Zein/MnO2 Nanosheet Composites Integrated with a Smartphone for Colorimetric Sensors for On-Site Detection of Adulterants in Milk

Abstract

Milk and its derivatives are essential sources of nutrients for humans. However, the widespread adulteration of milk poses a significant challenge for ensuring the safety and integrity of these products. Here, a zein/manganese dioxide nanosheet (MnO2 NS) composite-based colorimetric sensor integrated with a smartphone platform was developed for on-site and quantitative analysis of hydrogen peroxide (H2O2) and lactic acid, two common adulterants in milk samples. Sensing platforms were fabricated by spraying composite solutions onto various cost-effective and environmentally friendly substrates, including filter paper and masking tape, using a simple airbrush system. These platforms displayed remarkable sensitivity and suitable limit of detection (LOD) of 7.2 × 10-4 mol L-1 for H2O2 and 7.5 × 10-4 mol L-1 for lactic acid, respectively. These concentrations fall within the ranges established by diverse international regulatory bodies responsible for quality assurance protocols. Therefore, the dual detection of H2O2 and lactic acid in milk samples was successfully achieved in a rapid and cost-effective way, which opens possibilities for the design and implementation of field-deployable sensors for food safety surveillance and quality control.