In this paper, the reduced graphene oxide and multiwall carbon nanotubes hybrid materials (RGO–MWNTs) were prepared and a novel strategy for the simultaneous determination of multiple environmental ...contaminations has been proposed on the basis of RGO–MWNTs hybrid materials modified electrode. The hybrid materials were characterized by the scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and N2 sorption–desorption isotherms. Due to the excellent catalytic activity, enhanced electrical conductivity, high surface area and porous structure of the RGO–MWNTs, the RGO–MWNTs/GCE achieved the simultaneous measurement of hydroquinone (HQ), catechol (CC), p-cresol (PC) and nitrite (NO2−) with well-separate four peaks. Scheme 1a illuminated the preparation process of the RGO–MWNTs hybrid materials. Scheme 1b explains the electron mediating properties of RGO–MWNTs/GCE towards the oxidation of HQ, CC, PC and NO2−. Scheme 1c presented the SEM image of RGO–MWNTs hybrid materials. Scheme 1d and e showed the 2D and 3D AFM images of RGO–MWNTs films, respectively. Display omitted
► The novel RGO–MWNTs hybrid materials were synthesized. ► The simultaneous detection of four environmental contaminations was achieved. ► SEM, AFM, XPS was employed to characterize the RGO–MWNTs hybrid materials.
In this paper, the reduced graphene oxide and multiwall carbon nanotubes hybrid materials (RGO–MWNTs) were prepared and a strategy for detecting environmental contaminations was proposed on the basis of RGO–MWNTs modified electrode. The hybrid materials were characterized by the scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and N2 sorption–desorption isotherms. Due to the excellent catalytic activity, enhanced electrical conductivity and high surface area of the RGO–MWNTs, the simultaneous measurement of hydroquinone (HQ), catechol (CC), p-cresol (PC) and nitrite (NO2−) with four well-separate peaks was achieved at the RGO–MWNTs modified electrode. The linear response ranges for HQ, CC, PC and NO2− were 8.0–391.0μM, 5.5–540.0μM, 5.0–430.0μM and 75.0–6060.0μM, correspondingly, and the detection limits (S/N=3) were 2.6μM, 1.8μM, 1.6μM and 25.0μM, respectively. The outstanding film forming ability of RGO–MWNTs hybrid materials endowed the modified electrode enhanced stability. Furthermore, the fabricated sensor was applied for the simultaneous determination of HQ, CC, PC and NO2− in the river water sample.
The reduced graphene oxide (rGO) could strongly adsorb and quench the fluorescence of dye-labeled single-stranded DNA (ssDNA); thus, it is widely applied in fluorescent sensors. However, these ...sensors may suffer from a limited sensitivity due to the low fluorescence recovery when adding the complementary DNA (cDNA) sequence. In this work, the powerful DNA branched junctions were constructed to improve the fluorescence recovery of FAM-labeled probe on rGO. In the presence of target Pb
2+
, the ribonucleotide (rA) in the substrate was cleaved specifically and the catalytic hairpin assembly of three metastable hairpins was further initiated, accompanied by the formation of DNA branched junctions. Then, the liberated Pb
2+
could be recyclable. Impressively, the DNA branched junctions not only hybridize with the FAM-labeled probes with a high efficiency, but also are significantly undesirable for the rGO. Thus, a high fluorescence recovery of FAM-labeled probe on rGO was expected. The integration of the high fluorescence recovery and dual-cycle signal amplification endows the sensing strategy with a good performance for Pb
2+
detection, including low detection limit (0.17 nM), good selectivity, and satisfactory practical applicability. The proposed DNA branched junctions offer a novel avenue to improve the fluorescence recovery of the dye-labeled probes on rGO for biological analysis.
Direct electrochemistry, a direct electron transfer process between enzymes and electrode possesses, has important fundamental significance in bioelectrochemistry while offering very efficient ...electrocatalysis for enzyme‐based sensors. Herein, the pore structure of bacterial cellulose porous carbon nanofibers (BPCNFs) is tailored by controlled thermal carbonization. It is discovered that rising mesopores can realize a fast direct electrochemistry of glucose oxidase (GOx) for highly sensitive detection of glucose, achieving a sensitivity of 123.28 µA mmol L−1 cm−2 and a detection limit of 0.023 µmol L−1. The enhancement mechanism for the mesopores is ascribed to the most adequate mesopores of BPCNF900, which offer size‐matched “nests” to trap GOx for intimate contacts with the conductive carbon nanofiber enabling fast direct electrochemistry. In addition, with the BPCNF900 sensing platform, the mechanisms for GOx‐direct‐electrochemistry‐catalyzed glucose oxidation and oxygen reduction are systematically investigated to further clarify the confusions of glucose sensing in air and N2‐saturated solutions. This work demonstrates fundamental insights for the direct electrochemistry enabled by rationally designing a pore structure matching the target proteins, thus possessing universal significance in protein‐based electrochemical devices while offering a facile route to fabricate a highly sensitive glucose sensor for practical clinic diagnosis.
Bacterial cellulose porous carbon nanofibers (BPCNF)900 with the most adequate mesopores offer size‐matched “nests” to trap glucose oxidase (GOx) for intimate contacts with the conductive carbon nanofiber enabling fast direct electrochemistry of GOx without any electron mediator. The glucose sensor fabricated by the BPCNF900 shows a fast direct electrochemistry of glucose oxidase to catalyze GOx for highly sensitive and selective sensors with a rapid response time.
Electropolymerization of Im on the GCE, the PIm modified electrode was denoted as PIm/GCE. Subsequently, the PIm/GCE was washed with doubly distilled water, and then transferred to 0.1M PBS (pH 4.0) ...for electrochemical oxidation at +1.8V for 250s. The obtained electrode was denoted as PImox/GCE (Fig. A). Then, the deposition of GNPs on PImox/GCE was carried out. The obtained electrode was described as GNPs/PImox/GCE (Fig. B). Display omitted
► The electropolymerization of imidazole (Im) on GCE was first reported. ► The PIm film can be overoxidized to form the overoxidized polyimidazole (PImox). ► PImox allows dispersing of Au and generates additional electrocatalytic sites. ► The overlapping voltammetric response of AA, DA, UA and Trp is well-resolved.
A novel electrode was developed through electrodepositing gold nanoparticles (GNPs) on overoxidized-polyimidazole (PImox) film modified glassy carbon electrode (GCE). The combination of GNPs and the PImox film endowed the GNPs/PImox/GCE with good biological compatibility, high selectivity and sensitivity and excellent electrochemical catalytic activities towards ascorbic acid (AA), dopamine (DA), uric acid (UA) and tryptophan (Trp). In the fourfold co-existence system, the peak separations between AA–DA, DA–UA and UA–Trp were large up to 186, 165 and 285mV, respectively. The calibration curves for AA, DA and UA were obtained in the range of 210.0–1010.0μM, 5.0–268.0μM and 6.0–486.0μM with detection limits (S/N=3) of 2.0μM, 0.08μM and 0.5μM, respectively. Two linear calibrations for Trp were obtained over ranges of 3.0–34.0μM and 84.0–464.0μM with detection limit (S/N=3) of 0.7μM. In addition, the modified electrode was applied to detect AA, DA, UA and Trp in samples using standard addition method with satisfactory results.
In order to examine the seismic behavior of high-strength steel extended end-plate connections, a three-dimensional efficient finite-element model in Abaqus was established subjected to cyclic ...loading at the beam end. Geometrical dimensions, boundary conditions, element types, contact properties between the bolts, end-plate and column flange, and material cyclic constitutive models were described in detail. Geometry and material nonlinearity were adequately considered. In particular, a cyclic plasticity model for high-strength steels was employed that was easily calibrated based on the tension coupon test, so as to describe the complicated cyclic hardening and softening response. The simulated results of the finite-element model were compared to the test ones in terms of both deformation modes and hysteresis loops. The results showed that the bending deformation of the end-plate and column flange was accurately captured, and the gap phenomena among the bolt nuts, the end-plate, and column flange was described in a satisfactory manner as well. The hysteresis loops from the simulation agreed well with the test results, reproducing the pinched shape due to the end-plate gap evolution under cyclic loading as well as the quite plump shape with stable energy dissipation when the panel zone dominated the cyclic response. Therefore, the accuracy of the finite-element model was verified and it provided a strong benchmark tool for investigating the cyclic or seismic performance of this kind of connection. The connection failure including the bolt fracture and cracking in the end-plate needs further numerical study by calibrating accurate material failure models for high-strength steels and bolts.
A high-precision real-time troposphere model is constructed by combining ground-based GNSS observation data and the latest European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis ...(ERA5). First, the zenith tropospheric delay (ZTD) is extracted in real time with high accuracy by combining the data of more than 500 GNSS stations in the Crustal Movement Observation Network of China (CMONOC) and national reference station network (NRSN); second, a grid model of the elevation normalization model (ENM) in China using ERA5 data is constructed, which takes into account the annual, semiannual and daily cycles. The ZTD estimated by GNSS stations at different heights based on precise point positioning (PPP) is normalized to a uniform height based on ENM; in addition, the optimal smoothing factors of the Gauss distance weighting function in different seasons are determined based on ERA5, which contributes to improved accuracy of ZTD interpolated from GNSS-derived ZTD to ZTD at grid points; finally, a real-time 1° × 1°ZTD grid model of China is created; the broadcast interval is extended to 6 min from few seconds. The new ZTD model has been evaluated using the data of 15 GNSS stations in China in 2020. The test results show that the new ZTD model deviates from the reference value with a mean value better than − 0.09 cm and RMSE, better than 1.44 cm compared with the ZTD estimated by post-processing GNSS, while the mean value of the deviation is -0.13 cm, and the RMSE is approximately 3.11 cm compared with radiosonde-derived ZTD. The new ZTD grid model can be used to enhance GNSS/PPP. Two weeks of GNSS observations, one week in winter and another in summer, were randomly collected for PPP processing. The statistical results show the convergence time in the vertical directions is shortened by 37.4% and 38.6% at the 95% and 68% confidence levels after ZTD constraints are applied to the float PPP solution, respectively.
A chloro 3,7,12,17-tetramethyl-8,13-divinylporphyrin-2,18-dipropanoato (2−)iron(III)/multi-walled carbon nanotubes (Fe(III)P/MWCNTs) composites and a modified glassy carbon electrode (GCE) was ...fabricated and successfully used for the simultaneous determination of ascorbic acid (AA), dopamine (DA), uric acid (UA) and nitrite (NO
2
−). Fe(III)P/MWCNTs composites were characterized by ultraviolet–visible absorption spectroscopy (UV–vis) and scanning electron microscopy (SEM), and the results revealed a pair of direct redox peaks from the Fe
III/Fe
II couple. Moreover, the combination of Fe(III)P and MWCNTs endowed the electrode with a large surface area, good biological compatibility and stability and high selectivity and sensitivity. The linear calibration plots for AA, DA and UA were obtained over the range of 14.00
μM to 2.50
mM, 0.70
μM to 3.60
mM and 5.80
μM to 1.30
mM with detection limits of 3.00
μM, 0.09
μM and 0.30
μM, respectively. Two linear calibrations for NO
2
− were obtained over ranges of 1.00
μM to 0.60
mM and 0.60
mM to 1.60
mM with detection limits of 0.50
μM. In addition, the modified electrode was successfully applied for the determination of analytes in urine and serum samples using the standard adding method with satisfactory results.
As an important glycoprotein of the lectin family, soybean agglutinin (SBA) is an anti-nutritional factor with considerable toxic and side effects and plays a significant role in tumor analysis. In ...order to achieve the sensitive detection of SBA, a sandwich-structured electrochemiluminescence (ECL) biosensor was constructed using carboxylated carbon nitride (C-g-C
3
N
4
) as luminophore and D-galactosamine (galM) as a recognition element. A glassy carbon electrode (GCE) was modified with Au nanoparticles (Au NPs) for capturing the galM via Au-N bond, and further capturing the target SBA by specific recognition between galM and SBA. In the presence of SBA, the composite C-g-C
3
N
4
-galM was immobilized onto the electrode. With the increase in the concentration of SBA, the ECL signal from C-g-C
3
N
4
increased, thus achieving a signal-on detection of SBA. The linear range of the biosensor was 1.0 ng/mL~10 μg/mL and detection limit for SBA was as low as 0.33 ng/mL. In this construction strategy, C-g-C
3
N
4
not only acted as an excellent signal probe, but also as an immobilization matrix to easily achieve a high loading of the small molecule recognition element galM. This strategy provides a simple alternative SBA detection platform.
Graphical abstract
A novel biosensor has been constructed by the electrodeposition of Au-nanoclusters (nano-Au) on poly(3-amino-5-mercapto-1,2,4-triazole) (
p-TA) film modified glassy carbon electrode (GCE) and ...employed for the simultaneous determination of dopamine (DA), ascorbic acid (AA), uric acid (UA) and nitrite (NO
2
−). NH
2 and SH groups exposed to the
p-TA layer are helpful for the electrodeposition of nano-Au. The combination of nano-Au and
p-TA endow the biosensor with large surface area, good biological compatibility, electricity and stability, high selectivity and sensitivity and flexible and controllable electrodeposition process. In the fourfold co-existence system, the linear calibration plots for AA, DA, UA and NO
2
− were obtained over the range of 2.1–50.1
μM, 0.6–340.0
μM, 1.6–110.0
μM and 15.9–277.0
μM with detection limits of 1.1
×
10
−6
M, 5.0
×
10
−8
M, 8.0
×
10
−8
M and 8.9
×
10
−7
M, respectively. In addition, the modified biosensor was applied to the determination of AA, DA, UA and NO
2
− in urine and serum samples by using standard adding method with satisfactory results.
High strength steel (HSS) with the nominal yield strength
f
y
≥460 MPa has been applied in numerous modern building and bridge structures all over the world. Steel structures using high strength ...steel have obvious advantages in structural, architectural, economical, environment protection and energy saving aspects. After a brief introduction of early studies, recent research advances of high strength steel structures in Tsinghua University in China are comprehensively reviewed. Systematic investigations have been carried out on static- and cyclic-loading behavior of high strength steels and their welded connections, residual stress of high strength steel hot-rolled and welded sections, overall and local buckling behavior of high strength steel columns under axial compression, seismic behavior of high strength steel columns under combined bending and compression, bearing and slip resistance of bolted connections with high strength steel slices. The research results show that mechanical behavior of high strength steel structures has been improved much compared with ordinary strength steel structures, so the design methods in current design codes or specifications need be updated to be applicable to high strength steel structures. Therefore, as the chief-editor institute, Tsinghua University has organized 34 institutes including universities, design and research institutes, steel structure fabricators, and steel manufacturers, to codify a new code, i.e. Design Specification of High Strength Steel Structures in China. Based on the above research results, new design methods and calculation formulae applicable to high strength steel structures are incorporated into this design specification. The outline of this specification is discussed in detail in this paper.
