Scalable Production of Molybdenum Disulfide Based Biosensors

Scalable biomimetic sensing system with membrane receptor dual-monolayer probe and graphene transistor arrays

Affinity-based biosensing can enable point-of-care diagnostics and continuous health monitoring, which commonly follows bottom-up approaches and is inherently constrained by bioprobes' intrinsic properties, batch-to-batch consistency, and stability in biofluids. We present a biomimetic top-down platform to circumvent such difficulties by combining a "dual-monolayer" biorecognition construct with graphene-based field-effect-transistor arrays. The construct adopts redesigned water-soluble membrane receptors as specific sensing units, positioned by two-dimensional crystalline S-layer proteins as dense antifouling linkers guiding their orientations. Hundreds of transistors provide statistical significance from transduced signals. System feasibility was demonstrated with rSbpA-ZZ/CXCR4QTY-Fc combination. Nature-like specific interactions were achieved toward CXCL12 ligand and HIV coat glycoprotein in physiologically relevant concentrations, without notable sensitivity loss in 100% human serum. The construct is regeneratable by acidic buffer, allowing device reuse and functional tuning. The modular and generalizable architecture behaves similarly to natural systems but gives electrical outputs, which enables fabrication of multiplex sensors with tailored receptor panels for designated diagnostic purposes.

An ultrasensitive FET biosensor based on vertically aligned MoS2 nanolayers with abundant surface active sites

Molybdenum disulfide (MoS₂) nanolayers are one of the most promising two-dimensional (2D) nanomaterials for constructing next-generation field-effect transistor (FET) biosensors. In this article, we report an ultrasensitive FET biosensor that integrates a novel format of 2D MoS₂, vertically-aligned MoS₂ nanolayers (VAMNs), as the channel material for label-free detection of the prostate-specific antigen (PSA). The developed VAMNs-based FET biosensor shows two distinctive advantages. First, the VAMNs can be facilely grown using the conventional chemical vapor deposition (CVD) method, permitting easy fabrication and potential mass device production. Second, the unique advantage of the VAMNs for biosensor development lies in its abundant surface-exposed active edge sites that possess a high binding affinity with thiol-based linkers, which overcomes the challenge of molecule functionalization on the conventional planar MoS₂ nanolayers. The high binding affinity between 11-mercaptoundecanoic acid and the VAMNs was demonstrated through experimental surface characterization and theoretical calculations via density functional theory. The FET biosensor allows rapid (within 20 min) and ultrasensitive PSA detection in human serum with simple operations (limit of detection: 800 fg mL^-1). This FET biosensor offers excellent features such as ultrahigh sensitivity, ease of fabrication, and short assay time, and thereby possesses significant potential for early-stage diagnosis of life-threatening diseases.

Self-assembled GA-Repeated Peptides as a Biomolecular Scaffold for Biosensing with MoS2 Electrochemical Transistors

Biosensors with two-dimensional materials have gained wide interest due to their high sensitivity. Among them, single-layer MoS2 has become a new class of biosensing platform owing to its semiconducting property. Immobilization of bioprobes directly onto the MoS2 surface with chemical bonding or random physisorption has been widely studied. However, these approaches potentially cause a reduction of conductivity and sensitivity of the biosensor. In this work, we designed peptides that spontaneously align into monomolecular-thick nanostructures on electrochemical MoS2 transistors in a non-covalent fashion and act as a biomolecular scaffold for efficient biosensing. These peptides consist of repeated domains of glycine and alanine in the sequence and form self-assembled structures with sixfold symmetry templated by the lattice of MoS2. We investigated electronic interactions of self-assembled peptides with MoS2 by designing their amino acid sequence with charged amino acids at both ends. Charged amino acids in the sequence showed a correlation with the electrical properties of single-layer MoS2, where negatively charged peptides caused a shift of threshold voltage in MoS2 transistors and neutral and positively charged peptides had no significant effect on the threshold voltage. The transconductance of transistors had no decrease due to the self-assembled peptides, indicating that aligned peptides can act as a biomolecular scaffold without degrading the intrinsic electronic properties for biosensing. We also investigated the impact of peptides on the photoluminescence (PL) of single-layer MoS2 and found that the PL intensity changed sensitively depending on the amino acid sequence of peptides. Finally, we demonstrated a femtomolar-level sensitivity of biosensing using biotinylated peptides to detect streptavidin.

Predicting Biomolecule Adsorption on MoS2 Nanosheets with High Structural Fidelity

A new force field, MoSu-CHARMM, for the description of bio-interfacial structures at the aqueous MoS2 interface is developed, based on quantum chemical data. The force field describes non-covalent interactions between...

The Challenges of Developing Biosensors for Clinical Assessment: A Review

Emerging research in biosensors has attracted much attention worldwide, particularly in response to the recent pandemic outbreak of coronavirus disease 2019 (COVID-19). Nevertheless, initiating research in biosensing applied to the diagnosis of diseases is still challenging for researchers, be it in the preferences of biosensor platforms, selection of biomarkers, detection strategies, or other aspects (e.g., cutoff values) to fulfill the clinical purpose. There are two sides to the development of a diagnostic tool: the biosensor development side and the clinical side. From the development side, the research engineers seek the typical characteristics of a biosensor: sensitivity, selectivity, linearity, stability, and reproducibility. On the other side are the physicians that expect a diagnostic tool that provides fast acquisition of patient information to obtain an early diagnosis or an efficient patient stratification, which consequently allows for making assertive and efficient clinical decisions. The development of diagnostic devices always involves assay developer researchers working as pivots to bridge both sides whose role is to find detection strategies suitable to the clinical needs by understanding (1) the intended use of the technology and its basic principle and (2) the preferable type of test: qualitative or quantitative, sample matrix challenges, biomarker(s) threshold (cutoff value), and if the system requires a mono- or multiplex assay format. This review highlights the challenges for the development of biosensors for clinical assessment and its broad application in multidisciplinary fields. This review paper highlights the following biosensor technologies: magnetoresistive (MR)-based, transistor-based, quartz crystal microbalance (QCM), and optical-based biosensors. Its working mechanisms are discussed with their pros and cons. The article also gives an overview of the most critical parameters that are optimized by developing a diagnostic tool.

Novel variants of engineered water soluble mu opioid receptors with extensive mutations and removal of cysteines

We have shown that water-soluble variants of the human mu opioid receptor (wsMOR) containing a reduced number of hydrophobic residues at the lipid-facing residues of the transmembrane (TM) helices can be expressed in E. coli. In this study, we tested the consequences of increasing the number of mutations on the surface of the transmembrane domain on the receptor's aqueous solubility and ligand binding properties, along with mutation of 11 cysteine residues regardless of their solvent exposure value and location in the protein. We computationally engineered 10 different variants of MOR, and tested four of them for expression in E. coli. We found that all four variants were successfully expressed and could be purified in high quantities. The variants have alpha helical structural content similar to that of the native MOR, and they also display binding affinities for the MOR antagonist (naltrexone) similar to the wsMOR variants we engineered previously that contained many fewer mutations. Furthermore, for these full-length variants, the helical content remains unchanged over a wide range of pH values (pH 6 ~ 9). This study demonstrates the flexibility and robustness of the water-soluble MOR variants with respect to additional designed mutations in the TM domain and changes in pH, whereupon the protein's structural integrity and its ligand binding affinity are maintained. These variants of the full-length MOR with less hydrophobic surface residues and less cysteines can be obtained in large amounts from expression in E. coli and can serve as novel tools to investigate structure-function relationships of the receptor.

Fluorometric discrimination of tyrosine isomers based on the inner filter effect of chiral Au nanoparticles on MoS2 quantum dots

A fluorescent chiral sensor is proposed based on the inner filter effect (IFE) of chiral Au nanoparticles (AuNPs) on MoS2 quantum dots (MoS2 QDs), which can be used for the discrimination of the isomers of tyrosine (Tyr). l-Tyrosine (l-Tyr) can induce obvious agglomeration of the chiral AuNPs, leading to an attenuated IFE of the chiral AuNPs and greatly restored fluorescence of the MoS2 QDs, and thus the enantioselective recognition of the Tyr isomers can be achieved. Also, l-Tyr but not d-Tyr induced agglomeration of the chiral AuNPs is confirmed by the larger association constant between l-Tyr and the chiral sensor.

Bio-Separated and Gate-Free 2D MoS2 Biosensor Array for Ultrasensitive Detection of BRCA1

2D molybdenum disulfide (MoS₂)-based thin film transistors are widely used in biosensing, and many efforts have been made to improve the detection limit and linear range. However, in addition to the complexity of device technology and biological modification, the compatibility of the physical device with biological solutions and device reusability have rarely been considered. Herein, we designed and synthesized an array of MoS₂ by employing a simple-patterned chemical vapor deposition growth method and meanwhile exploited a one-step biomodification in a sensing pad based on DNA tetrahedron probes to form a bio-separated sensing part. This solves the signal interference, solution erosion, and instability of semiconductor-based biosensors after contacting biological solutions, and also allows physical devices to be reused. Furthermore, the gate-free detection structure that we first proposed for DNA (BRCA1) detection demonstrates ultrasensitive detection over a broad range of 1 fM to 1 μM with a good linear response of R² = 0.98. Our findings provide a practical solution for high-performance, low-cost, biocompatible, reusable, and bio-separated biosensor platforms.

Nanoscale Friction Behavior of Transition-Metal Dichalcogenides: Role of the Chalcogenide

Despite extensive research on the tribological properties of MoS₂, the frictional characteristics of other members of the transition-metal dichalcogenide (TMD) family have remained relatively unexplored. To understand the effect of the chalcogen on the tribological behavior of these materials and gain broader general insights into the factors controlling friction at the nanoscale, we compared the friction force behavior for a nanoscale single asperity sliding on MoS₂, MoSe₂, and MoTe₂ in both bulk and monolayer forms through a combination of atomic force microscopy experiments and molecular dynamics simulations. Experiments and simulations showed that, under otherwise identical conditions, MoS₂ has the highest friction among these materials and MoTe₂ has the lowest. Simulations complemented by theoretical analysis based on the Prandtl-Tomlinson model revealed that the observed friction contrast between the TMDs was attributable to their lattice constants, which differed depending on the chalcogen. While the corrugation amplitudes of the energy landscapes are similar for all three materials, larger lattice constants permit the tip to slide more easily across correspondingly wider saddle points in the potential energy landscape. These results emphasize the critical role of the lattice constant, which can be the determining factor for frictional behavior at the nanoscale.

Direct electron-beam patterning of monolayer MoS2 with ice

Two-dimensional transition metal dichalcogenides (TMDCs) are considered strong competitors for next generation semiconductor materials. In this paper, we propose direct electron-beam patterning of monolayer MoS2 inspired by an emerging ice lithography technique. Compared to conventional resist-based nanofabrication, ice-assisted patterning is free of contaminations from polymer resist and allows in situ processing of MoS2. The effects of electron beam dose and energy are investigated and nanoribbons with width below 30 nm are attainable. This method is expected to be applicable also to other TMDCs, providing a promising alternative for nanofabrication of 2D material devices.

Phase Transition in a Memristive Suspended MoS2 Monolayer Probed by Opto- and Electro-Mechanics

Semiconducting monolayers of a 2D material are able to concatenate multiple interesting properties into a single component. Here, by combining opto-mechanical and electronic measurements, we demonstrate the presence of a partial 2H-1T' phase transition in a suspended 2D monolayer membrane of MoS₂. Electronic transport shows unexpected memristive properties in the MoS₂ membrane, in the absence of any external dopants. A strong mechanical softening of the membrane is measured concurrently and may only be related to the 2H-1T' phase transition, which imposes a 3% directional elongation of the topological 1T' phase with respect to the semiconducting 2H. We note that only a few percent 2H-1T' phase switching is sufficient to observe measurable memristive effects. Our experimental results combined with first-principles total energy calculations indicate that sulfur vacancy diffusion plays a key role in the initial nucleation of the phase transition. Our study clearly shows that nanomechanics represents an ultrasensitive technique to probe the crystal phase transition in 2D materials or thin membranes. Finally, a better control of the microscopic mechanisms responsible for the observed memristive effect in MoS₂ is important for the implementation of future devices.

Wafer-Scale Uniform Carbon Nanotube Transistors for Ultrasensitive and Label-Free Detection of Disease Biomarkers

Carbon nanotube (CNT) field-effect transistor (FET)-based biosensors have shown great potential for ultrasensitive biomarker detection, but challenges remain, which include unsatisfactory sensitivity, difficulty in stable functionalization, incompatibility with scalable fabrication, and nonuniform performance. Here, we describe ultrasensitive, label-free, and stable FET biosensors built on polymer-sorted high-purity semiconducting CNT films with wafer-scale fabrication and high uniformity. With a floating gate (FG) structure using an ultrathin Y₂O₃ high-κ dielectric layer, the CNT FET biosensors show amplified response and improved sensitivity compared with those sensors without Y₂O₃, which is attributed to the chemical gate-coupling effect dominating the sensor response. The CNT FG-FETs are modified to selectively detect specific disease biomarkers, namely, DNA sequences and microvesicles, with theoretical record detection limits as low as 60 aM and 6 particles/mL, respectively. Furthermore, the biosensors exhibit highly uniform performance over the 4 in. wafer as well as superior bias stress stability. The FG CNT FET biosensors could be extended as a universal biosensor platform for the ultrasensitive detection of multiple biological molecules and applied in highly integrated and multiplexed all CNT-FET-based sensor architectures.

Oxygen Vacancy-Enhanced Electrochemiluminescence Sensing Strategy Using Luminol Thermally Encapsulated in Apoferritin as a Transducer for Biomarker Immunoassay

Oxygen vacancies (OVs) enhanced electrochemiluminescence (ECL) biosensing strategy using luminol thermally encapsulated in apoferritin (Lum@apoFt) as an efficient transducer was investigated for ultrasensitive biomarker detection. By applying the oxygen-defect engineering (ODE) strategy, the OVs enriched cobalt-iron oxide (r-CoFe₂O₄) was fabricated as the sensing substrate to boost the electron mobility and catalyze the generation of superoxide anion radical (O₂^•-) for signal amplification. It should be noted that r-CoFe₂O₄ with higher OVs density dramatically accelerated the ECL reaction between O₂^•- and luminol anionic radicals, achieving 6.5-fold stronger ECL output than CoFe₂O₄ with no or low OVs density. Moreover, facile encapsulation of approximate 412 luminol molecules in a single apoFt cavity was first realized by an efficient thermal-induction method. The obtained Lum@apoFt complexes exhibited well-maintained ECL efficiency and excellent biocompatibility for biological modifications. On this basis, a biosensor was developed for early diagnostics of squamous cell carcinomas by detecting its representative biomarker named cytokeratin 19 fragment 21-1 (CYFRA 21-1), from which excellent linearity was achieved in 0.5 pg/mL to 50 ng/mL with a detection limit of 0.14 pg/mL. This work not only put forward a novel idea of creating OVs enriched sensing interface with excellent signal-amplification function but also proposes a facile and robust methodology to design apoFt-based transducers for developing more practical nanoscale biosensors in early diagnostics of diseases.

Universal In Situ Substitutional Doping of Transition Metal Dichalcogenides by Liquid-Phase Precursor-Assisted Synthesis

Doping lies at the heart of modern semiconductor technologies. Therefore, for two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs), the significance of controlled doping is no exception. Recent studies have indicated that, by substitutionally doping 2D TMDs with a judicious selection of dopants, their electrical, optical, magnetic, and catalytic properties can be effectively tuned, endowing them with great potential for various practical applications. Herein, and inspired by the sol-gel process, we report a liquid-phase precursor-assisted approach for in situ substitutional doping of monolayered TMDs and their in-plane heterostructures with tunable doping concentration. This highly reproducible route is based on the high-temperature chalcogenation of spin-coated aqueous solutions containing host and dopant precursors. The precursors are mixed homogeneously at the atomic level in the liquid phase prior to the synthesis process, thus allowing for an improved doping uniformity and controllability. We further demonstrate the incorporation of various transition metal atoms, such as iron (Fe), rhenium (Re), and vanadium (V), into the lattice of TMD monolayers to form Fe-doped WS₂, Re-doped MoS₂, and more complex material systems such as V-doped in-plane W_xMo_1-xS₂-Mo_xW_1-xS₂ heterostructures, among others. We envisage that our developed approach is universal and could be extended to incorporate a variety of other elements into 2D TMDs and create in-plane heterointerfaces in a single step, which may enable applications such as electronics and spintronics at the 2D limit.

Environmental Analysis with 2D Transition-Metal Dichalcogenide-Based Field-Effect Transistors

Field-effect transistors (FETs) present highly sensitive, rapid, and in situ detection capability in chemical and biological analysis. Recently, two-dimensional (2D) transition-metal dichalcogenides (TMDCs) attract significant attention as FET channel due to their unique structures and outstanding properties. With the booming of studies on TMDC FETs, we aim to give a timely review on TMDC-based FET sensors for environmental analysis in different media. First, theoretical basics on TMDC and FET sensor are introduced. Then, recent advances of TMDC FET sensor for pollutant detection in gaseous and aqueous media are, respectively, discussed. At last, future perspectives and challenges in practical application and commercialization are given for TMDC FET sensors. This article provides an overview on TMDC sensors for a wide variety of analytes with an emphasize on the increasing demand of advanced sensing technologies in environmental analysis.

MoS2-enabled dual-mode optoelectronic biosensor using a water soluble variant of μ-opioid receptor for opioid peptide detection

Owing to their unique electrical and optical properties, two-dimensional transition metal dichalcogenides have been extensively studied for their potential applications in biosensing. However, simultaneous utilization of both optical and electrical properties has been overlooked, yet it can offer enhanced accuracy and detection versitility. Here, we demonstrate a dual-mode optoelectronic biosensor based on monolayer molybdenum disulfide (MoS₂) capable of producing simultaneous electrical and optical readouts of biomolecular signals. On a single platform, the biosensor exhibits a tunable photonic Fano-type optical resonance while also functioning as a field-effect transistor (FET) based on a optically transparent gate electrode. Furthermore, chemical vapor deposition grown MoS₂ provides a clean surface for direct immobilization of a water-soluble variant of the μ-opioid receptor (wsMOR), via a nickel ion-mediated linker chemistry. We utilize a synthetic opioid peptide to show the operation of the electronic and optical sensing modes. The responses of both modes exhibit a similar trend with dynamic ranges of four orders of magnitude and detection limits of <1 nM. Our work explores the potential of a versatile multimodal sensing platform enabled by monolayer MoS₂, since the integration of electrical and optical sensors on the same chip can offer flexibility in read-out and improve the accuracy in detection of low concentration targets.

Characterization of an engineered water-soluble variant of the full-length human mu opioid receptor

A water-soluble variant of the transmembrane domain of the human mu opioid receptor (wsMOR-TM) was previously characterized. This study explored whether the full-length version of the engineered water-soluble receptor, (wsMOR-FL), could be overexpressed in Escherichia coli and if it would retain water solubility, binding capability and thermostability. wsMOR was over-expressed and purified in E. coli BL21(DE3) cells (EMD/Novagen) as we reported previously for the wsMOR-TM. Both native N and C termini were added back to the highly engineered wsMOR-TM. Six His-tag was added in the N terminus for purification purposes. The wsMOR-FL was characterized using atomic force microscope for its monomeric state, circular dichroism for its secondary structure and thermostability. Its binding with naltrexone is also determined. Compared to the native human MOR, wsMOR-FL displays similar helical secondary structure content and comparable affinity (nM) for the antagonist naltrexone. The secondary structure of the receptor remains stable within a wide range of pH (6-9). In contrast to the transmembrane portion, the secondary structure of full-length receptor tolerated a wide range of temperature (10-90 °C). The receptor remains predominantly as a monomer in solution, as directly imaged using atomic force microscopy. This study demonstrated that functional full-length water-soluble variant of human mu receptor can be over-expressed and purified using an E. coli over-expression system. This provides a novel tool for the investigation of structural and functional properties of the human MOR. N- and C-termini strengthened the thermostability of the protein in this specific water soluble variant. Communicated by Ramaswamy H. Sarma.

High-stability pH sensing with a few-layer MoS2 field-effect transistor

Recently, molybdenum disulfide (MoS₂), an emerging 2D material, has become an alternative candidate for ultra-sensitive biosensors due to its semiconducting behavior and the unique layer-by-layer atomic structure. Here, we report on highly stable and repeatable real-time pH sensing with few-layer MoS₂ field-effect transistor (FET) biosensors, fabricated with both HfO₂ and Al₂O₃/HfO₂ gate dielectrics on top of MoS₂ flakes exfoliated from natural crystals onto SiO₂/Si samples. Both types of sensors demonstrate a highly linear, stable and repeatable response over a wide pH range with near-ideal pH sensitivity close to the theoretical limit of 59.6 mV pH^-1. Ascribing from a different device operation regime in the pH sensing test-subthreshold regime for a sensor with an Al₂O₃/HfO₂ dielectric and linear regime for a sensor with HfO₂-a sensor with Al₂O₃/HfO₂ shows significantly higher current sensitivity (∼105-fold) and relatively better linearity than a sensor with HfO₂, while the latter shows relatively higher stability and higher repeatability. An Al₂O₃/HfO₂-coated MoS₂ FET reveals a high sensitivity or low detection limit of 0.01 pH.

Origin of Nanoscale Friction Contrast between Supported Graphene, MoS2, and a Graphene/MoS2 Heterostructure

Ultralow friction can be achieved with 2D materials, particularly graphene and MoS₂. The nanotribological properties of these different 2D materials have been measured in previous atomic force microscope (AFM) experiments sequentially, precluding immediate and direct comparison of their frictional behavior. Here, friction is characterized at the nanoscale using AFM experiments with the same tip sliding over graphene, MoS₂, and a graphene/MoS₂ heterostructure in a single measurement, repeated hundreds of times, and also measured with a slowly varying normal force. The same material systems are simulated using molecular dynamics (MD) and analyzed using density functional theory (DFT) calculations. In both experiments and MD simulations, graphene consistently exhibits lower friction than the MoS₂ monolayer and the heterostructure. In some cases, friction on the heterostructure is lower than that on the MoS₂ monolayer. Quasi-static MD simulations and DFT calculations show that the origin of the friction contrast is the difference in energy barriers for a tip sliding across each of the three surfaces.

Novel Graphene Biosensor Based on the Functionalization of Multifunctional Nano-bovine Serum Albumin for the Highly Sensitive Detection of Cancer Biomarkers

A simple, convenient, and highly sensitive bio-interface for graphene field-effect transistors (GFETs) based on multifunctional nano-denatured bovine serum albumin (nano-dBSA) functionalization was developed to target cancer biomarkers. The novel graphene-protein bioelectronic interface was constructed by heating to denature native BSA on the graphene substrate surface. The formed nano-dBSA film served as the cross-linker to immobilize monoclonal antibody against carcinoembryonic antigen (anti-CEA mAb) on the graphene channel activated by EDC and Sulfo-NHS. The nano-dBSA film worked as a self-protecting layer of graphene to prevent surface contamination by lithographic processing. The improved GFET biosensor exhibited good specificity and high sensitivity toward the target at an ultralow concentration of 337.58 fg mL^-1. The electrical detection of the binding of CEA followed the Hill model for ligand-receptor interaction, indicating the negative binding cooperativity between CEA and anti-CEA mAb with a dissociation constant of 6.82 × 10^-10 M. The multifunctional nano-dBSA functionalization can confer a new function to graphene-like 2D nanomaterials and provide a promising bio-functionalization method for clinical application in biosensing, nanomedicine, and drug delivery.

Uniform Vapor-Pressure-Based Chemical Vapor Deposition Growth of MoS2 Using MoO3 Thin Film as a Precursor for Coevaporation

Chemical vapor deposition (CVD) is a powerful method employed for high-quality monolayer crystal growth of 2D transition metal dichalcogenides with much effort invested toward improving the growth process. Here, we report a novel method for CVD-based growth of monolayer molybdenum disulfide (MoS₂) by using thermally evaporated thin films of molybdenum trioxide (MoO₃) as the molybdenum (Mo) source for coevaporation. Uniform evaporation rate of MoO₃ thin films provides uniform Mo vapors which promote highly reproducible single-crystal growth of MoS₂ throughout the substrate. These high-quality crystals are as large as 95 μm and are characterized by scanning electron microscopy, Raman spectroscopy, photoluminescence spectroscopy, atomic force microscopy, and transmission electron microscopy. The bottom-gated field-effect transistors fabricated using the as-grown single crystals show n-type transistor behavior with a good on/off ratio of 10⁶ under ambient conditions. Our results presented here address the precursor vapor control during the CVD process and is a major step forward toward reproducible growth of MoS₂ for future semiconductor device applications.

Ultra-thin bimetallic alloy nanowires with porous architecture/monolayer MoS2 nanosheet as a highly sensitive platform for the electrochemical assay of hazardous omethoate pollutant

A novel electrochemical biosensor was designed for sensitive detection of organophosphate pesticides based on three-dimensional porous bimetallic alloy architecture with ultrathin nanowires (PdCo NWs, PdCu NWs, PdNi NWs) and monolayer MoS₂ nanosheet (m-MoS₂). The bimetallic alloy NWs/m-MoS₂ nanomaterials were used as a sensing platform for electrochemical analysis of omethoate, a representative organophosphate pesticide, via acetylcholinesterase inhibition pathway. We demonstrated that all three bimetallic alloy NWs enhanced electrochemical responses of enzymatic biosensor, benefited from bimetallic synergistic action and porous structure. In particular, PdNi NWs outperformed other two bimetallic alloy. Moreover, PdNi NWs/m-MoS₂ as an electronic transducer is superior to the corresponding biosensor in the absence of monolayer MoS₂ nanosheet, which arise from synergistic signal amplification effect between different components. Under optimized conditions, the developed biosensor on the basis of PdNi NWs/m-MoS₂ shows outstanding performance for the electrochemical assay of omethoate, such as a wide linear range (10^-13 M∼10^-7 M), a low detection limit of 0.05 pM at a signal-to-noise ratio of 3, high sensitivity and long-time stability. The results demonstrate that bimetallic alloy NWs/m-MoS₂ nanocomposites could be excellent transducers to promote electron transfer for the electrochemical reactions, holding great potentials in the construction of current and future biosensing devices.

Oxidation-Induced Topological Phase Transition in Monolayer 1T'-WTe2

Monolayer (ML) tungsten ditelluride (WTe₂) is a well-known quantum spin Hall (QSH) insulator with topologically protected gapless edge states, thus promising dissipationless electronic devices. However, experimental findings exhibit the fast oxidation of ML WTe₂ in ambient conditions. To reveal the changes of topological properties of WTe₂ arising from oxidation, we systematically study the surface oxidation reaction of ML 1T'-WTe₂ using first-principles calculations. The calculated results indicate that the fast oxidation of WTe₂ originates from the existence of H₂O in air, which significantly promotes the oxidation of ML 1T'-WTe₂. More importantly, this low-coverage oxidized WTe₂ loses its topological features and is changed into a trivial insulator. Furthermore, we propose a fully oxidized ML WTe₂ that can still possess the QSH insulator states. The topological phase transition induced by oxidation provides exotic insight into understanding the topological features of layered transition-metal dichalcogenide materials.

Molybdenum disulfide field-effect transistor biosensor for ultrasensitive detection of DNA by employing morpholino as probe

This work reports on a molybdenum disulfide (MoS₂) based field-effect transistor (FET) biosensor for ultrasensitive label-free detection of DNA via phosphorodiamidate morpholino oligos (PMO)-DNA hybridization. After the chip was fabricated and the sensing channel was modified with positive charges, the negatively charged MoS₂ nanosheet was drop-casted onto the channel, enabling MoS₂ to tightly bind to the sensing surface via electrostatic interactions. Meanwhile, DNA analogue, PMO, was immobilized on the MoS₂ surface, and detection of PMO-DNA hybridization was conducted by the fabricated MoS₂ FET biosensor. Due to the neutral character and high affinity of PMO, a limit of detection (LOD) down to 6 fM was obtained, which is lower than that of the previously reported MoS₂ FET DNA biosensor based on DNA-DNA hybridization. In addition, the MoS₂ FET biosensor also showed high sequence specificity capable of distinguishing the complementary DNA from one-base mismatched DNA, three-base mismatched DNA and noncomplementary DNA. Moreover, the unique FET biosensor was able to detect DNA in complex sample like serum, making the method potential in disease diagnostics.

Chemical Vapor Transport Deposition of Molybdenum Disulfide Layers Using H2O Vapor as the Transport Agent

Molybdenum disulfide (MoS2) layers show excellent optical and electrical properties and have many potential applications. However, the growth of high-quality MoS2 layers is a major bottleneck in the development of MoS2-based devices. In this paper, we report a chemical vapor transport deposition method to investigate the growth behavior of monolayer/multi-layer MoS2 using water (H2O) as the transport agent. It was shown that the introduction of H2O vapor promoted the growth of MoS2 by increasing the nucleation density and continuous monolayer growth. Moreover, the growth mechanism is discussed.

Chemical Vapor Deposition Growth and Applications of Two-Dimensional Materials and Their Heterostructures

Two-dimensional (2D) materials have attracted increasing research interest because of the abundant choice of materials with diverse and tunable electronic, optical, and chemical properties. Moreover, 2D material based heterostructures combining several individual 2D materials provide unique platforms to create an almost infinite number of materials and show exotic physical phenomena as well as new properties and applications. To achieve these high expectations, methods for the scalable preparation of 2D materials and 2D heterostructures of high quality and low cost must be developed. Chemical vapor deposition (CVD) is a powerful method which may meet the above requirements, and has been extensively used to grow 2D materials and their heterostructures in recent years, despite several challenges remaining. In this review of the challenges in the CVD growth of 2D materials, we highlight recent advances in the controlled growth of single crystal 2D materials, with an emphasis on semiconducting transition metal dichalcogenides. We provide insight into the growth mechanisms of single crystal 2D domains and the key technologies used to realize wafer-scale growth of continuous and homogeneous 2D films which are important for practical applications. Meanwhile, strategies to design and grow various kinds of 2D material based heterostructures are thoroughly discussed. The applications of CVD-grown 2D materials and their heterostructures in electronics, optoelectronics, sensors, flexible devices, and electrocatalysis are also discussed. Finally, we suggest solutions to these challenges and ideas concerning future developments in this emerging field.

Molecular interactions between single layered MoS2 and biological molecules

In this research, molecular interactions between several de novo designed alpha-helical peptides and monolayer MoS₂ have been studied.

Two-dimensional (2D) materials such as graphene, molybdenum disulfide (MoS₂), tungsten diselenide (WSe₂), and black phosphorous are being developed for sensing applications with excellent selectivity and high sensitivity. In such applications, 2D materials extensively interact with various analytes including biological molecules. Understanding the interfacial molecular interactions of 2D materials with various targets becomes increasingly important for the progression of better-performing 2D-material based sensors. In this research, molecular interactions between several de novo designed alpha-helical peptides and monolayer MoS₂ have been studied. Molecular dynamics simulations were used to validate experimental data. The results suggest that, in contrast to peptide–graphene interactions, peptide aromatic residues do not interact strongly with the MoS₂ surface. It is also found that charged amino acids are important for ensuring a standing-up pose for peptides interacting with MoS₂. By performing site-specific mutations on the peptide, we could mediate the peptide–MoS₂ interactions to control the peptide orientation on MoS₂.

Synthesis and Physical Properties of Phase-Engineered Transition Metal Dichalcogenide Monolayer Heterostructures

Heterostructures of transition metal dichalcogenides (TMDs) offer the attractive prospect of combining distinct physical properties derived from different TMD structures. Here, we report direct chemical vapor deposition of in-plane monolayer heterostructures based on 1H-MoS₂ and 1T'-MoTe₂. The large lattice mismatch between these materials led to intriguing phenomena at their interface. Atomic force microscopy indicated buckling in the 1H region. Tip-enhanced Raman spectroscopy showed mode structure consistent with Te substitution in the 1H region during 1T'-MoTe₂ growth. This was confirmed by atomic resolution transmission electron microscopy, which also revealed an atomically stitched, dislocation-free 1H/1T' interface. Theoretical modeling revealed that both the buckling and absence of interfacial misfit dislocations were explained by lateral gradients in Te substitution levels within the 1H region and elastic coupling between 1H and 1T' domains. Phase field simulations predicted 1T' morphologies with spike-shaped islands at specific orientations consistent with experiments. Electrical measurements across the heterostructure confirmed its electrical continuity. This work demonstrates the feasibility of dislocation-free stitching of two different atomic configurations and a pathway toward direct synthesis of monolayer TMD heterostructures of different phases.

Lysozyme orientation and conformation on MoS2 surface: Insights from molecular simulations

Two-dimensional molybdenum disulfide (MoS₂) has attracted intense interest owing to its unique properties and promising biosensor applications. To develop effective biocompatible platforms, it is crucial to understand the interactions between MoS₂ and biological molecules such as proteins, but little knowledge exists on the orientation and conformation of proteins on the MoS₂ surface at the molecular level. In this work, the lysozyme adsorption on the MoS₂ surface was studied by molecular dynamics simulations, wherein six different orientations were selected based on the different faces of lysozyme. Simulation results showed that lysozyme tends to adsorb on the MoS₂ surface in an "end-on" orientation, indicating that orientations within this range are favorable for stable adsorption. The end-on orientation could be further categorized into "bottom end-on" and "top end-on" orientations. The driving forces responsible for the adsorption were dominated by van der Waals interactions and supplemented by electrostatic interactions. Further, the conformations of the lysozyme adsorbed on the MoS₂ surface were basically preserved. This simulation study promotes the fundamental understanding of interactions between MoS₂ and proteins and can guide the development of future biomedical applications of MoS₂.

Large-area synthesis of high-quality monolayer 1T'-WTe2 flakes

Large-area growth of monolayer films of the transition metal dichalcogenides is of the utmost importance in this rapidly advancing research area. The mechanical exfoliation method offers high quality monolayer material but it is a problematic approach when applied to materials that are not air stable. One important example is 1T'-WTe2, which in multilayer form is reported to possess a large non saturating magnetoresistance, pressure induced superconductivity, and a weak antilocalization effect, but electrical data for the monolayer is yet to be reported due to its rapid degradation in air. Here we report a reliable and reproducible large-area growth process for obtaining many monolayer 1T'-WTe2 flakes. We confirmed the composition and structure of monolayer 1T'-WTe2 flakes using x-ray photoelectron spectroscopy, energy-dispersive x-ray spectroscopy, atomic force microscopy, Raman spectroscopy and aberration corrected transmission electron microscopy. We studied the time dependent degradation of monolayer 1T'-WTe2 under ambient conditions, and we used first-principles calculations to identify reaction with oxygen as the degradation mechanism. Finally we investigated the electrical properties of monolayer 1T'-WTe2 and found metallic conduction at low temperature along with a weak antilocalization effect that is evidence for strong spin-orbit coupling.

Copper sulfide-functionalized molybdenum disulfide nanohybrids as nanoenzyme mimics for electrochemical immunoassay of myoglobin in cardiovascular disease

Myoglobin is one of the most commonly used cardiac biomarkers for the clinical diagnosis of acute myocardial infarction, which is the leading cause of mortality worldwide.

Green synthesis of luminescent and defect-free bio-nanosheets of MoS2: interfacing two-dimensional crystals with hydrophobins

High quality luminescent nanosheets of MoS₂ interfaced with the amphiphilic protein Vmh2.

Two-dimensional nanomaterial-based field-effect transistors for chemical and biological sensing

This review highlights the recent progress in graphene-, 2D transition metal dichalcogenide-, and 2D black phosphorus-based FET sensors for detecting gases, biomolecules, and water contaminants.

Highly Sensitive and Quick Detection of Acute Myocardial Infarction Biomarkers Using In2O3 Nanoribbon Biosensors Fabricated Using Shadow Masks

We demonstrate a scalable and facile lithography-free method for fabricating highly uniform and sensitive In₂O₃ nanoribbon biosensor arrays. Fabrication with shadow masks as the patterning method instead of conventional lithography provides low-cost, time-efficient, and high-throughput In₂O₃ nanoribbon biosensors without photoresist contamination. Combined with electronic enzyme-linked immunosorbent assay for signal amplification, the In₂O₃ nanoribbon biosensor arrays are optimized for early, quick, and quantitative detection of cardiac biomarkers in diagnosis of acute myocardial infarction (AMI). Cardiac troponin I (cTnI), creatine kinase MB (CK-MB), and B-type natriuretic peptide (BNP) are commonly associated with heart attack and heart failure and have been selected as the target biomarkers here. Our approach can detect label-free biomarkers for concentrations down to 1 pg/mL (cTnI), 0.1 ng/mL (CK-MB), and 10 pg/mL (BNP), all of which are much lower than clinically relevant cutoff concentrations. The sample collection to result time is only 45 min, and we have further demonstrated the reusability of the sensors. With the demonstrated sensitivity, quick turnaround time, and reusability, the In₂O₃ nanoribbon biosensors have shown great potential toward clinical tests for early and quick diagnosis of AMI.