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.

In this work, we fabricated a yolk–shell magnetic composite that contains mesoporous TiO2 as the inner shell and flowerlike NiO as the outer shell (denoted as Fe3O4@H-TiO2@f-NiO) to reduce the limitations of single-component metal oxides in phosphopeptide enrichment. The NiO nanosheets play a synergistic role in phosphopeptide enrichment. And the unique flowerlike structure of NiO with sufficient space can facilitate the reversible insertion/extraction of peptides, which will have less impact on the enrichment process of the inner TiO2 shell. The yolk–shell structure and two types of porous nanostructures endowed this composite with a high surface area (156.58 m2 g−1) and a large pore volume (0.37 cm3 g−1). Owing to the high surface area and combined properties of TiO2 and NiO, the Fe3O4@H-TiO2@f-NiO microspheres showed a better performance for phosphopeptide enrichment than the same material without NiO nanosheets (Fe3O4@H-TiO2). According to the LC-MS/MS results, 972 unique phosphopeptides were identified from HeLa cell extracts with a high selectivity (91.9%) by Fe3O4@H-TiO2@f-NiO relative to 837 phosphopeptides (selectivity: 60.2%) by Fe3O4@H-TiO2. The results demonstrated that, compared with single-component metal oxides, composite metal oxides could enhance the selectivity and sensitivity for phosphopeptide enrichment.

Calcination of metal-organic frameworks (MOFs) with designed condition is an efficient and flexible method to synthesize electrocatalysts with high activity toward various applications. In this work, we propose a facile calcination procedure under N2 atmosphere utilizing zeolitic imidazolate framework-67 (ZIF-67) as the precursor to obtain cobalt nanoparticles-porous carbon composites (denoted as ZIF-N2) for nonenzymatic glucose detection in alkaline media. At the same time, calcination of ZIF-67 under air atmosphere with the same temperature was also carried out. The resulting product (denoted as ZIF-Air) was used as a comparison when evaluating the electrochemical performance of ZIF-N2. By means of a series of physicochemical and electrochemical characterizations, different calcination atmosphere show great effect on the properties of the resulting materials. ZIF-N2 shows the specific morphology with Co nanoparticles loaded on the porous carbon matrix, with superior conductivity, mass activity, and electrochemical effective surface area to ZIF-Air. Based on these distinct parameters, nearly 10 times higher response of ZIF-N2 is obtained toward glucose than that of ZIF-Air. The sensitivity of ZIF-N2 is calculated to be 0.227 mA mM− 1 cm− 2 in the linear range of 0.1–1.1 mM, with LOD of 5.69 μM. Finally, the nonenzymatic glucose sensing performance of ZIF-N2 modified screen-printed carbon electrode including selectivity, long-term stability and reproducibility were also proved to be outstanding. This work demonstrates the calcination of MOFs under designed condition can be a promising method to obtain electrocatalysts for electrochemical sensing application.

In this work, a highly sensitive enzyme- and metal-free electrochemical method for superoxide anion (O2−) 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 O2−, 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 O2−.A highly sensitive enzyme- and metal-free electrochemical sensor for superoxide anion (O2−) detection has been developed based on nitrogen doped hollow mesoporous carbon spheres (N-HMCS) modified screen-printed carbon electrodes (N-HMCS/SPCE).Download high-res image (126KB)Download full-size image

Three ferrites of type MFe2O4 (where M is bivalent Fe, Co or Mn) dispersed on multi-walled carbon nanotubes (MWCNTs) were prepared by a coprecipitation method. Their electrocatalytic properties toward the reduction of H2O2 at pH 7.4 were systematically compared. Catalytic reduction rates at an applied potential of −0.4 V (vs. Ag/AgCl) and pseudo Michaelis-Menten constants show the electrocatalytic ability to follows the order Fe3O4 > CoFe2O4 > MnFe2O4. This diversity is attributed to the differences in the M(II) used and its occupancy on the lattice surface. The sensitivities are 120.98 ± 0.15, 48.45 ± 0.23 and 32.25 ± 0.27 μA cm−2 mM−1, and the limits of detection are 0.98, 2.59 and 5.64 μM of H2O2 (at an S/N ratio of 3).

•A captivating porous Pt–Pd interface for the immobilization of SOD.•Ultrahigh sensitive and selective sensing of O2∙−.•Capturing the trace level of O2∙− released from stimulated cells.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 1536 μM (R2=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.

•Macroporous Cu foams with large surface were assembled by electrodeposition assisted with hydrogen evolution.•The synthesized Cu was substituted by metallic Pt through facile galvanic replacement, forming Pt monolayer-support alloy structures with highly catalytic activity.•The electrochemical oxidation behavior of glucose on this interface was investigated.•Favorable properties for nonenzymatic glucose detection were obtained at the proposed sensor based on Pt-placed Cu frameworks.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.

As ferrite nanoparticles (MFe2O4) have been widely used in biomedical field, their safety evaluation has been paid great attention both in vitro and in vivo. In this paper, the ultra-small MFe2O4 (M = Fe, Mn, Co) nanoparticles with the average size less than 5 nm were prepared by thermal decomposition method and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and vibrating sample magnetometry (VSM). The toxic effect on human lung epithelial A549 cells treated with MFe2O4 nanoparticles at the different concentrations was evaluated in vitro. Mitochondrial function (MTT assay), cellular morphology, reactive oxygen species (ROS), superoxide dismutase (SOD), membrane lipid peroxidation (LPO) and glutathione (GSH) were assessed as toxicity end points. The results showed that the cytotoxicity of ultra-small MFe2O4 nanoparticles was in a dose- and time-dependent manner. Moreover, ultra-small Fe3O4 nanoparticles were found to be nearly non-toxic in A549 cells, while MnFe2O4 nanoparticles exhibited cytotoxic effects, and CoFe2O4 nanoparticles exerted higher cytotoxic effects among the three studied particles at the same concentration.

•Polymerization of dopamine leads to reduction of graphene oxide: a green chemistry method.•A captivating electrochemical sensing interface for the immobilization of enzyme like SOD.•PtPd-PDARGO promote the electron transfer and provide enhanced performance for O2●− sensing.•Outstanding sensitivity and excellent selectivity for O2●− determination.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 (R2=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.

We have synthesized nitrogen-doped graphene nanoribbons (N-GrNRs) by unzipping multi-walled carbon nanotubes (CNTs) under strongly oxidizing conditions and subsequent doping with nitrogen by a low-temperature hydrothermal method. The N-GNRs were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy, and assembled on a disposable screen-printed carbon electrode to give a sensor for H2O2 that was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, chronocoulometry and chronoamperometry. The nano-modified electrode displays enhanced electron transfer ability, and has a large active surface and a large number of catalytically active sites that originate from the presence of nitrogen atoms. This results in a catalytic activity towards H2O2 reduction at near-neutral pH values that is distinctly improved compared to electrodes modified with CNTs or unzipped (non-doped) CNTs only. At a working potential of −0.4 V (vs. Ag/AgCl), the amperometric responses to H2O2 cover the 5 to 2785 μM concentration range, with a limit of detection as low as 1.72 μM. This enzyme-free electrochemical sensor exhibits outstanding selectivity and long-term stability for H2O2 detection.

•A captivating electrochemical sensing interface for the immobilization of SOD.•Pt–Pd/MWCNTs promote the electron transfer and provide enhanced performance for O2∙− sensing.•Outstanding sensitivity and excellent selectivity for O2∙− determination.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 (R2=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.

Cancer theranostics, the ability to simultaneously diagnose and treat cancer, has become one of the major driving forces in nanobiotechnology. In the present work, a multifunctional system, methylene blue-incorporated folate-functionalized Fe3O4/mesoporous silica core–shell magnetic nanoparticles (MNPs), for simultaneous near-infrared (NIR) fluorescence imaging and targeting photodynamic therapy (PDT) has been developed. The core Fe3O4 MNPs offers the function of magnetically guided drug delivery, the mesoporous silica shell acts as an efficient drug loaded carrier, the photosensitizer methylene blue (MB) exhibits excellent NIR fluorescence imaging and PDT efficiency, and the folic acid (FA) can effectively enhance the delivery of MB to the targeting cancer cells, which overexpress the folate receptor. The results indicated that the multifunctional system could effectively be used in NIR fluorescence imaging. Moreover, it exhibited a synergistic effect of magnetic targeted PDT of cancer under NIR laser irradiation. Thus, the multifunctional system is promising for simultaneous cancer diagnosis and therapy.

•Porous Cu foam with tunable porosity.•As an electrochemical interface for enzymeless glucose sensing.•Showing high electrocatalytic activity for glucose oxidation in alkaline media.•Exhibiting good sensitivity and excellent selectivity for glucose detection.•Possessing attractive durability of performance thanks to robust architectures.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 +0.35 V vs. Ag/AgCl in 0.1 M 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 1.81 mA cm−2 mM−1 for glucose in the linear concentration ranges of 2–80 μM and 0.1–5 mM, respectively. The limit of detection is calculated to be as low as 0.98 μM 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.

A new screen-printed carbon electrode with porous architectures prepared using an extremely facile and low-cost approach is introduced. The preparation mainly involved a printing procedure of a graphite-based layer doped with CaCO3 powders and a subsequent dissolution of these powders. The resulting porous screen-printed carbon electrode (P-SPCE) can offer large surface, broad potential window, low background current and high electrochemical reactivity. Moreover, the proposed P-SPCE provides enhanced performance for enzyme-free H2O2 sensing compared to conventional glassy carbon electrodes and screen-printed carbon electrodes. These attractive properties of the P-SPCE are expected to be of wider applications.Highlights► CaCO3 powder doped graphite-based ink. ► Porous screen-printed carbon electrode. ► Wide potential window, low background current and high electrochemical reactivity. ► Enhanced performance for nonenzymatic H2O2 sensing.

Novel snowflake-like Pt–Pd bimetallic nanoclusters (Pt–PdBNC) were synthesized on a screen-printed gold nanofilm electrode (SPGFE) substrate by electrochemically reducing precursors with a new constant potential/multi-potential step deposition strategy. The electrocatalytic behavior of the modified electrode (SPGFE/Pt–PdBNC) towards H2O2 was investigated. The results indicate that the as-prepared Pt–PdBNC significantly enhances the electrochemical reduction of H2O2 in neutral media, exhibiting preferable electrocatalytic performance compared to Pt and Pd monometallic nanoclusters. Under optimum conditions, SPGFE/Pt–PdBNC offers linear responses for H2O2 in the concentration range from 0.005 to 6 mM with an ultrahigh sensitivity of 804 mA M−1 cm−2 and excellent selectivity. Furthermore, glucose oxidase was immobilized on the Pt–PdBNC structure, and the fabricated biosensor presents favorable properties for glucose sensing.Highlights► Novel 3D Pt–Pd bimetallic nanoclusters (Pt–PdBNC) on a gold nanofilm substrate. ► as-prepared SPGFE/Pt–PdBNC significantly enhances the reduction of H2O2. ► Enzyme-free sensor exhibits ultrahigh sensitivity for H2O2 detection. ► Fabricated GOx biosensor shows favorable performance for glucose sensing.

The screen-printed three-electrode system was applied to fabricate a new type of disposable amperometric xanthine oxidase biosensor. Carbon-working, carbon-counter and Ag/AgCl reference electrodes were all manually printed on the polyethylene terephthalate substrate forming the screen-printed three-electrode system by the conventional screen-printing process. As a mediator, Prussian blue could not only catalyze the electrochemical reduction of hydrogen peroxide produced from the enzyme reaction, but also keep the favorable potential around 0 V. The optimum operational conditions, including pH, potential and temperature, were investigated. The sensitivities of xanthine and hypoxanthine detections were 13.83 mA/M and 25.56 mA/M, respectively. A linear relationship was obtained in the concentration range between 0.10 μM and 4.98 μM for xanthine and between 0.50 μM and 3.98 μM for hypoxanthine. The small Michaelis-menten constant value of the xanthine oxidase biosensor was calculated to be 3.90 μM. The results indicate that the fabricated xanthine oxidase biosensor is effective and sensitive for the detection of xanthine and hypoxanthine.