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This study reports an osmium-based redox reporter that enables pH-insensitive and fast DNA-based molecular sensing, offering new possibilities for the study of short-lived dynamic molecular events.

The measurement of serum vancomycin levels at the clinic is critical to optimizing dosing given the narrow therapeutic window of this antibiotic. Current approaches to quantitate serum vancomycin levels are based on immunoassays, which are multistep methods requiring extensive processing of patient samples. As an alternative, vancomycin-binding electrochemical, aptamer-based sensors (E-ABs) were developed to simplify the workflow of vancomycin monitoring. E-ABs enable the instantaneous measurement of serum vancomycin concentrations without the need for sample dilution or other processing steps. However, the originally reported vancomycin-binding E-ABs had a dissociation constant of 45 μM, which is approximately 1 order of magnitude higher than the recommended trough concentrations of vancomycin measured in patients. This limited sensitivity hinders the ability of E-ABs to accurately support vancomycin monitoring. To overcome this problem, here we sought to optimize the length of the vancomycin-binding aptamer sequence to enable a broader dynamic range in the E-AB platform. Our results demonstrate, via isothermal calorimetry and E-AB calibrations in undiluted serum, that superior affinity and near-equal sensor gain in vitro can be achieved using a one-base-pair-longer aptamer than the truncated sequence originally reported. We validate the impact of the improved binding affinity in vivo by monitoring vancomycin levels in the brain cortex of live mice following intravenous administration. While the original sequence fails to resolve vancomycin concentrations from baseline noise (SNR = 1.03), our newly reported sequence provides an SNR of 1.62 at the same dose.

Rapid diagnostics that can accurately inform patients of disease risk and protection are critical to mitigating the spread of the current COVID-19 pandemic and future infectious disease outbreaks. To be effective, such diagnostics must rely on simple, cost-effective, and widely available equipment and should be compatible with existing telehealth infrastructure to facilitate data access and remote care. Commercial glucometers are an established detection technology that can overcome the cost, time, and trained personnel requirements of current benchtop-based antibody serology assays when paired with reporter molecules that catalyze glucose conversion. To this end, we developed an enzymatic reporter that, when bound to disease-specific patient antibodies, produces glucose in proportion to the level of antibodies present in the patient sample. Although a straightforward concept, the coupling of enzymatic reporters to secondary antibodies or antigens often results in low yields, indeterminant stoichiometry, reduced target binding, and poor catalytic efficiency. Our enzymatic reporter is a novel fusion protein that comprises an antihuman immunoglobulin G (IgG) antibody genetically fused to two invertase molecules. The resulting fusion protein retains the binding affinity and catalytic activity of the constituent proteins and serves as an accurate reporter for immunoassays. Using this fusion, we demonstrate quantitative glucometer-based measurement of anti-SARS-CoV-2 spike protein antibodies in blinded clinical sample training sets. Our results demonstrate the ability to detect SARS-CoV-2-specific IgGs in patient serum with precise agreement to benchmark commercial immunoassays. Because our fusion protein binds all human IgG isotypes, it represents a versatile tool for detection of disease-specific antibodies in a broad range of biomedical applications.

We investigated the carboxylated conjugated polymer poly 3-(3-carboxypropyl)thiophene-2,5-diyl as a nanosized (200–350 nm) biomolecule receptor layer on the channel of organic electrochemical trans...

This work was funded by the Ministerio de Ciencia e Innovación, Project PID2021-123183OB-I00 MICIN/AEI/10.13039/501100011033/FEDER, UE. M.A.P. thanks Fundación Científica Asociación Española Contra el Cáncer (AECC) for the postdoctoral fellowship supporting his research.

Methylene blue is widely used as a redox reporter in DNA-based electrochemical sensors and, in particular, it is the benchmark DNA-bound reporter used in electrochemical, aptamer-based sensors (E-A...

Electrochemical, aptamer-based (E-AB) sensors uniquely enable reagentless, reversible, and continuous molecular monitoring in biological fluids. Because of this ability, E-AB sensors have been proposed for therapeutic drug monitoring. However, to achieve translation from the bench to the clinic, E-AB sensors should ideally operate reliably and continuously for periods of days. Instead, because these sensors are typically fabricated on gold surfaces via self-assembly of alkanethiols that are prone to desorption from electrode surfaces, they undergo significant signal losses in just hours. To overcome this problem, our group is attempting to migrate E-AB sensor interfaces away from thiol-on-gold assembly towards stronger covalent bonds. Here, we explore the modification of carbon electrodes as an alternative substrate for E-AB sensors. We investigated three strategies to functionalize carbon surfaces: (I) anodization to generate surface carboxylic groups, (II) electrografting of arenediazonium ions, and (III) electrografting of primary aliphatic amines. Our results indicate that electrografting of primary aliphatic amines is the only strategy achieving monolayer organization and packing densities closely comparable to those obtained by alkanethiols on gold. In addition, the resulting monolayers enable covalent tethering of DNA aptamers and support electrochemical sensing of small molecule targets or complimentary DNA strands. These monolayers also achieve superior stability under continuous voltammetric interrogation in biological fluids relative to benchmark thiol-on-gold monolayers when a positive voltage scan window is used. Based on these results, we postulate the electrografting of primary aliphatic amines as a path forward to develop carbon-supported E-AB sensors with increased operational stability. Graphical abstract

Electrochromic sensors are electrochemical devices exploiting colour changes as a means to simplify device construction and instrumentation requirements. Despite their advantages, electrochromic sensors have begun to emerge only recently. Mainly based on the works appeared in the literature over the past 2 years, we describe the construction and operation of these devices. A simple framework is proposed to understand and classify these devices more easily. This is based on the sensor architecture, their power source, and how information is displayed. Despite their youth, electrochromic sensors are already demonstrated in a number of applications, mostly related to health and point of care devices.

Electrochemical, aptamer-based (E-AB) sensors support continuous, real-time measurements of specific molecular targets in complex fluids such as undiluted serum. They achieve these measurements by using redox-reporter-modified, electrode-attached aptamers that undergo target binding-induced conformational changes which, in turn, change electron transfer between the reporter and the sensor surface. Traditionally, E-AB sensors are interrogated via pulse voltammetry to monitor binding-induced changes in transfer kinetics. While these pulse techniques are sensitive to changes in electron transfer, they also respond to progressive changes in the sensor surface driven by biofouling or monolayer desorption and, consequently, present a significant drift. Moreover, we have empirically observed that differential voltage pulsing can accelerate monolayer desorption from the sensor surface, presumably via field-induced actuation of aptamers. Here, in contrast, we demonstrate the potential advantages of employing cyclic voltammetry to measure electron-transfer changes directly. In our approach, the target concentration is reported via changes in the peak-to-peak separation, ΔEP, of cyclic voltammograms. Because the magnitude of ΔEP is insensitive to variations in the number of aptamer probes on the electrode, ΔEP-interrogated E-AB sensors are resistant to drift and show decreased batch-to-batch and day-to-day variability in sensor performance. Moreover, ΔEP-based measurements can also be performed in a few hundred milliseconds and are, thus, competitive with other subsecond interrogation strategies such as chronoamperometry but with the added benefit of retaining sensor capacitance information that can report on monolayer stability over time.

Altres ajuts: 2016 Leonardo grant from the BBVA Foundation (TIC-TIC-0007) Electrochromic materials are becoming increasingly important in analytical devices and applications. Their opto-electronic properties make them particularly useful in the development of electronics-free, self-powered sensors. However, the mass manufacture of such devices is often limited by the need for transparent electrodes and liquid electrolyte systems. The self-powered biosensor presented here overcomes these limitations by means of a coplanar construction and a gel electrolyte. This configuration enables an effective separation between the sample and the electrochromic component, which allows the naked eye readout of the analyte concentration even if coloured or dark samples, such as blood, are used. This lack of contact between sample and electrochromic material also prevents the action of possible interferents on the electrochromic display, which is an additional advantage. Moreover, because the device is entirely screen-printed, its mass production is also feasible. The fabricated device features a glucose biosensor connected to a Prussian-Blue electrode, displaying a dynamic range between 2.5 mM-10 mM that makes it suitable for blood testing and diabetes screening.

Spectroelectrochemistry studies spectral changes as a function of applied potential or current. While there is no standard experimental setup, transparent electrodes are most typically used in transmission mode. Working in reflection mode forces light across the sample twice, resulting in higher sensitivities, but in turn requires the use of highly reflective electrodes. Here we present the production and characterization of screen-printed electrodes made from different antimony tin oxide (ATO) conducting particles. The resulting electrodes display excellent spectroelectrochemical properties, such as reflectivities up to 20 times higher than conventional graphite screen-printed electrodes, but with comparable electron transfer rates. These electrodes represent an attractive alternative to conventional materials and widen the choice of suitable electrode materials for electrochemistry in general and spectroelectrochemistry in particular, FEDER funds managed by the Catalan Secretary of Universities and Research through project PROD-0000114 (Enterprise and Knowledge, Industry Department, Generalitat de Catalunya).

This article proposes the exploitation of ohmic drop in the development of novel electrochromic devices. Electrochromic materials enable the construction of more efficient self-powered biosensors i...

Paper has been used for a long time in the production of low-cost point-of-care (POC) detection devices, most of which rely on the detection of colored bands by the user. However, test strips rarely provide the quantitative detection of biomarkers in clinical samples. In contrast, electrochemical detection enables quantitative detection in paper-based immunoassays. Here, we demonstrate the production of a simple and economical lateral-flow electrode device using only screen printing. Contrary to previous work, this device is used to simplify the washing and detection of a short and sensitive immunomagnetic assay for myeloperoxidase (MPO) detection. As we show, after incubation of the sample with magnetic beads (MBs) and detection antibody (Ab) for only 5 min, the whole reaction mixture can be directly pipetted onto the strip. Washing and detection can then be performed, as the MBs are retained with the aid of a magnet, and minimal user intervention is needed. The obtained results reveal that MPO can be detected in 1 : 100 diluted serum with limits of detection and quantification of 0.18 and 0.62 ng mL−1, respectively, in less than 15 min.

Prussian Blue (PB)-modified graphite screen-printed electrodes are increasingly being used in electrochemical biosensors. However, they do not allow the observation of the electrochromism of PB. This work presents the construction of PB-based, electrochromic screen-printed biosensors. Although electrically more resistive than their graphite counterparts, these new PB-based electrodes enable both the amperometric and colorimetric detection of hydrogen peroxide. This is the first time that this has been achieved using screen-printed electrodes, and we demonstrate it spectroelectrochemically on a glucose biosensor. The biosensor electrochemical performance equals that of previously reported PB/graphite electrodes, being able to detect down to 4 µM H2O2 and 54 µM glucose. At the same time, and in contrast to PB/graphite electrodes, the new PB-based electrodes afford the optical detection of these two analytes down to 1.2 µM and 15 µM, respectively. The dynamic ranges of the glucose biosensors obtained at the PB-based electrodes are 0.1-1 mM (amperometric) and 0.025-2.5 mM (Colorimetric), matching the physiological glucose concentration range in body fluids other than blood or serum.

One of the limitations of many skin-patch wearable sensors today is their dependence on silicon-based electronics, increasing their complexity and unit cost. Self-powered sensors, in combination with electrochromic materials, allow simplifying the construction of these devices, leading to powerful analytical tools that remove the need for external detection systems. This work describes the construction, by screen-printing, of a self-powered electrochromic device that can be adapted for the determination of metabolites in sweat by the naked eye in the form of a 3 × 15 mm colour bar. The device comprises a lactate oxidase and osmium-polymer –based anode connected to a coplanar 3 × 15 mm Prussian Blue, PB, cathode printed over a transparent poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, PEDOT:PSS electrode. An ion-gel composed of Poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-co-HFP, a gelling agent, and ionic liquid 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate, EMIM-Tf, effectively separates the cathode display from the biosensing anode, protecting it from the sample. Despite its cathodic electrochromism, the PEDOT:PSS has a transmission above 90% and does not mask the Prussian Blue colour change because the cathode does not operate below 0 V vs Ag/AgCl at any time. The sensor displays lactate concentrations in the range of 0–10 mM over the length of the electrochromic display, which has a contrast ratio of 1.43. Although full response takes up to 24 min, 85% of the colour change is displayed within 10 min.

A straightforward and very cost effective method is proposed to prototype electrodes using pressure sensitive adhesives (PSA) and a simple cutting technique. Two cutting methods, namely blade cutting and CO2 laser ablation, are compared and their respective merits are discussed. The proposed method consists of turning the protective liner on the adhesive into a stencil to apply screen-printing pastes. After the electrodes have been printed, the liner is removed and the PSA can be used as a backing material for standard lateral flow membranes. We present the fabrication of band electrodes down to 250 μm wide, and their characterization using microscopy techniques and cyclic voltammetry. The prototyping approach presented here facilitates the development of new electrochemical devices even if very limited fabrication resources are available. Here we demonstrate the fabrication of a simple lateral-flow device capable of determining glucose in blood. The prototyping approach presented here is highly suitable for the development of novel electroanalytical tools., This work has been funded by the Spanish Ministry of Economy through the DADDi2 project (Grant TEC2013-48506). MK acknowledges funding through the Beatriu de Pinós program (BP-DGR-2013), supported by the Secretary for Universities and Research of the Ministry of Economy and Knowledge of the Government of Catalonia and the Cofund programme of the Marie Curie Actions of the 7th R&D Framework Programme of the European Union. We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)

The desire to improve and decentralize diagnostic platforms to facilitate highly precise and personalized medicine has motivated the development of a large number of electrochemical sensing technologies. Such a development has been facilitated by electrochemistry's unparalleled ability to achieve highly specific molecular measurements in complex biological fluids, without the need for expensive instrumentation. However, for decades, progress in the field had been constrained to systems that depended on the chemical reactivity of the analyte, obstructing the generalizability of such platforms beyond redox- or enzymatically active clinical targets. Thus, the pursuit of alternative, more general strategies, coupled to the timely technological advances in DNA sequencing, led to the development of DNA-based electrochemical sensors. The analytical value of these arises from the structural customizability of DNA and its ability to bind analytes ranging from ions and small molecules to whole proteins and cells. This versatility extends to interrogation methods, as DNA-based sensors work through a variety of detection schemes that can be probed via many electroanalytical techniques. As a reference for those experienced in the field, and to guide the unexperienced scientist, here we review the specific advantages of the electroanalytical methods most commonly used for the interrogation of DNA-based sensors.

Electrochromic materials can be used in self-powered electrochemical sensors to display quantitative information without the need for silicon-based electronics or external instrumentation., Self-powered sensors are analytical devices able to generate their own energy, either from the sample itself or from their surroundings. The conventional approaches rely heavily on silicon-based electronics, which results in increased complexity and cost, and prevents the broader use of these smart systems. Here we show that electrochromic materials can overcome the existing limitations by simplifying device construction and avoiding the need for silicon-based electronics entirely. Electrochromic displays can be built into compact self-powered electrochemical sensors that give quantitative information readable by the naked eye, simply controlling the current path inside them through a combination of specially arranged materials. The concept is validated by a glucose biosensor coupled horizontally to a Prussian blue display designed as a distance-meter proportional to (glucose) concentration. This approach represents a breakthrough for self-powered sensors, and extends the application of electrochromic materials beyond smart windows and displays, into sensing and quantification.

Oscillating chemical reactions (OCRs) have been known since 1828, with the Belousov–Zhabotinskii (BZ) reaction the most studied example. Initially, OCRs were considered to be special cases due to the small number detected and because the oscillatory behavior did not seem to agree with the second law of thermodynamics. However, OCRs have become increasingly important not only in chemistry, but also in biology as they are the foundation of several significant phenomena: glycolysis, nerve signal transmission, heartbeats, and so forth. The BZ reaction has been examined both experimentally and theoretically. Temporal oscillations appear in both cases, but discrepancies are found between experimental results and theoretical calculations. This article addresses the discrepancies by describing (i) a simple, clear, and inexpensive experimental procedure for carrying out the reaction and determining the oscillation period and (ii) an innovative methodology that includes the effect of temperature on the original mod...

We present a small, compact and low-power electronic instrumentation for a point-of-care (PoC) device for the early diagnosis of diabetes mellitus and associated risk factors. The presented system consists of a low-power 4-channel potentiostat, a transducer with 4 separate electrochemical cells featuring different biosensors, and a low-cost printed battery. The system is designed to measure key parameters on diabetes mellitus analysis, such as: glucose, cholesterol and triglycerides. It has been designed as a disposable device using a single blood drop to quantify these parameters, enhancing disposition decision time and improving patient satisfaction when compared with current analytical methodology. The electronic instrumentation has been designed to simultaneously control and read the measurement of the 4 different sensors on the transducer block/chip. In this paper, we present the previous evaluation of the system through different cyclic voltammetry and chronoamperometry analysis compared with a commercial multichannel potentiostat 1030B from CH Instruments. The system presents accurate and reliable performance powered by a printed electrochemical battery.

We present a small, compact and portable envisaged lab-on-a-chip (LoC) device for point-of-care (PoC) detection of different key parameters on diabetes mellitus analysis; glucose, cholesterol, triglycerides and hematocrit. These four parameters, present in blood samples, are important in the standardized analysis affecting different patients with different medical conditions. The quantification of glucose, cholesterol, triglycerides and hematocrit it is performed with a single disposable device using a single blood drop, enhancing disposition decision time and improving patient satisfaction when compared with actual analytical methodology, and it is an easy to use device and no skilled personnel is needed to use it, avoiding the use of more complicated processes like phlebotomy. The presented device consists of a custom sensing system, low power electronic instrumentation and an easy user interpretation readout display, powered by a single battery.

The development of a low-cost multiparametric platform for enzymatic electrochemical biosensing that can be integrated in a disposable, energy autonomous analytical device is the target of the current work. We propose a technology to fabricate nano-electrodes and ultimately biosensors on flexible polymeric-based substrates (cyclo olefin polymer, and polyimide) using standard microfabrication (step and repeat lithography and lift-off) and rapid prototyping techniques (blade cutting). Our target is towards the fabrication of a miniaturized prototype that can work with small sample volumes in the range of 5-10μL without the need for external pumps for sample loading and handling. This device can be used for the simultaneous detection of metabolites such as glucose, cholesterol and triglycerides for the early diagnosis of diabetes.