Trace-Level, Multi-Gas Detection for Food Quality Assessment Based on Decorated Silicon Transistor Arrays

Tunning the Gas Sensing Properties of rGO with In2O3 Nanoparticles

Here, we discuss the effect of In2O3 nanoparticles on the reduced graphene oxide (rGO) gas-sensing potentialities. In2O3 nanoparticles were prepared with the polymer precursors method, while the nanocomposites were prepared by mixing an In2O3 nanoparticle suspension with an rGO suspension in different proportions. The gas-sensing performance of our materials was tested by exposing our materials to known concentrations of a target toxic gas in a dry airflow. Our results demonstrate that In2O3 nanoparticles enhance the rGO sensitivity for strong oxidizing species such as O3 and NO2, while a negative effect on its sensitivity for NH3 sensing is observed. Furthermore, our measurements towards H2S suggest that the concentration of In2O3 nanoparticles can induce an uncommon transition from p-type to n-type semiconductor nature when rGO–In2O3 nanocomposites operate at temperatures close to 160 °C.

A Bioinspired Adhesive-Integrated-Agent Strategy for Constructing Robust Gas-Sensing Arrays

Gas sensors based on organic molecules are attractive for their tailored molecular structures and controllable functions, but weak interfacial adhesion between sensing materials and supporting substrates has severely hampered their practical applications, particularly in harsh environments. Here, inspired by the combined anchoring-recognizing feature of natural olfactory systems, an adhesive-integrated-agent strategy to integrate the adhesive unit (poly(dimethylsiloxane)) with the sensing unit (organoplatinum(II)) into one chemistry entity, creating robust and sensitive nanobelt array gas sensors is demonstrated. Systematic theoretical and experimental studies reveal that incorporating adhesive units significantly enhances the interfacial adhesion of the array sensors and gas-bridged super-exchange electronic couplings of sensing units ensure their efficient gas-sensing performance. The high shear strength of ≈7.05 × 10⁶ N m^-2 allows these arrays to resist aggressive ultrasonication, tape peeling, or repeated bending without compromising their sensing performance. This molecular engineering strategy opens a new guideline to develop robust gas sensors.

Noble Metal Nanoparticles Decorated Metal Oxide Semiconducting Nanowire Arrays Interwoven into 3D Mesoporous Superstructures for Low-Temperature Gas Sensing

Mesoporous materials have been extensively studied for various applications due to their high specific surface areas and well-interconnected uniform nanopores. Great attention has been paid to synthesizing stable functional mesoporous metal oxides for catalysis, energy storage and conversion, chemical sensing, and so forth. Heteroatom doping and surface modification of metal oxides are typical routes to improve their performance. However, it still remains challenging to directly and conveniently synthesize mesoporous metal oxides with both a specific functionalized surface and heteroatom-doped framework. Here, we report a one-step multicomponent coassembly to synthesize Pt nanoparticle-decorated Si-doped WO₃ nanowires interwoven into 3D mesoporous superstructures (Pt/Si-WO₃ NWIMSs) by using amphiphilic poly(ethylene oxide)-block-polystyrene (PEO-b-PS), Keggin polyoxometalates (H₄SiW₁₂O₄₀) and hydrophobic (1,5-cyclooctadiene)dimethylplatinum(II) as the as structure-directing agent, tungsten precursor and platinum source, respectively. The Pt/Si-WO₃ NWIMSs exhibit a unique mesoporous structure consisting of 3D interwoven Si-doped WO₃ nanowires with surfaces homogeneously decorated by Pt nanoparticles. Because of the highly porous structure, excellent transport of carriers in nanowires, and rich WO₃/Pt active interfaces, the semiconductor gas sensors based on Pt/Si-WO₃ NWIMSs show excellent sensing properties toward ethanol at low temperature (100 °C) with high sensitivity (S = 93 vs 50 ppm), low detection limit (0.5 ppm), fast response-recovery speed (17-7 s), excellent selectivity, and long-term stability.

Fabrication of Robust and Porous Lead Chloride-Based Metal-Organic Frameworks toward a Selective and Sensitive Smart NH3 Sensor

Organolead halide materials have shown promising optoelectronic properties that are suitable for light-emitting diodes (e.g., strong photoluminescence, narrow emission width, and high charge carrier mobility). However, the vast majority of them have no open porosity or open metal sites for host-guest interactions and are therefore not widely applicable in intrinsic fluorescent sensing of small molecules. Herein, we report a lead chloride-based metal-organic framework (MOF) with high porosity and stability and promising photoluminescent characteristics, performing as a sensitive, selective, and long-term stable fluorescence probe for NH3. For the first time, a homemade dynamic real-time photoluminescence monitoring system was developed, which showed that our haloplumbate-based MOF has an immediate response and an extremely low limit of detection (12 ppm) toward NH3. A variety of experimental characterization and theoretical calculations evidenced that the photoluminescence quenching was ascribed to the coordination between NH3 guests and exposed Pb2+ centers in MOFs. Moreover, a portable on-site smart NH3 detector was designed based on this haloplumbate-MOF using a 3D printer, and the quantitative recovery experiment demonstrated the effective detection of NH3 in the range of 15-150 ppm. This study opens a new pathway to design organolead halide-based MOFs to perform on-site chemical sensing of small molecules and shows their high potential to monitor safety concentrations of NH3 in different industrial sites.

Recent Advances in Silicon FET Devices for Gas and Volatile Organic Compound Sensing

Highly sensitive and selective gas and volatile organic compound (VOC) sensor platforms with fast response and recovery kinetics are in high demand for environmental health monitoring, industry, and medical diagnostics. Among the various categories of gas sensors studied to date, field effect transistors (FETs) have proved to be an extremely efficient platform due to their miniaturized form factor, high sensitivity, and ultra-low power consumption. Despite the advent of various kinds of new materials, silicon (Si) still enjoys the advantages of excellent and reproducible electronic properties and compatibility with complementary metal–oxide–semiconductor (CMOS) technologies for integrated multiplexing and signal processing. This review gives an overview of the recent developments in Si FETs for gas and VOC sensing. We categorised the Si FETs into Si nanowire (NW) FETs; planar Si FETs, in which the Si channel is either a part of the silicon on insulator (SOI) or the bulk Si, as in conventional FETs; and electrostatically formed nanowire (EFN) FETs. The review begins with a brief introduction, followed by a description of the Si NW FET gas and VOC sensors. A brief description of the various fabrication strategies of Si NWs and the several functionalisation methods to improve the sensing performances of Si NWs are also provided. Although Si NW FETs have excellent sensing properties, they are far from practical realisation due to the extensive fabrication procedures involved, along with other issues that are critically assessed briefly. Then, we describe planar Si FET sensors, which are much closer to real-world implementation. Their simpler device architecture combined with excellent sensing properties enable them as an efficient platform for gas sensing. The third category, the EFN FET sensors, proved to be another potential platform for gas sensing due to their intriguing properties, which are elaborated in detail. Finally, the challenges and future opportunities for gas sensing are addressed.

MOF-Derived Porous Hollow Co3O4@ZnO Cages for High-Performance MEMS Trimethylamine Sensors

Trimethylamine (TMA) sensors based on metal oxide semiconductors (MOS) have drawn great attention for real-time seafood quality evaluation. However, poor selectivity and baseline drift limit the practical applications of MOS TMA sensors. Engineering core@shell heterojunction structures with accumulation and depletion layers formed at the interface is regarded as an appealing way for enhanced gas sensing performances. Herein, we design porous hollow Co₃O₄@ZnO cages via a facile ZIF-67@ZIF-8-derived approach for TMA sensors. These sensors demonstrate great TMA resistive sensing performance (linear response at moderate TMA concentrations (<33 ppm)), and a high sensitivity of ∼41 is observed when exposed to 33 ppm TMA, with a response/recovery time of only 3/2 s. This superior performance benefits from the Co₃O₄@ZnO porous hollow structure with maximum heterojunctions and high surface area. Furthermore, great capacitive TMA sensing with linear sensitivity over the full testing concentration range (0.33-66 ppm) and better baseline stability were investigated. A possible capacitive sensing mechanism of TMA polarization was proposed. For practical usage, a portable sensing prototype based on the Co₃O₄@ZnO sensor was fabricated, and its satisfactory sensing behavior further confirms the potential for real-time TMA detection.

Fully integrated ultra-sensitive electronic nose based on organic field-effect transistors

Modern solid-state gas sensors approaching ppb-level limit of detection open new perspectives for process control, environmental monitoring and exhaled breath analysis. Organic field-effect transistors (OFETs) are especially promising for gas sensing due to their outstanding sensitivities, low cost and small power consumption. However, they suffer of poor selectivity, requiring development of cross-selective arrays to distinguish analytes, and environmental instability, especially in humid air. Here we present the first fully integrated OFET-based electronic nose with the whole sensor array located on a single substrate. It features down to 30 ppb limit of detection provided by monolayer thick active layers and operates in air with up to 95% relative humidity. By means of principal component analysis, it is able to discriminate toxic air pollutants and monitor meat product freshness. The approach presented paves the way for developing affordable air sensing networks for the Internet of Things.

Multifunctional Latex/Polytetrafluoroethylene-Based Triboelectric Nanogenerator for Self-Powered Organ-like MXene/Metal-Organic Framework-Derived CuO Nanohybrid Ammonia Sensor

Self-powered sensors are crucial in the field of wearable devices and the Internet of Things (IoT). In this paper, an organ-like Ti₃C₂T_x MXene/metal-organic framework-derived copper oxide (CuO) gas sensor was powered by a triboelectric nanogenerator (TENG) based on latex and polytetrafluoroethylene for the detection of ammonia (NH₃) at room temperature. The peak-to-peak value of open-circuit voltage and short-circuit current generated by the prepared TENG can reach up to 810 V and 34 μA, respectively. The TENG can support a maximum peak power density of 10.84 W·m^-2 and light at least 480 LEDs. Moreover, a flexible TENG under a single-electrode working mode was demonstrated for human movement stimulation, which exhibits great potential in wearable devices. The self-powered NH₃ sensor driven by TENG has an excellent response (V_g/V_a = 24.8 @ 100 ppm) at room temperature and exhibits a great potential in monitoring pork quality. Ti₃C₂T_x MXene and CuO were characterized by SEM, TEM, EDS, XRD, and XPS to analyze the properties of the materials. The NH₃ sensing performance of the self-powered sensor based on MXene/CuO was greatly improved, and the mechanism of the enhanced sensing properties was systematically discussed.

Innovations in Smart Packaging Concepts for Food: An Extensive Review

Innovation in food packaging is mainly represented by the development of active and intelligent packing technologies, which offer to deliver safer and high-quality food products. Active packaging refers to the incorporation of active component into the package with the aim of maintaining or extending the product quality and shelf-life. The intelligent systems are able to monitor the condition of packaged food in order to provide information about the quality of the product during transportation and storage. These packaging technologies can also work synergistically to yield a multipurpose food packaging system. This review is a critical and up-dated analysis of the results reported in the literature about this fascinating and growing field of research. Several aspects are considered and organized going from the definitions and the regulations, to the specific functions and the technological aspects regarding the manufacturing technologies, in order to have a complete overlook on the overall topic.

Oxygen Content-Controllable Synthesis of Non-Stoichiometric Silicon Suboxide Nanoparticles by Electrochemical Anodization

A facile route to producing non-stoichiometric silicon suboxide nanoparticles (SiO_x NPs, 0 < x < 1) with an adjustable oxygen content is proposed. The process is based on electrochemical anodization involving the application of a strong electric field near the surface of a Si electrode to directly convert the Si electrode into SiO_x NPs. The difference in ion mobility between oxygen species (O²⁻ and OH⁻), formed during anodization, causes the production of non-stoichiometric SiO_x on the surface of the Si while, simultaneously, fluoride ions in the electrolyte solution etch the formed SiO_x layer, generating NPs under the intense electric field. The adjustment of the applied voltage and anodization temperature alters the oxygen content and the size of the SiO_x NPs, respectively, allowing the characteristics of the NPs to be readily controlled. The proposed approach can be applied for mass production of SiO_x NPs and is highly promising in the field of batteries and optoelectronics.