Array of potentiometric sensors for simultaneous analysis of urea and potassium

Urea biosensors based on urease immobilized by crosslinking with BSA and glutharaldehyde coupled to ammonium ion-selective electrodes were included in arrays together with potassium, sodium and ammonium PVC membrane ion-selective electrodes. Multivariate calibration models based on PCR and PLS2 were built and tested for the simultaneous determination of urea and potassium. The results show that it is possible to obtain PCR and PLS2 calibration models for simultaneous determination of these two species, based on a very small set of calibration samples (nine samples). Coupling of biosensors with ion-selective electrodes in arrays of sensors raises a few problems related to the limited stability of response and unidirectional cross-talk of the biosensors, and this matter was also subjected to investigation in this work. Up to three identical urea biosensors were included in the arrays, and the data analysis procedure allowed the assessment of the relative performance of the sensors. The results show that at least two urea biosensors should be included in the array to improve urea determination. The prediction errors of the concentration of urea and potassium in the blood serum samples analyzed with this array and a PLS2 calibration model, based on nine calibration samples, were lower than 10 and 5%, respectively.     

Quinoprotein glucose dehydrogenase modified thick-film electrodes for the amperometric detection of phenolic compounds in flow injection analysis

The use of thick-film electrodes as basic transducers for highly sensitive amperometric biosensors using PQQ (pyrroloquinoline quinone) dependent glucose dehydrogenase (GDH) with short response times is described. The enzyme is embedded in a polyurethane matrix on top of a platinum based thick film electrode and its ability to reduce oxidized phenolic compounds is exploited. The electrochemical amplification is based on the oxidation of the analyte on the surface of the electrode followed by its enzymatic reduction. Different parameters of the glucose dehydrogenase electrode system using dopamine as a model analyte were optimized, e.g., membrane thickness, pH value, buffer system, flow rate and storage conditions. Using optimized parameters the sensitivity and detection limits for various phenolic compounds were evaluated. The comparison of electrodes from the identical as well as from different batches shows the ability to produce a number of well reproducible sensors showing remarkably small differences with respect to parameters as sensitivity, response times and measuring range.     

Quinoprotein glucose dehydrogenase modified thick-film electrodes for the amperometric detection of phenolic compounds in flow injection analysis

The use of thick-film electrodes as basic transducers for highly sensitive amperometric biosensors using PQQ (pyrroloquinoline quinone) dependent glucose dehydrogenase (GDH) with short response times is described. The enzyme is embedded in a polyurethane matrix on top of a platinum based thick film electrode and its ability to reduce oxidized phenolic compounds is exploited. The electrochemical amplification is based on the oxidation of the analyte on the surface of the electrode followed by its enzymatic reduction. Different parameters of the glucose dehydrogenase electrode system using dopamine as a model analyte were optimized, e.g., membrane thickness, pH value, buffer system, flow rate and storage conditions. Using optimized parameters the sensitivity and detection limits for various phenolic compounds were evaluated. The comparison of electrodes from the identical as well as from different batches shows the ability to produce a number of well reproducible sensors showing remarkably small differences with respect to parameters as sensitivity, response times, and measuring range. Received: 15 August 2000 / Revised: 17 October 2000 / Accepted: 24 October 2000     

Recent advances in the application of nanomaterials in enzymatic glucose sensors

Due to the critical role of glucose level in the diagnosis and treatment of diabetes, as well as the increasing number of diabetics, there is an overwhelming demand for developing glucose sensors. It is well acknowledged that these sensors, especially those based on glucose oxidase, have played an important role in blood glucose detection. Inspired by the attractive properties, nanomaterials, especially nanostructured carbon and metal/metal oxides, have been extensively explored to develop enzymatic glucose sensors with high sensitivity, fast response time, and satisfied stability. In this review, a brief history of glucose biosensors is firstly presented. Furthermore, we discuss the currently available fabrication possesses in the field of enzymatic glucose biosensors based on nanomaterials, focusing on the carbon-based, metal-based, and metal oxides-based nanocomposites. What is more, we discuss the challenges and attempt to give an outlook on the possible further developments.     

Urea Biosensors Based on PVC Membrane Ion-Selective Electrodes

Abstract

This paper presents a general method of enzyme immobilization at the surface of ion selective membranes. Covalent binding of enzymes directly on the electrode surface is a very effective method that results in stable enzymatic membranes. As an example the construction of enzymatic sensors for urea determination based on ammonium and hydrogen carbonate ion selective electrodes is presented. The optimum working conditions for these biosensors were found. Bioelectrodes based on an ammonium sensor show very good analytical parameters: dynamic stability - over 2 months without decrease of sensitivity, response time - shorter then 20 s. high sensitivity, determination range from 0.3 to 70 mM. In the contrast to the ammonium ion based biosensors, those constructed on the basis of anion selective electrodes have worse analytical parameters. It is mainly due to poor selectivity and instability of an applied ion selective electrode. In spite of this, both types of urea biosensors were used for measurements in the differential potentiometry mode. The application of such system increased the sensitivity of urea determination.     

Potentiometric Biosensor System Based on Recombinant Urease and Creatinine Deiminase for Urea and Creatinine Determination in Blood Dialysate and Serum

A biosensor system for simultaneous determination of creatinine and urea in blood serum and dialysate samples was developed. It consisted of creatinine and urea biosensors based on a potentiometric transducers with two identical pH‐sensitive field‐effect transistors. In creatinine biosensor, creatinine deiminase immobilized via photopolymerization in PVA/SbQ polymer on one transistor served as a biorecognition element, while bovine serum albumin in PVA/SbQ polymer placed on the second transistor was used for reference. The urea biosensor was created in the same way but recombinant urease was used instead of creatinine deiminase. The linear ranges of creatinine and urea measurement were 0.02–2 mM and 0.5–15 mM, correspondingly, which allowed simultaneous determination of the metabolites. Response time of the biosensor system was 2–3 min; RSD of responses did not exceeded 5 %. The biosensors demonstrated absence of non‐selective response towards components of blood dialysate and serum. Urea and creatinine concentrations were determined in 20 samples of blood dialysate and serum. The results correlated well with traditional methods of analysis. Creatinine and urea biosensors were stable during five months of storage (during this time the responses decreased by about 10 %). The proposed biosensor system can be effectively used for analysis of serum samples and for hemodialysis control.     

Sol-gel derived ceramic-carbon enzyme electrodes: Glucose oxidase as a test case

Several types of amperometric biosensors comprised of immobilized glucose oxidase in chemically-modified ceramic-carbon matrices are compared. The electrodes are comprised of several building blocks each performing a specific function. Glucose oxidase is used to catalyze the bio-oxidation of glucose; carbon powder imparts conductivity and favorable electrochemical characteristics; the Ormosil network provides rigidity and porosity; and the organic modification of the Ormosil imparts controlled surface polarity. Additionally, hydrophilic chemical modifiers are incorporated in order to control the size of the wetted, electroactive layer; high dispersion of inert metal catalysts is used to enhance hydrogen peroxide oxidation and redox mediators may be co-immobilized when oxygen independent response is desirable. The electrodes can be prepared either in the form of thick supported film, useful for disposable electrodes or as bulk-modified, disk shape electrodes, which can be used as renewable surface electrodes.     

Glucose oxidase-incorporated hydrogel thin film for fast optical glucose detecting under physiological conditions

Hydrogel biosensors usually suffer from a slow response, which severely hinders their practical applications. Here a new optical glucose biosensor was designed, using glucose-sensitive hydrogel films as both glucose-sensing material and Fabry-Perot cavity. The film was fabricated by layer-by-layer assembly from partially oxidized dextran (PO-Dex), chitosan, and glucose oxidase (GOD). The film responds to glucose because the incorporated GOD converts glucose to gluconic acid, and thus lowers the local pH in the film, and, in turn, triggers the pH-sensitive film to swell. The glucose-induced swelling causes a shift of Fabry?Perot fringes on the reflection spectra of the film, from which the glucose concentration can be reported. The new sensor works well under physiological conditions. Potential interferents, such as diols for phenylboronic acid-based sensors and electroactive compounds for electrochemical sensors, do not influence the new sensor. The sensor can respond reversibly over a wide range of glucose concentration. Particularly, it responds linearly within the clinically relevant glucose range (0–20 mM). More importantly, because the film is very thin, the new sensor can respond quickly, making it potential for real-time, continuous glucose monitoring.     

Array of potentiometric sensors for the analysis of creatinine in urine samples

The development of potentiometric biosensors for creatinine based on creatinine iminohydrolase (E.C. 3.5.4.21) immobilized on chitosan membranes coupled to a nonactin based ammonium ion selective electrode is described. The response characteristics of three types of biosensors with the enzyme immobilized by three different procedures were evaluated. The biosensors with better response characteristics were obtained by coupling the ammonium ion selective electrodes to chitosan membranes with the enzyme immobilized by adsorption. The linear response range of these biosensors to creatinine was 10(-4) to 10(-2) M, the response time was between 30 and 60 s, they showed an operational lifetime of 44 days and the slope of the response to creatinine in the first day varied between 50 and 52 mV decade-1. An array of six potentiometric sensors, constituted by two creatinine biosensors and four ion selective electrodes for potassium, sodium, ammonium and calcium was calibrated and a multivariate model based on PLS1 for the response to creatinine was obtained and validated. The array was used for the analysis of creatinine in urine samples and the results were compared with the results of a clinical analysis laboratory, based on the Jaffé reaction.     

A New Route for the Enzymeless Trace Level Detection of Creatinine Based on Reduced Graphene Oxide/Silver Nanocomposite Biosensor

Renal insufficiencies and muscle diseases can be easily identified from the concentration of creatinine in blood and urine. Although various chemical sensors have been developed to detect creatinine, selectivity and robustness of chemical sensors are the main obstacles for many researchers. To overcome these difficulties, finding a suitable chemical biosensor with long‐term stability, low cost, high sensitivity and selectivity for the detection of creatinine is immensely desirable. Herein, we have developed a novel enzymeless creatinine biosensor for the trace level detection of creatinine using reduced graphene oxide (RGO)/ silver nanoparticles (AgNPs) which was prepared by simple one step electrochemical potentiodyanamic method. The anodic peak current of AgNPs gradually decreased when the concentration of creatinine was increased. Based on the decrease of anodic peak current, we have introduced a new platform for the detection of creatinine. The adsorption of creatinine on AgNPs was confirmed by various techniques. The newly proposed biosensor exhibited a very low detection limit of 0.743 pM with linear range from 10 pM to 120 pM. The demonstrated sensor can detect creatinine even in the presence of other interfering biomolecules such as glucose, ascorbic acid, uric acid, urea and creatine.     

Laser-induced Graphene in Facts,Numbers, and Notes in View of Electroanalytical Applications: A Review

In this review, laser-induced graphene (LIG) -based electrodes are discussed by covering such essential areas, as a characterization of LIG material properties necessary for electroanalysis, including data on LIG sheet resistance, wettability, spatial resolution, electrochemical characteristics, as well as correlations of “process” - “properties” - “electroanalytical characteristics”of LIG-electrodes. Moreover, typical and innovative LIG-based electrodes designs for electroanalytical applications, including combined multi-analyte multimodal wearable sensors, interdigitated electrodes, are shown. The essential data related to LIG in electroanalysis are summarized in tables. The authors also discussed recent LIG-based electroanalytical applications. Close attention has been paid to LIG glucose sensors and biosensors.     

A Review of Glucose Biosensors Based on Graphene/Metal Oxide Nanomaterials

In recent years, considerable attention has been paid to developing economical yet rapid glucose sensors using graphene and its composites. Recently, the excellent properties of graphene and metal oxide nanoparticles have been combined to provide a new approach for highly sensitive glucose sensors. This review focuses on the development of graphene functionalized with different nanostructured metal oxides (such as copper oxide, zinc oxide, nickel oxide, titanium dioxide, iron oxide, cobalt oxide, and manganese dioxide) for use as glucose biosensors. Additionally, a brief introduction of the electrochemical principles of glucose biosensors (including amperometric, potentiometric, and conductometric) is presented. Finally, the current status and future prospects are outlined for graphene/metal oxide nanomaterials in glucose sensing.     

Screen-printed electrodes for biosensing: a review (2008–2013)

Screen-printing is one of the most promising approaches towards simple, rapid and inexpensive production of biosensors. Disposable biosensors based on screen printed electrodes (SPEs) including microelectrodes and modified electrodes have led to new possibilities in the detection and quantitation of biomolecules, pesticides, antigens, DNA, microorganisms and enzymes. SPE-based sensors are in tune with the growing need for performing rapid and accurate in-situ analyses and for the development of portable devices. This review (with 226 refs.) first gives an introduction into the topic and then is subdivided into sections (a) on DNA sensors (including methods for the detection of hybridization and damage), (b) on aptasensors (for thrombin, OTA, immunoglobulins and cancer biomarkers), (c) on immunosensors (for microorganisms, immunoglobulins, toxins, hormones, lactoferrin and biomarkers), (d) on enzymatic biosensors (for glucose, hydrogen peroxide, various pharmaceuticals, neurotransmitters, amino acids, NADH, enzyme based sensors).

Polyurethane Enzyme Membranes for Chip Biosensors

Abstract

The coverage of electrochemical chip sensors based on silicon technology with a polyurethane enzyme membrane is described. After crosslinking of the surface by polyfunctional isocyanates the enzyme membrane shows good adhesion, complete retention of the enzyme molecules, and low diffusional resistance to both analytes and products. Using thin film noble metal electrodes and ion sensitive field effect transistors, glucose and urea sensors with good long term stability and short response time have been prepared.     

Application of heated electrodes operating in a non-isothermal mode for interference elimination with amperometric biosensors

Heated electrodes were applied for the non-isothermal operation of amperometric glucose biosensors based on glucose oxidase immobilised on the electrode surface by entrapment within a polymer layer. The localised deposition of the polymer film under simultaneous entrapment of the enzyme was achieved by an electrochemically induced pH-modulation in the diffusion zone in front of the electrode, thus altering the solubility of the polymer chains. This non-manual sensor preparation protocol could be successfully used for the modification of a novel indirectly heated electrode. The non-isothermal operating mode allows working at the optimum temperature of the enzyme sensors without any thermal distortion of the bulk solution. Increased surface temperature of the sensor thus accelerates transport as well as kinetic processes, resulting in an enhanced amperometric signal.In the presence of interfering compounds such as ascorbic acid, the proposed technique allows use of the diverging thermal impact on the sensing process, for different electrochemically active compounds, for a deconvolution of the amperometric signal at different electrode temperatures. A calculation method for determination of glucose in the presence of one interfering compound is presented as a basis for a calculative interference elimination.     

Modified graphitized carbon black as transducing material for reagentless H2O2 and enzyme sensors

Direct electron transfer between redox enzymes and electrodes is the basis for the third generation biosensors. We established direct electron transfer between quinohemoprotein alcohol dehydrogenase (PQQ-ADH) and modified carbon black (CBs) electrodes. Furthermore, for the first time, this phenomenon was observed for pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase (PQQ-GDH). Reagentless enzyme biosensors suitable for the determination of ethanol, glucose and sensors for hydrogen peroxide were designed using CB electrodes and screen-printing technique. Aiming to create an optimal transducing material for biosensors, a set of CB batches was synthesized using the matrix of Plackett-Burman experimental design. Depending on the obtained surface functional groups as well as the nano-scale carbon structures in CBs batches, the maximal direct electron transfer current of glucose and ethanol biosensors can vary from 20 to 300 nA and from 30 to 6300 nA for glucose and ethanol, respectively. Using modified CB electrodes, an electrocatalytic oxidation of H₂O₂ takes place at more negative potentials (0.1-0.4 V versus Ag/AgCl). Moreover, H₂O₂ oxidation efficiency depends on the amount and morphology of fine fraction in the modified CBs.     

Toward the optimization of an e-tongue system using information visualization: a case study with perylene tetracarboxylic derivative films in the sensing units

The wide variety of molecular architectures used in sensors and biosensors and the large amount of data generated with some principles of detection have motivated the use of computational methods, such as information visualization techniques, not only to handle the data but also to optimize sensing performance. In this study, we combine projection techniques with micro-Raman scattering and atomic force microscopy (AFM) to address critical issues related to practical applications of electronic tongues (e-tongues) based on impedance spectroscopy. Experimentally, we used sensing units made with thin films of a perylene derivative (AzoPTCD acronym), coating Pt interdigitated electrodes, to detect CuCl(2) (Cu(2+)), methylene blue (MB), and saccharose in aqueous solutions, which were selected due to their distinct molecular sizes and ionic character in solution. The AzoPTCD films were deposited from monolayers to 120 nm via Langmuir-Blodgett (LB) and physical vapor deposition (PVD) techniques. Because the main aspects investigated were how the interdigitated electrodes are coated by thin films (architecture on e-tongue) and the film thickness, we decided to employ the same material for all sensing units. The capacitance data were projected into a 2D plot using the force scheme method, from which we could infer that at low analyte concentrations the electrical response of the units was determined by the film thickness. Concentrations at 10 μM or higher could be distinguished with thinner films--tens of nanometers at most--which could withstand the impedance measurements, and without causing significant changes in the Raman signal for the AzoPTCD film-forming molecules. The sensitivity to the analytes appears to be related to adsorption on the film surface, as inferred from Raman spectroscopy data using MB as analyte and from the multidimensional projections. The analysis of the results presented may serve as a new route to select materials and molecular architectures for novel sensors and biosensors, in addition to suggesting ways to unravel the mechanisms behind the high sensitivity obtained in various sensors.     

Electric cell-substrate impedance sensing with screen printed electrode structures

Impedance sensors in thick film technology have been tested as a tool for electric cell-substrate impedance sensing. The screen printed Pt electrodes have a width of 250-400 microm. Electrodes and the surrounding ceramic chip substrate could be homogeneously grown with L-929 and Hela cells. The performance of a screen printed interdigitated electrode structure (IDES) was compared with that of thin film structures with the same layout geometry. The thick film impedance sensors allowed to correctly record the morphological response of confluent Hela cell layers to stimulation with histamine. A thick film conductivity sensor also revealed impedance values which were dependent on cell growth on the electrode surface, even at a very low frequency range of approximately 1 Hz.     

In vivo glucose monitoring: towards 'Sense and Act' feedback-loop individualized medical systems

Glucose biosensors are key components of closed-loop glycaemic control (insulin delivery) systems for effective management of diabetes. By providing a fast return of the analytical information in a timely fashion, such sensors offer direct and reliable assessment of rapid changes in the glucose level, as desired for making optimal and timely therapeutic interventions in cases of hypo- and hyperglycemia. The majority of sensors used for continuous glucose monitoring are amperometric enzyme electrodes. The successful realization of closed-loop glycaemic control requires innovative approaches for addressing major challenges of biofouling, inflammatory response, calibration, stability, selectivity, power, miniaturization, common to other remote sensor systems. The goal of this review article is to demonstrate how these challenges are being addressed towards achieving reliable continuous subcutaneous monitoring of glucose. While the concept is presented here in connection to the management of diabetes, such loop-based individualized integrated (sensing/release) medical systems should lead to a fine-tune drug therapy and should have an enormous impact upon the treatment and management of different diseases.