# Nitrite: From Application to Detection and Development
## 4 Biosensors
Furthermore, not only can it be seen to be comparable to traditional modified electrodes in terms of analytical properties, but the surface treatment of the 3D printed sensor also provided improved electrochemical performance for the direct determination of nitrite [90]. Nitrite detection in medicine has suffered from low sensitivity and cumbersome operation, which make it hard to meet the immediate detection needs of nitrite detection in precision medicine. Thus, researchers proposed a cyanocobalamin (VB12) bionic enzyme-assisted ion-selective amperometry biosensor based on a 3D porous conductive matrix (PCM). This can facilitate rapid and accurate nitrite monitoring in complex biofluids with results that are very close to those of commercial nitrite analyzers. Most importantly, it costs less than commercial nitrite analyzers and can be a useful tool in home healthcare realization by providing a possible tool [91]. Biosensors have been effectively used to determine the levels of the environmental pollutant nitrite. It is reported that a new type of electrochemical biosensors based on the MT-NBEB (metronidazolezole-treated biocathode), a novel electrochemical biosensor for nitrite-reducing bacteria successfully detected nitrite in five wastewaters [92]. [PERSON] et al. have conducted studies that have determined the nitrite content of wastewater. This provides a feasible direction for future biosensors to detect the corresponding specific substances [93]. Furthermore, it is worth mentioning that when detecting nitrite in the environment, biosensors based on microbial fuel cells (MFCs) are more likely to be in bioelectrochemical early warning devices [94]. Electro enzyme sensors have been a very promising nitrite detector, while the difficulty of its production and storage stability remains a difficult problem. The transformation of the process (Figure 7a-c) should be studied again, thus reducing the difficulty of manufacturing and further storage stability [95]. For example, the synthesis of a surfactant-free CuBr@Pt nanoparticles (CuBr@Pt NPs) contributed to the reduction of the electrocatalyst and the increase in the detection range. CuBr@Pt-15% has also shown a better behavior than previous work, which reveals the material is promising [96]. In this aspect of cost reduction, a wooden (bio)sensing device fabricated by a diode laser-induced graphitization provides an idea for related scientific work. It is worth mentioning that this sensor has a wide range of applicability [97]. Therefore, cost reductions and process improvements are important. Research in recent years has been moving toward multifunctionality and multi-analyte biosensor (Figure 7d). This is a trend for future development [98]. Continuous technological innovation has led to a shift from traditional enzyme-based sensors to cellular receptor-based biosensors. This shift has improved the sensitivity and specificity of detection and broadened their application in complex samples. Despite significant progress, biosensors remain challenges in nitrite detection. For instance, to meet the requirements of long-term monitoring, it is necessary to further enhance the stability and reusability of the sensors. Additionally, further research and optimization are required to enable the detection of extreme environmental conditions, such as high salinity or extreme pH conditions. The development of biosensors will continue to focus on achieving high sensitivity, high selectivity, low cost, and user-friendliness. Some of important methods described above and the involved detection information are shown in Table 1. Definitions and explanations corresponding to the abbreviations are shown in Table 2.  
From the several representative detection methods listed in the Table 1, it can be found that the fluorescence method based on BDP-OPD for the detection of nitrite concentration has a relatively low detection limit, which can be as low as 0.17 nM; that is to say, its detection sensitivity is higher.