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Signal amplification strategies are widely used for improving the sensitivity of lateral flow immunoassays (LFiAs). Herein, the artificial miniaturized peroxidase Fe(III)-MimochromeVI*a (FeMC6*a), immobilized on gold nanoparticles (AuNPs), is used as a strategy to obtain catalytic signal amplification in sandwich immunoassays on lateral flow strips. The assay scheme uses AuNPs decorated with the mini-peroxidase FeMC6*a and anti-human-IgG as a detection antibody (dAb), for the detection of human-IgG, as a model analyte. Recognition of the analyte by the capture and detection antibodies is first evidenced by the appearance of a red color in the test line (TL), due to the accumulation of AuNPs. Subsequent addition of 3,3',5,5'-tetramethylbenzidine (TMB) induces an increase of the test line color, due to the TMB being converted into an insoluble colored product, catalyzed by FeMC6*a. This work shows that FeMC6*a acts as an efficient catalyst in paper, increasing the sensitivity of an LFiA up to four times with respect to a conventional LFiA. Furthermore, FeMC6*a achieves lower limits of detection that are found in control experiments where it is replaced with horseradish peroxidase (HRP), its natural counterpart. This study represents a significant proof-of-concept for the development of more sensitive LFiAs, for different analytes, based on properly designed artificial metalloenzymes.

The majority of lateral flow assays (LFAs) use single-color optical labels to provide a qualitative naked-eye detection, however this detection method displays two important limitations. First, the use of a single-color label makes the LFA prone to results misinterpretation. Second, it does not allow the precise modulation of the sensitivity and dynamic range of the test. To overcome these limitations, a ratiometric approach is developed. In particular, using anti-HIgG functionalized red-fluorescent quantum dots on the conjugate pad (as target dependent labels) and blue-fluorescent nanoparticles fixed on the test line (as target independent reporters), it is possible to generate a wide color palette (blue, purple, pink, red) on the test line. It is believed that this strategy will facilitate the development of LFAs by easily adjusting their analytical properties to the needs required by the specific application., The authors acknowledge financial support from NACANCELL project PCIN-2016-066 (program Euronanomed 2). This work was also funded by the CERCA Program/Generalitat de Catalunya. The ICN2 was funded by the CERCA program/Generalitat de Catalunya. ICN2 acknowledges the support of the Spanish MINECO for the Project MAT2017-87202-P and through the Severo Ochoa Centres of Excellence Program under Grant SEV2201320295. A.I. was supported by PROBIST postdoctoral fellowship funded by European Research Council (Marie Sklodowska Curie) grant agreement No. 754510). C.P. acknowledges support from the Spanish Ministry of Science and Innovation and State Research Agency through the “Centro de Excelencia Severo Ochoa 2019-2023” Program (CEX2018-000806-S), and support from the Generalitat de Catalunya through the CERCA Program.

The interaction of drugs with DNA has been searched thoroughly giving rise to an endless number of findings of undoubted importance, such as a prompt alert to harmful substances, ability to explain most of the biological mechanisms, or provision of important clues in targeted development of novel chemotherapeutics. The existence of some drugs that induce oxidative damage is an increasing point of concern as they can cause cellular death, aging, and are closely related to the development of many diseases. Because of a direct correlation between the response, strength/ nature of the interaction and the pharmaceutical action of DNA‐targeted drugs, the electrochemical analysis is based on the signals of DNA before and after the interaction with the DNA‐targeted drug. Nowadays, nanoscale materials are used extensively for offering fascinating characteristics that can be used in designing new strategies for drug‐DNA interaction detection. This work presents a review of nanomaterials (NMs) for the study of drug‐nucleic acid interaction. We summarize types of drug‐DNA interactions, electroanalytical techniques for evidencing these interactions and quantification of drug and/or DNA monitoring., The ICN2 is funded by the CERCA programme/Generalitat de Catalunya. ICN2 acknowledges the support of the Spanish MINECO for the Project MAT2017‐87202‐P and through the Severo Ochoa Centers of Excellence Program under Grant SEV2201320295. KDCM thank the CONACyT for the support through the scholarship #817447.

Proteins and antibodies are key biomarkers for diagnosing and monitoring specific medical conditions. Currently, gold standard techniques used for their quantification require laborious multi-step procedures, involving high costs and slow response times. It is possible to overcome these limitations by exploiting the chemistry and programmability of DNA to design a reagentless electrochemical sensing platform. Specifically, three DNA single strands are engineered that can self-assemble into a Y-shaped DNA nanostructure that resembles one of the IgGs. In order to convert this DNA nanostructure into a responsive DNA-scaffold bioreceptor, it is modified including two recognition elements, two redox tag molecules, and a thiol group. In the absence of the target, the scaffold receptor can efficiently collide with the electrode surface and generate a strong electrochemical signal. The presence of the target induces its bivalent binding, which produces steric hindrance interactions that limit the receptor's collisional activity. In its bound state, the redox tags can therefore approach the surface at a slower rate, leading to a signal decrease that is quantitatively related to the target concentration. The Y-shape DNA scaffold sensor can detect nanomolar concentrations of antibodies and proteins in, ICN2 was funded by the CERCA programme, Generalitat de Catalunya. ICN2 was supported by the Severo Ochoa Centres of Excellence programme and funded by the Spanish Research Agency (AEI, grant no. SEV-2017-0706). The authors acknowledge Consejo Superior de Investigaciones Científicas (CSIC) for the project “COVID19-122” granted in the call “Nuevas ayudas extraordinarias a proyectos de investigación en el marco de las medidas urgentes extraordinarias para hacer frente al impacto económico y social del COVID-19 (Ayudas CSIC-COVID-19)”. A.I. was supported by PROBIST postdoctoral fellowship funded by the European Research Council (Marie Skłodowska-Curie grant agreement no. 754510). C.P. acknowledges the Marie Skłodowska-Curie Actions Individual Fellowship; this project received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 795635. C.P. (ISGlobal) also acknowledges support from the Spanish Ministry of Science and Innovation** and State Research Agency through the “Centro de Excelencia Severo Ochoa 2019–2023” Program (CEX2018-000806-S), and support from the Generalitat de Catalunya through the CERCA Program. R.A.D. received financial support from the EU Graphene Flagship Core 3 Project (No. 881603)., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2018-000806-S)

In this study, we propose an electrochemical immunoassay into a disposable microfluidic platform, using quantum dots (QDs) as labels and their enhanced detection using bismuth as an alternative to mercury electrodes. CdSe@ZnS QDs were used to tag human IgG as a model protein and detected through highly sensitive stripping voltammetry of the dissolved metallic component (cadmium in our case). The modification of the screen printed carbon electrodes (SPCEs) was done by a simple electrodeposition of bismuth that was previously mixed with the sample containing QDs. A magneto-immunosandwich assay was performed using a micromixer. A magnet placed at its outlet in order to capture the magnetic beads used as solid support for the immunoassay. SPCEs were integrated at the end of the channel as detector. Different parameters such as bismuth concentration, flow rate, and incubation times, were optimized. The LOD for HIgG in presence of bismuth was 3.5 ng/mL with a RSD of 13.2%. This LOD was about 3.3-fold lower than the one obtained without bismuth. Furthermore, the sensitivity of the system was increased 100-fold respect to experiments carried out with classical screen-printed electrodes, both in presence of bismuth.

Class I hydrophobin Vmh2, a peculiar surface active and versatile fungal protein, is known to self-assemble into chemically stable amphiphilic fi lms, to be able to change wettability of surfaces, and to strongly adsorb other proteins. Herein, a fast, highly homogeneous and effi cient glass functionalization by spontaneous self-assembling of Vmh2 at liquid–solid interfaces is achieved (in 2 min). The Vmh2-coated glass slides are proven to immobilize not only proteins but also nanomaterials such as graphene oxide (GO) and quantum dots (QDs). As models, bovine serum albumin labeled with Alexa 555 fl uorophore, anti-immunoglobulin G antibodies, and cadmium telluride QDs are patterned in a microarray fashion in order to demonstrate functionality, reproducibility, and versatility of the proposed substrate. Additionally, a GO layer is effectively and homogeneously self-assembled onto the studied functionalized surface. This approach offers a quick and simple alternative to immobilize nanomaterials and proteins, which is appealing for new bioanalytical and nanobioenabled applications.

Between their many applications bismuth nanoparticles (BiNPs) are showing interest as pre-concentrators in heavy metals detection while being applied as working electrode modifiers used in electrochemical stripping analysis. From the different reported methods to synthesize BiNPs we are focused on the typical polyol method, largely used in these types of metallic and semi-metallic nanoparticles. This study presents the strategy for an easy control of the shape and size of BiNPs including nanocubes, nanosferes and triangular nanostructures. To improve the BiNP size and shape, different reducing agents (ethylene glycol or sodium hypophosphite) and stabilizers (polyvinyl pyrrolidone, PVP, in different amounts) have been studied. The efficiency of BiNPs for heavy metals analysis in terms of detection sensitivity while being used as modifiers of screen-printed carbon electrodes including the applicability of the developed device in real sea water samples is shown. A parallel study between the obtained nanoparticles and their performance in heavy metal sensing has been described in this communication.

This work is supported by theMICINN (Spain) grant for the Spain-Japan International Bilateral PIB2010JP-00278 project. A.L.M. thanks the Generalitat of Catalunya for the FI2010 predoctoral scholarship given. L.H. and J.L. thank the support of the Scientific Grant Agency VEGA of the Slovak Republic (Project 1/0182/11).

The fabrication, characterization, and applications of paper-based screen-printed carbon electrodes (SPCE) are discussed. In particular, microscopy images of the working electrode surface show a reproducible 3D pattern that enhances the performance of the device compared to that of a polyester-based SPCE. Gold nanoparticles and CdSe@ZnS quantum dots are detected using different electrochemical techniques. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nanomaterials based sensing systems provide a new class of rapid and low cost detection alternatives with interest in the field of safety and security applications. In this review we report the recent trends in the use of various nanomaterials such as nanoparticles, carbon nanotubes, nanowires and graphene to detect different safety and security related analytes (i.e. microorganisms, toxins, pesticides and explosives). Nanomaterials are used either as modifiers of the electrochemical transducers or as labels with the objective to enhance the electrochemical signal, improve the stability and in general the performance of the detection systems including their cost-efficiency. Most of the developed systems are shown to bring excellent improvements while being used in the laboratory. Their application in real sample and during in-field monitoring still needs a long way while issues such as the reproducibility, stability, mass production capability of the designed devices etc. shouldn’t still yet be resolved.

Carbon nanotubes (CNTs) are offering a great promise for developing electrochemical sensors. Distinctive properties of CNTs such as a high surface area, ability to accumulate analyte, minimization of surface fouling and electrocatalytic activity are very attractive for electrochemical sensing. The electrochemical study of a glassy carbon (GC) electrode coated with a matrix based in multiwall carbon nanotubes (MWCNTs), tetrahydrofuran (THF) mixed with poly(vinyl chloride) (PVC) and with a glutaraldehyde (GA) solution (MWCNTs-TPG/GC), for β-Nicotinamide adenine dinucleotide (NADH) detection is discussed in this work using cyclic voltammetry (CV) and chronoamperometry. The used CNTs matrix promotes better the electron transfer of NADH minimizing the fouling effect. The obtained results show remarkable electrochemical and mechanical advantages of MWCNTs-TPG/GC electrode compared to bare glassy carbon electrode with a great promise for future amperometric biosensors applications.

The presented work includes the development of a microbial biosensor based on a carbon-nanotube epoxy composite (CNTEC) platform used as supporting electrode for cell immobilization. For this purpose, cells of Pseudomonas fluorescens were immobilized on the surface of the CNTEC electrode by means of gelatin which was then cross linked with glutaraldehyde. After optimization of experimental parameters like cell amount, pH and temperature, the system was calibrated for glucose. From the calibration graph the linear range was estimated as 0.5 – 4.0 mM with a response time of 100 s. Furthermore, substrate specificity and operational stability were investigated. Finally, the results that were obtained with CNTEC electrodes were compared with conventional graphite epoxy composite electrode (GECE) and as a result, higher current values (2 to 3 folds) were observed with CNTEC microbial biosensor.

The electrochemical properties of gold nanoparticles (AuNPs) have led to their widespread use as DNA labels. This fact has improved the design strategies for the electrochemical detection of DNA through hybridization event monitoring. The reported DNA hybridization detection modes are based on either AuNP detection after dissolving or the direct detection of the AuNP/DNA conjugates anchored onto the genosensor surface. Various enhancement strategies have been reported so as to improve the detection limit. Most are based on catalytic deposition of silver onto AuNP. Other strategies based on the use of AuNPs as carrier/amplifier of other labels will be also revised. The developed techniques are characterized by sensitivities and specificities that enable further applications of the developed DNA sensors in several fields.

This minireview looks at the latest trends in the use of nanoparticles (NPs) in electrochemical biosensing systems. It includes electrochemical characterization of NPs for use as labels in affinity biosensors and other applications. DNA analysis involving NPs is one of the most important topics of current research in bionanotechnology. The advantages of the use of NPs in designing novel electrochemical sensors for DNA analysis are reviewed. Electrochemical NPs can also be used in designing immunoassays, offering the possibility of easy, low cost and simultaneous detection of several proteins. Research into NP applications in electrochemical analysis is in its infancy. Several aspects related to sensitivity as well integration of all the assay steps into a single one need to be improved.

This report studies the electrochemical response of wall-jet detector for microchip electrophoresis (microCE). It shows that in wall-jet configuration, the electrochemical detector operates in coulometric mode and that there is an influence of detection potential upon peak width and therefore upon the resolution of solutes. Upon raising the detection potential from +0.3 to +0.9 V, the resolution between model analytes, dopamine and catechol, increases from 0.63 to 2.90. The reasons for this behavior originate in wall-jet detector design and in its typically significant higher detector volume than the volume of injected sample. The conversion efficiency of the wall-jet electrochemical detection cell was found to be 97.4% for dopamine and 98.0% for catechol. The paper brings deeper understanding of operations of wall-jet electrochemical detectors for microchip devices, and it explains previously reported significantly sharper peaks when electrocatalytic electrodes (i.e., palladium and carbon nanotube) were used in microCE-electrochemistry wall-jet detector.

A new rigid graphite-epoxy composite electrode for electrochemical detection in microchip electrophoresis is described. The end-column wall-jet detection design relying on tubular rigid composite working electrode shows favorably low noise level and high signal-to-noise ratio when compared to glassy carbon detector. The performance of rigid graphite-epoxy composite detector was compared to glassy carbon detector using dopamine and catechol as model analytes. The various parameters of the microchip electrophoresis-rigid graphite-epoxy composite detector were optimized.

Grup de Sensors i Biosensors, Departament de Qumica, Universitat Auto`noma de Barcelona, Bellaterra, Catalonia, Spain*e-mail: arben.merkoci@uab.esReceived: October 19, 2004Accepted: November 5, 2004AbstractThe attractive performance of graphite-epoxy composite electrodes (GECE) surface-modified with a bismuth film(Bi-GECE) for simultaneous and separate stripping determination of trace amounts of heavy metals (lead, cadmiumand zinc) is described. Several key parameters have been optimized. Bi-GECEi electrode shows superioraccumulation properties when compared to bare GECE or even to Hg-GECE. Bi-GECE exhibits well-defined,undistorted, reproducible and sharp stripping signals with RSD of 2.99%, 1.56% and 2.19% for lead, cadmium andzinc respectively. Detection limits of 23.1, 2.2 and 600 mg/L for lead, cadmium and zinc were obtained. Sharp peakswith high resolution (of neighboring signals) that permit convenient multi-elemental measurements resulted. Theapplicability of the electrodes to the real samples (tap water and soil sample) was also tested and promising resultswith good recoveries were obtained.Keywords: Bismuth film, Graphite-epoxy composite electrode, Square-wave anodic stripping voltammetry, Lead,Cadmium, Zinc

Boron-doped diamond thin-film electrodes display negligible fouling effects in the presence of high levels of surface-active materials, including proteins. Dramatic improvements in the stability of the analyte response (compared to common glassy carbon and carbon paste electrodes) are illustrated using bovine serum albumin (BSA), gelatin, and Triton X-100 in connection with repetitive square-wave voltammetric (SWV) measurements. The voltammetric response of ascorbic acid at the diamond electrode exhibits negligible shifts in peak potentials and minimal depressions of current signals over a wide range of surfactant concentrations (0–750 ppm). For example, the diamond electrode exhibited 70, 50 and 60 mV potential shifts for 10 repetitive voltammetric scans in the presence of 100 ppm BSA, gelatin and Triton X-100, respectively, compared to 120, 190, and 280 mV shifts observed at the glassy carbon electrode. Furthermore, only 4.3 and 6.2% of the initial current decays were observed in the presence of 100 ppm Triton X-100 and gelatin, respectively (compared to 45.2 and 34.4% diminutions at the glassy carbon electrode). Such improved performance was also confirmed from the SWV measurements of uric acid, dihydroxyphenylacetic acid, and catechol. The greatly improved resistance to surfactant interference reflects the fact that the as-grown diamond thin film, composed of oxide-free and hydrogen-terminated surface, has a relatively lower surface energy and minimal electrostatic attributes, either specific or general, so that little adsorption of surface-active agents occurs. The topographic AFM images of the diamond electrode surface confirm a negligible BSA fouling effect after repetitive SWV measurements. Such enhanced antifouling features make diamond electrodes very attractive for numerous real-life electroanalytical applications.

A PCR-genosensor based assay for detecting the IS200 DNA sequence specific to Salmonella spp is reported. This rapid test is based on PCR, where amplicon detection is achieved electrochemically using GEC (graphite-epoxy composite) genosensor. The amplicon is immobilized onto GEC electrodes by simple dry-adsorption and the detection is carried out using an enzymatic labeling system. Results demonstrate that this new electrochemical genosensor fulfils the requirements desired for these devices: easy preparation – as dry-adsorption of DNA is very simple –, robustness, sensitivity, low cost, simple use and fast response. Additionally, the assay can be produced as a kit format, increasing its commercial potentiality. Also, the electrode material can be implemented for screen-printing procedures for the mass production of genosensors.

A graphene oxide rolled‐up tube production process is reported using wax‐printed membranes for the fabrication of on‐demand engineered micromotors at different levels of oxidation, thickness, and lateral dimensions. The resultant graphene oxide rolled‐up tubes can show magnetic and catalytic movement within the addition of magnetic nanoparticles or sputtered platinum in the surface of graphene‐oxide‐modified wax‐printed membranes prior to the scrolling process. As a proof of concept, the as‐prepared catalytic graphene oxide rolled‐up micromotors are successfully exploited for oil removal from water. This micromotor production technology relies on an easy, operator‐friendly, fast, and cost‐efficient wax‐printed paper‐based method and may offer a myriad of hybrid devices and applications., This work was supported by the Severo Ochoa Program (MINECO, Grant No. SEV‐2013‐0295) and Generalitat de Cataluña (Grant No. 2014 SGR 260). The ICN2 is funded by the CERCA programme/Generalitat de Catalunya.

A graphene(G)/Silicon(Si) heterojunction Schottky diode and a simple method that evaluates its electrical response to different chemical vapors using electrochemical impedance spectroscopy (EIS) are implemented. To study the impedance response of the device of a given vapor, relative impedance change (RIC) as a function of the frequency is evaluated. The minimum value of RIC for different vapors corresponds to different frequency values (18.7, 12.9 and 10.7 KHz for chloroform, phenol, and methanol vapors respectively). The impedance responses to phenol, beside other gases used as model analytes for different vapor concentrations are studied. The equivalent circuit of the device is obtained and simplifi ed, using data fi tting from the extracted values of resistances and capacitances. The resistance corresponding to interphase G/Si is used as a parameter to compare the performance of this device upon different phenol concentrations and a high reproducibility with a 4.4% relative standard deviation is obtained. The effi ciency of the device fabrication, its selectivity, reproducibility and easy measurement mode using EIS makes the developed system an interesting alternative for gases detection for environmental monitoring and other industrial applications., The authors would like to acknowledge MICINN for MAT2011–25870 project that have funded this research.

In this review we discuss how nanomaterials can be integrated in diagnostic paper-based biosensors for the detection of proteins, nucleic acids and cells. In particular first the different types and properties of paper-based nanobiosensors and nanomaterials are briefly explained. Then several examples of their application in diagnostics of several biomarkers are reported. Finally our opinions regarding future trends in this field are discussed.

The complexation process of copper(II) with oxamates was followed by the use of a copper solid state ion selective electrode. The shape of the recorded potential vs. time was interpreted on the basis of the known kinetic expressions for a two step reaction, monitoring the consumption of the reagent. The potential changes of the electrode are attributed to a decrease in the copper concentration. The curves are of an exponential form with two distinct parts, the first due to the intermediate activated complex, which is produced very rapidly, and the second is due to the slow formation of the soluble chelate. The effects of various parameters are studied in relation to the retardation of the first step. The reaction rate constant k, the equilibrium constant K* for the first step, the stability constant K, the activation energy Ea, the change in enthalpy, and the product (pZ) of the frequency and steric factors were determined. On the basis of the above data, a mechanistic scheme for this complexation reaction is proposed.

This tutorial review surveys the latest achievements in the use of nanoparticles to detect cancer biomarkers and cancer cells with a focus on optical and electrochemical techniques. Nanoparticle based cancer diagnostics are becoming an increasingly relevant alternative to traditional techniques. Although some drawbacks exist in relation to the obtained sensitivity the use of nanoparticle-based sensors in biomarker detection or cancer cell detection offers some advantages in comparison to conventional methods. The developed techniques can be interesting and relevant for their use in point-of-care of cancer diagnostics. The methods can be of low cost and in addition easy to be incorporated into user-friendly sensing platforms.