First-Principles Insight into a Ru-Doped SnS2 Monolayer as a Promising Biosensor for Exhale Gas Analysis

Solvothermally Synthesized Nickel-Doped Marigold-Like SnS2 Microflowers for High-Performance Supercapacitor Electrode Materials

Two-dimensional transition-metal dichalcogenides (TMDs) have emerged as promising capacitive materials for supercapacitors owing to their layered structure, high specific capacity, and large surface area. Herein, Ni-doped SnS2 microflowers were successfully synthesized via a facile one-step solvothermal approach. The obtained Ni-doped SnS2 microflowers exhibited a high specific capacitances of 459.5 and 77.22 F g-1 at current densities of 2 and 10 A g-1, respectively, in NaClO4 electrolyte, which was found to be higher than that of SnS2-based electrodes in various electrolytes such as KOH, KCl, Na2SO4, NaOH, and NaNO3. Additionally, these microflowers demonstrate a good specific energy density of up to 51.69 Wh kg-1, at a power density of 3204 Wkg-1. Moreover, Ni-doped SnS2 microflowers exhibit a capacity retention of 78.4% even after 5000 cycles. Better electrochemical performance of the prepared electrode may be attributed to some important factors, including the utilization of a highly ionic conductive and less viscous NaClO4 electrolyte, incorporation of Ni as a dopant, and the marigold flower-like morphology of the Ni-doped SnS2. Thus, Ni-doped SnS2 is a promising electrode material in unconventional high-energy storage technologies.

Synergistic effect between transition metal single atom and SnS2 toward deep CO2 reduction

The electrochemical reduction of CO2 is an efficient channel to facilitate energy conversion, but the rapid design and rational screening of high-performance catalysts remain a great challenge. In this work, we investigated the relationships between the configuration, energy, and electronic properties of SnS2 loaded with transition metal single atom (TM@SnS2) and analyzed the mechanism of CO2 activation and reduction by using density functional theory. The "charge transfer bridge" promoted the adsorption of CO2 on TM@SnS2, thus enhancing the binding of HCOOH∗ to the catalyst for further hydrogenation and reduction to high-value CH4. The research revealed that the binding free energy of COOH∗ on TM@SnS2 formed a "volcano curve" with the limiting potential of CO2 reduction to CH4, and the TM@SnS2 (TM = Cr, Ru, Os, and Pt) at the "volcano top" exhibited a high CH4 activity.

Au- and Pd-Doped SnS2 Monolayers for Lung Cancer Biomarkers (C3H6O, C6H6, and C5H8) Detection: A Density Functional Theory Investigation

An efficient and noninvasive method of sensing lung cancer at an early stage is through detecting its biomarkers in the patient's exhaled breath. Acetone (C3H6O), benzene (C6H6), and isoprene (C5H8) emerged as crucial biomarkers, which were significantly elevated in lung cancer patients. Here, we investigated the adsorption behaviors of the three gas molecules on pristine and transition metal (TM)-doped (Au and Pd) SnS2 monolayers using the density functional theory (DFT) method. Our findings indicate that both Au- and Pd-doped SnS2 display higher adsorption energies (-0.53 to -1.313 eV) than that of the pure SnS2 monolayer (0.031 to 0.066 eV). Specifically, Pd-SnS2 exhibits smaller adsorption energy compared to that of Au-SnS2 when capturing C3H6O, C6H6, and C5H8. The estimated recovery times for Pd-SnS2 (8.016 × 10-4 to 16.02 s) are shorter compared to those of Au-SnS2 (1.11 to 1.14 × 1010 s), indicating the superior capability of Pd-SnS2 over Au-SnS2 as a reversible sensor. Afterward, calculations of band structure, projected density of states (PDOS), and charge transfer were performed, which further substantiates the more promising potentials for Pd-doped SnS2 monolayer as gas sensors over the others. Overall, our results suggest that Pd-SnS2 is a better candidate for C3H6O, C6H6, and C5H8 detection over Au-SnS2 and pristine SnS2.

Highly Sensitive Gas Sensor for Detection of Air Decomposition Pollutant (CO, NOx): Popular Metal Oxide (ZnO, TiO2)-Doped MoS2 Surface

When partial discharges occur in air-insulated equipment, the air decomposes to produce a variety of contamination products, resulting in a reduction in the insulation performance of the insulated equipment. By monitoring the concentration of typical decomposition products (CO, NO, and NO2) within the insulated equipment, potential insulation faults can be diagnosed. MoS2 has shown promising applications as a gas-sensitive semiconductor material, and doping metal oxides can improve the gas-sensitive properties of the material. Therefore, in this work, MoS2 has been doped using the popular metal oxides (ZnO, TiO2) of the day, and its gas-sensitive properties to the typical decomposition products of air have been analyzed and compared using density functional theory (DFT) calculations. The stability of the doped system was investigated using molecular dynamics methods. The related adsorption mechanism was analyzed by adsorption configuration, energy band structure, density of states (DOS) analysis, total electron density (TED) analysis, and differential charge density (DCD) analysis. Finally, the practical application of related sensing performance is evaluated. The results show that the doping of metal oxide nanoparticles greatly improves the conductivity, gas sensitivity, and adsorption selectivity of MoS2 monolayer to air decomposition products. The sensing response of ZnO-MoS2 for CO at room temperature (25 °C) reaches 161.86 with a good recovery time (0.046 s). TiO2-MoS2 sensing response to NO2 reaches 3.5 × 106 at 25 °C with a good recovery time (0.108 s). This study theoretically solves the industrial challenge of recycling sensing materials and provides theoretical value for the application of resistive chemical sensors in air-insulated equipment.

Ab initio investigation of functionalization of titanium carbide Ti3C2 MXenes to tune the selective detection of lung cancer biomarkers

Selected volatile organic compounds (VOCs), such as benzene (C6H6), cyclohexane (C6H12), isoprene (C5H8), cyclopropanone (C3H4O), propanol (C3H8O), and butyraldehyde butanal (C4H8O), in exhaled human breath can act as indicators or biomarkers of lung cancer diseases. Detection of such VOCs with low density would pave the way for an early diagnosis of the disease and thus early treatment and cure. In the present investigation, the density-functional theory (DFT) is applied to study the detection of the mentioned VOCs on Ti3C2TX MXenes, saturated with the functional groups Tx = O, F, S, and OH. For selectivity, comparative sensing of other interfering air molecules from exhaled breath, such as O2, N2, CO2, and H2O is further undertaken. Three functionalization (Tx = O, F, and S) are found promising for the selective detection of the studied VOCs, in particular Ti3C2O2 MXenes has shown distinct sensor response toward the C5H8, C6H6, C6H12, and C3H4O. The relatively strong physisorption ([Formula: see text]), triggered between VOC and MXene due to an enhancement of van der Waals interaction, is found responsible to affect the near Fermi level states, which in turn controls the conductivity and consequently the sensor response. Meanwhile, such intermediate-strength interactions remain moderate to yield small desorption recovery time (of order [Formula: see text] using visible light at room temperature. Thus, Ti3C2O2 MXenes are found promising candidate material for reusable biosensor for the early diagnosis of lung cancer diseases through the VOC detection in exhaled breath.

Molecular modeling and simulation of transition metal-doped molybdenum disulfide biomarkers in exhaled gases for early detection of lung cancer

BACKGROUND

The presence of volatile organic compounds (VOCs) in the exhaled breath of lung cancer patients is the only available source for detecting the disease at its initial stage. Exhaled breath analysis depends purely on the performance of the biosensors. The interaction between VOCs and pristine MoS₂ is repulsive in nature. Therefore, modifying MoS₂ via surficial adsorption of the transition metal nickel is of prime importance. The surficial interaction of six VOCs with Ni-doped MoS₂ led to substantial variations in the structural and optoelectronic properties compared to those of the pristine monolayer. The remarkable improvement in the conductivity, thermostability, good sensing response, and recovery time of the sensor exposed to six VOCs revealed that a Ni-doped MoS₂ exhibits impressive properties for the detection of exhaled gases. Different temperatures have a significant impact on the recovery time. Humidity has no effect on the detection of exhaled gases upon exposure to VOCs. The obtained results may encourage the use of exhaled breath sensors by experimentalists and oncologists to enable potential advancements in lung cancer detection.

METHODS

The surface adsorption of transition metal and its interaction with volatile organic compounds on a MoS₂ surface was studied by using Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA). The pseudopotentials used in the SIESTA calculations are norm-conserving in their fully nonlocal forms. The atomic orbitals with finite support were used as a basis set, allowing unlimited multiple-zeta and angular momenta, polarization, and off-site orbitals. These basis sets are the key for calculating the Hamiltonian and overlap matrices in O(N) operations. The present hybrid density functional theory (DFT) is a combination of PW92 and RPBE methods. Additionally, the DFT+U approach was employed to accurately ascertain the coulombic repulsion in the transition elements.

Contactless Photoelectrochemical Biosensor Based on the Ultraviolet-Assisted Gas Sensing Interface of Three-Dimensional SnS2 Nanosheets: From Mechanism Reveal to Practical Application

This work reports a contactless photoelectrochemical biosensor based on an ultraviolet-assisted gas sensor (UV-AGS) with a homemade three-dimensional (3D)-SnS₂ nanosheet-functionalized interdigitated electrode. After rigorous examination, it was found that the gas responsiveness accelerated and the sensitivity increased using the UV irradiation strategy. The effects of the interlayer structure and the Schottky heterojunction on the gas-sensitive response of O₂ and NH₃ under UV irradiation were further investigated theoretically by 3D electrostatic field simulations and first-principles density functional theory to reveal the mechanism. Finally, a UV-AGS device was developed to quantify the blood ammonia bioassay in a small-volume whole blood sample by alkalizing blood to release gas-phase ammonia with a linear range of 25-5000 μM with a limit of detection (LOD) of 29.5 μM. The device also enables a rapid immunoassay of human cardiac troponin I (cTnI) with a linear range of 0.4-25.6 ng/mL and an LOD of 0.37 ng/mL using a urease-labeled antibody as the immune recognition molecule. Both analyses showed satisfying specificity and stability, suggesting that the device can be applied to practical assays and is of great potential to increase the value of gas-sensitive sensors in chemical biosensing.

A room temperature all-optical sensor based on two-dimensional SnS2 for highly sensitive and reversible NO2 sensing

Fiber-optic gas sensors have been considered a low-cost, effective, and robust approach for monitoring nitrogen dioxide (NO₂) gas which is a major toxic gaseous pollutant. The integration of functional nanoscale materials provides additional dimensions for realizing ultra-sensitive and selective NO₂ detection, however, the trade-off is the need for sophisticated photonic structures or external non-optical peripherals (e.g. electrical heaters). In this work, we demonstrate the development of a room temperature, all-optical, and high-performance NO₂ sensor based on a simple D-shaped optical fiber incorporated with ultra-thin two-dimensional (2D) tin disulfide (SnS₂). A visible light source at 473 nm is used to power the optical fiber, and at the same time excite the 2D SnS₂ layer via the evanescent field, to generate extra charge carriers. Upon exposure to NO₂ at room temperature, the physisorbed gas molecules induce charge exchange with the 2D SnS₂. This significantly re-distributes the photo-excited charge carriers in the ultra-thin material, therefore manipulating the corresponding optical absorption and scattering. As a result, the optical output power intensity varies as the sensor output through the evanescent field coupling. This all-optical sensor demonstrates an optical power variation of up to 7 µW upon the exposure of NO₂ gas at a low concentration of 50 ppb. This response is fully reversible with an extremely low limit of detection (LOD) of 0.464 ppb. We consider that this work provides a feasible and simple solution to realize high-performance optical gas sensors without the integration of external non-optical peripherals for effective monitoring of environmentally hazardous gases.

Reversible Room Temperature H2 Gas Sensing Based on Self-Assembled Cobalt Oxysulfide

Reversible H2 gas sensing at room temperature has been highly desirable given the booming of the Internet of Things (IoT), zero-emission vehicles, and fuel cell technologies. Conventional metal oxide-based semiconducting gas sensors have been considered as suitable candidates given their low-cost, high sensitivity, and long stability. However, the dominant sensing mechanism is based on the chemisorption of gas molecules which requires elevated temperatures to activate the catalytic reaction of target gas molecules with chemisorbed O, leaving the drawbacks of high-power consumption and poor selectivity. In this work, we introduce an alternative candidate of cobalt oxysulfide derived from the calcination of self-assembled cobalt sulfide micro-cages. It is found that the majority of S atoms are replaced by O in cobalt oxysulfide, transforming the crystal structure to tetragonal coordination and slightly expanding the optical bandgap energy. The H2 gas sensing performances of cobalt oxysulfide are fully reversible at room temperature, demonstrating peculiar p-type gas responses with a magnitude of 15% for 1% H2 and a high degree of selectivity over CH4, NO2, and CO2. Such excellent performances are possibly ascribed to the physisorption dominating the gas-matter interaction. This work demonstrates the great potentials of transition metal oxysulfide compounds for room-temperature fully reversible gas sensing.

InP3 Monolayer as a Promising 2D Sensing Material in SF6 Insulation Devices

In this letter, we perform a first-principles study on the adsorption performance of the InP3 monolayer upon three SF6 decomposed species, including SO2, SOF2, and SO2F2, to investigate its potential as a resistance-type, optical or field-effect transistor gas sensor. Results indicate that the InP3 monolayer exhibits strong chemisorption upon SO2 but weak physisorption upon SO2F2. The most admirable adsorption behavior is upon SOF2, which provides a favorable sensing response (-19.4%) and recovery property (10.4 s) at room temperature as a resistance-type gas sensor. A high response of 180.7% upon SO2 and a poor one of -1.9% upon SO2F2 are also identified, which reveals the feasibility of the InP3 monolayer as a resistance-type sensor for SO2 detection with recycle use via a heating technique to clean the surface. Moreover, the InP3 monolayer is a promising optical sensor for SO2 detection due to the obvious changes in adsorption peaks within the range of ultraviolet and is a desirable field-effect transistor sensor for selective and sensitive detection of SO2 and SOF2 given the evident changes of Q T and E g under the applied electric field.

First-Principle Study of Rh-Doped Nitrogen Vacancy Boron Nitride Monolayer for Scavenging and Detecting SF6 Decomposition Products

The scavenging and detection of sulfur hexafluoride (SF6) decomposition products (SO2, H2S, SO2F2, SOF2) critically matters to the stable and safe operation of gas-insulated switchgear (GIS) equipment. In this paper, the Rh-doped nitrogen vacancy boron nitride monolayer (Rh-VNBN) is proposed as a gas scavenger and sensor for the above products. The computational processes are applied to investigate the configurations, adsorption and sensing processes, and electronic properties in the gas/Rh-VNBN systems based on the first-principle calculations. The binding energy (Eb) of the Rh-VNBN reaches -8.437 eV, while the adsorption energy (Ead) and band gap (BG) indicate that Rh-VNBN exhibits outstanding adsorption and sensing capabilities. The density of state (DOS) analysis further explains the mechanisms of adsorption and sensing, demonstrating the potential use of Rh-VNBN in sensors and scavengers of SF6 decomposition products. This study is meaningful as it explores new gas scavengers and sensors of SF6 decomposition products to allow the operational status assessment of GIS equipment.

VOCs Sensing by Metal Oxides, Conductive Polymers, and Carbon-Based Materials

This review summarizes the recent research efforts and developments in nanomaterials for sensing volatile organic compounds (VOCs). The discussion focuses on key materials such as metal oxides (e.g., ZnO, SnO2, TiO2 WO3), conductive polymers (e.g., polypyrrole, polythiophene, poly(3,4-ethylenedioxythiophene)), and carbon-based materials (e.g., graphene, graphene oxide, carbon nanotubes), and their mutual combination due to their representativeness in VOCs sensing. Moreover, it delves into the main characteristics and tuning of these materials to achieve enhanced functionality (sensitivity, selectivity, speed of response, and stability). The usual synthesis methods and their advantages towards their integration with microsystems for practical applications are also remarked on. The literature survey shows the most successful systems include structured morphologies, particularly hierarchical structures at the nanometric scale, with intentionally introduced tunable "decorative impurities" or well-defined interfaces forming bilayer structures. These groups of modified or functionalized structures, in which metal oxides are still the main protagonists either as host or guest elements, have proved improvements in VOCs sensing. The work also identifies the need to explore new hybrid material combinations, as well as the convenience of incorporating other transducing principles further than resistive that allow the exploitation of mixed output concepts (e.g., electric, optic, mechanic).

First-Principle Insight into the Ru-Doped PtSe2 Monolayer for Detection of H2 and C2H2 in Transformer Oil

Using first-principles theory, this paper investigates the sensing behavior of the Ru-doped PtSe₂ (Ru-PtSe₂) monolayer for two dominant gases, namely, H₂ and C₂H₂, in the transformer oil to explore its potential as a gas sensor to evaluate the operation status of the electrical transformers. Ru-doping prefers to go through the S₁ site with the largest E _b of -3.71 eV. Chemisorption is identified in the H₂ and C₂H₂ systems with E _ad obtained as -0.83 and - 2.09 eV, respectively, indicating the stronger performance of the Ru-PtSe₂ monolayer upon C₂H₂ adsorption. Meanwhile, the obvious improvement of bandgap in the C₂H₂ system suggests the potential of Ru-PtSe₂ monolayer as a resistance-type gas sensor for C₂H₂ detection. Moreover, the applied biaxial strains ranging at 1-5% give rise to various Q _T and E _g in two systems, indicating the tunable sensing response of the Ru-PtSe₂ monolayer for gas detection with modulated strains. Our calculation proposes a novel 2D sensing material for H₂ and C₂H₂ detection, which would be beneficial to stimulate more edge-cutting research in the gas sensing field as well.

Theoretical Insight on the Biosensing Applications of 2D Materials

The research on the design of efficient, reliable, and cost-effective biosensors is expanding given its high demand in various fields such as health care, environmental surveillance, agriculture, diagnostics, industries, and so forth. In the last decade, various fascinating and interesting 2D materials with extraordinary properties have been experimentally synthesized and theoretically predicted. 2D materials have been explored for the sensing of different biomolecules because of their large surface area and strong interaction with different biomolecules. Theoretical simulations can bring important insight on the interaction of biomolecules on 2D materials, charge transfer, orbital interactions, and so forth and may play an important role in the development of efficient biosensors. Quantum simulation techniques, such as density functional theory (DFT), are very powerful and are gaining popularity especially with the advent of high-speed computing facilities. This review article provides theoretical insight regarding the interaction of various biomolecules on different 2D materials and the charge transfer between the biomolecules and 2D materials leading to electrochemical signals, which can then provide experimentalists the useful design parameters for fabrication of biosensors. It also includes an overview of quantum simulations, use of the DFT method for simulating biomolecules on 2D materials, parameters obtained from theoretical simulations and sensitivity, and limitations of computational techniques for sensing biomolecules on 2D materials. Furthermore, this review summarizes the recent work in first-principles investigation of 2D materials for the purpose of biomolecule sensing. Beyond the traditional graphene or 2D transition-metal dichalcogenides, some novel and recently proposed 2D materials such as pentagraphene, haeckelite, MXenes, and so forth which have exhibited good sensing applications have also been highlighted.

Cu-Doped MoSe2 Monolayer: A Novel Candidate for Dissolved Gas Analysis in Transformer Oil

Dissolved gas analysis (DGA) in transformer oil is a workable approach to evaluate the operation status of transformers. In this paper, we proposed a Cu-doped Se-vacancy MoSe2 (Cu-MoSe2) monolayer as a promising sensing material for DGA based on first-principles theory. Three typical dissolved gases, namely, CO, C2H2, and C2H4, are the representatives to investigate the potential of the Cu-MoSe2 monolayer upon their adsorption and sensing. Our results indicate that Cu-doping causes strong n-doping for the Se-vacancy MoSe2 monolayer, and the Cu-MoSe2 monolayer exhibits strong chemisorption the three gas molecules, with a calculated adsorption energy (E ad) of -1.25, -1.06, and -1.16 eV, respectively. Such strong interactions lead to remarkable changes in the electrical conductivity of the Cu-MoSe2 monolayer, allowing its application as a resistance-type sensor. Besides, work function (WF) analysis shows the potential of the Cu-MoSe2 monolayer as a promising field-effect transistor sensor as well. It is our hope that our work can stimulate more leading-edge studies of the TM-doped MoSe2 monolayer for sensing applications in many fields.