Synthesis of NiO/Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposites as substrate for the construction of electrochemical biosensors

The exploration of substrate materials to construct electrochemical biosensors for glucose monitoring in the field of clinical diagnosis, especially for diabetes is still being investigated extensively. In this paper, NiO/Fe₂O₃ nanocomposites are designed and synthesized by two-step hydrothermal approach in combination with calcinations. The morphology and microstructure are studied by SEM, XRD, XPS, and TEM systematically. Optimized NiO/Fe₂O₃ nanocomposites are employed as substrate to construct glucose biosensors, and the electrochemical properties are carried out by cyclic voltammetric and chronoamperometric techniques. The results indicate as-prepared biosensors achieve a high sensitivity of 230.5 μA cm^?2 mM^?1, wide linear range between 50 and 2867 μM, and low detection limit of 3.9 μM towards glucose detection. The synergistic effect between NiO and Fe₂O₃ as substrate to construct glucose biosensors is elucidated. The selectivity is acceptable based on the detection of glucose concentration for diabetics.     

Application of screen-printed microband biosensors incorporated with cells to monitor metabolic effects of potential environmental toxins

Microband biosensors were fabricated from a screen-printed water-based carbon ink containing cobalt phthalocyanine redox mediator and glucose oxidase or lactate oxidase enzyme. The microbiosensors were characterised for their ability to monitor ferrocyanide and H₂O₂ in phosphate buffer solution: sigmoidal cyclic voltammograms, high current density values and steady-state amperometric responses confirmed the existence of radial-diffusion-limiting microelectrode behaviour. The lactate microband biosensors were then used, in conjunction with a screen-printed Ag/AgCl reference and platinum counter electrode, to monitor lactate levels in culture medium, with a linear range of 0.5–5 mM, sensitivity of 20 nA.mM^?1, and dynamic range up to >9 mM. The lactate microband biosensors could operate continuously in culture medium over extended times (up to 24 h) at 37 °C. These biosensors were then applied to detect changes in lactate release from cultured cells in response to toxic challenge: m-dinitrobenzene (500 μM) caused a reduction in lactate production by high-passage number HepG2 single cells; D-galactosamine (20 mM) induced release of lactate by HepG2 spheroid cultures. This novel use of microband biosensors in cell culture has the potential for further application in toxicity monitoring, in both environmental and pharmaceutical areas.     

PANI–TiC nanocomposite film for the direct electron transfer of hemoglobin and its application for biosensing

A novel polyaniline and titanium carbide (PANI–TiC) nanocomposite was synthesized by an in situ chemical oxidative polymerization method, and a hydrogen peroxide (H₂O₂) biosensor was fabricated by PANI–TiC with hemoglobin (Hb)-modified glassy carbon electrode (GCE). Scanning electron microscope and energy dispersive X-ray spectroscopy showed the morphology and ingredient of PANI–TiC. Electrochemical investigation of the biosensor showed a pair of well-defined, quasi-reversible redox peaks with E _pa?=??0.318 V and E _pc?=??0.356 V (vs SCE) in 0.1 M, pH 7.0 sodium phosphate-buffered saline at the scan rate of 150 mV s^?1. Transfer rate constant (k _s) was 2.01 s^?1. The Hb/PANI–TiC/GCE showed a good electrochemical catalytic response for the reduction of H₂O₂ with the linear range from 0.5 to 285.5 μM and the detection limit of 0.2 μM (S/N?=?3). The apparent Michaelis–Menten constant (K _m) was estimated to be 1.21 μM. Therefore, the PANI–TiC as a novel matrix opened up a further possibility for study on the design of enzymatic biosensors with potential applications.     

Optical choline sensor based on a water-soluble fluorescent conjugated polymer and an enzyme-coupled assay

We report on a simple and sensitive water-soluble fluorescent conjugated polymer for use in a choline biosensor. Choline is oxidized by the enzyme choline oxidase (ChOx), and the hydrogen peroxide (H₂O₂) formed is used to oxidize catechol via catalysis by horseradish peroxidase. The product of oxidation acts as a quencher of the photoluminescence of a fluorescent conjugated polymer. The ratio of the fluorescence intensity of the system in the presence and absence of the choline, respectively, serves as the analytical information. It is proportional to the concentration of choline in the 0.1 μM to 20 μM concentration range. The detection limit for choline is 50 nM. The biosensor was successfully applied to the determination of choline in milk samples with satisfactory reproducibility and accuracy. This is the first biosensor where a ChOx/HRP enzyme-coupled assay is used in combination with a water-soluble conjugated polymer for the fluorescent detection of choline. In our opinion, it provides a common platform for further development of enzymatic biosensors based on fluorescent conjugated polymers.

Mediated electron transfer of cellobiose dehydrogenase and glucose oxidase at osmium polymer-modified nanoporous gold electrodes

Nanoporous and planar gold electrodes were utilised as supports for the redox enzymes Aspergillus niger glucose oxidase (GOx) and Corynascus thermophilus cellobiose dehydrogenase (CtCDH). Electrodes modified with hydrogels containing enzyme, Os-redox polymers and the cross-linking agent poly(ethylene glycol)diglycidyl ether were used as biosensors for the determination of glucose and lactose. Limits of detection of 6.0 (±0.4), 16.0 (±0.1) and 2.0 (±0.1) μM were obtained for CtCDH-modified lactose and glucose biosensors and GOx-modified glucose biosensors, respectively, at nanoporous gold electrodes. Biofuel cells composed of GOx- and CtCDH-modified gold electrodes were utilised as anodes, together with Myrothecium verrucaria bilirubin oxidase (MvBOD) or Melanocarpus albomyces laccase as cathodes, in biofuel cells. A maximum power density of 41 μW/cm² was obtained for a CtCDH/MvBOD biofuel cell in 5 mM lactose and O₂-saturated buffer (pH 7.4, 0.1 M phosphate, 150 mM NaCl).     

Gold nanoparticles and a glucose oxidase based biosensor: an attempt to follow-up aging by XPS

Amperometric biosensors are widely used for clinical, food industry and environmental control. A universal platform allowing immobilization of different enzymes could provide a fast and easy way to design new sensors, but the main drawback effect with oxidase based biosensors is the production of hydrogen peroxide. The direct electron transfer is a way to limit the H₂O₂ production. A modified electrode described by Zhao et al. (Bioelectrochemistry, 69(2):158, 2006), based on immobilization of glucose oxidase/colloidal gold nanoparticles on a glassy carbon electrode by Nafion film, has been used. Its sensitivity is 0.4 μA mM^?1 cm^?2, reproducibility is 3.0%, detection limit is 0.37 mM, response to glucose is linear up to 20 mM; limit of detection is 0.37 mM and response time is about 1.5 min. This sensor displays a formal redox potential compatible with a direct electron transfer, and has been tested for its response in time and GOx denaturation by X-ray photoelectron spectroscopy. Vanishing of disulphide bonds of GOx has been observed after a period in a saturating solution of glucose but this does not appear determinant in loss of enzyme activity.     

Potential of glucose measurement in soil and food sample using low molecular weight O-(2-hydroxyl)propyl-3-trimethylammonium chitosan chloride nanoparticle-glucose oxidase immobilised on a natural fibre membrane

Low, medium and high molecular weights O-(2-hydroxyl)propyl-3-trimethylammonium chitosan chloride nanoparticles (L-, M- and H-O-HTCC NP) have been synthesised and used to immobilise glucose oxidase on eggshell membranes for glucose biosensing. Among these O-HTCC NP-based biosensors, L-O-HTCC NP provides the highest sensitivity to glucose with a linear response of 0.012–0.60 mM and a detection limit of 12 μM (S/N = 3). The effect of L-O-HTCC NP and enzyme loading ratio, pH, temperature and phosphate buffer concentration on the sensitivity of the biosensor was studied in detail. The biosensor exhibits fast response time (40 s), good repeatability (3.0%, n = 10) and storage stability (95% of initial sensitivity after 1-year storage). Common interferents including acetic acid, DL-α-alanine, L-ascorbic acid, butyric acid, citric acid, DL-cysteine, ethanol, folic acid, glycine, lactic acid, lactose, propionic acid, sodium benzoate and sucrose do not cause significant interference on the L-O-HTCC NP biosensor. The recoveries 88.3%–102% and 102%–116% and relative standard deviations (RSDs) 3.90%–5.56% and 1.25%–3.00% are respectively, for the soil and food sample analyses. The proposed biosensor method has been applied to determine glucose in soil and food samples with good accuracy and recovery, inferring that it has potential for detection and quantification of diversified samples of different matrices. Finally, it has successfully monitored the changes of glucose contents in soil samples at various incubation times, demonstrating its potential use in environmental and geochemical analysis.     

Flow Injection Analysis of Hydrogen Peroxide,Sulfite, Formaldehyde and Hydroxymethanesulfonic Acid in Precipitation Samples

Abstract

Hydroxymethanesulfonic acid (HMSA), the reaction product of sulfite and formaldehyde plays an important part in the aqueous phase conversion of sulfite to sulfate. HMSA is fairly stable under acidic conditions and in presence of hydrogen peroxide. Sulfite is unstable under these conditions.

A flow injection set-up was developed, which allows the determination of H₂O₂, sulfite, formaldehyde and hydroxymethanesulfonic acid.

H₂O₂ analysis by amperometric detection offers the possibility of a simple, robust field instrument. The detection limit is 5μg/l and the method is linear up to 5mg/l.

Based on the 4,4-dithiodipyridine/sulfite reaction selective and sensitive spectrophotometric detections were developed for sulfite, formaldehyde and hydroxymethanesulfonic acid. The detection limit of these compounds is 50μg/l and the method is linear up to 5mg/l.

A large fraction of S(IV) is present as HMSA in fog, dew and precipitation samples in The Netherlands.     

Synergetic effect of Prussian blue film with gold nanoparticle graphite–wax composite electrode for the enzyme-free ultrasensitive hydrogen peroxide sensor

Enzyme-free amperometric ultrasensitive determination of hydrogen peroxide (H₂O₂) was investigated using a Prussian blue (PB) film-modified gold nanoparticles (AuNPs) graphite–wax composite electrode. A stable PB film was obtained on graphite surface through 2-aminoethanethiol (AET)-capped AuNPs by a simple approach. Field emission scanning electron microscope studies results in formation of PB nanoparticle in the size range of 60–80 nm. Surface modification of PB film on AET–AuNPs–GW composite electrode was confirmed by Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy studies. Highly sensitive determination of H₂O₂ at a peak potential of ?0.10 V (vs. SCE) in 0.1 M KCl PBS, pH?=?7.0) at a scan rate of 20 mVs^?1 with a sensitivity of 23.58 μA/mM was observed with the modified electrode using cyclic voltammetry. The synergetic effect of PB film with AuNPs has resulted in a linear range of 0.05 to 7,800 μM with a detection limit of 0.015 μM for H₂O₂ detection with the present electrode. Chronoamperometric studies recorded for the successive additions of H₂O₂ with the modified electrode showed an excellent linearity (R ²?=?0.9932) in the range of 4.8?×?10^?8 to 7.4?×?10^?8 M with a limit of detection of 1.4?×?10^?8 M. Selective determination of H₂O₂ in presence of various interferents was successfully demonstrated. Human urine samples and stain remover solutions were also investigated for H₂O₂ content.     

Hydrogen peroxide biosensor based on direct electrochemistry of hemoglobin immobilized on gold nanoparticles in a hierarchically porous zeolite

Highly dispersed gold nanoparticles (AuNPs) were introduced into a hierarchically porous zeolite of the MFI type that contains mesopores and an inherently microporous structure. These represent a novel matrix for the immobilization of biomolecules. The composites were characterized by FTIR, X-ray diffraction, UV–vis spectroscopy, transmission electron microscopy, nitrogen sorption measurements, and electrochemical impedance spectroscopy. The crystallinity and morphology of the zeolite is not compromised by incorporating the AuNPs with their size of 3–20 nm. A sensor for hydrogen peroxide (H₂O₂) was fabricated by incorporating hemoglobin into the matrix and placing it on the surface of a glassy carbon electrode. The resulting biosensor exhibits excellent bioelectrocatalytic capability for the reduction of H₂O₂. The amperometric response at ?0.4 V linearly depends on H₂O₂ in the 1.0 μM to 18 mM concentration range. The detection limit is 0.8 μM (at an S/N of 3). Its good sensitivity, stability and reproducibility make the modified hierarchically porous zeolite a promising new matrix material for protein immobilization and the construction of biosensors.

Detection of hydrogen peroxide releasing from prostate cancer cell using a biosensor

In this work, highly sensitive and selective hydrogel microstructures to detect hydrogen peroxide releasing from cancer cell based on electrochemical biosensors are proposed. Gold nanoparticles (AuNPs) were conjugated with horseradish peroxidase and were dispersed in the prepolymer solution of poly(ethylene glycol) diacrylate. The prepolymer solution was photolithographically patterned in alignment with an array of Au microelectrodes fabricated on glass. Performance of this biosensor was characterized by transmission electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. Under the optimal condition, the proposed biosensor can detect hydrogen peroxide (H₂O₂) in a wide linear range from 2 to 100 μM with a low detection limit of 0.01 μM. It can be also directly used to mark out extracellular H₂O₂ released from prostate cells. Furthermore, the reproducibility, stability, and selectivity of the biosensor are analogous with the previous report, so this methodology can be used in physiological and pathological detection of H₂O₂ in the future.     

Optical determination of glucose and hydrogen peroxide using a nanocomposite prepared from glucose oxidase and magnetite nanoparticles immobilized on graphene oxide

Fe₃O₄ nanoparticles were deposited on sheets of graphene oxide (GO) by a precipitation method, and glucose oxidase (GOx) was then immobilized on this material to produce a GOx/Fe₃O₄/GO magnetic nanocomposite containing crosslinked enzyme clusters. The 3-component composite functions as a binary enzyme that was employed in a photometric method for the determination of glucose and hydrogen peroxide where the GOx/Fe₃O₄/GO nanoparticles cause the generation of H₂O₂ which, in turn, oxidize the substrate N,N-diethyl-p-phenylenediamine to form a purple product with an absorption maximum at 550 nm. The absorbance at 550 nm can be correlated to the concentration of glucose and/or hydrogen peroxide. Under optimized conditions, the calibration plot is linear in the 0.5 to 600 μM glucose concentration range, and the detection limit is 0.2 μM. The respective plot for H₂O₂ ranges from 0.1 to 10 μM, and the detection limit is 0.04 μM. The method was successfully applied to the determination of glucose in human serum samples. The GOx/Fe₃O₄/GO nanoparticles are reusable.

Titanium dioxide nanorod-based amperometric sensor for highly sensitive enzymatic detection of hydrogen peroxide

Titanium dioxide nanorods (TNR) were grown on a titanium electrode by a hydrothermal route and further employed as a supporting matrix for the immobilization of nafion-coated horseradish peroxidase (HRP). The strong electrostatic interaction between HRP and TNR favors the adsorption of HRP and facilitates direct electron transfer on the electrode. The electrocatalytic activity towards hydrogen peroxide (H₂O₂) was investigated via cyclic voltammetry and amperometry. The biosensor exhibits fast response, a high sensitivity (416.9 μA·mM^?1), a wide linear response range (2.5 nM to 0.46 mM), a detection limit as low as 12 nM, and a small apparent Michaelis-Menten constant (33.6 μM). The results indicate that this method is a promising technique for enzyme immobilization and for the fabrication of electrochemical biosensors.

Direct electrochemistry and bioelectrocatalysis of a class II non-symbiotic plant haemoglobin immobilised on screen-printed carbon electrodes

In this study, direct electron transfer (ET) has been achieved between an immobilised non-symbiotic plant haemoglobin class II from Beta vulgaris (nsBvHb2) and three different screen-printed carbon electrodes based on graphite (SPCE), multi-walled carbon nanotubes (MWCNT-SPCE), and single-walled carbon nanotubes (SWCNT-SPCE) without the aid of any electron mediator. The nsBvHb2 modified electrodes were studied with cyclic voltammetry (CV) and also when placed in a wall-jet flow through cell for their electrocatalytic properties for reduction of H₂O₂. The immobilised nsBvHb2 displayed a couple of stable and well-defined redox peaks with a formal potential (E°′) of ?33.5 mV (vs. Ag|AgCl|3 M KCl) at pH 7.4. The ET rate constant of nsBvHb2, k _s, was also determined at the surface of the three types of electrodes in phosphate buffer solution pH 7.4, and was found to be 0.50 s^?1 on SPCE, 2.78 s^?1 on MWCNT-SPCE and 4.06 s^?1 on SWCNT-SPCE, respectively. The average surface coverage of electrochemically active nsBvHb2 immobilised on the SPCEs, MWCNT-SPCEs and SWCNT-SPCEs obtained was 2.85?×?10^?10 mol cm^?2, 4.13?×?10^?10 mol cm^?2 and 5.20?×?10^?10 mol cm^?2. During the experiments the immobilised nsBvHb2 was stable and kept its electrochemical and catalytic activities. The nsBvHb2 modified electrodes also displayed an excellent response to the reduction of hydrogen peroxide (H₂O₂) with a linear detection range from 1 μM to 1000 μM on the surface of SPCEs, from 0.5 μM to 1000 μM on MWCNT-SPCEs, and from 0.1 μM to 1000 μM on SWCNT-SPCEs. The lower limit of detection was 0.8 μM, 0.4 μM and 0.1 μM at 3σ at the SPCEs, the MWCNT-SPCEs, and the SWCNT-SPCEs, respectively, and the apparent Michaelis–Menten constant, $ {\hbox{K}}_{\rm{M}}^{\rm{app}} $ , for the H₂O₂ sensors was estimated to be 0.32 mM , 0.29 mM and 0.27 mM, respectively.     

Determination of hydrogen peroxide and glucose using a novel sensor platform based on Co0.4Fe0.6LaO3 nanoparticles

We report on a novel nonenzymatic sensor platform for the determination of hydrogen peroxide and glucose. It is based on a carbon paste electrode that was modified with Co_0.4Fe_0.6LaO₃ nanoparticles synthesized by the sol–gel method. The structure and morphology of Co_0.4Fe_0.6LaO₃ nanoparticles were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The electrochemical performance of this sensor was evaluated by cyclic voltammetry and amperometry, and the results demonstrated that it exhibits strong electrocatalytical activity towards the oxidation of H₂O₂ and glucose in an alkaline medium. The sensor has a limit of detection as low as 2.0 nM of H₂O₂ and a linear range that extends from 0.01 to 800 μM. The response to glucose is characterized by two analytical ranges of different slope, viz. from 0.05 to 5 μM and from 5 to 500 μM, with a 10 nM limit of detection. The glucose sensor has a fast response and good long term stability.

Optimization and characterization of a biosensor assembly for detection of <Emphasis Type="Italic">Salmonella</Emphasis> Typhimurium

The performance of biosensors depends directly on the strategies adopted during their development. In this paper, a fast and sensitive biosensor for Salmonella Typhimurium detection was assembled by using optimization studies in separate stages. The pre-treatment assays, biomolecular immobilization (primary antibody and protein A concentrations), and analytical response (hydroquinone and hydrogen peroxide concentrations) were optimized via voltammetric methods. In the biosensor assembly, a gold surface was modified via the self-assembled monolayer technique (SAM) using cysteamine thiol and protein A for immobilization of anti-Salmonella antibody. The analytical response of the biosensor was obtained through the use of a secondary antibody labeled with a peroxidase enzyme, and the signal was evaluated by applying the chronoamperometry technique. The biosensor was characterized by infrared spectroscopy and cyclic voltammetry. Optimization of protein A and primary antibody concentrations enabled higher analytical signals of 7.5 and 75 mg mL^?1, respectively, to be achieved. The hydroquinone and H₂O₂ concentrations selected were 3 and 300 mM, respectively. The biosensor developed attained a very low detection limit of 10 CFU mL^?1 and a fast response with a final detection time of 125 min. These results indicate that this biosensor is very promising for the food safety and emergency response applications.     

Carbon cloth-supported cobalt phosphide as an active matrix for constructing enzyme-based biosensor

A self-supported nanoporous cobalt phosphide (CoP) nanowire arrays on the carbon cloth (CC) as an active matrix was fabricated and utilized as an interface for the construction of hemoglobin (Hb)-based biosensors. This matrix was wrapped in a thin aluminum sheet by handmade. Moreover, the electrochemistry and electrocatalytic properties of Hb were investigated on such a matrix. The results revealed that the self-supported nanoporous CoP nanowire arrays on CC significantly enhanced the electrochemical responses of Hb. In the meantime, the immobilized Hb remained its good bioactivity and high catalytic activity to hydrogen peroxide (H₂O₂). This matrix is thus a suitable platform to develop highly sensitive enzyme-based biosensor, which has the linear range of H₂O₂ concentration from 2 to 2670 μM with a detection limit of 0.7 μM (S/N?=?3). Consequently, it is desirable to explore the possibility of developing a kind of simpler and cheaper matrix electrode.     

Amperometric determination of sulfite with sulfite oxidase immobilized at a platinum electrode surface

Sulfite oxidase is immobilized on collagen membrane at the surface of a platinum electrode and catalyzes the oxidation of sulfite to sulfate with stoichiometric production of hydrogen peroxide. The hydrogen peroxide is detected amperometically at the platinum electrode at an applied potential of 700 mV. The system responds linearly to sulfite in the range 1–150 μM, with a detection limit of 0.2 μM. The enzyme retains over 95% of its activity for three weeks if stored at ?20° C when the probe is not in use.     

Ag nanoparticles decorated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/chitosan nanocomposite: synthesis,characterization and application toward electrochemical sensing of hydrogen peroxide

We studied a rapid, sensitive and selective amperometric sensor for determination of hydrogen peroxide by electrodeposited Ag NPs on a modified glassy carbon electrode (GCE). The modified GCE was constructed through a step by step modification of magnetic chitosan functional composite (Fe₃O₄–CH) and high-dispersed silver nanoparticles on the surface. The resulted Ag@Fe₃O₄–CH was characterized by various analytical methods including Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy and cyclic voltammetry. The proposed sensor employed Ag@Fe₃O₄–CH/GCE as the working electrode with a linear current response to the hydrogen peroxide concentration in a wide range from 0.01 to 400 µM with a low limit of detection (LOD = 0.0038 µM, S/N = 3). The proposed sensor showed superior reproductivity, sensitivity and selectivity for the detection of hydrogen peroxide in environmental and clinical samples.     

Direct electrochemistry of horseradish peroxidase based on hierarchical porous calcium phosphate microspheres

Biomorphic calcium phosphate (CaP) microspheres with hierarchical porous structure were synthesized using natural cole pollen grains as templates and were further employed for the immobilization of horseradish peroxidase (HRP). Scanning electron microscopy and Fourier transform infrared spectroscopy revealed (a) the porous structure of the CaP microspheres, (b) the effective immobilization, and (c) the retention of the conformation of HRP on CaP. The immobilized HRP was placed on a glassy carbon electrode where it underwent a direct, fully reversible, and surface-controlled redox reaction with an electron transfer rate constant of 1.96 s^?1. It also exhibits high sensitivity to the reduction of H₂O_2. The response to H₂O₂ is linear in the 5.00 nM to 1.27 μM concentration range, and the sensitivity is 30357 μA?mM^?1?cm^?2. The detection limit (at an SNR of 3) is as low as 1.30 nM. The apparent Michaelis–Menten constant (K _M ^app ) of the immobilized enzyme is 0.92 μM. This new CaP with hierarchical porous structure therefore represents a material that can significantly promote the direct electron transfer between HRP and an electrode, and is quite attractive with respect to the construction of biosensors.