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Two kinds of carbon-based nanozymes were constructed from the same precursor of zeolitic imidazolate framework-8 (ZIF-8) for O 2 •- determination. Hollow carbon cubic nanomaterial (labelled as HCC) was obtained by chemically etching ZIF-8 with tannic acid and a subsequent calcination. A porous carbon cubic nanomaterial (labelled as PCC) was prepared by directly pyrolysis. Then HCC and PCC were immobilized on the surface of screen printed carbon electrodes (SPCE), fabricating HCC and PCC modified electrodes (denoted as HCC/SPCE and PCC/SPCE). HCC/SPCE, best operated at -0.5 V (vs. Ag/AgCl), has a sensitivity of 6.55 × 10 2  nA μM -1  cm -2 with a detection limit of 207 nM (at S/N = 3) for O 2 •- sensing. And PCC/SPCE, best operated at -0.4 V (vs. Ag/AgCl), exhibited a superior performance for O 2 •- detection with a sensitivity of 1.14 × 10 3  nA μM -1  cm -2 and a low detection limit of 140 nM (at S/N = 3). The two sensors possess excellent reproducibility and stability. They were used to sense O 2 •- released from HeLa cells. Graphical abstract Illustration of the synthesis of the hollow carbon cubic nanomaterial (HCC) and of the porous carbon cubic nanomaterial (PCC), and the scheme for detection of superoxide anions in HeLa cell.

Transition metal phosphates have shown great potential as nanozymes for selective detection of reactive oxygen species (ROS), but its application has been hindered by the complicated synthesis and difficulty in shape and size control. Herein, we present a facile method to fabricate transition metal phosphates by using hollow carbon structures as substrates. Manganese phosphate is a typical Nanozyme used in this design and the shape and size of the Mn x (PO 4 ) y layer can be efficiently controlled by altering the carbon substrates. Characterization demonstrated that Mn x (PO 4 ) y layer modified hollow carbon sphere (Mn-MPSA-HCS) and hollow carbon cubic (Mn-MPSA-HCC) were successfully prepared and used as nanozymes for superoxide detection. The established electrochemical sensor was employed in the online monitoring of drug stimulated superoxide anions released from cancer cells. This method can be adapted as a general way to prepare transition metal phosphate layers with various controllable shapes and sizes as nanozymes for different uses in the future.

Here we present a new method to fabricate enzyme-mimic metal-free catalysts for electrochemical detection of superoxide anion (O 2 •- ) by introducing phosphate groups into graphene-based foam. Through a template-free hydrothermal process, graphene oxide (GO) was treated with different amount of phytic acid (PA) to obtain 3D porous graphene-based foam (PAGF). Characterizations demonstrate that phosphate groups were successfully modified on the surface and inter layer structure of PAGF materials and the defects and disorder degree of PAGF could be controlled by adjusting the addition of PA precursors. Meanwhile, the synthesized PAGF was successfully immobilized on screen printed carbon electrodes (SPCEs) and employed in O 2 •- detection. With PA treated on graphene structure, the resulted PAGF/SPCEs exhibit distinct characteristic redox peaks, showing enzyme-mimic catalytic activity toward O 2 •- dismutation. Also, the amount of modified phosphate groups has caused a considerable variety on the performance of PAGF-based electrodes. Apart from high sensitivity, wide liner range, low detection limit, good selectivity and long-term stability, our sensors also present satisfying performance in the real-time monitoring of drug-induced O 2 •- released from Hela cells. The reliability of the biological measurement was further demonstrated via electron paramagnetic resonance (EPR) to characterize the released O 2 •- from stimulated cells by using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) to trap the transient O 2 •- . The above results indicate that our established sensors hold potential application in the real-time detection of O 2 •- in biological samples., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The detection of superoxide anions (O 2 •- ) is widely considered as a potential way for cancer diagnosis and the development of enzyme-mimic catalysts is the main challenge in the establishment of electrochemical sensors for O 2 •- sensing in real samples. Here we present a novel enzyme- and metal-free electrochemical catalyst for superoxide (O 2 •- ) sensing based on the widely-used carbon nanotubes (CNT). Through a one-step hydrothermal process induced by phytic acid (PA), CNT-based porous foam (PACNTF) was successfully obtained. Characterizations demonstrated the enhanced defect and disorder degree of PACNTF after PA treatment, which leaded to the increased active sites of PACNTF for electron transfer and the adhesion of O 2 •- during the electrochemical process. As a result, the PACNTF presented higher conductivity and larger current response toward O 2 •- sensing when compared with CNT precursor and CNTF without PA treatment. The sensitivity of PACNTF/SPCE was calculated to be 1230 μA cm -2  mM -1 in the linear range of 0-193.6 μM (R 2  = 0.965) and 373 μA cm -2  mM -1 in the linear range of 193.6-1153.6 μM (R 2  = 0.995) with a limit of detection of 0.16 μM (S/N = 3). Further, the PACNTF/SPCE presented fast response toward cell-released O 2 •- stimulated by Zymosan A. The above results indicated that the fabricated sensor holds potential usage in biological samples., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Quantification of superoxide anions (O 2 •- ) is significant in the monitoring of many serious diseases and the design of enzyme-mimic catalysts plays the main role in the development of non-enzymatic O 2 •- sensors. Herein, we proposed a facile self-assembly process to synthesize manganese phosphate modified carbon networks using three kinds of widely-used carbon materials (MWCNTs, NGS and GO) as pillar connectors. Characterizations demonstrate that manganese phosphate is widely dispersed inside and on the surface of carbon networks without visible morphology. Meanwhile, all three kinds of synthesized catalysts were successfully immobilized on the screen-printed carbon electrodes to evaluate the electrochemical performance of fabricated sensors. The results indicate that sensors based on Mn x (PO 4 ) y modified MWCNTs exhibit high sensitivity with an extremely low detection limit of 0.127μM (S/N = 3) and a wide liner range of 0-1.817mM (R 2 = 0.998). We further employed the recommended sensors in the real-time monitoring of HepG2 cells released O 2 •- under the stimulating of Zymosan (20mg/mL). Noticeably, the proposed sensors exhibit not only sensitive response but also stable current steps upon different addition of Zymosan. The calculated concentrations of cell-released O 2 •- vary from 6.772 to 24.652pM cell -1 for the Zymosan amount used in this work. The established novel sensors display low background current and signal noises, thus holding unique advantages in the trace analysis of O 2 •- in biological samples and in vivo environment., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Considering the critical roles of superoxide anion (O2(∙-)) in pathological conditions, it is of great urgency to establish a reliable and durable approach for real-time determination of O2(∙-). In this study, we propose a porous Pt-Pd decorated superoxide dismutase (SOD) sensor for qualitative and quantitative detection O2(∙-). The developed biosensor exhibits a fast, selective and linear amperometric response upon O2(∙-) in the concentration scope of 16 to 1,536 μM (R(2)=0.9941), with a detection limit of 0.13 μM (S/N=3) and a low Michaelis-Menten constant of 1.37 μM which indicating a high enzymatic activity and affinity to O2(∙-). Inspiringly, the proposed sensor possesses an ultrahigh sensitivity of 1270 μA mM(-1)cm(-2). In addition, SOD/porous Pt-Pd sensor exhibits excellent anti-interference property, reproducibility and long-term storage stability. Beyond our expectation, the trace level of O2(∙-) released from living cells has also been successfully captured. These satisfactory results are mainly ascribed to (1) the porous interface with larger surface area and more active sites to provide a biocompatible environment for SOD (2) the specific biocatalysis of SOD towards O2(∙-) and (3) porous Pt-Pd nanomaterials fastening the electron transfer. The superior electrochemical performance makes SOD/porous Pt-Pd sensor a promising candidate for monitoring the dynamic changes of O2(∙-)in vivo., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Monitoring of reactive oxygen species like superoxide anion (O2(∙-)) turns to be of increasing significance considering their potential damages to organism. In the present work, we fabricated a novel O2(∙-) 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 O2(∙-) detection was systematically investigated by several electrochemcial techniques. Thanks to the specific biocatalysis of SOD towards O2(∙-) 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 O2(∙-) 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 O2(∙-) in biological systems., (Copyright © 2014 Elsevier B.V. All rights reserved.)

In the present work, a high-performance enzyme-based electrochemical sensor for the detection of superoxide anion radical (O2(●-)) is reported. Firstly, we employed a facile approach to synthesize PtPd nanoparticles (PtPd NPs) on chemically reduced graphene oxide (RGO) coated with polydopamine (PDA). The prepared PtPd-PDARGO composite was well characterized by transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectra, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical methods. Then the assembled composite was used as a desired electrochemcial interface for superoxide dismutase (SOD) immobilization. Owing to the PDA layer as well as the synergistic effect of PtPd NPs, the fabricated SOD/PtPd-PDARGO sensor exhibited an outstanding sensitivity of 909.7 μA mM(-1) cm(-2) upon O2(●-) in a linear range from 0.016 mM to 0.24 mM (R(2)=0.992), with a low detection limit of 2 μM (S/N=3) and excellent selectivity, good reproducibility as well as favorable long-term stability., (Copyright © 2015 Elsevier B.V. All rights reserved.)

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 Quantification of superoxide anions (O 2 −) is of great significance for the pathological research of many diseases. In this work, a non-enzymatic electrochemical sensor for superoxide sensing was fabricated on the basis of metal-organic frameworks (MOFs)-derived porous carbon matrix loaded with Pt and Co nanoparticles (denoted as Pt-Co-PC). Zeolitic imidazolate framework-67 (ZIF-67) was utilized as the precursor through a one-step calcination under N 2 atmosphere to prepare cobalt nanoparticles-porous carbon composites (denoted as Co-PC). Pt-Co-PC was then obtained by using a facile galvanic replacement procedure with Co-PC and chloroplatinic acid solution. Furthermore, the home-made screen printed gold electrodes (SPGEs) were used to immobilize the as-synthesized materials, constructing Pt-Co-PC modified electrochemical sensors. The recommended Pt-Co-PC/SPGE sensors exhibit excellent electrochemical performance for the detection of O 2 − with an extremely low detection limit of 0.118 μM (S/N = 3) and a high sensitivity of 6.218 × 10−4 mA μM−1 cm−2. Meanwhile, the proposed sensors possess superior reproducibility and stability. More importantly, our sensors have successfully captured the electrochemical signals of O 2 − released from Hela cells, which means the fabricated sensors have potential application of monitoring O 2 − in pathological and biological fields. Highlights • A facile method to fabricate porous carbon matrix loaded with Pt and Co nanoparticles. • A novel non-enzymatic O 2 − sensor was established. • The recommended sensors can successfully capture the electrochemical signals of O 2 − released from Hela cells. [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]

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]

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]

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]

• 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]

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]