Construction of a highly sensitive non-enzymatic nitrite sensor using electrochemically reduced holey graphene

A dual-mode nanoprobe based on silicon nanoparticles and Fe(II)-phenanthroline for the colorimetric and fluorescence determination of nitrite

A fluorometric and colorimetric dual-modal nanoprobe (denoted as Fe²⁺-Phen/SiNPs) has been developed for selective and sensitive determination of nitrite (NO₂^-). The mechanism is based on fluorescence quenching between silicon nanoparticles (SiNPs) and Fe(II)-phenanthroline complex (Fe²⁺-Phen) via inner filter effect and redox. With the addition of increasing NO₂^-, Fe²⁺ is oxidized to Fe³⁺, recovering the fluorescence of SiNPs. Meanwhile, the color of the system gradually changes from orange-red to colorless, which enables colorimetric measurement. The NO₂^- concentration shows a wide linear relationship with fluorescence intensity from 0.1 to 1.0 mM (R² = 0.9955) with a detection limit of 2.4 μM in the fluorometric method (excitation wavelength: 380 nm). By contrast, the linear range of the colorimetric method ranges from 0.01 to 0.35 mM (R² = 0.9953) with a limit of detection of 6.8 μM (proposed selective absorbance: 510 nm). The probe has been successfully applied to nitrite determination in water, salted vegetables, and hams demonstrating broad application prospects for the determination of nitrite in complicated matrices.

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%).

Highly Sensitive and Interference-Free Electrochemical Nitrite Detection in a 3D Printed Miniaturized Device

3D printing has a significant impact on various applications as it facilitates greater control over the designed shapes, leads to rapid prototyping and mass production with transferable designs at a lower cost. These attributes provide great versatility and thus make the devices industry-friendly. Herein, we demonstrate a simple and disposable 3D printed device, fabricated in single-step, as an electrochemical nitrite sensor using commercially available carbon loaded polylactic acid (PLA) filament. Nitrite, usually ingested through water and food, can be harmful when taken in excess. Thus, its efficient and accurate on-site detection becomes imperative. The device showed appreciable sensitivity and good selectivity towards nitrite having a limit-of-detection (LOD) of [Formula: see text]. Furthermore, the device has been shown to monitor nitrite in real soil and water samples with appreciable recovery values. Eventually, the device is capable to be multiplexed with varying soil parameters.

A dual-modal fluorometric and colorimetric nanoprobe based on graphitic carbon nitrite quantum dots and Fe (II)-bathophenanthroline complex for detection of nitrite in sausage and water

A fluorometric and colorimetric dual-mode sensing platform based on graphitic carbon nitrite quantum dots (g-CNQDs) and Fe (II)-bathophenanthroline complex (BPS-Fe²⁺) was designed to the sensitive detection of nitrite (NO₂^-) in sausage and water. In this system, the fluorescence of g-CNQDs was quenched by BPS-Fe²⁺ complex due to the inner filter effect (IFE). When NO₂^- was present, Fe²⁺ was oxidized by nitrite to form BPS-Fe³⁺ complex with BPS, leading to the recovery of the fluorescence from g-CNQDs. Therefore, we constructed a "turn-off-on" fluorescence probe for detection of NO₂^-. Moreover, with the increase of NO₂^- concentration, the color of the solution changed from red to colorless, so the UV-vis measurements and on-site visual detection were realized. The method is capable of detecting NO₂^- in the concentration range of 2.32-34.8 μM with good selectivity and high sensitivity. In addition, the method has the potential to determine NO₂^- in water samples and sausage samples.

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.

Surface Engineering of Carbon Fiber Paper toward Exceptionally High-Performance and Stable Electrochemical Nitrite Sensing

In this work, we introduce our recent finding that the carbon fiber paper (CFP) treated by simple air annealing (OCFP) could be used for exceptionally high-performance electrochemical nitrite sensing. The air-annealing process endows the pristine CFP with higher defective edge/plane sites, more oxygen-containing functional groups, higher roughness, and improved wettability. The electrochemical studies show that the OCFP exhibits excellent sensing performance for nitrite, with an ultralow determination limit of 0.1 μM and a detection limit of 0.07 μM, an ultrawide linear determination range of 0.1-3838.5 μM, a fast current response of 1 s, and a high sensitivity of 930.4 μA mM^-1 cm^-2. These performance values are comparable or even superior to those for most reported noble- or transition-metal-based advanced nitrite sensors. Besides, this electrode also presents satisfactory stability, reproducibility, and feasibility of nitrite sensing in food samples. As an ideal monolithic and metal-free catalyst with ultrahigh and stable detection performance, the OCFP has a high potential to be integrated into next-generation electrochemical sensing devices.

A review of the advanced developments of electrochemical sensors for the detection of toxic and bioactive molecules

The recent developments made regarding the novel, cost-effective, and environmentally friendly nanocatalysts for the electrochemical sensing of biomolecules, pesticides, nitro compounds and heavy metal ions are discussed in this review article.

Hyaluronate-Functionalized Graphene for Label-Free Electrochemical Cytosensing

Electrochemical sensors for early tumor cell detection are currently an important area of research, as this special region directly improves the efficiency of cancer treatment. Functional graphene is a promising alternative for selective recognition and capture of target cancer cells. In our work, an effective cytosensor of hyaluronate-functionalized graphene (HG) was prepared through chemical reduction of graphene oxide. The as-prepared HG nanostructures were characterized with Fourier transform infrared spectroscopy and transmission electron microscopy coupled with cyclic voltammograms and electrochemical impedance spectroscopy, respectively. The self-assembly of HG with ethylene diamine, followed by sodium hyaluronate, enabled the fabrication of a label-free electrochemical impedance spectroscopy cytosensor with high stability and biocompatibility. Finally, the proposed cytosensor exhibited satisfying electrochemical behavior and cell-capture capacity for human colorectal cancer cells HCT-116, and also displayed a wide linear range, from 5.0 × 10² cells∙mL-1 to 5.0 × 10⁶ cells∙mL-1, and a low detection limit of 100 cells∙mL-1 (S/N = 3) for quantification. This work paves the way for graphene applications in electrochemical cytosensing and other bioassays.