A novel electrochemical sensor based on nitrite-oxidizing bacteria for highly specific and sensitive detection of nitrites

Fast preparing bioelectrode with conductive bioink for nitrite detection in high sensitivity and stability

Electrochemically active biofilms (EABs) for nitrite detection have high specificity, rapid response, operational simplicity, and extended lifespan advantages. However, their scale production remains challenging due to time-consuming and uniform preparation. In this study, a novel approach was proposed to fast fabricate an EAB biosensor with a synthetic biofilm electrode for nitrite detection. The biofilm electrode was prepared by coating bioinks with varying conductive materials onto the surface of the graphite sheets, showing short incubation time and good reproducibility. Incorporating conductive materials into the bioinks remarkably enhanced the maximum voltage of the first cycle of bioelectrode incubation, with an increase of up to 633% for carbon nanofibers. The nitrite reduction current was amplified by a factor of 2.97, due to the enhancement of extracellular electron transfer (EET). The developed nitrite biosensor exhibited a detection range of 0.1-15 mg NO2--N L-1, with a high sensitivity of 610.8 μA mM-1 cm-2, and a stabilization operation time of at least 280 cycles. This study not only provided valuable insights into conductive materials for synthetic biofilms but also presented a practical approach for the rapid preparation, scale production, and optimization of highly sensitive and stable EAB sensors.

A Simultaneous Calibration and Detection Strategy for Electrochemical Sensing with High Accuracy in Complex Water

The electrochemical sensors loaded with nanomaterials have exhibited a great sensitivity. Nonetheless, the field detection for complex waterbodies can be affected by cross-sensitivity, environmental conditions such as temperature and pH value, as well as the relatively low reproducibility and stability of nanomaterials. In this paper, a simultaneous calibration and detection (SCD) strategy is proposed to introduce a simultaneous and precise calibration during field electrochemical detection, which is composed of a linear regression algorithm and a compact electrochemical sensor containing a series of identical sensing cells. This design can significantly mitigate cross-sensitivity in complex water and the inconsistency of sensing materials. Applied in the NO2- detection for practical waterbodies, the SCD strategy has exhibited a relative error of no more than 9.6% for the measurement compared to the results obtained by the standard Griess method and higher accuracy than the normal electrochemical method. The SCD strategy is independent of sensing materials, indicating that it can be widely applied to various detections by just switching the corresponding sensing material.

Technical Evaluation of a Paper-Based Electrochemical Strip to Measure Nitrite Ions in the Forensic Field

Nitrite is a compound used as a food additive for its preservative action and coloring capability, as well as an industrial agent for its antifreezing action and for preventing corrosion, and it is also used as a pharmaceutical in cyanide detoxification therapy. However, even recently, because of its high toxicity, it has been used as a murder and suicidal agent due to its affordability and ready availability. In this technical report, we describe an electrochemical paper-based device for selectively determining nitrite in complex biofluids, such as blood, cadaveric blood, vitreous humor, serum, plasma, and urine. The approach was validated in terms of the linearity of response, selectivity, and sensitivity, and the accuracy of the determination was verified by comparing the results with a chromatographic instrumental method. A linear response was observed in the micromolar range; the sensitivity of the method expressed as the limit of detection was 0.4 μM in buffer measurements. The simplicity of use, the portability of the device, and the performance shown make the approach suitable for detecting nitrite in complex biofluids, including contexts of forensic interest, such as murders or suicides in which nitrite is used as a toxic agent. Limits of detection of ca. 1, 2, 4, 5, 3, and 4 μM were obtained in vitreous humor, urine, serum and plasma, blood, and cadaveric blood, also highlighting a satisfactory accuracy comprised between 91 and 112%.

Recent Developments and Applications of Microbial Electrochemical Biosensors

This chapter provides a comprehensive overview of microbial electrochemical biosensors, which are a unique class of biosensors that utilize the metabolic activity of microorganisms to convert chemical signals into electrical signals. The principles and mechanisms of these biosensors are discussed, including the different types of microorganisms that can be used. The various applications of microbial electrochemical biosensors in fields such as environmental monitoring, medical diagnostics, and food safety are also explored. The chapter concludes with a discussion of future research directions and potential advancements in the field of microbial electrochemical biosensors.

Nitrite determination in food using electrochemical sensor based on self-assembled MWCNTs/AuNPs/poly-melamine nanocomposite

A nanocomposite of multi-walled carbon nanotubes/gold nanoparticles/poly-melamine (MWCNTs/AuNPs/PM) was designed using layer-by-layer self-assembled method on glassy carbon electrode (GCE) by electrochemical deposition to construct an electrochemical sensor for sensitive detection of nitrite. First, a layer of MWCNTs was modified on electrode, and then gold nanoparticles and melamine were in-situ polymerized onto MWCNTs through self-assembled technique to form GCE/MWCNTs/AuNPs/PM. MWCNTs have large specific surface area, which increased the number of gold nanoparticles deposited on MWCNTs. Meanwhile, the doping of gold nanoparticles also improved the polymerization of melamine. The synergistic interaction of nanocomposite further improved the catalytic effect on nitrite. Under optimized conditions, the detection range for nitrite was from 0.4 to 1475 μM and the detection limit was 0.041 μM. Through the detection of nitrite in food samples, the recovery rates were from 93.16% to 108.68%. Therefore, the method can be used as a practical platform for nitrite detection in food.

Cobalt-Nitrogen Co-Doped Carbon as Highly Efficient Oxidase Mimics for Colorimetric Assay of Nitrite

Transition metal-N-doped carbon has been demonstrated to mimic natural enzyme activity; in this study, cobalt-nitrogen co-doped carbon (Co-N-C) nanomaterial was developed, and it could be an oxidase mimic. Firstly, Co-N-C with oxidase-like activity boosts the chromogenic reaction of 3,3',5,5'-tetramethylbenzidine (TMB) to produce the oxidized TMB (oxTMB). And the aromatic primary amino group of oxTMB reacts with nitrite (NO₂^-) to form diazo groups. Based on this background, we developed a cascade system of a Co-N-C-catalyzed oxidation reaction and a diazotization reaction for nitrite determination. The low detection limit (0.039 μM) indicates that Co-N-C is superior compared with the vast majority of previously reported nitrite assays. This study not only provides a novel nanozyme with sufficiently dispersed active sites, but it also further applies it to the determination of nitrite, which is expected to expand the application of nanozymes in colorimetric analysis.

Selective determination of nitrite in water and food samples using zirconium oxide (ZrO2)@MWCNTs modified screen printed electrode

Nitrite ions are being used in different forms as food preservatives acting as flavor enhancers or coloring agents for food products. However, continuous ingestion of nitrite may have severe health implications due to its mutagenic and carcinogenic effects. Thus, this study constructed an electrochemical assay using disposable nano-sensor chip ZrO₂@MWCNTs screen printed electrodes (SPE) for the rapid, selective, and sensitive determination of nitrite in food and water samples. As a sensing platform, the use of nanomaterials, including metal oxide nanostructures and carbon nanotubes, exhibited a superior electrocatalytic activity and conductivity. Morphological, structural, and electrochemical analyses were performed using electron microscopy (SEM and TEM), Fourier-transform infrared (FTIR) spectroscopy, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and chronoamperometry (CA). Accordingly, a wide dynamic linear range (5.0 μM to 100 μM) was obtained with a limit of detection of 0.94 μM by the chronoamperometric technique. In addition, the sensor's selectivity was tested when several non-target species were exposed to the sensor chips while no obvious electrochemical signals were generated when the nitrite ions were not present. Eventually, real food and water sample analysis was conducted, and a high recovery was achieved.

Reduced graphene oxide-wrapped La0·8Sr0·2MnO3 microspheres sensing electrode for highly sensitive nitrite detection

An electrochemical nitrite sensor based on perovskite oxides La_0·8Sr_0·2MnO₃ (LSM) microspheres-decorated reduced graphene oxide (rGO) composite was presented to take the merit of the excellent electrocatalytic activity of the LSM and the large surface area of rGO. The content of rGO has been finely adjusted and the electrochemical sensor employing 15 wt% rGO has shown an ultralow nitrite detection limit of 0.016 μM and a high sensitivity of 0.041 μA μM^-1 cm^-2 and 0.039 μA μM^-1 cm^-2 in the range of 2-100 and 100-5000 μM, respectively. In addition, the proposed electrode shows good selectivity, reproducibility and stability, suitable for detection of nitrite at various pH values. The sensor was used to determine the nitrite level in environmental water samples with acceptable relative error, demonstrating its feasibility for practical environmental monitoring.

Binary organic-inorganic nanocomposite of polyaniline-MnO2 for non-enzymatic electrochemical detection of environmental pollutant nitrite

Due to wide usage as nitrogen fertilizer in agriculture and food additive in industry, nitrite, as one of inorganic environmental pollutants, could cause detrimental effects to the ecological environment. Therefore, accurate, sensitive and rapid detection of nitrite is necessary. In this work, binary hybrid polyaniline-MnO₂ organic-inorganic nanocomposite is prepared chemically and characterized via X-ray diffraction spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Polyaniline-MnO₂ organic-inorganic nanocomposite serves as excellent electrode modifier for electrochemical sensing of nitrite by two modes of cyclic voltammetry and chronoamperometry, achieving broad linear ranges and low limits of detection for both methods. Moreover, the organic-inorganic nanocomposite displays satisfactory sensing performance in real water sample analysis. Amine and imino groups of polyaniline contribute to the better adsorption behavior of nitrite onto the nanocomposite, which improves the nanocomposite's sensing performance. In summary, the synergistic effects between polyaniline and MnO₂ is taken advantaged in the nanocomposite for effective electrochemical sensor development.