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a Amperometric current-time curve of the AuNPs/MnO2-GP-CNTs/GCE at an applied potential of 0.8 V in 0.1 M PBS (pH 7) on consecutive step changes of nitrite concentration. b The relationship between response current and nitrite concentration
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A novel 3D composite of gold nanoparticle (AuNP)-decorated MnO2-graphene (GP)-carbon nanotube (CNT)-modified glassy carbon electrode (GCE) was fabricated by drop casting the as-synthesized AuNP/MnO2-GP-CNT suspension onto the surface of GCE. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images indicate the successful...
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... The conventional methods to deposit GO for electrochemical sensors are drop-casting and dip coating. 53,54 However, these methods oen result in non-uniform deposition due to the aggregation of GO sheets and weak adhesion to the electrode surface. On the other hand, the solvent's rapid evaporation during spin coating produces a smoother surface with minimal wrinkling. ...
In this work, we studied several important parameters regarding the standardization of a portable sensor of nitrite, a key biomarker of inflammation in the respiratory tract in untreated EBC samples. The storage of the EBC samples and electrical properties of both EBC samples and the sensor as main standardization parameters were investigated. The sensor performance was performed using differential pulse voltammetry (DPV) in a standard nitrite solution and untreated EBC samples. The storage effect was monitored by comparing sensor data of fresh and stored samples for one month at -80 °C. Results show, on average, a 20 percent reduction of peak current for stored solutions. The sensor's performance was compared with a previous EBC nitrite sensor and chemiluminescence method. The results demonstrate a good correlation between the present sensor and chemiluminescence for low nitrite concentrations in untreated EBC samples. The electrical behavior of the sensor and electrical variation between EBC samples were characterized using methods such as noise analysis, electrochemical impedance spectroscopy (EIS), electrical impedance (EI), and voltage shift. Data show that reduced graphene oxide (rGO) has lower electrical noise and a higher electron transfer rate regarding nitrite detection. Also, a voltage shift can be applied to calibrate the data based on the electrical variation between different EBC samples. This result makes it easy to calibrate the electrical difference between EBC samples and have a more reproducible portable chip design without using bulky EI instruments. This work helps detect nitrite in untreated and pure EBC samples and evaluates critical analytical EBC properties essential for developing portable and on-site point-of-care sensors.
... Synthetic manganese (IV) oxide is used in various fields [1][2][3][4][5][6][7][8][9]. Thus, MnO2 nanoparticles are widely used in energy storage devices taking into account the vector of "green" energy [30], catalysts [30; 32; 33], sensors [23][24][25][26], adsorbents, biochemical and medical fields [34; 36]. The specific capacitance of such capacitors can reach 272 F/g (for the crystallographic form of δ-MnO2) and 311 F/g (for γ-MnO2), moreover, nanosheets retain up to 91 % of the initial capacity after 10,000 charge/discharge cycles. ...
З використанням методів квантово-хімічного моделювання досліджено вплив ненасичених двоосновних органічних кислот на термодинамічні характеристики реакції одноелектронного окиснення ацидоаквакомплексів Mn2+, які визначають базовий рівень енергоефективності процесу електрохімічного синтезу MnO2. Показано, що монодентатні аніонні форми малеїнової (НМ–) та фумарової (HF–) кислот не мають будь-яких переваг відносно аніонів монокарбонових кислот, зокрема, – ацетат-йонів. Навіть навпаки, утворення водневих зв’язків з внутрішньосферними молекулами води другою карбоксильною групою, яка не зв’язана з центральним атомом, суттєво погіршує ефективність впливу аніонів НМ– i HF– на стадію вилучення електрона з комплексів [Mn2+(L)(H2O)5]. Величина стандартного редокс-потенціалу E0(Mn2+/Mn3+) йонних систем з однозарядними аніонами малеїнової і фумарової кислот становить 1.05 В і 0.99 В відповідно, що значно перевищує E0(Mn2+/Mn3+) ацетатних комплексів (0.66 В), наразі рекомендованих до практичного використання. Присутність у внутрішній координаційній сфері ацидоаквакомплексів Mn2+ бідентатно зв’язаного двозарядного аніона малеїнової кислоти зменшує E0(Mn2+/Mn3+) до 0.32 В, а це вдвічі менше, ніж в ацетатному електроліті. Перспективність малеїнатних електролітів посилюється також здатністю ненасичених аніонів М2– каталізувати стадію диспропорціонування комплексів Mn3+.
... Li et al. synthesized three-dimensional composites for nitrite detection using graphene [53], AuNPs, MnO 2 and carbon nanotubes. In this 3D composite, Gr/CNTs form a three-dimensional high conductivity network for fast electron transport, mass diffusion and structural stability. ...
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.
... Manganese oxides (MnO x ) have great application prospects in electrochemical sensors, due to their unique characteristics involving low cost, abundance, variable valences, and excellent electrochemical properties. MnO x /Gr composites such as MnO 2 /GO, 102 3D Au NPs/MnO 2 /Gr/CNT, 101 and Mn 3 O 4 /GO 103 exhibited obvious synergistic electrocatalytic effect toward nitrite oxidation, which could improve the amperometric response of nitrite and detection ability greatly. These MnO x /Gr composites decorated screen-printed electrode or GCE could detect nitrite at tens of nanomolar level. ...
Nitrite (NO2−) has been extensively applied in agricultural and industrial products and is often found in various foodstuff, tap water, biological samples and environmental systems. However, NO2− as a toxic contaminant probably threaten the human health by producing highly carcinogenic N-nitrosamines. Compared with the traditional analytical techniques, electroanalytical method has considerable advantages such as cost-effective, rapidness, facile operation, and easy miniaturization. Graphene nanocomposites have significant synergistic electrocatalytic effect toward the nitrite redox, which could eventually amplify the electrochemical response signals, and improve the selectivity, sensitivity, and practicability for the nitrite detection in various real samples. The recent developments on graphene-based nitrite electrochemical sensors are reviewed from the view of sensing materials, including graphene, metal nanoparticle/graphene composites, nanostructured metal compound/graphene composites, polymer/graphene composites, MOF/graphene composites, enzyme/graphene composites, MWCNT/graphene composites, and electron mediator/graphene composites. Moreover, the sensing performances including detection ranges, limit of detection (LOD) and sensitivity are tabulated. Finally, the major drawbacks, opportunities and challenges of graphene-based nitrite electrochemical sensors are also discussed.
... Manganese dioxide (MnO 2 ), a familiar metal oxide semiconductor has been utilized in the area of electrochemical sensing because of its abundance, high chemical stability, non-toxicity, electro-catalytic activity, and ease of synthesis [11,12]. Amongst several MnO 2 polymorphs [13e15], a-MnO 2 exhibits high catalytic activities due to the presence of double chains of edge-sharing MnO 6 octahedral [16,17]. ...
... Amongst several MnO 2 polymorphs [13e15], a-MnO 2 exhibits high catalytic activities due to the presence of double chains of edge-sharing MnO 6 octahedral [16,17]. However, in electrochemical sensing applications, the usage of pristine MnO 2 nanostructures is limited because of its poor electrical conductivity [11]. To enhance the electrical conductivity of MnO 2 and the sensitivity of MnO 2 based electrochemical sensors, integration of MnO 2 nanostructures with other appropriate nanomaterials has been taken up as an attractive possibility. ...
In this work, a novel composite constituted by α-MnO2 nanorods and hierarchical MoS2 microspheres is synthesized by a simple, template-cum-catalysis free two-step hydrothermal method for ultra-sensitive and selective detection of nitrite. The nitrite sensor (with optimal MnO2-MoS2 weight ratio) showed a limit of detection of 16 μM, the short response time (<5 s), outstanding selectivity, reproducibility, and sensitivity of 515.84 μA mM−1 cm−2 (R2 = 0.996) in the range of 100–800 μM in an optimized electrolytic pH of 4. The excellent sensing ability of the sensor can be attributed to the heterogeneous interface between two material constituents that results in unimpeded electrical transport due to the presence of intertwined nanosheets in MoS2 and 1D α-MnO2 nanorods, high number of active sites emanating from huge numbers of edges and defects in MoS2, high proportion of metallic (1T) phase than semiconducting (2H) phase in MoS2 and the combined effect of 1D α-MnO2 nanorods and MoS2 nanosheets. The fabricated sensor was also effectively assessed for the detection of nitrite in potable water. This novel, binder-free, MnO2-MoS2 composite based electrode material paves a new way for the development of simple, non-enzymatic and inexpensive electrochemical sensors for analytical applications.
A nanocomposite with highly dispersed AuNPs coated poly[2-(methacryloyloxy) ethyl] trimethylammonium chloride (PMTC) supported upon jute carbon (AuNPs-PMTC-JC) was prepared in aqueous medium for the selective determination of nitrite (NO 2 −) ions. Quaternary ammonium groups of PMTC in the nanocomposite results in a positive zeta potential, elevating the electrocatalytic properties of the modified electrode for negatively charged NO 2 − ions oxidation. The AuNPs-PMTC-JC composite was characterized using UV-vis, FESEM, TEM, SAED, XRD, EDS, CV and EIS. The LOD (S/N = 3) value for NO 2 − determination is 0.16 µM in the linear range of 0.4-706.5 µM based on the it current response, while it is 1.28 µM based on CV responses in the wide range of 10-1000 µM. The modified electrode is highly selective for NO 2 − ions and shows highly stable, and reproducible results. CV was used to analyze tap water spiked with NO 2 − and a recovery close to 100 % was observed.
In this study, an ultrasensitive electrochemical miRNA-21 biosensor is described. Manganese dioxide-gold nanoparticle (MnO2-Au NP) nanoconjugates were employed as sensing base materials, miRNA-21 was selected as a model analyte, and hybridization chain reaction (HCR) was employed to form long DNA concatemers using two different oligonucleotides with a complementary sequence. Thus, lots of biotin were loaded on DNA concatemers and one of them was labelled with biotin at its 3' terminal. The biosensor was designed as follows: a sulfhydryl-hairpin probe (HP) was first dropped on the surface of the glassy carbon electrode (GCE) modified with MnO2-Au NP nanoconjugates (HP/MnO2-AuNPs/GCE). After it was treated with MCH, the modified electrode was hybridized with miRNA-21, resulting in the loop of HP being opened to form a vertical structure. Subsequently, the modified electrode (miRNA-21/HP/MCH/MnO2-AuNPs/GCE) was incubated with DNA concatemers to form a sandwich structure of HP-miRNA-21-DNA concatemers on the modified electrode surface. Finally, the streptavidin-HRP conjugates were linked to the sandwich structure by specific recognition interaction between biotin and avidin. Differential pulse voltammetry (DPV) was used to measure the electrochemical response of the biosensor in the phosphate-buffered solution (0.10 M PBS, pH 7.0) containing 2.0 mM hydroquinone (HQ) and 1.8 mM H2O2. As a result, a larger reductive signal was obtained at a potential of -0.17 V (vs. SCE). Various experimental conditions were optimized, including solution pH, incubation time, and the amount of DNA concatemers. Under optimal conditions, the biosensor showed good sensing performance, such as a wide linear response range (0.1 fM and 100 nM) and low detection limit (0.063 fM, at S/N = 3). Meanwhile, the biosensor can discriminate single base matched miRNA-21, indicating that the biosensor had good selectivity.
The inclusion of methylmercury (CH3Hg+) in the environment and food chain has aroused wide concern due to its high neurotoxicity and cumulative effects. Herein, a highly sensitive electrochemical sensor based on manganese dioxide (MnO2)/gold nanoparticles (AuNPs) composites is fabricated for CH3Hg+ detection in food. The MnO2/AuNPs nanocomposites were synthesized in situ on the surface of a glassy carbon electrode by an electrodeposition method and were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The resulting MnO2/AuNPs modified electrode exhibited a large active surface area, enhanced conductivity and excellent electrocatalytic activity toward CH3Hg+ due to the synergistic effect of MnO2 and AuNPs. Square wave anodic stripping voltammetry (SWASV) was used as the sensing technique for CH3Hg+, and the stripping peak current showed a good linear relationship with CH3Hg+ concentration in the range of 0.7-15 μg L-1 with a detection limit of 0.051 μg L-1. Besides, the interference from Hg2+ associated with CH3Hg+ detection can be avoided by the addition of diethylene triamine pentaacetic acid (DTPA). The as-prepared sensor was applied to detect CH3Hg+ in various food samples with satisfactory recoveries, thus providing a promising platform for rapid screening of methylmercury residues.
Nitrite exists in the natural environment widely and is often used in human daily life. It causes varying degrees of harm to the water ecosystem and human health when the nitrite concentration exceeds the standard. Therefore, it is necessary to develop reliable nitrite detection methods. Compared with others, the electrochemical method for detecting nitrite has a series of advantages such as easier, lower cost, and faster analysis. The present research on the detection of nitrite by electrochemical methods focuses on the modification of electrodes. Numerous studies have shown that the addition of precious metals can increase the electronic transfer rate and the electrocatalytic active sites of the electrode, significantly improving the catalytic oxidation ability of the modified electrode for nitrite. This article reviews the research progress of precious metals (Au, Pd, Ag, Pt) in the preparation of nitrite electrochemical sensors in the past 10 years, including the application of single metal nanomaterials and bimetal or alloy materials. The performance and advantages of precious metal nanomaterials in the development of nitrite electrochemical sensors are discussed in detail. The challenges and application prospects of precious metal nanomaterials applied to nitrite electrochemical sensing platforms are proposed.
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