Modelling carbon nanotube based biosensor

This paper presents a two-dimensional-in-space mathematical model of an amperometric biosensor based on an enzyme-loaded carbon nanotubes layer deposited on a perforated membrane. The developed model is based on non-linear non-stationary reaction-diffusion equations. By changing input parameters the output results are numerically analysed with a special emphasis to the influence of the geometry and the catalytic activity of the biosensor to its response. The numerical simulation at transition and steady state conditions was carried out using the finite difference technique. The mathematical model and the numerical solution were validated by experimental data. The obtained agreement between the simulation results and experimental data was admissible at different concentrations of the substrate and the mediator.     

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 the Behaviour of Potentiometric Membrane Biosensors

This paper presents a mathematical model of a potentiometric biosensor based on a potentiometric electrode covered with an enzyme membrane. The model is based on the reaction–diffusion equations containing a non-linear term related to theMichaelis–Menten kinetics of the enzymatic reaction. Using computer simulation the influence of the thickness of the enzyme membrane on the biosensor response was investigated. The digital simulation was performed using the finite difference technique. Results of the numerical simulation were compared with known analytical solutions.      

Modelling Dynamics of Amperometric Biosensors in Batch and Flow Injection Analysis

A mathematical model of amperometric biosensors has been developed. The model is based on non-stationary diffusion equations containing a non-linear term related to Michaelis–Menten kinetic of the enzymatic reaction. Using digital simulation, the influence of the substrate concentration as well as maximal enzymatic rate on the biosensor response was investigated. The digital simulation was carried out using the finite difference technique. The model describes the biosensor action in batch and flow injection regimes.     

An Analysis of Mixtures Using Amperometric Biosensors and Artificial Neural Networks

This paper presents a sensor system based on a combination of an amperometric biosensor acting in batch as well as flow injection analysis with the chemometric data analysis of biosensor outputs. The multivariate calibration of the biosensor signal was performed using artificial neural networks. Large amounts of biosensor calibration as well as test data were synthesized using computer simulation. Mathematical and corresponding numerical models of amperometric biosensors have been built to simulate the biosensor response to mixtures of compounds. The mathematical model is based on diffusion equations containing a non-linear term related to Michaelis–Menten kinetics of the enzymatic reaction. The principal component analysis was applied for an optimization of calibration data. Artificial neural networks were used to discriminate compounds of mixtures and to estimate the concentration of each compound. The proposed approach showed prediction of each component with recoveries greater that 99% in flow injection as well as in batch analysis when the biosensor response is under diffusion control.     

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.     

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.     

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.     

Mathematical modeling of the action of biosensor possessing variable parameters

Electrochemical biosensor containing flat semi-permeable membrane covering enzyme-containing layer has been investigated. Mathematical modeling of the action modes of electrochemical biosensors with outer diffusion membrane was performed. Operation of the biosensor under the conditions when the permeability of the membrane and the activity of the biocatalytic layer depend on the parameters of the probe has been examined. The pH and temperature were selected as the main parameters which often affect the action of biosensors. A set of parameters was selected when the biosensor operates in kinetic and diffusion modes of action. The response time of the biosensor was shown to be sensitive to the mode of the biosensor action especially in the boundary region of the biosensor action. The linearity of the biosensor (the linear dependence of the biosensor response on the substrate concentration) in the deep diffusion mode can be increased by several magnitudes, whereas the response time increases only several times.     

Nafion 膜固定的新亚甲基蓝为介体生物传感器

以Nafion膜固定的新亚甲基蓝为辣根过氧化物酶和玻碳电极间的电子传递介体,制成电流型单酶过氧化氢生物传感器和双酶葡萄糖生物传感器。探讨了工作电位、pH值、温度和干扰物质等对生物传感器的影响。     

Response Behavior of Amperometric Glucose Biosensors Based on Different Carbon Substrate Transducers Coated with Enzyme‐Active Layer: A Comparative Study

Carbon electrodes (glassy carbon, GC, screen‐printed carbon, SPC, and carbon fiber, CF) were used as substrate transducers to prepare glucose biosensors of different sizes and geometries, based on iron‐ruthenium hexacyanoferrate as H₂O₂ reduction mediator and glucose oxidase immobilized in a poly(1,2‐phenylenediamine) membrane. Their response behavior under hydrodynamic amperometric conditions at an operating potential of ?0.02 V vs. Ag/AgCl was studied and compared. While the GC and SPC based conventional size biosensors showed enzymatic catalysis controlled current response with nonlinear concentration dependence, the CF based micro‐biosensor exhibited, due to diffusion‐controlled current response, extended linear range calibration curves with relatively lower sensitivity and longer response times. Several preparation parameters responsible for the improvement of biosensor performance were also investigated.     

Development of electrochemical biosensors based on sol-gel enzyme encapsulation and protective polymer membranes

Protective polymer coatings have been used to enhance the retention of enzymes in sol-gel films as immobilisation phases in electrochemical biosensors. Carbon film electrodes were electrochemically modified with poly(neutral red) (PNR). These electrodes were coated with oxysilane sol-gels incorporating glucose oxidase and an outer coating of carboxylated PVC (CPVC) or polyurethane (PU), with and without Aliquat-336 or isopropyl myristate (IPM) plasticizer, was applied. The biosensors were characterised electrochemically using cyclic voltammetry and amperometry, electrochemical impedance spectroscopy and scanning electron microscopy. Impedance spectra showed that the electrode surface is most active when the sol-gel–GOx layer is not covered with a membrane. However, membranes without plasticizer extend the lifetime of the biosensor to more than 2 months when PU is used as an outer membrane. The linear range of the biosensors was found to be 0.05–0.50 mM of glucose and the biosensor with PU outer membrane exhibited higher sensitivity (ca.117 nA mM⁻¹) in the region of linear response than that with CPVC. The biosensors were applied to glucose measurement in natural samples of commercial orange juice.     

Electrochemical sensor with flavin-containing monooxygenase for triethylamine solution

A bioelectronic sensor for triethylamine (TEA) was developed with a flavin-containing monooxygenase type 3 (FMO-3). The TEA biosensor consisted of a Clark-type dissolved-oxygen electrode and an FMO-3 immobilized membrane. The FMO-3 solution was mixed with a poly(vinyl alcohol) containing stilbazolium groups (PVA-SbQ), coated on to the dialysis membrane, and the membrane was irradiated with a fluorescent light to immobilize the enzyme. In order to amplify the biosensor output, a substrate regeneration cycle, obtained by coupling the monooxygenase with l-ascorbic acid (AsA) as reducing reagent system, was applied. The effect of pH on the determination of TEA was studied. The maximum response was achieved at pH >9.0. A drop of the phosphate buffer solution with the AsA was put on the sensing area of the oxygen electrode, and the FMO-3 immobilized membrane was placed on the oxygen electrode and covered with a supporting Nylon mesh net which was secured with a silicone O-ring. A measurement system for TEA solution was constructed using the FMO-3 biosensor, a personal computer, a computer-controlled potentiostat, and an A/D converter. The FMO-3 biosensor was used to measure TEA solution from 0.5 to 4.0 mmol L⁻¹ with 10.0 mmol L⁻¹ AsA. The biosensor also had good reproducibility, for example a 6.31% coefficient of variation for five measurements, and the output current was maintained over a few hours. In order to improve the selectivity of the TEA biosensor, three type of biosensor with FMO isomer types 1, 3, and 5 were constructed and used to measure nitrogen and sulfur compounds. The outputs of the isomer biosensors indicated individual patterns for each sample solution. The selectivity of TEA biosensor would be improved, and determination of sulfur and nitrogen compounds would be possible, by using the different output of biosensors prepared from different FMO isomers.     

Mathematical modeling of biosensor action in the region between diffusion and kinetic modes

We describe the action of electrochemical enzyme-based biosensor by applying mathematical modeling. We consider two types of biosensors: a biosensor containing a single heterogeneous enzyme layer and biosensor containing an additional protecting polymer-based layer. The initial parameters of the biosensor were selected on the basis of typical immobilized glucose oxidase-based electrochemical biosensor. A phenomenon of the accumulation of the electrochemically active product inside the biocatalytic layer was evaluated. It was shown that accumulation of the product can increase sensitivity of the biosensor no more than 2.6 times. Due to the asymmetric distribution of the electrochemically active product inside the enzyme-containing membrane and asymmetric diffusion of the substrate, it was shown that the thickness of the membrane possesses an optimal value. For the selected set of initial parameters, the optimal thickness of the enzyme-containing layer was 2.9–4.5  $\upmu $ m. Real profiles of the impact of the thickness of the membranes were evaluated. A method for the evaluation of acceptable fluctuations of the membrane diffusion parameters on biosensor response was created, and the profiles of the dependence were calculated. These dependencies can be used for development of the software for biosensor monitoring.     

Enzymatic Biosensor Based on the ISFET and Photopolymeric Membrane for the Determinaion of Urea

An ISFET based enzymatic biosensor was developed for the determination of urea. Immobilization of urease was accomplished by the use of liquid mixture which contained vinylpyrrolidone, oligouretane metacrylate and oligocarbonate metacrylate and which can form a polymer under the influence of ultraviolet. The biosensor has the following characteristics: the linear field of responses is in the range of 0.05–20 mM, curve slope – 38 mV/pC, and response time 5–10 min. The increase of the temperature from 28 to 41 °C leads to 15% increase in the intensity of the response of the biosensor. The maximum response is observed at pH 6.0–6.5. At the increase of the NaCl concentration in solution up to 300 mM the biosensor response drops off and achieves half of its initial level. NH₄Cl causes a stronger inhibition of enzyme activity comparing to NaCl. The results obtained with the developed biosensor correlate with the data of standard calorimetric methods. The intensity of the biosensor response decreases gradually during 40 days up to 80% of the initial level. The biosensors prepared with a fresh membrane or membrane preserved during 46 days at 2 °C gave similar responses in solution with an equal concentration of a substrate. It is concluded that the developed enzymatic biosensor is perspective for its clinical application for the determination of urea in blood and that the proposed method to prepare a selective biological membrane may be in a simple way included in integral technology of the semiconductor transducer manufacturing.     

Degradation of substrate and/or product: mathematical modeling of biosensor action

Mathematical model for evaluation of the multilayer heterogeneous biocatalytic system has been elaborated. The model consists of nonlinear system of partial differential equations with initial values and boundary conditions. An algorithm for computing the numerical solution of the mathematical model has been applied. Two cases: when product diffuses out of the biosensor and when the outer membrane is impermeable for product (product is trapped inside the biosensor) have been dealt with by adjusting boundary conditions in the mathematical model. Profiles of the impact of the substrate and product degradation rates on the biosensor response have been constructed in both cases. Value of the degradation impact has been analyzed as a function of the outer membrane thickness. The initial substrate concentration also affects influence of the degradation rates on the biosensor response. Analytical formulae, defining approximate values of relationships between the degradation rates and the outer membrane thickness or the initial substrate concentration, have been obtained. These formulae can be employed for monitoring of the biosensor response.     

Amperometric biosensors employing an insoluble oxidant as an interference-removing agent

A strong oxidant membrane is introduced to amperometric biosensors in order to solve the problem associated with interference from readily oxidizable species. The proposed biosensors are in planar format, and are composed of four components, i.e. a base amperometric transducer, an enzyme layer, a protecting membrane, and an oxidant membrane. In this sensor format, interfering species are removed by an oxidation reaction during their diffusion through the oxidant membrane. The oxidant membrane is introduced by dispensing a mixture of an oxidant and a polymer matrix as dissolved in an organic solvent, and thus, could be easily adapted to mass fabrication of miniature biosensors. In this work, several different reagents are examined as oxidants: BaO₂, CeO₂, MnO₂ and PbO₂. Of these, PbO₂ is shown to yield biosensors with the best performance, in terms of reducing interfering signals. Two different matrix systems are devised for use in formulating oxidant membranes: hydrophilic polyurethane (HPU) and cellulose acetate incorporating poly(ethylene glycol) (CA/PEG). While the CA/PEG-type sensor displays better sensitivity and faster response behavior, the HPU-type is shown to exhibit more pronounced interference-removing ability. The analytical utility of the proposed oxidant membrane is demonstrated by fabricating amperometric glucose and creatinine sensors as the model biosensor systems, and by investigating their response characteristics.     

Enhanced optical immunosensor based on surface plasmon resonance for determination of transferrin

Wavelength modulation surface plasmon resonance biosensors (SPR) using colloidal Au nanoparticles and double-linker sensing membrane enhancement are reported for determination of transferrin. The 2-mercaptoethylamine (MEA) was immobilized on the biosensor surface with traditional amine coupling method. The interaction between colloidal Au nanoparticles and MEA was investigated. The anti-transferrin was immobilized on the biosensor surface prepared with staphylococcal protein A (SPA). The interaction of the antibody and antigen was monitored in real time. The good response was obtained in the concentration range 1-20, 0.1-20 and 0.05-20 μg/mL for directly immune assay, double-linker assay and colloidal Au-amplified assay. The result clearly demonstrates that these methods may obtain significantly enhancement of sensitivity for the wavelength modulation SPR biosensor.     

Application of Different Zeolites for Improvement of the Characteristics of a pH‐FET Biosensor Based on Immobilized Urease

Different modifications of the zeolites Na⁺‐Beta and LTA were applied for improving the working characteristics of a urea biosensor. The bioselective membrane of the biosensor was based on urease and different zeolites co‐immobilized with bovine serum albumin on the surface of a pH‐FET. It was shown that the biosensors modified with the zeolites H⁺‐Beta30 and H⁺‐Beta50 are characterized by increased sensitivity to urea. The influence of the zeolite concentration on the sensitivity of the biosensors was studied. The optimal concentration of the zeolites H⁺‐Beta30 and H⁺‐Beta50 in the bioselective membrane was 15 %. Different variants of co‐immobilization of urease and zeolite H⁺‐Beta30 were studied and the optimal method was selected. Thus, a general conclusion is that the urea biosensor sensitivity can be improved using zeolite H⁺‐Beta30 for urease immobilization in the bioselective membrane.     

Lifetime Improvement of Glucose Biosensor by Epoxy‐Enhanced PVC Membrane

A new approach using epoxy resin to enhance the durability and adhesion of a diffusion‐limiting membrane in amperometric biosensors is described. The polymer membrane was mainly composed of commercially available fast epoxy adhesive ATACS 5104, poly(vinyl chloride) (PVC) and plasticizers such as isopropyl myristate (IMP) and Aliquat 336 (AL). It can be readily deposited on various substrates by using coating and other thin film fabrication methods. The effect of epoxy resin in the membrane composition was investigated using a coil‐type glucose biosensor containing extra enzyme. The ideal membrane was found to include approximately 1/3 epoxy resin, 1/3 plasticizer and 1/3 PVC. Such a membrane was verified to be porous and permeable to small molecules like glucose and can tightly adhere to other beneath layers such as a Nafion membrane, which serves as the interference‐eliminating layer. These epoxy‐based glucose biosensors showed excellent electrochemical response properties including a long lifetime and can be used for microanalysis of solutions and biological fluids. With an additional PU outermost layer, the present glucose biosensors can potentially be used for in vivo measurements.