•Shortened and acidified multi-walled carbon nanotubes (S-MWCNTs) were synthesized.•Fe3O4 nanoparticles were hybridized with S-MWCNTs to form a nanohybrid.•The nanohybrid has excellent electrocatalysis towards omeprazole.•The hybrid and poly(2,6-pyridinedicarboxylic acid) were used to detect omeprazole.Three types of shortened and acidified multi-walled carbon nanotubes (S-MWCNTs) were synthesized by ultrasonication of the raw long carbon nanotubes in H2SO4/HNO3 mixed acids. A comparative electrochemical investigation was performed in 5 μM omeprazole (OMZ) solution. It demonstrated that S-MWCNTs with specific length and acidity showed higher electrocatalysis to the oxidation of OMZ. Magnetite nanoparticles Fe3O4 were hybridized with S-MWCNTs to form a nanohybrid (S-MWCNTs-Fe3O4) through a simple, effective and reproducible chemical co-precipitation method. The nanohybrid was characterized by transmission electron microscope (TEM), X-ray diffractometer (XRD), thermogravimetric analyses (TGA), and field emission scanning electron microscopy (FESEM). The electrochemical response characteristic of S-MWCNTs-Fe3O4 modified GCE toward OMZ was investigated by cyclic voltammetry. It showed that the nanohybrid enhanced the electrocatalytic oxidation to OMZ. Linear sweep voltametry (LSV) was applied to determine low concentrations of OMZ on S-MWCNTs-Fe3O4/poly (2,6-pyridinedicarboxylic acid) modified electrode. A linear relationship was found between peak currents (ip,a) and the concentration of OMZ within 0.05–9.0 μM with an estimated detection limit of 15 nM.

No work studied and compared Fe3O4-functionalized carbon-based nanomaterials. Also, no work investigated their application for detecting bisphenol A (BPA), an important organic chemical raw material, which had been proved to cause malformation, cancers, sexual precocity, and neural and behavioral changes in infants and children. In this work, Fe3O4 magnetite nanoparticles were stably anchored on carbon materials to synthesize three types of nanohybrids, i.e. hybrids of graphene oxide with Fe3O4 (GO–Fe3O4), carbon nanotubes with Fe3O4 (CNTs–Fe3O4), and graphene oxide and carbon nanotubes with Fe3O4 (GO–CNTs–Fe3O4). These nanohybrids were characterized using a transmission electron microscope (TEM), X-ray diffractometer (XRD), and Fourier transform infrared spectrometer (FT-IR). GO–Fe3O4, CNTs–Fe3O4, and GO–CNTs–Fe3O4 were immobilized on the surface of a GCE using electro-poly(glutamic acid). The electrochemical response characteristic of bisphenol A (BPA) on different modified electrodes was investigated by cyclic voltammetry. It showed that these three types of nanohybrids greatly enhanced the anodic peak current of BPA. Then, these hybrids were applied to determine BPA by differential pulse voltammetry. Their determination performance was compared with each other. Among them, the GO–CNTs–Fe3O4 modified electrode exhibited wider linear ranges of 0.003–0.2 and 0.2–30.0 μmol L−1 with a lower estimated detection limit of 1.0 nmol L−1.

A nanocomposite of graphene oxide encapsulated multiwalled carbon nanotubes (GO@MWNTs) was produced by a simple method. The composite displayed good dispersibility. An antiaromatic dimesityl-substituted nickel (II) norcorrole complex (NiNC) was noncovalently assembled on the GO@MWNTs to form a novel triad hybrid (GO@MWNTs-NiNC). The hybrid was characterized by different analytical techniques containing AFM, TEM, UV–vis spectroscopy, FT-IR spectroscopy, and TGA. Based on the excellent electrocatalytic properties of the triad hybrid towards dopamine (DA), a new electrochemical sensing platform for the selective and sensitive determination of DA was proposed. Under optimized conditions, the linear response range for determining DA were obtained over the range of 0.03–80 μM with the estimated detection limit of 0.012 μM (S/N = 3). The fabricated sensor also exhibits such features as good stability, selectivity, and reproducibility.

The authors report on the synthesis of a hybrid material consisting of the porphyrinoid metal complex nickel(II) norcorrole that was noncovalently bound to carbon nanotubes (CNT-NiNC). The hybrid was characterized by UV–vis, FTIR spectroscopy, and thermogravimetric analysis. The CNT-NiNC hybrid possesses high catalytic activity and selectivity toward the oxidation of ascorbic acid, dopamine, and uric acid. It was used to modify a glassy carbon electrode which then is shown to enable simultaneous or individual determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA) at pH 6.5 and typical working potentials of −70, 200 and 380 mV (vs. SCE). The detection limits (at an SNR of 3) are 2.0 μM for AA, 0.1 μM for DA, and 0.4 μM for UA.

•A nanohybrid of graphene oxide and multiwalled carbon nanotubes (GO-CNTs) was synthesized.•The nickel–cobalt hexacyanoferrate decorated GO-CNTs were prepared by electrodeposition.•The resulted hybrid exhibited greatly improved electrocatalysis to hydroxylamine.A nanohybrid of graphene oxide and multiwalled carbon nanotubes (GO-CNTs) was synthesized through π–π interaction. The nickel–cobalt hybrid hexacyanoferrate decorated GO-CNTs (NiCoHCF/GO-CNTs) was prepared by electrodeposition of NiCoHCF in different ratios of Co2 + to Ni2 + solution on GO-CNTs. The characterization was performed by UV–vis, FT-IR, Raman spectroscopy, and SEM. The electrochemistry behavior of NiCoHCF/GO-CNTs was studied by cyclic voltammetry. The NiCoHCF/GO-CNT modified GCE (NiCoHCF/GO-CNT/GCE) exhibited greatly improved electrocatalytic activity towards electrooxidation of hydroxylamine. The modified electrode exhibited a wide linear range from 0.2 μM to 150 μM and a low detection limit (LOD) of 0.08 μM.

•The designed assay scheme is suitable for high throughput transcription factors analysis.•A dumbell probe-mediated rolling circle amplification strategy was used.•The strategy allows us to achieve large dynamic range and femtomolar sensitivity.Highly sensitive detection of transcription factors (TF) is essential to proteome and genomics research as well as clinical diagnosis. We describe herein a novel fluorescent-amplified strategy for ultrasensitive, quantitative, and inexpensive detection of TF. The strategy consists of a hairpin DNA probe containing a TF binding sequence for target TF, a dumbbell-shaped probe, a primer DNA probe designed partly complementary to hairpin DNA probe, and a dumbbell probe. In the presence of target TF, the binding of the TF with hairpin DNA probe will prohibit the hybridization of the primer DNA probe with the “stem” and “loop” region of the hairpin DNA probe, then the unhybridized region of the primer DNA will hybridize with dumbbell probe, subsequently promote the ligation reaction and the rolling circle amplification (RCA), finally, the RCA products are quantified via the fluorescent intensity of SYBR Green I (SG). Using TATA-binding protein (TBP) as a model transcription factor, the proposed assay system can specifically detect TBP with a detection limit as low as 40.7 fM, and with a linear range from 100 fM to 1 nM. Moreover, this assay related DNA probe does not involve any modification and the whole assay proceeds in one tube, which makes the assay simple and low cost. It is expected to become a powerful tool for bioanalysis and clinic diagnostic application.

The nanocomposites (Fc–GO) of ferrocene (Fc) hybridized graphene oxide (GO) were prepared by π–π stacking interactions. Fc–GO and Au(III) are electrochemically co-reduced to obtain Au nanoparticles (AuNPs) and Fc hybridized electrochemically reduced graphene oxide (Fc–ERGO) nanocomposites (AuNPs/Fc–ERGO). Scanning electron microscopy reveals that Au particles are about 10 nm and are dispersed uniformly on Fc–ERGO. The electrochemical behavior of AuNPs/Fc–ERGO demonstrates great electrochemical activity and stability. The AuNPs/Fc–ERGO was applied in a highly sensitive immunosensor of the biomarker carbohydrate antigen 15-3 (CA 15-3). This unique immunosensor, with AuNPs/Fc–ERGO as the immobilization platform and signal probe, exhibited significant sensitivity toward CA 15-3. Under optimal conditions, the peak current of differential pulse voltammetry (DPV) of the immunosensor decreased with increasing CA 15-3 concentration, showing two linear ranges of 2.0–25.0 U mL−1 and 0.05–2.0 U mL−1 with a low detection limit of 0.015 U mL−1. The strategy developed for this immunosensor provides a promising approach for clinical research and diagnostic applications.

•A noncovalent nanohybrid of cobalt tetraphenylporphyrin with chemically reduced graphene oxide was prepared.•The nanohybrid was characterized by UV–vis spectroscopy, Raman spectroscopy, and atomic force microscopy.•The nanohybrid can be applied to simultaneously detect AA, DA and UA with high sensitivity and low detection limit.A noncovalent nanohybrid of cobalt tetraphenylporphyrin (CoTPP) with chemically reduced graphene oxide (CRGO) was prepared through π–π stacking interaction between CRGO and CoTPP. The hybrid (CoTPP-CRGO) was characterized by UV–vis spectroscopy, Raman spectroscopy, and atomic force microscopy. The electrochemical behaviors of ascorbic acid (AA), dopamine (DA), and uric acid (UA) at CoTPP-CRGO modified glass carbon electrode (CoTPP-CRGO/GCE) were studied by cyclic voltammetry (CV). Three well-resolved oxidation peaks were obtained. The peak potential separations were 225 and 140 mV for AA and DA, DA and UA respectively. Owing to the synergistic effect of CoTPP and CRGO, CoTPP-CRGO showed faster electron transfer and stronger electrocatalysis than CoTPP, CRGO or their mixture. The proposed modified electrode exhibited linear responses to AA, DA and UA in the ranges of 5.0–200.0 μM, 0.1–12.0 μM, 0.5–40 μM, respectively. The detection limits were 1.2, 0.03, and 0.15 μM, respectively. It was also applied to detect real samples with a satisfactory result.

A nanoscale hybrid of chemically reduced graphene oxide (CRGO) with ferrocene (Fc) was prepared through π–π stacking interaction between Fc and CRGO. FT-IR, Raman spectroscopy, SEM and cyclic voltammetry were utilized to characterize the nanohybrid of Fc with CRGO (Fc-CRGO). Fc-CRGO exhibited good stability and greatly improved electron-transfer behavior. Fc-CRGO and HRP were casted on the surfaces of glass carbon electrode (GCE) with the aid of chitosan for determination of H2O2. The choline oxidase (CHOD) cross-linked with chitosan was further dropped on the surface of modified electrode for detection of choline. The excellent biosensor performance was obtained by combining the advantages of nanohybrid and enzymes. Amperometric determination for choline has been performed at a very low applied potential of −0.10 V. The linear response range was of 1.0 ∼ 400 μM with a detection limit of 0.35 μM. The current reached 95% of maximum response within 8 s.

The nanocomposites (Fc–GO) of ferrocene (Fc) hybridized graphene oxide (GO) were prepared by π–π stacking interactions. Fc–GO and Au(III) are electrochemically co-reduced to obtain Au nanoparticles (AuNPs) and Fc hybridized electrochemically reduced graphene oxide (Fc–ERGO) nanocomposites (AuNPs/Fc–ERGO). Scanning electron microscopy reveals that Au particles are about 10 nm and are dispersed uniformly on Fc–ERGO. The electrochemical behavior of AuNPs/Fc–ERGO demonstrates great electrochemical activity and stability. The AuNPs/Fc–ERGO was applied in a highly sensitive immunosensor of the biomarker carbohydrate antigen 15-3 (CA 15-3). This unique immunosensor, with AuNPs/Fc–ERGO as the immobilization platform and signal probe, exhibited significant sensitivity toward CA 15-3. Under optimal conditions, the peak current of differential pulse voltammetry (DPV) of the immunosensor decreased with increasing CA 15-3 concentration, showing two linear ranges of 2.0–25.0 U mL−1 and 0.05–2.0 U mL−1 with a low detection limit of 0.015 U mL−1. The strategy developed for this immunosensor provides a promising approach for clinical research and diagnostic applications.