Design and analysis of a 2D grapheneplus (G+)-based gas sensor for the detection of multiple organic gases.

A new member of the 2D carbon family, grapheneplus (G+), has demonstrated excellent properties, such as Dirac cones and high surface area. In this study, the electronic transport properties of G+, NG+, and BG+ monolayers in which the NG+/BG+ can be obtained by replacing the center sp3 hybrid carbon atoms of the G+ with N/B atoms, were studied and compared using density functional theory and the non-equilibrium Green's function method. The results revealed that G+ is a semi-metal with two Dirac cones, which becomes metallic upon doping with N or B atoms. Based on the electronic structures, the conductivities of the 2D G+, NG+ and BG+-based nanodevices were analyzed deeply. It was found that the currents of all the designed devices increased with increasing the applied bias voltage, showing obvious quasi-linear current-voltage characteristics. IG+ was significantly higher than ING+ and IBG+ at the same bias voltage, and IG+ was almost twice IBG+, indicating that the electron mobility of G+ can be controlled by B/N doping. Additionally, the gas sensitivities of G+, NG+, and BG+-based gas sensors in detecting C2H4, CH2O, CH4O, and CH4 organic gases were studied. All the considered sensors can chemically adsorb C2H4 and CH2O, but there were only weak van der Waals interactions with CH4O and CH4. For chemical adsorption, the gas sensitivities of these sensors were considerably high and steady, and the sensitivity of NG+ to adsorb C2H4 and CH2O was greater as compared to G+ and BG+ at higher bias voltages. Interestingly, the maximum sensitivity difference for BG+ toward C2H4 and CH2O was 17%, which is better as compared to G+ and NG+. The high sensitivity and different response signals of these sensors were analyzed by transmission spectra and scattering state separation at the Fermi level. Gas sensors based on G+ monolayers can effectively detect organic gases such as C2H4 and CH2O, triggering their broad potential application prospects in the field of gas sensing.

A novel sensor based on Ti3C2 MXene/Co3O4/carbon nanofibers composite for the sensitive detection of 4-aminophenol.

A novel, sensitive Ti3C2 MXene/Co3O4/carbon nanofibers (Ti3C2 MXene/Co3O4/CNFs) composite was synthesized via a HF exfoliating Ti3AlC2 strategy, followed by doping Co3O4 and Ti3C2 MXene into the CNFs via a combination electrospinning and thermal annealing process. Ti3C2 MXene/Co3O4/CNFs composite exhibits higher catalytic effect, conductivity, chemical stability, and electrochemical performance than Co3O4 and Ti3C2 MXene in electrochemical impedance, differential pulse stripping voltammetry, chronocoulometry, and cyclic voltammetry tests. This Ti3C2 MXene/Co3O4/CNFs hybrid modified electrode provides fast analysis of 4-aminophenol (4-AP) with ultrahigh sensitivity, enhanced reproducibility and strong anti-interference capability. Furthermore, the level of 4-AP was quantified by this electrode with a wide linear range from 0.5 to 150 µM (R2 > 0.99) and a low detection limit about 0.018 µM was achieved. Finally, the fabricated electrode was used for fast and sensitive analysis of 4-AP spiked in tap water and blood serum samples. This work presents the new Ti3C2 MXene/Co3O4/CNFs electrode provides a platform for 4-AP monitoring and has the advantages of high selectivity, accuracy, simplicity, and rapid analysis.

Rapid quantitative detection of luteolin using an electrochemical sensor based on electrospinning of carbon nanofibers doped with single-walled carbon nanoangles.

In this study, single-walled carbon nanoangles/carbon nanofibers (SWCNHs/CNFs) were synthesized by electrospinning, followed by annealing in a N2 atmosphere. The synthesized composite was structurally characterized by scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The electrochemical sensor was fabricated by modifying a glassy carbon electrode (GCE) for luteolin detection, and its electrochemical characteristics were investigated using differential pulse voltammetry, cyclic voltammetry, and chronocoulometry. Under optimized conditions, the response range of the electrochemical sensor to luteolin was 0.01-50 µM, and the detection limit was 3.714 nM (S/N = 3). The SWCNHs/CNFs/GCE sensor showed excellent selectivity, repeatability, and reproducibility, thus enabling the development of an economical and practical electrochemical method for the detection of luteolin.

Electrochemiluminescence Sensor based on Electrospun Crosslinked Carbon Nanofibers for the Detection of Difenidol Hydrochloride.

BACKGROUND: Cross-linked porous carbon nanofibers (CNF) were successfully prepared by electrospinning and high-temperature carbonization. Polyacrylonitrile (PAN) as the carbon source and genipin as the cross-linking agent were used to prepare cross-linked porous carbon nanofibers (CNF). MATERIALS AND METHODS: The field emission scanning electron microscopy (SEM), transmission electron microscope (TEM), automatic specific surface and porosity analyzer Brunner Emmet Teller (BET), X-ray diffraction (XRD), and a laser confocal microspectroscope (Raman, XploRA PLUS, Horiba) were used to characterize the materials. The CNF suspension was dropped on the surface of the bare glassy carbon electrode by the drip coating method to obtain a CNF-modified electrode. Cyclic voltammetry was used to study the electrochemiluminescence behavior of difenidol hydrochloride on CNF-modified glassy carbon electrode (Glassy Carbon Electrode, GCE). RESULTS AND DISCUSSION: Herein, we synthesised a kind of crosslinked carbon nanofibers and designed a novel ECL biosensor. Under the optimal conditions, the concentration of difenidol hydrochloride exhibited a linear relationship with the peak current in the range of 8.0×10-8 to 1.0×10-4 mol/L, with the correlation coefficient of R2=0.997, and a low detection limit (1.2×10-8 mol/L). Difenidol hydrochloride in difenidol hydrochloride tablets was tested, and the recovery rate of sample addition was estimated to be 83.17%-92.17%, and the RSD value to be <5.0%. The designed platform exhibited excellent analytical performance for difenidol hydrochloride determination.

Learning to Overcome Noise in Weak Caption Supervision for Object Detection.

We propose the first mechanism to train object detection models from weak supervision in the form of captions at the image level. Language-based supervision for detection is appealing and inexpensive: many blogs with images and descriptive text written by human users exist. However, there is significant noise in this supervision: captions do not mention all objects that are shown, and may mention extraneous concepts. We first propose a technique to determine which image-caption pairs provide suitable signal for supervision. We further propose several complementary mechanisms to extract image-level pseudo labels for training from the caption. Finally, we train an iterative weakly-supervised object detection model from these image-level pseudo labels. We use captions from four datasets (COCO, Flickr30K, MIRFlickr1M, and Conceptual Captions) whose level of noise varies. We evaluate our approach on two object detection datasets. Weighting the labels extracted from different captions provides a boost over treating all captions equally. Further, our primary proposed technique for inferring pseudo labels for training at the image level, outperforms alternative techniques under a wide variety of settings. Both techniques generalize to datasets beyond the one they were trained on.

Sensitive and selective electrochemical determination of uric acid in urine based on ultrasmall iron oxide nanoparticles decorated urchin-like nitrogen-doped carbon.

Hypercrosslinked pyrrole was synthesized via the Friedel-Crafts reaction and then carbonized to obtain urchin-like nitrogen-doped carbon (UNC). Ultrasmall iron oxide nanoparticles were then supported on UNC, and the composite was used to prepare an electrochemical sensor for detecting uric acid (UA) in human urine. FexOy/UNC was characterized and analyzed via scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. A glassy carbon electrode (GCE) modified with FexOy/UNC was used as an electrochemical sensor to effectively identify UA. The electrochemical behavior of the FexOy/UNC-based UA sensor was studied using differential pulse stripping voltammetry, and the optimal conditions were determined by changing the amount of FexOy/UNC, pH of the buffer solution, deposition potential, and deposition time. Under optimal conditions, the FexOy/UNC-based electrochemical sensor detected UA in the range of 2-200 µM, where the limit of detection (LOD) for UA was 0.29 µM. Anti-interference experiments were performed, and the sensor was applied to the actual analysis of human urine samples. Urea, glucose, ascorbic acid, and many cations and anions present at 100-fold concentrations relative to UA did not strongly interfere with the response of the sensor to UA. The FexOy/UNC electrochemical sensor has high sensitivity and selectivity for uric acid in human urine samples and can be used for actual clinical testing of UA in urine.

A facile fabrication of a hierarchical ZIF-8/MWCNT nanocomposite for the sensitive determination of rutin.

In this paper, a novel type of zeolitic imidazolate framework-8 (ZIF-8) polyhedron/multi-walled carbon nanotube (MWCNT) modified electrode was successfully prepared for effective on-site detection of rutin. The morphology and microstructure of the ZIF-8/MWCNT nanocomposite were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The electrochemical performance of the ZIF-8/MWCNT based electrode for the determination of rutin was studied by cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPV). The as-prepared sensor illustrates better electrocatalytic activity and lower background current than the MWCNT modified electrode for the oxidation of rutin. Besides, the ZIF-8/MWCNTs sensor offers a remarkable linear response for rutin concentrations from 0.1 to 15 µM. The detection limit (LOD) was calculated to be 0.26 nM (S/N = 3). Also, the ZIF-8/MWCNT electrode showed high anti-interference ability towards common interfering species. More importantly, the fabricated electrode was quickly evaluated for determination of rutin in medicine tablets with satisfactory recoveries and the obtained results successfully achieved good consistency with the data from high performance liquid chromatography (HPLC). Finally, the method shows an enhanced electrocatalytic property and sensitivity for the analysis of rutin, which may provide an economical and promising electrochemical sensor for practical on-site detection of rutin.

Double-shelled yolk-shell Si@C microspheres based electrochemical sensor for determination of cadmium and lead ions.

In this work, we report double-shelled yolk-shell Si@C structure as a high-performance electrochemical sensing material for heavy metal ions. A SiO2-assisted polybenzoxazine (PB) coating strategy is used to synthesize highly monodispersed Si@C microspheres. After thermal carbonization of PB layers and selective removal of the SiO2 layers, Si@C microspheres were prepared. The resultant Si@C microspheres exhibit uniform spherical morphology and clearly double-shelled yolk-shell structures. The obtained Si@C microspheres are employed to prepare the chemically modified electrode for the sensitive determination of Cd(II) and Pb(II). By the method of anodic stripping voltammetry, the Si@C-based electrode shows a very wide linear dynamic range for target ions (e.g., 0.5-400 µg L-1 for Cd(II) and Pb(II)) and low limit of detections (e.g., 0.068 µg L-1 for Cd(II) and for 0.105 µg L-1 Pb(II)). The remarkable results, such as excellent resistance to interference ions, good repeatability, and reproducibility were also obtained. Furthermore, compared with those Cd(II) and Pb(II) sensors known in the literature, the analytical performance of Si@C-based electrode is better. Finally, when further used to determine Cd(II) and Pb(II) in tap water and lake water, the results of fabricated electrode successfully achieve good consistency with the data obtained from inductively coupled plasma-mass spectrometry (ICP-MS).