A Flexible and Wearable Nylon Fiber Sensor Modified by Reduced Graphene Oxide and ZnO Quantum Dots for Wide-Range NO2 Gas Detection at Room Temperature

Scientific Insights into the Quantum Dots (QDs)-Based Electrochemical Sensors for State-of-the-Art Applications

Size-dependent optical and electronic properties are unique characteristics of quantum dots (QDs). A significant advantage is the quantum confinement effect that allows their precise tuning to achieve required characteristics and behavior for the targeted applications. Regarding the aforementioned factors, QDs-based sensors have exhibited dramatic potential for the diverse and advanced applications. For example, QDs-based devices have been potentially utilized for bioimaging, drug delivery, cancer therapy, and environmental remediation. In recent years, use of QDs-based electrochemical sensors have been further extended in other areas like gas sensing, metal ion detection, monitoring of organic pollutants, and detection of radioactive isotopes. Objective of this study is to rationalize the QDs-based electrochemical sensors for state-of-the-art applications. This review article comprehensively illustrates the importance of aforementioned devices along with sources from which QDs devices have been formulated and fabricated. Other distinct features of QDs devices are associated with their extremely high active surfaces, inherent ability of reproducibility, sensitivity, and selectivity for the targeted analyte detection. In this review, major categories of QD materials along with justification of their key roles in electrochemical devices have been demonstrated and discussed. All categories have been evaluated with special emphasis on the advantages and drawbacks/challenges associated with QD materials. However, in the interests of readers and researchers, recent improvements also have been included and discussed. On the evaluation, it has been concluded that despite significant challenges, QDs-based electrochemical sensors exhibit excellent performances for state-of-the-art and targeted applications.

Porous PDMS-ZnO Wearable Gas Sensor for Acetone Biomarker Detection and Breath Analysis

In response to the growing demand for global health monitoring, we report a nonintrusive health detection method using a compact, conformal wearable ultraviolet (UV)-assisted gas-sensing system based on an intrinsically flexible porous polydimethylsiloxane (PDMS)-zinc oxide (ZnO) composite layer (PPZL) for the breath acetone (BrAce) detection and breath event analysis. The enhanced acetone response is attributed to the synergistic effect of UV irradiation and the high surface area of the porous structure, which also improves the mechanical robustness. The UV-assisted wearable sensor reliably detects acetone concentrations ranging from 1 to 100 ppm at room temperature under 4.05 mW/cm2 UV intensity, even under mechanical strains such as a bending radius of 5 mm and 60% tensile strain. It accurately analyzes different breathing patterns (12-20 breaths per minute) and BrAce concentrations, maintaining a stable performance over 20 days with less than 5% signal degradation. The sensor exhibits response and recovery times of average 110-150 and 130-180 s, respectively, and maintains a consistent 3 ppm BrAce response under varying humidity levels up to 70% relative humidity, ensuring accurate detection of BrAce concentrations during real-world breath tests. Additionally, the sensor targets only specific gases, and the sensor's selectivity is not a key concern. This flexible acetone gas sensor offers a portable solution for health management and a fabrication method for designing flexible metal oxide materials.

Advances on chalcogenide quantum dots-based sensors for environmental pollutants monitoring

Water contamination represents a significant ecological impact with global consequences, contributing to water scarcity worldwide. The presence of several pollutants, including heavy metals, pharmaceuticals, pesticides, and pathogens, in water resources underscores a pressing global concern, prompting the European Union (EU) to establish a Water Watch List to monitor the level of these substances. Nowadays, the standard methods used to detect and quantify these contaminants are mainly liquid or gas chromatography coupled with mass spectrometry (LC/GC-MS). While these methodologies offer precision and accuracy, they require expensive equipment and experienced technicians, and cannot be used on the field. In this context, chalcogenide quantum dots (QDs)-based sensors have emerged as promising, user-friendly, practical, and portable tools for environmental monitoring. QDs are semiconductor nanocrystals that possess excellent properties, and have demonstrated versatility across various sensor types, such as fluorescent, electrochemical, plasmonic, and colorimetric ones. This review summarizes recent advances (2019-2023) in the use of chalcogenide QDs for environmental sensing, highlighting the development of sensors capable of detect efficiently heavy metals, anions, pharmaceuticals, pesticides, endocrine disrupting compounds, organic dyes, toxic gases, nitroaromatics, and pathogens.

RGO/CuCl-Based Flexible Gas Sensor for High-Concentration Carbon Monoxide Gas Detection at Room Temperature

Carbon monoxide (CO) gas sensors are widely used, especially for environmental monitoring in confined spaces such as the landscape of mining cave ruins in mining parks, which is essential for ensuring the health and safety of tourists and staff. In this paper, a flexible CO gas sensor based on polyimide, interdigital electrodes, and reduced graphene oxide (RGO)/cuprous chloride (CuCl) composite film is designed and manufactured for reliable room temperature detection of high-concentration CO gas. The structure size of RGO/CuCl gas-sensitive film is 5 × 5 mm. The RGO with a 62.65% C-C bond is prepared by the thermal reduction method. The test results show that the sensor has a high response in the range of 400-2000 ppm CO gas concentration, and the maximum response is 1.56. The linear correlation coefficient of the sensor is 0.981, which indicates that the sensor has good output response characteristics. The response time of the sensor for 400 ppm CO gas is 332 s, which indicates that the sensor has a fast response rate. Furthermore, compared with other gases, the sensor shows higher gas selectivity for CO gas. This sensor has the characteristics of small size and easy attachment; therefore, it can be installed on the shoulder or helmet of tourists' safety suits, providing personalized real-time warning prompts for tourists' physical health status.

High-response room-temperature NO2 gas sensor fabricated with thermally reduced graphene oxide-coated commercial cotton fabric

Electronic textile-based gas sensors with a high response for NO2 gas were fabricated using reduced graphene oxide (rGO)-coated commercial cotton fabric (rGOC). Graphene oxide (GO) was coated on cotton fabric by simply dipping the cotton into a GO solution. To investigate the relationship between the degree of reduction and the sensing response, the GO-coated fabrics were thermally reduced at various temperatures (190, 200, 300, and 400 °C). The change in the amount of oxygen functional groups on the rGOCs was observed by x-ray photoelectron spectroscopy, Raman spectroscopy, and x-ray diffraction patterns. The maximum sensing response of 45.90 % at 10 ppm of NO2 gas at room temperature was exhibited by the rGOC treated at 190 °C, which was the lowest heat-treatment temperature. The high response comes from the greater amount of oxygen functional groups compared to other rGOC samples, and the tubular structure of the cotton.

Proteomics and Metabolomics Analysis Reveals the Toxicity of ZnO Quantum Dots on Human SMMC-7721 Cells

Purpose

ZnO quantum dots (QDs) are composed of less toxic metals than other QDs but have the same interesting photochemical properties. Thus, they have received considerable attention recently. Nevertheless, their toxicity cannot be ignored.

Methods

In this study, we incubated ZnO QDs with human SMMC-7721 cells for 24 h to assess their nanotoxicity through proteomics (Fold change >1.5 and p-value <0.05) and metabolomics (Fold change ≥ 1.5; VIP ≥ 1; p-value < 0.05) analyses.

Results

Both of 174 and 219 significantly changed metabolites were identified in human SMMC-7721 cells treated with 20 and 50 µg/mL ZnO QDs, respectively. ZnO QDs significantly modified metabolic pathways, including purine metabolism, ferroptosis, morphine addiction, alcoholism, cGMP-PKG signaling, and Cushing syndrome. Moreover, we identified 105 and 8 differentially expressed proteins in cells treated with 20 and 50 µg/mL ZnO QDs, and the pathways of alcoholism and Cushing syndrome were enriched.

Conclusion

ZnO QDs did not affect cell viability in a CCK8 assay, but disturbed the level of intracellular metabolites and proteins at 20 µg/mL. The KEGG analyses of the metabolomics and proteomics data both enriched the alcoholism and Cushing syndrome pathways. These results provide an experimental basis for future research on the safe use of nanomaterials.

In-Situ Growth of Graphene Films to Improve Sensing Performances

Graphene films made by chemical vapor deposition (CVD) are a popular method to modify sensors by virtue of large-scale and reproducibility, but suffer from various surface contamination and structural defects induced during transfer procedures. In-situ growth of graphene films is proposed in this review article to improve sensing performance. Root causes of the surface contamination and structural defects are revealed with several common transfer methods. In-situ approaches are introduced and compared, growing graphene films with clean surfaces and few defects. This allows graphene film to display superior sensing performance for sensor applications. This work may reasonably be expected to offer a good avenue for synthesis of graphene films applicable for sensing applications.