Amperometric biosensor for xanthine with supramolecular architecture

Xanthine oxidase modified with 1-adamantanyl residues was supramolecularly immobilized on Au electrodes coated with Au nanoparticles coated with a perthiolated beta-cyclodextrin polymer; the analytical response of the electrode toward xanthine was evaluated.     

Design of an amperometric xanthine biosensor based on a graphite transducer patterned with noble metal microparticles

A mesoporous graphite material micro-structured with palladium-platinum deposits (mixed in the ratio of 70:30% Pd:Pt) has been used as a cost-effective electrode material for designing an amperometric biosensor for xanthine. The here reported biosensor shows significantly improved operational parameters as compared to previously published results. At a constant applied potential of −0.05 V (vs. Ag/AgCl) it is distinguished with enhanced selectivity of the determination: at the working potential the current from the electrochemical transformation of various electrochemically active substances usually attending biological fluids (incl. uric acid, L-ascorbic acid, glutathione and paracetamol) has been eliminated. The effect of both the temperature and buffer composition on the analytical performance of the sensor has been investigated. Under optimal operational conditions (25°C, −0.05 V vs. Ag/AgCl, phosphate buffer, pH 8.4), the following have been defined for the biosensor: sensitivity 0.39 μA μM⁻¹, strict linearity of the response up to xanthine concentration 70 μM, detection limit of 1.5 μM (S/N=3) and a response time of at most 60 s.     

Xenon biosensor amplification via dendrimer-cage supramolecular constructs

Polyamidoamine dendrimers were synthesized with a single biotin moiety and used with cryptophane-A cages to form supramolecular biosensor constructs. These new biosensors amplified the NMR signals obtained from polarized xenon 8 times more than the original Xe biosensor.     

A simple model for an amperometric channel biosensor

A simple model is presented for the channel biosensor where an oxidase enzyme layer is located upstream of a detector electrode. In this model the enzyme kinetics are restricted to the linear region. The model enables the elucidation of the parameters important in tuning the response of the biosensor. Two extreme regimes of operation are identified; the kinetically limited and mass transport limited regimes both provide features which overcome reproducibility problems associated with the classical enzyme electrode geometry.     

Ionic liquid-functionalized graphene for fabricating an amperometric acetylcholinesterase biosensor

This work reports a sensitive amperometric biosensor for organophosphate pesticides (OPs) fabricated by modifying a glassy carbon electrode with acetylcholinesterase (AChE) immobilized on ionic liquid-functionalized graphene (IL-G). The functionalized graphene sheets had good dispersibility and long-term stability in various solvents. The as-prepared biosensor showed high affinity to acetylthiocholine (ATCl) with a Michaelis-Menten constant (K(m)) value of 0.77 mM. Furthermore, based on the inhibition by OPs of the enzymatic activity of the immobilized AChE, and using carbaryl as a model compound, the inhibition of carbaryl was proportional to its concentration ranging from 0.0025 to 0.48 and 0.48 to 1.42 μg mL(-1) with a detection limit of 0.8 ng mL(-1) (S/N = 3). The developed biosensor exhibited a good performance for OPs detection, including good reproducibility and acceptable stability, which provided a new and promising tool for the analysis of enzyme inhibitors.     

Amino oxidase amperometric biosensor for polyamines

An improved amino oxidase enzyme electrode has been constructed and applied to the determination of the amount of polyamines present in real samples. The electrode is based on the amperometric detection of H₂O₂ produced in the enzymatic oxidation of polyamines by amino oxidase. Amino oxidase from soybean seedlings, characterized by an extremely high activity for cadaverine and putrescine, was used. The enzyme was immobilized in an agarose matrix in the presence of glutaraldehyde and bovine serum albumin on the surface of a Pt electrode. Cadaverine, in concentrations between 0.5 and 500 μM, can be quantitatively determined by use of the amino oxidase electrode, the linear calibration range being 0.5–10 μM. The lower detection limit was 0.2 μM and the response time was 15 to 60 s. Putrescine showed similar behaviour. The maximum current response for cadaverine was 5.1 μA/cm², with an apparent Michaelis-Menten constant (K_m′) of 0.175 mM. The sensor response was stable for more than 32 hours of continuous operation at room temperature and, in the presence of fish or meat homogenates, no change in the signal-to-noise ratio was observed. The long-term stability, pH and temperature response of the biosensor has also been studied.     

Penicillinase-based amperometric biosensor for penicillin G

A biosensor for penicillin G was created by immobilizing penicillinase to a gold electrode by means of a cysteine self-assembled monolayer. The biosensor amperometrically monitored the catalytic hydrolysis of penicillin in a very sensible manner. Furthermore, it was successfully used to measure the Michaelis–Menten enzymatic constant and a low limit of detection of 4.5 nM was obtained.     

TiO2-decorated graphene nanohybrids for fabricating an amperometric acetylcholinesterase biosensor

This work describes a highly sensitive and rapid amperometric biosensor for organophosphate compounds (OPs) based on immobilization of acetylcholinesterase (AChE) on a novel TiO(2)-decorated graphene (TiO(2)-G) nanohybrid, which was constructed by in situ growth of TiO(2) nanoparticles (NPs) on the graphene sheet. The well-dispersed TiO(2) NPs eliminated the restacking of TiO(2)-G nanohybrids. Due to the integrating of TiO(2)-G nanohybrids, the as-prepared biosensor showed high affinity to acetylthiocholine (ATCl) with a Michaelis-Menten constant (K(m)) value of 0.22 mM, and rapid inhibition time (3 min). Further, based on the inhibition of OPs on the enzymatic activity of the immobilized AChE, and using carbaryl as a model compound, the inhibition of carbaryl was proportional to its concentration ranging from 0.001 to 0.015 and 0.015 to 2 μg mL(-1) with a detection limit of 0.3 ng mL(-1) (S/N = 3). The developed biosensor exhibited a good performance for organophosphate pesticide detection, including good reproducibility and acceptable stability, which provided a new and promising tool for the analysis of enzyme inhibitors.     

Studies towards an amperometric phosphate ion biosensor for urine and water analysis

An amperometric biosensor for phosphate ion is described that is based on a cobalt phthalocyanine modified screen-printed carbon electrode (CoPC-SPCE). The biosensor operation is based on the enzyme pyruvate oxidase (PyOd) which catalyses the oxidative decarboxylation of pyruvate, in the presence of inorganic phosphate and O₂, to acetyl phosphate, hydrogen peroxide (H₂O₂) and CO₂. The transducer allows the electrocatalytic oxidation of H₂O₂ in order to generate the analytical signal. The enzyme was immobilised onto the CoPC-SPCE using a sandwich format. The inner membrane was formed in situ by depositing an acetone solution containing cellulose acetate first onto the transducer surface. The enzyme and cofactors were then deposited onto this layer and allowed to dry; finally a second aliquot of the cellulose acetate solution was deposited onto the enzyme layer and allowed to dry. The biosensor was characterised by amperometry in stirred solution to produce current-voltage curves and for calibration studies. From these it was deduced that a reliable electrocatalytic response was obtained for phosphate ion; an operating potential of +0.4 V was selected for the analysis of urine samples. The precision of the response for urine analysis and recovery data for potable water suggests that the biosensor could have applications in clinical and environmental monitoring.     

Enzyme-less amperometric biosensor for l-ascorbate using poly-l-histidine-copper complex as an alternative biocatalyst

A poly-l-histidine(PLH)-copper(II) complex can be used as an alternative biocatalyst in an O(2) detection-type amperometric enzyme-less l-ascorbate (AsA) sensor. The PLH-Cu(II) membrane was simply prepared by entrapping the PLH in polyacrylamide gel and subsequent treatment of the gel with CuCl(2) solution. This enzyme-less biosensor can be used over a relatively wide pH region from 4 to 11 and enables precise determination of AsA (RSD less than 3%, n=10) at pH 7.0. The fundamental performance characteristics (sensitivity, response time, and linear range) of this PLH-Cu(II)-based sensor is comparable to those of a native ascorbate oxidase-based sensor. Unfortunately, the selectivity is inherently rather low and, as a result, the response was degraded in the presence of higher concentrations (more than mM order) of quinones. However, reducing sugars caused no interference and the sensor could be used to detect AsA in some fruits and drinks. This enzyme-less sensor has excellent stability for at least 3 months of repeated analysis (more than 300 samples) without loss of ordinal activity.     

Encapsulation of tyrosinase within liposome bioreactors for developing an amperometric phenolic compounds biosensor

A novel tyrosinase (Tyr) biosensor based on liposome bioreactor and chitosan (CS) nano-composite has been developed for the detection of phenolic compounds. Liposome-based bioreactors were prepared by encapsulating the enzyme Tyr in l-α-phosphatidylcholine liposome resulting in spherical bioreactor with a mean diameter of 8.5?±?1.25 μm. The encapsulation efficiency and drug loading content of the Tyr-loaded liposome-based bioreactors were about 46.35?±?0.85 and 41.15?±?0.95 %, respectively. Porins were embedded into the lipid membrane, allowing for the free substrate transport, but not that of the enzyme due to size limitations. The glassy carbon electrode (GCE) was alternately immersed in CS and Tyr liposome bioreactor (TLB) to assemble bilayer films [(CS/TLB)/GCE]. The presence of Tyr in the biosensor was confirmed by scanning electron microscopy, cyclic voltammetry, and electrochemical measurements. The results indicated that the biosensor was applied to detect phenol with a broad linear range from 0.25 nM to 25 μM, the detection limit was brought down to 0.091 nM. The apparent Michaelis–Menten constant, K _m, for the enzymatic reaction was 34.78 μM. The novel biosensor exhibits good repeatability and stability. Such new biosensor based on encapsulation of Tyr within liposome bioreactors shows great promise for rapid, simple, and cost-effective analysis of phenolic contaminants in environmental samples. The proposed strategy can be extended for the development of other enzyme-based biosensors.     

Using novel polysaccharide-silica hybrid material to construct an amperometric biosensor for hydrogen peroxide

A new type of sol-gel organic-inorganic hybrid material was developed and used for the fabrication of an amperometric hydrogen peroxide biosensor. This material was prepared from natural chitosan and recently introduced completely water-soluble precursor, tetrakis(2-hydroxyethyl) orthosilicates (THEOS), by the sol-gel process without the addition of organic solvents and catalysts. The gelation time for the sol-gel transition and dynamic rheological properties of the resultant gel matrix could be modulated by the amount of added THEOS. The structure of the hybrid gel was made up of a network and spherical particles, as confirmed by SEM observation. By electrochemical experiments, it was found that such a hybrid gel matrix could retain the native biocatalytic activity of the entrapped horseradish peroxidase and provide a fast amperometric response to hydrogen peroxide. The linear range for the determination of hydrogen peroxide was found to be from 1.0 x 10(-6) to 2.5 x 10(-4) mol/L with a detection limit of 4.0 x 10(-7) mol/L. The apparent Michaelis-Menten constant was determined to be 2.198 mmol/L. To improve the analytical characteristics of the fabricated biosensor, the effects of applied potential and pH value on the steady-state current were studied. Under the optimized experimental conditions, the fabricated biosensor was found to have good analytical performance, reproducibility, and storage stability.     

Chemically glycosylation improves the stability of an amperometric horseradish peroxidase biosensor

We constructed a biosensor by electrodeposition of gold nano-particles (AuNPs) on glassy carbon (GC) and subsequent formation of a 4-mercaptobenzoic acid self-assembled monolayer (SAM). The enzyme horseradish peroxidase (HRP) was then covalently immobilized onto the SAM. Two forms of HRP were employed: non-modified and chemically glycosylated with lactose. Circular dichroism (CD) spectra showed that chemical glycosylation did neither change the tertiary structure of HRP nor the heme environment. The highest sensitivity of the biosensor to hydroquinone was obtained for the biosensor with HRP-lactose (414 nA μM⁻¹) compared to 378 nA μM⁻¹ for the one employing non-modified HRP. The chemically glycosylated form of the enzyme catalyzed the reduction of hydroquinone more rapidly than the native form of the enzyme. The sensor employing lactose-modified HRP also had a lower limit of detection (74 μM) than the HRP biosensor (83 μM). However, most importantly, chemically glycosylation improved the long-term stability of the biosensor, which retained 60% of its activity over a four-month storage period compared to only 10% for HRP. These results highlight improvements by an innovative stabilization method when compared to previously reported enzyme-based biosensors.     

Development of an amperometric biosensor for the determination of phenolic compounds in reversed micelles

The possibilities of amperometric enzyme electrodes in reversed micellar systems for the determination of phenol, 4-chloro-3-methylphenol and 2,4-dimethylphenol are illustrated. The used enzymatic reaction consisted of the oxidation of the phenolic compounds by oxygen, catalysed by tyrosinase. The reduction of the liberated quinones was amperometrically detected. The concentration of the components of the reversed micelles, as well as the potential applied to the tyrosinase electrode have been optimized. The stability of the enzyme electrode with time was also evaluated. The effect of the analyte solubility in water upon the analytical performance of the electrode was explored. Advantages of amperometric biosensors in reversed micelles are shown with respect to aqueous media and organic phase enzyme electrodes.     

A novel amperometric biosensor for the detection of nitrophenol

We report on a novel amperometric biosensor for detecting phenolic compounds based on the co-immobilization of horseradish-peroxidase (HRP) and methylene blue (MB) with chitosan on Au-modified TiO₂ nanotube arrays. The titania nanotube arrays were directly grown on a Ti substrate using anodic oxidation first; a gold thin film was then coated onto the TiO₂ nanotubes by an argon plasma technique. The morphology and composition of the fabricated Au-modified TiO₂ nanotube arrays were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Cyclic voltammetry and amperometry were used to study the proposed electrochemical biosensor. The effect of pH, applied electrode potential and the concentration of H₂O₂ on the sensitivity of the biosensor have been systemically investigated. The performance of the proposed biosensor was tested using seven different phenolic compounds, showing very high sensitivity; in particular, the linearity of the biosensor for the detection of 3-nitrophenol was observed from 3 × 10⁻⁷ to 1.2 × 10⁻⁴ M with a detection limit of 9 × 10⁻⁸ M (based on the S/N = 3).     

One-step separation-free amperometric biosensor for the detection of protein

A novel enzyme biosensor for the detection of protein is presented. The biosensor was made from a screen-printed three-electrode configuration. Amino acid oxidase was immobilized with glutaraldehyde and polyethylenimine on a working electrode made of rodinised carbon. A protease was immobilized on an immunodyne membrane and was placed on the electrode. A protein sample was deposited on the membrane, and was subsequently hydrolyzed to amino acids in the presence of the protease. This in turn produced hydrogen peroxide by the immobilized amino acid oxidase. The oxidation of hydrogen peroxide was then detected at +400 mV vs. an Ag/AgCl reference electrode. The method was very effective at detecting a very low level of protein. The sensor does not require any washing step. The sensor works with only 40 μl of sample per detection, and may be used on-site as a disposable sensor using a hand-held meter. The electrodes are also stable for more than 6 weeks.     

An amperometric monoamine oxidase biosensor for determining some antidepressants

An amperometric biosensor based on a platinum screen-printed electrode and immobilized monoamine oxidase is developed to determine antidepressants of different classes. Petylyl, pyrazidol, and flu-oxetine can be determined with determination limits of 8 × 10^?9, 8 × 10^?7, and 8 × 10^?10 M, respectively. A procedure is proposed for determining fluoxetine in tablets. It is shown that petylyl can be selectively determined by an immunochemical technique using the developed biosensor and immobilized antibodies in the concentration range from 1 × 10^?4 to 1 × 10^?8 M.     

Construction of amperometric biosensor modified with conducting polymer/carbon dots for the analysis of catechol

Phenolic compounds used in food industries and pesticide industry, are environmentally toxic and pollute the rivers and ground water. For that reason, detection of phenolic compounds such as catechol by using simple, efficient and cost-effective devices have been becoming increasingly popular. In this study, a suitable and a novel matrix was composed using a novel conjugated polymer, namely poly[1-(5-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophen-2-yl)furan-2-yl)-5-(2-ethylhexyl)-3-(furan-2-yl)-4H thieno[3,4-c]pyrrole-4,6(5H)-dione] (PFTBDT) and carbon dots (CDs) to detect catechol. PFTBDT and CDs were synthesized and the optoelectronic properties of PFTBDT were investigated via electrochemical and spectroelectrochemical studies. Laccase enzyme was immobilized onto the constructed film matrix on the graphite electrode. The proposed biosensor was found to have a low detection limit (1.23 μM) and a high sensitivity (737.44 μA/mM.cm⁻²) with a linear range of 1.25–175 μM. Finally, the applicability of the proposed enzymatic biosensor was evaluated in a tap water sample and a satisfactory recovery (96–104%) was obtained for catechol determination.     

Sol-gel based amperometric biosensor incorporating an osmium redox polymer as mediator for detection of L-lactate

A novel amperometric biosensor for the determination of lactate was constructed by first immobilizing lactate oxidase and an osmium redox polymer ([Os(bpy)(2)(PVP)(10)Cl]Cl; abbreviated Os-polymer) on the surface of a glassy carbon electrode, followed by coating with a sol-gel film derived from methyltriethoxysilane (MTEOS). The electrooxidation current of this electrode was found to be diffusion controlled. In the presence of lactate, a clear electrocatalytic oxidation wave was observed, and lactate could be determined amperometrically at 400 mV versus Ag AgCl . The concentration range of linear response, slope of linear response and detection limit were 0.1-9 mM, 1.02 microA mM(-1), and 0.05 mM, respectively. Although L-ascorbate was electrooxidized at this potential, uric acid, paracetamol and glucose were found not to interfere.     

Construction of biosensor for hypoxanthine determination by immobilization of xanthine oxidase and uricase in polypyrrole-paratoluenesulfonate film

Journal of Solid State Electrochemistry - A highly selective and stable amperometric biosensor for the determination of the hypoxanthine (Hx) molecule was designed in this study. For this purpose,...