Hydrogen peroxide responsive smart colorimetric indicator based on titanium oxysulfate/guar gum coating for monitoring the freshness of milk

Abstract

Food adulteration, especially in most consumed beverages like milk, severely threatens human health and the economy. Most of the detection methodologies are expensive and limited to laboratory scale. Herein, we present a printable, flexible, and efficient colorimetric indicator for the rapid detection of hydrogen peroxide (H2O2) in milk using titanium oxysulfate (TiOSO4), a stable and readily available inorganic compound. The fabricated indicator employs a printable reagent solution containing varying concentrations of TiOSO4 and guar gum as a binder. The solution is screen-printed onto a paper substrate, resulting in a flexible indicator. This indicator can potentially detect H2O2 as low as 200 ppm. The color change (ΔE) is evident to the naked eye and is valued at 6.31 ± 2.59 and 65.66 ± 0.39 for H2O2 concentrations of 0.02% and 5.00%, respectively. CIELAB parameters exhibit a proportional relationship with H2O2 concentration. The viscosity shown by the prepared reagent paste at lower and higher Newtonian regions is 231 Pa s and 0.35 Pa s, respectively, thereby enhancing the quality of printing. Field emission electron microscopy (FESEM), and atomic force microscopy (AFM), confirm the stability, uniformity, and reduced roughness of the printed indicators. The roughness exhibited by the unprinted and printed paper substrate is 15.90 nm and 0.76 nm, respectively. Compared to the unprinted paper substrate, the maximum roughness has been reduced by∼93%. Rub resistance exhibited by the indicator is quantified at 1.00 ± 0.03, indicating the durability of the indicators. The TiOSO4-based colorimetric indicator provides a simple, inexpensive, and rapid method for the detection of H2O2 in milk, addressing the challenges associated with current detection techniques.