Search

In this work, a novel and ultrasensitive electrochemical biosensor was constructed for DNA detection based on functionalized gold clusters/graphene nanohybrids (AuNCs/GR nanobybrids) and exonuclease III (Exo III)-aided cascade target recycling. By utilizing the capacity of GR as universal template, different metal nanoclusters including AuNCs/GR nanobybrids and PtNCs/GR nanohybrids were synthesized through convenient ultrasonic method. Exo III-aided cascade recycling was initiated by target DNA, generating the final cleavage product (S2), which acted as a linkage between capture probe and the functionalized metal nanoclusters/GR conjugates in the construction of the biosensor. The AuNCs/GR-DNA-enzyme conjugates acted as interfaces of enzyme-catalyzed silver deposition reaction, achieving DNA detection ranging from 0.02 fM to 20 pM with a detection limit of 0.057 fM. In addition, PtNCs/GR-DNA conjugates presented peroxidase-like activity and the functionalized PtNCs/GR nanohybrids-based electrochemical biosensor also realized DNA detection by catalyzing the 3,3',5,5'-tetramethylbenzidine-hydrogen peroxide (TMB-H2O2) system to produce electrochemical signal. This metal clusters/GR-based multiple-amplified electrochemical biosensor provided an universal method for DNA detection.

In this paper, a novel label-free electrochemical impedance aptasensor for highly sensitive detection of IFN-γ based on target-induced exonuclease inhibition was constructed. For this purpose, we designed a DNA hairpin modified on the gold electrode whose loop was the aptamer of the IFN-γ, and the stem was 5′-thiol-modified. In the absence of IFN-γ, Exonuclease III (Exo III) and Exonuclease I (Exo I) digested the double-stranded and single-stranded strands of the hairpin DNA, respectively, causing smaller impedance value on the surface of the electrode. In the presence of IFN-γ, the function of Exo III was greatly inhibited by the binding of the aptamer with the target, and it stopped after cutting three bases of the hairpin DNA. Forming a major target-bound aptamer digestion product, it could not be digested by Exo I, so there was larger impedance on the electrode surface. The calibration curve for IFN-γ was linear in the range of 1 pM–50 nM with the detection limit (LOD) of 0.7 pM. The proposed aptasensor proved good selectivity and reproducibility, and low cost. In addition, the biosensor was able to detect IFN-γ in serum samples successfully, which is expected to provide an efficient method for TB diagnosis at early stages.

In this work, we have developed an electrochemical aptasensor for high-sensitivity determination of carcinoembryonic antigen (CEA) based on lead ion (Pb2+)-dependent DNAzyme-assisted signal amplification and graphene quantum dot-ionic liquid-nafion (GQDs-IL-NF) composite film. We designed hairpin DNA containing CEA-specific aptamers and DNAzyme chains. In the presence of CEA, hairpin DNA recognized the target and performed a DNAzyme-assisted signal amplification reaction to yield a large number of single-stranded DNA. The GQDs-IL-NF composite film was immobilized on the glassy carbon electrode for the interaction with single-stranded DNA through noncovalent π-π stacking interaction. Therefore, the methylene blue-labeled substrate DNA (MB-substrate) was fixed on the electrode and exhibited an initial electrochemical signal. Under optimal conditions, the response current change was proportional to the concentration of CEA, demonstrating a wide linear range from 0.5 fg mL−1 to 0.5 ng mL−1, with a low detection limit of 0.34 fg mL−1. Furthermore, the proposed aptasensor was successfully applied in determining CEA in serum samples, showing its superior prospects in clinical diagnosis.

A novel strategy to improve the sensitivity of molecularly imprinted polymer (MIP) sensors was proposed for the determination of β2-agonists. The imprinted sol-gel film was prepared by mixing silica sol with a functional monomer of antimony-doped tin oxide (ATO) and a template of β2-agonists. ATO, which was embedded in the surface of the molecularly imprinted sol-gel film, not only provides the excellent conductivity for biosensor but also increases the stability and the surface area of the MIP film. The imprinted sensor was characterised by field emission scanning electron microscope, fourier transform infrared spectroscopy and electrochemical methods. Under the optimal experimental conditions, the peak current was linear with the logarithm of the concentration of clenbuterol (CLB) in the range of 5.5 nM–6.3 µM, and a detection limit of 1.7 nM was obtained. Meanwhile, the electrochemical sensor showed excellent specific recognition of the template molecule among structurally similar coexisting substances. Furthermore, the proposed sensor was satisfactorily applied to determine β2-agonists in human serum samples. The good results indicated that highly effective molecularly imprinted sol-gel films doped with ATO can be employed for other analytes.

The direct electrochemistry and electrocatalysis of heme proteins entrapped in carbon-coated nickel magnetic nanoparticle–chitosan–dimethylformamide (CNN–CS–DMF) composite films were investigated in the hydrophilic ionic liquid [bmim][BF 4 ]. The surface morphologies of a representative set of films were characterised via scanning electron microscopy. The proteins immobilised in the composite films were shown to retain their native secondary structure using UV–vis spectroscopy. The electrochemical performance of the heme proteins–CNN–CS–DMF films was evaluated via cyclic voltammetry and chronoamperometry. A pair of stable and well-defined redox peaks was observed for the heme protein films at formal potentials of − 0.151 V (HRP), − 0.167 V (Hb), − 0.155 V (Mb) and − 0.193 V (Cyt c ) in [bmim][BF 4 ]. Moreover, several electrochemical parameters of the heme proteins were calculated by nonlinear regression analysis of the square-wave voltammetry. The addition of CNN significantly enhanced not only the electron transfer of the heme proteins but also their electrocatalytic activity toward the reduction of H 2 O 2 . Low apparent Michaelis–Menten constants were obtained for the heme protein–CNN–CS–DMF films, demonstrating that the biosensors have a high affinity for H 2 O 2 . In addition, the resulting electrodes displayed a low detection limit and improved sensitivity for detecting H 2 O 2 , which indicates that the biocomposite film can serve as a platform for constructing new non-aqueous biosensors for real detection.

Oxidative DNA damage is one of the most significant and extensively studied mechanisms of neurodegenerative diseases such as Parkinson and Alzheimer. This study was devoted to proposing an electrochemical method for monitoring oxidative DNA damage by hydroxyl radical through dopamine reacted with the localization of ferric catalytic. A hydrophobic room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), was applied as nonaqueous solvent for the generation of free radicals. DNA damage could be detected by differential pulse voltammetry signals of the electroactive indicator [Co(bpy)3]3+ and electrochemical impedance spectroscopy signals of [Fe(CN)6]3−/4−. More dramatic damage degree of DNA film initiated by dopamine/Fe2(SO4)3 reaction in [bmim][PF6] compared with that in an aqueous solution indicated that ionic liquid was much more suitable for the investigation of radicals induced DNA damage. The influences of incubation time and the molar ratio of dopamine/Fe2(SO4)3 to current respond were also explored. The most likely mechanism of DNA damage here was that the hydroxyl radical generated from the ferric ions facilitated oxidation of dopamine disturbed DNA double helix structure or caused DNA strand break. Furthermore, it turned out that both ascorbic acid and rutin could protect DNA from oxidative damage efficiently under certain conditions.

A novel electrochemical aptamer biosensor was designed based on the signal amplification of gold nanoparticles (AuNPs) for the detection of a tumor biomarker, carcinoembryonic antigen (CEA). The electrochemical biosensor was constructed by sandwiching the CEA between an Au electrode modified with thiol-terminated CEA aptamer-1 (Apt1) and the AuNPs with thiol-terminated CEA aptamer-2 (Apt2) and 6-ferrocenyl hexanethiol (Fc). Amperometric detection of Fc by differential pulse voltammetry (DPV) on the electrochemical biosensor was used to quantify the concentration of CEA. The biosensor provided a linear range from 1 to 200 ng/mL for CEA with a detection limit of 0.5 ng/mL. Its performance was successfully evaluated with human serum spiked with CEA, indicating that the aptasensor has great potential for practical application. In addition, the electrochemical biosensor exhibited excellent selectivity responses and good stability toward the target analyte. Keywords: Carcinoembryonic antigen, Aptamer, Electrochemical biosensor, Gold nanoparticles

This paper proposed an electrochemical biosensor supporting the viewpoints of oxidatively damaged DNA in neurodegeneration during the natural aging process and in neurodegenerative diseases. The presence of dopamine, a kind of redox-active catecholamine neurotransmitters, coupled with catalytic ferric ions could induce oxidatively DNA damage. [Co(bpy)3]3+ was employed in the detection of DNA damage by differential pulse voltammetry. The formed hydroxyl radical, as the substantial cause of DNA damage, was validated by Ultraviolet–visible spectroscopy. Electrochemical impedance spectroscopy (0.1 M [Fe(CN)6]3−/[Fe(CN)6]4− as the indicator) was also used for verifying that DNA charge transport was attenuated during the process of DNA damage. The optimizations of incubation time and dopamine/Fe2(SO4)3 molar ratio on DNA damage were explored. Moreover, the experimental results testified that both ascorbic acid and rutin could protect DNA from oxidative damage efficiently. Keywords: Hydroxyl radical, DNA damage, Dopamine, Electrochemical biosensors

We report on a glassy carbon electrode modified with carbon-coated nickel nanoparticles (C-Ni/GCE) that can be used to study the electrochemical properties of rutin and its interaction with bovine serum albumin (BSA) via cyclic voltammetry and differential pulse voltammetry. The effects of pH value, accumulation potential, accumulation time and reaction time were optimized. A pair of reversible peaks is found in the potential range of 0 to around 0.6 V at pH 5.0. Two linear response ranges (with different slopes) are found, one in the 2 to 210 nM concentration range, the other between 0.21 and 1.72 μM. The detection limit is as low as 0.6 nM. On addition of BSA to the rutin solution, a decrease of the current is observed that is proportional to the concentration of BSA. The binding constant and stoichiometric ratio were calculated.

A facile means to generate carbon dots/ionic liquids (ILs) blend using ionic liquid-assisted electrochemical exfoliation was demonstrated. Two kinds of ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), were used in this work. Transmission electron microscopy and UV–vis spectrum were employed to characterize the formed carbon dots/ILs. The carbon dots/ILs were used for fabricating quasi-solid-state dye-sensitized solar cells (DSSCs), where 1-butyl-3-methylimidazolium iodide and LiI/I2 were added to enhance the performance of DSSCs. Effects of the varied contents of components in the complex on the performance of DCCSs have been studied in detail at ambient temperature. The electrochemical impedance spectroscopy showed that the introduction of carbon dots into ionic liquids can enhance the electrical properties by facilitating charge transfer processes of the electrolytes. The overall energy-conversion efficiency (η) was 2.71% and 2.41% for carbon dots/[bmim][PF6] and carbon dots/[bmim][BF4] based blend electrolytes, respectively. A 82% enhancement in η was obtained by introduction of carbon dots into [bmim][PF6] comparing with pure [bmim][PF6] (η = 1.49%). In addition, the cells exhibited good stability under continuous illumination in room temperature without any further sealing.

Herein, we report a convenient approach to purify water-soluble dihydrolipoic acid (DHLA)-capped Ag nanoclusters (Ag NCs) by pH-induced precipitation under acidic conditions. The fluorescence of Ag NCs could be completely recovered by re-dispersing the precipitate into a basic solution using DHLA and NaBH4 as stabilizing ligands and etching reagent. DHLA-Ag NCs-doped agarose hydrogels have been prepared to monitor pH with a wide range from 8.0 to 4.0. When pH decreased, the fluorescence of the hydrogels under a UV lamp decreased and completely disappeared after pH 5. The DHLA-Ag NCs-doped agarose hydrogels biosensor showed low cytotoxicity and long stability. Accordingly, a fluorescent pH sensor for bacterial monitoring has been employed based on the "OFF-ON" signal switch of the Ag NCs-agarose hydrogel.

In this study, one-step electrochemical polymerized method for the fabrication of poly( o -aminophenol)/multi-walled carbon nanotubes (PoAP/MWCNTs) composite film was developed for the quantitative determination of levofloxacin. Scanning electron microscopy and electrochemical methods were used to characterize the PoAP/MWCNTs nanocomposite film. The sensor fabricated from the nanocomposite film showed good stability and enhanced electrocatalytic ability for the detection of levofloxacin. The large current response of levofloxacin on PoAP/MWCNTs composite film-modified electrode could be ascribed to the synergistic effect of the electrocatalytic property of PoAP and MWCNTs. The oxidative peak current increased linearly with the concentration of levofloxacin in the range of 3.0–200 μM by differential pulse voltammetry, and the detection limit was 1.0 μM (S/N = 3). The proposed modified electrode also can be successfully applied to the determination of levofloxacin hydrochloride in pharmaceutical formulations.

Electrochemical analysis of Fenton-mediated oxidative damage to protein was successfully investigated using a hydrophilic room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium tetrafluoroborate, as a medium. RTIL served as a nonaqueous solvent for monitoring bovine serum albumin (BSA) damage induced by hydroxyl radical. The oxidation signal of poly-o-phenylenediamine was used as a probe for the sensitive detection of BSA damage based on the attenuation of film conductivity after damage. More dramatic damage in IL compared with that in an aqueous solvent media confirmed that IL was suitable medium for the electrochemical detection of BSA damage. Dependence of damage degree on H2O2 concentration, the ratio of Fe2+ and H2O2 and the incubation time was obtained. Protection of BSA from damage by antioxidants was also investigated. The results showed that antioxidants could quench free radicals and combine with biomacromolecules in order to protect them. These conclusions proved that RTIL could be a promising application in the study of damage.

Detection of nitromethane (CH3NO2) has received scientists’ attention recently. However, its detection with the direct electrochemical measurement method was reported rarely. In this work, we explore an electrochemical biosensor for CH3NO2 based on immobilization of four heme proteins, sodium carboxymethyl cellulose (CMC), room temperature ionic liquid—1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) and multi-walled carbon nanotubes (MWNTs) biocomposite films. The surface morphologies of the representative heme proteins hybrid films were demonstrated by scanning electron microscopy (SEM). The different parameters, including working potential, pH of supporting electrolyte and the scan rate that governed the performance of the biosensor have been studied in detail and optimized. Electrocatalytic parameters for the determination of CH3NO2 with the four heme proteins film electrodes were evaluated by chronoamperometry.

Nitric oxide (NO) is a key signaling molecule in different physiological processes of plants. It is therefore very important to establish a simple, fast, sensitive and accurate detection method for NO detection. In this study, a novel amperometric biosensor based on immobilization of hemoglobin (Hb), chitosan (CS), graphene (GR) and the surfactant hexadecyltrimethylammonium bromide (CTAB) on a glassy carbon electrode was constructed to quantitatively measure NO. Atomic force microscopy, scanning electron microscopy and electrochemical methods were used to characterize the Hb–CS/GR–CTAB nanocomposite film. The biosensor fabricated from the nanocomposite film showed direct electrochemistry with a fast electron-transfer rate (60.3 s −1 ) and high electrocatalytic activity towards the reduction of NO. Under optimal conditions, the resulting biosensor exhibited a high sensitivity of 615 μA mM −1 , a low detection limit of 6.75 × 10 −9 M (S/N = 3) and a small apparent Michaelis–Menten constant of 0.315 μM. These results were superior to those for biosensors based on the graphite, GR/ionic liquid and carbon nanotubes. The biosensor was also used successfully for detection of additional NO in oilseed rape leaf homogenate samples. Furthermore, the biosensor had excellent long-term storage stability, as well as reproducibility and selectivity, and should have a potential application in monitoring NO in plant samples.

Oxidative protein damage is the most critical factor implicated in carcinogenesis and other disorders. However, the electrochemical detection of oxidative protein damage and the protections of protein from damage by antioxidants have been reported rarely. In this work, a novel, sensitive and inexpensive method for direct electrochemical detection of bovine serum albumin (BSA) damage in aqueous solutions is described. The simple electrochemical procedure has been constructed on the glassy carbon electrode (GCE) surface by BSA direct adsorption technique. Co(bpy)33+ was used as a redox indicator to monitor BSA damage induced by hydroxyl radical ( OH), which was produced from Fenton reaction. The simplest fabrication procedure and the most classic method of free radical production were used to research the protein damage, demonstrating obvious virtues of brachylogy, rigor and precise. The electrochemical behaviors of the underlying electrodes were characterized by differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Ultraviolet–visible (UV–vis) spectroscopy was used to verify the BSA damage with the universal index of the protein carbonyl group content. The optimizations of the Fe2+/H2O2 ratio and incubation time on BSA damage were explored. Moreover, the protections of BSA from damage by antioxidants were investigated. These conclusions demonstrated that the proposed method could be used to detect protein damage induced by Fenton reaction through a simple electrochemical approach.

The electrochemical oxidation behaviors of bilirubin (BR) at the bare glassy carbon electrode (GCE) were studied in dimethyl formamide (DMF) containing 1 vol.% of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) as the supporting electrolyte. Some electrochemical parameters of BR oxidation were investigated by cyclic voltammetry and chronocoulometry. The oxidation products were identified by the spectrophotometric technique. The basic BR showed good linear relationship in the range of 2.6×10 -5 to 2.5×10 -4 M, and the neutral BR presented two linear relationships in the range of 5.4×10 -4 to 1.1×10 -3 and 1.1×10 -3 to 1.6×10 -3 M. The mechanisms for the successive electro-oxidation of BR in different

The electrochemical behavior of aloe-emodin (AE), an important herbal antitumor drug, was investigated at a carbon-coated nickel magnetic nanoparticles modified glassy carbon electrode (CNN/GCE). A couple of well-defined redox peaks was obtained. Some electrochemical parameters of AE at a CNN/GCE, such as the charge number, exchange current density, standard heterogeneous rate constant, were measured. The square wave voltammetry (SWV) response of AE was linear with the concentration over two concentration intervals viz. 6.24×10−9−1.13×10−6 M and 1.13×10−6−1.23×10−5 M, with a detection limit of 2.08 nM. A fast, simple and sensitive detection and analysis of AE was developed.

A DNA-modified carbon paste electrode (DNA-CPIE) was designed by using a mixture of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate and paraffin oil as the binder. The electrochemistry of rutin at the DNA-CPIE was investigated by cyclic voltammetry and differential pulse voltammetry. Rutin exhibits a pair of reversible redox peaks in buffer solutions of pH 3.0, and respective electrochemical parameters are established. Under the optimal conditions, the oxidative peak current is linear with the concentration of rutin in the range from 8 × 10−9 to 1 × 10−5 mol L−1, and the detection limit is 1.3 × 10−9 mol L−1 (at S/N = 3). The electrode exhibits higher sensitivity compared to DNA modified carbon paste electrode without ionic liquid and better selectivity comparing with electrodes without DNA. It also showed good performance, stability, and therefore represents a viable method for the determination of rutin.

An ionic liquid-type carbon paste electrode (CPIE) was fabricated from 1-butyl-3-methylimidazolium hexafluorophosphate mixed with paraffin oil as the binder. The electrochemistry of Aloe-emodin (AE) at the electrode was investigated at pH 1.0 by cyclic voltammetry and differential pulse voltammetry. The ionic liquid as a binder distinctly enhances the electron transfer rate between AE and the electrode. A redox mechanism is discussed. The CPIE showed good sensitivity, selectivity and stability, and was applied to determine the concentration of AE. Under the optimal conditions, the oxidative peak current increased linearly with the concentration of AE in the range from 10 nM to 12.4 µM, with a correlation coefficient of 0.9973. The detection limit is 3.0 nM (at S/N = 3).

Electrochemical properties of nicotine at the glassy carbon electrode modified with multi-walled carbon nanotubes were explored. Nicotine underwent irreversible reduction at the modified electrode, which was an adsorption-controlled process with two protons and two electrons. The reductive peak current of nicotine significantly increased at the modified electrode compared with the bare glassy carbon electrode, suggesting that the multi-walled carbon nanotubes can enhance the electron transfer rate. The current was proportional to the concentration of nicotine over two line ranges, and the detection limit was 9.3 µM (at S/N = 3). For ten parallel detections of 0.62 mM nicotine, the relative standard deviation was 2.67%, suggesting that the film modified electrode had excellent reproducibility. The modified electrode was applied to the direct determination of nicotine in tobacco samples with good sensitivity, selectivity and stability.

The studies of the interaction between nicotine and DNA on the solid electrode were proposed for the first time. The electrochemical behaviors of nicotine and its interaction with DNA were explored by differential pulse voltammetry (DPV) at the DNA modified glassy carbon electrode (DNA/GCE). In 0.05 M Na2C2O4 (pH 4.24), nicotine at DNA/GCE showed an irreversible reductive behavior in the range of −1.6 to −1.1 V. The presence of DNA led to the decrease in the peak current of nicotine and the negative shift in the potential, indicating that nicotine could interact with DNA by electrostatic mode. The binding ratio between nicotine and DNA was calculated to be 2:1 and the binding constant was 8.31(±0.36) × 102. The interaction between nicotine and DNA could be further verified by UV–vis spectroscopy. Keywords: DNA, Nicotine, Interaction, Electrostatic mode, DPV

A carbon nanotube paste electrode was prepared by dispersion of multi-wall carbon nanotubes in mineral oil. An electrochemical study on acetaminophen showed that the peak current had increased and that the peak potential was negatively shifted compared to a carbon paste electrode without nanotubes, thus resulting in an electrode for acetaminophen. The linear range for the response ranges from 0.15 µM to 126 µM, and the detection limit is 43 nM (at S/N = 3). Electron transfer number, diffusion coefficient and proton number have been calculated. The relative standard deviation (n = 10; at 20 µM of acetaminophen) is 1.9%. The electrode was applied to determine acetaminophen in effervescent dosage samples.

The electrochemical properties of catechin at single-walled carbon nanotubes (SWNTs)–cetylramethylammonium bromide (CTAB) modified glassy carbon electrodes (GCE) were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The SWNTs–CTAB film was characterized with transmission electron microscopy (TEM). A series of parameters including pH of supporting electrolyte, accumulation potential and accumulation time were optimized. There were three peaks of catechin at SWNTs–CTAB/GCE in the potential range of − 0.4–1.0 V in PBS (pH 7.0): a reversible pair of peaks and an irreversible peak of the anodic peak. The reductive peak current increased linearly with the concentration of catechin in the range from 3.72 × 10 − 10 to 2.38 × 10 − 9 M. The detection limit was 1.12 × 10 − 10 M. The SWNTs–CTAB/GCE showed good stability and low detection limit, and could be applied to detect trace catechin.

The fast, visual discrimination of β2-agonist drugs is needed for the on-site screening of various types of β2-agonists in blood and urine samples. We developed a simple, rapid, one-step colorimetric method to detect phenolic β2-agonists by use of a tyrosinase catalytic reaction, which involved the oxidation of the phenol group on the benzene rings of β2-agonists. The enzymatic oxidation products of β2-agonists with phenolic groups exhibited different color transitions based on the different substituent groups on the aromatic ring, whereas β2-agonists with the aniline group or the resorcinol group remained colorless. This visual color discrepancy has been used to intuitively and conveniently differentiate the phenolic group β2-agonists, such as ractopamine, isoxsuprine, ritodrine, and fenoterol. The oxidation products of these compounds have been identified using mass spectrometry, and the possible reaction mechanisms between β2-agonists and tyrosinase have been deduced. The parameters that govern the analytical performance of the reaction product, including the pH of the buffer solution, the concentration of tyrosinase, and the incubation time, have been studied and optimized using ultraviolet-visible (UV-vis) spectroscopy and electrochemical methods. Under the optimal experimental conditions, the absorbance intensity and electrochemical signal were found to increase proportionally to the concentrations of the phenolic group β2-agonists, which gave a quantitative description of the β2-agonists in solution.

A novel platform based on a hairpin oligonucleotide (HO) switch, gold nanoparticles (AuNPs), and enzyme signal amplification for the ultrasensitive detection of mucin 1 protein (MUC1) was developed in this assay. This HO aptamers and horseradish peroxidase (HRP) were immobilised on the AuNPs to yield HO-AuNP-HRP conjugates. AuNPs were used as labels and bridges between the HO and HRP. HRP was also used as label for catalysing the oxidation of o-phenylenediamine by H2O2. The reaction product was 2,3-diaminophenazine (DAP), which was reduced and could be detected at surface of modified electrode. The reduction signal of DAP was used as a probe for the sensitive detection. After the recognition between oligonucleotide and MUC1, biotin was exposed. Biotin, along with the conjugate, was captured by streptavidin onto the surface of modified electrode. Therefore, the detection of target MUC1 which was a membrane-associated glycoprotein of the mucin family could be sensitively transduced via detection of the electrochemical reduction signal of DAP. Compared to other aptasensors, this biosensor has a good linear correlation ranges from 8.8 nM to 353.3 nM and a lower detection limit of 2.2 nM for MUC1. The proposed method provided a new electrochemical approach for the detection of MUC1.

Two imidazolium-based ionic liquids (ILs), hydrophilic 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) and hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), have been chosen as solvents for investigating bioelectroanalysis of four heme proteins. Heme proteins including hemoglobin, myoglobin, catalase and horseradish peroxidase immobilized in DNA can form stable and electrochemically active films on glassy carbon electrode. The morphology studies of films were demonstrated by atomic force microscopy. The direct electrochemistry of heme proteins were performed in ILs, and a pair of well-defined and nearly reversible redox peaks were observed. The electron transfer rate and reversibility of heme proteins in [bmim][BF4]/water were better than those in [bmim][PF6]. Through comparing several electrochemical parameters such as formal potentials and electron transfer rate constant of proteins in ILs, this paper tried to explain the differences of electrochemical properties of proteins as a function of viscosity, solubility characteristics, etc. of ILs. The possibility to specifically vary the properties of ILs by the selection of suitable cations and anions make them ideal candidates for wide applications in cell biological processes.

A novel nanocomposite film of tyrosinase-chitosan-carbon-coated nickel nanoparticles (CNi) had been constructed for the detection of catechol. The tyrosinase-chitosan-CNi bionanocomposite film was characterized with scanning electron microscopic (SEM) and electrochemical impedance spectroscopy (EIS). In pH 6.5 phosphate buffer solutions (PBS), the biosensor was applied to detect catechol with a broad linear range from 0.25 nM to 27 μM, the detection limit was brought down to 0.083 nM (S/N=3). The proposed biosensor demonstrated rapid response, as well as good reproducibility and stability. The chitosan-CNi film was propitious to the immobilization of tyrosinase and to the retention of its bioactivity to a large extent. Therefore, the film has potential applications in the immobilization of other enzyme-based biosensors.

A sensitive electrochemical procedure based on bovine serum albumin (BSA)/poly-o-phenylenediamine (PoPD)/carbon-coated nickel (C-Ni) nanobiocomposite film modified glassy carbon electrode (BSA/PoPD/C-Ni/GCE) has been developed to explore the electrochemical detection of BSA damage induced by hydroxyl radical. It is the first time that the electrochemical method has been applied for the analysis of Fenton-mediated oxidative damage to proteins. The hydroxyl radical was generated by Fenton reaction (Fe(2+)/H(2)O(2)), which was also validated by ultraviolet-visible (UV-vis) spectroscopy. The decrease in intensity of the PoPD oxidation signals was used as an indicator for the detection of BSA damage. Damage to BSA was also validated by horizontal Attenuation Total Reflection Fourier Transform Infra-red (ATR-FTIR) spectroscopy and the change of protein carbonyl group content achieved by UV-vis spectroscopy. Effects of H(2)O(2) concentration, the ratio of Fe(2+) and H(2)O(2) and incubation time on BSA damage were examined. Protections of BSA from damage by antioxidants were also investigated. These conclusions demonstrated that the proposed electrochemical method is expected to the further application for protein damage studies.

A novel biosensor for detecting glucose had been constructed by the immobilization of glucose oxidase (GOD) on chitosan-boron-doped carbon-coated nickel (BCNi) nanoparticle modified electrode. The GOD-chitosan-BCNi bionanocomposite film was characterized with scanning electron microscope (SEM). The film was propitious to the immobilization of GOD and to the retention of its bioactivity. The direct electrochemistry and electrocatalysis of GOD on modified electrode had been investigated by cyclic voltammogram (CV) and amperometric measurements. The GOD displayed a pair of stable, well-defined and quasi-reversible redox peaks in pH 7.0 phosphate buffer solution (PBS). Furthermore, the biosensor was applied to detect glucose with a broad linear range from 2.50 × 10 −5 to 1.19 × 10 −3 M, the detection limit was brought down to 8.33 × 10 −6 M at a signal to noise ratio of 3 and with an applied potential of −0.2 V. The proposed biosensor showed rapid response (within 3 s), low detection limit, high affinity to glucose and accepted storage stability over one-month period, which demonstrated that the chitosan-BCNi film has potential applications in the immobilization of other third-generation enzyme biosensors.

A novel amperometric biosensor for nitromethane (CH(3)NO(2)) based on immobilization of graphene (GR), chitosan (CS), hemoglobin (Hb) and room temperature ionic liquid (IL) on a glassy carbon electrode (GCE) was developed for the first time. The surface morphologies of a set of representative membranes were characterized by means of scanning electron microscopy (SEM). The electrochemical performance of the biosensor was evaluated by cyclic voltammetry (CV) and chronoamperometry. A pair of stable and well-defined redox peaks of Hb with a formal potential of -0.240 V was observed at the GR-CS/Hb/GR/IL/GCE. The effects of phosphate buffer pH, scan rate, and temperature on the biosensor were investigated to provide optimum analytical performance. Moreover, several electrochemical parameters, e.g., the heterogeneous electron transfer rate constant (k(s)), were calculated in detail. The presence of both GR and IL not only dramatically facilitated the electron transfer of Hb, but also greatly enhanced electrocatalytic activity towards CH(3)NO(2). The apparent Michaelis-Menten constant was down to 0.16 μM, indicating that the biosensor possessed high affinity to CH(3)NO(2). Besides this, the proposed biosensor exhibited fast amperometric response (