Hydrogel microsphere-based portable sensor for colorimetric detection of nitrite in food with matrix influence-eliminated effect

Abstract

Rapid and accurate nitrite ions (NO2−) detection is necessary to ensure food safety. Herein, a new portable method for detecting NO2− using hydrogel microspheres is proposed. Specifically, N-(1-naphthyl) ethylenediamine (NED) was immobilized on sodium alginate (SA) to obtain the SA-NED conjugate via covalent linking. The SA-NED microspheres were prepared in a Ca2+ solution using an extrusion strategy based on the strong chelation between SA and Ca2+. The SA-NED microspheres exhibited superior adsorption capacity for NO2−, which agrees with the Langmuir isotherm model. Then, based on the Griess reaction, a microsphere-based colorimetric sensor was developed for rapid, quantitative, and on-site NO2− detection via a smartphone-based sensing platform. The entire detection procedure can be completed within 35 min. The microsphere-based sensor exhibited a detection limit of 0.02 μg mL–1 with recoveries ranging from 89.7% to 104.8% in different food samples. Moreover, the microsphere-based sensor showed good tolerance to the complex food matrix. Water and milk samples could be directly measured without pretreatment, and pickles and sausages only required simple homogenization before measurements. Our study provides an effective approach for rapid and on-site monitoring of NO2−.