The present work addresses the need for a simple, cost-effective, and portable tool to detect specific nucleic acid sequences. Current nucleic acid detection methods are often complex and expensive, limiting their applicability in decentralized settings. The proposed approach utilizes a colorimetric, paper-based assay employing the sequence-specific cyanine dye DiSC₂(5) without the need for surface modification or sophisticated labelling systems. This portable device integrates a 3D-printed dark chamber with smartphone-based detection, allowing for image capture and analysis with the open-access ImageJ tool. A TATA box sequence, characterized by alternating A/T base pairs, was used as the model target in this study. The target was stored on a paper-based disk and subsequently detected through the blue color produced by the binding of DiSC₂(5). The assay effectively identifies TATA sequences, with the intensity of the blue color being directly correlated to target concentration. Specificity studies confirmed the assay's capability to differentiate between alternating and random A/T-containing sequences, highlighting its reliability. Furthermore, applications to synthetic PCR products demonstrate a limit of detection down to 10 nM. These results suggest that this portable, all-in-one, and low-cost platform could be effectively used for real-world samples, offering a promising alternative to traditional nucleic acid detection methods in point-of-care diagnostics and resource-limited settings.