Naked-eye sensing of phytic acid, one of the most abundant antinutrients, was achieved in 100% water medium using a charge transfer complex, composed of pyranine and methyl viologen. Since both the ingredients are commercially available, the design of such sensory systems needs zero synthetic effort, which essentially makes it economically viable. Only the physical mixture of both of these compounds showed a color-changing response from brown to yellow in the presence of phytic acid with a turn-on fluorescence response (LOD: 0.56 nM). The electrostatic interaction leads to charge pairing between phytic acid and methyl viologen, which releases free pyranine in solution. Considering its high sensitivity, low-cost test strips were developed for the on-site detection of phytic acid, even in remote locations. Additionally, estimation of phytic acid was achieved in grain samples with a sufficiently high accuracy, as evident from a sufficiently low relative standard deviation (<5%).