Biosensor for bisphenol A leaching from baby bottles using a glassy carbon electrode modified with DNA and single walled carbon nanotubes

We have developed a biosensor for highly sensitive and selective determination of the endocrinic disruptor bisphenol A (BPA). It is based on glassy carbon electrode modified with calf thymus DNA and a composited prepared from single walled carbon nanotubes (SWNT) and Nafion. The interaction between BPA and DNA was studied by voltammetry. The binding constant was determined to be 3.55?×?10³ M^?1, and the binding site has a length of 4.3 base pairs. These electrochemical studies provide further information for a better understanding of the toxicity and carcinogenicity of BPA. Under optimal conditions, the biosensor displays a linear electrochemical response to BPA in the 10 nM to 20 μM concentration range, with a detection limit as low as 5.0 nM (at an S/N of 3). The method was successfully applied to the quantification of BPA in leachates from plastic baby bottles. Recoveries range from 94.0 % to 106.0 % which underpins the excellent performance of this SWNT-based DNA sensor.

Reagentless amperometric glucose biosensor based on the immobilization of glucose oxidase on a ferrocene@NaY zeolite composite

Ferrocene (Fc) was encapsulated in the cavities of a NaY zeolite by vapor diffusion via sublimation at below 100?°C. The resulting Fc@NaY zeolite composite was investigated by power X-ray diffraction, diffuse reflectance UV?Cvis and FT-IR spectroscopy, and by cyclic voltammetry. The results indicated that Fc was encapsulated into the zeolite whose microporous structure had remained intact. The Fc in the silica matrix had retained its electroactivity and did not leach out. A glucose biosensor was obtained by immobilization of the modified zeolite and glucose oxidase on a carbon paste electrode. It displays a linear response to glucose (from 0.8???M to 4.0?mM), a detection limit of 0.2???M, and a response time of 4?s. The good performance of the biosensor is ascribed to the biocompatibility of the zeolite and presence of Fc which facilitates the electron transfer from the enzyme to the surface of the electrode.

Amperometric biosensor for bisphenol A based on a glassy carbon electrode modified with a nanocomposite made from polylysine, single walled carbon nanotubes and tyrosinase

We have prepared a nanocomposite consisting of single-walled carbon nanotubes and polylysine. It was characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and by UV/vis and FTIR spectroscopy. Tyrosinase was covalently immobilized on the nanocomposite, and the resulting bioconjugate deposited on a glassy carbon electrode to form a biosensor for bisphenol A. The biosensor was characterized by scanning electron microscopy and electrochemical impedance spectroscopy. Under optimized experimental conditions, the biosensor gives a linear response to bisphenol A in the 4.00 nM to 11.5 μM concentration range. Its sensitivity is 788 mA M^?1 cm^?2, and the lower detection limit is 0.97 nM (at an S/N of 3). The biosensor shows good repeatability, reproducibility and long-term stability. In a preliminary practical application, it was successfully applied to the determination of bisphenol A in leachates of plastic spoons.

Chronocoulometric DNA biosensor based on a glassy carbon electrode modified with gold nanoparticles, poly(dopamine) and carbon nanotubes

We describe a sensitive chronocoulometric biosensor for the sequence-specific detection of DNA. It is based on a glassy carbon electrode modified with multi-walled carbon nanotubes, polydopamine, and gold nanoparticles. The ruthenium(III)hexammine complex acts as the electrochemical indicator. Electrochemical impedance spectra and scanning electron microscopy are employed to investigate the assembly of the electrode surface. The signals of the ruthenium complex electrostatically bound to the anionic phospho groups of the DNA strands are measured by chronocoulometry before and after hybridization. The difference in signal intensity is linearly related to the logarithm of the concentration of the target DNA in the range of 1.0 nM to 10 fM with a detection limit of 3.5fM (S/N?=?3) under optimal conditions. This biosensor exhibits excellent sensitivity and selectivity and has been used for an assay of complementary target DNA in human serum sample with satisfactory results.

Ultra-sensitive electrochemical DNA biosensor based on signal amplification using gold nanoparticles modified with molybdenum disulfide,graphene and horseradish peroxidase

We have developed an ultra-sensitive electrochemical DNA biosensor by assembling probe ssDNA on a glassy carbon electrode modified with a composite made from molybdenum disulfide, graphene, chitosan and gold nanoparticles. A thiol-tagged DNA strand coupled to horseradish peroxidase conjugated to AuNP served as a tracer. The nanocomposite on the surface acts as relatively good electrical conductor for accelerating the electron transfer, while the enzyme tagged gold nanoparticles provide signal amplification. Hybridization with the target DNA was studied by measuring the electrochemical signal response of horseradish peroxidase using differential pulse voltammetry. The calibration plot is linear in the 5.0?×?10^?14 and 5.0?×?10^?9 M concentration range, and the limit of detection is 2.2?×?10^?15 M. The biosensor displays high selectivity and can differentiate between single-base mismatched and three-base mismatched sequences of DNA. The approach is deemed to provide a sensitive and reliable tool for highly specific detection of DNA.

Label-free electrochemical DNA biosensor based on a glassy carbon electrode modified with gold nanoparticles, polythionine, and graphene

We describe the fabrication of a sensitive label-free electrochemical biosensor for the determination of sequence-specific target DNA. It is based on a glassy carbon electrode (GCE) modified with graphene, gold nanoparticles (Au-NPs), and polythionine (pThion). Thionine was firstly electropolymerized on the surface of the GCE that was modified with graphene by cyclic voltammetry. The Au-NPs were subsequently deposited on the surface of the pThion/graphene composite film by adsorption. Scanning electron microscopy and electrochemical methods were used to investigate the assembly process. Differential pulse voltammetry was employed to monitor the hybridization of DNA by measuring the changes in the peak current of pThion. Under optimal conditions, the decline of the peak current is linearly related to the logarithm of the concentration of the target DNA in the range from 0.1 pM to 10 nM, with a detection limit of 35 fM (at an S/N of 3). The biosensor exhibits good selectivity, acceptable stability and reproducibility.

A glassy carbon electrode modified with graphene and tyrosinase immobilized on platinum nanoparticles for sensing organophosphorus pesticides

An amperometric biosensor is described for the detection of organophosphorus pesticides. It is based on the enzyme tyrosinase immobilized on platinum nanoparticles and the use of a glassy carbon electrode modified with graphene. Tyrosinase was immobilized on the electrode surface via electrostatic interaction between a monolayer of cysteamine and the enzyme. In the presence of catechol as a substrate, the pesticides chlorpyrifos, profenofos and malathion can be determined as a result of their inhibition of the enzyme which catalyzes the oxidation of catechol to o-quinone. Platinum nanoparticles and graphene effectively enhance the efficiency of the electrochemical reduction of o-quinone, thus improving sensitivity. Under optimum experimental conditions, the inhibition effect of the pesticides investigated is proportional to their concentrations in the lower ppb-range. The detection limits are 0.2, 0.8 and 3?ppb for chlorpyrifos, profenofos and malathion, respectively. The biosensor displays good repeatability and acceptable stability.

A lipase-based electrochemical biosensor for target DNA

A lipase-based electrochemical biosensor has been fabricated for the quantitative determination of target DNA. It is based on a stem-loop nucleic acid probe labeled with ferrocene containing a butanoate ester that is hydrolyzed by lipase. The other end of the probe DNA is linked, via carboxy groups, to magnetic nanoparticles. The binding of target DNA transforms the hairpin structure of the probe DNA and causes the exposure of ester bonds. This results in the release of electro-active ferrocene after hydrolysis of the ester bonds, and in an observable electrochemical response. The quantity of target DNA in the concentration range between 1?×?10^?12 mol·L^?1 and 1?×?10^?8 mol·L^?1 can be determined by measuring the electrochemical current. The method can detect target DNA with rapid response (30 min) and low interference.

Sensing Lorazepam with a glassy carbon electrode coated with an electropolymerized-imprinted polymer modified with multiwalled carbon nanotubes and gold nanoparticles

We report on an electrode for the amperometric determination of lorazepam. A glassy carbon electrode was coated with a molecular imprint made by electropolymerization of ortho-phenylenediamine and filled with multiwalled carbon nanotubes and gold nanoparticles, which enhances the transmission of electrons. The sensor was studied with respect to its response to hexacyanoferrate (III) as a probe and by electrochemical impedance spectroscopy, cyclic voltammetry and square wave voltammetry. The linear response range to Lorazepam is from 0.5 nM to 1.0 nM and from 1.0 nM to 10.0 nM, with a detection limit of 0.2 nM (at an S/N of 3). The electrode was successfully applied to determine Lorazepam in spiked human serum.

Biocompatible and label-free amperometric immunosensor for hepatitis B surface antigen using a sensing film composed of poly(allylamine)-branched ferrocene and gold nanoparticles

An amperometric immunosensor has been developed for sensitive determination of hepatitis B surface antigen as a model protein. A glassy carbon electrode was modified with an assembly of positively charged poly(allylamine)-branched ferrocene (PAA-Fc) and negatively charged gold nanoparticles (Au NPs). The formation of PAA-Fc effectively avoids the leakage of Fc, retains its electrochemical activity, and enhances the conductivity of the composite. The adsorption of Au NPs onto the PAA-Fc matrix provides sites for the immobilization of the antigen and a favorable micro-environment to maintain its activity. The morphologies and electrochemistry of the sensing film were investigated via scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. Factors influencing the performance of the immunosensor were studied in detail. The concentration of the antigen can be quantitated (by measuring the decrease of the amperometric response resulting from the specific binding between antigen and antibody) in the range between 0.1 and 150?ng?mL^?C1, with a detection limit of 40?pg?mL^?C1 (S/N = 3). The method is economical, efficient, and potentially attractive for clinical immunoassays.

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.

Engineering a DNA-cleaving DNAzyme and PCR into a simple sensor for zinc ion detection

The development of a simple sensor (9NL27-Zn) based on DNAzyme and PCR and aimed at the detection of low concentrations of zinc (II) ions is described. A specific Zn(II)-dependent DNAzyme (9NL27) with DNA-cleaving activity was employed. In the presence of zinc (II), the DNAzyme hydrolyzed DNA substrate into two pieces (5′ and 3′ fragments), forming 3′-terminal hydroxyl in the 5′ fragment and 5′-phosphate in the 3′ fragments. Subsequently, the 5′ fragment left the DNAzyme and bound a short DNA template. The 5′ fragment was used as a primer and extended a single-stranded full-length template by Taq polymerase. Finally, this full-length template was amplified by PCR. The amplified products had a quantitative relationship with Zn(II) concentration. Under our experimental conditions, the DNA sensor showed sensitivity (10 nM) and high specificity for zinc ion detection. After improvement of the DNA sensor, the detection limit can reach 1 nM. The simple DNA sensor may become a DNA model for the detection of trace amounts of other targets.

Amperometric hydrogen peroxide biosensor based on a glassy carbon electrode modified with polythionine and gold nanoparticles

We report on a novel hydrogen peroxide biosensor that was fabricated by the layer-by-layer deposition method. Thionine was first deposited on a glassy carbon electrode by two-step electropolymerization to form a positively charged surface. The negatively charged gold nanoparticles and positively charged horseradish peroxidase were then immobilized onto the electrode via electrostatic adsorption. The sequential deposition process was characterized using electrochemical impedance spectroscopy by monitoring the impedance change of the electrode surface during the construction process. The electrochemical behaviour of the modified electrode and its response to hydrogen peroxide were studied by cyclic voltammetry. The effects of the experimental variables on the amperometric determination of H₂O₂ such as solution pH and applied potential were investigated for optimum analytical performance. Under the optimized conditions, the biosensor exhibited linear response to H₂O₂ in the concentration ranges from 0.20 to 1.6?mM and 1.6 to 4.0?mM, with a detection limit of 0.067?mM (at an S/N of 3). In addition, the stability and reproducibility of this biosensor was also evaluated and gave satisfactory results.

Direct electrochemistry of hemoglobin on an ionic liquid carbon electrode modified with zinc tungstate nanorods

We have constructed a new electrochemical biosensor by immobilization of hemoglobin (Hb) and ZnWO₄ nanorods in a thin film of chitosan (CTS) on the surface of carbon ionic liquid electrode. UV–vis and FT-IR spectra reveal that Hb remains in its native conformation in the film. The modified electrode was characterized by scanning electron microscopy, electrochemical impedance spectroscopy and cyclic voltammetry. A pair of well-defined redox peaks appears which indicates direct electron transfer from the electrode. The presence of CTS also warrants biocompatibility. The electron transfer coefficient and the apparent heterogeneous electron transfer rate constant were calculated to be 0.35 and 0.757 s^?1, respectively. The modified electrode displays good electrocatalytic activity for the reduction of trichloroacetic acid with the detection limit of 0.613 mmol L^?1 (3σ). The results extend the protein electrochemistry based on the use of ZnWO₄ nanorods.

Glucose biosensor based on glucose oxidase immobilized on unhybridized titanium dioxide nanotube arrays

A glucose biosensor has been fabricated by immobilizing glucose oxidase (GOx) on unhybridized titanium dioxide nanotube arrays using an optimized cross-linking technique. The TiO₂ nanotube arrays were synthesized directly on a titanium substrate by anodic oxidation. The structure and morphology of electrode material were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical performances of the glucose biosensor were conducted by cyclic voltammetry and chronoamperometry measurements. It gives a linear response to glucose in the 0.05 to 0.65 mM concentration range, with a correlation coefficient of 0.9981, a sensitivity of 199.6 μA mM^?1 cm^?2, and a detection limit as low as 3.8 µM. This glucose biosensor exhibited high selectivity for glucose determination in the presence of ascorbic acid, sucrose and other common interfering substances. This glucose biosensor also performed good reproducibility and long-time storage stability. This optimized cross-linking technique could open a new avenue for other enzyme biosensors fabrication.

Electrochemical detection of in situ DNA damage induced by enzyme-catalyzed Fenton reaction. Part I: in phosphate buffer solution

We report on a biosensor for the electrochemical detection of the damage of DNA and of antioxidant protecting DNA. The biosensor was constructed by co-immobilization of DNA and glucose oxidase (GOx) on a glassy carbon electrode. Under aerobic conditions, GOx catalyzes the oxidation of glucose, and the hydrogen peroxide produced reacts with ferrous ions in a Fenton-type reaction to generate hydroxy radical. This was validated by UV–vis spectroscopy. The hydroxy radical can cause serious oxidative damage to DNA, and this can be detected by square wave voltammetry of the electroactive indicator Co(bpy) ₃ ³⁺ . The effects of pH value, incubation time, and the concentration of glucose and ferrous ion were optimized. The effects of the antioxidants ascorbic acid and aloe emodin on DNA damage were also investigated within the concentration range from 0.05 to 200?μM. This work provides an in-vitro model system to mimic the processes in oxidative DNA damage by a simple electrochemical approach.

Electrochemical DNA biosensor for the detection of Trichoderma harzianum based on a gold electrode modified with a composite membrane made from an ionic liquid, ZnO nanoparticles and chitosan, and by using acridine orange as a redox indicator

An electrochemical DNA biosensor was developed that is based on a gold electrode modified with a nanocomposite membrane made from an ionic liquid, ZnO nanoparticles and chitosan. A single-stranded DNA probe was immobilized on this electrode. Acridine orange was used as the hybridization probe for monitoring the hybridization of the target DNA. The biosensor was capable of detecting target DNA in the concentration range from 1.0?×?10?C14 to 1.8?×?10?C4?mol?L-1, with a detection limit of 1.0?×?10?C15?mol?L-1. The approach towards constructing a DNA biosensor allows studies on the hybridization even with crude DNA fragments and also to analyze sample obtained from real samples. The results show that the DNA biosensor has the potential for sensitive detection of a specific sequence of the Trichoderma harzianum gene and provides a quick, sensitive and convenient method for the study of microorganisms.

Enhanced luminol electrochemiluminescence triggered by an electrode functionalized with dendrimers modified with titanate nanotubes

We have constructed a novel electrochemiluminescence (ECL) platform by functionalizing a poly(amidoamine) dendrimer (PAAD) with titanate nanotubes (TiNTs). The PAAD has an open spherical structure that possesses a high density of active groups and thus favors mass transport, while the TiNTs possess excellent electronic conductivity and thus can promote electron transfer on the surface of a glassy carbon electrode (GCE). A study on the intensity and stability of the ECL of luminol on the modified GCE revealed a substantial improvement compared to that of a bare GCE. The effects of the concentration of TiNTs, the pH value of the solution, and of electrochemical parameters on the intensity of the ECL of luminol were studied and resulted in a sensitive ECL sensor for hydrogen peroxide (H₂O₂) that works in the concentration range of 1 nM to 0.9 μM. The scavenging effect of superoxide dismutase (SOD) on the H2O2 electrode ECL was then exploited to design a biosensor for the determination of SOD in concentrations between 50 and 500 nM.

Sensitive DNA-hybridization biosensors based on gold nanoparticles for testing DNA damage by Cd(II) ions

A DNA biosensor was constructed by immobilizing a 20-mer oligonucleotide probe and hybridizing it with its complementary oligomer on the surface of a glassy carbon electrode modified with gold nanoparticles. The properties of the biosensor and its capability of recognizing its complementary sequence were studied by electrochemical impedance spectroscopy. The oxidative stress caused by cadmium ions can be monitored by differential pulse voltammetry using the cobalt(III)tris(1,10-phenanthroline) complex and methylene blue as electrochemical indicators. The biosensor is capable of indicating damage caused by Cd(II) ions in pH 6.0 solution. The results showed that the biosensor can be used for rapid screening for DNA damage.