Molybdenum disulfide (MoS2) is a promising material for applications in sensors, energy storage, energy conversion devices, solar cells, and fuel cells. Because many of those applications require conductive materials, we recently developed a method for preparing a conductive form of MoS2 (c-MoS2) using dilute aqueous hydrogen peroxide in a simple and safe way. Here, we investigate modulating the chemical and mechanical surface properties of c-MoS2 thin films using diazonium chemistry. In addition to a direct passivation strategy of c-MoS2 with diazonium salts for electron-withdrawing groups, we also propose a novel in situ synthetic pathway for modification with electron-donating groups. The obtained results are examined by Raman spectroscopy and X-ray photoelectron spectroscopy. The degree of surface passivation of pristine and functionalized c-MoS2 films was tested by exposing them to aqueous solutions of different metal cations (Fe2+, Zn2+, Cu2+, and Co2+) and detecting the chemiresistive response. While pristine films were found to interact with several of the cations, modified films did not. We propose that a surface charge transfer mechanism is responsible for the chemiresistive response of the pristine films, while both modification routes succeeded at complete surface passivation. Functionalization was also found to lower the coefficient of friction for semiconducting 2H-MoS2, while all conductive materials (modified or not) also had lower coefficients of friction. This opens up a pathway to a palette of dry lubricant materials with improved chemical stability and tunable conductivity. Thus, both in situ and direct diazonium chemistries are powerful tools for tuning chemical and mechanical properties of conductive MoS2 for new devices and lubricants based on conductive MoS2.

Molybdenum disulfide (MoS 2 ) has long been used in catalysis and is a promising material for energy conversion devices.

Hydrogen peroxide (H2O2) is an intermediate molecule generated in numerous peroxidase assays used to measure concentrations of biomolecules such as glucose, galactose, and lactate. Here, we develop a solid-state reagent-free chemiresistive H2O2 sensor, which can measure H2O2 over a wide measuring range of 0.5–1000 ppm (0.015–29.4 mM). The sensor was fabricated using a network of functionalized single-walled carbon nanotubes (SWCNTs) as a sensitive layer and a xurographically patterned gold leaf as a contact electrode. The SWCNTs were functionalized with crystal violet to impart selective detection of H2O2. The crystal violet was self-assembled on the SWCNT film and subsequently polymerized via cyclic voltammetry to improve its retention on the sensing layer. The functionalized sensor exhibited good selectivity against common interferents such as uric acid, urea, glucose, and galactose. In addition, the sensor was used to measure in situ H2O2 generated during peroxidase assays performed using enzymes like glucose oxidase. The sensor was tested in standard buffer solutions for both enzymes. The glucose oxidase assay was also demonstrated in spiked pooled human plasma samples. The glucose oxidase-coated sensor exhibited a glucose detection range of 2–20 mM in standard buffer and blood plasma solutions, with a good recovery rate (∼95–107%) for glucose measurements in blood plasma.

Metal leaves are commercially available for decoration purposes and offers a low-cost alternative to sputtering thin metal films. Although thin metal leaves have been sparingly used in physical and chemical sensing and solar cells, their application has been limited primarily due to lack of a simple patterning methods and to form microscale features with them. Here, a low-cost, rapid and simple xurography based cutting method has been developed for direct pattering of metal leaves. The method was able to pattern features with line width of < 100 µm and it was also able to cut patterns with a pitch of < 100 µm. Conductive lines < 250 µm were also achieved which is a sufficient resolution for application in sensors and most biomedical devices. The versatile capability of this method to cut various geometric shapes like circle, rectangle, triangles and hexagons was also demonstrated. The method is robust and can be applied to pattern leaves made of several materials or which gold, silver, palladium, aluminum and copper were demonstrated. This patterning method was used to fabricate contact electrodes for chemiresistive sensors with low and high surface roughness. These sensors were evaluated using the resistance and noise characteristics. The peak-to-peak noise for gold contact electrodes (11.5 nA) for chemiresistive sensors was significantly lower than the copper tape contact electrodes (18.2 nA). The process was also used to fabricate gold interdigitated electrodes for biamperometric glucose sensing at low potential (~10 mV). Finally, the method was used to indirectly pattern gold leaf on a shrink film to fabricate high surface 3D electrodes costing around one-fifth (~20%) of a sputtered gold electrode.

• Chemiresistive sensors can be fabricated from percolation networks of few-layer graphene (FLG) flakes. • Functionalization with suitable ligands can achieve selective sensor response to Ag + ions in the 3 ppb to 1 ppm range. • Sensors are robust and reusable, can be reset at pH3 due to a shift in the complexation equilibrium. • The sensor response was tested in an environmental sample (river water) and found to correlate well with ICP-MS data. Silver is used as a water disinfectant in hospital settings as well as in purifiers for potable water. Although there are no strict regulations on the concentration of silver in water, adverse effects such as argyria and respiratory tract irritation have been correlated to excess silver consumption. Based on this, the levels of silver in water are recommended to be maintained below 100 ppb to ensure safety for human consumption. In this work, we present a silver sensor for use in aqueous media that utilizes bathocuproine, a silver selective chromophore, adsorbed onto few-layer graphene (FLG) flake networks for the chemiresistive detection of silver. Complexation of silver to bathocuproine modulates the conductivity of the FLG film, which can be probed by applying a small voltage bias. The decrease in resistance of the film correlates with the concentration of silver in solution between 3 ppb and 1 ppm. Exposing the sensor to a lower pH resets the sensor, allowing it to be reused and reset multiple times. This sensor demonstrates a new pathway to chemiresistive cation sensing using known selective complexing agents adsorbed onto graphitic thin films. This concept can be expanded to the detection of other relevant analytes in domestic, industrial and environmental water sources.

Conductive forms of MoS 2 are important emerging 2D materials due to their unique combination of properties such as high electrical conductivity, availability of active sites in edge and basal planes for catalytic activity and expanded interlayer distances. Consequently, there has been a drive to find synthetic routes toward conductive forms of MoS 2 . Naturally occurring or synthetically grown semiconducting 2H-MoS 2 can either be converted into metallic 1T-MoS 2 , or various dopants may be introduced to modulate the electronic band gap of the 2H-MoS 2 phase and increase its conductivity. Chemical and electrochemical intercalation methods, hydrothermal and solvothermal processes, and chemical vapor deposition have all been developed to synthesize conductive MoS 2 . Conductive MoS 2 finds applications in energy storage devices, electrocatalytic reactions, and sensors. Here, we summarize a detailed understanding of the atomic structure and electronic properties of conductive MoS 2 which is crucial for its applications. We also discuss various fabrication methods that have been previously reported along with their advantages and disadvantages. Finally, we will give an overview of current trends in different applications in energy storage and electrocatalytic reactions in order to help researchers to further explore the applications of conductive MoS 2 .

Applications of molybdenum disulfide (MoS2) in energy storage devices, solar cells, electrocatalysts, and sensors require good electrical conductivity. However, neither of the current ways to prepa...

Hydrogen peroxide (H2O2) is a key molecule in numerous physiological, industrial, and environmental processes. H2O2 is monitored using various methods like colorimetry, luminescence, fluorescence, and electrochemical methods. Here, we aim to provide a comprehensive review of solid state sensors to monitor H2O2. The review covers three categories of sensors: chemiresistive, conductometric, and field effect transistors. A brief description of the sensing mechanisms of these sensors has been provided. All three sensor types are evaluated based on the sensing parameters like sensitivity, limit of detection, measuring range and response time. We highlight those sensors which have advanced the field by using innovative materials or sensor fabrication techniques. Finally, we discuss the limitations of current solid state sensors and the future directions for research and development in this exciting area.