A Simple and Novel Electrochemical Sensor Based on Phosphomolybdic‐Polypyrrole Film Modified Electrode for Highly Sensitive Detection of Cholic Acid

A simpe electrochemical sensor for detection of cholic acid (CA) was designed by modifying phosphomolybdate (PMo₁₂) doped polypyrrole (PPy) film on glassy carbon electrode (PMo₁₂‐PPy/GCE). The electrochemical behavior of CA on PMo₁₂‐PPy/GCE was investigated by cyclic voltammetry and 0.5 order differential voltammetry. The results indicated that CA had high inhibitory activity toward the peak currents of PMo₁₂‐PPy/GCE. The reduction peak currents were linearly related to the logarithmic value of the concentration of CA from 1.0×10^?7 to 1.0×10^?3 mol/L with a low detection limit of 1.0×10^?8 mol/L. The developed sensor exhibited excellent sensitivity, selectivity and stability for detection of CA, and it could be successfully applied to detect the level of CA in the urine samples. Moreover, the response mechanism of CA on the PMo₁₂‐PPy/GCE was discussed in detail.     

Electrochemical DNA Biosensor Based on Partially Reduced Graphene Oxide Modified Carbon Ionic Liquid Electrode for the Detection of Transgenic Soybean A2704‐12 Gene Sequence

In this work a partially reduced graphene oxide (p‐RGO) modified carbon ionic liquid electrode (CILE) was prepared as the platform to fabricate an electrochemical DNA sensor, which was used for the sensitive detection of target ssDNA sequence related to transgenic soybean A2704‐12 sequence. The CILE was fabricated by using 1‐butylpyridinium hexafluorophosphate as the binder and then p‐RGO was deposited on the surface of CILE by controlling the electroreduction conditions. NH₂ modified ssDNA probe sequences were immobilized on the electrode surface via covalent bonds between the unreduced oxygen groups on the p‐RGO surface and the amine group at the 5′‐end of ssDNA, which was denoted as ssDNA/p‐RGO/CILE and further used to hybridize with the target ssDNA sequence. Methylene blue (MB) was used as electrochemical indicator to monitor the DNA hybridization. The reduction peak current of MB after hybridization was proportional to the concentration of target A2704‐12 ssDNA sequences in the range from 1.0×10^?12 to 1.0×10^?6 mol/L with a detection limit of 2.9×10^?13 mol/L (3σ). The electrochemical DNA biosensor was further used for the detection of PCR products of transgenic soybean with satisfactory results.     

In Vivo Monitoring of the Thiols in Rat Striatum by Liquid Chromatography with Amperometric Detection at a Functionalized Multi‐Wall Carbon Nanotubes Modified Electrode

A new chemically modified electrode (CME) was fabricated, which was based on the immobilization of multi‐wall carbon nanotubes fuctionalized with carboxylic group (MWNT‐COOH). The results indicated that the CME exhibited efficiently electrocatalytic oxidation for L ‐cysteine and glutathione with relatively high sensitivity, stability and long‐life. Coupled with HPLC, the MWNT‐COOH CME was utilized for amperometric detection of the thiols. The peak currents of L ‐cysteine and glutathione were linear to their concentrations ranging from 3.0×10^?7 to 1.0×10^?3 mol/L with the calculated detection limit (S/N=3) of 1.2×10^?7, 2.2×10^?7 mol/L, respectively. The method had been successfully applied to assess the contents of L ‐cysteine and glutathione in rat striatal microdialysates.     

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.     

Electrochemical aptamer sensor for highly sensitive detection of mercury ion with Au/Pt@carbon nanofiber‐modified electrode

In this paper, an electrochemical aptamer sensor was proposed for the highly sensitive detection of mercury ion (Hg²⁺). Carbon nanofiber (CNF) was prepared by electrospinning and high‐temperature carbonization, which was used for the loading of platinum nanoparticles (PtNPs) by the hydrothermal method. The Pt@CNF nanocomposite was modified on the surface of carbon ionic liquid electrode (CILE) to obtain Pt@CNF/CILE, which was further decorated by gold nanoparticles (AuNPs) through electrodeposition to get Au/Pt@CNF/CILE. Self‐assembling of the thiol‐based aptamer was further realized by the formation of Au‐S bond to get an electrochemical aptamer sensor (Aptamer/Au/Pt@CNF/CILE). Due to the specific binding of aptamer probe to Hg²⁺ with the formation of T‐Hg²⁺‐T structure, a highly sensitive quantitative detection of Hg²⁺ could be achieved by recording the changes of current signal after reacting with Hg²⁺ within the concentration range from 1.0 × 10^?15 mol/L to 1.0 × 10^?6 mol/L and the detection limit of 3.33 × 10^?16 mol/L (3σ). Real water samples were successfully analyzed by this method.     

An Electrochemical DNA Sensor Based on Electrodepositing Aluminum Ion Films on Stearic Acid‐Modified Carbon Paste Electrode and Its Application for the Detection of Specific Sequences Related to Bar Gene and CP4 Epsps Gene

An electrochemical DNA biosensor was fabricated by immobilizing DNA probe on aluminum ion films that were electrodeposited on the surface of the stearic acid‐modified carbon paste electrode (CPE). DNA immobilization and hybridization were characterized with cyclic voltammetry (CV) by using methylene blue (MB) as indicator. MB has a couple of well‐defined voltammetric redox peaks at the CPE. The currents of redox peaks of MB decreased after depositing aluminum ion films on the CPE (Al(III)/CPE) and increased dramatically after immobilizing DNA probe (ssDNA/Al(III)/CPE). Hybridization of DNA probe led to a marked decrease of the peak currents of MB, which can be used to detect the target single‐stranded DNA. The conditions for the preparation of Al(III)/CPE, and DNA immobilization and hybridization were optimized. The specific sequences related to bar transgene in the transgenic corn and the PCR amplification of CP4 epsps gene from the sample of transgenic roundup ready soybean were detected by differential pulse voltammetry (DPV) with this new electrochemical DNA biosensor. The difference between the peak currents of MB at ssDNA/Al(III)/CPE and that at hybridization DNA modified electrode (dsDNA/Al(III)/CPE) was applied to determine the specific sequence related to the target bar gene with the dynamic range comprised between 1.0×10^?7 mol/L to 1.0×10^?4 mol/L. A detection limit of 2.25×10^?8 mol/L of oligonucleotides can be estimated.     

Nano Au/TiO2 hollow microsphere membranes for the improved sensitivity of detecting specific DNA sequences related to transgenes in transgenic plants

Gold nanoparticles (nano Au)/titanium dioxide (TiO₂) hollow microsphere membranes were prepared on the carbon paste electrode (CPE) for enhancing the sensitivity of DNA hybridization detection. The immobilization of nano Au and TiO₂ microsphere was investigated with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The hybridization events were monitored with EIS using [Fe(CN)₆]^3?/4? as indicator. The sequence-specific DNA of the 35S promoter from cauliflower mosaic virus (CaMV35S) gene was detected with this DNA electrochemical sensor. The dynamic detection range was from 1.0×10^?12 to 1.0×10^?8 mol/L DNA and a detection limit of 2.3×10^?13 mol/L could be obtained. The polymerase chain reaction (PCR) amplification of the terminator of nopaline synthase (NOS) gene from the real sample of a kind of transgenic soybean was also satisfactorily detected.     

Chiral Recognition of Penicillamine Enantiomers Based on DNA‐MWNT Complex Modified Electrode

Double‐stranded DNA and multiwalled carbon nanotube (MWNT) complex modified glassy carbon electrodes (DNA‐MWNT‐GCE) were employed to discriminate penicillamine (PA) enantiomers. Cyclic voltammetry, electrochemical impedance spectroscopy, atomic force microscopy and ultraviolet‐visible spectroscopy were used to characterize the enantioselective phenomenon. The results indicated that the binding effect between L ‐PA and DNA‐MWNTs was stronger than that of D ‐PA and DNA‐MWNTs. In addition, the influencing factors of the modified electrodes were systematically investigated. The modified electrodes exhibited a linear response towards PA enantiomers from 1.0×10^?1 to 1.0×10^?8 mol L^?1 and detection limits of 3.1×10^?9 and 3.3×10^?8 mol L^?1 for L ‐PA and D ‐PA, respectively.     

Electrochemical and Spectroscopic Studies on the Interaction of Gallocyanine with DNA

The interaction of gallocyanine (GC) with double‐stranded DNA (dsDNA) in pH 3.5 Tris‐HCl buffer solution was investigated by electrochemical methods and spectrophotometric methods as well. In the potential scan range of ‐0.25 ? +0.18 V(vs. SCE), GC had a couple of well‐defined redox peaks at ‐0.022 V and ‐0.069 V on a cyclic voltammogram at the scan rate of 100.0 mV/s, respectively. After the addition of dsDNA into the GC solution, the redox‐peak currents decreased obviously and the peak potentials shifted positively. The results demonstrated that GC binding to DNA was caused by intercalation. Electrochemical parameters such as the electron number (n), the charge transfer coefficient (α) and the electrochemical reaction standard rate constant (k_s) were calculated and compared in the absence and presence of dsDNA. Almost unchanged values of the electrochemical parameters after adding dsDNA showed that non‐electroactive complexes were formed when GC interacted with DNA. The results indicated that the decrease of the redox‐peak currents was caused by the decrease of the free concentration of GC in the reaction solution. The binding constant and binding ratio were investigated by spectrophotometric methods. DNA concentration can be determined by the decrease of the peak current of GC. The linear range for dsDNA was in the range of 1.45 × 10^?7 ? 1.45 × 10^?6mol/Land 1.45 × 10^?6 ? 1.45 × 10^?5 mol/L, respectively with the linear regression equation as Δi_P (10^?7 A) = 0.037 + 0.018C (10^?7mol/L), and Δi_P (10^?7 A) = 0.25 + 0.041C (10^?6mol/L), respectively, and the detection limit (3σ) was 1.13 × 10^?7 mol/L.     

Molecularly Imprinted Electrochemical Luminescence Sensor Based on Enzymatic Amplification for Ultratrace Isoproturon Determination

A new molecularly imprinted electrochemical luminescence sensor (MIP‐ECL sensor) was developed for isoproturon (IPU) determination based on the competition reaction between IPU and glucose oxidase labeled IPU (GOD‐IPU). After competition, hydrogen peroxide produced by residual GOD‐IPU on the MIP reacted with luminol to emit electrochemiluminescence (ECL) signal. The ECL intensity decreased when the GOD‐IPU molecules were replaced by IPU molecules in the samples. IPU could be determined in the concentration range from 9×10^?11 mol/L to 5.1×10^?9 mol/L with a detection limit of 3.78×10^?12 mol/L. Water samples were assayed and recoveries ranging from 98.5 % to 102.1 % were obtained.     

Self-assembly of ultra-small gold nanoparticles on an indium tin oxide electrode for the enzyme-free detection of hydrogen peroxide

A novel enzyme-free electrochemical sensor for H₂O₂ was fabricated by modifying an indium tin oxide (ITO) support with (3-aminopropyl) trimethoxysilane to yield an interface for the assembly of colloidal gold. Gold nanoparticles (AuNPs) were then immobilized on the substrate via self-assembly. Atomic force microscopy showed the presence of a monolayer of well-dispersed AuNPs with an average size of ~4 nm. The electrochemical behavior of the resultant AuNP/ITO-modified electrode and its response to hydrogen peroxide were studied by cyclic voltammetry. This non-enzymatic and mediator-free electrode exhibits a linear response in the range from 3.0?×?10^?5 M to 1.0?×?10^?3 M (M?=?mol?·?L^?1) with a correlation coefficient of 0.999. The limit of detection is as low as 10 nM (for S/N?=?3). The sensor is stable, gives well reproducible results, and is deemed to represent a promising tool for electrochemical sensing.

Flow—injection Chemiluminescence Sensor for the Determination of Gallic Acid by Immobilizing Luminol and Periodate on Anionexchange Resin

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Study on the Electrochemical Behavior of Dopamine and Uric Acid at a 2‐Amino‐5‐mercapto‐[1,3,4] Triazole Self‐Assembled Monolayers Electrode

Selected from a series of structurally related heteroaromatic thiols, a newly synthesized reagent 2‐amino‐5‐mercapto‐[1,3,4] triazole (MATZ) was used to fabricate self‐assembled monolayers (SAMs) on gold electrode for the first time. The MATZ/Au SAMs was characterized by electrochemical methods and scanning electronic microscopy (SEM). In 0.04 mol/L Britton–Robinson buffer solution (pH 5), the electrochemical behavior of dopamine showed a quasireversible process at the MATZ/Au SAMs with an electrode kinetic constant 0.1049 cm/s. However, the electrochemical reaction of uric acid at the SAMs electrode showed an irreversible oxidation process, the charge‐transfer kinetics of uric acid was promoted by the SAMs. By Osteryoung square‐wave voltammetry (OSWV), the simultaneous determination of dopamine and uric acid can be accomplished with an oxidation peak separation of 0.24 V, the peak current of dopamine and uric acid were linearly to its concentration in the range of 2.5×10^?6–5.0×10^?4 mol/L for dopamine and 1×10^?6–1×10^?4 mol/L for uric acid with a detection limit of 8.0×10^?7 mol/L for dopamine and 7.0×10^?7 mol/L for uric acid. The MATZ/Au SAMs electrode was used to detect the content of uric acid in real urine and serum sample with satisfactory results.     

Electrochemical Detection of DNA Hybridization Based on the Probe Labeled with Carbon‐Nanotubes Loaded with Silver Nanoparticles

A sensitive electrochemical method for the detection of DNA hybridization based on the probe labeled with multiwall carbon‐nanotubes (MWNTs) loaded with silver nanoparticles (Ag‐MWNTs) has been developed. MWNTs were electroless‐plated with a large number of silver nanoparticles to form Ag‐MWNTs. Probe single strand DNA (ss‐DNA) with a thiol group at the 3′‐terminal labeled with Ag‐MWNTs by self‐assembled monolayer (SAM) technique was employed as an electrochemical probe. Target ss‐DNA with a thiol group was immobilized on a gold electrode by SAM technique and then hybridized with the electrochemical probe. Binding events were monitored by differential pulse voltammetric (DPV) signal of silver nanoparticles. The signal difference permitted to distinguish the match of two perfectly complementary DNA strands from the near perfect match where just three base pairs were mismatched. There was a linear relation between the peak current at +120 mV (vs. SCE) and complementary target ss‐DNA concentration over the range from 3.1×10^?14 to 1.0×10^?11 mol/L with a detection limit of 10 fmol/L of complementary target ss‐DNA. The proposed method has been successfully applied to detection of the DNA sequence related to cystic fibrosis. This work demonstrated that the MWNTs loaded with silver nanoparticles offers a great promising approach for sensitive detection of DNA hybridization.     

Sensitive Electrochemical Determination of Catechol with a Graphene Modified Carbon Ionic Liquid Electrode

In this paper a graphene (GR) modified carbon ionic liquid electrode (CILE) was fabricated and used as the voltammetric sensor for the sensitive detection of catechol. Due to the specific physicochemical characteristics of GR such as high surface area, excellent conductivity and good electrochemical properties, the modified electrode exhibits rapid response and strong catalytic activity with high stability toward the electrochemical oxidation of catechol. A pair of well‐defined redox peaks appeared with the anodic and the cathodic peak potential located at 225 mV and 133 mV (vs.SCE) in pH 6.5 phosphate buffer solution, respectively. Electrochemical behaviors of catechol on the GR modified CILE were carefully investigated and the electrochemical parameters were calculated with the results of the electrode reaction standard rate constant (k_s) as 1.24 s^?1, the charge transfer coefficient (α) as 0.4 and the electron transfer number (n) as 2. Under the selected conditions the differential pulse voltammetric peak current increased linearly with the catechol concentrations in the range from 1.0 × 10^‐7 to 7.0 × 10^?4mol L‐1 with the detection limit as 3.0 × 10^?8mol L‐1 (3σ). The proposed method was further applied to the synthetic waste water samples determination with satisfactory results     

The electrochemical oxidation of pentachlorophenol and its sensitive determination at chitosan modified carbon paste electrode

We report on a novel electrochemical method to detect trace pentachlorophenol (PCP) by using a chitosan (CS) modified carbon paste electrode (CS/CPE). Compared with that at a bare carbon paste electrode (CPE), the current response was greatly improved at the CS/CPE due to the enhancement effect of CS. Under optimal working conditions, the oxidation peak current of PCP was proportional to its concentration in the range of 1.0 × 10^?7 to 5.0 × 10^?6 and 5.0 × 10^?6 to 1.0 × 10^?4 mol/L, with an extremely low detection limit of 4.0 × 10^?8 mol/L. Our method was successfully used to detect the PCP concentration in vegetable samples.     

A Nitric Oxide Biosensor Based on Myoglobin Adsorbed on Multi‐Walled Carbon Nanotubes

Myoglobin (Myb) of horse heart is incorporated on multi‐walled carbon nanotubes (MWNTs) and immobilized at a glassy carbon (GC) electrode surface. Its electrochemical behavior and enzyme activity are characterized by employing electrochemical methods. The results indicate that MWNTs can obviously promote the direct electron transfer between Myb and electrode, and that the Myb on MWNTs behaves as an enzyme‐like activity towards the electrochemical reduction of nitric oxide (NO). Accordingly, an unmediated NO biosensor is constructed. Experimental results reveal that the peak current related to NO is linearly proportional to its concentration in the range of 2.0×10^?7–4.0×10^?5 mol/L. The detection limit is estimated to be 8.0×10^?8 mol/L. Considering a relative standard deviation of 2.1% in seven independent determinations of 1.0×10^?5 mol/L NO, this biosensor shows a good reproducibility. The biosensor based on Myb/MWNTs modified electrode can be used for the rapid determination of trace NO in aqueous solution with a good stability, nice selectivity and easy construction.     

Highly Selective Molecularly Imprinted Polymer Sensor for Indium Detection Based on Recognition of In‐Alizarin Complexes

A highly selective molecularly imprinted polymer electrochemical sensor for In³⁺ detection was proposed. In³⁺ ion was chelated with alizarin red S to form a complex In‐ARS. The complex was used as the template molecule to prepare a molecularly imprinted polymer (MIP) based sensor. The selectivity of the sensor was improved significantly due to the three‐dimensional specific structure of the complex, and the selective complexation of ligands for metal ions. Moreover, the sensitivity of the proposed sensor was improved by recording the reductive current of ligand in complex. This technique was highly sensitive for quantitative analysis of In³⁺ in the concentrations ranged from 1×10^?8 mol/L to 2.5×10^?7 mol/L with a detection limit of 4.7×10^?9 mol/L. The proposed sensor has been successfully used in detecting In³⁺ in real samples.     

Amperometric Sensor for Hydroxylamine Based on Hybrid Nickel‐Cobalt Hexacyanoferrate Modified Electrode

Hybrid nickel‐cobalt hexacyanoferrate (NiCoHCF) particles were immobilized onto a glassy carbon electrode by cyclic voltammetry. Characterization of these particles by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction and electrochemistry revealed that NiCoHCF was a substitution‐type hybrid hexacyanoferrate rather than a simple mixture system. As an important reducing agent, hydroxylamine could be electrocatalytically oxidized at the NiCoHCF modified electrode. The effects of the solution pH and the applied potential on the amperometric response of hydroxylamine were examined. Under optimum conditions, the catalytic peak current was proportional to the concentration of hydroxylamine in the range 2.0×10^?5–1.0×10^?2 mol/L with a detection limit of 2.3×10^?7 mol/L. Furthermore, detection results obtained with this sensor showed high sensitivity, fast response time, good stability and anti‐interference ability.     

A novel sensor based on multi-walled carbon nanotubes and boron-doped double-layer molecularly imprinted membrane for the analysis of SCZ in pharmaceutical and biological samples

ABSTRACT

A molecularly imprinted electrochemical sensor for the rapid detection of the anti-parasitic drug Secnidazole (SCZ) is reported. In this work, the build electrochemical sensor was based on a carbon paste electrode (CPE) modified with multi-wall carbon nanotubes (MWCNTs) and boron-embedded duplex molecularly imprinted composite membranes (B-DMICMs), that significantly increased the efficiency of the sensor for the detection of template molecule SCZ. Density functional theory (DFT) was employed to study the interactions between the template and monomers to select appropriate functional monomers for rational design of the B-DMICMs.The optimal experimental conditions were optimised for the factors affecting the performance of the sensor. Under the optimal conditions, the reduction peak currents of SCZ by differential pulse voltammetry increased linearly with SCZ concentration in the range from 3.0 × 10^?4 to 1.0 × 1.0^?6 mol L^?1 and 1.0 × 1.0^?6 to 1.91 × 10^?8 mol L^?1 with a detection limit of 1.72 × 10^?8 mol L^?1 for secnidazole, which is significantly lower than those in the currently used methods and in previous reports. This method offers low cost, sensitive and effective determination of SCZ and can potentially be used for detection of SCZ in pharmaceutical and biological samples with good precision and accuracy.