A 3D printed platform for sample treatment and detection of phytic acid in spinach leaves using a paper-based electrochemical biosensor

Phytic acid is a phosphorylated derivative of myo-inositol that is ubiquitous in plants and serves as the primary storage form of phosphorus. In human nutrition, phytic acid is considered an anti-nutrient because it chelates essential minerals, including calcium, iron, and zinc. This binding action reduces the bioavailability of these metals, highlighting the importance of monitoring phytic acid in food. Herein, we reported a novel and fully printed analytical platform for the quantification of phytic acid in spinach leaves. The integrated device comprises an electrochemical biosensor fabricated on office paper, combined with a custom-designed 3D printed grinder to accomplish the phytic acid extraction from ground spinach leaves using HCl. The solution extracted from the leaves containing phytic acid is transferred onto a filter pad in contact with the biosensor using a 3D printed funnel. The detection of phytic acid was made by using paper-based printed electrode modified with phytase enzyme. The enzymatic by-product, phosphate, reacts with ammonium molybdate preloaded on the filter pad to form an electroactive phosphomolybdic complex, which is then quantified at the working electrode surface using cyclic voltammetry. A linear range comprised between 1.8 and 50 mu M was observed, with a limit of detection of 0.5 mu M. Additionally, the biosensing platform exhibits high selectivity in the presence of potential interferents, including myo-inositol, ascorbic acid, and divalent metal cations. The accuracy of the biosensor was evaluated in spinach leaf samples, with percentage recoveries between 91 % and 109 %.