Selective extraction of maleic hydrazide in foods using magnetic molecularly imprinted polymers and colorimetric detection via smartphone.

Maleic hydrazide (MH) is a plant growth regulator, herbicide, and sprout inhibitor used to improve the growth and quality of certain vegetables and fruits, unfortunately, MH has genotoxic and carcinogenic effects; thus, MH residues in food need to be analyzed. Herein, magnetic molecularly imprinted polymers (MagMIP) were synthesized by radical polymerization in just 30 min using a microwave for rapid and selective extraction of MH. The colorimetric detection of MH using the immobilized Folin Ciocalteau's reagent (FCR) on 96-well microplate via smartphone sensor exhibits useful sensitivity for MH with a limit of detection (LOD = 0.6 ppm) which is far lower than the maximum residue limits (higher than 5 ppm). The immobilized FCR was stored dry at two different storage conditions at +4 °C and room temperature without losing its performance over six months. The coupling MagMIP-extraction/clean-up and smartphone determination were tested towards food samples (i.e., potatoes, and carrots), obtaining good recovery (79-96 %), high repeatability (RSD 4.5 %; n = 10), and high selectivity for MH determination.