarily relies on the inner filter effect. We applied an emerging and captivating approach to pattern recognition, the deep-learning method, which enables machines to "learn" patterns through training, eliminating the need for explicit programming of recognition methods. This attribute endows deep-learning with immense potential in the realm of sensing data analysis. Here, analyzing the array-based sensing data, the deep-learning technique, "convolution neural networks", has achieved 93% accuracy in determining the contribution of VB12 and VB9.

An Overview of Nanomaterial Applications in Pharmacology

Nanotechnology has become one of the most extensive fields of research. Nanoparticles (NPs) form the base for nanotechnology. Recently, nanomaterials (NMs) are widely used due to flexible chemical, biological, and physical characteristics with improved efficacy in comparison to bulk counterparts. The significance of each class of NMs is enhanced by identifying their properties. Day by day, there is an emergence of various applications of NMs, but the toxic effects associated with them cannot be avoided. NMs demonstrate therapeutic abilities by enhancing the drug delivery system, diagnosis, and therapeutic effects of numerous agents, but determining the benefits of NMs over other clinical applications (disease-specific) or substances is an ongoing investigation. This review is aimed at defining NMs and NPs and their types, synthesis, and pharmaceutical, biomedical, and clinical applications.

Molybdenum-oxo-sulfide quantum dot-based nanocarrier: Efficient generation of reactive oxygen species via photo/chemodynamic therapy and stimulus-induced drug release

The fabrication of multifunctional nano-therapies has increased gradually to strengthen the therapeutic performance and minimize adverse effects of traditional cancer treatment strategies. Currently, we have designed a facile preparation drug-loaded nanocarrier for multimodal cancer therapy upon external stimuli. First, defect-rich molybdenum oxo-sulfide (MoO_xS_2-x) quantum dots (QDs) was synthesized via rapid biomineralization techniques with superior optical quantum yield reaching upto 37.28%. The presence of the Fenton ion, Mo^+IV/+VI, enables MoO_xS_2-x QDs to efficiently catalyze peroxide solutions to produce •OH radicals for chemodynamic treatment (CDT) and also deactivate the intracellular glutathione (GSH) enzymes through redox reaction for boosted reactive oxygen species (ROS)-mediated therapies. In addition, upon laser combination, MoO_xS_2-x QDs generate ROS for photodynamic therapy (PDT). Also, due to a large amount of sulfide content, MoO_xS_2-x QDs showed excellent H₂S gas release in acidic pH for cancer gas therapy. Then, MoO_xS_2-x QDs was further conjugated with ROS-responsive thioketal linked Camptothecin (CPT-TK-COOH) drug, forming a multitargeted MoO_xS_2-xCPT anticancer agent with better drug-loading efficiency (38.8%). After triggering the ROS generation through the CDT and PDT mechanisms, the thioketal linkage was disrupted, releasing up to 79% of the CPT drug in 48 h. Besides, in vitro experiments verified that MoO_xS_2-x QDs possess higher biocompatibility with 4T1 and HeLa cells but also showed considerable toxicity in the presence of laser/H₂O₂, resulting in 84.45% cell death through PDT/CDT and chemotherapeutic effects. Therefore, the designed MoO_xS_2-xCPT exhibited outstanding therapeutic benefits for image-guided cancer therapy.

Layer-Structured Anisotropic Metal Chalcogenides: Recent Advances in Synthesis, Modulation, and Applications

The unique electronic and catalytic properties emerging from low symmetry anisotropic (1D and 2D) metal chalcogenides (MCs) have generated tremendous interest for use in next generation electronics, optoelectronics, electrochemical energy storage devices, and chemical sensing devices. Despite many proof-of-concept demonstrations so far, the full potential of anisotropic chalcogenides has yet to be investigated. This article provides a comprehensive overview of the recent progress made in the synthesis, mechanistic understanding, property modulation strategies, and applications of the anisotropic chalcogenides. It begins with an introduction to the basic crystal structures, and then the unique physical and chemical properties of 1D and 2D MCs. Controlled synthetic routes for anisotropic MC crystals are summarized with example advances in the solution-phase synthesis, vapor-phase synthesis, and exfoliation. Several important approaches to modulate dimensions, phases, compositions, defects, and heterostructures of anisotropic MCs are discussed. Recent significant advances in applications are highlighted for electronics, optoelectronic devices, catalysts, batteries, supercapacitors, sensing platforms, and thermoelectric devices. The article ends with prospects for future opportunities and challenges to be addressed in the academic research and practical engineering of anisotropic MCs.

Recent Advances in the Synthesis of MXene Quantum Dots

Quantum dots (QDs) with ultrahigh surface-to-volume ratio, abundant edge active sites, forceful quantum confinement and other remarkable physio-chemical properties, have garnered considerable research interest. MXene QDs, as an emerging member of them, have also attracted wide attention in the last six years, and shown great achievements in many fields. This critical review systematically summarizes the various methods for synthesizing MXene QDs. The characteristics and corresponding applications of various MXene QDs are also presented. The advantages and disadvantages of various synthetic methods, and the limitations of corresponding MXene QDs are compared and highlighted. Finally, the challenges and perspectives of synthesizing MXene QDs are proposed. We hope this review will enlighten researchers to the fabrication of more advancing and promising MXene-based QDs with proprietary properties in diverse applications.

Tungsten-based Nanomaterials in the Biomedical Field: A Bibliometric Analysis of Research Progress and Prospects

Tungsten-based nanomaterials (TNMs) with diverse nanostructures and unique physicochemical properties have been widely applied in the biomedical field. Although various reviews have described the application of TNMs in specific biomedical fields, there are still no comprehensive studies that summarize and analyze research trends of the field as a whole. To identify and further promote the development of biomedical TNMs, a bibliometric analysis method is used to analyze all relevant literature on this topic. First, general bibliometric distributions of the dataset by year, country, institute, referenced source, and research hotspots are recognized. Next, a comprehensive review of the subjectively recognized research hotspots in various biomedical fields, including biological sensing, anticancer treatments, antibacterials, and toxicity evaluation, is provided. Finally, the prospects and challenges of TNMs are discussed to provide a new perspective for further promoting their development in biomedical research.

Exfoliation of MoS2 Quantum Dots: Recent Progress and Challenges

Although, quantum dots (QDs) of two-dimensional (2D) molybdenum disulfide (MoS₂) have shown great potential for various applications, such as sensing, catalysis, energy storage, and electronics. However, the lack of a simple, scalable, and inexpensive fabrication method for QDs is still a challenge. To overcome this challenge, a lot of attention has been given to the fabrication of QDs, and several fabrication strategies have been established. These exfoliation processes are mainly divided into two categories, the 'top-down' and 'bottom-up' methods. In this review, we have discussed different top-down exfoliation methods used for the fabrication of MoS₂ QDs and the advantages and limitations of these methods. A detailed description of the various properties of QDs is also presented.

Superlow Power Consumption Artificial Synapses Based on WSe2 Quantum Dots Memristor for Neuromorphic Computing

As the emerging member of zero-dimension transition metal dichalcogenide, WSe₂ quantum dots (QDs) have been applied to memristors and exhibited better resistance switching characteristics and miniaturization size. However, low power consumption and high reliability are still challenges for WSe₂ QDs-based memristors as synaptic devices. Here, we demonstrate a high-performance, superlow power consumption memristor device with the structure of Ag/WSe₂ QDs/La_0.3Sr_0.7MnO₃/SrTiO₃. The device displays excellent resistive switching memory behavior with a R_OFF/R_ON ratio of ~5 × 10³, power consumption per switching as low as 0.16 nW, very low set, and reset voltage of ~0.52 V and~ -0.19 V with excellent cycling stability, good reproducibility, and decent data retention capability. The superlow power consumption characteristic of the device is further proved by the method of density functional theory calculation. In addition, the influence of pulse amplitude, duration, and interval was studied to gradually modulating the conductance of the device. The memristor has also been demonstrated to simulate different functions of artificial synapses, such as excitatory postsynaptic current, spike timing-dependent plasticity, long-term potentiation, long-term depression, and paired-pulse facilitation. Importantly, digit recognition ability based on the WSe₂ QDs device is evaluated through a three-layer artificial neural network, and the digit recognition accuracy after 40 times of training can reach up to 94.05%. This study paves a new way for the development of memristor devices with advanced significance for future low power neuromorphic computing.

Defect-Rich Molybdenum Sulfide Quantum Dots for Amplified Photoluminescence and Photonics-Driven Reactive Oxygen Species Generation

Transition metal dichalcogenide (TMD) quantum dots (QDs) with defects have attracted interesting chemistry due to the contribution of vacancies to their unique optical, physical, catalytic, and electrical properties. Engineering defined defects into molybdenum sulfide (MoS₂ ) QDs is challenging. Herein, by applying a mild biomineralization-assisted bottom-up strategy, blue photoluminescent MoS₂ QDs (B-QDs) with a high density of defects are fabricated. The two-stage synthesis begins with a bottom-up synthesis of original MoS₂ QDs (O-QDs) through chemical reactions of Mo and sulfide ions, followed by alkaline etching that creates high sulfur-vacancy defects to eventually form B-QDs. Alkaline etching significantly increases the photoluminescence (PL) and photo-oxidation. An increase in defect density is shown to bring about increased active sites and decreased bandgap energy; which is further validated with density functional theory calculations. There is strengthened binding affinity between QDs and O₂ due to lower gap energy (∆E_ST ) between S₁ and T₁ , accompanied with improved intersystem crossing (ISC) efficiency. Lowered gap energy contributes to assist e^- -h⁺ pair formation and the strengthened binding affinity between QDs and ³ O₂ . Defect engineering unravels another dimension of material properties control and can bring fresh new applications to otherwise well characterized TMD nanomaterials.

Improving Thermal and Photostability of Polymer Solar Cells by Robust Interface Engineering

As the power conversion efficiency (PCE) of organic photovoltaics (OPVs) approaches 19%, increasing research attention is being paid to enhancing the device's long-term stability. In this study, a robust interface engineering of graphene oxide nanosheets (GNS) is expounded on improving the thermal and photostability of non-fullerene bulk-heterojunction (NFA BHJ) OPVs to a practical level. Three distinct GNSs (GNS, N-doped GNS (N-GNS), and N,S-doped GNS (NS-GNS)) synthesized through a pyrolysis method are applied as the ZnO modifier in inverted OPVs. The results reveal that the GNS modification introduces passivation and dipole effects to enable better energy-level alignment and to facilitate charge transfer across the ZnO/BHJ interface. Besides, it optimizes the BHJ morphology of the photoactive layer, and the N,S doping of GNS further enhances the interaction with the photoactive components to enable a more idea BHJ morphology. Consequently, the NS-GNS device delivers enhanced performance from 14.5% (control device) to 16.5%. Moreover, the thermally/chemically stable GNS is shown to stabilize the morphology of the ZnO electron transport layer (ETL) and to endow the BHJ morphology of the photoactive layer grown atop with a more stable thermodynamic property. This largely reduces the microstructure changes and the associated charge recombination in the BHJ layer under constant thermal/light stresses. Finally, the NS-GNS device is demonstrated to exhibit an impressive T₈₀ lifetime (time at which PCE of the device decays to 80% of the initial PCE) of 2712 h under a constant thermal condition at 65 °C in a glovebox and an outstanding photostability with a T₈₀ lifetime of 2000 h under constant AM1.5G 1-sun illumination in an N₂ -controlled environment.

Novel charm of 2D materials engineering in memristor: when electronics encounter layered morphology

The family of two-dimensional (2D) materials composed of atomically thin layers connected via van der Waals interactions has attracted much curiosity due to a variety of intriguing physical, optical, and electrical characteristics. The significance of analyzing statistics on electrical devices and circuits based on 2D materials is seldom underestimated. Certain requirements must be met to deliver scientific knowledge that is beneficial in the field of 2D electronics: synthesis and fabrication must occur at the wafer level, variations in morphology and lattice alterations must be visible and statistically verified, and device dimensions must be appropriate. The authors discussed the most recent significant concerns of 2D materials in the provided prose and attempted to highlight the prerequisites for synthesis, yield, and mechanism behind device-to-device variability, reliability, and durability benchmarking under memristors characteristics; they also indexed some useful approaches that have already been reported to be advantageous in large-scale production. Commercial applications, on the other hand, will necessitate further effort.

A review and revisit of nanoparticles for antimicrobial drug delivery

Antimicrobials are widely used to treat bacteria, viruses, fungi, and protozoa. Therefore, research and development of newer types of antimicrobials are important. Antimicrobial resistance has emerged as a major challenge to the healthcare system, although various alternative antimicrobials have been proposed. However, none of these show consistent and comparable efficacy to antimicrobials in clinical trials. More recently, nanoparticles have emerged as a potential solution to antimicrobial agents to overcome antimicrobial resistance. This article revisits and updates applications of various types of nanoparticles for the delivery of antimicrobial agents and their characterization. Though nanoparticle technology has some limitations, it provides an innovative approach to pharmaceutical technology. Furthermore, nanoparticles offer a variety of advantages, such as enhancement of solubility and permeation, leading to better efficacy. In this article, approaches commonly employed to improve antimicrobial therapy are discussed. These approaches have advantages and applications and provide a broader opportunity for pharmaceutical scientists to choose the proper method per the desired outcome.

Versatile Preparation of Mesoporous Single-Layered Transition-Metal Sulfide/Carbon Composites for Enhanced Sodium Storage

Transition-metal sulfides are promising electrochemical energy storage materials due to their abundant active sites, large interlayer space, and high theoretical capacities, especially for sodium storage. However, the low conductivity and poor cycling stability at high current densities hamper their applications. Herein, a versatile dual-template method is reported to elaborate ordered mesoporous single-layered MoS₂ /carbon composite with high specific area, uniform pore size, and large pore volume. The single-layered MoS₂ is confined in the carbon matrix. The mesopores between the composite nanorods provide fast electrolyte diffusion. The obtained nanocomposite shows a high sodium-storage capability, excellent rate capacity, and very good cycling performance. A capacity of 310 mAh g^-1 can remain at 5.0 A g^-1 after 2500 cycles. Furthermore, a sodium-ion battery (SIB) full cell composed of the MoS₂ /carbon composite anode and a Na₃ V₂ (PO₄ )₃ (NVP) cathode maintains a specific capacity of 330 mAh g^-1 at 1.0 A g^-1 during 100 cycles. The mechanism is investigated by in situ and ex situ characterizations as well as density functional theory (DFT) calculations.

MOF-templated synthesis of photoluminescent MoS2 QDs

MOF-templated synthesis of photoluminescent MoS2 QDs.

Facile Preparation of Oxygen-Vacancy-Engineered MoOx Nanostructures for Photoreversible Switching Systems

Photochromic materials have attracted increasing attention. Here, we report a novel photo-reversible color switching system based on oxygen-vacancy-engineered MoO_x nanostructures with water/N-methyl-2-pyrrolidone (NMP) as solvents. In this work, the system rapidly changed from colorless to blue under UV irradiation (360-400 nm) and slowly recovered its colorless state under visible light irradiation. The obtained oxygen vacancy-engineered MoO_x nanostructures exhibited good repeatability, chemical stability, and cycling stability. Upon UV light irradiation, H⁺ was intercalated into layered MoO_x nanostructures and the Mo⁶⁺ concentration in the H_xMoO_x decreased, while the Mo⁵⁺ concentration increased and increased oxygen vacancies changed the color to blue. Then, it recovered its original color slowly without UV light irradiation. What is more, the system was highly sensitive to UV light even on cloudy days. Compared with other reported photochromic materials, the system in this study has the advantage of facile preparation and provides new insights for the development of photochromic materials without dyes.

Nanodots Derived from Layered Materials: Synthesis and Applications

Layered 2D materials, such as graphene, transition metal dichalcogenides, transition metal oxides, black phosphorus, graphitic carbon nitride, hexagonal boron nitride, and MXenes, have attracted intensive attention over the past decades owing to their unique properties and wide applications in electronics, catalysis, energy storage, biomedicine, etc. Further reducing the lateral size of layered 2D materials down to less than 10 nm allows for preparing a new class of nanostructures, namely, nanodots derived from layered materials. Nanodots derived from layered materials not only can exhibit the intriguing properties of nanodots due to the size confinement originating from the ultrasmall size, but also can inherit some unique properties of ultrathin layered 2D materials, making them promising candidates in a wide range of applications, especially in biomedicine and catalysis. Here, a comprehensive summary on the materials categories, advantages, synthesis methods, and potential applications of these nanodots derived from layered materials is provided. Finally, personal insights about the challenges and future directions in this promising research field are also given.

Scalable production of intrinsic WX2(X = S, Se, Te) quantum sheets for efficient hydrogen evolution electrocatalysis

Mass production of transition-metal dichalcogenides has attracted much attention to replace platinum-based catalysts for the hydrogen evolution reaction (HER). Herein, we demonstrate a general strategy for the scalable production of the intrinsic tungsten dichalcogenide (WX₂(X = S, Se, Te)) quantum sheets (QSs) by an all-physical top-down method. The method combines silica-assisted ball-milling and sonication-assisted solvent exfoliation and thus enables production of WS₂QSs, WSe₂QSs, and WTe₂QSs in exceedingly high yields of 28.2, 21.3, 19.9 wt%, respectively. The WX₂QSs are confirmed as intrinsic and defect-free, which could be determinative to their improved HER performance. The overpotentials of 285, 331, 435 mV at the current density of 10 mA cm^-2and Tafel slopes of 116, 78, 162 mV dec^-1in acidic media, as well as charge transfer resistance values of 171, 242, 1973 Ω, are derived for WS₂QSs, WSe₂QSs, and WTe₂QSs, respectively, which are much better than those of bulk materials. The WX₂QSs exhibit high stability during the electrocatalysis as well. This work offers a powerful approach for fabrication of intrinsic QSs as efficient and robust electrocatalysts.

Colloidal BaZrS3 chalcogenide perovskite nanocrystals for thin film device fabrication

The theoretical optoelectronic properties of chalcogenide perovskites (e.g., BaZrS3) are as good as those of halide perovskites (e.g., CH3NH3PbI3). But the fabrication of optoelectronic devices is rarely reported, mainly because researchers still do not know how to prepare good quality thin films of chalcogenide perovskites. Here, we report colloidal BaZrS3 nanocrystals (NCs, 40-60 nm) and their solution processed thin film transistors. BaZrS3 NCs are first prepared using a solid-state synthesis route, and the subsequent surface modifications lead to a colloidal dispersion of NCs in both polar N-methyl-2-pyrrolidinone and non-polar chloroform solvents. The NCs exhibit good thermal (15-673 K) and aqueous stability. Colloidal BaZrS3 NCs in chloroform are then used to make field effect transistors showing ambipolar properties with a hole mobility of 0.059 cm2 V-1 s-1 and an electron mobility of 0.017 cm2 V-1 s-1. This report of solution processed chalcogenide perovskite thin films with reasonable carrier mobility and optical absorption and emission is expected to pave the way for future optoelectronic devices of chalcogenide perovskites.

Quantum dots in cell imaging and their safety issues

When quantum dots are used as fluorescent probes or drug tracers for in vivo imaging, the quantum dots in the blood will come into direct contact with vascular endothelial cells. Thus, it is necessary to study whether quantum dots can affect endothelial function after being injected into blood vessels as imaging agents. In recent years, there have been numerous studies on the toxicity of quantum dots. Herein, we focused on five types of quantum dots (Cd-containing quantum dots, CuInS2 quantum dots, black phosphorus quantum dots, MXene quantum dots, and carbon-based quantum dots) for cell imaging and their toxicity in vivo and in vitro. Although current research on the toxicity of quantum dots has not reached a consistent conclusion, it can guide the next step in evaluating their cytotoxicity.

MoS2 quantum dots for on-line fluorescence determination of the food additive allura red

This work presents an on-line fluorescence method for the allura red (AR) determination. The method is based on the fluorescence quenching of dots of MoS₂ because of their interaction with the non-fluorescence dye. MoS₂-dots were synthetized and characterized by spectroscopic techniques and High Resolution Transmission Electronic Microscopy (HR-TEM). The simultaneous injection of the nanomaterial and the dye in a flow injection analysis system allows the determination of allura red at 1.7 × 10^-6 M concentration level with a very good accuracy and precision (Er minor than 10% and RSD lower than 8%) and a sampling frequency of 180 samples per hour. Moreover, the interaction fluorophore-quencher results a dynamic inhibition mechanism. The proposed methodology was applied to the AR analysis in soft beverages and powders for gelatine preparation. Colourant concentrations of 63 ± 2 mg/L (n = 3) and 0.30 ± 0.01 mg/g (n = 3) were found, respectively. These results were validated by high performance liquid chromatography technique.

High-Yield Production of Water-Soluble MoS2 Quantum Dots for Fe3+ Detection and Cell Imaging

Uniform water-soluble MoS2 quantum dots (WS-MSQDs) were synthesized via a sequential combination of sintering/etching/exfoliation method and solvothermal route. The obtained WS-MSQDs with average size of approximately 3.4 nm exhibited sufficient water solubility and remarkable fluorescence properties. The WS-MSQDs were utilized as a probe for detection of Fe3+ ions with high selectivity and specificity. Furthermore, the WS-MSQDs exhibited high fluorescence stability under different conditions. Finally, the WS-MSQDs were successfully applied for the fluorescence imaging of Fe3+ in living cells, which exhibited practical potential for biomedical applications.

Antimonene Quantum Dots as an Emerging Fluorescent Nanoprobe for the pH-Mediated Dual-Channel Detection of Tetracyclines

Antimonene quantum dots (AMQDs) are attracting considerable attention due to their fascinating physicochemical properties. However, research on their semiconductor characteristics, especially the photoluminescence performance, is still in a preliminary stage and the experimental verification is scarcely reported, significantly restricting their further applications. Herein, the photoluminescence property of AMQDs is experimentally verified. The AMQDs are prepared by probe sonication-assisted liquid-phase exfoliation and show robust blue fluorescence, and the photoluminescence is hardly affected by pH. In view of the derivatization reaction of tetracyclines (TET) at different pHs, AMQDs are developed as a pH-mediated dual-channel ratiometric fluorescent probe for TET detection. Under acidic conditions, the AMQDs' probe exhibits unique recognition behavior due to the inherent fluorescence of TET and the solvent-enhancing effect, that is, the fluorescence changes from blue to red. Under alkaline conditions, this fluorescent probe realizes the transition from blue to yellow-green because of the decomposition of TET. The limits of detection are 27 × 10^-9 and 74 × 10^-9 m, respectively. The high sensitivity and remarkable fluorescence changes make AMQDs ideal probes for TET sensing. Additionally, this is the first report on the photoluminescence property of AMQDs. It is believed that this work will open a new avenue for AMQDs in optical sensing fields.

Electrode Materials for Supercapacitors: A Review of Recent Advances

The advanced electrochemical properties, such as high energy density, fast charge–discharge rates, excellent cyclic stability, and specific capacitance, make supercapacitor a fascinating electronic device. During recent decades, a significant amount of research has been dedicated to enhancing the electrochemical performance of the supercapacitors through the development of novel electrode materials. In addition to highlighting the charge storage mechanism of the three main categories of supercapacitors, including the electric double-layer capacitors (EDLCs), pseudocapacitors, and the hybrid supercapacitors, this review describes the insights of the recent electrode materials (including, carbon-based materials, metal oxide/hydroxide-based materials, and conducting polymer-based materials, 2D materials). The nanocomposites offer larger SSA, shorter ion/electron diffusion paths, thus improving the specific capacitance of supercapacitors (SCs). Besides, the incorporation of the redox-active small molecules and bio-derived functional groups displayed a significant effect on the electrochemical properties of electrode materials. These advanced properties provide a vast range of potential for the electrode materials to be utilized in different applications such as in wearable/portable/electronic devices such as all-solid-state supercapacitors, transparent/flexible supercapacitors, and asymmetric hybrid supercapacitors.

Photothermal augment stromal disrupting effects for enhanced Abraxane synergy chemotherapy in pancreatic cancer PDX mode

Cancer-associated fibroblasts (CAFs) are crucial for forming the desmoplastic stroma that is associated with chemoresistance in pancreatic ductal adenocarcinoma (PDAC). In the clinic, depleting dense stroma in PDAC tumor tissue is a promising chemotherapeutic strategy. In this study, we report that the local hyperthermia can reduce the number of CAFs in the PDAC PDX mouse mode, which further augments chemotherapeutic efficiency in the PDAC therapy. To achieve this goal, a photothermal-chemotherapeutic agent termed as Abraxane@MoSe₂ as a vehicle-saving theranostic probe is prepared by simply mixing an FDA-approved Abraxane and hydrophobic MoSe₂ nanosheets via electrostatic and hydrophobic interactions. After labeling with indocyanine green (ICG) dye on the Abraxane@MoSe₂, a relatively high fluorescence signal (near infrared second (NIR II)) in PDX tumors can be obtained, which can be precisely imaging-guide local photothermal-chemotherapy upon the 808 nm laser irradiation in vivo. Importantly, the synergy therapeutic efficiency in PDAC is enhanced by the photothermal effect reduction of the number of CAFs, which is confirmed viaα-SMA and vimentin immunofluorescence analysis. This combined therapeutic strategy may provide a new sight for PDAC therapy.

Sonochemical synthesis of carbon dots, mechanism, effect of parameters, and catalytic, energy, biomedical and tissue engineering applications

Carbon-based nanomaterials are gaining more and more interest because of their wide range of applications. Carbon dots (CDs) have shown exclusive interest due to unique and novel physicochemical, optical, electrical, and biological properties. Since their discovery, CDs became a promising material for wide range of research applications from energy to biomedical and tissue engineering applications. At same time several new methods have been developed for the synthesis of CDs. Compared to many of these methods, the sonochemical preparation is a green method with advantages such as facile, mild experimental conditions, green energy sources, and feasibility to formulate CDs and doped CDs with controlled physicochemical properties and lower toxicity. In the last five years, the sonochemically synthesized CDs were extensively studied in a wide range of applications. In this review, we discussed the sonochemical assisted synthesis of CDs, doped CDs and their nanocomposites. In addition to the synthetic route, we will discuss the effect of various experimental parameters on the physicochemical properties of CDs; and their applications in different research areas such as bioimaging, drug delivery, catalysis, antibacterial, polymerization, neural tissue engineering, dye absorption, ointments, electronic devices, lithium ion batteries, and supercapacitors. This review concludes with further research directions to be explored for the applications of sonochemical synthesized CDs.

Molybdenum disulfide nanosheets: From exfoliation preparation to biosensing and cancer therapy applications

Over the past few decades, nanotechnology has developed rapidly. Various nanomaterials have been gradually applied in different fields. As a kind of two-dimensional (2D) layered nanomaterial with a graphene-like structure, molybdenum disulfide (MoS₂) nanosheets have broad research prospects in the fields of tumor photothermal therapy, biosensors and other biomedical fields because of their unique band gap structure and physical, chemical and optical properties. In this paper, the latest research progress on MoS₂ is briefly summarized. Several commonly used exfoliation methods for the preparation of MoS₂ nanosheets are reviewed based on the studies in the past five years. Additionally, the current research status of MoS₂ nanosheets in the field of biomedicine is introduced. At the end of this review, a brief overview of the limitations of MoS₂ research and its future prospects in the field of biomedicine is also provided.

Boosted electrochemical ammonia synthesis by high-percentage metallic transition metal dichalcogenide quantum dots

The electrochemical method can directly convert N2 into the high-value-added NH3 under ambient conditions and is considered to be a green and sustainable alternative to the traditional Haber-Bosch process. However, the electrochemical nitrogen reduction reaction (NRR) suffers from a low ammonia yield rate over the reported electrocatalysts. Herein, we have developed a general strategy to boost the NRR performance, enabled by the metallic 1T phase dominated transition metal dichalcogenide quantum dots (TMD QDs). Impressively, the obtained MoSe2 QDs achieved a superior ammonia yield rate of 340 μg mg-1 cat. h-1 with excellent ammonia generation sustainability. Experimental and theoretical studies revealed that the excellent catalytic activity of MoSe2 QDs mainly originates from the ultra-small quantized size (high surface area and high-density active edge/defect sites) and high-percentage metallic 1T phase (the N2 adsorption on the 1T phase is spontaneous, and the energy barrier of the potential determining step on the 1T phase is very low). Most importantly, our concept is universal for TMD materials (i.e., MoS2, WSe2, WS2 and NbSe2) that also exhibit a much-enhanced ammonia yield rate as compared to other electrocatalysts.

Tantalum disulfide quantum dots: preparation, structure, and properties

Tantalum disulfide (TaS₂) two-dimensional film material has attracted wide attention due to its unique optical and electrical properties. In this work, we report the preparation of 1 T-TaS₂ quantum dots (1 T-TaS₂ QDs) by top-down method. Herein, we prepared the TaS₂ QDs having a monodisperse grain size of around 3 nm by an effective ultrasonic liquid phase exfoliation method. Optical studies using UV-Vis, PL, and PLE techniques on the as-prepared TaS₂ QDs exhibited ultraviolet absorption at 283 nm. Furthermore, we found that dimension reduction of TaS₂ has led to a modification of the band gap, namely a transition from indirect to direct band gap, which is explained using first-principle calculations. By using quinine as reference, the fluorescence quantum yield is 45.6%. Therefore, our results suggest TaS₂ QDs have unique and extraordinary optical properties. Moreover, the low-cost, facile method of producing high quality TaS₂ QDs in this work is ideal for mass production to ensure commercial viability of devices based on this material. TaS₂ quantum dots having a monodisperse grain size of around 3 nm have been prepared by an ultrasonic liquid phase exfoliation method, it has been found that the dimension reduction of TaS₂ has led to a transition from indirect to direct band gap that results in the unique and extraordinary optical properties (PL QY: 45.6%).

Modified top-down approach for synthesis of molybdenum oxide quantum dots: sonication induced chemical etching of thin films

A simple and modified top-down approach to synthesize molybdenum oxide (MoO_x: x = 2, 3) quantum dots (QDs) is proposed in this study. This modified approach involves the conversion of a bulk powder material into thin films followed by a sonication induced chemical etching process for synthesising QDs. X-Ray Diffraction (XRD) is used for crystal structural characterization of MoO_x thin films. The crystal structure properties of the MoO_x QDs are analysed by High Resolution Transmission Electron Microscopy (HRTEM) images and corresponding Selected Area Electron Diffraction (SAED) patterns. The optical band gap is estimated by Tauc's plot from UV-Vis-NIR absorption spectra. The excitation dependent photoluminescence (PL) emission of MoO_x QDs as a function of acid concentration is investigated. The growth mechanism of QDs in different crystalline phases as a function of acid concentration is also exemplified in this work. The micro-Raman and Fourier Transform of Infrared (FTIR) spectra are recorded to analyse the vibrational spectrum of the molybdenum–oxygen (Mo–O) bonds in the MoO_x QDs.

A simple and modified top-down approach to synthesize molybdenum oxide (MoO_x: x = 2, 3) quantum dots (QDs) is proposed in this study.

Phototherapy with layered materials derived quantum dots

Quantum dots (QDs) originating from two-dimensional (2D) sheets of graphitic carbon nitride (g-C₃N₄), graphene, hexagonal boron nitride (h-BN), monoatomic buckled crystals (phosphorene), germanene, silicene and transition metal dichalcogenides (TMDCs) are emerging zero-dimensional materials. These QDs possess diverse optical properties, are chemically stable, have surprisingly excellent biocompatibility and are relatively amenable to surface modifications. It is therefore not difficult to see that these QDs have potential in a variety of bioapplications, including biosensing, bioimaging and anticancer and antimicrobial therapy. In this review, we briefly summarize the recent progress of these exciting QD based nanoagents and strategies for phototherapy. In addition, we will discuss about the current limitations, challenges and future prospects of QDs in biomedical applications.

Linearly Polarized Luminescence of Atomically Thin MoS2 Semiconductor Nanocrystals

Atomically thin layers of transition-metal dichalcogenides semiconductors, such as MoS₂, exhibit strong and circularly polarized light emission due to inherent crystal symmetries, pronounced spin-orbit coupling, and out-of-plane dielectric and spatial confinement. While the layer-by-layer confinement is well-understood, the understanding of the impact of in-plane quantization in their optical spectrum is far behind. Here, we report the optical properties of atomically thin MoS₂ colloidal semiconductor nanocrystals. In addition to the spatial-confinement effect leading to their blue wavelength emission, the high quality of our MoS₂ nanocrystals is revealed by narrow photoluminescence, which allows us to resolve multiple optically active transitions, originating from quantum-confined excitons (coupled electron-hole pairs). Surprisingly, in stark contrast to monolayer MoS₂, the luminescence of the lowest-energy levels is linearly polarized and persists up to room temperature, meaning that it could be exploited in a variety of light-emitting applications.

Wet-Chemical Synthesis and Applications of Semiconductor Nanomaterial-Based Epitaxial Heterostructures

Semiconductor nanomaterial-based epitaxial heterostructures with precisely controlled compositions and morphologies are of great importance for various applications in optoelectronics, thermoelectrics, and catalysis. Until now, various kinds of epitaxial heterostructures have been constructed. In this minireview, we will first introduce the synthesis of semiconductor nanomaterial-based epitaxial heterostructures by wet-chemical methods. Various architectures based on different kinds of seeds or templates are illustrated, and their growth mechanisms are discussed in detail. Then, the applications of epitaxial heterostructures in optoelectronics, catalysis, and thermoelectrics are described. Finally, we provide some challenges and personal perspectives for the future research directions of semiconductor nanomaterial-based epitaxial heterostructures.

Facile Bottom-up Preparation of WS2-Based Water-Soluble Quantum Dots as Luminescent Probes for Hydrogen Peroxide and Glucose

Photoluminescent zero-dimensional (0D) quantum dots (QDs) derived from transition metal dichalcogenides, particularly molybdenum disulfide, are presently in the spotlight for their advantageous characteristics for optoelectronics, imaging, and sensors. Nevertheless, up to now, little work has been done to synthesize and explore photoluminescent 0D WS2 QDs, especially by a bottom-up strategy without using usual toxic organic solvents. In this work, we report a facile bottom-up strategy to synthesize high-quality water-soluble tungsten disulfide (WS2) QDs through hydrothermal reaction by using sodium tungstate dihydrate and L-cysteine as W and S sources. Besides, hybrid carbon quantum dots/WS2 QDs were further prepared based on this method. Physicochemical and structural analysis of QD hybrid indicated that the graphitic carbon quantum dots with diameters about 5 nm were held onto WS2 QDs via electrostatic attraction forces. The resultant QDs show good water solubility and stable photoluminescence (PL). The excitation-dependent PL can be attributed to the polydispersity of the synthesized QDs. We found that the PL was stable under continuous irradiation of UV light but can be quenched in the presence of hydrogen peroxide (H2O2). The obtained WS2-based QDs were thus adopted as an electrodeless luminescent probe for H2O2 and for enzymatic sensing of glucose. The hybrid QDs were shown to have a more sensitive LOD in the case of glucose sensing. The Raman study implied that H2O2 causes the partial oxidation of QDs, which may lead to oxidation-induced quenching. Overall, the presented strategy provides a general guideline for facile and low-cost synthesis of other water-soluble layered material QDs and relevant hybrids in large quantity. These WS2-based high-quality water-soluble QDs should be promising for a wide range of applications in optoelectronics, environmental monitoring, medical imaging, and photocatalysis.

Carbon dots with molecular fluorescence and their application as a "turn-off" fluorescent probe for ferricyanide detection

Highly fluorescent carbon dots (CDs) exhibiting molecular fluorescence were synthesized and successfully used for sensing ferricyanide based on fluorescence quenching. We conducted dialysis to purify the CDs and found that the dialysate is also fluorescent. From the mass spectra and quantum yield analyses of the dialysate, it is demonstrated that molecular fluorophores were also synthesized during the synthesis of CDs. By the comparison of fluorescence spectra between CDs and dialysate, it is established that the fluorescence emission of CDs partly originates from fluorophores that are attached to CDs' surface. The fluorescence quenching caused by ferricyanide is proved to be the overlap of absorption spectra between ferricyanide and CDs. The changes of the absorbance and fluorescence spectra are combined to enhance the detection sensitivity, and the limit of detection is calculated to be 1.7 μM. A good linear response of fluorescence-absorbance combined sensing toward ferricyanide is achieved in the range of 5-100 µM. This method is highly selective to ferricyanide among other common cations and anions, and it is also successfully applied in detecting ferricyanide in real water samples.

Synthesis, characterisation and anti-tumour activity of biopolymer based platinum nanoparticles and 5-fluorouracil loaded platinum nanoparticles

A facile and green synthesis of platinum nanoparticles [gum kondagogu platinum nanoparticles (GKPtNP)] using biopolymer- gum kondagogu was developed. The formation of GKPtNP was confirmed by ultraviolet (UV)-visible spectroscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, Zeta potential, Fourier transform infrared, inductively coupled plasma mass spectroscopy. The formed GKPtNP are well dispersed, homogeneous with a size of 2-4 ± 0.50 nm, having a negative zeta potential (-46.1 mV) indicating good stability. 5-Fluorouracil (5FU) was loaded onto the synthesised GKPtNP, which leads to the development of a new combination of nanomedicine (5FU-GKPtNP). The in vitro drug release studies of 5FU-GKPtNP in pH 7.4 showed a sustained release profile over a period of 120 min. Agrobacterium tumefaciens induced in vitro potato tumour bioassay was employed for screening the anti-tumour potentials of GKPtNP, 5FU, and 5FU-GKPtNP. The experimental results suggested a complete tumour inhibition by 5FU-GKPtNP at a lower concentration than the GKPtNP and 5FU. Furthermore, the mechanism of anti-tumour activity was assessed by their interactions with DNA using agarose gel electrophoresis and UV-spectroscopic analysis. The electrophoresis results revealed that the 5FU-GKPtNP totally diminishes DNA and the UV-spectroscopic analysis showed a hyperchromic effect with red shift indicating intercalation type of binding with DNA. Over all, the present study revealed that the combined exposure of the nanoformulation resulted in the enhanced anti-tumour effect.

Ultrasonic exfoliated ReS2 nanosheets: fabrication and use as co-catalyst for enhancing photocatalytic efficiency of TiO2 nanoparticles under sunlight

Rhenium disulfide (ReS₂) is an interesting kind of transition metal dichalcogenide (TMD) because of its thickness-independent and suitable direct-bandgap structure, which could enable highly efficient solar-energy conversion efficiency. Here, we demonstrate an ultrasonic liquid exfoliation technique in combination with grinding to produce high quality ReS₂ nanosheets (NSs) on a large scale. After combination with TiO₂ nanoparticles, the co-catalytic performance of TiO₂@ReS₂ nanocomposites is investigated, which presents dramatically enhanced degradation activity of organic pigments under sunlight illumination in comparison with pure TiO₂ nanoparticles. The underlying mechanism of enhanced photocatalytic activity can be attributed to improved separation efficiency of photogenerated electron-hole pairs in TiO₂@ReS₂ nanocomposites, which is confirmed by photoluminescence analysis and photoelectrochemical measurements. Our results demonstrate that the layered ReS₂ NS is a promising two-dimensional supporting platform for photocatalysis and moreover it could also provide a new perspective on TMDs co-catalyst.

Configurable multi-state non-volatile memory behaviors in Ti3C2 nanosheets

MXenes have drawn considerable attention in both academia and industry due to their attractive properties, such as a combination of metallic conductivity and surface hydrophilicity. However, to the best of our knowledge, the potential use of MXenes in non-volatile resistive random access memories (RRAMs) has rarely been reported. In this paper, we first demonstrated a RRAM device with MXene (Ti3C2) as the active component. The Ti3C2-based RRAM exhibited typical bipolar switching behavior, long retention characteristics, low SET voltage, good mechanical stability and excellent reliability. By adjusting different compliance currents in the SET process, multi-state information storage was achieved. The charge trapping assisting hopping process is considered to be the main mechanism of resistive switching for this fabricated Ti3C2-based RRAM, which was verified by conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM). Moreover, this flexible Ti3C2-based RRAM, with good mechanical stability and long retention properties, was successfully fabricated on a plastic substrate. Ti3C2-based RRAMs may open the door to additional applications and functionalities, with high potential for application in flexible electronics.

Boronic acid-functionalized molybdenum disulfide quantum dots for the ultrasensitive analysis of dopamine based on synergistic quenching effects from IFE and aggregation

Herein, a novel fluorescent material, boronic acid-functionalized molybdenum disulfide quantum dots (B-MoS₂ QDs) produced by an amidation reaction between 3-aminobenzeneboronic acid and previously prepared molybdenum disulfide quantum dots (MoS₂ QDs), was prepared to fabricate a rapid and sensitive platform for the quantitative analysis of dopamine. This material exhibits strong fluorescence, excellent salt tolerance and light fastness. In particular, the quantum yield of this material is about 21.1 times that of its fundamental material, MoS₂ QDs. Notably, owing to an interesting synergistic effect between the inner filter effect and the aggregation quenching effect, this material was successfully applied for the determination of dopamine in the linear range 0.25-35 μmol L^-1 with the detection limit of 0.087 μmol L^-1; moreover, B-MoS₂ QDs manifested better selectivity in the presence of multiple interferences due to their inert surface. As expected, this proposed material shows satisfactory performance in human serum; thus, the present study exploits a new avenue for the application of functionalized MoS₂ QDs in fluorescence sensing.

A Chemiluminescent Method for the Detection of H₂O₂ and Glucose Based on Intrinsic Peroxidase-Like Activity of WS₂ Quantum Dots

Currently, researchers are looking for nanomaterials with peroxidase-like activity to replace natural peroxidase enzymes. For this purpose, WS₂ quantum dots (WS₂ QDs) were synthesized via a solvothermal method, which improved the mimetic behavior. The resulting WS₂ QDs with a size of 1⁻1.5 nm had a high fluorescence emission, dependent on the excitation wavelength. WS₂ QDs with uniform morphology showed a high catalytic effect in destroying H₂O₂. The peroxidase-like activity of synthesized nanostructures was studied in H₂O₂ chemical and electrochemical reduction systems. The mimetic effect of WS₂ QDs was also shown in an H₂O₂⁻rhodamine B (RB) chemiluminescence system. For this aim, a stopped-flow chemiluminescence (CL) detection system was applied. Also, in order to confirm the peroxidase-like effect of quantum dots, colorimetry and electrochemical techniques were used. In the enzymatic reaction of glucose, H₂O₂ is one of the products which can be determined. Under optimum conditions, H₂O₂ can be detected in the concentration range of 0⁻1000 nmol·L-1, with a detection limit of 2.4 nmol·L-1. Using this CL assay, a linear relationship was obtained between the intensity of the CL emission and glucose concentration in the range of 0.01⁻30 nmol·L-1, with a limit of detection (3S) of 4.2 nmol·L-1.

Self-Assembled Networked PbS Distribution Quantum Dots for Resistive Switching and Artificial Synapse Performance Boost of Memristors

With the advent of the era of big data, resistive random access memory (RRAM) has become one of the most promising nanoscale memristor devices (MDs) for storing huge amounts of information. However, the switching voltage of the RRAM MDs shows a very broad distribution due to the random formation of the conductive filaments. Here, self-assembled lead sulfide (PbS) quantum dots (QDs) are used to improve the uniformity of switching parameters of RRAM, which is very simple comparing with other methods. The resistive switching (RS) properties of the MD with the self-assembled PbS QDs exhibit better performance than those of MDs with pure-Ga₂ O₃ and randomly distributed PbS QDs, such as a reduced threshold voltage, uniformly distributed SET and RESET voltages, robust retention, fast response time, and low power consumption. This enhanced performance may be attributed to the ordered arrangement of the PbS QDs in the self-assembled PbS QDs which can efficiently guide the growth direction for the conducting filaments. Moreover, biosynaptic functions and plasticity, are implemented successfully in the MD with the self-assembled PbS QDs. This work offers a new method of improving memristor performance, which can significantly expand existing applications and facilitate the development of artificial neural systems.

Defect engineered bioactive transition metals dichalcogenides quantum dots

Transition metal dichalcogenide (TMD) quantum dots (QDs) are fundamentally interesting because of the stronger quantum size effect with decreased lateral dimensions relative to their larger 2D nanosheet counterparts. However, the preparation of a wide range of TMD QDs is still a continual challenge. Here we demonstrate a bottom-up strategy utilizing TM oxides or chlorides and chalcogen precursors to synthesize a small library of TMD QDs (MoS₂, WS₂, RuS₂, MoTe₂, MoSe₂, WSe₂ and RuSe₂). The reaction reaches equilibrium almost instantaneously (~10–20 s) with mild aqueous and room temperature conditions. Tunable defect engineering can be achieved within the same reactions by deviating the precursors’ reaction stoichiometries from their fixed molecular stoichiometries. Using MoS₂ QDs for proof-of-concept biomedical applications, we show that increasing sulfur defects enhanced oxidative stress generation, through the photodynamic effect, in cancer cells. This facile strategy will motivate future design of TMDs nanomaterials utilizing defect engineering for biomedical applications.

Transition metal dichalcogenide (TMD) quantum dots (QDs) have promising electronic properties which might be further tailorable by defect engineering. Here the authors describe a room temperature aqueous based synthesis of TMD QDs with controlled defect concentration, and demonstrate the correlation between defect concentration and biomedical activity.