Cathodic and anodic deposition of FeS2 thin films and their application in electrochemical reduction and amperometric sensing of H2O2

Electrochemically Grown Hole-Rich NiO(OH) Thin Films toward Hole-Mediated Very Fast and Selective Enzyme-Free Electrochemical Sensing of Dopamine under Simulated Environment

This work aimed to develop an enzyme-free semiconductor-assisted electrochemical technique for the selective detection of the neurotransmitter dopamine. In this case, electrochemically grown nickel oxyhydroxide [NiO(OH)] thin films were chosen to fabricate the sensing platform, i.e., the electrodes. Chronoamperometry was used to deposit the films on indium tin oxide (ITO) coated glass substrates. The films were thoroughly characterized to establish their structure, composition, phase purity, and electrochemical attributes. Electrochemical sensing characteristics were investigated by means of cyclic and differential pulse voltammetry, steady-state amperometry, and electrochemical impedance spectroscopy. The effects of several interfering agents like glucose, sodium chloride, methanol, hydrogen peroxide, and paracetamol were also studied on the detection attributes of dopamine. Significantly high value of sensitivity (11.87 μA μM-1 cm-2) was obtained for dopamine sensing that was associated with a limit of detection (LoD) of 0.22 μM of dopamine. However, the sensitivity (2.51 μA μM-1 cm-2) and LoD (1.20 μM) obtained for serotonin were inferior compared to those of dopamine. The performance of the electrode toward dopamine sensing was not compromised either in the presence of only serotonin or a series of other electroactive interfering agents, which makes the electrode very much dopamine selective. The dopamine response time was 200 ms, which is notably fast. Extensive studies on the effect of temperature, pH and scan rate on the detection of dopamine by the developed electrode material have also been carried out. The developed electrodes were also found to be notably stable for dopamine detection with a decay of only 6.6% in oxidation peak current density after the 50th cycle. Real-life application of the developed electrode material was checked with urine samples from adult male humans and yielded encouraging results.

A multifunctional Ni-doped iron pyrite/reduced graphene oxide composite as an efficient counter electrode for DSSCs and as a non-enzymatic hydrogen peroxide electrochemical sensor

Nickel-doped FeS₂/rGO composites were synthesized as multifunctional materials via a facile hydrothermal method. The synthesized materials were characterized with XRD, FESEM, XPS, and TEM-SAED for structural, morphological and chemical studies. To study their electrochemical properties, all the synthesized composites were subjected to cyclic voltammetry tests. The optimum composite revealed high catalytic activity with high peak current density, limiting current, and efficiency of 7.60% for DSSC, which surpassed that of a platinum-based counter electrode (6.69%). The efficiency of the DSSC was significantly supported by interfacial studies and electron lifetime studies, and it exhibited lower charge transfer resistance and higher electron lifetime, respectively. Moreover, the fabricated DSSCs with high efficiency were subjected to transient photo-response studies and showed a stable current response with multiple photo-ON and OFF cycles for a period of 600 s. To broaden the application of the synthesized material, it was used as an electrochemical sensor for the efficient sensing of hydrogen peroxide (H₂O₂). The sensing electrode was modified with the optimum Ni-doped FeS₂/rGO composite, and voltammetric detection was carried out in the hydrogen peroxide concentration range of 4-100 μM. Thus, the synthesized material can be applied in DSSCs and as an electrochemical H₂O₂ sensor.

Modulation of Weak Interactions in Structural Isomers: Positional Isomeric Effects on Crystal Packing and Physical Properties and Solid-State Thin-Film Fabrication

Selective formation of positional isomers and accordingly tuning the physicochemical properties of small conjugated organic molecules through structural isomers is an effective crystal engineering for a fascinating successful delivery of thermally stable and photophysically exciting compounds. By small structural skeleton changes, the single crystal of the naphthalenemaleonitrile isomers is found to exhibit a drastic change in crystal packing array, which in turn is found to tune the thermal and physicochemical properties. The α-isomer (A) forms the "herringbone packing" (HP) due to peri-interaction-sensitive C-H···(Ar)π (Ar = naphthalene ring) interactions, and the β-isomer (B) forms the "bricklayer packing" (BP) due to π(C≡N)···π(Ar) stacking interactions. These two positional isomers have revealed insight of molecular packing-dependent structure-property relationship. In this report, we show that a simple modification of relatively less common weak interactions, such as C-H···π(Ar) ↔ π(C≡N)···π(Ar), through the preparation of isomers, can lead to a drastic change in crystal packing (HP ↔ BP). Also, this report demonstrates that by a small structural diversity, one can obtain significant changes in the physicochemical properties like melting behavior, enthalpy, entropy, and electrical properties in the solid state. Therefore, it transpires from this study that structural isomer provides a useful complement to intermolecular nonbonding interactions as a tool to design new promising materials.

Two-Dimensional Materials in Biosensing and Healthcare: From In Vitro Diagnostics to Optogenetics and Beyond

Since the isolation of graphene in 2004, there has been an exponentially growing number of reports on layered two-dimensional (2D) materials for applications ranging from protective coatings to biochemical sensing. Due to the exceptional, and often tunable, electrical, optical, electrochemical, and physical properties of these materials, they can serve as the active sensing element or a supporting substrate for diverse healthcare applications. In this review, we provide a survey of the recent reports on the applications of 2D materials in biosensing and other emerging healthcare areas, ranging from wearable technologies to optogenetics to neural interfacing. Specifically, this review provides (i) a holistic evaluation of relevant material properties across a wide range of 2D systems, (ii) a comparison of 2D material-based biosensors to the state-of-the-art, (iii) relevant material synthesis approaches specifically reported for healthcare applications, and (iv) the technological considerations to facilitate mass production and commercialization.

Facile Hydrothermal Synthesis of Nanocubic Pyrite Crystals Using Greigite Fe3S4 and Thiourea as Precursors

Nanocubic pyrite (FeS2) crystals with exposed (100) crystal faces and sizes of 100–200 nm were successfully synthesized via a facile hydrothermal method using greigite (Fe3S4) as the iron precursor and thiourea (NH2CSNH2) as the sulfur source. When the concentration of thiourea was 40 mmol/L, both pyrite and hematite were observed in the as-prepared sample, indicating incomplete conversion of greigite into pyrite. With an increased thiourea concentration to 80 mmol/L, pyrite was found to be the only crystalline phase in the synthesized samples. All greigite could be transformed to pyrite within 24 h via the hydrothermal method, while further prolonging the hydrothermal time had insignificant effect on the crystal phase composition, crystallinity, and morphologies of the prepared nanocubic pyrite crystals. In contrast, when a mixture of Na2S and S powder was used to replace the thiourea as the sulfur source, tetragonal, orthorhombic, cubic, and irregular pyrite crystal particles with sizes of 100 nm–1 μm were found to co-exist in the prepared samples. These results demonstrate the critical influence of sulfur source on pyrite morphology. Furthermore, our hydrothermal process, using a combination of greigite and thiourea, is proved to be effective in preparing nanocubic pyrite crystals. Our findings can also provide new insight into the formation environments and pathways of nanocubic pyrite under hydrothermal conditions.

A turn-on fluorogenic chemosensor for Fe3+ and a Schottky barrier diode with frequency-switching device applications

A novel highly sensitive and selective fluorescent chemosensor L has been synthesized and characterized by various physicochemical techniques.

Reusable iron sulfide nanospheres towards promoted photocatalytic and electrocatalytic activities

Electrochemically deposited FeS nanospheres were found to degrade efficiently a series of toxic pigments and phenol in the presence of visible light. The material also showed excellent hydrogen peroxide sensing properties.

Mesoporous CuO–ZnO p–n heterojunction based nanocomposites with high specific surface area for enhanced photocatalysis and electrochemical sensing

Mesoporous and core–shell like (p)CuO–(n)ZnO nanocomposites were prepared using microstructural refinement and solid state reactions, which showed enhanced photochemical and electrochemical performances.

Morphology controllable syntheses of micro- and nano-iron pyrite mono- and poly-crystals: a review

This review provides comprehensive information of the outline of current knowledge regarding the morphology controllable syntheses of micro- and nano-iron pyrite mono- and poly-crystals.

Pyrite nanoparticles: an Earth-abundant mineral catalyst for activation of molecular hydrogen and hydrogenation of nitroaromatics

Pyrite (FeS₂) nanoparticles, a kind of Earth-abundant mineral, can efficiently activate molecular hydrogen under mild conditions.

Recent developments in 2D layered inorganic nanomaterials for sensing

Two dimensional layered inorganic nanomaterials (2D-LINs) have recently attracted huge interest because of their unique thickness dependent physical and chemical properties and potential technological applications. The properties of these layered materials can be tuned via both physical and chemical processes. Some 2D layered inorganic nanomaterials like MoS2, WS2 and SnS2 have been recently developed and employed in various applications, including new sensors because of their layer-dependent electrical properties. This article presents a comprehensive overview of recent developments in the application of 2D layered inorganic nanomaterials as sensors. Some of the salient features of 2D materials for different sensing applications are discussed, including gas sensing, electrochemical sensing, SERS and biosensing, SERS sensing and photodetection. The working principles of the sensors are also discussed together with examples.

High Performance Non-enzymatic Glucose Sensor Based on One-Step Electrodeposited Nickel Sulfide

Nanostructured NiS thin film was prepared by a one-step electrodeposition method and the structural, morphological characteristics of the as-prepared films were analyzed by X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray analysis (EDAX). The electrocatalytic activity of NiS thin film towards glucose oxidation was investigated by fabricating a non-enzymatic glucose sensor and the sensor performance was studied by cyclic voltammetry (CV) and amperometry. The fabricated sensor showed excellent sensitivity and low detection limit with values of 7.43 μA μM(-1)  cm(-2) and 0.32 μM, respectively, and a response time of <8 s.