1 Introduction
Among nitrogen-containing inorganic ions, three ions, i.e., NH4+, NO2−, and NO3−, in the environment are essential nutrients for the growth of plants and in the food industry (Flores and Toldrá, 2021). Sodium and potassium salts of nitrite and nitrate have long been used in the meat industry as food preservatives. They work by prolonging the shelf life of processed meat, giving it a better taste, and fixing its color (Majou and Christieans, 2018). Nitrite is more frequently detected in groundwater than in surface water. Livestock waste, artificial fertilizers, and erosion of natural deposits are its main sources (Greer et al., 2005). The Environmental Protection Agency (EPA) of the United States has defined the maximum contamination level (MCL) of nitrite in drinking water and food products to be 21.7 mM (Ozdestan and Uren, 2010) and 125 mg/kg, respectively (Singh et al., 2019). The excess intake of NO2− reported different medical issues, such as birth defects and methemoglobinemia, commonly known as blue baby syndrome (Brender, 2020), affecting the nervous system (Wang et al., 2016), spleen, and kidneys, and also causing esophageal cancer (Ozdestan and Uren, 2010). Due to the strong reactivity of nitrite, rapid and accurate analytical techniques are required to reduce human health risks. It is vital to identify and monitor the NO2− concentration of food products and environmental, organic, and inorganic samples.
Carboxylic acids are the most common organic compounds and belong to the class of green solvents, possessing no or low toxicity and being relatively inexpensive (Teles et al., 2017). They have significant applications in the petrochemical, food, dye, and stabilizer industries, as well as in nanotechnology (Odedairo et al., 2013). In addition to stabilizing nanoparticles, they can also affect the solubility, reactivity, size, and shape of nanoparticles, as well as the surface modification of nanostructures (Sarkar et al., 2005). Carboxylic acids are used as stabilizers because they can easily coordinate with the surface of nanoparticles (Hosseini-Monfared et al., 2015). Moreover, the functionalization of nanoparticles with the carboxylic group produces more active sites for sensing (Sáenz-Galindo et al., 2018).
Numerous methods have been employed to detect nitrite, such as chromatographic (Lim et al., 2022), chemiluminescence (Basu et al., 2022), electroanalytical (Gao et al., 2020), and spectrophotometric methods (Karrat et al., 2022). However, the aforementioned analytical techniques have some limitations when used on a daily basis for nitrite detection. Due to complicated sample preparation procedures, expensive and complicated instruments, and highly trained operators, these techniques have become undesirable in laboratories, especially with limited financial resources. Therefore, it is desirable to develop such techniques, which could be more efficient, more fruitful, and less expensive. Usually, scientists try to translate the analyte signals into colors, which can be easily detected with the naked eye. A very simple and cheap colorimetric sensor is particularly attractive for nitrite detection in food and water samples (Zhang et al., 2012). Simple, cost-effective design, and quick response are the cornerstones of colorimetric sensors (Nishan et al., 2021a). Prior to becoming a bulky and complicated device, a sensor’s various functional components, such as the transducer, recycling unit, and discovery unit, were crucial to a delayed detector response (Cheng et al., 2014). Recently, electrocatalyst materials have played important roles in colorimetric sensors due to their desirable characteristics, including strong surface plasmon resonance and distance-dependent optical properties, as well as the fact that their performance events may be seen with the naked eye (Nishan et al., 2021b). Currently, a number of electrocatalytic materials, including metallic oxides, carbon nanomaterials, and metal nanomaterials, have been employed to create nitrite sensors (Lin et al., 2011; Wang et al., 2014).
For the colorimetric detection of nitrite, various nanomaterials have been reported, such as Au NPs-rGO (Amanulla et al., 2017), Ag/Au NPs (Li et al., 2015), MTT-G NPs (Nam et al., 2014), Au NPs (Ye et al., 2015), Er2O3 NPs@RGO (Rajaji et al., 2019), Fe3O4@SiO2/Au magnetic nanoparticles (Chen et al., 2016), shell-isolated nanoparticles (Zhang et al., 2013), Pd NPs (Pourreza and Abdollahzadeh, 2019), Ag NPs (Kumar and Anthony, 2014), Fe3O4/MWCNTs (Qu et al., 2015), AuNP-CeO2 NP@GO (Adegoke et al., 2021), and MnO2 NPs (Nishan et al., 2022). Compared to different inorganic oxides, such as V2O5, NiO, and Co3O4, copper oxide nanoparticles (CuO NPs) have gained much attention because of their low cost, availability, and lack of toxicity (Jaiswal et al., 2017). CuO NPs are exceptional materials for the optical detection of nitrite due to their surface plasmon properties.
The current research reports the drug-mediated production of CuO nanostructures via using the Augmentin drug as a reducing and stabilizing agent. It is the first study on the production of CuO NPs via drug-mediated means without the need for any additional reduction agents. Furthermore, to overcome the problem of agglomeration of the nanoparticles and the availability of surface area for reactions, acetic acid has been employed as a deagglomerating and capping agent. The platform of acetic acid-capped CuO NPs has been successfully used as a colorimetric sensor for the detection of nitrite. Comprehensive optimization of various parameters, such as loading of nanoparticles, pH, reaction time, and concentration of nitrite, was carried out. The sensing platform was also successfully applied to real samples.
