# Nitrite: From Application to Detection and Development
## 5 Electrochemical Sensors  
Electrochemical sensor is a kind of instrument that uses the electrochemical properties of the measured substance to convert its chemical quantity into electrical quantity. With high sensitivity and selectivity, it is widely used in detecting the content of nitrite. Its specific working principle is to use the material and nitrite to interact; the redox reaction occurs, producing an electrochemical active substance. This active substance can be converted into the detected electrochemical signals, and nitrite can be oxidized directly on the surface of the electrode. According to different output signals, electrochemical sensors can be classified as potentiometric, voltamric, impedance, and other sensors. There are also many different methods, such as differential pulse voltammetry, amperometry, etc. However, in the actual measurement of nitrite, it is the material used in the electrochemical sensor that affects the accuracy to a great extent. The applications of different nanomaterials in the field of electrode materials in recent years has been reviewed, providing a reference for the screening and application of suitable electrode materials for nitrite electrochemical detection sensors in the future. The nanomaterials are classified into three categories, namely, precious metal materials, carbon materials, and nanocomposites. Among the three, nanocomposites are nowadays widely used in the fabrication of chemical sensors for nitrite, which has a very good development prospect. The detection range and limit of detection of different electrodes for the determination of nitrite are shown in Table 3. Definitions and explanations corresponding to the abbreviations are shown in Table 4.  
Some of the advances in metal nanomaterials include the development by researchers of an easily produced bimetallic composite of palladium and silver bimetallic nanopar \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Detection Methods** & **Material or Equipment** & **Detection Range** & **Detection Limit** & **References** \\ \hline Colorimetric/Fluorescence & r-CDs (dual-mode detection) & & 0.193 \(\mu\)M (colorimetric) & [44] \\ Fluorescence & g-CNQDs/BPS-Fe2\({}^{+}\) & 2.32–34.8 \(\mu\)M & & [58] \\ Fluorescence & Methanobactin-AuNPs & 0–8.0 \(\mu\)M & 16.21 nM & [70] \\ Fluorescence & BDP-OPD & 0–4.0 \(\mu\)M & 0.17 nM & [75] \\ Biosensors & NrfA from S. oneidensis & 1–140 \(\mu\)M & 0.59 \(\mu\)M & [91] \\  & LE antibody/Avidin/EDC- & 0.2–9.5; & & \\ Biosensors & NHS/PEDOT-COOH/GCE & 10.1–89.7; & 0.2 \(\mu\)M & [94] \\  & & 90.3–590 \(\mu\)M & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: \(Cont.\) \begin{table}
\begin{tabular}{c c} \hline \hline
**Nomenclature** & **Definitions and Explanations** \\ \hline
3-Aph/ADC & 3-aminophenylalanine/antibody coupled drug, \\  & a form of drug formed by linking 3-aminophenylalanine to an antibody \\ PAD & Paper-based analytical device \\ UV–Vis & Ultraviolet-Visible Spectroscopy \\ CuO NPs & copper oxide nanoparticles \\ g-CNQDs/BPS-Fe2\({}^{+}\) & graphitic carbon nitrite quantum dots/Fe (II)-bathophenanthroline complex \\ BDP-OPD & practical sensing platform based on 8-(o-phenylenediamine)-boron dipyrromethene \\ NrfA & a pentahaem, C2-symmetric nitrite reductase with crystal size around 5.15 \(\times\) 9.59 \(\times\) 22.38 nm \\ _S. oneidensis_ & Shewanella oneidensis, a Gram-negative bacterium \\ LE antibody & Leukocyte esterase antibody, which is an antibody that binds specifically to leukocyte esterase \\ Avidin & anti-biotin protein, a protein that binds specifically to biotin \\ EDC-NHS & 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and N-hydroxysuccinimide, commonly used in \\  & biocoupling reactions \\ PEDOT-COOH & Poly(3,4-ethylenedioxythiophene)-carboxylic acid, a conductive polymer \\ GCE & Glassy carbon electrode, a commonly used electrode material \\ \hline \hline \end{tabular}
\end{table}