A disposable rhodium nanoparticle-modified screen-printed sensor for direct determination of bromide anions

The demand for bromide determination has increased over recent years. Sources of bromide contamination can be found in brines from hydraulic fracturing, pesticides and brominated polymers. Widely used in different applications, the bromide anion is present in the composition of several compounds. In this paper, we present a new selective voltammetric method for bromide determination, based on a screen-printed carbon electrode (SPCE) modified with rhodium nanoparticles (Rh-Nps), that is used as a sensing platform. The modification of the electrode surface with Rh-Nps and the presence of chloride in the sample, improved device performance, increasing the sensitivity of the Rh/SPCE-based sensor for bromide determination. The proposed sensor is simple to manufacture, easy to operate, and it offers a fast and accurate analysis. A single drop of the sample on the sensor is sufficient for the determination of bromide through measurement of voltammetric cathodic peaks, generated after a previous anodic stripping step. This disposable sensor offers a detection limit of 39 μM, with a calibration range up to 40 mM, and a sensitivity of 23.28 μA/mM. Its application to real-life samples evidenced recovery values close to 100%, demonstrating the powerful analytical performance of the proposed method.Spanish Ministry of Science and Innovation (MICINN), Ministry of Economy and Competitiveness (MINECO) and the European Regional Development Fund (FEDER) (TEC20013-40561-P and MUSSEL RTC-2015-4077-2). Hugo Cunha-Silva would like to acknowledge funding from the Spanish Ministry of Economy (BES-2014-068214

Development of a selective chloride sensing platform using a screen-printed platinum electrode

A new and selective voltammetric method for chloride determination is proposed, based on platinum and chloride interactions. A screen-printed platinum electrode (SPPtE) functions as a sensing platform, which promotes the formation of chloro-adsorbed species on the electrode surface, acting as an effective means of anion-determination in several matrices. The pretreatment of the SPPtE and careful control of the cathodic stripping voltammetric parameters yielded a well-defined electrochemical signal. This cathodic peak was due to the adsorption of chlorine, which had previously been oxidized from chloride anions in the initial anodic deposition step. It offers a simple, low-cost, fast, reproducible (RSD < 6%) and precise method for selective chloride determination, with limit of detection of 0.76 mM, and a sensitivity of − 24.147 µA mM −1 for a broad determination range of up to 150 mM. Chloride determination was correctly performed with single drops of environmental, pharmaceutical and food samples. In addition, the sensor was successfully adapted as a flexible screen-printed platinum electrode sensor using Gore-Tex® as support for printing.Spanish Ministry of Science and Innovation (MICINN), Ministry of Economy and Competitiveness (MINECO) and the European Regional Development Fund (FEDER) (TEC20013-40561-P and MUSSEL RTC-2015-4077-2). Hugo Cunha-Silva would like to acknowledge funding from the Spanish Ministry of Economy (BES-2014-068214)

Dual range lactate oxidase-based screen printed amperometric biosensor for analysis of lactate in diversified samples

Lactate concentration is studied as an indicator of physical performance in sports activities, and is also analyzed in health care applications, as well as in the food and cosmetic industries. This organic acid is routinely determined in different concentration ranges, depending on the type of samples for analysis. This paper describes the development of a screen-printed lactate oxidase (LOx) based biosensor to determine lactate in broad concentration range. The Cu-MOF (copper metallic framework) crosslinking of 0.25U LOx in a chitosan layer, allows to determine the enzymatic product generated on a platinum modified working electrode, at 0.15 V (vs SPE Ag/AgCl). The biosensor responds linearly in two different concentration ranges: a first catalysis range of 14.65 µA mM−1, from 0.75 µM to 1 mM, followed by a saturation zone from 1 to 4 mM, after which a substrate enzymatic inhibition of 0.207 µA mM−1, is observed up to 50 mM. These two ranges of analysis would allow the biosensor to be used for the determination of lactate in different types of samples, with low and high content of lactate. The method reproducibility was kept below 7% and a limit of detection of 0.75 µM was obtained. The device was successfully used in the determination of lactate in sweat and saliva, as a low cost noninvasive analysis, and also in wine samples.Spanish Ministry of Science and Innovation (MICINN) (TEC20013-40561-P), Ministry of Economy and Competitiveness (MINECO) (RTC-2015-4077-2) and the European Regional Development Fund (FEDER

Immobilization of Acetylcholinesterase on Screen-Printed Electrodes. Application to the Determination of Arsenic(III)

Enzymatic amperometric procedures for measuring arsenic, based on the inhibitive action of this metal on acetylcholinesterase enzyme activity, have been developed. Screen-printed carbon electrodes (SPCEs) were used with acetylcholinesterase covalently bonded directly to its surface. The amperometric response of acetylcholinesterase was affected by the presence of arsenic ions, which caused a decrease in the current intensity. The experimental optimum working conditions of pH, substrate concentration and potential applied, were established. Under these conditions, repeatability and reproducibility of biosensors were determined, reaching values below 4% in terms of relative standard deviation. The detection limit obtained for arsenic was 1.1 × 10−8 M for Ach/SPCE biosensor. Analysis of the possible effect of the presence of foreign ions in the solution was performed. The method was applied to determine levels of arsenic in spiked tap water samples.Junta de Castilla y León (BU022A07, Q0968272E) and the Ministerio de Ciencia e Innovación (TEC2008-01367/TEC) is gratefully acknowledged

Determination of halides using Ag nanoparticles-modified disposable electrodes. A first approach to a wearable sensor for quantification of chloride ions

This work reports a simple voltammetric method for the determination of chloride, bromide, and iodide ions using screen-printed carbon electrodes modified with silver nanoparticles electrochemically deposited on the working electrode surface. UV/Vis absorption spectroelectrochemistry was used to study the electrodeposition of silver nanoparticles on the working carbon electrode on PET or Gore-Tex® supports, and their subsequent oxidation in the presence of halide ions. The main figures of merit of the developed sensors, such as reproducibility and detection limit, have been calculated. Reproducibility values of 2.22%, 2.83% and 3.23% were obtained for chloride, bromide and iodide determinations, respectively. Additionally, the lowest detected amount of chloride, bromide and iodide ions were 3.0·10−6 M, 5.0·10−6 M and 5.0·10−6 M, respectively. Taking into account the relevance of the determination of chloride ion concentration in sweat, the voltammetric method for the determination of halides has been successfully transferred to a Gore-Tex® support to build a first approach to a wearable sensor that facilitates the quantification of this ion in sweat samples. The Gore-Tex® sensor provides a good reproducibility (RSD = 1.61%).Spanish Ministry of Science and Innovation (MICINN), Ministry of Economy and Competitiveness (MINECO) and the European Regional Development Fund (TEC20013-40561-P and MUSSEL RTC-2015-4077-2)

Modified Laccase-Gold Nanoparticles-Tetrathiafulvalene-SPCEs Based Biosensor to Determine W(VI) in Water

It was developed an amperometric biosensor to determine tungsten in water, based on the inhibition of laccase enzyme, by tungsten ions using pyrocathecol as a substrate. The enzyme was immobilized with a proper mixture containing, bovine serum albumin, and glutaraldehyde, for a cross-linking process over screen-printed carbon electrodes, previously modified with tetrathiafulvalen and gold nanoparticles. Optimized experimental conditions are: pyrocatechol in cell 0.040 mM in a phosphate buffer pH 6.5 and applied potential +350 mV. The repeatability and reproducibility, in terms of relative standard deviation values, of de developed biosensor were 3.3 % (n=3), and 2.2 % (n = 5) respectively, and detection limit was 1.8 × 10-7 mol L-1. Additionally it was determined the kinetics of the systems by means of Michaelis-Menten Km apparent constants, calculated using Lineweaver-Burk plots, with and without tungsten. Kinetic study resembles to be competitive inhibition. A recovery study was performed with spiked blanks with a tungsten certified reference standard, traceable to NIST, giving as a result 102.3 ± 6.7 %; tap water samples analyzed presented a mean concentration of 1.75 µM, and recovery of the tungsten certified reference standard on the tap water samples gave 98.8 ± 3.1 %.Universidad de Costa Rica/[804-B5-164]/UCR/Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Electroquímica y Energía Química (CELEQ

A Disposable Alkaline Phosphatase-Based Biosensor for Vanadium Chronoamperometric Determination

A chronoamperometric method for vanadium ion determination, based on the inhibition of the enzyme alkaline phosphatase, is reported. Screen-printed carbon electrodes modified with gold nanoparticles were used as transducers for the immobilization of the enzyme. The enzymatic activity over 4-nitrophenyl phosphate sodium salt is affected by vanadium ions, which results in a decrease in the chronoamperometric current registered. The developed method has a detection limit of 0.39 ± 0.06 µM, a repeatability of 7.7% (n = 4) and a reproducibility of 8% (n = 3). A study of the possible interferences shows that the presence of Mo(VI), Cr(III), Ca(II) and W(VI), may affect vanadium determination at concentration higher than 1.0 mM. The method was successfully applied to the determination of vanadium in spiked tap waterResearch Vicerrectory of Costa Rica University (Project 804-B0-058) and Spanish Ministry of Science and Innovation (TEC-2009/12029). This work was supported by the Spanish Ministry of Science and Innovation (MICINN) 410 and the European Regional Development Fund (FEDER) (INNPACTO SERIBIO 2011-411 2014) and TEC2009-12029, as well as through Junta de Castilla y León (BU212A12-2)

Sensor system based on flexible screen-printed electrodes for electrochemical detection of okadaic acid in seawater

The monitoring of marine dinophysistoxin okadaic acid in seawater can serve as an early alert system for preventing the potential negative effects this toxin can have on the food industry and human health in general. A disposable sensor system for electrochemical detection of this toxin has been developed using screen-printed electrodes. The method described is based on the inhibition of protein phosphatase type 2A by okadaic acid, evaluating the enzyme activity. p-Nitrophenyl phosphate, 4-methylumbelliferyl phosphate and phenyl phosphate have been tested as substrates achieving good limits of detection of 2.7·10–12 M of okadaic acid. The proposed method has been successfully applied to okadaic acid determination in seawater samples. A study of divalent cations present in seawater that can interfere with the measurement has been carried out. The electrode systems were printed on both rigid and textile backing materials to observe the influence of those materials on the final performance of the sensor.Ministerio de Ciencia e Innovación (MICINN) (TEC2013-405661-P) Ministerio de Economía y Competitividad (MINECO) and European Regional Development Fund (FEDER) (MUSSEL RTC-2015-4077-2)

Rapid Determination of the ‘Legal Highs’ 4-MMC and 4-MEC by Spectroelectrochemistry: Simultaneous Cyclic Voltammetry and In Situ Surface-Enhanced Raman Spectroscopy

The synthetic cathinones mephedrone (4-MMC) and 4-methylethcathinone (4-MEC) are two designer drugs that represent the rise and fall effect of this drug category within the stimulants market and are still available in several countries around the world. As a result, the qualitative and quantitative determination of ‘legal highs’, and their mixtures, are of great interest. This work explores for the first time the spectroelectrochemical response of these substances by coupling cyclic voltammetry (CV) with Raman spectroscopy in a portable instrument. It was found that the stimulants exhibit a voltammetric response on a gold screen-printed electrode while the surface is simultaneously electro-activated to achieve a periodic surface-enhanced Raman spectroscopy (SERS) substrate with high reproducibility. The proposed method enables a rapid and reliable determination in which both substances can be selectively analyzed through the oxidation waves of the molecules and the characteristic bands of the electrochemical SERS (EC-SERS) spectra. The feasibility and applicability of the method were assessed in simulated seized drug samples and spiked synthetic urine. This time-resolved spectroelectrochemical technique provides a cost-effective and user-friendly tool for onsite screening of synthetic stimulants in matrices with low concentration analytes for forensic applications.Universidad de Costa Rica//UCR/Costa RicaMinisterio de Innovación, Ciencia, Tecnología y Telecomunicaciones//MICITT/Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Electroquímica y Energía Química (CELEQ)UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Químic

Inhibited enzymatic reaction of crosslinked lactate oxidase through a pH-dependent mechanism

Lactate oxidase (LOx), recognized to selectively catalyze the lactate oxidation in complex matrices, has been highlighted as preferable biorecognition element for the development of lactate biosensors. In a previous work, we have demonstrated that LOx crosslinking on a modified screen-printed electrode results in a dual range lactate biosensor, with one of the analysis linear range (4 to 50 mM) compatible with lactate sweat levels. It was advanced that such behavior results from an atypical substrate inhibition process. To understand such inhibition phenomena, this work relies in the study of LOx structure when submitted to increased substrate concentrations. The results found by fluorescence spectroscopy and dynamic light scattering of LOx solutions, evidenced conformational changes of the enzyme, occurring in presence of inhibitory substrate concentrations. Therefore, the inhibition behavior found at the biosensor, is an outcome of LOx structural alterations as result of a pH-dependent mechanism promoted at high substrate concentrations.Spanish Ministry of Science and Innovation (MICINN), Ministry of Economy and Competitiveness (MINECO) and the European Regional Development Fund (FEDER) (TEC20013-40561-P and MUSSEL RTC-2015-4077-2). Hugo Cunha-Silva would like to acknowledge funding from the Spanish Ministry of Economy (BES-2014-068214