Single-drop electrodeposition of nanoneedle-like bismuth on disposable graphene electrode for on-site electrochemical detection of cadmium and lead.

A novel cost-effective disposable porous graphene electrode (P-GE) modified with bismuth nanoneedles (nano-BiNDs) is proposed as a "mercury-free" sensor for detecting heavy metals through smartphone-assisted electrochemical sensing. The P-GE was fabricated using screen-printing. Nano-BiNDs were generated on the P-GE by potentiostatic electrodeposition. Using an optimal potential of -1.20 V (vs. pseudo-Ag/AgCl) and a deposition time of 200 s, the nano-BiNDs had an average length and width of 189 ± 5 nm and 20 ± 2 nm, respectively. The analytical performances of the fabricated sensing platform were demonstrated by detecting Cd2+ and Pb2+ using square-wave anodic stripping voltammetry (SWASV) under optimized conditions. In the optimal conditions, the fabricated sensor exhibited sharp, well-defined stripping peaks for Cd2+ and Pb2+ with excellent peak-to-peak separation. The linear detection ranges were from 0.01 to 50 µg mL-1 for Cd2+ and 0.006-50 µg mL-1 for Pb2+. The detection limits for Cd2+ and Pb2+ were 3.51 and 2.10 ng mL-1, respectively. The developed portable sensor demonstrated high sensitivity, good repeatability, reproducibility, and anti-interference properties. The proposed portable sensor quantified Cd2+ and Pb2+ in commercial seaweed products with good accuracy, consistent with the results obtained using the standard ICP-OES method.

Nano-palladium-decorated bismuth sulfide microspheres on a disposable electrode integrated with smartphone-based electrochemical detection of nitrite in food samples.

Nitrite (NO2-) is widely used as an additive to extend the shelf life of food products. Excessive nitrite intake not only causes blood-related diseases but also has the potential risk of causing cancers. A disposable screen-printed electrode was modified with nano­palladium decorated bismuth sulfide microspheres (nanoPd@Bi2S3MS/SPE), and integrated with a smartphone-interfaced potentiostat to develop a portable, electrochemical nitrite sensor. NanoPd@Bi2S3MS was prepared by the hydrothermal reduction of a Bi2S3MS and Pd2+ dispersion and drop cast on the SPE. The nanoPd@Bi2S3MS/SPE was coupled with a smartphone-controlled portable potentiostat and applied to determine nitrite in food samples. The linear range of the sensor was 0.01-500 µM and the limit of detection was 0.0033 µM. The proposed system showed good repeatability, reproducibility, catalytic stability, and immunity to interferences. The proposed electrode material and a smartphone-based small potentiostat created a simple, portable, fast electrochemical sensing system that accurately measured nitrite in food samples.

A reusable screen-printed carbon electrode-based aptasensor for the determination of chloramphenicol in food and environment samples.

An electrochemical aptasensor was developed for the determination of chloramphenicol (CAP) in fresh foods and food products. The aptasensor was developed using Prussian blue (PB) and chitosan (CS) film. PB acts as a redox probe for detection and CS acts as a sorption material. The aptamer (Apt) was immobilized on a screen-printed carbon electrode (SPCE) modified with gold nanoparticles (AuNPs). Under optimum conditions, the linearity of the aptasensor was between 1.0 and 6.0 × 106 ng L-1 with a detection limit of 0.65 and a quantification limit of 2.15 ng L-1. The electrode could be regenerated up to 24 times without the use of chemicals. The aptasensor showed good repeatability (RSD <11.2%) and good reproducibility (RSD <7.7%). The proposed method successfully quantified CAP in milk, shrimp pond water and shrimp meat with good accuracy (recovery = 88.0 ± 0.6% to 100 ± 2%). The proposed aptasensor could be especially useful in agriculture to ensure the quality of food and the environment and could be used to determine other antibiotics.

Fabrication of a 96-electrode array using carbon dioxide laser ablation.

The 96 laser-induced multigraphene electrode (96L-MGE) integrated microwell plate (96 L-MGE-MP) is described. Each cell includes separate working, auxiliary, and reference electrodes, and the array sits on a poly-methyl methacrylate (PMMA) well. The 96 electrochemical cells were fabricated by laser ablation of polyimide adhesive tape, which created laser-induced graphene electrodes (L-GE). The microwell was produced using laser ablation of the PMMA sheet as well. The morphology and electrochemical characterization of L-GE were controlled by tuning the laser processing. L-GE fabricated at laser power-laser speed ratios of 0.008-0.02 W s mm-1displayed good electrochemical behaviors. Under the optimal condition of L-GE fabrication, the measured L-GE surface roughness was 475.47 nm. The 96 L-MGE can be fabricated in 24.2 min and is compatible with various analytes. 10 benchmark redox compounds were shown as electrocatalytic examples. The performance of each analyte was investigated by voltammetry. As proof of concept, 96 L-MGE-MP was connected to a 96× connector for multichannel detection. The RSD of the 96 L-MGE-MPwas below 5.3%, which demonstrated good fabrication reproducibility.

A novel 3D-printed portable electroplating device enhances latent fingerprints on metal substrates.

This work introduces a 3D-printed portable electroplating device for the visualization of latent fingerprints (LFPs) on metallic substrates. An electroplating solution of Ag+-Cu2+ in a deep eutectic solvent (DES) is used. The electroplating is performed by two electrodes equivalent to an anode (+) and a cathode (-). The cathode is connected to the metal surface with the magnetic or alligator clip for carrying the LFP. The anode is connected to cotton dipped in the electroplating solution. The device was optimized in terms of the electroplating solution composition, and electroplating potential, current, and time. The device produced images with good resolution, revealing LFP ridges in minute detail of more than 12 points. The device also exhibited good repeatability and images were assessed against guidelines from the Centre for Applied Science and Technology (CAST) and the International Fingerprint Research Group (IFRG). The developed device could be applied to visualize LFPs in forensic investigations.

Electropolymerization of poly(phenol red) on laser-induced graphene electrode enhanced adsorption of zinc for electrochemical detection.

We present a highly sensitive and selective electrode of laser-induced graphene modified with poly(phenol red) (P(PhR)@LIG) for measuring zinc nutrition in rice grains using square wave anodic stripping voltammetry (SWASV). The physicochemical properties of P(PhR)@LIG were investigated with scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), Fourier infrared spectroscopy (FT-IR) and Raman spectroscopy. The modified electrode demonstrated an amplified anodic stripping response of Zn2+ due to the electropolymerization of P(PhR), which enhanced analyte adsorption during the accumulation step of SWASV. Under optimized parameters, the developed sensor provided a linear range from 30 to 3000 µg L-1 with a detection limit of 14.5 µg L-1. The proposed electrode demonstrated good reproducibility and good anti-interference properties. The sensor detected zinc nutrition in rice grain samples with good accuracy and the results were consistent with the standard ICP-OES method.

A dual-electrode label-free immunosensor based on in situ prepared Au-MoO3-Chi/porous graphene nanoparticles for point-of-care detection of cholangiocarcinoma.

A novel label-free electrochemical immunosensor was prepared for the detection of carbohydrate antigen 19-9 (CA19-9) and carcinoembryonic antigen (CEA) as biomarkers of cholangiocarcinoma (CCA). A nanocomposite of gold nanoparticles, molybdenum trioxide, and chitosan (Au-MoO3-Chi) was layer-by-layer assembled on the porous graphene (PG) modified a dual screen-printed electrode using a self-assembling technique, which increased surface area and conductivity and enhanced the adsorption of immobilized antibodies. The stepwise self-assembling procedure of the modified electrode was further characterized morphologically and functionally. The electroanalytical detection of biomarkers was based on the interaction between the antibody and antigen of each marker via linear sweep voltammetry using ferrocyanide/ferricyanide as an electrochemical redox indicator. Under optimized conditions, the fabricated immunosensor showed linear relationships between current change (ΔI) and antigen concentrations in two ranges: 0.0025-0.1 U mL-1 and 0.1-1.0 U mL-1 for CA19-9, and 0.001-0.01 ng mL-1 and 0.01-1.0 ng mL-1 for CEA. The limits of detection (LOD) were 1.0 mU mL-1 for CA19-9 and 0.5 pg mL-1 for CEA. Limits of quantitation (LOQ) were 3.3 mU mL-1 for CA19-9 and 1.6 pg mL-1 for CEA. The selectivity of the developed immunosensor was tested on mixtures of antigens and was then successfully applied to determine CA19-9 and CEA in human serum samples, producing satisfactory results consistent with the clinical method.

Molecularly imprinted polymer dual electrochemical sensor for the one-step determination of albuminuria to creatinine ratio (ACR).

The urinary albumin to creatinine ratio (ACR) is a convenient and accurate biomarker of chronic kidney disease (CKD). An electrochemical sensor for the quantification of ACR was developed based on a dual screen-printed carbon electrode (SPdCE). The SPdCE was modified with carboxylated multiwalled carbon nanotubes (f-MWCNTs) and redox probes of polymethylene blue (PMB) for creatinine and ferrocene (Fc) for albumin. The modified working electrodes were then molecularly imprinted with coated with polymerized poly-o-phenylenediamine (PoPD) to form surfaces that could be separately imprinted with creatinine and albumin template molecules. The seeded polymer layers were polymerized with a second coating of PoPD and the templates were removed to form two different molecularly imprinted polymer (MIP) layers. The dual sensor presented recognition sites for creatinine and albumin on different working electrodes, enabling the measurement of each analyte in one potential scan of square wave voltammetry (SWV). The proposed sensor produced linear ranges of 5.0-100 ng mL-1 and 100-2500 ng mL-1 for creatinine, and 5.0-100 ng mL-1 for albumin. LODs were 1.5 ± 0.2 ng mL-1 and 1.5 ± 0.3 ng mL-1, respectively. The dual MIP sensor was highly selective and stable for seven weeks at room temperature. The ACRs obtained using the proposed sensor compared well (P > 0.05) with the results from immunoturbidimetric and enzymatic methods.

Craft-and-Stick Xurographic Manufacturing of Integrated Microfluidic Electrochemical Sensing Platform.

An innovative modular approach for facile design and construction of flexible microfluidic biosensor platforms based on a dry manufacturing "craft-and-stick" approach is developed. The design and fabrication of the flexible graphene paper electrode (GPE) unit and polyethylene tetraphthalate sheet (PET)6/adhesive fluidic unit are completed by an economic and generic xurographic craft approach. The GPE widths and the microfluidic channels can be constructed down to 300 µm and 200 µm, respectively. Both units were assembled by simple double-sided adhesive tapes into a microfluidic integrated GPE (MF-iGPE) that are flexible, thin (<0.5 mm), and lightweight (0.4 g). We further functionalized the iGPE with Prussian blue and glucose oxidase for the fabrication of MF-iGPE glucose biosensors. With a closed-channel PET fluidic pattern, the MF-iGPE glucose biosensors were packaged and sealed to protect the integrated device from moisture for storage and could easily open with scissors for sample loading. Our glucose biosensors showed 2 linear dynamic regions of 0.05-1.0 and 1.0-5.5 mmol L-1 glucose. The MF-iGPE showed good reproducibility for glucose detection (RSD < 6.1%, n = 6) and required only 10 µL of the analyte. This modular craft-and-stick manufacturing approach could potentially further develop along the concept of paper-crafted model assembly kits suitable for low-resource laboratories or classroom settings.

A portable electrochemical immunosensor for ovarian cancer uses hierarchical microporous carbon material from waste coffee grounds.

A simple label-free electrochemical immunosensor for ovarian cancer (OC) detection was developed using a hierarchical microporous carbon material fabricated from waste coffee grounds (WCG). The analysis method exploited near-field communication (NFC) and a smartphone-based potentiostat. Waste coffee grounds were pyrolyzed with potassium hydroxide and used to modify a screen-printed electrode. The modified screen-printed electrode was decorated with gold nanoparticles (AuNPs) to capture a specific antibody. The modification and immobilization processes were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The sensor had an effective dynamic range of 0.5 to 50.0 U mL-1 of cancer antigen 125 (CA125) tumor marker with a correlation coefficient of 0.9995. The limit of detection (LOD) was 0.4 U mL-1. A comparison of the results obtained from human serum analysis with the proposed immunosensor and the results obtained from the clinical method confirmed the accuracy and precision of the proposed immunosensor.

Disposable label-free electrochemical immunosensor based on prussian blue nanocubes for four breast cancer tumor markers.

A compact and low-cost multi-electrode array (MEA) is presented, comprising four working electrodes with shared reference and auxiliary electrodes. Prussian blue was electrodeposited on the MEA using chronoamperometry with a positive potential of 0.3 V. Prussian blue nanocubes (PBNCs) were formed, which were observed using scanning electron microscopy. The precision of the four working electrodes was demonstrated using ferric/ferro cyanide (RSD <5.8%). The surface roughness of the working electrodes of the fabricated MEA was investigated by atomic force microscopy and compared with that of a commercial MEA. The PBNCs were the platform for a label-free immunosensor that detected four breast cancer tumor markers (CEA, CA125, CA153, and CA199) using specific antibodies. The processes of antibody immobilization were investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The immunosensor was evaluated using real human serum samples, yielding acceptable recoveries (95.1-104.1%, RSD < 3.9) for the four tumor markers. These findings confirmed that our label-free immunosensor based on PBNCs could be a promising device for point-of-care testing and could pave the way for the establishment of new platforms for the screening of various breast cancer tumor markers.

Novel biosensor platform for glucose monitoring via smartphone based on battery-less NFC potentiostat.

Near-field communication (NFC) was used to control a portable glucose biosensor for diabetes diagnosis. The system comprised a smartphone and an NFC potentiostat connected to a screen-printed carbon electrode (SPCE) modified with Prussian blue-graphene ink and functionalized with gold nanoparticles-embedded poly (3,4ethylene dioxythiophene):polysulfonic acid coated with glucose oxidase (GOx-AuNPs-PEDOT:PSS/PB-G). GOx catalyzed the glucose redox reaction while the conductivity and sensitivity of the AuNPs-PEDOT:PSS composite enhanced electron transfer to the PB-G, which was used as a mediator. The fabrication process was characterized by scanning electron microscopy (SEM) with energy dispersibe x-ray analysis (EDX). The platform was electrochemically characterized by electrical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The NFC biosensing device was then applied to quantify glucose in human blood serum by amperometry. The linear concentration range and detection limit for glucose were 0.5-500 µM and 0.15 µM, respectively. The accuracy of the device was good and results were in agreement with the results obtained from the standard hospital method. This NFC glucose sensing device can be a simple, sensitive, selective and portable platform for medical diagnosis.

A wireless smartphone-based "tap-and-detect" formaldehyde sensor with disposable nano-palladium grafted laser-induced graphene (nanoPd@LIG) electrodes.

We developed a fully integrated smart sensing device for on-site testing of food to detect trace formaldehyde (FA). A nano-palladium grafted laser-induced graphene (nanoPd@LIG) composite was synthesized by one-step laser irradiation of a Pd2+-chitosan-polyimide precursor. The composite was synthesized in the form of a three-electrode sensor on a polymer substrate. The electrochemical properties and morphology of the fabricated composite were characterized and the electrochemical kinetics of FA oxidation at the nanoPd@LIG electrode were investigated. The nanoPd@LIG electrode was combined with a smart electrochemical sensing (SES) device to determine FA electrochemically. The proposed SES device uses near field communication (NFC) to receive power and transfer data between a smartphone interface and a battery-free sensor. The proposed FA sensor exhibited a linear detection range from 0.01 to 4.0 mM, a limit of detection of 6.4 µM, good reproducibility (RSDs between 2.0 and 10.1%) and good anti-interference properties for FA detection. The proposed system was used to detect FA in real food samples and the results correlated well with the results from a commercial potentiostat and a spectrophotometric analysis.

Detection and discrimination of sedative-hypnotics in spiked beverage dry residues using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy combined with chemometrics.

Drugs-facilitated crimes (DFCs) involve the incapacitation of victims under the influence of drugs. Conventionally, a drug administration act is often determined through the examination of biological samples; however, dry residues from any surface, such as drinking glass if related to a DFC could be a potential source of evidence. This study was aimed to establish an attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy coupled with chemometrics for the determination of spiked sedative-hypnotics from dry residues of a drug-spiked beverage. In this study, four sedative-hypnotics, namely diazepam, ketamine, nimetazepam, and xylazine were examined using ATR-FTIR spectroscopy. Subsequently, the ATR-FTIR profiles were compared and decomposed by principal component analysis (PCA) followed by linear discriminant analysis (LDA) for their detection and discrimination. Visual comparison of ATR-FTIR profiles revealed distinct spectra among the tested drugs. An initial unsupervised exploratory PCA model indicated the separation of four main sedative-hypnotics clusters, and the proposed PCA score-LDA model had allowed for a 100% accurate classification. Discrimination of sedative-hypnotics from a dry beverage previously spiked with these drugs was also possible upon an additional extraction procedure. In conclusion, ATR-FTIR coupled with PCA score-LDA model was useful in detecting and discriminating sedative-hypnotics, including those that had been previously spiked into a beverage.

Electrochemical sensor based on molecularly imprinted polymer cryogel and multiwalled carbon nanotubes for direct insulin detection.

Insulin is the polypeptide hormone that regulates blood glucose levels. It is used as an indicator of both types of diabetes. An electrochemical insulin sensor was developed using a gold electrode modified with carboxylated multiwalled carbon nanotubes (f-MWCNTs) and molecularly imprinted polymer (MIP) cryogel. The MIP provided specific recognition sites for insulin, while the macropores of the cryogel promoted the mass transfer of insulin to the recognition sites. The f-MWCNTs increased the effective surface area and conductivity of the sensor and also reduced the potential required to oxidize insulin. Insulin oxidation was directly measured in a flow system using square wave voltammetry. This MIP cryogel/f-MWCNTs sensor provided a linear range of 0.050-1.40 pM with a very low limit of detection (LOD) of 33 fM. The sensor exhibited high selectivity and long-term stability over 10 weeks of dry storage at room temperature. The results of insulin determination in human serum using the sensor compared well with the results of the Elecsys insulin assay. The developed MIP sensor offers a promising alternative for the diagnosis and treatment of diabetes.

A microplate spectrophotometric method for analysis of indole-3-carbinol in dietary supplements using p-dimethylaminocinnamaldehyde (DMACA) as a chromogenic reagent.

This work presents the development of a microplate spectrophotometric method for determination of indole-3-carbinol in dietary supplements. The colorimetric procedure is based on the reaction of indole-3-carbinol with the p-dimethylaminocinnamaldehyde (DMACA) reagent under acidic conditions. The absorbance of the colored product measured at 675 nm was used to determine the target analyte. To achieve optimal spectrophotometric performance, the DMACA reagent concentration, the hydrochloric acid concentration, and the reaction time were optimized. The developed technique performed well under the optimal conditions, with a linear calibration range of 30 to 300 mg L-1 and a high correlation coefficient (r2 = 0.9954). The limit of detection and limit of quantification were 7.8 mg L-1 and 26.2 mg L-1, respectively. This approach demonstrated good repeatability (intra- and inter-day precision) with a % RSD lower than 9.4%, good accuracy with acceptable relative recoveries in the range of 98 to 106%, and high sample throughput (24 detection per min). This simple, rapid, and multi-sample analysis approach for routine analysis of indole-3-carbinol has the potential to be used for the quality control of dietary supplements.

Flow Injection Amperometric Measurement of Formalin in Seafood.

Formalin is illegally used as an antibacterial and a preservative in seafood products. It is extremely important for public health reasons to be able to simply, rapidly, and accurately detect formalin in fresh seafood. In this work, we developed a flow injection amperometric (FI-Amp) formalin sensor based on a glassy carbon electrode modified with a composite of palladium particles and carbon microspheres (PdPs-CMs/GCE). The CMs were decorated with PdPs via an electroless deposition method. The surface morphology of the CMs and the PdPs-CMs composite was characterized by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX). The electrochemical behavior and measurement of formalin at the PdPs-CMs/GCE was evaluated by cyclic voltammetry and amperometry. The modified electrode demonstrated good electrocatalytic performance for the oxidation of formalin. The synthesis method and FI-Amp operating conditions were optimized. Under the optimal conditions, the developed sensor showed a linear range of 0.025 to 15.00 mmol L-1 and a detection limit of 8 µmol L-1. Repeatability (RSD < 4.1%, n = 30), reproducibility (RSD = 0.25%, n = 5), stability (RSD = 3.2%, n = 80), and selectivity were good. The fabricated sensor achieved recoveries of formalin in seafood between 96 ± 1 to 105 ± 3 (n = 3).

Nanocoral-like Polyaniline-Modified Graphene-Based Electrochemical Paper-Based Analytical Device for a Portable Electrochemical Sensor for Xylazine Detection.

A portable electrochemical device for xylazine detection is presented for the first time. An electrochemical paper-based analytical device (ePAD) was integrated with a smartphone. The fabrication of the ePAD involved wax printing, low-tack transfer tape, and cutting and screen-printing techniques. Graphene ink was coated on the substrate and modified with nanocoral-like polyaniline, providing an electron transfer medium with a larger effective surface area that promoted charge transfer. The conductive ink on the ePAD presented a thickness of 25.0 ± 0.9 µm for an effective surface area of 0.374 cm2. This sensor was then tested directly on xylazine using differential pulse voltammetry. Two linear responses were obtained: from 0.2 to 5 µg mL-1 and from 5 to 100 µg mL-1. The detection limit was 0.06 µg mL-1. Reproducibility was tested on 10 preparations. The relative standard deviation was less than 5%. The applicability of the sensor was evaluated with beverage samples spiked with trace xylazine. Recoveries ranged from 84 ± 4 to 105 ± 2%. The developed sensor demonstrated excellent accuracy in the detection of trace xylazine. It would be possible to develop the portable system to detect various illicit drugs to aid forensic investigations.

Vortex-assisted dispersive liquid-liquid microextraction-gas chromatography (VADLLME-GC) determination of residual ketamine, nimetazepam, and xylazine from drug-spiked beverages appearing in liquid, droplet, and dry forms.

Presently, investigations of drug-facilitated crimes (DFCs) rely on the detection of substances extracted from biological samples following intake by the victim. However, such detection requires rapid sampling and analysis prior to metabolism and elimination of the drugs from the body. In cases of suspected DFCs, drug-spiked beverage samples, whether in liquid, droplet, or even dried form, can be tested for the presence of spike drugs and used as evidence for the occurrence of DFCs. This study aimed to quantitatively determine three sedative-hypnotics (ketamine, nimetazepam, and xylazine) from drug-spiked beverages using a vortex-assisted dispersive liquid-liquid microextraction-gas chromatography (VADLLME-GC) approach. In this study, a GC method was first developed and validated, followed by the optimization of the VADLLME protocol, which was then applied to quantify the target substances in simulated forensic case scenarios. The developed GC method was selective, sensitive (limit of detection: 0.08 µg/ml [ketamine]; 0.16 µg/ml [nimetazepam]; 0.08 µg/ml [xylazine]), linear (R2 > 0.99), precise (%RSD <7.2%), and accurate (% recovery: 92.8%-103.5%). Higher recoveries were achieved for the three drugs from beverage samples in liquid form (51%-97%) as compared to droplet (48%-96%) and dried (44%-93%) residues. The recovery was not hindered by very low volumes of spiked beverage and dried residues. In conclusion, the developed VADLLME-GC method successfully recovered ketamine, nimetazepam, and xylazine from spiked beverages that are likely to be encountered during forensic investigation of DFCs.

A Fabrication of Multichannel Graphite Electrode Using Low-Cost Stencil-Printing Technique.

Multichannel graphite electrodes (MGrEs) have been designed and fabricated in this study. A template was cut from an adhesive plastic sheet using a desktop cutting device. The template was placed on a polypropylene substrate, and carbon graphite ink was applied with a squeegee to the template. The size of the auxiliary electrode (AE) as well as the location of the reference electrode (RE) of MGrEs design were investigated. Scanning electron microscopy was used to determine the thickness of the ink on the four working electrodes (WEs), which was 21.9 ± 1.8 µm. Cyclic voltammetry with a redox probe solution was used to assess the precision of the four WEs. The intra-electrode repeatability and inter-electrode reproducibility of the MGrEs production were satisfied by low RSD (<6%). Therefore, the MGrEs is reliable and capable of detecting four replicates of the target analyte in a single analysis. The electrochemical performance of four WEs was investigated and compared to one WE. The sensitivity of the MGrEs was comparable to the sensitivity of a single WE. The MGrEs' potential applications were investigated by analyzing the nitrite in milk and tap water samples (recoveries values of 97.6 ± 0.4 to 110 ± 2%).