Development of a colorimetric sensor utilizing itaconic acid-mediated Griess reaction for sensitive detection of nitrite and nitrate in agricultural products

Abstract

The presence of nitrite (NO₂⁻) and nitrate (NO₃⁻) in agricultural products causes significant health risks, highlighting the need for sensitive and selective detection methods. In this study, we developed a colorimetric sensor based on the Griess assay under organic acidic conditions to detect these compounds, where the formation of a pink color suggests the presence of NO₂⁻ and NO₃⁻. We synthesized 4-aminobenzenesulfonohydrazide (C) and 2-(2-(naphthalen-1-ylamino)ethoxy)ethanol (E). N-(1-Naphthyl)ethylenediamine dihydrochloride (F), and commercially available organic dicarboxylic acid “itaconic acid” was used for the investigation. Two chemosensors were designed, one with compounds C and E (known as CE) and another containing compounds C and F (known as CF). These two chemosensors formed pink azo–dyes in the presence of NO₂⁻ in acidic conditions (using itaconic acid). The sensing ability was evaluated using UV-spectroscopy, and different sensitivity was demonstrated for the analyte (NO₂⁻). The binding constants for sensors CE and CF were determined to be 5.06 × 10⁻⁴ M⁻¹ and 16.7 × 10⁻⁴ M⁻¹, respectively, based on the Benesi–Hildebrand (B–H) plot. Under the optimized conditions, chemosensor CE showed a linear range of 0.005–0.421 mM with a detection limit (LOD) of 0.62 mM, while chemosensor CF exhibited a range of 0.01–0.453 mM with a LOD of 0.52 mM. A smartphone-assisted NO₂⁻ sensing device was designed based on the RGB value of the generated pink color, which demonstrates the sensor's ability towards real-time detection of NO₂⁻ ions. Additionally, the system was extended to paper-based test strips for on-site detection. Our proposed sensor system is also capable of detecting NO₃⁻ by using Zn dust as a reducing agent to convert NO₃⁻ to NO₂⁻. Real sample testing demonstrated excellent recovery, confirming the potential of this colorimetric sensor for NO₂⁻ and NO₃⁻ detection in agricultural products.