Comparative study of screen printed electrodes for ammonia gas sensing in ionic liquids

Magnetic dispersive solid-phase extraction (MDSPE) is combined with electrochemical detection by using a screen-printed carbon electrode modified with gold nanoparticles to determine lead(II). A zeolite-based magnetic composite was used as sorbent during sample preparation, thus combining the unique properties of zeolites as sorbent materials with the remarkable advantages provided by magnetic materials. Three different zeolite-based magnetic composites were initially investigated and characterized. ZSM-5/Fe2O3 treated with HNO3 (ZSM-5/Fe2O3(tr)) was finally selected as sorbent. Lead was extracted from urine samples using ZSM-5/Fe2O3(tr). After extraction, the phases were separated by using an external magnet. Subsequently, the magnetic composite carrying the analyte was directly deposited onto the working electrode of a modified screen-printed carbon electrode for final electrochemical detection. Thereby, the elution and detection of Pb(II) were carried out in a single step. A multivariate approach was employed to optimize the experimental parameters affecting extraction. Under optimized conditions and at a typical working potential of -0.23V (vs. Ag pseudo-reference electrode), response is linear in the 0 to 25μgL-1 Pb(II) concentration range. The empirical limit of detection ranged from 1.0 to 2.0μgL-1. The method was used to analyze Pb(II)-spiked urine samples, and apparent recoveries ranged between 99 and 107%, with coefficients of variation of <20%. Graphical abstractSchematic presentation of the analytical method to determine lead(II) in urine samples. Magnetic dispersive solid-phase extraction using a zeolite-based composite (ZSM-5/Fe2O3(tr)) is directly combined with electrochemical detection by using a screen-printed carbon electrode modified with gold nanoparticles (SPCnAuE).

In this work, the electrodeposition method was utilized to form gold nanoparticles on a carbon screen-printed electrode (SPE) using chronoamperometry at -0.4 V with various durations from 50 to 200 seconds. Scanning Electron Microscopy (SEM) images have proven that the electrodeposition method is capable of uniformly forming AuNPs on SPE (AuNPs- SPE). Apart from that, electrodeposition durations have increased the size of AuNPs by up to 66% based on average size measurements using ImageJ software. It can be observed that long electrodeposition durations permit the agglomeration of AuNPs on the electrode surface. The effect of electrodeposition duration on electrocatalytic performance in potassium ferricyanide and electrochemiluminescence (ECL) intensity of nitrogen-doped carbon dots (NCDs) was evaluated. Cyclic voltammetry (CV) of ferricyanide demonstrates that as the electrodeposition duration increases, AuNPs-SPE shows better electrochemical performance than bare SPE. ECL of NCDs displays that 100 s electrodeposition durations give the highest ECL intensity of 184% compared to bare SPE and have been chosen as the optimum parameter. The ECL mechanisms of bare SPE and AuNPs-SPE reveal that AuNPs- SPE has greater electrochemical and ECL performance than bare SPE, as evidenced by the CV of AuNPs-SPE having a faster reduction current, which rises to 87.2% ECL intensity and 510 mV faster ECL occurrence. These phenomena confirmed that the electrodeposition of AuNPs has improved the conductivity of SPE.

Development of disposable amperometric sulfur dioxide biosensors based on screen printed electrodes

Development of a voltammetric sensor for chromium(VI) determination in wastewater sample

The detection of ammonia (NH3) gas at low concentrations is of great importance due to its use in a wide range of industries e.g. the oil and gas industry, fertilizer industry, refrigeration industry1 and due to its high toxicity. Concentrations as low as 500 ppm can be lethal, and the current (USA) Occupational Health and Safety Permissible Exposure Limit (OSHA PEL) is 25 ppm in the gas phase. There are commercially available electrochemical gas sensors to monitor ammonia, mostly based on amperometric gas sensors (AGSs). However one problem with AGSs is that their solvent/electrolyte combinations are typically water/sulphuric acid, and can dry-up quickly, thus making the lifetime of these sensors very limited. Room Temperature Ionic Liquids (RTILs) have been attracting a great attention as replacement electrolytes in AGSs2 due to their unique physical properties such as wide electrochemical windows, high intrinsic conductivity, low volatility and negligible vapor pressure, high chemical and thermal stability and their ability to dissolve a wide range of compounds. Importantly, they do not evaporate when exposed to a high gas flow, and can function in hot and dry environments. In our work, we are investigating commercially available thin-film metal electrode surfaces as new sensing surfaces, consisting of three electrodes that are incorporated onto a small area on an inert substrate. Their small size means that only a few microliters RTIL solvent needed, and the small amount of inert metal required (e.g. platinum) minimizes the overall cost of the sensor. Four different techniques will be employed for ammonia oxidation: linear sweep voltammetry (LSV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV), and potential-step chronoamperometry (PSC) over the concentration range of 10-100 ppm NH3. The results on commercially available Pt thin-film electrodes, screen-printed electrodes, and microarray thin-film electrodes will be compared to “ideal” Pt microdisk electrodes. Calibration curves (current vs. concentration) for all voltammetric techniques on all four surfaces will be presented, showing excellent linearity with increased concentrations of NH3. The limits of detection found on all four surfaces for all four techniques are in the range of ca. 2-5 ppm, much lower than minimum exposure limit (25 ppm) for NH3. These results are highly encouraging and suggest that RTILs and low-cost miniaturised electrodes can be combined in sensor devices to detect ammonia gas at low ppm concentrations.

Improved screen-printed carbon electrode for multiplexed label-free amperometric immuniosensor: Addressing its conductivity and reproducibility challenges

Chitosan-assisted self-assembly of flower-shaped ε-Fe2O3 nanoparticles on screen-printed carbon electrode for Impedimetric detection of Cd2+, Pb2+, and Hg2+ heavy metal ions in various water samples

Screen-printed carbon electrode (SPCE) is one of the most interesting designs to combine a working (from carbon based material), reference, and counter electrode in a single-printed substrate. SPCE has been used in many electrochemical measurements due to its advantages for analysis in microscale. This paper summarises the main information about SPCE fabrication from the material and fabrication technique aspect on the flat substrate based on the work that has been published in the last 30 years. The success of SPCE fabrication is highly dependent on the composition of conductive ink which consists of conductive materials, binder, and solvents; substrate; and fabrication techniques. Among the carbon-based materials, the most widely used for SPCE fabrications are graphite, graphene, and carbon nanotubes. The frequent binder used are polymer-based materials such as polystyrene, polyaniline, poly 3,4-ethylenedioxythiophene:polystyrene sulfonate (PEDOT:PSS), and polyvinyl chloride. The solvents used for SPCE fabrication are varied including water and various organic solvents. The main characteristics of the SPCE substrate should be inert in order to avoid any interferences during electrochemical measurements. The screen printing and inkjet printing technique are preferred for SPCE fabrication due to easy fabrication and the possibility for mass production of SPCE.

IntroductionNitroaromatics like 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT) are long-lasting organic pollutants in natural water and soil caused mainly by the military usage. Nano structured electrodes are established in detection of such compounds in water by linear sweep voltammetry (DP) [1]. On the other hand, it could be shown that screen printed carbon electrodes [2] and such made of pyrolytic deposited carbon are also suited for that purpose [3]. Both kind of electrodes were investigated regarding the determination of nitroaromatic compounds in aqueous solution. The aim of this paper is to compare the performance of both electrodes in comparison to commercial electrodes respecting sensitivity, selectivity and long-term stability.ExperimentalElectrodes using carbon nano-tubes and gold nano-particles on printed carbon are commercially available (DropSens, Spain DRP-110CNT-GNP). Screen printed electrodes (SPCE) of 3mm in diameter were industrially like produced on an alumina substrate with a commercial carbon ink (DuPont) carbon paste. Pyrolytic graphite layer were deposited by high temperature decomposition (1050 °C) of aromatic vapor for 15 min with high reproducibility (PyGE). Solid state analyses as XRD and SEM analysis show crystalline carbon with a sp2 hybridization (Fig. 1). The setup of the electrodes is seen in Fig. 2. All experiments were performed in a three electrode arrangement using platinum counter electrode and Ag/AgCl,Cl--reference electrode in a buffer solution. Voltammetric experiments were performed by a PalmSens potentiostate (Palm Instruments, NL). DRP-110CNT-GNP were investigated by linear sweep voltammetrie. SPCE and PyGE were measured in differential pulse voltammetry mode (DPV). The parameter for the DPV were selected as follows: scan rates of 15 mV∙s-1 to 20 mV∙s-1, amplitude of 50 mV and step height of 5 mVResults and discussionThe potentials of the single reduction peak of nitro-aromates can be clearly separated (Fig. 3) for both kind of electrodes, SPCE and PyGE. The nitroaromates trinitrotoluene (TNT) and dinitrotoluene (DNT) are reduced and dopamine is oxidized in DPV mode (Fig.4). The peak currents are proportional to the TNT concentrations with a sensitivity of 2.7 nA/ppb for SPCE (Fig.5) and 0.78 for PyGE (Fig. 6) at the characteristic peak potential of -0.59 V (R²=0.99). Commercial electrodes DRP-110CNT-GNP made of carbon with gold nano particles require a special treatment in cyclo-voltammertic mode up to stable measuring conditions. The sensitivity of 2.8 nA/ppb is high compared to PyGEs. The relative errors in measuring cycles (35 %) are very much higher than those for PyGEs (5 %). PyGE do not need a special pretreatment before use.Screen printed and pyrolytic deposited carbon electrodes can be applied in air saturated aqueous solutions like in field application. For both electrodes, SCPE and PyGE, the oxygen reduction peak do not interfere with the reduction of the nitro groups. The manufacturing tolerances become smaller in the row DRP-110CNT-GNP, SPCE, PyGE. PyGEs can be produced in few steps with very small deviations. They can stored in air or in water over years without a loss of performance. Commercial electrodes are very complex in setup and obviously not so easy to produce in proper quality. Furthermore, their signals are remarkably influenced by oxygen so that measurements in air are not possible.

This article describes a general method for stabilizing microdroplets of mercury on thick‐film screen printed electrodes (SPEs). Electrodes modified with nickel metal powder are compared with amalgam stabilized mercury SPEs. Application of the electrodes to the measurement of organic materials is demonstrated by the electrochemical determination of 2‐furaldehyde, a marker for power transformer condition monitoring. The electrodes were characterized by cyclic voltammetry and subsequently a square‐wave voltammetric method was used to extend the detection limit of the measurement. The resulting cathodic currents for the reduction of 2‐furaldehyde was proportional to the concentration of 2‐furaldehyde. Plots of 2‐furaldehyde concentration against response at a nickel‐modified carbon SPE gave linear regions for concentrations in the range 3.7–14.3 ppm (regression equation; Y = 0.99 + 0.15x,r = 0.999, n = 3), and linear regions at mercury‐coated silver‐modified carbon SPEs in the range 8.9–36.4 ppm (regression equation; Y = 1.71 + 0.14x,r = 0.999, n = 3) and in the range 0.9–8.9 ppm (regression equation; Y = 1.34 + 0.17x,r = 0.980, n = 3), respectively. A particular advantage of using the mercury‐modified SPE rather than the nickel‐modified base card is that the well‐defined electrochemistry of furan derivatives allow them to be individually distinguished. The half‐wave potentials at the mercury SPE for 2‐furaldehyde (E1/2 = −1.15 V vs. Ag/AgCl) and two possible interferents 2‐acetyl‐furan and 5‐methyl‐2‐furaldehyde (E1/2 = −1.2 and −1.31 V vs. Ag/AgCl) are sufficiently well separated to allow the individual components to be resolved whereas at a nickel‐modified SPE a combined signal is observed.

Rapid voltammetric detection of kojic acid at a multi-walled carbon nanotubes screen-printed electrode

A fast, sensitive, and selective method for the simultaneous determination of one pair of synthetic colorants commonly found mixed in food products, Amaranth (AM) and Tartrazine (TZ), based on their adsorption and oxidation on a screen-printed electrode (SPE) is presented. The variation of peak current with pH, supporting electrolyte, adsorption time, and adsorption potential were optimized using square wave adsorptive voltammetry. The optimal conditions were found to be: pH 3.2 (PBS), Eads 0.00 V, and tads 30 s. Under these conditions, the AM and TZ signals were observed at 0.56 and 0.74 V, respectively. A linear response were found over the 0.15 to 1.20 µmol L−1 and 0.15 to 0.80 µmol L−1 concentrations, with detection limits (3σ/slope) of 26 and 70 nmol L−1 for AM and TZ, respectively. Reproducibility for 17.7 µmol L–1 AM and TZ solutions were 2.5 and 3.0% (n = 7), respectively, using three different electrodes. The method was validated by determining AM and TZ in spiked tap water and unflavored gelatin spiked with AM and TZ. Because a beverage containing both AM and TZ was not found, the method was applied to the determination of AM in a kola soft drink and TZ in an orange jelly and a soft drink powder.

A comparative study of graphene-based electrodes for electrochemical detection of visceral leishmaniasis in symptomatic and asymptomatic patients

A highly sensitive fenobucarb electrochemical sensor based on graphene nanoribbons-ionic liquid-cobalt phthalocyanine composites modified on screen-printed carbon electrode coupled with a flow injection analysis

Screen-printed electrode (SPE) strips are widely used for electrochemical detection owing to their low cost, ease of fabrication, and suitability for point-of-care testing. Their electrochemical performance must remain reproducible across multiple uses, varied solution conditions, and extended measurement times; however, relevant studies are rare. In this study, we demonstrate that the electrochemical behavior of SPEs is significantly influenced by (i) dynamic changes in the real electrode area of carbon SPEs (working electrodes) and (ii) potential drifts in Ag SPEs (reference electrodes). The gradual wetting of pores in the carbon SPEs, which is affected by the solution composition and incubation time, increases the real electrode area and the non-Faradaic capacitive charging current. Notably, rapid wetting occurs in surfactant-containing and biological solutions. The wetting process also affects the Faradaic current of an electroactive species to a certain extent. Furthermore, the potential of Ag SPEs exhibits shifts with repeated use and under different incubation conditions, particularly in the presence of an electroactive species. These findings demonstrate that variations in the real electrode area and reference electrode potential play critical roles in SPE strip-based electrochemical measurements. Addressing these factors is essential for achieving accurate and reproducible results, particularly in repeated or long-term measurements, and in measurements involving surfactant-containing or biological solutions.