Computational modelling of amperometric biosensors in the case of substrate and product inhibition

In this paper the response of an amperometric biosensor at mixed enzyme kinetics and diffusion limitations is modelled in the case of the substrate and the product inhibition. The model is based on non-stationary reaction–diffusion equations containing a non-linear term related to non-Michaelis–Menten kinetics of an enzymatic reaction. A numerical simulation was carried out using a finite difference technique. The complex enzyme kinetics produced different calibration curves for the response at the transition and the steady-state. The biosensor operation is analysed with a special emphasis to the conditions at which the biosensor response change shows a maximal value. The dependence of the biosensor sensitivity on the biosensor configuration is also investigated. Results of the simulation are compared with known analytical results and with previously conducted researches on the biosensors.     

Computational Modelling of Biosensors with Perforated and Selective Membranes

This paper presents a two-dimensional-in-space mathematical model of amperometric biosensors with perforated and selective membranes. The model is based on the diffusion equations containing a non-linear term of the Michaelis–Menten enzymatic reaction. Using numerical simulation of the biosensors action, the influence of the geometry of the perforated membrane on the biosensor response was investigated. The numerical simulation was carried out using finite-difference technique. The calculations demonstrated non-linear and non-monotonous change of the biosensor steady-state current at various degree of the surface of the perforated membrane covering. The non-monotonous behaviour of the biosensor response was also observed when changing the thickness of the perforated membrane.     

Immobilised tyrosinase-based biosensor for the detection of tea polyphenols

An amperometric principle-based biosensor containing immobilized enzyme tyrosinase has been used for detection of polyphenols in tea. The immobilized tyrosinase-based biosensor could detect tea polyphenols in the concentration range 10–80 mmol L⁻¹. Immobilization of the enzyme by the crosslinking method gave good stable response to tea polyphenols. The biosensor response reached the steady state within 5 min. The voltage response was found to have a direct linear relationship with the concentration of polyphenols in black tea samples. Enzyme membrane fouling was observed with number of analyses with a single immobilised enzyme membrane. The tyrosinase-based biosensor gave maximum response to tea polyphenols at 30°C. The optimum pH was 7.0. This biosensor system can be applied for analysis of tea polyphenols. Variation in the biosensor response to black tea infusions gave an indication of the different amounts of theaflavins in the samples, which is an important parameter in evaluating tea quality. A comparative study of the quality attributes of a variety of commercially available brands of tea were performed using the biosensor and conventional analytical techniques such as spectrophotometry.     

A solid-state pH transducer fabricated from a self-plasticized methacrylic-acrylic membrane for potentiometric acetylcholine chloride biosensor

A solid-state pH sensor based on a self-plasticizing film of methacrylic-acrylic copolymer was developed. The sensor was able to detect changes in pH after tridodecylamine ionophore was immobilized together with a lipophilic anionic salt. The pH sensor exhibited almost a Nemstian response (57.6 mV pH⁻¹) with a linear pH response range of 6–10. It demonstrated a fast response (<2 min) to changes in pH and good selectivity against other common cations such as sodium, potassium, magnesium, lithium, and calcium. The sensor has a shelf life of at least 30 days without an obvious deterioration in response. By depositing a layer of poly(hydroxylethymethacrylate) immobilized with enzyme acetylcholinesterase on top of the pH selective methacrylic-acrylic film, the pH sensor was able to detect acetylcholine chloride (AChCl). The linear response range of the potentiometric biosensor to AChCl was dependent on the buffer concentrations used, and for a buffer concentration less than 1 mM, the linear response range obtained was 3.98–31.62 μM. The text was submitted by the authors in English     

Modelling synergistic action of laccase-based biosensor utilizing simultaneous substrates conversion

The response of a laccase-based amperometric biosensor that acts in a synergistic manner was modelled digitally. A mathematical model of the biosensor is based on a system of non-linear reaction diffusion equations. The modelling biosensor comprises three compartments, an enzyme layer, a dialysis membrane and an outer diffusion layer. By changing input parameters the biosensor action was analysed with a special emphasis to the influence of the species concentrations on the synergy of the simultaneous substrates conversion. The digital simulation was carried out using the finite difference technique.     

Development of an EnFET for the detection of organophosphorous and carbamate insecticides

A biosensor for the detection of insecticides based on an ion-sensitive field-effect transistor (ISFET) was developed. The resulting device combines the simplicity of potentiometric sensors and the use of associated electronic systems as powerful tools for the acquisition and the processing of data. The enzyme acetylcholinesterase (AChE) was entrapped in a membrane placed on the gate of the ISFET forming an enzyme field-effect transistor (EnFET). The biosensor is applied to the determination of pesticides in spiked real samples. Organophosphorous and carbamate insecticides were measured with a detection limit of 10(-8) mol L(-1). The measurement is based on the production of hydrogen ions due to the hydrolysis of acetylthiocholine by the enzyme. The resulting local pH change is picked up by the underlying pH-sensitive ISFET and transduced as potential variations. The preparation of the membrane is simple and reproducible. The analysis in spiked real samples was performed in tap water and showed detection limits comparable to those obtained by other researchers.     

A Practical Approach to Potentiometric Biosensors Based on Consolidated Composites: Construction and Evaluation of a D-Amygdalin Biosensor

A simple procedure to be used in an analytical chemistry laboratory by undergraduate students to prepare a potentiometric biosensor for D-amygdalin is given. The membrane material is prepared by simple compression of a solid sensing mixture (-glucosidase mixed with Ag₂S and AgI). This new technology has some advantages. It presents a simple way to prepare a biosensor membrane and this methodology adapts well to mass production technology. Simple polishing before each new measurement can renew the membrane. This type of biosensor produced by consolidated biocomposites can serve as a base material for different biosensing schemes.Using this technique, students can easily envision the functioning of a potentiometric biosensor where the classic detection mechanism as of an I-ISE is combined with the biological recognition of an enzyme.     

Catechol determination in compost bioremediation using a laccase sensor and artificial neural networks

An electrochemical biosensor based on the immobilization of laccase on magnetic core-shell (Fe₃O₄–SiO₂) nanoparticles was combined with artificial neural networks (ANNs) for the determination of catechol concentration in compost bioremediation of municipal solid waste. The immobilization matrix provided a good microenvironment for retaining laccase bioactivity, and the combination with ANNs offered a good chemometric tool for data analysis in respect to the dynamic, nonlinear, and uncertain characteristics of the complex composting system. Catechol concentrations in compost samples were determined by using both the laccase sensor and HPLC for calibration. The detection range varied from 7.5 × 10^–7 to 4.4 × 10^–4 M, and the amperometric response current reached 95% of the steady-state current within about 70 s. The performance of the ANN model was compared with the linear regression model in respect to simulation accuracy, adaptability to uncertainty, etc. All the results showed that the combination of amperometric enzyme sensor and artificial neural networks was a rapid, sensitive, and robust method in the quantitative study of the composting system. Figure Structure of the magnetic carbon paste electrode used in the electrochemical biosensor     

Modelling of Amperometric Biosensors with Rough Surface of the Enzyme Membrane

A two-dimensional-in-space mathematical model of amperometric biosensors has been developed. The model is based on the diffusion equations containing a nonlinear term related to the Michaelis–Menten kinetic of the enzymatic reaction. The model takes into consideration two types of roughness of the upper surface (bulk solution/membrane interface) of the enzyme membrane, immobilised onto an electrode. Using digital simulation, the influence of the geometry of the roughness on the biosensor response was investigated. Digital simulation was carried out using the finite-difference technique.     

Mathematical Model and Numerical Simulation of Conductometric Biosensor of Urea

In this article, a mathematical model was developed to describe and optimize the configuration of the urea biosensor. The biosensor is based on interdigitated gold microelectrodes modified with a urease enzyme membrane. The model presented here focuses on the enzymatic reaction and/or diffusion phenomena that occur in the enzyme membrane and in the diffusion layer. Numerical resolution of differential equations was performed using the finite difference technique. The mathematical model was validated using experimental biosensor data. The responses of the biosensor to various conditions were simulated to guide experiments, improve analytical performance, and reduce development costs.     

Development of a new biosensor for superoxide radicals

A superoxide dismutase (SOD) biosensor for determination of superoxide radicals has been developed by immobilization of superoxide dismutase within gelatin (G) on a Pt electrode surface. The properties of the biosensor have been investigated and optimum conditions–enzyme concentration, glutaraldehyde concentration, and pH–were determined. The response of the G-SOD biosensor was proportional to concentration and the detection limit was 0.01 mmol L⁻¹ at a signal-to-noise ratio of 3. The biosensor retained 89% and 60% of its sensitivity after use for three and four weeks, respectively. Immobilization of SOD on gelatin provides a biocompatible microenvironment around the enzyme and stabilizes the activity of the enzyme very efficiently. The superoxide dismutase biosensor was used to determine the antioxidant properties of acetylsalicylic acid-based drugs and the anti-radical activity of healthy and cancerous human brain tissues.     

Electrochemical detection of phenolic compounds using composite film of multiwall carbon nanotube/surfactant/tyrosinase on a carbon paste electrode

A new tyrosinase-based biosensor was developed for detection of phenolic compounds using composite film of multiwall carbon nanotube (MWCNT)/dimethylditetradecylammonium bromide (DTDAB)/tyrosinase (Tyr) on a Nafion-incorporated carbon paste electrode. The biosensor showed a sensitive electrochemical response to the reduction of the oxidation products of different phenolic compounds (phenol, catechol, p-cresol, and p-chlorophenol) by dissolved O₂ in the presence of the immobilized enzyme. The effects of pH, operating potential, MWCNT concentration, and the DTDAB/Tyr ratio on electrochemical response were explored for optimum analytical performance. The biosensor exhibited a linear response range of 1.5–25.0, 2.0–15.0, 2.0–15.0, and 2.5–25.0 μM and sensitivity of 2,900, 3,100, 3,100, and 1,500 μA/mM for phenol, catechol, p-cresol, p-chlorophenol, respectively. In addition, the response of the enzyme electrode showed Michaelis–Menten behavior at concentrations of the phenolic compounds higher than 5.0 μM. The stability and the application of the biosensor were also evaluated.     

Development of a novel enzyme reactor and application as a chemiluminescence flow-through biosensor

A novel enzyme reactor was prepared using calcium alginate fiber (CAF) and amine-modified nanosized mesoporous silica (AMNMS) as a support. Combination of the adsorption of the enzyme on AMNMS with the cage effect of the polymer greatly increases the catalytic activity and the stability of the immobilized enzyme. It was shown that the lifetime, stability, and catalytic activity of the enzyme reactor were greatly improved by incorporating AMNMS into CAF to efficiently encapsulate the enzyme. Glucose oxidase was chosen as a model enzyme to explore the possibility of using CAF–AMNMS as a matrix for enzyme immobilization in the design of a chemiluminescence (CL) flow-through biosensor. The sensitivity of the flow-through biosensor combined with a novel luminol-diperiodatonickelate CL system was higher than for other reported CL biosensors. The proposed biosensor exhibits short response time, easy operation, long lifetime, high catalytic activity, high sensitivity, and simple assembly.     

Amplification of bioelectrocatalytic signalling based on silver nanoparticles and DNA-derived horseradish peroxidase biosensors

Horseradish peroxidase (HRP) was immobilized onto a polyion complex membrane containing positively charged silver nanoparticles (nanosilver), double stranded DNA and poly(thionine) to fabricate highly sensitive and selective electrochemical hydrogen peroxide (H₂O₂) biosensor on a glassy carbon electrode. The presence of nanosilver provided a biocompatible microenvironment for enzyme molecules, greatly amplified the surface coverage of HRP on the electrode surface, and most importantly could act as a charge carrier. The process of the biosensor construction was characterized by scanning electron microscopy. Voltammetric and time-based amperometric techniques were employed to characterize the properties of the derived biosensor. Under optimal conditions, the biosensor has an electrocatalytic behavior towards the H₂O₂ reduction, and exhibits a linear range from 1.1 μM to 5.2 mM, with a lower detection limit of 0.2 μM. The apparent Michaelis–Menten constant of the biosensor to H₂O₂ was estimated to be 1.02 mM. Furthermore, the biosensor exhibited high sensitivity, good reproducibility, and acceptable stability. Importantly, the properties of composite film, together with the bioelectrochemical catalytic activity, could make them useful in the development of bioelectronic devices and investigation of protein electrochemistry at functional interface. Correspondence: Yan Liu, College of Chemistry, Chongqing Normal University, Chongqing 400047, P.R. China     

The Effect of Diffusion Limitations on the Response of Amperometric Biosensors with Substrate Cyclic Conversion

A mathematical model of amperometric biosensors in which chemical amplification by cyclic substrate conversion takes place in a single enzyme membrane has been developed. The model involves three regions: the enzyme layer where enzyme reaction as well as mass transport by diffusion takes place, a diffusion limiting region where only the diffusion takes place, and a convective region where the analyte concentration is maintained constant. Using computer simulation the influence of the thicknesses of the enzyme layer and the diffusion region on the biosensor response was investigated. This paper deals with conditions when the mass transport in the exterior region may be neglected to simulate the biosensor response in a well-stirred solution. The digital simulation was carried out using the finite difference technique.     

Amperometric biosensor based on tyrosinase immobilized in hydrotalcite-like compounds film for the determination of polyphenols

A tyrosinase (Tyr) biosensor has been constructed by immobilizing tyrosinase on the surface of Mg–Al–CO₃ hydrotalcite-like compound film (HTLc) modified glassy carbon electrode (GCE) for the determination of polyphenols. The negatively charged tyrosinase was adsorbed firmly on the surface of a positively charged HTLc/GCE by electrostatic interactions and retained its activity to a great degree. The modified electrode was characterized by cyclic voltammetry and AC impedance spectra. Polyphenols were determined by a direct reduction of biocatalytically generated quinone species. The different parameters, including pH, temperature, and enzyme loading were investigated and optimized. Under the optimum conditions, Tyr/HTLc electrode gave a linear response range of 3–300, 0.888–444, and 0.066–396 μM with a detection limit (S/N = 3) of 0.1, 0.05, and 0.003 μM for catechol, caffeic acid, and quercetin, respectively. In addition, the repeatability and stability of the enzyme electrode were estimated. Total polyphenol contents of real samples were also determined to study the potential applicability of the Tyr/HTLc/GCE biosensor.     

Creatinine biosensor based on ammonium ion selective electrode and its application in flow-injection analysis

A new, highly sensitive, fast responding and stable potentiometric biosensor for creatinine determination is developed. The biosensor is based on an ammonium ion-selective electrode. Creatinine deiminase (EC 3.5.4.21) is chemically immobilized on the surface of the polymeric ion-sensitive membrane in the form of monomolecular layer using a simple, one-step carbodiimide covalent attachment method. The resulting enzyme electrodes are useful for measurement under flow injection analysis (FIA) conditions. The biosensors exhibit excellent operational and storage stability. The enzyme electrodes retain over 70% of initial sensitivity after ten weeks of work under FIA conditions. The storage stability at 4 °C is longer than half a year without loss of sensitivity. Under optimized conditions near 30 samples per hour can be analyzed and the determination range (0.02-20.0 mmol l⁻¹) fully covers creatinine concentrations important from clinical and biomedical point of view. The simple biosensor/FIA system has been successfully used for determination of creatinine in urine, serum and posthemodialysate samples.     

Copper(II)-selective membrane electrode based on a recently synthesized naphthol-derivative Schiff’s base

A PVC membrane electrode for copper(II) ions based on a recently synthesized naphthol-derivative Schiff’s base as membrane carrier was prepared. The sensor exhibits a Nernstian response for Cu²⁺ ions over a wide concentration range (5.0 × 10^–6–5.0 × 10^–2 mol/L) with a detection limit of 3.1 × 10^–6 mol/L (0.2 μg/mL). It has a very short response time of about 5 s and can be used for ?3 months without any divergence in potential. The proposed electrode revealed good selectivities over a wide variety of other cations including alkali, alkaline earth, transition and heavy metal ions and could be used in a pH range of 4.0–7.0. It was successfully applied to the direct determination and potentiometric titration of copper ion. Received: 23 February 1999 / Revised: 4 May 1999 / Accepted: 5 May 1999     

Surface plasmon resonance biosensor based on Hg/Ag–Au film

Mercury or silver was electrodeposited on an Au surface to form an Hg–Au or Ag–Au film. Wavelength-modulation SPR biosensors based on this Hg/Ag–Au film were then used to determine human IgG and rabbit IgG. When direct immunoreactions were performed on the Au sensing surface, the range of concentrations of human IgG and rabbit IgG that could be determined were 2.00–40.00 μg/ml and 2.50–40.00 μg/ml, respectively. When Hg was electrodeposited onto the Au film for 1200 s, the range of concentrations of human IgG and rabbit IgG that could be determined were 0.50–40.00 μg/ml and 0.63–40.00 μg/ml, respectively. When Ag was electrodeposited onto the Au film for 1500 s, the range of concentrations of human IgG and rabbit IgG that could be determined were 0.25–20.00 and 0.42–20.00 μg/ml, respectively. The biosensor based on Ag–Au film was therefore found to be the most sensitive of the three types of biosensor tested, giving limits of determination that were up to eight times lower than those obtained with a biosensor based on Au film alone. Figure The relationship between the concentration of human IgG and the shift in the resonant wavelength Δλ _eq for different Ag electrodeposition times     

The Construction of Glucose Biosensor Based on Platinum Nanoclusters—Multiwalled Carbon Nanotubes Nanocomposites

One-step synthesis method was proposed to obtain the nanocomposites of platinum nanoclusters and multiwalled carbon nanotubes (PtNCs–MWNTs), which were used as a novel immobilization matrix for the enzyme to fabricate glucose biosensor. The fabrication process of the biosensor was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, atomic force microscopy and scanning electron microscope. Due to the favorable characteristic of PtNCs–MWNTs nanocomposites, the biosensor exhibited good characteristics, such as wide linear range (3.0 μM–12.1 mM), low detection limit (1.0 μM), high sensitivity (12.8 μA mM⁻¹), rapid response time (within 6 s). The apparent Michaelis–Menten constant ( K_m^\textapp K_m^{\text{app}} ) is 2.1 mM. The performance of the resulting biosensor is more prominent than that of most of the reported glucose biosensors. Furthermore, it was demonstrated that this biosensor can be used for the assay of glucose in human serum samples.