Au-Co nanoparticles-embedded N-doped carbon nanotube hollow polyhedron modified electrode for electrochemical determination of quercetin.

A core-shell ZIF-8@ZIF-67 was synthesized and pyrolyzed to get a Co nanoparticles-embedded N-doped carbon nanotube hollow polyhedron (Co@NCNHP). Then Au nanoparticles were formed on the surface and core of Co@NCNHP to obtain an Au-Co bimetal decorated NCNHP (Au-Co@NCNHP). The resultant nanocomposite was characterized by various methods including transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The Au-Co@NCNHP-based electrochemical sensor displayed an obviously high electrocatalytic response to the oxidation of quercetin, which was attributed to the synergistic effects of Au-Co bimetal nanoparticles and N-doped carbon nanotube with hollow polyhedron. Under the optimal conditions, the oxidation peak currents exhibited a wide linear dynamic range for quercetin concentration from 0.050 to 35.00 µmol/L, and the detection limit was 0.023 ± 0.002 µmol/L (S/N = 3). The analytical applications of the proposed electrochemical sensor were checked by determining the content of quercetin in medical and onion samples with satisfactory results. Grapical abstract.

Fabrication of ZIF-67@three-dimensional reduced graphene oxide aerogel nanocomposites and their electrochemical applications for rutin detection.

Three-dimensional reduced graphene oxide aerogel (3D rGA) was synthesized by hydrothermal method and cobalt imidazolate framework-67 (ZIF-67) was further grown in situ on the 3D rGA matrix directly. The resultant ZIF-67@3D rGA nanocomposite was checked by different techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectrophotometry (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA). The presence of 3D rGA acted as the backbone for the loading of ZIF-67, and the resultant ZIF-67@3D rGA nanocomposite exhibited an interconnected porous structure with large surface area and high conductivity due to synergistic effects, which was applied to the electrode modification and used for rutin detection. The developed method showed excellent performance with a wider linear range (0.05-200.0 µmol/L) and lower detection limit (0.028 ± 0.0016 µmol/L, S/N=3). Various samples including the compounded rutin tablets and onions were analyzed by this modified electrode with satisfactory results.

ZnO-reduced graphene oxide composite based photoelectrochemical aptasensor for sensitive Cd(II) detection with methylene blue as sensitizer.

In this paper a photoelectrochemical (PEC) aptasensor based on specific recognition with conformational changed after the target Cd(II) identification was fabricated. A ZnO and reduced graphene oxide (ZnO-rGO) nanocomposite with enhanced PEC activity was designed as photoactive material. After the further incorporation of gold nanoparticles (AuNPs) with ZnO-rGO nanocomposite, the enhanced photocurrent signal could be detected owing to the localized surface plasmon resonance and good conductivity of AuNPs. In addition, AuNPs were used as anchors for immobilization of -SH modified aptamer S1. After that aptamer S2 was paired with S1 sequence to form complementary double stranded DNA (dsDNA) on the electrode surface. Methylene blue (MB) was acted as sensitizer and assembled in dsDNA structure to amplify photocurrent response. When Cd(II) was bound to the aptamer presented on the sensing interface, S2 specifically recognized and captured Cd(II), which resulted in the unwinding of dsDNA structure and the separation of MB molecules from the electrode surface with photocurrent response decreased. The photocurrent was detected by a double-working-electrode system, which used the modified electrode as the first working electrode and glassy carbon electrode (GCE) as the second working electrode. Dopamine (DA) was added to the electrolyte and acted as the electron donor, which could be oxidized on the modified electrode and reduced on the GCE to form a cyclic reaction, leading to the enhanced photocurrent response with improved photocurrent stability. This MB sensitized PEC aptasensor exhibited a high sensitivity with a detection limit of 1.8 × 10-12 mol/L (3σ). Thus, a highly sensitive aptasensor with double-working-electrode detection method for Cd(II) determination were established and further applied to the water samples analysis.

Synthesis and utilization of Co3O4 doped carbon nanofiber for fabrication of hemoglobin-based electrochemical sensor.

In this paper cobalt oxide (Co3O4) nanoparticles were mixed with polyacrylonitrile to prepare Co3O4 doped carbon nanofiber (CNF) composite by electrospinning and carbonization, which was further used to modify on carbon ionic liquid electrode (CILE). Hemoglobin (Hb) was immobilized on Co3O4-CNF/CILE surface with Nafion acted as the protective film to fabricate an electrochemical biosensor (Nafion/Hb/Co3O4-CNF/CILE). Electrochemical behavior of Hb on the electrode was investigated with a pair of quasi-reversible redox peak appeared on cyclic voltammogram and electrochemical parameters were calculated. Moreover, this biosensor had good analytical capabilities for electrocatalytic reduction of different substrates including trichloroacetic acid, potassium bromate and sodium nitrite with wider detection range from 40.0 to 260.0 mmol L-1, 0.1 to 48.0 mmol L-1 and 1.0 to 12.0 mmol L-1 by cyclic voltammetry, respectively. The proposed method showed excellent anti-interferences ability with good selectivity and was successful used for quantitative detection of real samples, which displayed the potential applications to develop into a new analytical device.

A biomass-derived porous carbon-based nanocomposite for voltammetric determination of quercetin.

Porous carbon was prepared from wheat flour by alkali treatment and carbonization. The resulting biomass-derived porous carbon (BPC) was employed to prepare a Pt-Au-BPC nanocomposite by a hydrothermal method. The material was then placed on the surface of a carbon ionic liquid electrode (CILE). The Pt-Au-BPC was characterized by SEM, XPS, and the modified CILE by electrochemical methods. They revealed a porous structure, a large specific surface with high conductivity. Pt-Au-BPC/CILE was applied to the sensitive determination of quercetin. Electrochemical response was studied by cyclic voltammetry and differential pulse voltammetry (DPV). Under optimized experimental conditions, the oxidation peak current (measured at 0.48 V vs. Ag/AgCl by DPV) increases linearly in the 0.15 to 6.0 µM and in the 10.0 to 25.0 µM quercetin concentration range. The detection limit is 50.0 nM (at 3σ). The Pt-Au-BPC/CILE was applied to the direct determination of quercetin in ginkgo tablets sample and gave satisfactory results. Graphical abstract A Pt-Au-BPC nanocomposite modified carbon ionic liquid electrode was applied to differential pulse voltammetric determination of quercetin. BPC: biomass-derived porous carbon.

Photoelectrochemical aptasensor for lead(II) by exploiting the CdS nanoparticle-assisted photoactivity of TiO2 nanoparticles and by using the quercetin-copper(II) complex as the DNA intercalator.

A photoelectrochemical (PEC) aptasensor for Pb(II) detection is described. A nanocomposite consisting of CdS (2.5 µm) and TiO2 nanoparticles (10 nm) was used as a photoactive material, and gold nanochains (Au NCs) as the support for immobilization of the Pb(II)-binding aptamer. The quercetin-copper(II) complex was further employed as the intercalator for the improvement of the photoactivity by embedding it into dsDNA. In the presence of Pb(II), a Pb(II)-stabilized G-quadruplex was formed between Pb(II) and DNA S1. This is accompanied by unwinding of the dsDNA and the release of the quercetin-copper(II) complex from the surface of the sensor. This results in a decrease of the photocurrent that drops linearly from 5.0 × 10-12 to 1.0 × 10-8 mol·L-1 Pb(II) concentration range with a detection limit of 1.6 × 10-12 mol·L-1. The method was applied to the determination of Pb(II) in various samples and gave satisfactory results. Graphical abstractA photoelectrochemical aptasensor was fabricated for the detection of Pb(II) based on CdS-TiO2 nanocomposite modified indium tin oxide (ITO) electrode. Gold nanochains (AuNCs) were used as anchor to immobilize the aptamers S1 and S2 that form a double helix structure by DNA hybridization. After embedding of quercetin-copper(II) complex as intercalator and electron donor, the concentrations of Pb(II) were determined by the changes of photocurrents.

Myoglobin- and Hydroxyapatite-Doped Carbon Nanofiber-Modified Electrodes for Electrochemistry and Electrocatalysis.

In this paper, a hydroxyapatite (HAp)-doped carbon nanofiber (CNF)-modified carbon ionic liquid electrode (CILE) was prepared and used for the investigation on the direct electrochemistry and electrocatalysis of myoglobin (Mb). HAp nanoparticles were mixed within a polyacrylonitrile (PAN) solution, and a HAp@PAN nanofiber was synthesized by electrospinning process, which was further controlled by carbonization at 800 °C for 2 h in a nitrogen atmosphere to get a HAp@CNF nanocomposite. Various techniques were used to check the physicochemical properties of HAp@CNF. Mb was mixed with a HAp@CNF dispersion solution and casted on the surface of CILE to obtain an electrochemical sensing platform. The direct electrochemistry of Mb on the modified electrode was checked when a pair of enhanced redox waves appeared, indicating the direct electron transfer of Mb. HAp@CNF exhibited high conductivity, good biocompatibility, and large surface area, which was beneficial for Mb immobilization. The modified electrode showed excellent electrocatalytic activity toward the reduction of trichloroacetic acid and sodium nitrite, which was further used to establish a new electroanalytical method. Real samples were analyzed by the proposed method with satisfactory results.

Voltammetric sensing performances of a carbon ionic liquid electrode modified with black phosphorene and hemin.

A black phosphorene (BPE) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) hybrid was used for the immobilization of hemin on a carbon ionic liquid electrode (CILE). BPE inside the PEDOT:PSS film was stable without adverse effects of water and oxygen. The hemin-modified electrode facilitates electrochemical communication with a couple of well-shaped and enhanced redox waves. Therefore BPE exhibits an accelerating function to the electron movement. This sensor exhibits excellent electrocatalytic effects on the reduction of various substrates including trichloroacetic acid (TCA), nitrite and H2O2. As for TCA, the reduction current at -0.36 V (vs. Ag/AgCl) increases linearly in the concentration range from 2.0 to 180 mmol·L-1 with a detection limit of 0.67 mmol·L-1 (at 3σ). As for nitrite, the reduction current at -0.59 Vis linear in the 1.0 to 10.5 mmol·L-1 concentration range, and the detection limit is 0.33 mmol·L-1 (at 3σ). As for H2O2, the reduction current at -0.033 V (vs. Ag/AgCl) is linear in the concentration range from 4.0 to 35.0 mmol·L-1 and the detection limit is 1.3 mmol·L-1 (at 3σ). The real sample was analyzed with satisfactory results, which indicated that BPE had potential applications in the field of electrochemical biosensor. Graphical abstract Photos of (a) black phosphorene (BPE) solution, (b) poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), (c) BPE-PEDOT:PSS (1:5) dispersion, and the fabrication procedure of this electrochemical sensor. It was applied to the determination of trichloroacetic acid, nitrite and hydrogen peroxide.

Electrochemical performance of myoglobin based on TiO2-doped carbon nanofiber decorated electrode and its applications in biosensing.

A new biosensing strategy based on a TiO2-doped carbon nanofiber (CNF) composite modified electrode was developed. TiO2@CNF was prepared by electrospinning with further carbonization, before being characterized by various methods and used for electrode modification on the surface of carbon ionic liquid electrode (CILE). Myoglobin (Mb) was further immobilized on the modified electrode surface. The results of ultraviolet-visible (UV-vis) and Fourier transform infrared (FT-IR) spectroscopy showed that Mb maintained its native structure without denaturation in the composite film. Direct electron transfer and the electrocatalytic properties of Mb on the electrode surface were further investigated. A pair of quasi-reversible redox peaks appeared on the cyclic voltammogram, indicating that direct electrochemistry of Mb was realized in the nanocomposite film. This could be attributed to the specific properties of TiO2@CNF nanocomposite, including a large surface-to-volume ratio, good biocompatibility and high conductivity. Nafion/Mb/TiO2@CNF/CILE exhibited an excellent electrochemical catalytic ability in the reduction of trichloroacetic acid, NaNO2 and H2O2. All results demonstrated potential applications of TiO2@CNF in third-generation electrochemical biosensors.

Platinum nanoparticles decorating a biomass porous carbon nanocomposite-modified electrode for the electrocatalytic sensing of luteolin and application.

A sensitive electrochemical method was proposed for the determination of luteolin based on platinum (Pt) nanoparticles decorating a biomass porous carbon (BPC) composite-modified carbon ionic liquid electrode (CILE). For Pt-BPC/CILE, a pair of well-defined redox peaks of luteolin appeared with enhanced peak currents and the positive movement of peak potentials, proving the electrocatalytic activity of the Pt-BPC nanocomposite for redox reaction. The results can be ascribed to the porous structure of BPC, the catalytic activity of Pt nanoparticles and their synergistic effects. Electrochemical parameters were calculated via cyclic voltammetry and differential pulse voltammetry. The results showed that the oxidation peak currents increased linearly with the concentration of luteolin in the range from 0.008 to 100.0 µmol L-1, with a detection limit of 2.6 ± 0.054 nmol L-1. The analytical performance of this sensor was checked by the detection of luteolin contents in a real Duyiwei capsule sample with satisfactory results.