Formation of oxygen protective layer on monolayer MoS2 via low energy electron irradiation

Monolayer molybdenum disulfide (MoS2) semiconductors are the new generation of two-dimensional materials that possess several advantages compared to graphene due to their tunable bandgap and high electron mobility. Several approaches have been used to modify their physical properties for optical device applications. Here, we report a facile and non-destructive surface modification method for monolayer MoS2 via electron irradiation at a low, 5 kV accelerating voltage. After electron irradiation, the results of Raman and photoluminescence spectroscopy confirmed that the structure remains unchanged. However, when the modified surface was illuminated with a 532 nm laser for a prolonged period, the PL intensity was quenched as a result of oxygen desorption. Interestingly, the PL intensity can be recovered when left in ambient conditions for 10 h. The analysis of the PL spectrum revealed a decrease of trion, which is consistent with the readsorbed O2 molecules on the surface that deplete electrons and lead to PL recovery. We attribute this effect to the enhancement of the n-type character of monolayer MoS2 after electron irradiation. The sensitive nature of the modified surface to oxygen suggests that this approach may be used as a tool for the fabrication of MoS2 oxygen sensors.

Observation of Ultrahigh Photoconductivity in DNA-MoS2 Nano-Biocomposite

A nano-biocomposite film with ultrahigh photoconductivity remains elusive and critical for bio-optoelectronic applications. A uniform, well-connected, high-concentration nanomaterial network in the biological matrix remains challenging to achieve high photoconductivity. Wafer-scale continuous nano-biocomposite film without surface deformations and cracks plays another major obstacle. Here ultrahigh photoconductivity is observed in deoxyribonucleic acid-molybdenum disulfide (DNA-MoS2) nano-biocomposite film by incorporating a high-concentration, well-percolated, and uniform MoS2 network in the ss-DNA matrix. This is achieved by utilizing DNA-MoS2 hydrogel formation, which results in crack-free, wafer-scale DNA-MoS2 nano-biocomposite films. Ultra-high photocurrent (5.5 mA at 1 V) with a record-high on/off ratio (1.3 × 106) is observed, five orders of magnitude higher than conventional biomaterials (≈101) reported so far. The incorporation of the Wely semimetal (Bismuth) as an electrical contact exhibits ultrahigh photoresponsivity (2.6 × 105 A W-1). Such high photoconductivity in DNA-MoS2 nano-biocomposite could bridge the gap between biology, electronics, and optics for innovative biomedicine, bioengineering, and neuroscience applications.

Recent Advances in the Role of Different Nanoparticles in the Various Biosensors for the Detection of the Chikungunya Virus

Humans contract the Chikungunya virus (CHIKV), an alphavirus transmitted by mosquitoes that induces acute and chronic musculoskeletal discomfort and fever. Millions of cases of the disease have been attributed to CHIKV in the Indian Ocean region since 2004, and the virus has since spread to Europe, the Middle East, and the Pacific. The exponential proliferation of CHIKV in recent times underscores the critical nature of implementing preventative measures and exploring potential control strategies. The principal laboratory test employed to diagnose infection in serum samples collected over six days after the onset of symptoms is the detection of CHIKV or viral RNA. Although two commercially available real-time reverse transcription-polymerase chain reaction products exist, data on their validity are limited. A diagnostic instrument that is rapid, sensitive, specific, and cost-effective is, therefore an absolute necessity, particularly in developing nations. Biosensors have demonstrated considerable potential in the realm of pathogen detection. The rapid and sensitive detection of viruses has been facilitated by the development of numerous types of biosensors, including affinity-based nano-biosensors, graphene affinity-based biosensors, optical nano-biosensors, surface Plasmon Resonance-based optical nano-biosensors, and electrochemical nano-biosensors. Furthermore, the utilization of nanomaterials for signal extension, including but not limited to gold and silver nanoparticles, quantum dots, and iron oxide NPs, has enhanced the precision and sensitivity of biosensors. The developed innovative diagnostic method is time-efficient, precise, and economical; it can be implemented as a point-of-care device. The technique may be implemented in diagnostic laboratories and hospitals to identify patients infected with CHIKV. Throughout this article, we have examined a multitude of CHIKV nano-biosensors and their respective properties. Following a discussion of representative nanotechnologies for biosensors, numerous NPs-assisted CHIKV nano-biosensors are summarized in this article. As a result, we anticipate that this review will furnish a significant foundation for advancing innovative CHIKV nano-biosensors.

Genosensor on-chip paper for point of care detection: A review of biomedical analysis and food safety application

Over the last decade, paper-based biosensing has attracted considerable attention in numerous fields due to several advantages of them. To elaborate, using paper as a substrate of sensing approaches can be considered an affordable sensing approach owing to low cost of paper, and alongside that, the ability to operate without requiring external equipment. In many cases, cost-effective fabrication techniques such as screen printed and drop casting can be supposed as other benefits of these platforms. Despite the portability and affordability of paper-based assay, two important limitations including sensitivity and selectivity can decrease the application of these sensing approaches. Initially, decoration of paper substrate with nanomaterials (NMs) can improve the properties of paper due to high surface area and conductivity of them. Secondly, the presence of bioreceptors can provide a selective detection platform. Among different bioreceptors, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) can play a significant role. From this perspective, paper-based biosensors can be used for the detection of various gens which related to biomedical or food safety. In this review, we attempted to summarize recent trends and applications of paper-based genosensor, along with critical arguments in terms of NMs role in signal amplification. Furthermore, the lack of paper-based genosensors in field the of biomedical and food safety will be discussed in the following.

Covalently Modified MoS2 Bearing a Hamilton-Type Receptor for Recognizing a Redox-Active Ferrocene-Barbiturate Guest via Multiple H-Bonds

The covalent modification of the metallic phase of MoS2 with a Hamilton-type ligand is presented, transforming MoS2 to a recognition platform which is able to embrace barbiturate moieties via hydrogen bonding. The successful hydrogen bonding formation is easily monitored by simple electrochemical assessments, if a ferrocene-labeled barbiturate analogue is utilized as a proof of concept. Full spectroscopic, thermal, and electron microscopy imaging characterization is provided for the newly formed recognition system, along with valuable insights concerning the electrochemical sensing. The given methodology expands beyond the sensing applications, confidently entering the territory of supramolecular interactions on the surface of 2D transition metal dichalcogenides. The well-designed host-guest chemistry presented herein, constitutes a guide and an inspiration for hosting customized-structured functional building blocks on MoS2 and its relatives via hydrogen bonding, opening up new opportunities regarding potential applications.

Absorbance biosensors-based hybrid [Formula: see text] nanosheets for Escherichia coli detection

Detecting Escherichia coli is essential in biomedical, environmental, and food safety applications. In this paper, we have developed a simple, rapid, sensitive, and selective E. coli DNA sensor based on the novel hybrid-type [Formula: see text] and [Formula: see text] nanosheets. The sensor uses the absorbance measurement to distinguish among the DNA of E. coli, Vibrio proteolyticus, and Bacillus subtilis when implemented in conjunction with [Formula: see text]-probes. Our experiments showed that the absorbance increased when sensors detected E. coli DNA, whereas it decreased when sensors detected V. proteolyticus and B. subtilis DNA. To the best of authors' knowledge, there are no reports using the novel hybrid-[Formula: see text] and [Formula: see text] materials for differentiating three types of DNA using cost-effective and rapid absorbance measurements. In addition, the label-free E. coli DNA biosensor exhibited a linear response in the range of 0 fM to 11.65 fM with a limit of detection of 2 fM. The effect of [Formula: see text]-probes on our sensors' working performance is also investigated. Our results will facilitate further research in pathogen detection applications, which have not been fully developed yet.

Evolution Application of Two-Dimensional MoS2-Based Field-Effect Transistors

High-performance and low-power field-effect transistors (FETs) are the basis of integrated circuit fields, which undoubtedly require researchers to find better film channel layer materials and improve device structure technology. MoS₂ has recently shown a special two-dimensional (2D) structure and superior photoelectric performance, and it has shown new potential for next-generation electronics. However, the natural atomic layer thickness and large specific surface area of MoS₂ make the contact interface and dielectric interface have a great influence on the performance of MoS₂ FET. Thus, we focus on its main performance improvement strategies, including optimizing the contact behavior, regulating the conductive channel, and rationalizing the dielectric layer. On this basis, we summarize the applications of 2D MoS₂ FETs in key and emerging fields, specifically involving logic, RF circuits, optoelectronic devices, biosensors, piezoelectric devices, and synaptic transistors. As a whole, we discuss the state-of-the-art, key merits, and limitations of each of these 2D MoS₂-based FET systems, and prospects in the future.

Target-receptive structural switching of ssDNA as selective and sensitive biosensor for subsequent detection of toxic Pb2+ and organophosphorus pesticide

A structural switching in Single-stranded DNA (ssDNA) fluorescence biosensor for quick turn-on/off detection of Pb²⁺ ions and pesticide was reported. The design strategy of Hex-labelled ssDNA consists of two types of aptamer probe, G-rich base pair sequence forms G-quadruplex confirmation with Pb²⁺ ions. While other part of base pair sequence exhibits affinity to fold isocarbophos pesticide. MoS₂ nanosheets were identified as quick quencher of Hex fluorescence intensity via Vander-Waals interaction and its significance was compared with other nanomaterials. This sensing mechanism proposes a specific affinity of GA-rich ssDNA with Pb²⁺ to form G-quadruplex via G-Pb²⁺-G sequences. Consequently, ssDNA relived from MoS₂ nanosheets to restore the fluorescence intensity (turn-on). Subsequent addition of pesticide shows stronger affinity towards unfolded aptamer probe to form a random coil like structure. This causes Hex-labelled 5' end closer to the G-quadruplex connected at the 3' end of ssDNA resulting in a remarkable fluorescence quenching (turn-off) owing to PET process. Moreover, the sensing probe (Hex-labelled GA-rich ssDNA) was recycled by introducing acetylcholinesterase enzyme and thiocoline into the reaction mixture. The detection limits of Pb²⁺ and isocarbophos pesticide was estimated to be 0.6 nM and 0.018 μg/L respectively. Moreover, this study reveals a high sensitivity and selectivity towards target molecules in environmental samples.

Nanomaterial-Based Biosensors using Field-Effect Transistors: A Review

Field-effect transistor biosensors (Bio-FET) have attracted great interest in recent years owing to their distinctive properties like high sensitivity, good selectivity, and easy integration into portable and wearable electronic devices. Bio-FET performance mainly relies on the constituent components such as the bio-recognition layer and the transducer, which ensures device stability, sensitivity, and lifetime. Nanomaterial-based Bio-FETs are excellent candidates for biosensing applications. This review discusses the basic concepts, function, and working principles of Bio-FETs, and focuses on the progress of recent research in Bio-FETs in the sensing of neurotransmitters, glucose, nucleic acids, proteins, viruses, and cancer biomarkers using nanomaterials. Finally, challenges in the development of Bio-FETs, as well as an outlook on the prospects of nano Bio-FET-based sensing in various fields, are discussed.

Probing the adsorption behavior and free energy landscape of single-stranded DNA oligonucleotides on single-layer MoS2with molecular dynamics

Interfacing single-stranded DNA (ssDNA) with 2D transition metal dichalcogenides are important for numerous technological advancements. However, the molecular mechanism of this process, including the nature of intermolecular association and conformational details of the self-assembled hybrids is still not well understood. Here, atomistic molecular dynamics simulation is employed to study the distinct adsorption behavior of ssDNA on a single-layer MoS₂in aqueous environment. The ssDNA sequences [T₁₀, G₁₀, A₁₀, C₁₀, U₁₀, (GT)₅, and (AC)₅] are chosen on the basis that short ssDNA segments can undergo a spontaneous conformational change upon adsorption and allow efficient sampling of the conformational landscape. Differences in hybridization is attributed to the inherent molecular recognition ability of the bases. While the binding appears to be primarily driven by energetically favorable van der Waalsπ-stacking interactions, equilibrium structures are modulated by the ssDNA conformational changes. The poly-purines demonstrate two concurrently competingπ-stacking interactions: nucleobase-nucleobase (intramolecular) and nucleobase-MoS₂(intermolecular). The poly-pyrimidines, on the other hand, reveal enhancedπ-stacking interactions, thereby maximizing the number of contacts. The results provide new molecular-level understanding of ssDNA adsorption on the MoS₂surface and facilitate future studies in design of functional DNA/MoS₂structure-based platforms for DNA sequencing, biosensing (optical, electrochemical, and electronic), and drug delivery.

A bivalent binding aptamer-cDNA on MoS2 nanosheets based fluorescent aptasensor for detection of aflatoxin M1

To ensure the safety of dairy products, especially milk, and consequently protect human health, accurate and simple analytical techniques are highly necessary to determine the low concentration of aflatoxin M₁ (AFM₁) as an important carcinogen. Herein, a novel, accurate and simple fluorescent aptasensor was designed for selective detection of AFM₁ based on bivalent binding aptamer-cDNA (BBA-cDNA) structure. Moreover, MoS₂ nanosheets (MoS₂ NSs) were used as the fluorescent quencher and FAM-labeled complementary strand of aptamer (FAM-CS) was applied as a fluorescent probe. In this study, we achieved a new result. Unlike previous studies, in this work, the BBA-cDNA structure was not disassembled in the presence of the target. Therefore, as the AFM1 concentration increased, more targets were attached to the BBA-cDNA structure and as a result, the BBA-cDNA structure/AFM1 could not be placed on the surface of MoS2 NSs, leading to the more fluorescent intensity detection. Under optimized conditions, the developed fluorescent analytical method revealed great selectivity toward AFM₁ with a limit of detection (LOD) of 0.5 nM and a linear range from 0.7 to 10 nM. This fabricated aptasensor indicated excellent analytical performance for AFM₁ detection in milk samples with LOD of 0.1 nM. Overall, the proposed approach could provide an effective basis for small molecule analysis to guarantee food and human safety using appropriate aptamer sequences.

Influence of the choice of precursors on the synthesis of two-dimensional transition metal dichalcogenides

The interest in transition metal dichalcogenides (TMDCs; MEy/2; M = transition metal; E = chalcogenide, y = valence of the metal) has grown exponentially across various science and engineering disciplines due to their unique structural chemistry manifested in a two-dimensional lattice that results in extraordinary electronic and transport properties desired for applications in sensors, energy storage and optoelectronic devices. Since the properties of TMDCs can be tailored by changing the stacking sequence of 2D monolayers with similar or dis-similar materials, a number of synthetic routes essentially based on the disintegration of bulk (e.g., chemical exfoliation) or the integration of atomic constituents (e.g., vapor phase growth) have been explored. Despite a large body of data available on the chemical synthesis of TMDCs, experimental strategies with high repeatability of control over film thickness, phase and compositional purity remain elusive, which calls for innovative synthetic concepts offering, for instance, self-limited growth in the z-direction and homogeneous lateral topography. This review summarizes the recent conceptual advancements in the growth of layered van der Waals TMDCs from both mixtures of metal and chalcogen sources (multi-source precursors; MSPs) and from molecular compounds containing metals and chalcogens in one starting material (single-source precursor; SSPs). The critical evaluation of the strengths, limitations and opportunities of MSP and SSP approaches is provided as a guideline for the fabrication of TMDCs from commercial and customized molecular precursors. For example, alternative synthetic pathways using tailored molecular precursors circumvent the challenges of differential nucleation and crystal growth kinetics that are invariably associated with conventional gas phase chemical vapor transport (CVT) and chemical vapor deposition (CVD) of a mixture of components. The aspects of achieving high compositional purity and alternatives to minimize competing reactions or side products are discussed in the context of efficient chemical synthesis of TMDCs. Moreover, a critical analysis of the potential opportunities and existing bottlenecks in the synthesis of TMDCs and their intrinsic properties is provided.

Fabrication of label-free and ultrasensitive electrochemical immunosensor based on molybdenum disulfide nanoparticles modified disposable ITO: An analytical platform for antibiotic detection in food samples

Here, we aimed to fabricate a label-free immunosensing platform for the first time based on molybdenum disulfide nanoparticles (nMoS₂NPs) deposited on ITO) coated glass substrate for the electrochemical detection of ampicillin (AMP). The stable and high surface area of nMoS₂NPs were made by a low-temperature one-step hydrothermal route, bestowing the carrying capacity of anti-AMP (antibody against AMP) through an amide linkage. The spectroscopic, morphological, and structural characterization of the proposed electrodes were performed using various analytical and electrochemical techniques. The differential pulse voltammetry technique was utilized to evaluate anti-AMP and AMP interaction on the electrode surface. The developed immunosensor exhibits high sensitivity, a broad detection range having a significant detection limit towards detection of AMP having excellent selectivity, acceptable stability, and reproducibility. Furthermore, the applicability of the proposed immunosensor was tested in spiked milk, water, and orange juice, and the results confirmed the consistency of the immunosensor.

Synergizing Functional Nanomaterials with Aptamers Based on Electrochemical Strategies for Pesticide Detection: Current Status and Perspectives

Owing to the high toxicity and large-scale use of pesticides, it is imperative to develop selective, sensitive, portable, and convenient sensors for rapid monitoring of pesticide. Therefore, the electrochemical detection platform offers a promising analytical approach since it is easy to operate, economical, efficient, and user-friendly. Meanwhile, with advances in functional nanomaterials and aptamer selection technologies, numerous sensitivity-enhancement techniques alongside a widespread range of smart nanomaterials have been merged to construct novel aptamer probes to use in the biosensing field. Hence, this study intends to highlight recent development and promising applications on the functional nanomaterials with aptamers for pesticides detection based on electrochemical strategies. We also reviewed the current novel aptamer-functionalized microdevices for the portability of pesticides sensors. Furthermore, the major challenges and future prospects in this field are also discussed to provide ideas for further research.

Construction of ultrathin MoS2/Bi5O7I composites: Effective charge separation and increased photocatalytic activity

Ultrathin MoS₂ nanosheet hybridized Bi₅O₇I (MoS₂/Bi₅O₇I) nanorods were synthesized via a reactable ionic liquid assisted solvothermal process for the first time. The photocatalytic activity of MoS₂/Bi₅O₇I nanorods was determined by photodegrading bisphenol A (BPA), tetracycline hydrochloride (TC) and ciprofloxacin (CIP) under visible light irradiation. Experimental results showed that MoS₂/Bi₅O₇I owned the excellent photocatalytic properties and photostability. The efficient visible light driven photocatalytic performance was due to a larger specific surface area of MoS₂, which increased the close interfacial contact between pollutants and photocatalysts. Meanwhile, the introduction of ultrathin MoS₂ nanosheet was conducive to the separation and utilization of photoinduced charge carriers, thus further suppressed high recombination rate in pure Bi₅O₇I nanorods. Moreover, a possible charge transfer path in MoS₂/Bi₅O₇I composite material was also put forward.

Nanotip Contacts for Electric Transport and Field Emission Characterization of Ultrathin MoS2 Flakes

We report a facile approach based on piezoelectric-driven nanotips inside a scanning electron microscope to contact and electrically characterize ultrathin MoS₂ (molybdenum disulfide) flakes on a SiO₂/Si (silicon dioxide/silicon) substrate. We apply such a method to analyze the electric transport and field emission properties of chemical vapor deposition-synthesized monolayer MoS₂, used as the channel of back-gate field effect transistors. We study the effects of the gate-voltage range and sweeping time on the channel current and on its hysteretic behavior. We observe that the conduction of the MoS₂ channel is affected by trap states. Moreover, we report a gate-controlled field emission current from the edge part of the MoS₂ flake, evidencing a field enhancement factor of approximately 200 and a turn-on field of approximately 40 V/μm at a cathode–anode separation distance of 900 nm.

Quality enhancement of low temperature metal organic chemical vapor deposited MoS2: an experimental and computational investigation

Electronic quality of chemical vapor deposited MoS₂ is a function of crystallinity, which tends to decline with decrease in deposition temperature. Conventional thermal annealing can improve the quality but requires very high temperatures. In this study, we investigate a novel low temperature (room temperature to 400 °C) annealing process that exploits the electron wind force during passage of current. Here, moderate current density gives rise to atomic scale mechanical force whenever the electrons encounter defects in the lattice or grain boundaries (GBs). After hypothesizing that this force can significantly enhance defect mobility without any temperature field, we demonstrate the process using in situ transmission electron microscope and molecular dynamics simulation. Monolayer metal organic chemical vapor deposited MoS₂ deposited at 400 °C was post processed at temperature as low as 20 °C. Experimental results show five times enhancement in electrical conductivity, which is supported by electron diffraction patterns indicating significant grain growth. Discrete spots in diffraction indicate evolution of high crystallinity even at room temperature. Our computational model shows the mechanisms behind healing lattice defects as well as reorienting the GBs. The enhancement in microstructure of the specimen is also reflected in mechanical properties simulations on pre- and post-annealed specimens.

Self-Assembled Two-Dimensional Molybdenum Disulfide Nanosheet Geno-Interface for the Detection of Salmonella

This report presents a novel lab-on-a-paper (LoP)-based device coupled with a molybdenum disulfide nanosheet (MoS2NS)-modified electrochemical genosensor for detecting Salmonella-specific DNA. Conductive electrodes were grafted on a paper-based substrate employing a stencil printing technique, and MoS2NS was decorated on the working electrode. MoS2NS has strong affinity toward nucleo bases, which made it a best sensing interface for the immobilization of DNA. Morphological, optical, and structural characterizations were accomplished using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), UV-vis spectroscopy (UV-vis), and Raman spectroscopy, repectively. The current studies of an electrochemical genosensor demonstrated a good linear detection range from 100-20 nM and a low limit of detection of 20 nM toward Salmonella DNA with R 2 = 0.991. The proposed LoP-based genosensor confirmed as a better sensing podium and an effectual immobilization matrix for DNA.

Synergistic effect of MoS2 and diamond nanoparticles in electrochemical sensors: determination of the anticonvulsant drug valproic acid

The authors describe an electrochemical sensor based on the use of diamond nanoparticles (DNPs) and molybdenum disulfide (MoS₂) platelets. The sensor was applied to the voltammetric determination of the anticonvulsant valproic acid which was previously derivatized with ferrocene. The MoS₂ platelets were obtained by an exfoliation method, and the DNPs were directly dispersed in water and subsequently deposited on a glassy carbon electrode (GCE). The sensor response was optimized in terms of the solvent employed for dispersing the MoS₂ nanomaterial and the method for modifying the GCE. Sensors consisting of a first layer of MoS₂ dispersed in ethanol/water and a second layer of DNPs give better response. The single steps of sensor construction were characterized by atomic force microscopy and electrochemical impedance spectroscopy. The differential pulse voltammetric response of the GCE (measured at +0.18 V vs. Ag/AgCl) was compared to that of sensors incorporating only one of the nanomateriales (DNPs or MoS₂). The formation of a hybrid MoS₂-DNP structure clearly improves performance. The GCE containing both nanomaterials exhibits high sensitivity (740 µA ⋅ mM^-1 ⋅ cm^-2), a 0.27 μM detection limit, and an 8% reproducibility (RSD). The sensor retained 99% of its initial response after 45 days of storage. Graphical abstract Electrochemical sensor by co-immobilization of MoS₂ and diamond nanoparticles (DNP). The formation of a hybrid MoS₂-DNP structure enhances the performance of the sensor towards valproic acid derivatized with a ferrocene group, when compared with sensors incorporating only DNP or MoS₂.

Detection of chikungunya virus DNA using two-dimensional MoS2 nanosheets based disposable biosensor

Development of platforms for a reliable, rapid, sensitive and selective detection of chikungunya virus (CHIGV) is the need of the hour in developing countries. To the best of our knowledge, there are no reports available for the electrochemical detection of CHIGVDNA. Therefore, we aim at developing a biosensor based on molybdenum disulphide nanosheets (MoS₂ NSs) for the point-of-care diagnosis of CHIGV. Briefly, MoS₂ NSs were synthesized by chemical route and characterized using scanning electron microscopy, transmission electron microscopy, UV-Vis spectroscopy, Raman spectroscopy and X-Ray Diffraction. MoS₂ NSs were then subjected to physical adsorption onto the screen printed gold electrodes (SPGEs) and then employed for the detection of CHIGV DNA using electrochemical voltammetric techniques. Herein, the role of MoS₂ NSs is to provide biocompatibility to the biological recognition element on the surface of the screen printed electrodes. The detection strategy employed herein is the ability of methylene blue to interact differentially with the guanine bases of the single and double-stranded DNA which leads to change in the magnitude of the voltammetric signal. The proposed genosensor exhibited a wide linear range of 0.1 nM to 100 µM towards the chikungunya virus DNA.

Group 6 transition metal dichalcogenide nanomaterials: synthesis, applications and future perspectives

Group 6 transition metal dichalcogenides (G6-TMDs), most notably MoS₂, MoSe₂, MoTe₂, WS₂ and WSe₂, constitute an important class of materials with a layered crystal structure. Various types of G6-TMD nanomaterials, such as nanosheets, nanotubes and quantum dot nano-objects and flower-like nanostructures, have been synthesized. High thermodynamic stability under ambient conditions, even in atomically thin form, made nanosheets of these inorganic semiconductors a valuable asset in the existing library of two-dimensional (2D) materials, along with the well-known semimetallic graphene and insulating hexagonal boron nitride. G6-TMDs generally possess an appropriate bandgap (1-2 eV) which is tunable by size and dimensionality and changes from indirect to direct in monolayer nanosheets, intriguing for (opto)electronic, sensing, and solar energy harvesting applications. Moreover, rich intercalation chemistry and abundance of catalytically active edge sites make them promising for fabrication of novel energy storage devices and advanced catalysts. In this review, we provide an overview on all aspects of the basic science, physicochemical properties and characterization techniques as well as all existing production methods and applications of G6-TMD nanomaterials in a comprehensive yet concise treatment. Particular emphasis is placed on establishing a linkage between the features of production methods and the specific needs of rapidly growing applications of G6-TMDs to develop a production-application selection guide. Based on this selection guide, a framework is suggested for future research on how to bridge existing knowledge gaps and improve current production methods towards technological application of G6-TMD nanomaterials.

A comprehensive review on nano-molybdenum disulfide/DNA interfaces as emerging biosensing platforms

The development of nucleic acid-based portable platforms for the real-time analysis of diseases has attracted considerable scientific and commercial interest. Recently, 2D layered molybdenum sulfide (2D MoS₂ from here on) nanosheets have shown great potential for the development of next-generation platforms for efficient signal transduction. Through combination with DNA as a biorecognition medium, MoS₂ nanostructures have opened new opportunities to design and construct highly sensitive, specific, and commercially viable sensing devices. The use of specific short ssDNA sequences like aptamers has been proven to bind well with the unique transduction properties of 2D MoS₂ nanosheets to realize aptasensing devices. Such sensors can be operated on the principles of fluorescence, electro-cheumuluminescence, and electrochemistry with many advantageous features (e.g., robust biointerfacing through various conjugation chemistries, facile sensor assembly, high stability with regard to temperature/pH, and high affinity to target). This review encompasses the state of the art information on various design tactics and working principles of MoS₂/DNA sensor technology which is emerging as one of the most sought-after and valuable fields with the advent of nucleic acid inspired devices. To help achieve a new milestone in biosensing applications, great potential of this emerging technique is described further with regard to sensitivity, specificity, operational convenience, and versatility.

Transition metal dichalcogenide quantum dots: synthesis, photoluminescence and biological applications

We introduce the synthesis strategy, photoluminescence features and biological applications of TMD QDs.