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An enzyme-free, metal-free, and preconcentration-free electrochemical sensor for pentachlorophenol assay has been fabricated. The interface of the sensor is based on a hollow zeolitic imidazolate framework–derived mesoporous carbon material (denoted as HZC/SPCE). The sensor exhibits linear amperometric response upon pentachlorophenol at 0.82 V (vs. Ag/AgCl) in the concentration range 0.001 to 26.8 mg L−1 (3.75 × 10−8~1.006 × 10−4 M) (R2 = 0.997). The sensitivity of HZC/SPCE is 3.53 × 102 μA mM−1 cm−2 with a detection limit of 2.05 × 10−9 M (S/N = 3) for pentachlorophenol. The method has been applied to the determination of pentachlorophenol in spiked food packaging samples with recoveries in the range 92.0 to 107.0%. [ABSTRACT FROM AUTHOR]

Here we established a palm‐sized electrochemical sensor for the determination of cell‐released superoxide anions (O2.−) based on a self‐developed portable potentiostat (xenSTAT) which can perform fast analysis with visual real‐time data and customizable parameters. The xenSTAT was equipped with Bluetooth and USB interfaces, thus being able to be connected with both smartphones and computers for electrochemical analysis. A novel Nanozyme based on Mnx(PO4)y monolayer modified porous carbon cubic was synthesized and used as functional material on the surface of working electrode. By using cyclic voltammetry (CV) and chronoamperometry, xenSTAT was demonstrated to exhibit satisfying sensitivity and excellent stability for real‐time monitoring of O2.− released from cancer cells. With decreased cost, customizable development, small size and convenient usage, the xenSTAT described in this work could promote the commercialization and widespread of in‐house built electrochemical sensors for the monitoring of O2.− in the future. [ABSTRACT FROM AUTHOR]

Abstract: The performance of electrochemical sensors is mainly limited by the intrinsic properties of electrocatalysts fabricated on the electrode. Introducing a p‐n heterojunction into semiconducing electrocatalysts is an effective strategy to enhance the sensing performance. In this paper, p‐n‐heterojunction‐based CuO/CeO2 nanocomposites were synthesized by a simple hydrothermal process, and the effect of different Cu/Ce molar ratios was explored. p‐CuO/n‐CeO2 was found to exhibit higher conductivity and electrocatalytic activity toward the target superoxide anion (O2.−) when compared to both bare CuO and CeO2. Characterization shows that different Cu/Ce ratios in p‐CuO/n‐CeO2 materials result in a considerable variation in the Ce3+/Ce4+ level, and energy band gap of CeO2, greatly affecting the electrochemical performance of p‐CuO/n‐CeO2. Under optimized conditions, these sensors exhibit high sensitivity and low detection limit toward O2.−. These results demonstrate that the performance of semiconductor‐based electrochemical sensors may be enhanced by the electron‐transfer process of p‐n junction interfaces. [ABSTRACT FROM AUTHOR]

Abstract: The sluggish kinetic-controlled glucose oxidation reaction on Pt electrodes is well recognized as the most critical issue that blocks the development and commercialization of enzyme-free glucose sensors, and increasing attention is being focused on improving the analytical performances of these nonenzymatic sensors through exploring new Pt-based catalysts. In the present research, we synthesized novel Pt–Pd nanoflakes (Pt–Pd NFs) with three-dimensional architectures on a homemade screen-printed gold film electrode (SPGFE) substrate using a facile electrochemical deposition without any template, and further investigated the properties of the as-fabricated Pt–Pd NFs/SPGFE for enzymeless glucose detection. The results reveal that the proposed Pt–Pd nanostructure can provide preeminent electrocatalytic activity and excellent selectivity for enzyme-free glucose sensing under simulative physiological conditions, mainly attributing to its attractive structure, large active surface and appropriate applied potential. The resulting Pt–Pd NFs/SPGFE offers linear current responses for glucose with the concentration upper limit to 16mM. The obtained sensitivity is calculated to be as high as 48.0μAcm−2 mM−1 in the presence of 0.15M chlorides ions, and practical applications for blood sample analysis are also demonstrated. The proposed Pt–Pd structure is considered as a great potential building block for the fabrication of nonenzymatic electrochemical glucose sensors. [Copyright &y& Elsevier]

Electro-oxidizing glucose effectively is well known as the critical point in developing analytical sensors and carbohydrate-based fuel cells. Here we prepared a new electrode material, platinum nanoparticles encapsulated in carbon microspheres (Pt/GSH), to promote the glucose electrocatalytic oxidation reaction in neutral media. The Pt/GSH composite was synthesized by using a simple hydrothermal method, with reduced glutathione (R-GSH) as the capping agent and reductant simultaneously, followed by a calcination process. It was found that the obtained Pt particles with a mean size of 26.8 nm were well dispersed in the interconnected carbon microspheres, providing a stable and efficient catalytic platform for glucose electro-oxidation. As a result, the synthesized catalyst exhibited higher activity for electro-catalyzing glucose compared to commercial Pt black and Pt/C catalysts, with a mass activity of 15.4 μA μg −1 Pt , approximately 13 times of Pt black and 2.1 times of Pt/C. Besides, due to the decreased dissolution and agglomeration of Pt NPs in the carbon-encapsulated structure, the Pt/GSH catalyst kept quite stable activity upon reuse even in the presence of chloride ions. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel strategy for the simultaneous detection of Cd(II) and Pb(II) with high sensitivity is proposed. • Nitrogen-doped carbon-encapsulates Bi nanoparticles were synthesized. • Nitrogen-doped carbon nanosheets can help to improve electronic conductivity. • Uniformly dispersed Bi nanoparticles provide abundant active sites. Cadmium (Cd) and lead (Pb) are two of the most toxic heavy metals, which cause serious pollution to the environment. It is of great significance to develop electrochemical sensing platforms that can be used for the efficient and simultaneous detection of Cd(II) and Pb(II). Herein, bismuth nanoparticles encapsulated in nitrogen-doped carbon nanosheets (Bi@NC) were successfully synthesized. An electrochemical sensor based on Bi@NC was proposed for the high-performance determination of trace Cd(II) and Pb(II). Encapsulated and uniformly distributed Bi nanoparticles with abundant active sites form alloys with Cd(II) and Pb(II), and the conductive nitrogen-doped carbon nanosheet accelerates the electron transport rate, thus the electrochemical signals of Cd(II) and Pb(II) are significantly amplified. Under optimized conditions, Cd(II) and Pb(II) can be simultaneously detected in concentrations ranging from 1 to 150 μg L−1, with sensitivity of 0.48 μA μg−1 L and 0.36 μA μg−1 L, respectively. Meanwhile, the sensor possesses the outstanding advantages of ultra-high sensitivity, excellent selectivity, and storage stability, being able to serve as an electrochemical platform for Cd(II) and Pb(II) sensing in fruit and river water. [ABSTRACT FROM AUTHOR]

• CeO 2 /Co 3 O 4 materials with porous structure by calcination of ZIF-67. • The CeO 2 /Co 3 O 4 nanocomposites show high electrochemical activity towards DA. • The synergistic effect of CeO 2 /Co 3 O 4 enhances the electrocatalytic properties. • Sensor has excellent selectivity and reproducibility for dopamine in real samples. In the field of biosensing and disease diagnosis, rapid and sensitive detection of dopamine (DA) is essential. In this work, Co 3 O 4 with a porous structure was prepared by temperature-controlled calcination of the precursor template zeolite imidazole framework-67 (ZIF-67), and CeO 2 /Co 3 O 4 composites with a porous framework structure were prepared by hydrothermal methods. The porous structure of the Co 3 O 4 prevented the aggregation of the CeO 2 nanoparticles and allowed them to be dispersed in a uniform manner on the surface. The CeO 2 introduction led to changes in the specific surface area and pore size of the calcined Co 3 O 4 material, and more active sites were exposed, allowing better binding with CeO 2 thus achieving good catalytic performance and excellent synergistic properties. The CeO 2 /Co 3 O 4 modification on the surface of glassy carbon electrodes (GCE) showed good electrocatalytic activity, which was superior to that of pure Co 3 O 4 and CeO 2 , as determined by electrochemical methods, thanks to. The results show that CeO 2 /Co 3 O 4 /GCE has a limit of detection (LOD) of 0.13 μM for DA (S/ N = 3) and a linear range of 0.13 μM-60 μM, as well as good interference resistance and reproducibility. This work provides a new solution for excellent dopamine sensors in Co 3 O 4 and CeO 2 composites, which can be extended to other biosensing applications. Schematic diagram of a glassy carbon electrode based on CeO 2 /Co 3 O 4 nanocomposite for DA determination. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • PtPd@ERGO-CNT-CFME was prepared by adsorption and stepwise electro-deposition. • The unique morphology of dendrite PtPd alloy exposed abundant catalytic sites. • The microsensor achieved the detection of O 2 − with high sensitivity. • The microsensor realized the monitoring of O 2 − released from living cells. In this work, the carbon fiber microelectrode (CFME) coated by ERGO-CNT network was used as a substrate to support dendrite PtPd nanoclusters. An enzyme-free O 2 − electrochemical sensor (PtPd@ERGO-CNT-CFME) was prepared based on this strategy. Due to the brilliant loading and dispersing abilities of the substrate and the excellent electrochemical activity of the dendrite PtPd alloy, PtPd@ERGO-CNT-CFME demonstrated outstanding detection ability towards O 2 −. The as-constructed sensor showed a wide-linear range of 16–744 μM and 744–3064 μM with high sensitivity of 6967.3 μA mM−1 cm−2 and 4124.3 μA mM−1 cm−2, and the detection limit was 5.07 μM. Furthermore, PtPd@ERGO-CNT-CFME was successfully applied to monitor O 2 − released from living cells. This phenomenon indicated the application potential for O 2 − detection in biological samples. [ABSTRACT FROM AUTHOR]

The trend of developing electrochemical sensors toward cellular level detection put forward higher requirements of the electrodes in the detection performance. However, common disk electrodes or conventional screen printing electrodes meet up with some limitations in the electrocatalytic activity and electron transfer capability. In this work, we applied inkjet printing technology to fabricate electrodes to make some improvements. Highly conductive Ag nanoparticles based electrodes were obtained on plastic substrate by inkjet printing technology followed by a sintering process at room temperature. The resistivity of IPAgE is determined to be 64.0 ± 5.3 μΩ cm. With better conductivity and the nanoparticle-based interface, superb electrochemical response of IPAgE for H 2 O 2 was obtained, nearly 300-fold higher than the conventional screen printed Ag electrode. Moreover, high sensitivity of 287 μA mM −1 cm −2 with a LOD of 5.0 μM was obtained under the optimized 20 printed layers. The inkjet printed Ag electrodes were also credibly applied in the detection of H 2 O 2 release from living cells. This work demonstrates inkjet printing is a promising method for the high performance electrochemical sensors. [ABSTRACT FROM AUTHOR]

The electrochemical sensors with the ability of biomolecule detection can be used for human life and health monitoring. In this work, we developed an electrochemical sensor with a Schottky junction by electrostatic interaction, composed of Nb 2 C MXene and MnFe 2 O 4. Large reactive groups (O, OH, Cl, or F) are observed at the ends of the Nb 2 C MXene surface. Meanwhile, there are abundant oxygen vacancies and surfaces of MnFe 2 O 4 which bring it favorable heterogeneous catalytic properties. Among them, the chemical self-assembly of MnFe 2 O 4 nanoparticles on Nb 2 C MXene enhances the binding strength of the material through electrostatic interaction, promotes charge transfer across the interface, and modulates the electronic and nanostructural characteristics of the N-MFO (MnFe 2 O 4 /Nb 2 C MXene). The results demonstrate that the sensing performance of N-MFO4 for Acetaminophen (AP) and Dopamine (DA) is significantly improved compared to Nb 2 C MXene and MnFe 2 O 4 modified electrodes, respectively. The obtained limits of detection (LOD) of N-MFO4 modified electrode for AP and DA being 0.079 and 0.070 μM, respectively. The combination of electrodes modified with highly active nanomaterials is supposed to build a portable electrochemical analysis system with high sensitivity, good selectivity, favorable stability, simple operation and low cost, and promote the application of electrochemical sensors in related fields. [Display omitted] • Self-assembled N-MFO materials with electrostatically bonded Schottky junctions. • Heterogeneous structure of N-MFO with high conductivity and large active surface. • Dual-function N-MFO sensors exhibit excellent detection characteristics. [ABSTRACT FROM AUTHOR]

In this work, a highly sensitive enzyme- and metal-free electrochemical method for superoxide anion (O 2 − ) detection has been developed by employing screen-printed carbon electrodes (SPCE) modified by nitrogen doped hollow mesoporous carbon spheres (N-HMCS). For comparison, solid carbon spheres (SCS) and hollow mesoporous carbon spheres (HMCS) were also synthesized to fabricate the modified SPCE. Compared with SCS/SPCE and HMCS/SPCE, N-HMCS/SPCE displayed a higher electrochemical performance. When applied for electrochemical detection of O 2 − , N-HMCS/SPCE exhibited a high sensitivity of 1.49 μA cm −2 μM −1 , better than SCS/SPCE and HMCS/SPCE and many of enzyme- or metal-based superoxide anion sensors. N-HMCS is expected to become a new generation of sensing materials for electrochemical analysis of O 2 − . [ABSTRACT FROM AUTHOR]

Rapid and accurate detection of nicotine is important due to its detrimental effects on human beings and recent surge in the usage of electronic cigarettes. In this paper, we report an electrochemical sensor for nicotine detection by using screen-printed carbon electrodes (SPCE) modified with nitrogen-doped graphene sheets (NGS). NGS was synthesized and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectrometry. Due to the superior electron transfer capability and the doped nitrogen atoms, NGS shows high catalytic activity for the electro-oxidation of nicotine, with a significant decrease in the overpotential. Using the NGS-based nicotine sensor, we obtained detection sensitivity at 0.627 mA·cm − 2 mM − 1 with the limit of detection at 47 nM nicotine. Moreover, the sensor shows favorable selectivity and long-term stability for detecting nicotine in urine and tobacco samples. [ABSTRACT FROM AUTHOR]

The construction of uniformly dispersed structure with abundant active sites is crucial for fast electron transport and advancing electrocatalytic reactions. Herein, Fe x Co y O 4 -rGO was prepared by depositing Fe and Co bimetallic oxides in-situ on reduced graphene oxide through a simple process combined hydrothermal reaction and calcination. Fe was elaborately introduced into the synthesis of metal oxides to alleviate the aggregation of cobalt oxides and obtain nanocomposites with homogeneously structured and abundant redox sites, and the bimetallic oxides nanomaterials had enhanced electrocatalysis under the synergistic effect. The flexible electrode prepared from Fe x Co y O 4 -rGO exhibited excellent detection performance for glucose with a detection limit down low to 0.07 μM and a sensitivity of 1510 μM cm−2 mA−1. The adoption of flexible substrates improved the wearability of the electrode and broadened its practicality for detecting biomarkers on the skin surface. The constructed sensor was successfully used in the dynamic analysis of glucose content in tears, and the results were highly consistent with the test outcome of a commercial test kit, demonstrating its application prospects in non-invasive epidermal diabetes mellitus diagnosis. [Display omitted] • A novel bimetallic oxides composite was designed for sensitive glucose detection. • The introduction of Fe led the formation of composite with a uniformly dispersed structure. • The constructed flexible electrode was applied to the accurate detection of glucose in human tears. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) porous carbon-based composite nanosheets loaded with metal oxide nanoclusters are expected to be promising electrocatalysts for high-performance electrochemical sensors. However, for this complicated composite material, strict reaction conditions and complex synthesis steps limit its general application in electrochemical detection. Here we present a facile method to fabricate 2D mesoporous nitrogen-rich carbon nanosheets loaded with CeO 2 nanoclusters (2D-mNC@CeO 2), for fabricating superoxide anions (O 2 •−) electrochemical sensor. The method is based on block copolymers self-assembly and the affinity of polydopamine to metal ions to obtain organic-inorganic hybrid, which can be directly converted into 2D-mNC@CeO 2 through carbonization strategy without structural deterioration. Characterizations demonstrate that the 2D-mNC@CeO 2 owned the 2D N-doped carbon structure with an interlinked hierarchical mesoporous and the uniformly dispersed CeO 2 nanoclusters on the surface. Benefitted from the unique structure, the 2D-mNC@CeO 2 shortens electron transfer distance, enhances mass transfer efficiency, exposes numerous active sites, and obtain a high Ce3+/Ce4+ ratio for improving electrocatalytic performance. The 2D-mNC@CeO 2 /SPCEs sensors for O 2 •− detection has a detection limit of 0.179 μM (S/N = 3) and sensitivity of 401.4 μA cm-2 mM-1. The sensors can be applied to capture electrochemical signals of O 2 •− released from HepG2 cells, demonstrating the application potential of the sensors to monitor O 2 •− in biological fields. [ABSTRACT FROM AUTHOR]

With respect to a nonenzymatic electrochemical sensor for detection of small biomolecules like glucose, it is well recognized that an interface with highly electrocatalytic properties is desired. Our previous studies have demonstrated that porous Cu foams from hydrogen evolution assisted electrodeposition could provide beneficial structures for large active surface and mass transfer in glucose sensing ( Biosens. Bioelectron. , 2014, 51: 22-28), and decoration of micro-scale Pt cubes on this multiaperture substrate through manipulative deposition offered exciting activity and stability for electro-catalyzing glucose in neutral media ( Chem. Eur. J. , 2013, 19: 9534-9541). On the basis of these results here we further cover the porous Cu frameworks with a Pt monolayer through the galvanic replacement reaction, and fabricate a new electrochemical interface for high-performance determination of glucose. The sensing surface was facilely assembled by firstly electrodepositing porous Cu architectures with hydrogen evolution and then galvanically replacing the surface layer with Pt, and was well characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and energy dispersive spectroscopy. It was found that the unilaminar Pt-replaced Cu frameworks, with the profitable reaction surface derived from porous skeletons and the underlying activity of Pt-support composites, could supply the highly electrocatalytic oxidation of glucose in phosphate buffer solution (pH 7.4). As a result, the prepared enzymeless sensor provided linear amperometric responses for glucose in the concentration scope of 1∼11 mM, with a high sensitivity of 9.62 μA cm −2 mM −1 . [ABSTRACT FROM AUTHOR]

Monitoring of reactive oxygen species like superoxide anion (O 2 ∙− ) turns to be of increasing significance considering their potential damages to organism. In the present work, we fabricated a novel O 2 ∙− electrochemical sensor through immobilizing superoxide dismutase (SOD) onto a Pt–Pd/MWCNTs hybrid modified electrode surface. The Pt–Pd/MWCNTs hybrid was synthesized via a facile one-step alcohol-reduction process, and well characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. The immobilization of SOD was accomplished using a simple drop-casting method, and the performance of the assembled enzyme-based sensor for O 2 ∙− detection was systematically investigated by several electrochemcial techniques. Thanks to the specific biocatalysis of SOD towards O 2 ∙− and the Pt–Pd/MWCNTs – promoted fast electron transfer at the fabricated interface, the developed biosensor exhibits a fast, selective and linear amperometric response upon O 2 ∙− in the concentration scope of 40–1550 μM ( R 2 =0.9941), with a sensitivity of 0.601 mA cm −2 mM −1 and a detection limit of 0.71 μM ( S / N =3). In addition, the favorable biocompatibility of this electrode interface endows the prepared biosensor with excellent long-term stability (a sensitivity loss of only 3% over a period of 30 days). It is promising that the proposed sensor will be utilized as an effective tool to quantitatively monitor the dynamic changes of O 2 ∙− in biological systems. [ABSTRACT FROM AUTHOR]

Abstract: Facilitating the glucose electro-oxidation reaction is always of great scientific sense due to its wide applications in sensing, catalysis and biofuel cells. On the road to improving the electrocatalysis of glucose, one-dimensional materials mainly including nanowires and nanotubes are commonly proposed because of their fascinating characters, and both of them are reported capable of offering better catalytic performance compared to commercial Pt/C and Pt black catalysts. However, so far it still confuses us that which structure can provide more favorable properties towards the direct electro-oxidation of glucose. Here we carry out a systematically comparative study of nonenzymatic electrochemical sensors based on vertical nanowire and nanotube arrays for glucose detection. By using bimetallic Pt-Pd as a general model, we demonstrate that nanotube arrays, owing to their larger catalytic area and higher catalyst utilization, show higher activity for glucose electro-oxidation and enzyme-free analysis than nanowire arrays. These findings may be helpful for the future design of more efficient catalyst structures for glucose oxidation and other reactions. [Copyright &y& Elsevier]

Abstract: It is widely thought in electro-biochemical analysis that the sensing interfaces play a key role in the enzymeless detection of biomolecules like glucose, ascorbic acid, dopamine and uric acid. On the way to maximize the anti-poisoning sensitivity of nonenzymatic electrochemical glucose sensors as well as achieve favorable selectivity, we propose here a porous interface fabricated by a facile but effective approach for glucose monitoring in alkaline media containing dissolved oxygen. The sensing interface based on porous Cu foams is directly formed on a homemade disposable screen-printed carbon electrode (SPCE) substrate by electrodeposition assisted with hydrogen evolution simultaneously, and its porosity can be easily tailored through adjusting deposition conditions for the optimal electrocatalytic oxidation of glucose molecules. SEM and BET studies show that the generated Cu foam possesses robust hierarchical porous architectures with greatly enhanced surface area and pore volume, beneficial for the unimpeded mobility of glucose and reaction products. Cyclic voltammetric tests indicate that a diffusion-controlled glucose electro-oxidation reaction occurs at the Cu foam electrode at around +0.35V vs. Ag/AgCl in 0.1M NaOH. Chronoamperometric results obtained under optimized conditions reveal that the proposed sensor exhibits desired poison resistance ability in the presence of chloride ions and significant selectivity to glucose, providing fascinating sensitivities of 2.57 and 1.81mAcm−2 mM−1 for glucose in the linear concentration ranges of 2–80μM and 0.1–5mM, respectively. The limit of detection is calculated to be as low as 0.98μM according to the signal-to-noise ratio of three. In addition, the fabricated sensing interface shows attractive reproducibility (RSD of 5.1% and 7.0% for 15 repeated measurements on a sensor and for measurements on 15 prepared sensors, respectively) and outstanding long-term stability (less than 5% loss in sensitivity over 1 month) for glucose detection. The application of the Cu foam based sensor for monitoring glucose in practical samples is also successfully demonstrated. [Copyright &y& Elsevier]

Abstract: In this paper, a novel electrochemical biosensor for Hg2+ determination based on Hg2+-induced DNA hybridization is reported. A pair of oligonucleotides with seven strategically placed thymine–thymine (T–T) mismatched bases was introduced. Firstly, one oligonucleotide (P1) modified with hexanthiol at 5-terminal was immobilized on a screen-printed gold electrode (SPGE) via self-assembly. Then the other oligonucleotide (P2) tagged with a ferrocene derivative as electroactive indicator was able to hybridize with P1 by forming thymine–Hg2+–thymine (T–Hg2+–T) complexes in the presence of Hg2+, providing a detectable electrochemical signal of the ferrocene derivative. However, when Hg2+ was absent, the two oligonucleotides could not hybridize due to the T–T mismatched bases, and P2 could not be fixed on the electrode surface, with the indicator signal disappearing. Experimental results indicate that the proposed biosensor offers linear responses on Hg2+ concentration in the range of 10–0.001μM, with a detection limit of 0.6nM (S/N=3). This new Hg2+-induced DNA hybridization strategy is demonstrated valid and efficient to detect trace Hg2+ with high sensitivity and good selectivity. [Copyright &y& Elsevier]

[Display omitted] • A sandwich-type electrochemical biosensor for ctDNA detection was designed through facile steps. • The synthesized MWCNTs-PDA-Au-Pt shows excellent catalytic capacity and was used as SPs' label for signal amplification. • The electrochemical biosensor exhibits satisfactory sensitivity for ctDNA detection. • The proposed sandwich-type scheme is a promising method in clinical ctDNA diagnosis. It is of great importance to accurately analyze circulating tumor DNA (ctDNA), for the reason that it serves as one of the particularly informative cancer biomarkers for disease diagnosis, therapy, and prognosis. However, sensitive detection of ctDNA remains a challenging task and the design of feasible sensing method plays a significant role in ctDNA analysis. In this work, a novel sandwich-type electrochemical biosensor was developed through a facile way for sensitive detection of ctDNA using nanocomposites (MWCNTs-PDA-Au-Pt) as signal probes' (SPs) label (SPs-label) for signal amplification. The current response of the nanocomposites towards H 2 O 2 reduction was used to quantitatively detect target DNA and distinguish base-mismatched DNA sequences. Characterizations reveal that Au-Pt alloy nanoparticles are uniformly dispersed on MWCNTs-PDA and the resultant MWCNTs-PDA-Au-Pt shows excellent response toward the reduction of H 2 O 2 , which could largely amplify the current response. Electrochemical analysis of electrode modification process confirms that the sandwich-type structure was successfully formed through step-wise reactions, including fixation of capture probes (CPs) on the surface of the screen-printed gold electrode, recognition between CPs and target DNA (T-DNA), hybridization between T-DNA and SPs. Under optimal experimental conditions, the proposed ctDNA biosensor exhibits a wide linear range from 1 × 10−15 to 1 × 10−8 mol/L with a detection limit as low as 5 × 10−16 mol/L (S/N = 3), unprecedented selectivity towards T-DNA and other base-mismatched DNAs (even for only single base-mismatched sequences), and superb long-term stability. This work demonstrates the sandwich-type scheme is a promising method for practical applications in clinical ctDNA diagnosis. [ABSTRACT FROM AUTHOR]

[Display omitted] • A kind of hydrogel based on dopamine polymer doped polypyrrole (PDA-PPy) was synthesized in rapid one-pot method. • PDA-PPy hydrogel exhibited selective adsorption capacity for Pb(II). • PDA-PPy/SPCE showed good sensing performance for Pb(II) detection. Lead is one of the most common toxic heavy metals in the environment and it is easily accessible by the human body because there are residues in daily necessities and food. Therefore, it is significant to develop the high-performance detection method of lead ion (Pb(II)) in the environment and food. In this work, a sensitive and selective electrochemical sensing platform of Pb(II) was successfully constructed based on dopamine polymer doped polypyrrole (PDA-PPy) hydrogel modified screen-printed carbon electrode (SPCE) (noted as PDA-PPy/SPCE). PDA-PPy hydrogel was prepared by the hybridization of dopamine hydrochloride and pyrrole through a rapid and eco-friendly one-step synthesis method. Combined the selective adsorption capacity and good conductivity of PDA-PPy hydrogel, it was employed as the modified material for electrodes to achieve signal amplification. The result showed that PDA-PPy/SPCE exhibited excellent sensing performance towards Pb(II) with low detection limit of 0.15 μg L-1 and high sensitivity of 0.17 μg L-1 μA-1. Besides, acceptable recoveries were shown in real sample analysis, indicating that it has application prospects. [ABSTRACT FROM AUTHOR]

Here we presented a new facile strategy to fabricate ultrathin two-dimensional (2D) metal oxide nanosheets, by using polydopamine-coated graphene (rGO@PDA) as a template under simply wet-chemical conditions. Based on the strategy, graphene-like CeO 2 –TiO 2 mesoporous nanosheet (MNS-CeO 2 -TiO 2) was prepared and was loaded with dispersive Ag nanoparticles (AgNPs) to obtain effective electrocatalysts (denoted as Ag/MNS-CeO 2 -TiO 2) for electrochemical detection of superoxide anion (O 2 •−). Characterizations demonstrated that MNS-CeO 2 -TiO 2 exhibited ultrathin thickness, larger specific surface area, and pore volume in comparison with its bulk counterpart. The above properties of MNS-CeO 2 -TiO 2 shorten electron transmission distance, promotes mass transfer, and is conducive to the dispersion of post-modified AgNPs. Therefore, the recommended Ag/MNS-CeO 2 -TiO 2 sensors (denoted as Ag/MNS-CeO 2 -TiO 2 /SPCE) exhibited satisfactory properties, including the sensitivity of 737.1 μA cm−2 mM−1, the detection limit of 0.0879 μM (S/N = 3), and good selectivity. Meanwhile, the sensors also successfully realized in the online monitoring of O 2 •− released from HepG2 cells, meaning the prepared sensors had practical application potential towards the analysis of O 2 •− in biological samples. • A novel facile strategy for preparing ultrathin 2D metal oxide nanosheets was presented. • Based on above strategy, Ag/MNS-CeO 2 -TiO 2 were prepared with controllable morphology. • The superoxide anion (O 2 •−) electrochemical sensor was successfully fabricated with Ag/MNS-CeO 2 -TiO 2. [ABSTRACT FROM AUTHOR]

• MnFe 2 O 4 nanoparticles were evenly distributed on the rGO via a facile solvothermal method. • Synergetic effect of MnFe 2 O 4 and rGO provided enhanced performance for H 2 O 2 sensing. • MnFe 2 O 4 /rGO nanocomposites exhibited high current response with a LOD of 0.528 nM. Hydrogen peroxide (H 2 O 2) is a common oxidant and major active oxygen species in organisms. There is a great requirement for the accurate and rapid determination of H 2 O 2 in the fields of environmental analysis, clinical treatment, food safety, pharmaceuticals, etc. The electrochemical method is considered an ideal analytical technology due to its high sensitivity, fast response and low detection limit. Herein, a one-pot solvothermal synthesis method was used to prepare a manganese ferrite/reduced graphene oxide (MnFe 2 O 4 /rGO) composite, which was modified on the surface of home-made screen-printed electrodes to construct a new type of electrochemical sensor for the determination of H 2 O 2 , subsequently. Cyclic voltammetry and chronoamperometry were used to study the electrocatalytic performance of H 2 O 2 reduction in neutral conditions. The results showed that the sensor had good electrocatalytic activity for the reduction of H 2 O 2. The response time of the sensor is 5 s, and the linear detection range is 0.1 ~ 4.0 mM (R2 = 0.9991) with a low detection limit of 0.528 nM. Such sensor exhibited good long-term stability, and good anti-interfering ability from potential interfering species of glucose, ascorbic acid, dopamine, fructose and uric acid during the determination. This study thus provides a potential method to construct novel type of H 2 O 2 for practical application. [ABSTRACT FROM AUTHOR]

• Hierarchically porous carbon networks (HPCN) were prepared through TMB-induced self-assembly and carbonization strategy. • The introduction of TMB results in changed morphology, enriched pore structure, and improved defect degree. • The O 2 − sensor HPCN/SPCE has the potential to distinguish between cancer and normal cells by detecting cell-released O 2 −. Realizing the quantitative detection of superoxide anions (O 2 −) is of great significance to the pathological research based on the correlation between O 2 − and many diseases. Currently, the main challenge for O 2 − electrochemical detection in the actual sample is the development of effective nano-mimetic materials to replace natural enzymes to achieve high-selectivity detection of O 2 −. In this work, hierarchically porous carbon networks (HPCN) were successfully prepared through 1,3,5-trimethylbenzene (TMB)-induced self-assembly and carbonization strategy. Owing to the introduction of TMB, HPCN obtains the changed morphology, enriched pore structure, and improved defect degree, which promotes mass transfer and leads to faster electron transfer efficiency. Therefore, the non-enzymatic O 2 − electrochemical sensor fabricated with HPCN (denoted as HPCN/SPCE) exhibits high sensitivity (607.4 μA cm−2 mM-1) and excellent selectivity for detecting O 2 −. Importantly, the sensor successfully achieved the dynamic monitor of O 2 − released from living cells and has the potential to distinguish between cancer and normal cells. [ABSTRACT FROM AUTHOR]

• A simple modification method on carbon fiber microelectrodes (CFME) via in-situ reduction of AuAg bimetallic nanoparticles by polydopamine was proposed, and it offered a universal strategy to decorate novel metals onto microelectrode for different application in the future. • The bimetal synergistic effect enabled AuAg bimetallic decorated electrodes exhibited higher electrocatalytic activity (compared with Au and Ag monometallic decorated electrodes), showing an obvious enhancement toward H 2 O 2 sensing. • With a low detection limit (0.1 μM), the prepared 2Au1Ag-PDA/CFME was capable of detecting H 2 O 2 released from HepG2 living cells, indicating a potential usage of the fabricated electrode for H 2 O 2 detection in cancer cells. In this work, a facile in-situ reduction method was developed for the modification of carbon fiber microelectrode (CFME) to build novel electrochemical sensors for the detection of H 2 O 2. The polydopamine (PDA) was employed as the surface modification material for one-step decoration of AuAg bimetallic nanoparticles through in-situ reduction on the surface of PDA/CFME. Compared to Au-PDA/CFME and Ag-PDA/CFME, 2Au1Ag-PDA/CFME (immersed PDA/CFME in AgNO 3 for 1 h, HAuCl 4 •4H 2 O for 2 h in order) exhibited higher electrocatalytic activity toward H 2 O 2 sensing due to bimetal synergism. Under the optimal condition, the 2Au1Ag-PDA/CFME appeared a wide linear range of 0 μM - 55 μM (R2 = 0.990), 55 μM – 2775 μM (R2 = 0.991) with high sensitivity (12966 μA mM−1cm−2, 0–55 μM; 2534 μA mM−1 cm−2, 55–2775 μM), and low detection limit (0.12 μM). Furthermore, good selectivity and repeatability of 2Au1Ag-PDA/CFME favored its applications in biological samples, especially in cellular level. The detection of H 2 O 2 released from HepG2 living cells was realized by applying 2Au1Ag-PDA/CFME, indicating a potential usage of the fabricated electrode for H 2 O 2 detection in cancer cells. In addition, the above simple in-situ reduction method based on PDA's adhesion and reducibility offered a universal strategy to decorate noble metals onto microelectrode for different application in the future. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Developing nanomaterials as alternatives of enzymes is of great significance to realize qualification and quantitation of superoxide anion (O 2 −), which has been proved to play a crucial role in physiological condition. In this work, a novel electrochemical catalyst of cobalt nanoparticle doped porous cubic carbon (Co-PCC) was prepared through the calcination of zeolitic imidazolate framework-67 (ZIF-67), which was obtained from one-step synthesis. Then Co-PCC was used to construct enzyme-free electrochemical sensor for the detection of O 2 −. The response of H 2 O 2 , though much lower than that of O 2 −, was also caught by the Co-PCC/SPCE. The fabricated sensor exhibited obvious response towards O 2 − in the range of 0.8–76.8 μM (R2 = 0.997) with a high sensitivity of 3.59 × 10−4 mA μM−1 cm−2 and a limit of detection of 0.41 μM (S/N = 3). In addition, the proposed sensor can be used to detect O 2 − released from SK-BR-3 cells, which makes it possible to monitor the dynamic change of O 2 − in living cells. Unlabelled Image • Enzyme-free electrochemical sensor was developed for in-house electrochemical analysis. • A novel SOD-mimic nanozyme based on ZIF-67 was obtained from one-step synthesis. • The established sensor was used for electrochemical sensing of superoxide anions released from living cell. [ABSTRACT FROM AUTHOR]