A method based on electrodeposition of reduced graphene oxide on glassy carbon electrode for sensitive detection of theophylline

Graphene nanosheets were directly electrodeposited onto a glassy carbon electrode (GCE) from the electrolyte solution containing graphene oxide (GO); the resulting electrode (ED-GO/GCE) was characterized with scanning electron microscopy. A simple and rapid electrochemical method was developed for the determination of theophylline (TP), based on the excellent properties of ED-GO film. The result indicated that ED-GO film-modified GCE exhibited efficient electrocatalytic oxidation for TP with relatively high sensitivity and stability. The electrochemical behavior of TP at ED-GO/GCE was investigated in detail. Under the optimized conditions, the oxidation peak current was proportional to the TP concentration in the range of 8.0?×?10^?7 to 6.0?×?10^?5 mol?L^?1 with the detection limit of 1.0?×?10^?7 mol?L^?1 (S/N?=?3). The proposed method was successfully applied to green tea samples with satisfactory results.     

Employing Label‐free Electrochemical Biosensor Based on 3D‐Reduced Graphene Oxide and Polyaniline Nanofibers for Ultrasensitive Detection of Breast Cancer BRCA1 Biomarker

A label‐free DNA biosensor based on three‐dimensional reduced graphene oxide (3D‐rGO) and polyaniline (PANI) nanofibers modified glassy carbon electrode (GCE) was successfully developed for supersensitive detection of breast cancer BRCA1. The results demonstrated that 3D‐rGO and PANI nanofibers had synergic effects for reducing the charge transfer resistance (R_ct), meaning a huge enhancement in electrochemical activity of 3D‐rGO‐PANI/GCE. Probe DNA could be immobilized on 3D‐rGO‐PANI/GCE for special and sensitive recognition of target DNA (1.0×10^?15–1.0×10^?7 M) with a theoretical LOD of 3.01×10^?16 M (3S/m). Furthermore, this proposed nano‐biosensor could directly detect BRCA1 in real blood samples.     

Sensitive determination of the endocrine disruptor bisphenol A at ultrathin film based on nanostructured hybrid material SiO<Subscript>2</Subscript>/GO/AgNP

In this work, we described an electrochemical sensor using a nanocomposite based on graphene oxide (GO), silver nanoparticles (AgNP), and disordered mesoporous silica (SiO₂), which was used for the determination of bisphenol A in water samples. Initially, the hybrid material SiO₂/GO was synthesized via sol-gel process, subsequently decorated with AgNP with an approximate 20 nm particle size prepared directly on the surface of the SiO₂/GO using N, N-dimethylformamide (DMF) as an agent reducer. A glassy carbon electrode was modified with SiO₂/GO/AgNP and used in developing a sensitive electrochemical sensor for the determination of bisphenol A in phosphate buffer 0.1 mol L^?1 (pH 7.0). The detection limit was 45.2 nmol L^?1 with a linear response range between 1.0 × 10^?7 and 2.6 × 10^?6 mol L^?1 and a sensitivity of 1.27 × 10^?7 A mol^?1 L. Finally, the optimized electrochemical sensor was used for the quantitation of endocrine interfering in natural waters.     

Construction of a biointerface for glucose oxidase through diazonium chemistry and electrostatic self-assembly technique

In this study, a new procedure for the fabrication of biosensors was developed. The method is based on the covalent attachment of nitrophenyl groups to the electrode surface via diazonium salt reaction followed by their conversion to amine moieties through electrochemical reduction and electrostatic layer-by-layer (LbL) assembly technique. In this procedure, highly stable iron oxide (Fe₃O₄) nanoparticles (IONPs), chitosan (CHIt), GOx, and Nile blue (NB) were assembled on the surface of aminophenyl modified glassy carbon electrode (AP/GCE) by LbL assembly technique. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the interfaces. The surface coverage of the active GOx and Michaelis–Menten constant (K _M) of the immobilized GOx were Γ?=?3.38?×?10^?11 mol cm^?2 and 2.54 mM, respectively. The developed biosensor displayed a well-defined amperometric response for glucose determination with high sensitivity (8.07 μA mM^?1) and low limit of detection (LOD) of 19.0 μM. The proposed approach allows simple biointerface regeneration by increasing pH which causes disruption of the ionic interactions and release of the electrostatic attached layers. The biosensor can then be reconstructed again using fresh enzyme. Simple preparation, good chemical and mechanical stabilities, and easy surface renewal are remarkable advantages of the proposed biosensor fabrication procedure.     

Electrochemical sensor for monitoring the photodegradation of catechol based on DNA-modified graphene oxide

We have immobilized DNA on a glassy carbon electrode (GCE) modified with graphene oxide (GO) to develop an electrochemical biosensor for catechol. Compared to carbon nanotubes, the use of GO dramatically improved the electrooxidative current of the guanine and adenine moieties in DNA but retained the low background current of unmodified GCEs. Factors such as DNA adsorption time, DNA concentration and pH of solution were investigated to optimize experimental conditions. In the presence of catechol, the voltammetric response to DNA was inhibited due to the interaction between DNA and catechol. The response to adenine is linearly proportional to the concentration of catechol in the range from 1.0?×?10^?6 to 1.0?×?10^?4 mol·L^?1. If catechol is degraded by the combined action of UV light and hydrogen peroxide, the response to DNA is restored. Thus, the modified electrode can act as an efficient biosensor for monitoring the degradation of catechol.

Selective and low potential electrocatalytic oxidation of NADH using a 2,2-diphenyl-1-picrylhydrazyl immobilized graphene oxide-modified glassy carbon electrode

DPPH (2,2-diphenyl-1-picrylhydrazil), a free radical-containing organic compound, is used widely to evaluate the antioxidant properties of plant constituents. Here, we report an efficient electroactive DPPH molecular system with excellent electrocatalytic sensor properties, which is clearly distinct from the traditional free radical-based quenching mechanism. This unusual molecular status was achieved by the electrochemical immobilization of graphene oxide (GO)-stabilized DPPH on a glassy carbon electrode (GCE). Potential cycling of the DPPH adsorbed-GCE/GO between ??1 and 1 V (Ag/AgCl) in a pH 7 solution revealed a stable and well-defined pair of redox peaks with a standard electrode potential, E⁰′?=?0?±?0.01 V (Ag/AgCl). Several electrochemical characterization studies as well as surface analysis of the GCE/GO@DPPH-modified electrode by transmission electron microscopy, Raman, and infrared spectroscopy collectively identified the imine/amine groups as the redox centers of the electroactive DPPH on GO. The use of different carbon-supports showed that only oxygen-functionalized GO and MWCNTs could provide major electroactivity for DPPH. This highlights the importance of a strong hydrogen-bonded network structure assisted by the concomitant π-π interactions between the organic moiety and oxygen function groups of carbon for the high electroactivity and stability of the GCE/GO@DPPH-NH/NH₂-modified electrode. The developed electrode exhibited remarkable performance towards the electrocatalytic oxidation of NADH at 0 V (Ag/AgCl). The amperometric i-t sensing of NADH showed high sensitivity (488 nA μM^?1 cm^?2) and an extended linear range (50 to 450 μM) with complete freedom from several common biochemical/chemical interferents, such as ascorbic acid, hydrazine, glucose, cysteine, citric acid, nitrate, and uric acid.     

Label-Free Detection of DNA Hybridization Based on MnO2 Nanoparticles

Abstract

Nano-MnO₂/chitosan composite film modified glassy carbon electrode (MnO₂/CHIT/GCE) was fabricated and a DNA probe was immobilized on the electrode surface. The immobilization and hybridization events of DNA were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS was applied to the label-free detection of the target DNA. The human immunodeficiency virus (HIV) gene fragment was successfully detected by this DNA electrochemical sensor. The dynamic detection range was from 2.0 × 10^?11 to 2.0 × 10^?6 mol/L, with a detection limit of 1.0 × 10^?12 mol/L.     

Detection of Dexamethasone Sodium Phosphate in Blood Plasma: Application of Hematite in Electrochemical Sensors

We studied sensor application of a graphene oxide and hematite (α‐Fe₂O₃/GO) composite electrode well‐characterized by the SEM and XRD. Through differential pulse voltammetry (DPV), oxidation of dexamethasone sodium phosphate (DSP) was studied at the surface of a glassy carbon electrode (GCE) modified with graphene oxide nanosheets (GO) and the α‐Fe₂O₃/GO composite. The values of the transfer coefficient (α) and the diffusion coefficient (D) of DSP were 0.5961 and 4.71×10^?5 cm² s^?1 respectively. In the linear range of 0.1–50 μM, the detection limit (DL) was 0.076 μM. In the second step, a GCE was modified with α‐Fe₂O₃/GO composite and the DSP measurement step was repeated to analyzed and compare the effects of hematite nanoparticles present on graphene oxide surfaces. According to the results, α and D were 0.52 and 2.406×10^?4 cm² s^?1 respectively and the DL was 0.046 μM in the linear range of 0.1–10.0 μM. The sensor is simple, inexpensive and uses blood serum.     

Nano-ZnO/Chitosan Composite Film Modified Electrode for Voltammetric Detection of DNA Hybridization

Abstract

A sensitive electrochemical DNA biosensor based on nano-ZnO/chitosan composite matrix for DNA hybridization detection was developed. The Nano-ZnO was synthesized by the hydrothermal method and dispersed in chitosan, which was used to fabricate the modification of the glassy carbon electrode (GCE) surface. The ZnO/chitosan-modified electrode exhibited good biocompatibility and excellent electrochemical conductivity. The hybridization detection was monitored with differential pulse voltammetry (DPV) measurement using methylene blue (MB) as an indicator. The established biosensor can effectively discriminate complementary target sequence and two-base-mismatched sequence, with a detection limit of 1.09 × 10^?11 mol L^?1 of complementary target.     

Fabrication of a Sensitive Electrochemical Biosensor for Detection of DNA Hybridization Based on Gold Nanoparticles/CuO Nanospindles Modified Glassy Carbon Electrode

In this work, a sensitive electrochemical DNA biosensor for the detection of sequence‐specific target DNA was reported. Firstly, CuO nanospindles (CuO NS) were immobilized on the surface of a glassy carbon electrode (GCE). Subsequently, gold nanoparticles (Au NPs) were introduced to the surface of CuO NS by the electrochemical deposition mode. Probe DNA with SH (HS‐DNA) at the 5′‐phosphate end was covalently immobilized on the surface of the Au NPs through Au? S bond. Scanning electron microscopy (SEM) was used to elucidate the morphology of the assembled film, and electrochemical impedance spectroscopy technique (EIS) was used to investigate the DNA sensor assembly process. Hybridization detection of DNA was performed with differential pulse voltammetry (DPV) and the methylene blue (MB) was hybridization indicator. Under the optimal conditions, the decline of reduction peak current of MB (ΔI) was linear with the logarithm of the concentration of complementary DNA from 1.0×10^?13 to 1.0×10^?6 mol·L^?1 with a detection limit of 3.5×10^?14 mol·L^?1 (S/N=3). In addition, this DNA biosensor has good selectivity, and even can distinguish single‐mismatched target DNA.     

Nickel oxide nanoparticles decorated graphene quantum dot as an effective electrode modifier for electrocatalytic oxidation and analysis of clozapine

In the present work, a novel, simple, and sensitive clozapine (CLZ) sensor was developed based on nickel oxide nanoparticle (NiO)-decorated graphene quantum dot (GQD)-modified glassy carbon electrode (NiO/GQD/GCE). NiO/GQD/GCE was prepared by simple electrodeposition, the electrochemical behavior of CLZ at the surface of the prepared electrode was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), and an improved reversibility and increased peak current with negative shift in the oxidation potential were observed at the proposed electrode. The effect of some experimental parameters has been examined, and based on the results, an electron transfer–chemical reaction–electron transfer mechanism has been proposed for CLZ electrooxidation. The differential pulse voltammetric response of the NiO/GQD/GCE was linear to the concentration of CLZ in the range of 3?×?10^?9 to 1?×?10^?6 M, and the detection limit was found to be 0.55 nM (S/N?=?3). The method has been successfully used for the selective determination of the CLZ amount in the pharmaceutical preparations and human serum samples with good accuracy and precision.     

A novel electrochemical sensor based on gold nanorods and Nafion-modified GCE for the electrocatalytic oxidation of nitrite

The high-quality CTAB-stabilized gold nanorods (Au NRs) were prepared by the way of seed-mediated protocol. The microstructure and composition of the Au NRs were identified by transmission electron microscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and UV–visible spectroscopy. Further, a novel non-enzymatic electrochemical sensor of nitrite based on Au NRs–Nafion-modified glassy carbon electrode (GCE) was successfully developed. Under the optimum experimental conditions, the electrochemical behaviors of nitrite on the Au NRs–Nafion-modified GCE were systematically studied by electrochemical impedance spectroscopy, cyclic voltammetry and chronoamperometry. The electrochemical investigations indicated that the Au NRs–Nafion-modified GCE had a wide linear range of 3.0 × 10^?6–6.0 × 10^?3 mol L^?1, an acceptable sensitivity of 130.9 ± 0.05 μA mM^?1 cm^?2, a fast response time of 3 s and a low detection limit of 0.64 ± 0.02 μmol L^?1 at the signal-to-noise ratio of 3 (S/N = 3). Additionally, the electrochemical sensor also showed good stability and favorable anti-interference capability for the detection of nitrite.     

Direct electrochemistry of glucose oxidase immobilized on TiO2–graphene/nickel oxide nanocomposite film and its application

A novel electrochemical platform based on nickel oxide (NiO) nanoparticles and TiO₂–graphene (TiO₂–Gr) was developed for the direct electrochemistry of glucose oxidase (GOD). The electrochemical behavior of the sensor was studied using cyclic voltammetry and chronoamperometry. The experimental results demonstrated that the nanocomposite well retained the activity of GOD and the modified electrode GOD/NiO/TiO₂–Gr/GCE exhibited excellent electrocatalytic activity toward the redox of GOD as evidenced by the significant enhancement of redox peak currents in comparison with bare GCE. The biosensor responded linearly to glucose in the range of 1.0–12.0?mM, with a sensitivity of 4.129?μA?mM^?1 and a detection limit of 1.2?×?10^?6?M under optimized conditions. The response time of the biosensor was 3?s. In addition, the developed biosensor possessed good reproducibility and stability, and there was negligible interference from other electroactive components.     

Preparation of Co3O4/graphene Oxide Composites by a Depositing‐decompostion Method and its Application for Electrochemical Determination of Glucose

Co₃O₄/graphene oxide (GO) nanocomposites were successfully prepared by a depositing‐decomposition method. The as‐prepared samples were characterized by scanning electron microscopy (SEM) and Raman spectroscopy. Cyclic voltammetry (CV) was used to evaluate the electrochemical response of a glass carbon electrode (GCE) modified with Co₃O₄/GO nanocomposite towards glucose. Compared with the Co₃O₄/GCE, the Co₃O₄/GO/GCE exihibits higher electrocatalytic activity due to the synergistic effects of electrocatalytic ability of Co₃O₄ and large surface of GO. The Co₃O₄/GO/GCE was applied for glucose detection in alkaline solution. The linear current response range of glucose on Co₃O₄/GO/GCE covered the range from 9 × 10^?5 to 6.03 × 10^?3 M, with a detection limit of 5.2 × 10^?7 M (S/N = 3).     

An enhanced oxime-based biomimetic electrochemical sensor modified with multifunctional AuNPs–Co<Subscript>3</Subscript>O<Subscript>4</Subscript>–NG composites for dimethoate determination

An enhanced oxime-based electrochemical sensor decorated with gold nanoparticles (AuNPs) and Co₃O₄ hexagonal nanosheets coupled with nitrogen-doped graphene has been developed for dimethoate determination dramatically. The introduction of Co₃O₄ hexagonal nanosheets tackles agglomeration of AuNPs and also enhances the sensitivity of electrochemical sensors greatly. The structure and properties of the synthesized composites were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy, confirming the successful modification of 2-(4-mercaptobutoxy)-1-naphthaldehyde oxime and Co₃O₄ supported AuNPs in a great experiment. In addition, differential pulse voltammetry further revealed that the developed electrochemical sensor exhibited excellent selectivity, sensitivity and stability in real samples analysis. Under optimal conditions, the modified sensor displayed a broad linear range from 1?×?10^?14 M to 1?×?10^?6 M with a fairly low detection limit of 8.4?×?10^?14 M (S/N?=?3) and was expected to act as a superior method for dimethoate determination.     

Electro‐oxidized Monolayer CVD Graphene Film Transducer for Ultrasensitive Impedimetric DNA Biosensor

We report the effect of electrochemical anodization on the properties of monolayer graphene as the main aim of this research and consequently using the resulting label‐free impedimetric biosensor for DNA sequences detection. Monolayer graphene was grown by chemical vapor deposition (CVD) with methane as precursor on copper foil, transferred onto a glassy carbon electrode and electrochemically anodized. Raman spectroscopy and X‐Ray photo electron spectroscopy revealed enhancement of defect density, roughness and formation of C−O−C, C−O−H and C=O functional groups after anodization. Amine‐terminated poly T probe was linked covalently to the carboxylic groups of anodized graphene by the zero‐length linker to fabricate the impedance‐based DNA biosensor. The anodized graphene electrode demonstrated a superior performance for electrochemical impedance detection of DNA. The DNA biosensor showed a large linear dynamic range from 2.0×10⁻¹⁸ to 1.0×10⁻¹² M with a limit of detection of 1.0×10⁻¹⁸ M using electrochemical impedance spectroscopy (EIS) method. Equivalent circuit modeling shows that DNA hybridization is detected through a change in charge transfer resistance.     

An electrochemical biosensor for direct detection of DNA using polystyrene-g-soya oil-g-imidazole graft copolymer

A label-free electrochemical DNA biosensor was developed through the attachment of polystyrene-g-soya oil-g-imidazole graft copolymer (PS-PSyIm) onto modified graphene oxide (GO) electrodeposited on glassy carbon electrode (GC). GC/GO electrode was initially functionalised via electrochemical reduction of 4-nitrobenzene diazonium salt, followed by the electrochemical reduction of NO₂ to NH₂. Subsequent to the electrochemical deposition of gold nanoparticles on modified surface, the attachment of the PS-PSyIm graft copolymer on the resulting electrode was achieved. The interaction of PS-PSyIm with DNA at the bare glassy carbon electrode was studied by cyclic voltammetry technique, and it was found that interaction predominantly takes place through intercalation mode. The selectivity of developed DNA biosensor was also explored by DPV on the basis of considering hybridisation event with non-complementary, one-base mismatched DNA and complementary target DNA sequence. Large decrease in the peak current was found upon the addition of complementary target DNA. The sensitivity of the developed DNA biosensor was also investigated, and detection limit was found to be 1.20 nmol L^?1.     

A Sensitive Electrochemical Sensor Based on Graphene Oxide Nanosheets Decorated by Fe3O4@Au Nanostructure Stabilized on Polypyrrole for Efficient Triclosan Sensing

Triclosan is broadly utilized as preservative or antiseptic in various cosmetic and personal care products. It becomes hazardous for environmental safety and human health more than a certain concentration. In this research, graphene oxide (GO) nanosheets were prepared by composing Fe₃O₄@Au nanostructure decorated GO together with polypyrrole (PPy) (Fe₃O₄@Au‐PPy/GO nanocomposite) in a facile way. The composite excellent increased the electrochemical response, presenting a high sensitive electrochemical method for triclosan detection. The synthesized Fe₃O₄@Au‐PPy/GO nanocomposite was characterized for its morphological, magnetically and structural properties by FESEM‐mapping, TEM, and XRD. The Fe₃O₄@Au‐PPy/GO nanocomposites modified glassy carbon electrodes (GCE), Fe₃O₄@Au‐PPy/GO GCE, showed a higher sensitivity good stability, reproducibility, lower LOD (2.5×10^?9 M) and potential practical application in electrochemical detection of triclosan under optimized experimental conditions.     

Ultra-sensitive electrochemical DNA biosensor based on signal amplification using gold nanoparticles modified with molybdenum disulfide,graphene and horseradish peroxidase

We have developed an ultra-sensitive electrochemical DNA biosensor by assembling probe ssDNA on a glassy carbon electrode modified with a composite made from molybdenum disulfide, graphene, chitosan and gold nanoparticles. A thiol-tagged DNA strand coupled to horseradish peroxidase conjugated to AuNP served as a tracer. The nanocomposite on the surface acts as relatively good electrical conductor for accelerating the electron transfer, while the enzyme tagged gold nanoparticles provide signal amplification. Hybridization with the target DNA was studied by measuring the electrochemical signal response of horseradish peroxidase using differential pulse voltammetry. The calibration plot is linear in the 5.0?×?10^?14 and 5.0?×?10^?9 M concentration range, and the limit of detection is 2.2?×?10^?15 M. The biosensor displays high selectivity and can differentiate between single-base mismatched and three-base mismatched sequences of DNA. The approach is deemed to provide a sensitive and reliable tool for highly specific detection of DNA.

Determination of 1‐Naphthol with Denatured DNA–Modified Pretreated Glassy Carbon Electrode

Abstract

A highly sensitive electrochemical biosensor for the detection of trace amount of 1‐naphthol was designed. Acid‐denatured DNA were immobilized onto the pretreated glassy carbon electrode (GCE(ox)) surface. Two well‐defined oxidation peaks were observed on the denatured DNA‐modified GCE(ox) at about +0.80 V and +1.10 V (vs. Ag/AgCl) in 0.10‐M acetate buffer (pH 5.0). The peak current of the guanine residue decreased with increasing concentration of 1‐naphthol. The optimum experimental conditions for the detection of 1‐naphthol were explored, and the calibration was linear for 1‐naphthol in the range of 1.0×10^?8?1.1×10^?6 M, with a correlation coefficient of 0.998. The limit of detection (LOD) was 5.0×10^?9 M (S/N=3).