Customizing Wettability of Defect-Rich CeO2/TiO2 Nanotube Arrays for Humidity-Resistant, Ultrafast, and Sensitive Ammonia Response

Highly Selective, Room-Temperature Triethylamine Sensor Using Humidity-Resistant Novel TiZn Alloy Nanoparticles-Decorated MoS₂ Nanosheets

The future of environmental monitoring, medical diagnostics, and industrial safety depends on developing room-temperature, long-term operable, stable, miniaturized, ultrahigh-performance sensors integrated into the Internet of Things (IoT). While noble metals and high-entropy alloys (HEAs) lead in addressing the limitations of conventional transition-metal dichalcogenides (TMDs) like MoS₂, they face challenges such as high-cost, limited availability, and fabrication complexity. To address this, multifunctional, cost-effective, humidity-insensitive novel phase Ti₀.₅Zn₀.₅ (TiZn) alloy nanoparticle-decorated MoS₂ nanosheets (MoS₂_NP) is developed for ultra-selective and highly sensitive triethylamine (TEA) vapor detection at room temperature (RT). This exhibited a 24-fold increase in response compared to MoS₂, with a high signal-to-noise ratio, negligible humidity interference, sensitivity of 9.92 × 10⁻⁵ ppm⁻¹ at RT, and a detection limit of 48 ppm. The enhanced catalytic activity and defect concentration, the reduction of the edge oxidation resulting in strong Fermi-level pinning, and the relatively high adsorption energy lead to a target gas-specific carrier-type response, demonstrating the potential of binary alloy nanoparticles (NPs) as decorative materials for enhanced sensing applications. The superior performance of the sensor led to the development of a TEA detection prototype interfaced with a mobile device via IoT for continuous monitoring, enhancing practicality and usability by offering immediate access to critical information.

Enhanced photocurrents for photoelectrochemical immunoassay of alpha-fetoprotein with Pt-functionalized Bi2O2S nanoflowers

BACKGROUND

Designing heterojunctions with efficient electron-hole separation holds great promise for improving photoelectric response.

RESULTS

Herein, we reported a multifunctional Pt co-catalyst-modified Bi2O2S nanoflowers (BOS NFs) photocatalytic component for achieving an efficient photoelectric chemistry (PEC) immunosensor for alpha-fetoprotein (AFP). Briefly, the Pt co-catalyst improved the intrinsic band gap structure of BOS on the one hand, and on the other hand, it was able to achieve a rapid decomposition of hydrogen peroxide to hydroxyl radicals, which led to the improvement of electrochemical half-responses during the amplification of target immunosignals. In addition, Pt-functionalized BOS NFs (BOS-Pt) exhibited peroxidase-like enzymatic reaction activity and related properties. By enzyme-linked immunosorbent assay, a sandwich immuno-model in the presence of AFP catalyzed the production of hydrogen peroxide from the substrate glucose and the conversion of a sizable photoelectrochemical signal catalyzed by BOS-Pt. Following condition optimization, it was determined that the developed sensor exhibited a specific response to AFP over a wide linear range of 0.05-50 ng mL-1.

SIGNIFICANCE

This work provides a new strategy for developing efficient immunosensors from the perspective of modulating photoelectrochemical half-reactions.

Ultrahigh humidity-resistance ppb-level formaldehyde sensing at room temperature induced by fluorinated dipole based "umbrella" and "bridge"

Formaldehyde (HCHO) is a major indoor pollutant that is extremely harmful to human health even at ppb-level. Meanwhile, ppb-level HCHO is also a potential disease marker in the exhalation of patients with respiratory diseases. Higher humidity resistance and lower practical limit of detection (pLOD) both have to be pursued for practical HCHO sensors. In this work, by assembling indium oxide (In2O3) and fluorinated dipole modified reduced graphene oxide (rGO), we prepared a high-performance room temperature HCHO sensor (In2O3 @ATQ-rGO). Excellent sensing properties toward HCHO under visible illumination have been achieved, including ultra-low pLOD of 3 ppb and high humidity-resistance. By control experiments and density functional theory calculation, it is indicated that the introduced fluorinated dipoles act as not only an "umbrella" to improve the humidity resistance of the composite, but also a "bridge" to accelerate the electron transport, improving the sensitivity of the material. The significant practicality and reliability of the obtained sensors were verified by in-situ simulation experiments using a 3 m3 test chamber with a humidity control system and by detection of the simulated lung disease patient's exhalation. This work provides an effective strategy of simultaneously achieving high humidity-resistance and low pLOD of room temperature formaldehyde sensing materials.

Phase-Engineered MoSe2/CeO2 Composites for Room-Temperature Gas Sensing with a Drastic Discrimination of NH3 and TEA Gases

Detecting and distinguishing between hazardous gases with similar odors by using conventional sensor technology for safeguarding human health and ensuring food safety are significant challenges. Bulky, costly, and power-hungry devices, such as that used for gas chromatography-mass spectrometry (GC-MS), are widely employed for gas sensing. Using a single chemiresistive semiconductor or electric nose (e-nose) gas sensor to achieve this objective is difficult, mainly because of its selectivity issue. Thus, there is a need to develop new materials with tunable and versatile sensing characteristics. Phase engineering of two-dimensional materials to better utilize their physiochemical properties has attracted considerable attention. Here, we show that MoSe2 phase-transition/CeO2 composites can be effectively used to distinguish ammonia (NH3) and triethylamine (TEA) at room temperature. The phase transition of nanocomposite samples from semimetallic (1T) to semiconducting (2H) prepared at different synthesis temperatures is confirmed via X-ray photoelectron spectroscopy (XPS). A composite sensor in which the 2H phase of MoSe2 is predominant lacks discrimination capability and is less responsive to NH3 and TEA. An MoSe2/CeO2 composite sensor with a higher 1T phase content exhibits high selectivity for NH3, whereas one with a higher 2H phase content (2H > 1T) shows more selective behavior toward TEA. For example, for 50% relative humidity, the MoSe2/CeO2 sensor's signal changes from the baseline by 45% and 58% for 1 ppm of NH3 and TEA, respectively, indicating a low limit of detection (LOD) of 70 and 160 ppb, respectively. The composites' superior sensing characteristics are mainly attributed to their large specific surface area, their numerous active sites, presence of defects, and the n-n type heterojunction between MoSe2 and CeO2. The sensing mechanism is elucidated using Raman spectroscopy, XPS, and GC-MS results. Their phase-transition characteristics render MoSe2/CeO2 sensors promising for use in distributed, low-cost, and room-temperature sensor networks, and they offer new opportunities for the development of integrated advanced smart sensing technologies for environmental and healthcare.

Synergistic Etching and Hydrogen Bonding-Induced Self-Assembly of MXene/MOF Hybrid Aerogel for Flexible Room-Temperature Gas Sensing

Limited by insufficient active sites and restricted mechanical strength, designing reliable and wearable gas sensors with high activity and ductility remains a challenge for detecting hazardous gases. In this work, a thermally induced and solvent-assisted oxyanion etching strategy was implemented for selective pore opening in a rigid microporous Cu-based metal-organic framework (referred to as CuM). A conductive CuM/MXene aerogel was then self-assembled through cooperative hydrogen bonding interactions between the carbonyl oxygen atom in PVP grafted on the surface of defect-rich Cu-BTC and the surface functional hydroxyl group on MXene. A flexible NO2 sensing performance using the CuM/MXene aerogel hybridized sodium alginate hydrogel is finally achieved, demonstrating extraordinary sensitivity (S = 52.47 toward 50 ppm of NO2), good selectivity, and rapid response/recovery time (0.9/4.5 s) at room temperature. Compared with commercial sensors, the relative error is less than 7.7%, thereby exhibiting significant potential for application in monitoring toxic and harmful gases. This work not only provides insights for guiding rational synthesis of ideal structure models from MOF composites but also inspires the development of high-performance flexible gas sensors for potential multiscenario applications.

The Challenges and Opportunities for TiO2 Nanostructures in Gas Sensing

Chemiresistive gas sensors based on metal oxides have been widely applied in industrial monitoring, medical diagnosis, environmental pollutant detection, and food safety. To further enhance the gas sensing performance, researchers have worked to modify the structure and function of the material so that it can adapt to different gas types and environmental conditions. Among the numerous gas-sensitive materials, n-type TiO2 semiconductors are a focus of attention for their high stability, excellent biosafety, controllable carrier concentration, and low manufacturing cost. This Perspective first introduces the sensing mechanism of TiO2 nanostructures and composite TiO2-based nanomaterials and then analyzes the relationship between their gas-sensitive properties and their structure and composition, focusing also on technical issues such as doping, heterojunctions, and functional applications. The applications and challenges of TiO2-based nanostructured gas sensors in food safety, medical diagnosis, environmental detection, and other fields are also summarized in detail. Finally, in the context of their practical application challenges, future development technologies and new sensing concepts are explored, providing new ideas and directions for the development of multifunctional intelligent gas sensors in various application fields.