High-precision gas sensors operated at room temperature are attractive for various real-time gas monitoring applications, with advantages including low energy consumption, cost effectiveness and device miniaturization/flexibility. Studies on sensing materials, which play a key role in good gas sensing performance, are currently focused extensively on semiconducting metal oxide nanostructures (SMONs) used in the conventional resistance type gas sensors. This topical review highlights the designs and mechanisms of different SMONs with various patterns (e.g. nanoparticles, nanowires, nanosheets, nanorods, nanotubes, nanofilms, etc.) for gas sensors to detect various hazardous gases at room temperature. The key topics include (1) single phase SMONs including both n-type and p-type ones; (2) noble metal nanoparticle and metal ion modified SMONs; (3) composite oxides of SMONs; (4) composites of SMONs with carbon nanomaterials. Enhancement of the sensing performance of SMONs at room temperature can also be realized using a photo-activation effect such as ultraviolet light. SMON based mechanically flexible and wearable room temperature gas sensors are also discussed. Various mechanisms have been discussed for the enhanced sensing performance, which include redox reactions, heterojunction generation, formation of metal sulfides and the spillover effect. Finally, major challenges and prospects for the SMON based room temperature gas sensors are highlighted.

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Advances in designs and mechanisms of semiconducting metal oxide nanostructures for high-precision gas sensors operated at room temperature

A Review on Piezoelectric, Magnetostrictive, and Magnetoelectric Materials and Device Technologies for Energy Harvesting Applications

This article is an overview of the present and ongoing developments in the field of nanomaterial-based sensors for enabling fast, relatively inexpensive and minimally (or non-) invasive diagnostics of health conditions with follow-up by detecting volatile organic compounds (VOCs) excreted from one or combination of human body fluids and tissues (e.g., blood, urine, breath, skin). Part of the review provides a didactic examination of the concepts and approaches related to emerging sensing materials and transduction techniques linked with the VOC-based non-invasive medical evaluations. We also present and discuss diverse characteristics of these innovative sensors, such as their mode of operation, sensitivity, selectivity and response time, as well as the major approaches proposed for enhancing their ability as hybrid sensors to afford multidimensional sensing and information-based sensing. The other parts of the review give an updated compilation of the past and currently available VOC-based sensors for disease diagnostics. This compilation summarizes all VOCs identified in relation to sickness and sampling origin that links these data with advanced nanomaterial-based sensing technologies. Both strength and pitfalls are discussed and criticized, particularly from the perspective of the information and communication era. Further ideas regarding improvement of sensors, sensor arrays, sensing devices and the proposed workflow are also included.

Synergy between nanomaterials and volatile organic compounds for non-invasive medical evaluation

Electrochemical sensing platform based on the biomass-derived microporous carbons for simultaneous determination of ascorbic acid, dopamine, and uric acid.

Surface acoustic wave (SAW) resonators represent some of the most prominent acoustic devices for chemical sensing applications. As their frequency ranges from several hundred MHz to GHz, therefore they can record remarkably diminutive frequency shifts resulting from exceptionally small mass loadings. Their miniaturized design, high thermal stability and possibility of wireless integration make these devices highly competitive. Owing to these special characteristics, they are widely accepted as smart transducers that can be combined with a variety of recognition layers based on host-guest interactions, metal oxide coatings, carbon nanotubes, graphene sheets, functional polymers and biological receptors. As a result of this, there is a broad spectrum of SAW sensors, i.e., having sensing applications ranging from small gas molecules to large bio-analytes or even whole cell structures. This review shall cover from the fundamentals to modern design developments in SAW devices with respect to interfacial receptor coatings for exemplary sensor applications. The related problems and their possible solutions shall also be covered, with a focus on emerging trends and future opportunities for making SAW as established sensing technology.

Surface Acoustic Wave (SAW) for Chemical Sensing Applications of Recognition Layers.

A Surface Acoustic Wave (SAW) resonator operating at a frequency of 99.50 MHz using piezoelectric ST-cut quartz has been fabricated. The resonator device has been successfully integrated with ZnO sensing layer for detection of NO 2 gas. The fabricated sensor device is found to be detecting trace level concentration of NO 2 gas (400 ppb to 16 ppm) efficiently and selectively. The ZnO/Quartz SAW sensor is useful for wireless detection of NO 2 gas.

ZnO/ST-Quartz SAW resonator: An efficient NO2 gas sensor

In the present work, zinc oxide (ZnO) thin film based Love wave acoustic device has been exploited for realization of a biosensor. These Love wave devices have been fabricated on 36°YX lithium tantalate with ZnO thin film deposited using rf sputtering technique as the guiding layer. Polydimethylsiloxane (PDMS) microchannels have been prepared and integrated on the propagation path on the fabricated device. Detection of uric acid has been demonstrated using the developed biosensing device by measuring the shift in center frequency on interaction with uric acid. The developed uric acid sensor paves way towards the realization of handheld biosensor for future wireless sensing technology.

Highly sensitive Love wave acoustic biosensor for uric acid

Magnetoelectric (ME) coefficient of Lead Zirconium Titanate (PZT) thin films has been probed for possible energy harvesting applications. Single phase PZT thin films have been deposited on nickel substrate (PZT/Ni) using pulsed laser deposition (PLD) technique. The effect of PLD process parameters on the ME coupling coefficient in the prepared systems has been investigated. The as grown PZT films on Ni substrate were found to be polycrystalline with improved ferroelectric and ferromagnetic properties. The electrical switching behavior of the PZT thin films were verified using capacitance voltage. measurements, where well defined butterfly loops were obtained. The ME coupling coefficient was estimated to be in the range of 94.5 V cm(-1) Oe(-1) -130.5 V cm(-1) Oe(-1) for PZT/Ni system, which is large enough for harnessing electromagnetic energy for subsequent applications.

https://iopscience.iop.org/article/10.1088/1361-665X/26/3/035002/pdf

Performance of magnetoelectric PZT/Ni multiferroic system for energy harvesting application

Surface acoustic wave (SAW) devices provide a convenient platform for the realization of sensors in the present decade. 99.4 MHz SAW resonator has been fabricated over the ST cut quartz. Subsequently PZT thin film has been deposited by pulsed laser deposition technique as a sensing layer over the fabricated SAW resonator. Shift in resonance frequency was measured precisely for varying concentration of NO2 gas. The calibration curve was found to be linear having a sensitivity of 9.6 Hz/ppm. The fabricated sensor is advantageous for its room temperature, handheld and wireless sensing.

Fabrication of surface acoustic wave based wireless NO2 gas sensor

Lithium ion batteries play a crucial role in terms of good rechargeability, long cycles and higher shelf life. For the fabrication of such a Li ion battery, properties of cathode material can be engineered keeping anode and electrolyte fixed. In the present work, lithium iron phosphate (LiFePO4) has been utilized as cathode material and the properties of LiFePO4 have been tuned by doping manganese (Mn). LiFePO4 and different concentrations of Mn doped LiFePO4 were prepared by solid state route. X-Ray diffraction and Raman studies were performed to confirm the formation of LiFePO4 and Mn doped LiFePO4 in olivine structure. Cyclic voltammetry studies revealed maximum peak oxidation current (2.96 mA) and largest surface coverage (0.066 nanoMoles/cm2) for the LiFePO4 doped with 15% Mn (LiMn0.15Fe0.85PO4). AC-conductivity study was carried out for different frequencies at room temperature. The conductivity parameters estimated using Almond and West formalism support the cyclic voltammetry results. Ion-hopping rate (ω
 p
 ) and charge carrier concentration (K) maximize for 15% Mn doping (ω
 p
 : 582974.48719 Hz; K: 2.62447 × 10−6) and drop on either increasing (ω
 p
 : 167134.73521 Hz; K: 1.25647 × 10−7) or decreasing (ω
 p
 : 130726.49084 Hz; K: 2.52435 × 10−6) the Mn doping. The increase till 15% Mn doping has been attributed to the increase in unit cell volume with Mn doping while the sudden decrease at 20% Mn doping is due to dominance of back-hopping mechanism. The results clearly indicate that 15% Mn doped LiFePO4 is the most appropriate for the realization of a cathode for Li-ion battery.

Reema Gupta

Papers

ZnO/ST-Quartz SAW resonator: An efficient NO2 gas sensor

Highly sensitive Love wave acoustic biosensor for uric acid

Performance of magnetoelectric PZT/Ni multiferroic system for energy harvesting application

Fabrication of surface acoustic wave based wireless NO2 gas sensor

Effect of manganese doping on conduction in olivine LiFePO4