Amperometric glucose sensor based on enhanced catalytic reduction of oxygen using glucose oxidase adsorbed onto core-shell Fe3O4@silica@Au magnetic nanoparticles

Monodisperse Fe₃O₄ magnetic nanoparticles (NPs) were prepared under facile solvothermal conditions and successively functionalized with silica and Au to form core/shell Fe₃O₄@silica@Au NPs. Furthermore, the samples were used as matrix to construct a glucose sensor based on glucose oxidase (GOD). The immobilized GOD retained its bioactivity with high protein load of 3.92 × 10^? 9 mol·cm^? 2, and exhibited a surface-controlled quasi-reversible redox reaction, with a fast heterogeneous electron transfer rate of 7.98 ± 0.6 s^? 1. The glucose biosensor showed a broad linear range up to 3.97 mM with high sensitivity of 62.45 μA·mM^? 1 cm^? 2 and fast response (less than 5 s).     

Modified gold surfaces by 6-(ferrocenyl)hexanethiol/dendrimer/gold nanoparticles as a platform for the mediated biosensing applications

An electrochemical biosensor mediated by using 6-(Ferrocenyl) hexanethiol (FcSH) was fabricated by construction of gold nanoparticles (AuNPs) on the surface of polyamidoamine dendrimer (PAMAM) modified gold electrode. Glucose oxidase (GOx) was used as a model enzyme and was immobilized onto the gold surface forming a self assembled monolayer via FcSH and cysteamine. Cyclic voltammetry and amperometry were used for the characterization of electrochemical response towards glucose substrate. Following the optimization of medium pH, enzyme loading, AuNP and FcSH amount, the linear range for the glucose was studied and found as 1.0 to 5.0 mM with the detection limit (LOD) of 0.6 mM according to S/N = 3. Finally, the proposed Au/AuNP/(FcSH + Cyst)/PAMAM/GOx biosensor was successfully applied for the glucose analysis in beverages, and the results were compared with those obtained by HPLC.     

Direct electron transfer and biosensing of glucose oxidase immobilized at multiwalled carbon nanotube-alumina-coated silica modified electrode

Investigations are reported regarding the direct electrochemical performance of glucose oxidase (GOD) immobilized on a film of multiwalled carbon nanotube-alumina-coated silica (MWCNT-ACS). The surface morphology of the GOD/MWCNT-ACS nanobiocomposite is characterized by scanning electron microscopy. In cyclic voltammetric response, the immobilized GOD displays a pair of well-defined redox peaks, with a formal potential (E°′) of ? 0.466 V versus Ag/AgCl in a 0.1 M phosphate buffer solution (pH 7.5) at a scan rate of 0.05 V s^? 1; also the electrochemical response indicates a surface-controlled electrode process. The dependence of formal potential on solution pH indicates that the direct electron transfer reaction of GOD is a reversible two-electron coupled with a two-proton electrochemical reaction process. The glucose biosensor based on the GOD/MWCNT-ACS nanobiocomposite shows a sensitivity of 0.127 A M^? 1 cm^? 2 and an apparent Michaelis–Menten constant of 0.5 mM. Furthermore, the prepared biosensor exhibits excellent anti-interference ability to the commonly co-existed uric acid and ascorbic acid.     

Biopolymer-clay nanoparticles composite system (Chitosan-laponite) for electrochemical sensing based on glucose oxidase

Nanocomposite matrix based on chitosan/laponite was successfully utilized to construct a new type of amperometric glucose biosensor. This hybrid material combined the merits of organic biopolymer, chitosan, and synthesized inorganic clay, laponite. Glucose oxidase (GOD) immobilized in the material maintained its activity well as the usage of glutaraldehyde was avoided. The composite films were characterized by Fourier transform infrared (FT-IR). The parameters affecting the fabrication and experimental conditions of biosensors were optimized. The sensitivity of the proposed biosensor (33.9 mA M^− 1 cm^− 2) permitted the determination of glucose in the concentration range of 1 × 10^− 6–5 × 10^− 5 M with a detection limit of 0.3 μM based on S/N = 3. The apparent Michaelis–Menten constant (K_M^app) for the sensor was found to be 15.8 mM.     

Amperometric biosensor based on carbon nanotubes coated with polyaniline/dendrimer-encapsulated Pt nanoparticles for glucose detection

A novel amperometric glucose biosensor based on the nanocomposites of multi-wall carbon nanotubes (CNT) coated with polyaniline (PANI) and dendrimer-encapsulated Pt nanoparticles (Pt-DENs) is prepared. CNT coated with protonated PANI is in situ synthesized and Pt-DENs is absorbed on PANI/CNT composite surface by self-assembly method. Then Glucose oxidase (GOx) is crosslink-immobilizated onto Pt-DENs/PANI/CNT composite film. The results show that the fabricated GOx/Pt-DENs/PANI/CNT electrode exhibits excellent response performance to glucose, such as low detection limit (0.5 µM), wide linear range (1 µM–12 mM), short response time (about 5 s), high sensitivity (42.0 µA mM^? 1 cm^? 2) and stability (83% remains after 3 weeks).     

Carbon nanotube/chitosan/gold nanoparticles-based glucose biosensor prepared by a layer-by-layer technique

A new amperometric glucose biosensor was constructed, based on the immobilization of glucose oxidase (GOx) with cross-linking in the matrix of chitosan on a glassy carbon electrode, which was modified by layer-by-layer assembled carbon nanotube (CNT)/chitosan (CHIT)/gold nanoparticles (GNp) multilayer films. With the increasing of CNT/CHIT/GNp layers, the response current to H₂O₂ was changed regularly and the response current reached a maximum value when the number of CNT/CHIT/GNp layers was 8. The assembling process of multilayer films was simple to operate. With GOx as an enzyme model, a new glucose biosensor was fabricated. The excellent electocatalytic activity and special structure of the enzyme electrode resulted in good characteristics. The linear range was 6 × 10^? 6 ～ 5 × 10^? 3 M, with a detection limit of 3 × 10^? 6 M estimated at a signal-to-noise ratio of 3, fast response time (less than 6 s). Moreover, it exhibited good reproducibility and stability.     

Development of amperometric laccase biosensor through immobilizing enzyme in copper-containing ordered mesoporous carbon (Cu-OMC)/chitosan matrix

A functionalized copper-containing ordered mesoporous carbon (Cu-OMC) which shows good electrical properties was synthesized by carbonization of sucrose in the presence of cupric acetate inside SBA-15 mesoporous silica template. Based on this, a facilely fabricated amperometric biosensor by entrapping laccase into the Cu-OMC/chitosan (CS) film was developed. Laccase from Trametes versicolor was assembled on a composite film of Cu-OMC/chitosan (CS) modified Au electrode and the electrode was characterized. The optimum experimental conditions of biosensor for the detection of catechol were studied in details. Under the optimal conditions, the detection limit was 0.67 μM and the linear detection range was from 0.67 μM to 15.75 μM for catechol. The apparent Michaelis–Menten (K_M^app) was estimated using the Lineweaver–Burk equation and the K_M^app value was 40.2 μM. This work demonstrated that the Cu-OMC/CS composite provides a suitable support for laccase immobilization and construction of biosensor.     

Conductometric enzyme biosensors based on natural zeolite clinoptilolite for urea determination

Highly sensitive conductometric urea biosensors were developed by exploiting the successful combination of ammonium-sieving and ion exchange properties of clinoptilolite, with a unique biorecognition capacity of urease. To optimize the performance of urea biosensors based on clinoptilolite, the dependences of their analytical signals on pH, buffer capacity and ionic strength of phosphate buffer solution (PBS) were studied. Optimum pH for urea biosensors was found within the range of pH 6.0–7.0. The dependences of biosensors responses on buffer capacity and ionic strength of PBS were of the same profile as those obtained for the urea biosensor which was not modified with clinoptilolite.Analytical characteristics of urea biosensors based on clinoptilolite were evaluated by determination of the sensitivity, linear and dynamic ranges, detection limit, the apparent Michaelis–Menten constant and the response time. The optimum features in terms of sensitivity, dynamic range, and detection limit (20.36 μS/mM, 0–64 mM, and 10^?6 M, respectively) were found for the urea biosensor, based on a primary layer of clinoptilolite followed by a secondary layer of urease and clinoptilolite in a single bioselective membrane. The apparent Michaelis–Menten constants K_m for the developed urea biosensors based on clinoptilolite varied from 2.73 to 5.67 mM. These values differed significantly from the value of K_m for the urea biosensor which was not modified with zeolite (1.89 mM). All types of zeolite-modified biosensors showed high operational and storage stability.     

Sensitive detection of mercury (II) ion using water-soluble captopril-stabilized fluorescent gold nanoparticles

In our work, a simple, facile, and green method was developed for the synthesis of water-soluble and well-dispersed fluorescent gold nanoparticles (Au NPs) within 5 min, using captopril as a capping agent. The as-prepared Au NPs showed strong emission at 414 nm, with a quantum yield of 5.5%. The fluorescence of the Au NPs can be strongly quenched by mercury (II) ion (Hg^2 +) due to the stronger interactions between thiolates (RS^?) and Hg^2 +. It was applied to the detection of Hg^2 + in water samples in the linear ranges of 0.033–0.133 μM and 0.167–2.500 μM, with a detection limit of 0.017 μM. Therefore, the as-prepared Au NPs can meet the requirement for monitoring Hg^2 + in environmental samples.     

Amperometric choline biosensors based on multi-wall carbon nanotubes and layer-by-layer assembly of multilayer films composed of Poly(diallyldimethylammonium chloride) and choline oxidase

A layer-by-layer deposition technique combined with Multi-wall carbon nanotubes (MWCNTs) was employed for fabricating choline sensors. The terminals and side-walls were linked with oxygen-containing groups when MWCNTs were treated with concentrated acid mixtures. A film of MWCNTs was initially prepared on the platinum electrode surface. Based on the electrostatic interaction between positively charged polyallylamine (PAA) and negatively charged MWCNTs and poly(vinyl sulfate) (PVS), a polymer film of (PVS/PAA)₃ was alternately adsorbed on the modified electrode continuously to be used as a permselective layer. Then poly(diallyldimethylammonium) (PDDA) and choline oxidase(ChOx) multilayer films were assembled layer-by-layer on the pretreated electrode, so an amplified biosensor toward choline was constructed. The choline sensor showed a linear response range of 5 × 10^? 7 to 1 × 10^? 4 M with a detection limit of 2 × 10^? 7 M estimated at a signal-to-noise ratio of 3, and a sensitivity of 12.53 μA/mM with a response time of 7.6 s in the presence of MWCNTs. Moreover, it exhibited excellent reproducibility, long-term stability as well as good suppression of interference. This protocol could be used to immobilize other enzymes for biosensor fabrication.     

Multi-walled carbon nanotubes-based glucose biosensor prepared by a layer-by-layer technique

The loading of multi-walled carbon nanotubes (MWNTs) and glucose oxidase (GOx) in the alternate layers of a glucose biosensor was first optimized based on a layer-by-layer construction on the surface of a graphite disk electrode. With the increasing of MWNTs/GOx layers, the response current to glucose was changed regularly and the response current reached a maximum value when the number of MWNTs/GOx layers was 6. Owing to a good electrical conductivity, strong adsorption and excellent bioconsistency of MWNTs, the (MWNTs/GOx)₆ films-coated glucose biosensor had an excellent electrochemical properties. The response current of the (MWNTs/GOx)₆ films-coated biosensor to 3 × 10^− 2 M glucose was 1.63 μA while the response time was only 6.7 s. The linear range and the lowest detectable concentration of this biosensor was 5 × 10^− 4∼1.5 × 10^− 2 M and 0.9 × 10^− 4 M, respectively.     

Layer-by-layer assemblies of chitosan/multi-wall carbon nanotubes and glucose oxidase for amperometric glucose biosensor applications

A novel amperometric glucose biosensor based on multilayer films containing chitosan, multi-wall carbon nanotubes (MWCNTs) and glucose oxidase (GOD) was developed. MWCNTs were solubilized in chitosan (Chit-MWCNTs) used to interact with GOD. Poly (allylamine) (PAA) and polyvinylsulfuric acid potassium salt (PVS) were alternately deposited on the cleaned Pt electrode surface ((PVS/PAA)₃/Pt). The (PVS/PAA)₃/Pt electrode was alternately immersed in Chit-MWCNTs and GOD to assemble different layers of multilayer films. PBS washing was applied at the end of each assembly deposition for dissociating the weak adsorption. Micrographs of MWCNTs were obtained by scanning electron microscope, and properties of the resulting biosensors were measured by electrochemical measurements. Among the resulting biosensors, the biosensor based on eight layers of multilayer films was best. The resulting biosensor was able to efficiently monitor glucose, with the response time within 8 s, a detection limit of 21 μM estimated at a signal-to-noise ratio of 3, a linear range of 1–10 mM, the sensitivity of 0.45 μA/mM, and well stability. The study can provide a feasible simple approach on developing a new immobilization matrix for biosensors and surface functionalization.     

A new immobilized glucose oxidase using SiO2 nanoparticles as carrier

Using SiO₂ nanoparticles as a carrier, a novel immobilized glucose oxidase (GOD) (EC1.1.3.4) was prepared via crosslinking with glutaraldehyde (GA). The optimal immobilization condition was achieved with 1% (v/v) GA, 2% (v/v) 3-aminopropiltrietoxysilane (APTS), 2.5 mg GOD (in 34 mg carrier) and solution pH of 6.5. The immobilized GOD showed maximal catalytic activity at pH 7.0 and 60 °C, and more than 85% of initial activity at the temperature from 20 °C to 80 °C. After immobilization, the enzyme exhibited improved thermal, storage and operation stability. The immobilized GOD still maintained 85% of its initial activity after the incubation at 45 °C for 360 min, whereas free enzyme had only 23% of initial activity after the same incubation. After kept at 4 °C for 30 days, the immobilized and free enzyme retained 84% and 60% of initial activity, respectively. The immobilized GOD also preserved 87% of its initial activity after six consecutive operations.     

A highly-sensitive l-lactate biosensor based on sol-gel film combined with multi-walled carbon nanotubes (MWCNTs) modified electrode

A new type of amperometric l-lactate biosensor based on silica sol-gel and multi-walled carbon nanotubes (MWCNTs) organic–inorganic hybrid composite material was developed. The sol-gel film was used to immobilize l-lactate oxidase on the surface of glassy carbon electrode (GCE). MWCNTs were used to increase the current response and improve the performance of biosensor. The sol-gel film fabrication process parameters such as H₂O : TEOS and pH were optimized, Effects of some experimental variables such as applied potential, temperature, and pH on the current response of the biosensor were investigated. Analytical characteristics and dynamic parameters of the biosensors with and without MWCNTs in the hybrid film were compared, and the results showed that analytical performance of the biosensor could be improved greatly after introduction of the MWCNTs. Sensitivity, linear range, limit of detection (S / N = 3) were 2.097 μA mM^− 1, 0.3 to 1.5 mM, 0.8 × 10^− 3 mM for the biosensor without MWCNTs and 6.031 μA mM^− 1, 0.2 to 2.0 mM, 0.3 × 10^− 3 mM for the biosensor with MWCNTs, respectively. This method has been used to determine the l-lactate concentration in real human blood samples.     

Direct electrochemistry and electrocatalysis of myoglobin immobilized on zirconia/multi-walled carbon nanotube nanocomposite

Zirconia/multi-walled carbon nanotube (ZrO₂/MWCNT) nanocomposite was prepared by hydrothermal treatment of MWCNTs in ZrOCl₂·8H₂O aqueous solution. The morphology and structure of the synthesized ZrO₂/MWCNT nanocomposite were characterized by transmission electron microscopy and X-ray diffraction analysis. It was found that ZrO₂ nanoparticles homogeneously distributed on the sidewall of MWCNTs. Myoglobin (Mb), as a model protein to investigate the nanocomposite, was immobilized on ZrO₂/MWCNT nanocomposite. Ultraviolet–visible spectroscopy and electrochemical measurements showed that the nanocomposite could retain the bioactivity of the immobilized Mb to a large extent. The Mb immobilized in the composite showed excellent direct electrochemistry and electrocatalytic activity to the reduction of hydrogen peroxide (H₂O₂). The linear response range of the biosensor to H₂O₂ concentration was from 1.0 to 116.0 μM with the limit of detection of 0.53 μM (S/N = 3). The ZrO₂/MWCNT nanocomposite provided a good biocompatible matrix for protein immobilization and biosensors preparation.     

Application of graphene–pyrenebutyric acid nanocomposite as probe oligonucleotide immobilization platform in a DNA biosensor

A stable and uniform organic–inorganic nanocomposite that consists of graphene (GR) and pyrenebutyric acid (PBA) was obtained by ultrasonication, which was characterized by scanning electron microscopy (SEM) and UV–vis absorption spectra. The dispersion was dropped onto a gold electrode surface to obtain GR–PBA modified electrode (GR–PBA/Au). Electrochemical behaviors of the modified electrode were characterized by cyclic voltammetry and electrochemical impedance spectroscopy using [Fe(CN)₆]^3 ?/4 ? as the electroactive probe. A novel DNA biosensor was constructed based on the covalent coupling of amino modified oligonucleotides with the carboxylic group on PBA. By using methylene blue (MB) as a redox-active hybridization indicator, the biosensor was applied to electrochemically detect the complementary sequence, and the results suggested that the peak currents of MB showed a good linear relationship with the logarithm values of target DNA concentrations in the range from 1.0 × 10^? 15 to 5.0 × 10^? 12 M with a detection limit of 3.8 × 10^? 16 M. The selectivity experiment also showed that the biosensor can well distinguish the target DNA from the non-complementary sequences.     

Preparation and characterization of copper nanoparticles/zinc oxide composite modified electrode and its application to glucose sensing

We report a new method for selective detection of d(+)-glucose using a copper nanoparticles (Cu-NPs) attached zinc oxide (ZnO) film coated electrode. The ZnO and Cu-NPs were electrochemically deposited onto indium tin oxide (ITO) coated glass electrode and glassy carbon electrode (GCE) by layer-by-layer. In result, Cu-NPs/ZnO composite film topography was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. SEM and AFM confirmed the presence of nanometer sized Cu-NPs/ZnO composite particles on the electrode surface. In addition, X-ray diffraction pattern revealed that Cu-NPs and ZnO films were attached onto the electrode surface. Indeed, the Cu-NPs/ZnO composite modified electrode showed excellent electrocatalytic activity for glucose oxidation in alkaline (0.1 M NaOH) solution. Further, we utilized the Cu-NPs/ZnO composite modified electrode as an electrochemical sensor for detection of glucose. This glucose sensor showed a linear relationship in the range from 1 × 10^? 6 M to 1.53 × 10^? 3 M and the detection limit (S/N = 3) was found to be 2 × 10^? 7 M. The Cu-NPs/ZnO composite as a non-enzymatic glucose sensor presents a number of attractive features such as high sensitivity, stability, reproducibility, selectivity and fast response. The applicability of the proposed method to the determination of glucose in human urine samples was demonstrated with satisfactory results.     

Oriented immobilization of immunoglobulin G onto the cuvette surface of the resonant mirror biosensor through layer-by-layer assembly of multilayer films

A new method for oriented immobilization of immunoglobulin G (IgG) onto the cuvette surface of the resonant mirror biosensor through layer-by-layer (LBL) assembly of multilayer films composed of avidin/gold nanoparticles (GNp)/protein A/IgG was developed. First, avidin was added in the biotin cuvette, and then injected GNp, followed by the injection of protein A for oriented immobilization of IgG. The rinsing with PBS was applied at the end of each assembly deposition for dissociating the weak adsorption. Second, IgG was added in the protein A-coated cuvette, and regenerated by incubation with 0.1 M glycine–HCL buffer. Third, different concentrations of IgG were measured by repeating the second process. Film assembling and properties of the interaction between protein A and IgG were studied by resonant mirror biosensor and electrochemical measurements. Results confirmed that IgG was successfully oriented on the protein A-coated cuvette surface by LBL assembly of multilayer films. The interaction response was dose-dependent which showed a linear range of 0.1 – 1.6 g L^− 1 IgG, with a detection limit of 8.7 mg L^− 1 estimated at a signal-to-noise ratio of 3. Moreover, the assay for oriented immobilization of IgG exhibited a good reproducibility and a favorable reusability. This method can provide a promising platform for fabricating immunoassay and immunosensor systems, protein reactors or protein-modified substrates, and affinity probes.     

A nano-structured Ni(II)–chelidamic acid modified gold nanoparticle self-assembled electrode for electrocatalytic oxidation and determination of methanol

A nano-structured Ni(II)–chelidamic acid (2,6-dicarboxy-4-hydroxypyridine) film was electrodeposited on a gold nanoparticle–cysteine–gold electrode. The morphology of Ni(II)–chelidamic acid gold nanoparticle self‐assembled electrode was investigated by scanning electron microscopy (SEM). Electrocatalytic oxidation of methanol on the surface of modified electrode was studied by cyclic voltammetry and chronoamperometry methods. The hydrodynamic amperometry at a rotating modified electrode at constant potential versus reference electrode was used for detection of methanol. Under optimized conditions the calibration plots are linear in the concentration range 0–50 mM with a detection limit of 15 μM. The formed matrix in our work possessed a 3D porous network structure with a large effective surface area, high catalytic activity and behaved like microelectrode ensembles. The modified electrode indicated reproducible behavior and a high level stability during the experiments, making it particularly suitable for analytical purposes.     

Label-free detection of aflatoxin M1 with electrochemical Fe3O4/polyaniline-based aptasensor

The selective detection of ultratrace amounts of aflatoxin M1 (AFM1) is extremely important for food safety since it is the most toxic mycotoxin class that is allowed to be present on cow milk with strictly low regulatory levels. In this work, Fe₃O₄ incorporated polyaniline (Fe₃O₄/PANi) film has been polymerized on interdigitated electrode (IDE) as sensitive film for AFM1 electrochemical biosensor. The immobilized aptamers as an affinity capture reagent and magnetic nanoparticles for signal amplification element have been employed in the sensing platform. Label-free and direct detection of the aptamer-AFM1 on Fe₃O₄/PANi interface were performed via electrochemical signal change, acquired by cyclic and square wave voltammetries. With a simplified strategy, this electrochemical aptasensor shows a good sensitivity to AFM1 in the range of 6–60 ng·L^? 1, with the detection limit of 1.98 ng·L^? 1. The results open up the path for designing cost effective aptasensors for other biomedical applications.