Screen printed glucose electrodes based on platinised carbon particles and glucose oxidase

Screen-Printed Electrodes Modified with Metal Nanoparticles for Small Molecule Sensing

Recent progress in the field of electroanalysis with metal nanoparticle (NP)-based screen-printed electrodes (SPEs) is discussed, focusing on the methods employed to perform the electrode surface functionalization, and the final application achieved with different types of metallic NPs. The ink mixing approach, electrochemical deposition, and drop casting are the usual methodologies used for SPEs' modification purposes to obtain nanoparticulated sensing phases with suitable tailor-made functionalities. Among these, applications on inorganic and organic molecule sensing with several NPs of transition metals, bimetallic alloys, and metal oxides should be highlighted.

A promising solution to enhance the sensocompatibility of biosensors in continuous glucose monitoring systems

BACKGROUND

Continuous glucose monitors (CGMs) measure glucose in real time, making it possible to improve glycemic control. A promising technique involves glucose sensors implanted in subcutaneous tissue measuring glucose concentration in interstitial fluid. A major drawback of this technique is sensor bioinstability, which can lead to unpredictable drift and reproducibility. The bioinstability is partly due to sensor design but is also affected by naturally occurring subcutaneous inflammations. Applying a nonbiofouling coating to the sensor membrane could be a means to enhancing sensocompatibility.

METHODS

This study evaluates the suitability of a polyethylene-glycol-based coating on sensors in CGMs. Methods used include cross hatch, wet paper rub, paper double rub, bending, hydrophilicity, protein adsorption, bio-compatibility, hemocompatibility, and glucose/oxygen permeability testing.

RESULTS

Results demonstrate that coating homogeneity, adhesion, integrity, and scratch resistance are good. The coating repels lysozyme and bovine serum albumin, and only a low level of fibrin and blood platelet adsorption to the coating was recorded when testing in whole human blood. Cytotoxicity, irritation, sensitization, and hemolysis were assessed, and levels suggested good biocompatibility of the coating in subcutaneous tissue. Finally, it was shown that the coating can be applied to cellulose acetate membranes of different porosity without changing their permeability for glucose and oxygen.

CONCLUSIONS

These results suggest that the mechanical properties of the coating are sufficient for the given application, that the coating is effective in preventing protein adsorption and blood clot formation on the sensor surface, and that the coating can be applied to membranes without hindering their glucose and oxygen transport.

Amperometric immunosensor for the detection of Vibrio cholerae O1 using disposable screen-printed electrodes

A disposable amperometric immunosensor was studied for the rapid detection of Vibrio cholerae (V. cholerae), the causative agent of cholera, employing an indirect sandwich enzyme linked immunosorbent assay (ELISA) principle. Screen-printed electrodes (SPEs) were fabricated (by using commercial and homemade carbon inks), electrochemically characterized and the assay conditions were optimized for capturing antibodies and antigen. Whole cell lysate (WCL) of V. cholerae was used to raise antibodies in rabbits and mice. The antibodies raised against WCL of V. cholerae were found to be specific, and no cross reactivity was observed with other enteric bacteria. 1-Naphthyl phosphate was used as a substrate with the amperometric detection of its enzymatic hydrolysis product 1-naphthol at a potential of +400 mV vs. Ag/AgCl reference electrode. A comparison between the amperometric detection technique and the standard ELISA was made in terms of the total assay time, the amount of biological materials used and the sensitivity of detection. The minimum detection limit of the amperometric immunosensor for V. cholerae was found to be 10(5) cells/ml in 55 min, while ELISA detected 10(6) cells/ml in 4 h.

Spraying Enzymes in Microemulsions of AOT in Nonpolar Organic Solvents for Fabrication of Enzyme Electrodes

A new technique suitable for automated, large-scale fabrication of enzyme electrodes by air-spraying enzymes in organic inks is presented. Model oxidoreductases, tyrosinase (Tyr) and glucose oxidase (GOx), were adapted to octane-based ink by entrapment in a system of reverse micelles (RM) of surfactant AOT in octane to separate and stabilize the catalytically active forms of the enzymes in nonpolar organic media. Nonpolar caoutchouk polymer was also used to create a kind of "dry micelles" at the electrode/solution interface. Enzyme/RM/polymer-containing organic inks were air-brushed onto conductive supports and were subsequently covered by sprayed Nafion membranes. The air-brushed enzyme electrodes exhibited relevant bioelectrocatalytic activity toward catechol and glucose, with a linear detection range of 0.1-100 microM catechol and 0.5-7 mM glucose; the sensitivities were 2.41 A M(-1) cm(-2) and 2.98 mA M(-1) cm(-2) for Tyr and GOx electrodes, respectively. The proposed technique of air-brushing enzymes in organic inks enables automated construction of disposable enzyme electrodes of various designs on a mass-production scale.

Optimisation of the composition of a screen-printed acrylate polymer enzyme layer with respect to an improved selectivity and stability of enzyme electrodes

Glucose oxidase (GOD) was immobilized on screen-printed platinum electrodes by entrapment in a screen printable paste polymerized by irradiation with UV-light. The influences of different additives, in particular polymers and graphite, on the sensitivity and stability of the sensor and the permeability of the enzyme layer for a possible electrochemical interferent were investigated. The chosen additives were Gafquat 755N, poly-L-lysine, bovine serum albumin (BSA), sodium dodecylsulfate (SDS), polyethylene glycol (PEG), Nafion and graphite. All additives led to increases of glucose signals, i.e. improved the sensitivity of glucose detection with Gafquat 755N, poly-L-lysine, SDS and graphite showing the strongest influences with increases by a factor 4, 6.5, 5 and 10, respectively. Ascorbic acid was used as a model interferent showing the influence of the enzyme layer composition on the selectivity of the sensor. The addition of Gafquat 755N or poly-L-lysine led to higher signals not only for glucose, but also for ascorbic acid. SDS addition already reduced the influence of ascorbic acid, which was almost completely eliminated when Nafion (5%) and PEG (10%) were added. A comparable beneficial effect on the selectivity of the sensors was also observed for the addition of 0.5% graphite. Thus, the enzyme electrodes with PEG, Nafion or graphite as additives in the enzyme layer were applied to glucose determinations in food samples and samples obtained from E. coli cultivations.

Disposable electrochemical sensor for rapid determination of heavy metals in herbal drugs

Analysis of herbal drugs and extracts need rapid and affordable methods to assure the quality of products. The application of the electrochemical sensors in the field of quality control of herbal drugs, herbal drug preparations and herbal medicinal products appears very promising, advantageous and alternative to conventional methods due to their inherent specificity, simplicity and for the fast response obtained. This paper presents a proposal about the application of disposable electrochemical sensors associated with electroanalytical instrumentation for the detection of heavy metal analysis in herbal drugs. In particular samples of St. John's wort were analysed applying anodic stripping voltammetry. The content of Cd and Pb were evaluated. The ICP spectroscopy was used as reference method.

Amperometric Determination of Glucose with a Carbon Paste Biosensor

A simple glucose biosensor has been developed by bulk modification of a carbon paste electrode with glucose oxidase as a biocomponent and manganese dioxide as a mediator. The sensor was employed as amperometric detector in a flow-injection system at 21 °C in 0.2 M phosphate buffer (pH 7.5). At an applied working potential of 0.48 V vs Ag/AgCl and a flow rate of 0.2 ml min-1, the sensor exhibited well reproducible amperometric response to glucose. A linear relation between the peak current and the analyte concentration was found between 20 and 500 mg l-1 glucose with a detection limit (3σ) of 10.5 mg l-1 glucose. The sensor can be operated continuously for 12 h without any loss in the signal height and can be used for the determination of glucose in white wine samples.

A disposable amperometric sensor screen printed on a nitrocellulose strip: a glucose biosensor employing lead oxide as an interference-removing agent

A new type of disposable amperometric sensor is devised by screen printing thick-film electrodes directly on a porous nitrocellulose (NC) strip. The chromatographic NC strip is then utilized to introduce various sample pretreatment layers. As a preliminary application, a glucose biosensor based on hydrogen peroxide detection is constructed by immobilizing glucose oxidase (GOx) on the NC electrode strip and by formulating a strong oxidation layer (i.e., PbO2) at the sample loading area, placed below the GOx reaction band. The screen-printed PbO2 paste serves as a sample pretreatment layer that removes interference by its strong oxidizing ability. Samples applied are carried chromatographically, via the PbO2 paste, to the GOx layer, and glucose is catalyzed to liberate hydrogen peroxide, which is then detected at the electrode surface. The proposed NC/PbO2 strip sensor is shown to be virtually insusceptible to interfering species such as acetaminophen and ascorbic and uric acids and to exhibit good performance, in terms of the sensor-to-sensor reproducibility (standard deviation, +/-0.026 - +/-0.086 microA), the sensitivity (slope, -0.183 microA/mM), and the linearity (correlation coefficient, 0.994 in the range of 0-10 mM).

High-throughput flow-injection analysis of glucose and glutamate in food and biological samples by using enzyme/polyion complex-bilayer membrane-based electrodes as the detectors

The concentration of glucose was determined by a combination of flow injection analysis (FIA) with amperometric enzyme sensor detection. The enzyme sensor was prepared by immobilizing glucose oxidase on an electrode coated with a polyion complex layer consisting of poly-L-lysine and poly(4-styrenesulfonate). The inner, polyion complex layer was useful for preventing electrochemical interferents (e.g., L-ascorbic acid, uric acid and acetaminophen) from reaching the electrode surface, which was effective for reducing the interferential responses upon the injections of biological and food samples. The sensor-based system could be used for the determination of glucose from 10 microM to 3 mM with the sampling rate of 180 h-1, and was stable for more than 2 months. An FIA system for determining L-glutamic acid (3 microM-0.5 mM) was also prepared by using an enzyme electrode based on a glutamate oxidase/polyion complex-bilayer as the detector.

Measurement of soluble L-lactate in dairy products using screen-printed sensors in batch mode

Amperometric sensors based on lactate oxidase and platinized carbon were constructed entirely by screen-printing. They were used to estimate the lactate concentration in diluted samples of yoghurt and buttermilk. Estimates made in untreated (apart from dilution) solutions were subject to bias, relative to values obtained from spectrophotometric assays. Removal of cations improved the accuracy of the estimates. Calcium may have made a small contribution to the bias but the nature of the inhibition is otherwise unknown. With untreated samples, determinations of any accuracy require sufficient dilution to avoid such bias, although the smaller signals resulting from dilution place more demands on calibration and manufacturing standards. The relative standard deviations of estimates, based on variation among sensors, of the most dilute samples were generally too high for practical use. The errors of estimates at lower dilutions approached those of screen-printed sensors made under industrial conditions.