Highly sensitive acetone gas sensor based on ultra-low content bimetallic PtCu modified WO3·H2O hollow sphere

The Role of Nano-Sensors in Breath Analysis for Early and Non-Invasive Disease Diagnosis

Early-stage, precise disease diagnosis and treatment has been a crucial topic of scientific discussion since time immemorial. When these factors are combined with experience and scientific knowledge, they can benefit not only the patient, but also, by extension, the entire health system. The development of rapidly growing novel technologies allows for accurate diagnosis and treatment of disease. Nanomedicine can contribute to exhaled breath analysis (EBA) for disease diagnosis, providing nanomaterials and improving sensing performance and detection sensitivity. Through EBA, gas-based nano-sensors might be applied for the detection of various essential diseases, since some of their metabolic products are detectable and measurable in the exhaled breath. The design and development of innovative nanomaterial-based sensor devices for the detection of specific biomarkers in breath samples has emerged as a promising research field for the non-invasive accurate diagnosis of several diseases. EBA would be an inexpensive and widely available commercial tool that could also be used as a disease self-test kit. Thus, it could guide patients to the proper specialty, bypassing those expensive tests, resulting, hence, in earlier diagnosis, treatment, and thus a better quality of life. In this review, some of the most prevalent types of sensors used in breath-sample analysis are presented in parallel with the common diseases that might be diagnosed through EBA, highlighting the impact of incorporating new technological achievements in the clinical routine.

Hollow Mesoporous SnO2/Zn2SnO4 Heterojunction and RGO Decoration for High-Performance Detection of Acetone

In this article, the synthesis procedure and sensing properties toward acetone of rGO-HM-SnO₂/Zn₂SnO₄ composites with a hollow mesoporous structure are presented comprehensively. The rGO-HM-SnO₂/Zn₂SnO₄ heterojunction structure is prepared through a self-sacrificial template strategy with a concise acid-assisted etching method. The as-prepared hollow mesoporous architectures are investigated by SEM, TEM, and HRTEM. The phase structure and valence state are also characterized by XRD and XPS, respectively. It is obvious that the hollow mesoporous architecture affords a large specific surface area, which can provide more reaction active sites of sensing materials significantly. Compared to the initial SnO₂/Zn₂SnO₄ composites, the gas sensor fabricated by rGO-HM-SnO₂/Zn₂SnO₄ shows the best gas-sensing properties, and the response value toward 100 ppm acetone is as high as 107 at 200 °C. Moreover, the rGO-HM-SnO₂/Zn₂SnO₄ sensing material reveals excellent properties of shorter response-recovery times and higher long-term stability. This excellent performance can be ascribed to the synergistic effect of the hollow mesoporous n-n heterojunction and abundant-defect rGO. The relevant sensing mechanism of rGO-HM-SnO₂/Zn₂SnO₄ sensing materials is investigated in detail.

Characterization and Modeling of a Pt-In2O3 Resistive Sensor for Hydrogen Detection at Room Temperature

Sensitive H₂ sensors at low concentrations and room temperature are desired for the early warning and control of hydrogen leakage. In this paper, a resistive sensor based on Pt-doped In₂O₃ nanoparticles was fabricated using inkjet printing process. The H₂ sensing performance of the sensor was evaluated at low concentrations below 1% at room temperature. It exhibited a relative high response of 42.34% to 0.6% H₂. As the relative humidity of 0.5% H₂ decreased from 34% to 23%, the response decreased slightly from 34% to 23%. The sensing principle and the humidity effect were discussed. A dynamic current sensing model for dry H₂ detection was proposed based on Wolkenstein theory and experimentally verified to be able to predict the sensing behavior of the sensor. The H₂ concentration can be calculated within a short measurement time using the model without waiting for the saturation of the response, which significantly reduces the sensing and recovery time of the sensor. The sensor is expected to be a promising candidate for room-temperature H₂ detection, and the proposed model could be very helpful in promoting the application of the sensor for real-time H₂ leakage monitoring.

One-Step Hydrothermal Synthesis of 3D Interconnected rGO/In2O3 Heterojunction Structures for Enhanced Acetone Detection

Acetone detection is of great significance for environmental monitoring or diagnosis of diabetes. Nevertheless, fast and sensitive detection of acetone at low temperatures remains challenging. Herein, a series of rGO-functionalized three-dimensional (3D) In2O3 flower-like structures were designed and synthesized via a facile hydrothermal method, and their acetone-sensing properties were systematically investigated. Compared to the pure 3D In2O3 flower-like structures, the rGO-functionalized 3D In2O3 flower-like structures demonstrated greatly improved acetone-sensing performance at relatively low temperatures. In particular, the 5-rGO/In2O3 sensor with an optimized decoration exhibited the highest response value (5.6) to 10 ppm acetone at 150 °C, which was about 2.3 times higher than that of the In2O3 sensor (2.4 at 200 °C). Furthermore, the 5-rGO/In2O3 sensor also showed good reproducibility, a sub-ppm-level detection limit (1.3 to 0.5 ppm), fast response and recovery rates (3 s and 18 s, respectively), and good long-term stability. The extraordinary acetone-sensing performance of rGO/In2O3 composites can be attributed to the synergistic effect of the formation of p-n heterojunctions between rGO and In2O3, the large specific surface area, the unique flower-like structures, and the high conductivity of rGO. This work provides a novel sensing material design strategy for effective detection of acetone.

Bimetallic Au@Pt Nanocrystal Sensitization Mesoporous α-Fe2O3 Hollow Nanocubes for Highly Sensitive and Rapid Detection of Fish Freshness at Low Temperature

In this work, we present a new metal oxide semiconductor gas sensor for detecting trimethylamine (TMA) by bimetal Au@Pt-modified α-Fe₂O₃ hollow nanocubes (NCs) as sensing materials. The structure and morphological characteristics of Au@Pt/α-Fe₂O₃ were evaluated through multiple analyses, and their gas-sensitive performance was investigated. Compared with the pristine α-Fe₂O₃ NC sensor, the sensor based on Au@Pt/α-Fe₂O₃ NCs exhibited faster response time (5 s) and higher response (R_a/R_g = 32) toward 100 ppm TMA gas at a lower temperature (150 °C). Furthermore, we also assessed the Au@Pt/α-Fe₂O₃ NC sensor for detecting the freshness of Larimichthys crocea which have been observed by headspace solid-phase microextraction and gas chromatography-mass spectrometry. The high performance of the Au@Pt/α-Fe₂O₃ NCs is attributed to the special hollow morphology with a high specific surface area (212.9 m²/g) and the synergistic effect of the Au@Pt bimetal. The Au@Pt/α-Fe₂O₃ sensor shows promising application prospects in estimating seafood freshness on the spot.

Self-Hybrid Transition Metal Oxide Nanosheets Synthesized by a Facile Programmable and Scalable Carbonate-Template Method

2D transition metal oxides (TMO) nanosheets have attracted considerable attention in both fundamental research and practical applications. Herein, a convenient programmable and scalable carbonate crystals templating synthesis is developed to produce high-quality self-hybrid TMO nanosheets (Si-WO_{3- x} , Ta_x O_y , Mn_x O_y ) and their respective polymetallic oxide hybrid nanosheets with tunable composition, low-cost and high-yield. Taking tungsten oxide nanosheets as example, silicotungstic acid precursor is in situ converted into tungsten oxide nanosheets like scales on the surface of calcium carbonate crystals through the simple soaking-drying-calcination process, and after selectively dissolving calcium carbonate by etching, the dispersive tungsten oxide nanosheets with unique self-hybrid Si-doped h-WO₃ /ε-WO₃ /WO₂ compositions are obtained, which show excellent acetone gas-sensing performances at low temperatures. This carbonate-template method opens up the possibility to economically produce various functional TMO nanosheets with specific compositions for diverse applications.

Highly sensitive and fast-response hydrogen sensing of WO3 nanoparticles via palladium reined spillover effect

Hydrogen sensing simultaneously endowed with fast response, high sensitivity and selectivity is highly desired in detecting hydrogen leakages such as in hydrogen-driven vehicles and space rockets. Here, hydrogen sensing reined via a hydrogen spillover effect has been developed using palladium nanoparticles photochemically decorated on WO₃ nanoparticles (Pd-NPs@WO₃-NPs). Theoretically, the Pd-NP catalysts and WO₃-NP support are used to construct the hydrogen spillover system, in which Pd NPs possess high catalytic activity, promoting the electron transfer and therefore the reaction kinetics. Beneficially, the Pd-NPs@WO₃-NP sensor prototypes toward 500 ppm hydrogen simultaneously exhibit fast response time (∼1.2 s), high response (R_a/R_g = 22 867) and selectivity at a working temperature of 50 °C. Such advanced hydrogen sensing provides an experimental basis for the smart detection of hydrogen leakage in the future hydrogen economy.

Pd nanocrystal sensitization two-dimension porous TiO2 for instantaneous and high efficient H2 detection

Hydrogen (H₂) molecules are easy to leak during production, storage, transportation and usage. Because of their flammability and explosive nature, quick and reliable dectection of H₂ molecule is of great significance. Herein, an excellent H₂ gas sensor has been realized based on Pd nanocrystal sensitized two-dimensional (2D) porous TiO₂ (Pd/TiO₂). The formation of 2D porous TiO₂ with the removal of graphene oxide template has been monitored by an in-situ transmission electron microscope. It is found that the size of the GO template can be almost completely replicated by 2D TiO₂. The Pd/TiO₂ sensor exhibited an instantaneous response and a satisfactory low detection limit for H₂ detection. These excellent gas-sensing performances (good selectivity, unique linearity response and high stability) can be attributed to the unique 2D porous structure and the synergistic effect between oxidized Pd and TiO₂, including the unique adsorption properties of O₂ or/and H₂ on Pd/TiO₂, the reaction between PdO and H₂ gas, and the regulated depletion layer arising from p-type PdO to n-type TiO₂. This work demonstrates a rational design and synthesis of highly efficient H₂ sensitive materials for energy and manufacturing security.

The Ketogenic Diet: Breath Acetone Sensing Technology

The ketogenic diet, while originally thought to treat epilepsy in children, is now used for weight loss due to increasing evidence indicating that fat is burned more rapidly when there is a low carbohydrate intake. This low carbohydrate intake can lead to elevated ketone levels in the blood and breath. Breath and blood ketones can be measured to gauge the level of ketosis and allow for adjustment of the diet to meet the user’s needs. Blood ketone levels have been historically used, but now breath acetone sensors are becoming more common due to less invasiveness and convenience. New technologies are being researched in the area of acetone sensors to capitalize on the rising popularity of the diet. Current breath acetone sensors come in the form of handheld breathalyzer devices. Technologies in development mostly consist of semiconductor metal oxides in different physio-chemical formations. These current devices and future technologies are investigated here with regard to utility and efficacy. Technologies currently in development do not have extensive testing of the selectivity of the sensors including the many compounds present in human breath. While some sensors have undergone human testing, the sample sizes are very small, and the testing was not extensive. Data regarding current devices is lacking and more research needs to be done to effectively evaluate current devices if they are to have a place as medical devices. Future technologies are very promising but are still in early development stages.