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In this study, an implantable stereo-electroencephalography (sEEG) depth electrode was functionalised with an enzyme coating for enzyme-based biosensing of glucose and L-glutamate. This was done because personalised medicine could benefit from active real-time neurochemical monitoring on small spatial and temporal scales to further understand and treat neurological disorders. To achieve this, the sEEG depth electrode was characterised using cyclic voltammetry (CV), differential pulse voltammetry (DPV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS) using several electrochemical redox mediators (potassium ferri/ferrocyanide, ruthenium hexamine chloride, and dopamine). To improve performance, the Pt sensors on the sEEG depth electrode were coated with platinum black and a crosslinked gelatin-enzyme film to enable enzymatic biosensing. This characterisation work showed that producing a useable electrode with a good electrochemical response showing the expected behaviour for a platinum electrode was possible. Coating with Pt black improved the sensitivity to H2O2 over unmodified electrodes and approached that of well-defined Pt macro disc electrodes. Measured current showed good dependence on concentration, and the calibration curves report good sensitivity of 29.65 nA/cm2/μM for glucose and 8.05 nA/cm2/μM for L-glutamate with a stable, repeatable, and linear response. These findings demonstrate that existing clinical electrode devices can be adapted for combined electrochemical and electrophysiological measurement in patients and obviate the need to develop new electrodes when existing clinically approved devices and the associated knowledge can be reused. This accelerates the time to use and application of in vivo and wearable biosensing for diagnosis, treatment, and personalised medicine. [ABSTRACT FROM AUTHOR]

Clinical assessment based on a single biomarker is in many circumstances not sufficient for adequate diagnosis of a disease or for monitoring its therapy. Multiplexing, the measurement of multiple analytes from one sample and/or of the same target from different samples simultaneously, could enhance the accuracy of the diagnosis of diseases and their therapy success. Thus, there is a great and urgent demand for multiplexed biosensors allowing a low-cost, easy-to-use, and rapid on-site testing. In this work, we present a simple, flexible, and highly scalable strategy for implementing microfluidic multiplexed electrochemical biosensors (BiosensorX). Our technology is able to detect 4, 6, or 8 (different) analytes or samples simultaneously using a sequential design concept: multiple immobilization areas, where the assay components are adsorbed, followed by their individual electrochemical cells, where the amperometric signal readout takes place, within a single microfluidic channel. Here, first we compare vertical and horizontal designs of BiosensorX chips using a model assay. Owing to its easier handling and superior fluidic behavior, the vertical format is chosen as the final multiplexed chip design. Consequently, the feasibility of the BiosensorX for multiplexed on-site testing is successfully demonstrated by measuring meropenem antibiotics via an antibody-free β-lactam assay. The multiplexed biosensor platform introduced can be further extended for the simultaneous detection of other anti-infective agents and/or biomarkers (such as renal or inflammation biomarkers) as well as different (invasive and non-invasive) sample types, which would be a major step towards sepsis management and beyond. [ABSTRACT FROM AUTHOR]

Bioelectroanalytical procedures based on cathodic processes are often subject to interference from dissolved oxygen. At the potentials applied for analyte detection, oxygen reduction may occur directly at the electrode or may be catalyzed by the electron mediators or the sensing enzyme of the biosensor. These processes affect the background current and may thus result in erroneous analyte quantification. In this review, current strategies to circumvent these oxygen interferences are presented and critically assessed with respect to their compatibility for on-site monitoring with amperometric biosensing devices operating at low potential. The main strategies consist in (1) use of oxygen scavenging systems to remove dissolved oxygen from the sample, (2) design of bioelectroanalytical approaches to shift the applied potential for analyte detection to more positive values, and (3) development of electrode materials to increase the overpotential for the oxygen reduction reaction. The latest developments in these approaches have recently led to the first biosensing devices based on reductases fully compatible with on-site monitoring requirements and this opens up possibilities for their widespread application. [ABSTRACT FROM AUTHOR]

Functional nanomaterials have emerged as promising candidates in the development of an amperometric sensing platform for the detection and quantification of bioanalytes. The remarkable characteristics of nanomaterials based on metal and metal oxide nanoparticles, carbon nanotubes, and graphene ensure enhanced performance of the sensors in terms of sensitivity, selectivity, detection limit, response time, and multiplexing capability. The electrocatalytic properties of these functional materials can be combined with the biocatalytic activity of redox enzymes to develop integrated biosensing platforms. Highly sensitive and stable miniaturized amperometric sensors have been developed by integrating the nanomaterials and biocatalyst with the transducers. This review provides an update on recent progress in the development of amperometric sensors/biosensors using functional nanomaterials for the sensing of clinically important metabolites such as glucose, cholesterol, lactate, and glutamate, immunosensing of cancer biomarkers, and genosensing. [ABSTRACT FROM AUTHOR]

A selective and sensitive method is presented for biogenic amines (BA) determination. The novelty consists in coupling a highly selective electrochemical biosensor to a weak acid cation-exchange column for online detection of amines. A bienzyme design, based on a recently isolated amine oxidase from grass pea and commercial horseradish peroxidase, was used for the biosensor construction. The enzymes were co-immobilized on the surface of a graphite electrode together with the electrochemical mediator (Os-redox polymer). The electrochemical detection was performed at a low applied potential (−50 mV vs . Ag/AgCl, KCl0.1 M), where biases from interferences are minimal. The separation and determination of six BA, with relevance in food analysis (tyramine, putrescine, cadaverine, histamine, agmatine and spermidine), were investigated. Irrespective of the BA nature, the amine oxidase-based biosensor showed a linear response up to 5 mM, and its sensitivity decreases in the following order: cadaverine, putrescine, spermidine, agmatine, histamine and tyramine. The approach was used to estimate the BA content in fish samples, after their extraction with methanesulfonic acid. [ABSTRACT FROM AUTHOR]

The responses of a PQQ-GDH entrapped in a polymer structure to mixtures of glucose and maltose were evaluated. Each compound was considered in the concentration range of 0–0.2 mM. Imaging was performed at constant height in the enzymatic feedback mode of scanning electrochemical microscopy (SECM). The enzyme-polymer spot was discretized into 15 × 15 μm2 substructures which were treated as independent individual microsensors. The response surfaces of the individual microsensors were approximated with a linear regression model. The coefficients in the derived equations represent contributions from topography, glucose concentration, maltose concentration, and the competition of glucose and maltose for the same active site of PQQ-GDH to the measured signal. The ratio of glucose and maltose contributions to the current at the SECM tip was constant for all microsensors and it was predominantly determined by the ratio of the turnover rates of both analytes in the PQQ-GDH catalyzed reaction. Using the difference between these coefficients, it was possible to select the microsensors within the overall enzyme-polymer spot that provided the best data for quantifying glucose and maltose by the artificial neural network used. The quantification of glucose and maltose was successful, except when the contributions from the components of the mixture were n g = k n units of glucose and simultaneously n m = 1.86(1− k) n units of maltose, for each constant n > 0 and k∈<0,1>. [ABSTRACT FROM AUTHOR]

An amperometric biosensor has been developed for measurement of Umami, or the taste based on the amount of l-glutamate, in tomato foods. The biosensor is based on an enzyme-mediator system in which l-glutamate oxidase is used for biochemical oxidation of l-glutamate and a tetrafulvalene-tetracyanoquinodimethane (TTF-TCNQ) paste, prepared from the mixture of TTF-TCNQ salt, graphite powder, and silicone oil, serves as the mediator. The limit of detection, calculated by use of a four-parameter logistic model, was 0.05 mmol L−1, and the limit of quantification was 0.15 mmol L−1. The correlation coefficient ( R 2) was 0.990 and the relative standard deviation was no more than 1% ( n=5). The response time ( τ 95) was 20–50 s, depending on concentration. The repeatability of the sensor was better than 5% ( n=10). The sensor developed was stable for more than ten days. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Conducting electroactive polymers (CPs) are materials discovered just over 20 years ago which have aroused considerable interest on account of their electronic conducting properties and unique chemical and biochemical properties. Consequently, they have numerous (bio)analytical and technological applications. CPs are easily synthesized and deposited onto the conductive surface of a given substrate from monomer solutions by electrochemical polymerization with precise electrochemical control of their formation rate and thickness. Coating electrodes with CPs under mild conditions opens up enormous possibilities for the immobilization of biomolecules and bioaffinity or biorecognizing reagents, the improvement of their electrocatalytic properties, rapid electron transfer and direct communication to produce a range of analytical signals and new analytical applications. Co-immobilization of other molecules (enzymatic co-factors or charge-transfer mediators) by entrapment within electropolymerized films or by covalent binding on these films permits straightforward fabrication of reagentless biosensors. The characteristics of CPs and their uses, mainly in amperometric biosensors, are reviewed. The most recent applications and lines of research related to CP films are summarized in the different sections of the paper, and probable future trends are discussed. [ABSTRACT FROM AUTHOR]

An amperometric enzyme sensor for the analysis of glucose is described. The sensor uses benzoquinone as a mediator for electron transfer between immobilized glucose oxidase and a pyrolytic graphite electrode. A linear current response, proportional to glucose concentration in the range 1-50mM, is observed. The influence of oxygen, pH and operating potential on the sensor performance is examined. [ABSTRACT FROM AUTHOR]