Gold-coated silica-fiber hybrid materials for application in a novel hydrogen peroxide biosensor

We describe the preparation and characterization of a novel type of core-shell hybrid material for application in a novel hydrogen peroxide biosensor, where the structure consists of a continuous gold shell that encapsulates the silica fiber. The SiO(2)@Au nanofibers had been synthesized by electrospinning silica sol, and then golden seeds were in situ grown on the fiber, lastly the gold-seeded silica fibers were further coated by continuous gold shells. The above nanocomposites had satisfactory chemical stability, excellent biocompatibility and efficient electron transfer property, which may have potential application for the highly sensitive chemical or biological sensors. Cyclic voltammetry (CV) was used to evaluate the electrochemical performance of the SiO(2)@Au nanocomposites at indium tin oxide (ITO). The biosensor showed high sensitivity and fast response upon the addition of H(2)O(2) and the linear range to H(2)O(2) was from 5×10(-6) to 1.0×10(-3)M with a detection limit of 2 μM (S/N=3). The apparent Michaelis-Menten constant of the biosensor was 1.11 mmol L(-1). These results indicated that SiO(2)@Au nanocomposites have potential for constructing of a variety of electrochemical biosensors.     

One-step construction of biosensor based on chitosan-ionic liquid-horseradish peroxidase biocomposite formed by electrodeposition

A simple and controllable electrodeposition approach was established for one-step construction of hydrogen peroxide (H(2)O(2)) biosensors by in situ formation of chitosan-ionic liquid-horseradish peroxidase (CS-IL-HRP) biocomposite film on electrode surface. A highly porous surface with orderly three-dimensional network was revealed by scanning electron microscopy (SEM) investigation. The biocomposite provided improved conductivity and biocompatible microenvironment. The developed biosensor exhibited a fast amperometric response for the determination of H(2)O(2) and 95% of the steady-state current was obtained within 2s. The linear response of the developed biosensor for the determination of H(2)O(2) ranged from 6.0x10(-7) to 1.6x10(-4)M with a detection limit of 1.5x10(-7)M. Performance of the biosensor was evaluated with respect to possible interferences and a good selectivity was revealed. The fabricated biosensor exhibited high reproducibility and long-time storage stability. The ease of the one-step non-manual technique and the promising feature of biocomposite could serve as a versatile platform for the fabrication of electrochemical biosensors.     

HRP/[Zn-Cr-ABTS] redox clay-based biosensor: design and optimization for cyanide detection

A novel inexpensive and simple amperometric biosensor, based on the immobilization of HRP into redox active [Zn-Cr-ABTS] layered double hydroxide, is applied to the determination of cyanide. The electrochemical transduction step corresponds to the reduction at 0.0 V of ABTS+* enzymatically formed in the presence of H2O2. The biosensor has a fast response to H2O2 (8s) with a linear range of 1.7 x 10(-9) to 2.1 x 10(-6) M and a sensitivity of 875 mA M(-1) cm(-2). The apparent Michaelis-Menten constant (KMapp) is 12 microM. The detection of cyanide is performed via its non competitive inhibiting action on the HRP/[Zn-Cr-ABTS] electrode. The concentration range of the linear response and the apparent inhibition constant (ki) are 5 x 10(-9) to 4 x 10(-8) and 1.4 x 10 (-7) M, respectively.     

A novel enzymatic hydrogen peroxide biosensor based on Ag/C nanocables

A novel enzymatic hydrogen peroxide sensor was successfully fabricated based on the nanocomposites containing of Ag/C nanocables and gold nanoparticles (AuNPs). Ag/C nanocables have been synthesized by a hydrothermal method and then AuNPs were assembled on the surface of Ag/C nanocables. The nanocomposites were confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS). The above nanocomposites have satisfactory chemical stability and excellent biocompatibility. Cyclic voltammetry (CV) was used to evaluate the electrochemical performance of the Ag/C/Au nanocomposites at glassy carbon electrode (GCE). The results indicated that the Ag/C/Au nanocomposites exhibited excellent electrocatalytic activity to the reduction of H(2)O(2). It offered a linear range of 6.7×10(-9) to 8.0×10(-6) M, with a detection limit of 2.2×10(-9) M. The apparent Michaelis-Menten constant of the biosensor was 51.7×10(-6) M. These results indicated that Ag/C/Au nanocomposites have potential for constructing of a variety of electrochemical biosensors.     

BSA-stabilized Au clusters as peroxidase mimetics for use in xanthine detection

In this paper, we demonstrated that bovine serum albumin (BSA) stabilized Au clusters exhibited highly intrinsic peroxidase-like activity. Unlike nature enzymes, the BSA-Au clusters have strong robustness and can be used over a wide range of pH and temperature. Because of ultra-small size, good stability and high biocompatibility in water solution compare with other kinds of nanoparticles as peroxidase mimetics, such as Fe(3)O(4), FeS or graphene oxide, it is more competent for bioanalysis. Furthermore, we make use of the novel properties of BSA-Au clusters as peroxidase mimetics to detect H(2)O(2). The as-prepared BSA-Au clusters were used to catalyze the oxidation of a peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) by H(2)O(2) to the oxidized colored product, and which provides a colorimetric detection of H(2)O(2). As low as 2.0 × 10(-8)M H(2)O(2) could be detected with a linear range from 5.0 × 10(-7) to 2.0 × 10(-5)M via this method. More importantly, a sensitive and selective method for xanthine detection was developed using xanthine oxidase (XOD) and the as-prepared BSA-Au clusters. The detection limit of this assay for xanthine was 5 × 10(-7)M and the proposed method was successfully applied for the determination of xanthine in urine and human serum sample.     

Amperometric third-generation hydrogen peroxide biosensor based on the immobilization of hemoglobin on multiwall carbon nanotubes and gold colloidal nanoparticles

A convenient and effective strategy for preparation nanohybrid film of multi-wall carbon nanotubes (MWNT) and gold colloidal nanoparticles (GNPs) by using proteins as linker is proposed. In such a strategy, hemoglobin (Hb) was selected as model protein to fabricate third-generation H2O2 biosensor based on MWNT and GNPs. Acid-pretreated, negatively charged MWNT was first modified on the surface of glassy carbon (GC) electrode, then, positively charged Hb was adsorbed onto MWNT films by electrostatic interaction. The {Hb/GNPs}n multilayer films were finally assembled onto Hb/MWNT film through layer-by-layer assembly technique. The assembly of Hb and GNPs was characterized with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and transmission electron microscopy (TEM). The direct electron transfer of Hb is observed on Hb/GNPs/Hb/MWNT/GC electrode, which exhibits excellent electrocatalytic activity for the reduction of H2O2 to construct a third-generation mediator-free H2O2 biosensor. As compared to those H2O2 biosensors only based on carbon nanotubes, the proposed biosensor modified with MWNT and GNPs displays a broader linear range and a lower detection limit for H2O2 determination. The linear range is from 2.1x10(-7) to 3.0x10(-3) M with a detection limit of 8.0x10(-8) M at 3sigma. The Michaelies-Menten constant KMapp value is estimated to be 0.26 mM. Moreover, this biosensor displays rapid response to H2O2 and possesses good stability and reproducibility.     

Ambient temperature detection of PCR amplicons with a novel sequence-specific nucleic acid lateral flow biosensor

The spherical porous Pd nanoparticle assemblies (NPAs) have been successfully synthesized by starch-assisted chemical reduction of Pd(II) species at room temperature. Such Pd NPAs are not simply used to enlarge the surface area and to promote the electron transfer. They also catalyze the reduction of H(2)O(2) which are regarded as horseradish peroxidase (HRP) substitutes in electron transfer process. By using them as electrocatalysts, as low as 6.8×10(-7) M H(2)O(2) can be detected with a linear range from 1.0×10(-6) to 8.2×10(-4) M. Moreover, through co-immobilization of such Pd NPAs and glucose oxidase (GOx), a sensitive and selective glucose biosensor is developed. The detection principle lies on measuring the increase of cathodic current by co-reduction of dissolved oxygen and the in situ generated H(2)O(2) during the enzymatic reaction. Under optimal conditions, the detection limit is down to 6.1×10(-6) M with a very wide linear range from 4.0×10(-5) to 2.2×10(-2) M. The proposed biosensor shows a fast response, good stability, high selectivity and reproducibility of serum glucose level. It provides a promising strategy to construct fast, sensitive, stable and anti-interferential amperometric biosensors for early diagnosis and prevention of diabetes.     

TiO(2) nanocrystals electrochemiluminescence quenching by biological enlarged nanogold particles and its application for biosensing

Electrochemiluminescence (ECL) of TiO(2) nanocrystals with different crystal styles modified fluorine-doped tin oxide (FTO) electrode was investigated in H(2)O(2) solution. The amorphous TiO(2) nanospheres were facilely synthesized by the hydrothermal and condensation method. Crystal TiO(2), namely anatase and rutile, were prepared by calcination of the amorphous TiO(2) nanospheres at 450 and 800°C, respectively. The transmission electron microscope (TEM) and electron diffraction pattern were used to characterize the obtained TiO(2) nanoparticles morphology and the corresponding crystal styles. The electrochemical and ECL behaviors were investigated by cyclic voltammetry. The ECL quenching was observed by introduction of gold nanoparticles. Based on the quenching effect, a sensitive glucose ECL biosensor as a model was fabricated by in-situ growing-up gold seeds in AuCl(4)(-) solution induced by biologically generated H(2)O(2). The linear range to detect glucose is from 5.0×10(-7)M to 4.0×10(-3)M with the limit of detection of 2.5×10(-7)M.     

Amperometric hydrogen peroxide biosensor based on the immobilization of HRP on nano-Au/Thi/poly (p-aminobenzene sulfonic acid)-modified glassy carbon electrode

A novel hydrogen peroxide biosensor was fabricated for the determination of H(2)O(2). The precursor film was first electropolymerized on the glassy carbon electrode with p-aminobenzene sulfonic acid (p-ABSA) by cyclic voltammetry (CV). Then thionine (Thi) was adsorbed to the film to form a composite membrane, which yielded an interface containing amine groups to assemble gold nanoparticles (nano-Au) layer for immobilization of horseradish peroxidase (HRP). The electrochemical characteristics of the biosensor were studied by CV and chronoamperometry. The factors influencing the performance of the resulting biosensor were studied in detail. The biosensor responded to H(2)O(2) in the linear range from 2.6 x 10(-6) mol/L to 8.8 x 10(-3) mol/L with a detection limit of 6.4 x 10(-7) mol/L. Moreover, the studied biosensor exhibited good accuracy and high sensitivity. The proposed method was economical and efficient, making it potentially attractive for the application to real sample analysis.     

Reductive determination of hydrogen peroxide with MWCNTs-Pd nanoparticles on a modified glassy carbon electrode

This paper introduces the use of multi walled carbon nanotubes (MWCNTs) with palladium (Pd) nanoparticles in the electrocatalytic reduction of hydrogen peroxide (H(2)O(2)). We have developed and characterized a biosensor for H(2)O(2) based on Nafion(?) coated MWCNTs-Pd nanoparticles on a glassy carbon electrode (GCE). The Nafion(?)/MWCNTs-Pd/GCE electrode was easily prepared in a rapid and simple procedure, and its application improves sensitive determination of H(2)O(2). Characterization of the MWCNTs-Pd nanoparticle film was performed with transmission electron microscopy (TEM), Raman, and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) and amperometry (at an applied potential of -0.2V) measurements were used to study and optimize performance of the resulting peroxide biosensor. The proposed H(2)O(2) biosensor exhibited a wide linear range from 1.0 μM to 10 mM and a low detection limit of 0.3 μM (S/N=3), with a fast response time within 10s. Therefore, this biosensor could be a good candidate for H(2)O(2) analysis.     

A novel hydrogen peroxide biosensor based on the immobilization of horseradish peroxidase onto Au-modified titanium dioxide nanotube arrays

In this study, we report on a promising H(2)O(2) biosensor based on the co-immobilization of horseradish peroxidase (HRP) and chitosan onto Au-modified TiO(2) nanotube arrays. The titania nanotube arrays were directly grown on a Ti substrate using anodic oxidation first; a gold thin film was then uniformly coated onto the TiO(2) nanotube arrays by an argon plasma technique. The morphology and composition of the fabricated Au-modified TiO(2) nanotube arrays were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Cyclic voltammetry and chronoamperometry were used to study and to optimize the performance of the resulting electrochemical biosensor. The effect of pH, applied electrode potential, the presence of the electron-mediator methylene blue, and the anodic oxidation time of the Ti substrate on the electrochemical biosensor has been systemically studied. Our electrochemical measurements show that the Au-modified TiO(2) nanotube arrays provide excellent matrices for the immobilization of HRP and that the optimized electrochemical biosensor exhibits long linearity, a low detection limit, high stability and very good reproducibility for the detection of H(2)O(2). Under the optimized conditions the linearity of the developed biosensor for the detection of H(2)O(2) is observed from 5 x 10(-6) to 4 x 10(-4) moll(-1) with a detection limit of 2 x 10(-6) moll(-1) (based on the S/N=3).     

Synthesis of functional SiO₂-coated graphene oxide nanosheets decorated with Ag nanoparticles for H₂O₂ and glucose detection

In this paper, we report on the first preparation of well-defined SiO(2)-coated graphene oxide (GO) nanosheets (SiO(2)/GO) without prior GO functionalization by combining sonication with sol-gel technique. The functional SiO(2)/GO nanocomposites (F-SiO(2)/GO) obtained by surface functionalization with NH(2) group were subsequently employed as a support for loading Ag nanoparticles (AgNPs) to synthesize AgNP-decorated F-SiO(2)/GO nanosheets (AgNP/F-SiO(2)/GO) by two different routes: (1) direct adsorption of preformed, negatively charged AgNPs; (2) in situ chemical reduction of silver salts. The morphologies of these nanocomposites were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It is found that the resultant AgNP/F-SiO(2)/GO exhibits remarkable catalytic performance for H(2)O(2) reduction. This H(2)O(2) sensor has a fast amperometric response time of less than 2s. The linear range is estimated to be from 1×10(-4) M to 0.26 M (r=0.998) and the detection limit is estimated to be 4 × 10(-6) M at a signal-to-noise ratio of 3, respectively. We also fabricated a glucose biosensor by immobilizing glucose oxidase (GOD) into AgNP/F-SiO(2)/GO nanocomposite-modified glassy carbon electrode (GCE) for glucose detection. Our study demonstrates that the resultant glucose biosensor can be used for the glucose detection in human blood serum.     

Carboxymethylcellulose–gelatin–superoxidase dismutase electrode for amperometric superoxide radical sensing

A novel, highly sensitive superoxide dismutase biosensor for the direct and simultaneous determination of superoxide radicals was developed by immobilization of superoxide dismutase within carboxymethylcellulose-gelatin on a Pt electrode surface. The parameters affecting the performance of the biosensor were investigated. The response of the CMC-G-SOD biosensor was proportional to O (2) (·-) concentration and the detection limit was 1.25 × 10(-3) mM with a correlation coefficient of 0.9994. The developed biosensor exhibited high analytical performance with wider linear range, high sensitivity and low response time. The biosensor retained 89.8% of its sensitivity after use for 80 days. The support system enhanced the immobilization of superoxide dismutase and promoted the electron transfer of superoxide dismutase minimizing its fouling effect. The biosensor was quite effective not only in detecting O (2) (·-) , but also in determining the antioxidant properties of acetylsalicylic acid-based drugs and the anti-radical activity of healthy and cancerous human brain tissues.     

DNA electrochemical biosensor based on thionine-graphene nanocomposite

A novel protocol for development of DNA electrochemical biosensor based on thionine-graphene nanocomposite modified gold electrode was presented. The thionine-graphene nanocomposite layer with highly conductive property was characterized by scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. An amino-substituted oligonucleotide probe was covalently grafted onto the surface of the thionine-graphene nanocomposite by the cross-linker glutaraldehyde. The hybridization reaction on the modified electrode was monitored by differential pulse voltammetry analysis using an electroactive intercalator daunomycin as the indicator. Under optimum conditions, the proposed biosensor exhibited high sensitivity and low detection limit for detecting complementary oligonucleotide. The complementary oligonucleotide could be quantified in a wide range of 1.0 × 10(-12) to 1.0 × 10(-7)M with a good linearity (R(2)=0.9976) and a low detection limit of 1.26 × 10(-13)M (S/N=3). In addition, the biosensor was highly selective to discriminate one-base or two-base mismatched sequences.     

Glucose biosensor based on Au nanoparticles-conductive polyaniline nanocomposite

In this paper, we report a novel glucose biosensor based on composite of Au nanoparticles (NPs)-conductive polyaniline (PANI) nanofibers. Immobilized with glucose oxidase (GOx) and Nafion on the surface of nanocomposite, a sensitive and selective biosensor for glucose was successfully developed by electrochemical oxidation of H2O2. The glucose biosensor shows a linear calibration curve over the range from 1.0x10(-6) to 8.0x10(-4) mol/L, with a slope and detection limit (S/N=3) of 2.3 mA/M and 5.0x10(-7) M, respectively. In addition, the glucose biosensor system indicates excellent reproducibility (less than 5% R.S.D.) and good operational stability (over 2 weeks).     

An integrated microfluidic system for rapid screening of alpha-fetoprotein-specific aptamers

An electrically neutral cobalt complex, Co(Eim)(4)(NCS)(2) (Eim=1-ethylimidazole, NCS=isothiocyanate) was synthesized and its interaction with double-stranded DNA (dsDNA) was comprehensively studied by electrochemical methods on a glassy carbon electrode (GCE). The experimental results revealed that the cobalt complex could interact with dsDNA via a specific groove-binding mode with an affinity constant of 3.6×10(5)M(-1). The surface-based studies showed that Co(Eim)(4)(NCS)(2) could electrochemically accumulate within the immobilized dsDNA layer rather than single-stranded DNA (ssDNA) layer. Based on this fact, the cobalt complex was utilized as an electrochemical hybridization indicator for the detection of oligonucleotides related to CaMV35S promoter gene. The results showed that the developed biosensor presented very low background interference due to the negligible affinity of the Co(Eim)(4)(NCS)(2) complex with ssDNA. The hybridization specificity experiments further indicated that the biosensor could well discriminate the complementary sequence from the base-mismatched and the non-complementary sequences. The complementary target sequence could be quantified over the range from 5.0×10(-9)M to 2.0×10(-6)M with a detection limit of 2.0×10(-10)M.     

Electrochemical study of a new methylene blue/silicon oxide nanocomposition mediator and its application for stable biosensor of hydrogen peroxide

A novel organic-inorganic nanocomposite of methylene blue (MB) and silicon oxide was synthesized and characterized by TEM, FTIR, and UV-vis. The as-prepared material was able to transfer the electron of the MB to electrode and was different from other SiO2 spheres structurally. It can be used as mediator to construct a biosensor with horseradish peroxidase (HRP) coimmobilized in the gelatine matrix and cross-linked with formaldehyde. The resulting biosensor exhibited fast amperometric response and good stability to hydrogen peroxide (H2O2). The linear range for H2O2 determination was from 1 x 10(-5) to 1.2 x 10(-3) M, with a detection limit of 4 x 10(-6) M based on S/N = 3. Moreover, the lifetime is more than 3 months under dry conditions at 4 degrees C.     

Direct electron transfer and enzymatic activity of hemoglobin in a hexagonal mesoporous silica matrix

The direct electrochemistry of hemoglobin (Hb) immobilized on a hexagonal mesoporous silica (HMS)-modified glassy carbon electrode was described. The interaction between Hb and the HMS was investigated using UV-Vis spectroscopy, FT-IR, and electrochemical methods. The direct electron transfer of the immobilized Hb exhibited two couples of redox peaks with the formal potentials of -0.037 and -0.232 V in 0.1 M (pH 7.0) PBS, respectively, which corresponded to its two immobilized states. The electrode reactions showed a surface-controlled process with a single proton transfer at the scan rate range from 20 to 200 mV/s. The immobilized Hb retained its biological activity well and displayed an excellent response to the reduction of both hydrogen peroxide (H2O2) and nitrate (NO2-). Its apparent Michaelis-Menten constants for H2O2 and NO2- were 12.3 and 49.3 microM, respectively, showing a good affinity. Based on the immobilization of Hb on the HMS and its direct electrochemistry, two novel biosensors for H2O2 and NO2- were presented. Under optimal conditions, the sensors could be used for the determination of H2O2 ranging from 0.4 to 6.0 microM and NO2- ranging from 0.2 to 3.8 microM. The detection limits were 1.86 x 10(-9) M and 6.11 x 10(-7) M at 3sigma, respectively. HMS provided a good matrix for protein immobilization and biosensor preparation.     

Optical detection of choline and acetylcholine based on H₂O₂-sensitive quantum dots

In this paper, we have constructed a simple, rapid and sensitive biosensor for detection of choline and acetylcholine (ACh) based on the hydrogen peroxide (H(2)O(2))-sensitive quantum dots (QDs). The detection limit for choline was 0.1 μM and the linear range was 0.1-0.9 μM and 5-150 μM, respectively. The detection limit for ACh was found to be 10 μM and the linear range was 10-5000 μM. The wide linear ranges were shown to be suitable for routine analyses of choline and ACh. Possible mechanism of the fluorescence of QDs quenched by H(2)O(2) was an electron transfer (ET) process. The experimental conditions of biosensors were optimized, and anti-interference ability was also presented. We also detected the choline in milk samples and the linear range was 5-150 μM. The detection linear range of ACh in serum was 10-140 μM. Most importantly, the recovery of choline in milk and ACh in serum samples were both close to 99%. The excellent performance of this biosensor showed that the method can be used in practice detection of choline and ACh.     

Optical detection of organophosphorus compounds based on Mn-doped ZnSe d-dot enzymatic catalytic sensor

In this paper, we report a sensitive and selective method for detection of organophosphorus compounds (OPs) based on Mn:ZnSe d-dots-enzyme-hydrogen peroxide (H(2)O(2)) fluorescence quenching system. Acetylcholine esterase (AChE) can hydrolyze acetylcholine (ACh) to choline. Subsequently, choline oxidase (ChOx) oxidizes choline to generate H(2)O(2). The enzyme-generated H(2)O(2) can quench the fluorescence of Mn:ZnSe d-dots. When paraoxon are introduced in solution, it can interact with the active centers of AChE and decrease the enzyme activity. This leads to the decrease of the H(2)O(2) production and then the fluorescence quenching rate of Mn:ZnSe d-dots. Experimental results showed that the enzyme inhibition percentage of Mn:ZnSe d-dots-ChOx-AChE-ACh system was proportional to the logarithm of paraoxon in the range 4.84×10(-11) to 4.84×10(-6) mol/L with the detection limit (S/N=3) of 1.31×10(-11) mol/L. The proposed biosensor has been employed for quick determination of paraoxon in tap water and milk samples with satisfactory reproducibility and accuracy. This nano-biosensor was proved to be sensitive, rapid, simple and tolerance of most interfering substances.