Colorimetric sensing of sinapic acid in mustard seeds based on DES-modified imprinted polymers and Cu(II) complexation

Accurate in-field quantification of antioxidants in food is essential for straightforward assessment of nutritional value. To this purpose, a MIP-based colorimetric assay based on the strong chromogenic complexation between the natural antioxidant sinapic acid and Cu(II) for direct detection in food samples was developed. MIPs were synthesized based on a bio-based DES-modified monomer and their specificity (IF = 2.61), composition, particle size distribution and thermal stability characterized. MIPs were integrated into colorimetric assay based on the displacement of visible sinapic acid-Cu(II) complex. The response was optimized considering target binding kinetics, polymer mass, complexation time and pH. The optimized assay demonstrates high sensitivity with LOD of 0.33 and 0.72 μM by UV-Vis and smartphone respectively, dual linear ranges and outstanding selectivity against structural analogues. Quantification of sinapic acid in mustard seeds correlated strongly with LC-MS results with recoveries ranging from 99.0 to 111.3%, underscoring the method's real-world applicability.