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.

Phosphate is an important analyte to monitor in various water bodies. Cobalt based sensors are attractive for this application as they are solid-state, have a quick response time, are easy to fabricate and can perform reagent-less measurements. However, these sensors have lower sensitivity, limited dynamic range and require a chemical conditioning in a standard solution before measurement. In this study, an in situ anodic current pretreatment method in sample solution itself is used to enhance the sensitivity of the sensor and alleviate the need of chemical conditioning before measurement. With electrical pretreatment, the sensor exhibited a linear range from 10 −6 M to 10 −3 M with a sensitivity of −91.4 mV/decade of change in dihydrogen phosphate concentration. No significant interference was detected with common interfering anions that are typically present in field water samples such as nitrate, sulfate and chloride. Finally, the sensor was also responsive when tested real water samples such as tap water, lake water and creek water spiked with phosphate. • A new in situ electrical pretreatment method is used to enhance the sensitivity of cobalt based phosphate sensors. • The in situ electrical pretreatment method eliminates the need of the tedious chemical pretreatment in standard solution. • The rapid pretreatment protocol can even extend the range of measurements to much lower concentrations (10-8 M). • Use of electrical pretreatment makes this a practical format for field use as standard solutions are not needed.

Phosphate is an important analyte to monitor in various water bodies. Cobalt based sensors are attractive for this application as they are solid-state, have a quick response time, are easy to fabricate and can perform reagent-less measurements. However, these sensors have lower sensitivity, limited dynamic range and require a chemical conditioning in a standard solution before measurement. In this study, an in situ anodic current pretreatment method in sample solution itself is used to enhance the sensitivity of the sensor and alleviate the need of chemical conditioning before measurement. With electrical pretreatment, the sensor exhibited a linear range from 10 −6 M to 10 −3 M with a sensitivity of −91.4 mV/decade of change in dihydrogen phosphate concentration. No significant interference was detected with common interfering anions that are typically present in field water samples such as nitrate, sulfate and chloride. Finally, the sensor was also responsive when tested real water samples such as tap water, lake water and creek water spiked with phosphate. • A new in situ electrical pretreatment method is used to enhance the sensitivity of cobalt based phosphate sensors. • The in situ electrical pretreatment method eliminates the need of the tedious chemical pretreatment in standard solution. • The rapid pretreatment protocol can even extend the range of measurements to much lower concentrations (10-8 M). • Use of electrical pretreatment makes this a practical format for field use as standard solutions are not needed.

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.