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The general objective of Analytical Chemistry, nowadays, is to obtain best-quality information in the shortest time to contribute to the resolution of real problems. In this regard, electrochemical biosensors are interesting alternatives to conventional methods thanks to their great characteristics, both those intrinsically analytical (precision, sensitivity, selectivity, etc.) and those more related to productivity (simplicity, low costs, and fast response, among others). For many years, the scientific community has made continuous progress in improving glucose biosensors, being this analyte the most important in the biosensor market, due to the large amount of people who suffer from diabetes mellitus. The sensitivity of the electrochemical techniques combined with the selectivity of the enzymatic methodologies have positioned electrochemical enzymatic sensors as the first option. This review, focusing on the electrochemical determination of glucose using paper-based analytical devices, shows recent approaches in the use of paper as a substrate for low-cost biosensing. General considerations on the principles of enzymatic detection and the design of paper-based analytical devices are given. Finally, the use of paper in enzymatic electrochemical biosensors for glucose detection, including analytical characteristics of the methodologies reported in relevant articles over the last years, is also covered. [ABSTRACT FROM AUTHOR]

In this work, novel silver sulphide quantum dots (Ag2S QD) are electrochemically quantified for the first time. The method is based on the electrochemical reduction of Ag+ to Ag0 at −0.3 V on screen-printed carbon electrodes (SPCEs), followed by anodic stripping voltammetric oxidation that gives a peak of currents at +0.06 V which represents the analytical signal. The optimized methodology allows the quantification of water-stabilized Ag2S QD in the range of approximately 2 × 109–2 × 1012 QD·mL−1 with a good reproducibility (RSD: 5%). Moreover, as proof-of-concept of relevant biosensing application, Ag2S QD are evaluated as tags for Escherichia coli (E. coli) bacteria determination. Bacteria tagged with QD are separated by centrifugation from the sample solution and placed on the SPCE surface for quantitative analysis. The effect of two different Ag2S QD surface coating/stabilizing agents on both the voltammetric response and the bacteria sensing is also evaluated. 3-mercaptopropionic acid (3-MPA) is studied as model of short length coating ligand with no affinity for the bacteria, while boronic acid (BA) is evaluated as longer length ligand with chemical affinity for the polysaccharides present in the peptidoglycan layer on the bacteria cells surface. The biosensing system allows to detect bacteria in the range 10−1-103 bacteria·mL−1 with a limit of detection as low as 1 bacteria·mL−1. This methodology is a promising proof-of-concept alternative to traditional laboratory-based tests, with good sensitivity and short time and low cost of analysis. [ABSTRACT FROM AUTHOR]

Alzheimer's disease is one of the most common causes of dementia nowadays, and its prevalence increases over time. Because of this and the difficulty of its diagnosis, accurate methods for the analysis of specific biomarkers for an early diagnosis of this disease are much needed. Recently, the levels of unfolded isoform of the multifunctional protein p53 in plasma have been proved to increase selectively in Alzheimer's Disease patients in comparison with healthy subjects, thus entering the list of biomarkers that can be used for the diagnosis of this illness. We present here the development of an electrochemical immunosensor based on nanostructured screen-printed carbon electrodes for the quantification of unfolded p53 in plasma samples. The sensor shows a suitable linear range (from 2 to 50 nM) for its application in real blood samples and a very low limit of detection (0.05 nM). The concentration of unfolded p53 has been accurately detected in plasma of elderly people in healthy conditions, subjects with mild cognitive impairment (MCI) and Alzheimer's Disease (AD) subjects, obtaining results with no significant differences to those provided by an ELISA assay. These results support the possibility of measuring unfolded p53 levels with a cheap, simple and miniaturized device with a promising future for point-of-care applications in the early diagnosis of Alzheimer's dementia. Image 1 • An immunosensor for the detection of unfolded p53 protein, an emerging biomarker for Alzheimer's Disease, was developed. • A competitive immunoassay was carried out using screen-printed carbon electrodes nanostructured with gold nanoparticles. • A high selectivity is achieved using an antibody that only reacts with an epitope present in the unfolded p53 protein. • A wide dynamic range (2–50 nM) has been obtained with excellent analytical characteristics. • This biosensor was applied for unfolded p53 quantification in plasma samples with high accuracy. [ABSTRACT FROM AUTHOR]

The sensitive monitoring of mercury (II) selenide nanoparticles (HgSe NPs) is of great potential relevance in environmental studies, since such NPs are believed to be the ultimate metabolic product of the lifesaving mechanism pathway of Hg detoxification in biological systems. In this context, we take advantage of using gold-nanostructured screen-printed carbon electrodes (SPCE-Au) for the rapid, simple and sensitive electrochemical quantification of engineered water-stable HgSe NPs, as an advantageous alternative to conventional elemental analysis techniques. HgSe NPs are first treated in an optimized oxidative/acidic medium for Hg2+ release, followed by sensitive electrochemical detection by anodic stripping voltammetry (ASV). To the best of our knowledge, this is the first time that water-stable HgSe NPs are quantified using electrochemical techniques. The low limit of detection achieved (3.86 × 107 HgSe NPs/mL) together with the excellent repeatability (RSD: 3%), reproducibility (RSD: 5%) and trueness (relative error: 10%), the good performance in real sea water samples (recoveries of the analytical signal higher than 90%) and the simplicity/low cost of analysis make our method an ideal candidate for HgSe NPs monitoring in future environmental studies. fx1 • HgSe NPs have been synthesized, characterized and quantified using anodic stripping voltammetry. • Voltammetric detection takes advantage of the Hg underpotential deposition process on SPCE-Au electrodes. • First time that engineered water stabilized HgSe NPs are electrochemically quantified. • Electrochemical results are in agreement with ICP-MS analysis, being faster and cheaper. • Ideal method for HgSe NPs monitoring in future environmental studies. [ABSTRACT FROM AUTHOR]

In this work, mass-fabricated stainless-steel pins are used as low-cost electrodes in a batch injection analysis (BIA) system with electrochemical detection (BIA-ED). The system consists of a polypropylene container including a potentiostatic three-electrode configuration cell designed using a pin coated with carbon ink as working electrode and two bare pins as counter and reference electrodes. These pins are directly punched into the bottom of the container and connected to the potentiostat using a commercial female connection. The system shows good precision for measurements performed employing the same or different electrochemical cells (RSD 7.2 and 8.9% respectively). The platform is applied to the determination of epinephrine in a pharmaceutical real sample showing accurate results. As a proof-of-concept, the feasibility of constructing a multiplexed BIA-ED system based on pins is evaluated by incorporating eight pin-based working electrodes in the container. The electroanalytical platform is completed with one reference and one auxiliary pin electrodes that are shared for all the eight working electrodes. It demonstrates the versatility that pins can provide to the construction of different electroanalytical systems. Moreover, the system is designed in such a way that an eight-channel micropipette can be employed for injections, making the system simpler and faster. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrochemical biosensor for creatinine determination in a drop of whole human blood. • Differential chronoamperometry. • Calibrated using on a reference method based on Isotope Dilution Mass Spectrometry. • Validated with respect to two routine procedures on 50 real human samples. An electrochemical biosensor for creatinine determination in a drop of whole human blood was developed and applied to the determination of creatinine in real clinical samples. It is based on the modification of a dual carbon working electrode with a combination of three enzymes: creatinine amidohydrolase (CNN), creatine amidinohydrolase (CRN) and sarcosine oxidase (SOX). Electrochemical transduction is performed using horseradish peroxidase (HRP) and potassium hexacyanoferrate(II) as mediator. A drop of human blood is enough to carry out the measurements by differential chronoamperometry where one carbon electrode detects creatine and the other both creatine and creatinine. The integrated differential signal obtained in the biosensor is linear with the concentration of creatinine in blood in the range 0.5–15 mg/dL and the enzyme-modified electrodes are stable for at least 3 months at 4 °C. The biosensor was lined to a reference method based on Isotope Dilution Mass Spectrometry (IDMS) with 50 real human blood samples and the results compared with those obtained by alternative routine techniques based on Jaffé method and an enzymatic method (Cobas 8000 Roche®, Crep2 Roche®). There were no significant differences between the creatinine concentrations found by the routine techniques and the developed biosensor. [ABSTRACT FROM AUTHOR]

Chronic wounds represent an important healthcare challenge in developed countries, being wound infection a serious complication with significant impact on patients' life conditions. However, there is a lack of methods allowing an early diagnosis of infection and a right decision making for a correct treatment. In this context, we propose a novel methodology for the electrical monitoring of infection biomarkers in chronic wound exudates, using nanoporous alumina membranes. Lysozyme, an enzyme produced by the human immune system indicating wound infection, is selected as a model compound to prove the concept. Peptidoglycan, a component of the bacterial layer and the native substrate of lysozyme, is immobilized on the inner walls of the nanochannels, blocking them both sterically and electrostatically. The steric blocking is dependent on the pore size (20–100 nm) and the peptidoglycan concentration, whereas the electrostatic blocking depends on the pH. The proposed analytical method is based on the electrical monitoring of the steric/electrostatic nanochannels unblocking upon the specific degradation of peptidoglycan by lysozyme, allowing to detect the infection biomarker at 280 ng/mL levels, which are below those expected in wounds. The low protein adsorption rate and thus outstanding filtering properties of the nanoporous alumina membranes allowed us to discriminate wound exudates from patients with both sterile and infected ulcers without any sample pre-treatment usually indispensable in most diagnostic devices for analysis of physiological fluids. Although size and charge effects in nanochannels have been previously approached for biosensing purposes, as far as we know, the use of nanoporous membranes for monitoring enzymatic cleavage processes, leading to analytical systems for the specific detection of the enzymes has not been deeply explored so far. Compared with previously reported methods, our methodology presents the advantages of no need of neither bioreceptors (antibodies or aptamers) nor competitive assays, low matrix effects and quantitative and rapid analysis at the point-of-care, being also of potential application for the determination of other protease biomarkers. • Chronic wound infection represents an important healthcare challenge in developed countries. • There is a lack of methods allowing an early diagnosis of infection and a right decision making for a correct treatment. • A novel methodology for the monitoring of lysozyme infection biomarker in chronic wounds, using nanoporous alumina membranes is proposed. • The method is based on the electrical monitoring of the steric/electrostatic nanochannels unblocking upon the specific degradation of peptidoglycan by lysozyme. • Wound exudates from patients with both sterile and infected ulcers, without any sample pre-treatment, are successfully discriminated. [ABSTRACT FROM AUTHOR]

Nowadays, food allergy is a very important health issue, causing adverse reactions of the immune system when exposed to different allergens present in food. Because of this, the development of point-of-use devices using miniaturized, user-friendly, and low-cost instrumentation has become of outstanding importance. According to this, electrochemical aptasensors have been demonstrated as useful tools to quantify a broad variety of targets. In this work, we develop a simple methodology for the determination of β-lactoglobulin (β-LG) in food samples using a folding-based electrochemical aptasensor built on poly-L-lysine modified graphite screen-printed electrodes (GSPEs) and an anti-β-lactoglobulin aptamer tagged with methylene blue (MB). This aptamer changes its conformation when the sample contains β-LG, and due to this, the spacing between MB and the electrode surface (and therefore the electron transfer efficiency) also changes. The response of this biosensor was linear for concentrations of β-LG within the range 0.1–10 ng·mL−1, with a limit of detection of 0.09 ng·mL−1. The biosensor was satisfactorily employed for the determination of spiked β-LG in real food samples. [ABSTRACT FROM AUTHOR]

This review shows recent trends in the use of nanoparticles as labels for electrochemical immunosensing applications. Some general considerations on the principles of both the direct detection based on redox properties and indirect detection through electrocatalytic properties, before focusing on the applications for mainly proteins detection, are given. Emerging use as blocking tags in nanochannels-based immunosensing systems is also covered in this review. Finally, aspects related to the analytical performance of the developed devices together with prospects for future improvements and applications are discussed. [ABSTRACT FROM AUTHOR]