Screen-printed Sensors Research Articles

Fabrication of a novel screen-printed carbon electrode based disposable sensor for sensitive determination of an endocrine disruptor BPSIP in environmental and biological matrices

A screen-printed electrochemical sensor based on a graphene-modified screen-printed carbon electrode decorated with graphitic carbon nitride (g-C3N4@GN/SPCE) was examined for its ability to act as a sensitive and selective novel sensor for on-site monitoring of an endocrine disruptor, 4-(4-isopropoxy-benzenesulfonyl)-phenol (BPSIP). The successfully prepared g-C3N4 was thoroughly characterized using FESEM, TEM, EDX, FT-IR, XRD, UV– visible studies, and TGA. The prepared g-C3N4 was immobilized on GN/SPCE to prepare a low-cost and disposable sensor for electroanalytical measurement of BPSIP. The concentration of nanomaterial dispersion, pH, and composition of the buffer solution were also optimized for maximal response. At the optimized conditions, BPSIP was determined by cyclic voltammetry in two linear concentration ranges (1–100 µM and 100–1000 µM) with a very low detection limit of 0.02 ± 0.01 µM and unparalleled sensitivity of 0.9162 ± 0.0003 µA.µM−1.cm−2. Further, the electrochemical oxidation of BPSIP occurred at 0.65 V, suggesting the excellent electrocatalytic performance of g-C3N4@GN/SPCE. The proposed sensor has shown high repeatability and reproducibility as well as good anti-interference properties for BPSIP sensing. The feasibility of the as-prepared sensor is also tested in biological and water samples, with excellent recoveries in the range of 98–104 % for BPSIP sensing.

Point-of-care diagnostics for rapid determination of prostate cancer biomarker sarcosine: application of disposable potentiometric sensor based on oxide-conductive polymer nanocomposite

One of the most important reasons for an increased mortality rate of cancer is late diagnosis. Point-of-care (POC) diagnostic sensors can provide rapid and cost-effective diagnosis and monitoring of cancer biomarkers. Portable, disposable, and sensitive sarcosine solid-contact ion-selective potentiometric sensors (SC-ISEs) were fabricated as POC analyzers for the rapid determination of the prostate cancer biomarker sarcosine. Tungsten trioxide nanoparticles (WO3 NPs), polyaniline nanoparticles (PANI NPs), and PANI-WO3 nanocomposite were used as ion-to-electron transducers on screen-printed sensors. WO3 NPs and PANI-WO3 nanocomposite have not been investigated before as ion-to-electron transducer layers in potentiometric SC sensors. The designated sensors were characterized using SEM, XRD, FTIR, UV-VIS spectroscopy, and EIS. The inclusion of WO3 and PANI in SC sensors enhanced the transduction at the interface between the screen-printed SC and the ion-selective membrane, offering lower potential drift, a longer lifetime, shorter response time, and better sensitivity. The proposed sarcosine sensors exhibited Nernstian slopes over linear response ranges 10−3–10−7 M, 10−3–10−8 M, 10−5–10−9 M, and 10−7–10−12 M for control, WO3 NPs, PANI NPs, and PANI-WO3 nanocomposite-based sensors, respectively. From a comparative point of view between the four sensors, PANI-WO3 nanocomposite inclusion offered the lowest potential drift (0.5 mV h−1), the longest lifetime (4 months), and the best LOD (9.95 × 10−13 M). The proposed sensors were successfully applied to determine sarcosine as a potential prostate cancer biomarker in urine without prior sample treatment steps. The WHO ASSURED criteria for point-of-care diagnostics are met by the proposed sensors.Graphical abstract

Simultaneous electrochemical detection of dimethyl bisphenol A and bisphenol A using a novel Pt@SWCNTs-MXene-rGO modified screen-printed sensor

Since bisphenol A (BPA) and dimethyl bisphenol A (DM-BPA) are human endocrine disruptors (EDCs) with tiny potential differences (44 mV) and widespread applications, there is a lack of published reports on their simultaneous detection. Therefore, this study reports a novel electrochemical detection system capable of simultaneous direct detection of BPA and DM-BPA using screen-printed carbon electrodes (SPCE) as a sensing platform. To improve the electrochemical performance of the SPCE, the SPCE was modified by using a combination of Pt nanoparticles modified with single-walled carbon nanotubes (Pt@SWCNTs), MXene (Ti3C2), and graphene oxide (GO). In addition, the GO in Pt@SWCNTs-MXene-GO was reduced to reduced graphene oxide (rGO) by the action of electric field (−1.2 V), which significantly improved the electrochemical properties of the composites and effectively solved the problem of dispersion of the modified materials on the electrode surface. Under optimal experimental conditions, Pt@SWCNTs-Ti3C2-rGO/SPCE exhibited a suitable detection range (0.006–7.4 μmol L−1) and low detection limits (2.8 and 3 nmol L−1, S/N = 3) for the simultaneous detection of BPA (0.392 V vs. Ag/AgCl) and DM-BPA (0.436 V vs. Ag/AgCl)). Thus, this study provides new insights into detecting compounds with similar structures and slight potential differences. Finally, the developed sensor's reproducibility, stability, interference resistance and accuracy were demonstrated with satisfactory results.

Quality-by-Design R&D of a Novel Nanozyme-Based Sensor for Saliva Antioxidant Capacity Evaluation.

Oxidative stress is one of the main causes of cell damage, leading to the onset of several diseases, and antioxidants represent a barrier against the production of reactive species. Saliva is receiving increasing interest as a promising biofluid to study the onset of diseases and assess the overall health status of an individual. The antioxidant capacity of saliva can be a useful indicator of the health status of the oral cavity, and it is nowadays evaluated mainly through spectroscopic methods that rely on benchtop machines and liquid reagents. We developed a low-cost screen-printed sensor based on cerium oxide nanoparticles that can be used to assess the antioxidant capacity of biofluids as an alternative to traditional methods. The sensor development process was investigated via a quality-by-design approach to identify the most critical parameters of the process for further optimization. The sensor was tested in the detection of ascorbic acid, which is used as an equivalent in the assessment of overall antioxidant capacity. The LoDs ranged from 0.1147 to 0.3528 mM, while the recoveries varied from 80% to 121.1%, being therefore comparable with those of the golden standard SAT test, whose recovery value was 96.3%. Therefore, the sensor achieved a satisfactory sensitivity and linearity in the range of clinical interest for saliva and was validated against the state-of-the-art equipment for antioxidant capacity evaluation.

An Electrochemical Screen-Printed Sensor Based on Gold-Nanoparticle-Decorated Reduced Graphene Oxide-Carbon Nanotubes Composites for the Determination of 17-β Estradiol.

In this study, a screen-printed electrode (SPE) modified with gold-nanoparticle-decorated reduced graphene oxide-carbon nanotubes (rGO-AuNPs/CNT/SPE) was used for the determination of estradiol (E2). The AuNPs were produced through an eco-friendly method utilising plant extract, eliminating the need for severe chemicals, and remove the requirements of sophisticated fabrication methods and tedious procedures. In addition, rGO-AuNP serves as a dispersant for the CNT to improve the dispersion stability of CNTs. The composite material, rGO-AuNPs/CNT, underwent characterisation through scanning electron microscopy (SEM), ultraviolet-visible absorption spectroscopy (UV-vis), Fourier-transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). The electrochemical performance of the modified SPE for estradiol oxidation was characterised using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The rGO-AuNPs/CNT/SPE exhibited a notable improvement compared to bare/SPE and GO-CNT/SPE, as evidenced by the relative peak currents. Additionally, we employed a baseline correction algorithm to accurately adjust the sensor response while eliminating extraneous background components that are typically present in voltammetric experiments. The optimised estradiol sensor offers linear sensitivity from 0.05-1.00 µM, with a detection limit of 3 nM based on three times the standard deviation (3δ). Notably, this sensing approach yields stable, repeatable, and reproducible outcomes. Assessment of drinking water samples indicated an average recovery rate of 97.5% for samples enriched with E2 at concentrations as low as 0.5 µM%, accompanied by only a modest coefficient of variation (%CV) value of 2.7%.

Screen-printed, flexible, and eco-friendly thermoelectric touch sensors based on ethyl cellulose and graphite flakes inks

Despite the undoubtable interest in energy conversion, thermoelectric (TE) materials can be approached from a temperature-sensitive perspective, as they can detect small thermal stimuli, such as a human touch or contact with cold/hot objects. This feature offers possibilities for different applications one of them being the integration with scalable and cost-effective, biocompatible, flexible, and lightweight thermal sensing solutions, exploring the combination of sustainable Seebeck coefficient-holding materials with printing techniques and flexible substrates. In this work, ethyl cellulose and graphite flakes inks were optimized to be used as functional material for flexible thermal touch sensors produced by screen-printing. Graphite concentrations of 10, 20 and 30 wt% were tested, with 1, 2 and 3 printed layers on four different substrates—office paper, sticker label paper, standard cotton, and organic cotton. The conjugation of these variables was assessed in terms of printability, sheet resistance and TE response. The best electrical-TE output combination is achieved by printing two layers of the ink with 20 wt% of graphite on an office paper substrate. Subsequently, thermal touch sensors with up to 48 TE elements were produced to increase the output voltage response (>4.5 mV) promoted by a gloved finger touch. Fast and repeatable touch recognition were obtained in optimized devices with a signal-to-noise ratio up to 340 and rise times bellow 0.5 s. The results evidence that the screen-printed graphite-based inks are highly suitable for flexible TE sensing applications.

Synthesis and Fabrication of Graphite/WO3 Nanocomposite-Based Screen-Printed Flexible Humidity Sensor

The resistive type of graphite/WO3 nanocomposite-based humidity sensor is fabricated through screen printing on a flexible polyethylene terephthalate substrate. Three different nanocomposite-based humidity sensors have been fabricated and analyzed for their humidity-sensing characteristics. The structure elucidation of the nanocomposite was carried out using x-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy. By exposing the printed humidity sensor to relative humidity ranging from 11% to 97% at room temperature, its capabilities were studied. The relative resistance, sensitivity, dynamic response, and hysteresis were determined for all three devices, and they showed maximum responses towards relative humidity changes with the highest sensitivity of ≈ 60.8% and excellent hysteresis curves (maximum change of ≈ 1%). The screen-printed flexible humidity sensor exhibited less than a 5% change in the internal electrical resistance when subjected to various bending angles.

Comparison of different noble metal-based screen-printed sensors for detection of PIK3CA point-mutations as biomarker for circulating tumor DNA

Screen-printed electrochemical sensors are of particular interest for point-of-care diagnostic applications due to their high sensitivity, short analysis times, and cost-efficient large-scale fabrication. Especially noble metal-based sensors offer the possibility of easy surface modification via self-assembly of thiol-labelled compounds. We examined silver, gold, and palladium as electrode materials regarding their suitability for highly specific and sensitive DNA detection with a chronoamperometric enzyme-amplified electrochemical assay. Modification with either gold nanoparticles or silver-coated microbeads was tested as a possibility to improve the performance of the electrochemical sensors. The sensors were characterized regarding surface topography, sensitivity towards the redox-active substrate TMB, efficiency of capture probe immobilization, as well as mutation specificity. The highest sensitivity for oxidized TMB was observed for gold sensors that yielded a limit of detection of 2.1 µM, while no improvement in sensitivity was observed for sensors modified with gold nanoparticles or silver-coated microbeads. DNA probe immobilization and multiplexed target DNA detection was successful with all tested electrode materials. However, modification with silver-coated microbeads led to both reduced probe immobilization efficiency and hybridization specificity. Gold nanoparticle modification of both silver and of gold sensors induced a highly porous sensor surface after sintering, which increases the surface area of the electrodes. The gold nanoparticle modified sensors showed particularly appreciable results in terms of improved hybridization specificity, as demonstrated by successful multiplexed detection of three PIK3CA point-mutations (H1047R, E545K, and E542K). Average discrimination factors D of 2.7 and 2.1 were obtained for gold and silver sensors modified with one layer of gold nanoparticles, respectively.

Modified planar sensors for cefepime determination

Planar screen-printed potentiometric sensors sensitive to cefepime, cephalosporine antibiotic of the fourth generation, has been developed. Cefepime is an amphoteric antibiotic with carboxyl and aminothiazole groups which exists as a cation in a strongly acidic media, a zwitter-ion in a weakly acidic and neutral media, and as an anion in an alkaline media. The interval of pH = 1.5 - 2.0 is set for obtaining cationic electrode functions for the cefepime determination. Cefepime-tetraphenylborate associates are used as electrode-active components (EAC). The optimal EAC content for planar sensors is 2-3%. The electrode functions are linear in the range of 1 x 10 -5 - 1 x 10 -2 M, angular coefficients 50 ± 2 mV/pC, response time 20 sec for unmodified cefepime sensors. The role of the modifier, ZnO nanoparticles, in improving the electroanalytic properties of sensors is shown. The introduction of a binary mixture of zinc oxide and cetylpyridinium chloride into carbon-containing ink leads to a decrease in the detection limit of cefepime (1 x КГ6 M), an increase in the angular coefficient (58 ± 1 mV/pC) and the interval of linearity of electrode functions (1 x 10 -6 - 1 x 10 -2 mole/liter), sensor response time being 17 sec. The use of a surfactant as an electrode surface comodifier leads to stabilization of the nanoparticle dispersion. The use of modified screen-printed sensors for the cefepime determination in medicinal and biological media, in particular, in saliva, is shown.

Screen-Printed Electrochemical Biosensor for the Detection of Bacteriophage of Lactococcus Lactis for Dairy Production

In the dairy industry, the spreading of phages of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Lactococcus lactis</i> prevent the proper lactic fermentation, causing waste of contaminated products and economic losses. This work presents a cheap biosensing method for rapidly detecting the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L.lactis</i> phages. The detection is based on live <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L. lactis</i> bacteria covering the sensor electrodes, whose electrical response is measured by electrochemical impedance spectroscopy (EIS). Solutions contaminated by phages induce bacteria lysis, clearly reducing the bacteria coverage over the electrodes and leading to evident parametrical shifts in the charge transfer resistance and in the impedance phase at 400 Hz. Experimental tests with laboratory contaminated samples confirm that screen-printed sensors with gold and detection capability compared to interdigitated gold electrodes. Two measurement protocols, called spill-out and drop-in methods, are evaluated to optimize the sensor detection capability and time. The EIS results are compared with optical absorbance measurements at 600 nm, in order to validate the proposed detection method with 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> PFU/mL phages and with a detection time of about 5 hours. Lastly, the proposed method is tested successfully with milk-based solutions. Evident shifts are measured in the charge transfer resistance of more than one order of magnitude and impedance phase differences of 43° in phages contaminated sensors.

Novel Flexible Ag/AgCl Quasi-Reference Electrode with Fishbone Nanowire Structure for Remarkable Potential Stability, Long-Term Reliability, and Noninvasive Electrocardiography.

The roadblocks for the planar silver/silver chloride (Ag/AgCl) quasi-reference electrode (qRE) development are the potential stability and long-term reliability as potentiometric sensors. Although there is a significant amount of work on potentiometric screen-printed and inkjet-printed sensors, none of the REs has comparable performance to that of the conventional glass RE and knowledge on reliable planar Ag/AgCl qREs is still limited. Here, a novel fishbone-structured flexible Ag/AgCl qRE (Fishbone-Ag/AgCl qRE) was developed and its stability and long-term reliability were significantly improved. The stability of the Fishbone-Ag/AgCl qRE was comparable to that of a commercial glass Ag/AgCl RE. In a long-term stability test, the Fishbone-Ag/AgCl qRE could continuously and stably operate for more than 4 h. Shelf-life testing revealed a 6 month life span. The conductivity and diameter of the nanowires in the fishbone structure of the Ag/AgCl qRE had important influences on electrochemical properties. The conductivity of the qRE influenced the charge-transfer rate in the electrode so that it affected the potential stability. Thicker diameter and slight chlorination on the surface of the AgNWs resulted in enhanced long-term reliability of the qRE. The capabilities of this new nanostructured material were applied in vivo for noninvasive monitoring of electrocardiogram. The discovery is elementary and substantially informs improved nanostructure RE design for testing and commercial medical device applications.

A Disposable Screen Printed Electrodes with Hexagonal Ni(OH)2 Nanoplates Embedded Chitosan Layer for the Detection of Depression Biomarker.

Serotonin (5-hydroxytryptamine (5-HT)) is one of the important neurotransmitters which is released from the endocrine system. An abnormal level of this biomarker leads to several neurological diseases. The accurate assessment of serotonin is the utmost option to start treatment in the early stages of the disease. The current work is focused on the development of a disposable, screen-printed electrochemical sensor for the depression biomarker, serotonin in the physiological pH medium (pH 7.4) with the aid of a hexagonal, Ni(OH)2-nanoplate (NH-HNP)-embedded chitosan (Chit) and modified, screen-printed carbon electrode (SPCE). Initially, hexagonal nanoplates of Ni(OH)2 were synthesized by an eco-friendly and simple hydrothermal method. The prepared materials were well characterized by advanced analytical techniques to examine the physicochemical properties of the synthesized Ni(OH)2 hexagonal nanoplates. From the cyclic voltametric (CV) analysis, it was found that the oxidative current response of 5-HT at a NH-HNP-modified SPCE has about fivefold higher current values than over bare SPCE. The scan rate studies of NH-HNP-Chit/SPCE electrodes revealed that the oxidation mechanism of 5-HT is controlled by the diffusion behavior of the analyte. Differential pulse voltammetric tests of the NH-HNP-Chit/SPCE electrode exhibited a linear response in the dynamic concentration range of 0.1 to 30 µM, with a detection limit of about 60 nM. The sensor response is very reproducible from electrode to electrode, and the deactivation or surface-fouling of the sensor was not observed within the several experimental measurements. The sensor exhibited excellent storage stability over a period of twenty days. Finally, the fabricated, disposable SPCE sensor has shown respectable activity for the detection of depression biomarker 5-HT from synthetic urine and saliva samples.

Potentiometric planar platforms modified with a multiwalled carbon nanotube/polyaniline nanocomposite and based on imprinted polymers for erythromycin assessment

A screen-printed potentiometric sensor for the erythromycin macrolide antibiotic (ERY) that is affordable, highly selective, and sensitive is made, described, and used for drug monitoring.

Remote Monitoring of Skin Temperature Through a Wristband Employing a Printed VO Sensor

The need for highly sensitive, environmentally stable, mechanically flexible, and low-cost temperature sensors for on-body measurements has been increasing with the wide adoption of personal healthcare-Internet-of-Things (H-IoT) devices. Printed electronics (PE) is a good platform for such sensors because it enables the realization of flexible devices through simple and rapid methods at a relatively low cost. However, previously reported printed temperature sensors suffer from poor sensitivity and/or environmental instability. In this article, we report a custom tungsten (W)-doped vanadium dioxide (VO2) ink-based screen-printed temperature sensor having the highest temperature coefficient of resistance (TCR) of 2.78% C-1 with a resolution of 0.1 °C between 30 °C and 40 °C. To protect it from environmental effects, a fluoropolymer-basedpassivation layer is added for accurate temperature readings even in 90% relative humidity. The sensor is printed on a flexible substrate and shows minimal deterioration in performance over 1000 bending cycles. For wearability and remote monitoring, the sensor is integrated with a custom Bluetooth low energy (BLE) wireless readout in the form of wristband. The BLE readout comprises an ultrathin and flexible patch antenna optimized for both BLE bandwidth (BW) and human wearability. It demonstrates a minimal specific absorption rate (SAR) value of only 0.068 W/kg, making it safe to wear. Despite the antenna’s thin structure (0.004λ), it has a gain of 1.65 dBi, enabling an excellent communication range. The proposed wristband is tested on ten volunteers and under daily activities, which shows promising results with a maximum error of 0.16 °C with reference to those of a commercial thermometer.

Sensitive and Selective Voltammetric Sensor Based on Anionic Surfactant-Modified Screen-Printed Carbon for the Quantitative Analysis of an Anticancer Active Fused Azaisocytosine-Containing Congener

3-(4-Nitrophenyl)-8-(2,3-dimethylphenyl)-7,8-dihydroimidazo[2,1-c][1,2,4]triazin-4(6H)-one (NDIT) is one of the most promising candidates for anticancer agents. Hence, a sensitive and selective sodium dodecyl sulfate-modified screen-printed carbon sensor (SPCE/SDS) was used for its quantitative analysis. The SPCE/SDS, in contrast to the SPCE, showed excellent behavior in the electrochemical reduction of NDIT by differential-pulse adsorptive stripping voltammetry (DPAdSV). Cyclic voltammetric (CV) studies reveal an irreversible, two-stage and not purely diffusion-controlled reduction process in 0.01 M HNO3. The sensor was characterized by CV and electrochemical impedance spectroscopy (EIS). Under the optimized conditions (t 45 s, ΔE 175 mV, ν 150 mV/s, and tm 5 ms), the DPAdSV procedure with the SPCE/SDS presented a very wide linear range from 1 to 2000 nM and a low detection limit of 0.29 nM. A 1000-fold excess concentration of potential interferents commonly present in biological samples did not significantly alter the peak current of NDIT. The practical application of the proposed DPAdSV procedure with the SPCE/SDS was successfully checked by analyzing spiked human serum samples.

Voltammetric Quantification of Anti-Cancer Antibiotic Bleomycin Using an Electrochemically Pretreated and Decorated with Lead Nanoparticles Screen-Printed Sensor.

In this paper, we report a highly sensitive voltammetric sensor for the determination of the anti-cancer antibiotic bleomycin (BLM) based on a screen-printed carbon sensor that is electrochemically pretreated and decorated with lead nanoparticles in the sample solution (pSPCE/PbNPs). These sensor surface manipulations contribute to significant amplification of the analytical signal and improvement of its shape and repeatability. The effect of the electrochemical behavior of BLM on the pSPCE/PbNPs was examined by electrochemical strategies. CV, EIS, and XPS were used to compare the sensor surface modifications. The effects of the type and pH of the supporting electrolyte and the procedure parameters were optimized. The features of the proposed procedure include: (a) very low limits of detection and quantification (2.8 × 10-11 and 9.3 × 10-11 M, respectively), (b) linear ranges (1.0 × 10-10-2.0 × 10-9 M and 2.0 × 10-9-2.0 × 10-8 M, and (c) a high sensitivity of 0.32 µA/nM. The electrochemical sensor was successfully applied for the determination of BLM in wastewater and reference material of human urine samples.

Screen-Printed Sensors Coated with Polyaniline/Molecularly Imprinted Polymer Membranes for the Potentiometric Determination of 2,4-Dichlorophenoxyacetic Acid Herbicide in Wastewater and Agricultural Soil

2,4-Dichlorophenoxyacetic acid (2,4-D) is a widely used herbicide worldwide. However, its residues in agricultural products are extremely harmful to human health and to the environment in soil and water. Previous methods for determining 2,4-D in water and soil samples are expensive, cumbersome, and not highly selective. In this study, we developed a novel disposal sensor based on screen-printed electrodes (SPEs) for detecting 2,4-D in wastewater and soil samples. The SPEs were modified with conductive polyaniline (PANI) layer and polyvinyl chloride (PVC) membrane loaded with molecularly printed polymer (MIP). The MIP particles were prepared using 2,4-D as template, methacrylic acid (MAA) as monomer, ethylene glycol dimethacrylate (EGDMA) as cross-linker, and benzoyl peroxide as initiator. The best sensor shows a dynamic concentration range of 10−2 to 10−7 M 2,4-D, a detection limit (LOD) of 3.6 × 10−7 M, Nernst slope (response) of 29.9 mV/decade, and high selectivity over other interfering species previously reported in the literature. The sensors also achieved a short response time of 25 s, high reversibility, and a lifetime of over 2 weeks. The developed sensors were successfully used for determining 2,4-D in real wastewater and soil samples with high accuracy and precision.

A Co3O4 Nanoparticle-Modified Screen-Printed Electrode Sensor for the Detection of Nitrate Ions in Aquaponic Systems

In this study, a screen-printed electrode (SPE) modified with cobalt oxide nanoparticles (Co3O4 NPs) was used to create an all-solid-state ion-selective electrode used as a potentiometric ion sensor for determining nitrate ion (NO3-) concentrations in aquaculture water. The effects of the Co3O4 NPs on the characterization parameters of the solid-contact nitrate ion-selective electrodes (SC-NO3--ISEs) were investigated. The morphology, physical properties and analytical performance of the proposed NO3--ion selective membrane (ISM)/Co3O4 NPs/SPEs were studied by X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), potentiometric measurements, and potentiometric water layer tests. Once all conditions were optimized, it was confirmed that the screen-printed electrochemical sensor had high potential stability, anti-interference performance, good reproducibility, and no water layer formation between the selective membrane and the working electrode. The developed NO3--ISM/Co3O4 NPs/SPE showed a Nernstian slope of -56.78 mV/decade for NO3- detection with a wide range of 10-7-10-2 M and a quick response time of 5.7 s. The sensors were successfully used to measure NO3- concentrations in aquaculture water. Therefore, the electrodes have potential for use in aquaponic nutrient solution applications with precise detection of NO3- in a complicated matrix and can easily be used to monitor other ions in aquaculture water.

Highly Sensitive and Selective Graphene Nanoribbon Based Enzymatic Glucose Screen-Printed Electrochemical Sensor.

A simple, sensitive, cost effective, and reliable enzymatic glucose biosensor was developed and tested. Nitrogen-doped heat-treated graphene oxide nanoribbons (N-htGONR) were used for modification of commercially available screen-printed carbon electrodes (SPCEs), together with MnO2 and glucose oxidase. The resulting sensors were optimized and used to detect glucose in a wide linear range (0.05-5.0 mM) by a simple amperometric method, where the limit of detection was determined to be 0.008 mM. (lifetime), and reproducibility studies were also carried out and yielded favorable results. The sensor was then tested against potential interfering species present in food and beverage samples before its application to real matrix. Spiked beer samples were analyzed (with glucose recovery between 93.5 and 103.5%) to demonstrate the suitability of the developed sensor towards real food and beverage sample applications.

Design of highly selective, and sensitive screen-printed electrochemical sensor for detection of uric acid with uricase immobilized polycaprolactone/polyethylene imine electrospun nanofiber

Uric acid (UA) plays a significant role in nerve center, human metabolism, and kidney system. Therefore, it is necessary to establish a simple, rapid, and sensitive detection method for UA. In recent years, researchers have been highly attracted by nanomaterials with satisfactory functions in electrochemical applications. In this study, polycaprolactone (PCL)/polyethylene imine (PEI) nanofiber membranes were prepared and used for the immobilization of uricase (UOx). The prepared membranes were characterized in terms of structure, composition, and morphology. Afterward, the quantum dot screen printed electrode (QD SPCE) was modified with PCL/PEI nanofiber membranes with and without methylene blue (MB) as an electron mediator. The electrochemical performance of the developed sensors was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Under the optimal conditions, the modified sensors provided a broad linear range (5.0–52.0 µM) for the electrochemical detection of UA. Limit of detection (LoD) values were determined as 3.96 µM and 1.85 µM for the PCL/PEI/UOx/QD SPCE and PCL/PEI/UOx/MB/QD SPCE, respectively. The four-week stability results showed the change in current for the PCL/PEI/UOx/QD SPCE and PCL/PEI/UOx/MB/QD SPCE to be 92% and 87%, respectively. Additionally, in the mixed interference test remaining current ratios for UA were 95% and 82% for the PCL/PEI/UOx/QD SPCE and PCL/PEI/UOx/MB/QD SPCE, respectively. Most importantly, the effectiveness of the electrodes was also verified in real sample detection with satisfactory recovery (∼98-112%). Overall, the results showed that the PCL/PEI/UOx/QD SPCE and PCL/PEI/UOx/MB/QD SPCE have the advantages of simplicity, high sensitivity, and good selectivity for UA determination.