Highly sensitive amperometric sensing of nitrite utilizing bulk-modified MnO 2 decorated Graphene oxide nanocomposite screen-printed electrodes

Lab-on-a chip electrochemical sensing platform for simultaneous, ultra-sensitive and on-spot detection of 4-aminosalicylic acid and 5-aminosalicylic acid based on synergistic potential of chitosan functionalized MWCNTs supported on Ni doped Bi2S3

Mesalamine or 5-aminosalicylic acid (5-ASA) and its isomer 4-aminosalicylic acid (4-ASA), well known key therapeutic agents used to treat inflammatory bowel diseases (IBDs) can pose toxicity risks upon unregulated consumption. However, their simultaneous real-time detection from physiological fluids like urine remains unexplored. This study presents an innovative electrochemical sensing platform using modified screen-printed electrodes capable of simultaneous detection of both the drugs by harnessing the synergistic potential of a novel nanocomposite comprising chitosan functionalized multi-walled carbon nanotubes and nickel doped bismuth sulphide. Comprehensive optical and microstructural characterization validate the modified sensor platform's morphological characteristics. The sensor was evaluated using CV and DPV, exhibiting notably low detection limits which is of the value 39.559 μM for 5-ASA and 85.21 μM for 4-ASA. Sensitivity was found to be 0.174 μA μM-1cm-2 for the linear dynamic range (LDR) of 50 μM-5750 μM for 5-ASA and 0.139 μA μM-1cm-2 for the linear dynamic range (LDR) of 100 μM-2200 μM for 4-ASA. Moreover, the adaptability of the sensor for integration into hand-held point-of-care devices for practical application has been demonstrated in this paper. Experimental validation using real urine samples underscores the sensor's impressive recovery rate of 98-99.6 % for 5-ASA and 95.12-99.24 % for 4-ASA and its capability of detecting target drugs even when present with typical urinary constituents as interferences. The real-world applicability of this sensing platform is further emphasized by conducting experiments on miniaturized hand-held device thus making it a promising tool for on-the-spot detection, offering substantial potential for future integration into point-of-care diagnostic devices to monitor patients requiring precise medical monitoring. Our approach offers unprecedented real-time identification capabilities of 4-ASA and 5-ASA which has not been explored before.

Metal-free graphitic carbon nitride nanosheet for dual mode fluorescence and electrochemical detection of para-nitrophenol

para-Nitrophenol (p-NP) contamination poses significant risks to both environmental and human health, highlighting the urgent need for sensitive and selective methods for its detection. In this study, a graphitic carbon nitride sheet (g-CNS) synthesized via a one-step hydrothermal method is proposed as a bi-functional probe for p-NP sensing. The fluorescence activity of the g-CNS was first optimized, and its quenching on the addition of p-NP was used for the fluorometric detection of p-NP. A broad linear response to p-NP concentrations ranging from 1 to 100 μM was observed, with a detection limit of 36.76 nM. The sensor exhibited excellent performance in the presence of potential interferences and was successfully applied to real sample analysis. To enhance on-site detection applicability, a g-CNS modified voltammetric sensor was developed. The g-CNS was electrodeposited on a glassy carbon electrode (GCE) using cyclic voltammetry and characterized using a range of techniques to confirm the successful modification. When applied to p-NP detection, the modified GCE demonstrated high sensitivity, with a limit of detection (LOD) of 218 nM. Furthermore, the stability, reusability, and reproducibility of the modified electrode were thoroughly evaluated, confirming its reliability for long-term use in electrochemical sensing applications.

A sensitive and selective electrochemical detection and kinetic analysis of methyl parathion using Au nanoparticle-decorated rGO/CuO ternary nanocomposite

Detecting organophosphorus pesticide (OP) residues is essential for maintaining ecological integrity and monitoring public health concerns. This research developed a novel electrochemical sensor that employed composite materials based on copper oxide (CuO) nanostructures and reduced graphene oxide (rGO), customized with Au nanoparticles (AuNPs), to detect methyl parathion (MP) pesticide with high selectivity and sensitivity. The nanocomposite was synthesized in two facile steps, without the use of stabilizers or dispersants, utilizing a simple ultrasonication and photo-reduction process. Morphological analysis revealed a uniform distribution of AuNPs and rGO within the CuO nanostructure. Kinetic studies demonstrated that the electro-reduction of MP on a glassy carbon electrode (GCE) modified with Au@rGO/CuO exhibited irreversible, diffusion-controlled kinetics, with a transfer coefficient (α) value of 0.485. A sensing study employing the square wave voltammetry (SWV) technique exhibited exceptional sensitivity (3.46 μA μM-1 cm-2), with a limit of detection (LOD) of 0.045 μM. Moreover, the Au@rGO/CuO-based sensor electrode exhibited exceptional selectivity for MP in the presence of various organic and inorganic species, along with notable reproducibility, repeatability, and stability. Overall, this electrochemical method for effective MP detection suggests that the prepared nanocomposite could contribute to the development of viable electrocatalysts.

An electrochemical microfluidic sensor based on a Cu2O-GNP nanocomposite integrated hydrogel for nitrite detection in food samples

The integration of a nanocomposite composed of cuprous oxide-graphene nanoplatelet hydrogel (Cu2O-GNP hydrogel) has been investigated as an electrochemical interface for nitrite (NO2-) detection. The nanocomposite hydrogel was prepared through the sonochemical technique and characterized by Field Emission Scanning Electron Microscopy (FE-SEM), EDX (energy dispersive X-ray analysis), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Electrochemical performance was further evaluated using Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV), and Differential Pulse Voltammetry (DPV). Cu2O provides a catalytic active site that lower the activation energy for NO2- oxidation, while GNPs enhance the electrode conductivity and increase the surface area for superior electron transfer. Additionally, a PDMS-based microfluidic device was developed and integrated with an electrochemical detection system, enabling continuous and real-time monitoring of NO2-. A syringe pump was used to maintain a stable NO2- solution flow through the microfluidic channels at a 10 μL per min flow rate, ensuring sufficient diffusion of NO2- ions to the electrode surface, and preventing excess analyte accumulation that could lead to signal distortion. The integrated microfluidic sensor exhibited excellent electrochemical performance, achieving a high sensitivity of 13.97 μA μM-1 cm-2 and a low detection limit (LOD) of 0.56 μM, with a linear range of 5-130 μM. Cu2O-GNP hydrogel/SPCE exhibited excellent selectivity and reproducibility for NO2- sensing. The developed sensor demonstrated good recovery percentages in sausages, pickled vegetables, and water samples, confirming its suitability for the food industry.

Nanofibers decorated with high-entropy alloy particles for the detection of nitrites

Excessive residues of nitrite can pose a serious threat to human health, making the establishment of an efficient and effective electrochemical sensor for nitrite detection highly necessary. Herein, we report on a sensor based on nitrogen-doped carbon nanofibers, with FeCoNiCuAl high-entropy alloy (HEAs) nanoparticles in situ grown on the carbon fibers through a confinement effect. The FeCoNiCuAl/CNF sensor is capable of electrochemically detecting nitrite using both differential pulse voltammetry (DPV) and amperometric (I-t) methods. The DPV detection offers a linear range of 0.1-5000 μM and 5000-18 000 μM, with sensitivities of 150.6 μA mM-1 cm-2 and 80.1 μA mM-1 cm-2 and a detection limit of 0.023 μM (S/N = 3). The I-t detection covers a range of 1-10 000 μM, with a sensitivity of 337.84 μA mM-1 cm-2 and a detection limit of 0.12 μM. Moreover, the sensor exhibits excellent anti-interference properties, stability, and reproducibility, providing feasibility for nitrite detection in real-world environments.

Fabrication of an innovative electrochemical sensor based on graphene-coated silver nanoparticles decorated over graphitic carbon nitride for efficient determination of estradiol

Monitoring small amount of endocrine disrupting chemical, estradiol (E2) residue in environmental and biological samples is extremely important because of its possible connections to breast and prostate malignancies and gastrointestinal disorders. The newly synthesized graphene-coated silver nanoparticles (GN@Ag) decorated on graphitic carbon nitride (g-C3N4)-based hybrid nanomaterial (GN@Ag/g-C3N4) was used to modify glassy carbon electrode (GCE) for electroanalytical measurement of E2. The GN@Ag/g-C3N4 nanocomposite prepared through ultrasonic-assisted reflux methodology was characterized using various physicochemical methods. The scanning electron microscopy and transmission electron microscopy have shown that GN@Ag nanoparticles were decorated and randomly dispersed over g-C3N4 sheets. The exceptional electrochemical response towards the oxidation of E2 was observed through cyclic voltammetry due to the quick electron transfer ability and superior conductivity of GN@Ag/g-C3N4/GCE. The detection limit was found to be 0.002 μM with wide linear range of E2 concentration (0.005-8.0 μM) along with remarkable stability of the fabricated electrode for 21 days showing 91% retention in initial current. The kinetic parameters such as catalytic rate constant and diffusion coefficient for E2 were estimated to be 1.1 × 105 M-1 s-1 and 1.9 × 10-4 cm2 s-1, respectively, by employing chronoamperometry. The proposed sensor also demonstrated its practical applicability for E2 determination in environmental and biological samples with a recovery range of 95-104%. Furthermore, the developed sensing platform is much better compared to reported methods in terms of simplicity, accuracy, detection limit, linearity range, and usefulness in real sample for E2 sensing.

MnCo2O4 Spinel Nanorods for Highly Sensitive Electrochemical Detection of Nitrite

The rational design of nitrite sensors has attracted significant research interest due to their widespread use and the associated risks of methemoglobinemia and carcinogenicity. The undisclosed nitrite-sensing performance of the spinel cobaltite MnCo2O4 (MCO) prepared by an oxalate-assisted coprecipitation method is reported in this study. Spectroscopy and microscopy investigations revealed the formation of uniform MCO nanorods with a high aspect ratio. The electrocatalytic nitrite oxidation at the MCO-coated glassy carbon electrode (MCO/GCE) indicated the promising performance of the synthesized material for nitrite sensing. MCO/GCE detects nitrite in a concentration range of 5 μM to 3 mM and has a limit of detection of 0.95 μM with a higher sensitivity of 857 μA mM-1 cm-2 in a response time of 4 s. In MCO, the mixed-valence states of Co2+/Co3+ confer a high electrical conductivity, and higher valent redox couples of Mn and Co impart remarkable electrocatalytic activity toward nitrite oxidation. MCO spinel undergoes facile and ultrafast faradaic reactions to mediate nitrite oxidation. Additionally, the mesopores of MCO nanorods facilitate the rapid diffusion of electrolyte and nitrite ions. Employing the electrode in sensing nitrite in milk, lake, and tap water samples further validates its potential application in real-life testing. MCO spinel nanorods showcase promising scope for utilization in the electrochemical sensing of nitrite and inspire further exploration of transition-metal oxide-based mixed-spinel materials.

Simultaneous Electrochemical Detection of Dopamine and Uric Acid via Au@Cu-Metal Organic Framework

The incorporation of noble metals with metal-organic frameworks (MOFs) are conducive to the simultaneous electrochemical detection of analytes owing to multiple accessible reaction sites. Herein, Au@Cu-metal organic framework (Au@Cu-MOF) is successfully synthesized and modified as a screen-printed carbon electrode (SPCE), which serves as an excellent electrocatalyst for the oxidation of dopamine (DA) and uric acid (UA). The sensor shows a linear range from 10 μM to 1000 μM, with sensitivity and detection limit of 0.231 μA μM-1 cm-2 and 3.40 μM for DA, and 0.275 μA μM-1 cm-2 and 10.36 μM for UA. Au@Cu-MOF could realize the individual and simultaneous electrochemical sensing of DA and UA, with distinguishable oxidation peak potentials. Moreover, it exhibits reproducibility, repeatability, and stability. Ultimately, the sensor provides an avenue for an ultrasensitive label-free electrochemical detection of DA and UA.

Carbon nanotube-interconnected ruthenium phthalocyanine nanoparticles used for real-time monitoring of nitric oxide released from vascular endothelial barrier model

Real-time monitoring of nitric oxide (NO) is of great importance in diagnosing the physiological functions of neurotransmission, cardiovascular, and immune systems. This study reports the carbon nanotube-interconnected ruthenium phthalocyanine nanoparticle nanocomposite and its applicability in construction of an electrochemical platform, which could real-time detect NO released from the vascular endothelial barrier (VEB) model in cell culture medium. The nanocomposite exhibits regular morphology, uniform particle size, and excellent electro-catalytic activity to electrochemical oxidation of NO. Under optimal conditions, the electrochemical device has high sensitivity (0.871 μA μM-1) and can selectively detect NO down to the concentration of 6 × 10-10 M. The human brain microvascular endothelial cells were cultured onto the Transwell support to construct the VEB model. Upon stimulated by L-arginine, NO produced by the VEB diffuses into the bottom chamber of the Transwell, and is real-time monitored by the electrochemical device. Moreover, evaluation of the NO inhibition by drug is realized using the electrochemical device-Transwell platform. This simple and sensitive platform would be of great interesting for evaluating the endothelial function or its pathological states, and screening the related drugs or chemicals.

Electrochemical sensor for sensitive nitrite and sulfite detection in milk based on acid-treated Fe3O4@SiO2 nanoparticles

In this work, a simple electrochemical sensing platform based on acid-treated Fe3O4@SiO2 nanoparticles was successfully prepared for nitrite and sulfite detection. Fe3O4@SiO2 nanoparticles were synthesized through the sol-gel and hydrothermal methods. Fe3O4@SiO2 presented positive charges after acid treatment, which could enhance the electrostatic attraction between Fe3O4@SiO2 and nitrite and sulfite. The Fe3O4@SiO2(acid-treated) modified magnetic glassy carbon electrode (MGCE) was applied to detect nitrite and sulfite using differential pulse voltammetry and cyclic voltammetry. Under optimized conditions, the developed electrochemical sensor presented good analytical properties for nitrite and sulfite detection with detection limits of 3.33 μmol/L and 31.57 μmol/L, respectively. The good recoveries varied from 85.18% to 111.02%, with a relative standard deviation of 0.23-4.80%. Furthermore, the Fe3O4@SiO2(acid-treated) modified MGCE showed better selectivity, reproducibility, and repeatability in nitrite and sulfite detection. Therefore, this proposed electrochemical sensor provides a new method for developing a nitrite and sulfite detection sensor.

Voltammetric analysis of epinephrine using glassy carbon electrode modified with nanocomposite prepared from Co-Nd bimetallic nanoparticles, alumina nanoparticles and functionalized multiwalled carbon nanotubes

Herein, we investigated the electrochemical behaviour of fMWCNTs decorated with Co-Nd bimetallic nanoparticles and alumina nanoparticles (Co-Nd/Al2O3@fMWCNTs). The nanocomposites were synthesised using simple mechanical mixing and characterised by FT-IR, XRD, UV-visible studies, SEM, TEM and EDAX. Moreover, the crystalline size of the synthesised nanoparticles was also calculated using XRD data (Debye-Scherer formula) and was found in the nm range. The electrochemical behaviour of epinephrine (EP) was examined in the presence of Co-Nd/Al2O3@fMWCNTs nanocomposite modified glassy carbon electrode (GCE) using various electrochemical techniques such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), and chronocoulometry. Among all the above-mentioned techniques, the DPV response of the modified Co-Nd/Al2O3@fMWCNTs/GCE under optimal circumstances revealed a dual linear range (0.2 to 4000 µM and 4000 to 14,000 µM) and LOD of 0.015 µM (S/N = 3). The sensitivities were determined to be 0.00323 µAµM-1 and 0.0004 µAµM-1 in 0.2 to 4000 µM and 4000 to 14,000 µM concentration ranges. Using chronocoulometry, the surface coverage of Co-Nd/Al2O3@fMWCNTs/GCE was calculated to be 1.37 × 10-8 mol cm-2. The fabricated Co-Nd/Al2O3@fMWCNTs/GCE demonstrated remarkable repeatability, with an RSD of 0.09%, and storage stability of 3 weeks, with 89.6% current retention. Lastly, it was found that Co-Nd/Al2O3@fMWCNTs/GCE worked well for EP analysis in a variety of biological fluids.

Electrochemical biosensors based on in situ grown carbon nanotubes on gold microelectrode array fabricated on glass substrate for glucose determination

A highly sensitive electrochemical sensor is reported for glucose detection using carbon nanotubes grown in situ at low temperatures on photolithographically defined gold microelectrode arrays printed on a glass substrate (CNTs/Au MEA). One of the main advantages of the present design is its potential to monitor 64 samples individually for the detection of glucose. The selectivity of the fabricated MEA towards glucose detection is achieved via modification of CNTs/Au MEA by immobilizing glucose oxidase (GO_x) enzyme in the matrix of poly (paraphenylenediamine) (GO_x/poly (p-PDA)/CNTs/Au MEA). The electrocatalytic and electrochemical responses of the proposed sensing platform towards glucose determination were examined via cyclic voltammetry and electrochemical impedance spectroscopy. The developed impedimetric biosensor exhibits a good linear response towards glucose detection, i.e., 0.2-27.5 µM concentration range with sensitivity and detection limits of 168.03 kΩ^-1 M^-1 and 0.2 ± 0.0014 μM, respectively. The proposed glucose biosensor shows excellent reproducibility, good anti-interference property, and was successfully tested in blood serum samples. Further, the applicability of the proposed sensor was successfully validated through HPLC. These results supported the viability of using such devices for the simultaneous detection of multiple electroactive biomolecules of physiological relevance.

Hydrothermal Synthesis of MnO2/Reduced Graphene Oxide Composite for 4-Nitrophenol Sensing Applications

Recently, the electrochemical sensing approach has attracted materials/electrochemical scientists to design and develop electrode materials for the construction of electrochemical sensors for the detection of para-nitrophenol (4-NP). In the present study, we have prepared a hybrid composite of MnO2 and rGO (MnO2/rGO) using a hydrothermal approach. The morphological features of the prepared MnO2/rGO composite were studied by scanning electron microscopy, whereas the phase purity and formation of the MnO2/rGO composite were authenticated via the powder X-ray diffraction method. Energy-dispersive X-ray spectroscopy was also employed to analyze the elemental composition of the prepared MnO2/rGO composite. In further studies, a glassy carbon electrode (GCE) was modified with MnO2/rGO composite (MnO2/rGO/GCE) and explored as 4-nitrophenol (4-NP) sensor. The fabricated MnO2/rGO/GCE exhibited a reasonably good limit of detection of 0.09 µM with a sensitivity of 0.657 µA/µMcm2. The MnO2/rGO/GCE also demonstrates good selectivity, stability and repeatability in 50 cycles.

Determination of nitrite in food based on its sensitizing effect on cathodic electrochemiluminescence of conductive PTH-DPP films

Herein, a novel strategy for electrochemiluminescence (ECL) detection of nitrite based on its sensitization effect on cathode ECL emission of 3,6-di(2-thienyl)-2,5-dihydropyrrolo [3,4-c] pyrrole-1,4-dione (TH-DPP) polymeric films (PTH-DPP) was formulated, by means of a one-step electropolymerization of TH-DPP with a short time on the glassy carbon electrode (GCE). It was shown that the PTH-DPP film-modified GCE exhibited a strong ECL response when S₂O₈^2- was used as a co-reactant. The ECL emission could be greatly enhanced by PTH-DPP with nitrite in a K₂S₂O₈/PBS solution system and occurred at a relatively lower potential in comparison with traditional cathode ECL emitter, leading to high sensitivity and good selectivity. The ECL sensor exhibits excellent linear relationship in the ranges of 0.3 to 100 μM and 100 to 1000 μM for nitrite detection, with an outstanding detection limit of 0.08 μM (S/N = 3). The ECL sensor provides an impressive outcome for the detection of practical samples.

Application of MnO2 Nanorod–Ionic Liquid Modified Carbon Paste Electrode for the Voltammetric Determination of Sulfanilamide

The current work introduced a convenient single-phase hydrothermal protocol to fabricate MnO₂ nanorods (MnO₂ NRs). Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX) and field-emission scanning electron microscopy (FE-SEM) were used to determine the characteristics of MnO₂ NR. Then, ionic liquid (IL) and MnO₂ NRs were utilized to modify a carbon paste electrode (CPE) surface (MnO₂NR-IL/CPE) to voltammetrically sense the sulfanilamide (SAA). An enhanced voltammetric sensitivity was found for the as-developed modified electrode toward SAA when compared with a bare electrode. The optimization experiments were designed to achieve the best analytical behavior of the SAA sensor. Differential pulse voltammetry (DPV) in the optimized circumstances portrayed a linear dependence on various SAA levels (between 0.07 and 100.0 μM), possessing a narrow detection limit (0.01 μM). The ability of the modified electrode to be used in sensor applications was verified in the determination of SAA present in the actual urine and water specimens, with impressive recovery outcomes.

Electrochemical Sensing of Nitrite Ions Using Modified Electrode by Poly 1,8-Diaminonaphthalene/Functionalized Multi-Walled Carbon Nanotubes

A novel electrochemical sensor based on conducting polymer and multi-walled carbon nanotubes was reported for the detection of nitrite ions (NO₂⁻). The hybrid material poly 1,8-Diaminonaphthalene (poly 1,8-DAN)/functionalized multi-walled carbon nanotubes (f-MWCNT) was prepared by using a simple electrochemical approach which is based on the deposition of functionalized multi-walled carbon nanotubes (f-MWCNT) on the surface of the electrode followed by the electropolymerization of 1,8-DAN using cyclic voltammetry. The morphology and the electro-catalytic properties of the obtained electrodes were investigated with Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM), Cyclic Voltammetry (CV), and Electrochemical Impedance Spectroscopy (EIS) showing an improvement of the electronic transfer due to the synergic effect between the proprieties of poly 1,8-DAN and f-MWCNT. Under the optimum experimental conditions, the poly 1,8-DAN/f-MWCNT/CPE exhibited excellent electro-catalytic activity towards nitrite detection. The nitrite anodic peak potential decreased by 210 mV compared to the bare carbon paste electrode. The calibration plot of nitrite detection was linear in the range of concentration from 300 to 6500 nM with a low detection limit of 75 nM.

Analysis of imidacloprid residues in mango, cowpea and water samples based on portable molecular imprinting sensors

Imidacloprid is a neonicotinoid insecticide widely used in the production and cultivation of crops. In recent years, the extensive use of imidacloprid in agricultural production has resulted in large amounts of pesticide residues in agricultural products and the environment. Therefore, it is necessary to establish a rapid, accurate, sensitive and convenient method for detecting imidacloprid pesticide residues to ensure the safety of agricultural products and the environment. To clarify how to use the molecular imprinting method for the electrochemical rapid residue detection of imidacloprid. This paper selected reduced graphene oxide and gold nanoparticles as modifiers modified on screen-printed carbon electrodes (SPCE) chitosan as a functional monomer, and imidacloprid as template molecule to prepare molecularly imprinted polymer, and applied this sensor to the residue detection of imidacloprid. The results showed that the concentration of imidacloprid showed a good linear relationship with the peak response current, and the detection limit of imidacloprid was 0.5 μM, while the sensor had good repeatability and interference resistance. The recoveries of imidacloprid spiked on three samples, mango, cowpea and water, were in the range of 90-110% (relative standard deviation, RSD<5%), which proved the practicality and feasibility of the assay established in this paper. The results of this paper can be used as a basis for the research on the detection of imidacloprid pesticide residues in food or environment.

Disposable non-enzymatic electrochemical glucose sensors based on screen-printed graphite macroelectrodes modified via a facile methodology with Ni, Cu, and Ni/Cu hydroxides are shown to accurately determine glucose in real human serum blood samples

A three dimensional (3D) non-enzymatic glucose disposable electrochemical sensor based on screen-printed graphite macroelectrodes (SPEs), modified with nickel hydroxide (Ni(OH)₂/SPE), copper hydroxide (Cu(OH)₂/SPE) and mixed (Ni(OH)₂/Cu(OH)₂/SPE) microstructures were prepared by a facile and cost-effective electrochemical method for the first time. Their morphologies and structures were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The electrochemical performances of the modified SPEs were evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and amperometric measurements. EIS experiments showed lower charge transfer resistance R_ct values for the modified SPEs, calculated to be 29.24 kΩ, 22.58 kΩ, 13.27 kΩ and 36.48 kΩ for Ni(OH)₂/SPE, Cu(OH)₂/SPE, Ni(OH)₂/Cu(OH)₂/SPE, and SPE, respectively. Under optimal experimental conditions, the results reveal that CV, amperometry and EIS can be readily applied to determine glucose using all of the fabricated sensors, however in terms of an accessible and clinically relevant linear range for the electroanalytical detection of glucose, CV is preferred, where Cu(OH)₂/SPE exhibits the largest linear range from 1 μM to 20 mM (R² = 0.997). In terms of sensitivity and the detection limit however, amperometry appeared to be a better choice of technique, particularly with Ni(OH)₂/Cu(OH)₂/SPE which demonstrated the highest sensitivity of 2029 μA mM^-1 cm^-2 and the lowest detection limit of 0.2 μM (S/N = 3). Excellent selectivity was evident against common interfering species, and it was shown to be possible to obtain satisfactory results in human blood serum samples using the as-fabricated sensors. The low cost of the SPEs, the facile preparation and observed clinically relevant analytical sensitivities and limit of detections towards the sensing of glucose make these screen-printed macroelectrode based electrochemical sensing platforms promising for routine human blood serum glucose analysis.

Pd-Cu nanospheres supported on Mo2C for the electrochemical sensing of nitrites

The improper disposal in agricultural and industrial wastewater leads to high NO₂^- concentrations in the aquatic environment, which can cause cancer in humans and animals; thus, their quick and accurate detection is urgently needed to ensure public health and environmental safety. In this study, a reliable and selective electrochemical sensor consisting of Pd-Cu nanospheres (NSs) supported on molybdenum carbide was prepared via simple ultrasonication. Then, a glassy carbon electrode was realized using this composite (Pd-Cu-Mo₂C-modified GCE) to test its electrocatalytic sensing for NO₂^- in a 0.1 M phosphate-buffered solution (PBS) solution via cyclic voltammetry and amperometry; at a low oxidation potential, the anodic peak current of NO₂^- detected by this electrode was significantly higher than that of its unmodified and other modified electrodes. The sensor showed a broad linear response in the 5-165-nM NO₂^- concentration range, with a low detection limit (0.35 nM in 0.1 M PBS) and high sensitivity (3.308 μAnM^-1 cm^-2). Moreover, the fabricated electrode was successfully applied for detecting nitrites in sausages, river water, and milk, showing also good recovery.

Nanomaterials in Electrochemical Sensing Area: Applications and Challenges in Food Analysis

Recently, nanomaterials have received increasing attention due to their unique physical and chemical properties, which make them of considerable interest for applications in many fields, such as biotechnology, optics, electronics, and catalysis. The development of nanomaterials has proven fundamental for the development of smart electrochemical sensors to be used in different application fields such, as biomedical, environmental, and food analysis. In fact, they showed high performances in terms of sensitivity and selectivity. In this report, we present a survey of the application of different nanomaterials and nanocomposites with tailored morphological properties as sensing platforms for food analysis. Particular attention has been devoted to the sensors developed with nanomaterials such as carbon-based nanomaterials, metallic nanomaterials, and related nanocomposites. Finally, several examples of sensors for the detection of some analytes present in food and beverages, such as some hydroxycinnamic acids (caffeic acid, chlorogenic acid, and rosmarinic acid), caffeine (CAF), ascorbic acid (AA), and nitrite are reported and evidenced.

Ultrasensitive determination of nitrite based on electrochemical platform of AuNPs deposited on PDDA-modified MXene nanosheets

An ultrasensitive and high-performance electrochemical nitrite sensing platform based on gold nanoparticles deposited on poly (dimethyl diallyl ammonium chloride)-decorated MXene (Ti₃C₂T_x) (AuNPs/Ti₃C₂T_x-PDDA) was constructed. AuNPs/Ti₃C₂T_x-PDDA on the surface of electrode displayed synergetic catalytic effect for oxidizing NO₂^‾ originating from especially catalytic activity of AuNPs, large area and excellent conductivity of Ti₃C₂T_x, as well as electrostatic interaction of PDDA. The amperometry technique was employed for quantitative determination of nitrite, in which the AuNPs/Ti₃C₂T_x-PDDA/GCE sensing platform showed outstanding linear relationship in 0.1-2490 μM and 2490-13490 μM for nitrite, meanwhile the detection limit of 0.059 μM. Besides, the prepared sensor possessed high sensitivity of 250 μA mM^-1 cm^-2 yet excellent selectivity, stability and reproducibility. Furthermore, this platform also exhibited satisfactory feasibility of nitrite sensing in running water and ham sausage sample. This work would broaden a facile approach to construct high sensitivity electrochemical sensing platform via two-dimension materials and its nanocomposites.

Film Carbon Veil-Based Electrode Modified with Triton X-100 for Nitrite Determination

A film carbon veil-based electrode (FCVE) modified with non-ionic surfactant Triton X-100 (TrX100) has been developed for nitrite determination. A new simple and producible technique of hot lamination (heat sealing) has been used for the FCVE manufacturing. The paper presents the findings of investigating the FCVE and the TrX100/FCVE by using voltammetry, chronoamperometry, and scanning electron microscopy. Modification of the electrode with TrX100 improves the hydrophilic property of its surface, which results in a larger electrode active area and higher sensitivity. Optimal conditions for nitrite determination with the use of the TrX100/FCVE have been identified. The linear range (LR) and the limit of detection (LOD) are 0.1–100 μM and 0.01 μM, respectively. The relative standard deviation (RSD) does not exceed 2.3%. High selectivity of the sensor ensures its successful application for the analysis of real samples (sausage products and natural water). The obtained results accord well with the results of the standard spectrophotometric method.

Electrochemical (Bio)Sensors for Pesticides Detection Using Screen-Printed Electrodes

Pesticides are among the most important contaminants in food, leading to important global health problems. While conventional techniques such as high-performance liquid chromatography (HPLC) and mass spectrometry (MS) have traditionally been utilized for the detection of such food contaminants, they are relatively expensive, time-consuming and labor intensive, limiting their use for point-of-care (POC) applications. Electrochemical (bio)sensors are emerging devices meeting such expectations, since they represent reliable, simple, cheap, portable, selective and easy to use analytical tools that can be used outside the laboratories by non-specialized personnel. Screen-printed electrodes (SPEs) stand out from the variety of transducers used in electrochemical (bio)sensing because of their small size, high integration, low cost and ability to measure in few microliters of sample. In this context, in this review article, we summarize and discuss about the use of SPEs as analytical tools in the development of (bio)sensors for pesticides of interest for food control. Finally, aspects related to the analytical performance of the developed (bio)sensors together with prospects for future improvements are discussed.

Application of Graphene-Based Materials for Detection of Nitrate and Nitrite in Water-A Review

Nitrite and nitrate are widely found in various water environments but the potential toxicity of nitrite and nitrate poses a great threat to human health. Recently, many methods have been developed to detect nitrate and nitrite in water. One of them is to use graphene-based materials. Graphene is a two-dimensional carbon nano-material with sp² hybrid orbital, which has a large surface area and excellent conductivity and electron transfer ability. It is widely used for modifying electrodes for electrochemical sensors. Graphene based electrochemical sensors have the advantages of being low cost, effective and efficient for nitrite and nitrate detection. This paper reviews the application of graphene-based nanomaterials for electrochemical detection of nitrate and nitrite in water. The properties and advantages of the electrodes were modified by graphene, graphene oxide and reduced graphene oxide nanocomposite in the development of nitrite sensors are discussed in detail. Based on the review, the paper summarizes the working conditions and performance of different sensors, including working potential, pH, detection range, detection limit, sensitivity, reproducibility, repeatability and long-term stability. Furthermore, the challenges and suggestions for future research on the application of graphene-based nanocomposite electrochemical sensors for nitrite detection are also highlighted.

pH-regulated synthesis of CuOx/ERGO nanohybrids with tunable electrocatalytic oxidation activity towards nitrite sensing

CuO_x/ERGO nanohybrids with diverse morphologies prepared by pH-regulated synthesis display tunable electrocatalytic ability towards nitrite sensing.

Enzyme-Based Ultrasensitive Electrochemical Biosensors for Rapid Assessment of Nitrite Toxicity: Recent Advances and Perspectives

In the present era of rapid international globalization and industrialization, intensive use of nitrite as a fertilizing agent in agriculture, preservative, dyeing agent, food additive and as corrosion inhibitor in industrial sectors is adversely effecting environment, natural habitats and human health. The issue of toxicity and carcinogenicity due to excessive ingestion of nitrites via the dietary intake has led to an imminent need for its efficient real-time monitoring in situ. Nitrite detection employing electrochemical biosensors has been gaining high credibility in the field of clinical research. Nitrite biosensors have emerged as an outstanding choice for portable point of care testing of nitrite quantification owing to the excellent properties, such as rapidity, miniaturization, ultra-low limits of detection, multiplexing and enhanced detection sensitivity. The article is enclosed with an interesting outlook on latest emerging trends in the development of nitrite biosensors utilizing nanomaterials, such as metal nanoparticles, carbon nanotubes, metal oxide nanoparticles, nanocomposites, polymers and biomaterials. The present review embarks on the highlights relevant to the nitrite quantification in real samples, then proceeds with a meticulous description of the most pertinent electrochemical nitrite biosensors, which have been proposed by adopting diverse materials and strategies of fabrication and finally end with the achievements and future outlook signifying the application of these nanoengineered biosensors for environmental surveillance and human safety.

Large-scale production of CdO/Cd(OH)2 nanocomposites for non-enzyme sensing and supercapacitor applications

Recent advancements in electrode design are substantially linked to state-of-the-art nanomaterial fabrications. Herein, we report a simple one-pot hydrothermal synthesis of Cd(OH)₂ with a platelet-like morphology, which was subsequently annealed at relatively high temperatures to produce a CdO/Cd(OH)₂ nanocomposite for the first time. It was found that the control of thermal treatment allowed tunable charge transport across the nanometre scale due to the presence of CdO and Cd(OH)₂ mixed nanocrystals. The CdO/Cd(OH)₂ nanocrystals offer interesting prospects for the electrocatalytic oxidation of nitrite ions and for supercapacitor applications. The CdO/Cd(OH)₂ nanocomposite was blended with a trace amount of gold NPs for enhancing the electrochemical conductivity and electrocatalytic capability for nitrite oxidation with a sensitivity of 32.9 μA mM⁻¹. It afforded a promising electrocatalyst in a wide concentration range up to 10 mM with a low detection limit of 0.87 μM. Furthermore, the CdO/Cd(OH)₂ nanocomposite electrode was showed to be a highly active and stable supercapacitor, achieving a high specific capacitance in an alkaline medium of about 145 F g⁻¹ at a discharge current of 2.0 A g⁻¹. These results have revealed that the presence of mixed oxide/hydroxide nanocrystals in nanoscale dimensions will be very interesting for various electrochemical applications and provide for a new class of nanodevices based on electrochemistry with unique capabilities.

A simple fabrication of CdO/Cd(OH)₂ nanocomposites was developed and explored for electrochemical-based devices. The nanocomposite is shown to be a sensitive electrode material for nitrite determination in water samples as well as a promising supercapacitor.

MnO2 nanoarrays: an efficient catalyst electrode for nitrite electroreduction toward sensing and NH3 synthesis applications

A MnO₂ nanoarray on titanium mesh (MnO₂ NA/TM) is shown to be an efficient catalyst electrode for the electroreduction of nitrite.