Simultaneous Detection of Ascorbic Acid, Dopamine, and Uric Acid Using a Novel Electrochemical Sensor Based on Palladium Nanoparticles/Reduced Graphene Oxide Nanocomposite

A fresh strategy based on two-step electrochemical reduction for the fabrication of palladium nanoparticles/reduced oxide nanocomposite-modified glass carbon electrode (PdNPs/rGO/GCE) was established in this study. Field emission scanning electron microscopy (FESEM) images showed that spherical PdNPs were evenly distributed on the surface of rGO-modified electrode (rGO/GCE), and the introduction of PdNPs has no effect on the morphology of rGO. Electrochemical impedance spectroscopy (EIS) studies revealed that the conductivity of PdNPs/rGO/GCE was higher than that of rGO/GCE and bare GCE. The electrochemical performances of PdNPs/rGO/GCE sensor were investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and chronoamperometry using ascorbic acid (AA), dopamine (DA), and uric acid (UA) as analytes. At the optimized conditions, wide linear ranges of 0.5–3.5 mM (R2 = 0.99), 3–15 μM (R2 = 0.99) and 15–42 μM (R2 = 0.99), and 0.3–1.4 mM (R2 = 0.99) towards AA, DA, and UA in ternary mixture were observed, respectively. In addition to superior anti-interference capability, fast response (≤5 s), excellent reproducibility, and good long-term stability were also given by this sensor. These results suggested that PdNPs/rGO/GCE is promising for the simultaneous detection of AA, DA, and UA in practical application.

Multifunctional Encapsulating Gold Nanoparticles into Cu-Hemin/Metal-Organic Frameworks for Catechol Electrochemical Detection on Graphene-Based Electrode

A new type of multifunctional metal-organic frameworks (MOFs) was synthesized by encapsulating gold nanoparticles (AuNPs) into the Cu-hemin MOFs, and first applied to an electrochemical sensor to detect catechol (CT) with the aid of electrochemically reduced graphene oxide (ERGO) for signal amplification. First, ERGO was electrochemically deposited on a bare glass carbon electrode (GCE), followed by casting Cu-hemin MOFs on an ERGO-modified electrode, and then growing AuNPs in situ on Cu-hemin MOFs/ERGO/GCE by electrochemical deposition. Cyclic voltammetry (CV), scanning electron microscopy (SEM) and current–time ([Formula: see text]–[Formula: see text] were utilized to characterize the electrochemical performance and surface characteristics of the as-prepared sensor. The results demonstrated that Cu-hemin MOFs have not only been a matrix to avoid the aggregation of AuNPs but also an ideal loading platform for the adsorption of CT due to its large surface area and porosity. In addition, the ERGO also has the advantage of fast electron transfer, which can make synergy with AuNPs@Cu-hemin MOFs nanocomposites to amplify the electrical signal. The AuNPs/Cu-hemin MOFs/ERGO/GCE exhibited an excellent electrocatalytic activity with increased electrochemical signals towards the oxidation of CT. Under the optimum experimental conditions, the sensor shows a wide linear relationship over the range of [Formula: see text][Formula: see text]M to [Formula: see text][Formula: see text]M with a detection limit of [Formula: see text][Formula: see text]M. Moreover, the sensor presented the good reproducibility and the excellent anti-interference performance. This work would broaden the application of MOFs material in constructing more novel electrochemical sensing platform.

Ultrasensitive Electrochemical Sensor for Luteolin Based on Zirconium Metal-Organic Framework UiO-66/Reduced Graphene Oxide Composite Modified Glass Carbon Electrode

Luteolin is a kind of natural flavonoid with many bioactivities purified from a variety of natural herbs, fruits and vegetables. Electrochemical sensing has become an outstanding technology for the detection of luteolin in low concentration due to its fast response, easy operation and low cost. In this study, electroreduced graphene oxide (ErGO) and UiO-66 were successively modified onto a glassy carbon electrode (UiO-66/ErGO/GCE) and applied to the detection of luteolin. A combination of UiO-66 and ErGO showed the highest promotion in the oxidation peak current for luteolin compared with those of a single component. The factors affecting the electrochemical behavior of UiO-66/ErGO/GCE were evaluated and optimized including pH, accumulation potential, accumulation time and scan rate. Under optimum conditions, UiO-66/ErGO/GCE showed satisfactory linearity (from 0.001 μM to 20 μM), reproducibility and storage stability. The detection limit of UiO-66/ErGO/GCE reached 0.75 nM of luteolin and was suitable for testing real samples. Stable detection could be provided at least eight times by one modified electrode, which guaranteed the practicability of the proposed sensor. The fabricated UiO-66/ErGO/GCE showed a rapid electrochemical response and low consumption of materials in the detection of luteolin. It also showed satisfactory accuracy for real samples with good recovery. In conclusion, the modification using MOFs and graphene materials made the electrode advanced property in electrochemical sensing of natural active compounds.

Peptide-inspired green synthesis of hedgehog-like CuO nanoclusters on reduced graphene oxide for non-enzymatic hydrogen peroxide sensor

Bioinspired synthesis provides a potential green method for creating functional nanomaterials on graphene supports. In this study, we demonstrate the preparation of hedgehog-like cupric oxide nanoclusters (CuONCs) on peptide-modified reduced graphene oxide (RGO-Pep) nanohybrids through a solution-phase synthesis in which the bound peptide molecules (GNNQQNYEE) mediate the non-covalent modification of GO and provide the adsorption of Cu[Formula: see text] ions and the nucleation sites for the growth of CuONCs. The synthesized RGO-Pep-CuONCs hybrids were further utilized for the modification of a glass carbon electrode to fabricate a non-enzymatic electrochemical sensor for hydrogen peroxide (H2O2). It was found that the fabricated H2O2 sensor exhibited good performances for sensing H2O2 with a detection limit of [Formula: see text]M and two wide linear detection ranges. In addition, this sensor revealed good selectivity and stability. It is expected that the strategies used in this study will be valuable to inspire the creation of various functional biomolecule- and graphene-based hybrid bionanomaterials for the applications in materials science, sensors, biomedical engineering, tissue engineering, nanotechnology, and other fields.

An Ultra-Sensitive Electrochemical Sensor for the Detection of Carcinogen Oxidative Stress 4-Nitroquinoline N-Oxide in Biologic Matrices Based on Hierarchical Spinel Structured NiCo2O4 and NiCo2S4; A Comparative Study

Various factors leads to cancer; among them oxidative damage is believed to play an important role. Moreover, it is important to identify a method to detect the oxidative damage. Recently, electrochemical sensors have been considered as the one of the most important techniques to detect DNA damage, owing to its rapid detection. However, electrode materials play an important role in the properties of electrochemical sensor. Currently, researchers have aimed to develop novel electrode materials for low-level detection of biomarkers. Herein, we report the facile hydrothermal synthesis of NiCo2O4 micro flowers (MFs) and NiCo2S4 micro spheres (Ms) and evaluate their electrochemical properties for the detection of carcinogen-causing biomarker 4-nitroquinoline n-oxide (4-NQO) in human blood serum and saliva samples. Moreover, as-prepared composites were fabricated on a glass carbon electrode (GCE), and its electrochemical activities for the determination of 4-NQO were investigated by using various electrochemical techniques. Fascinatingly, the NiCo2S4-Ms showed a very low detection limit of 2.29 nM and a wider range of 0.005 to 596.64 µM for detecting 4-NQO. Finally, the practical applicability of NiCo2S4-Ms in the 4-NQO spiked human blood serum and saliva samples were also investigated.

A Novel Electrochemical Sensor Based on Electropolymerized Ion Imprinted PoPD/ERGO Composite for Trace Cd(II) Determination in Water

A novel electrochemical sensor based on electropolymerized ion imprinted poly (o-phenylenediamine) PoPD/electrochemical reduced graphene (ERGO) composite on glass carbon electrode (GCE) was fabricated for selective and sensitive determination of trace Cd(II) in water. ERGO was first deposited on the surface of GCE by electrochemical cyclic voltammetry (CV) scanning to enhance the electron transport activity at electrode surface. The ion imprinted polymer (IIP) of imprinted PoPD was then in situ electropolymerized on ERGO via CV scanning with oPD as functional monomer and Cd(II) ions as template, following removal of the template using electrochemical peroxidation method. The obtained imprinted PoPD/RERGO composites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray energy spectroscopy (EDS) for the observation of their morphologies and components. The electrochemical behavior of the imprinted PoPD/ERGO/GCE was performed by CV and SWASV. The fabricated sensor of the imprinted PoPD/ERGO/GCE showed a good selectivity toward target Cd(II) ions in the presence of other heavy metal ions. Under the optimized experimental conditions, the sensor exhibited a good linear relationship between SWASV stripping peak values and Cd(II) concentration in the range of 1 to 50 ng/mL, with the limit of detection as 0.13 ng/mL (S/N = 3). The proposed electrochemical sensor of imprinted PoPD/ERGO/GCE was successfully applied for trace Cd(II) determination in real water samples.