A Low-Cost Paper-Based Colorimetric Strip for Rapid and On-Site Detection of Phytochemicals

Abstract

Background: Phytochemicals are plant-derived compounds widely investigated in pharmaceutical development, food-quality assessment, and medicinal-plant research. Conventional qualitative screening is useful but is commonly performed in separate test tubes and can be laborious when multiple samples are evaluated. This study developed a simple paper-based colorimetric strip and compared its qualitative responses with the corresponding conventional procedures. Methods: Wax-defined reaction zones were prepared on chromatography paper and used for qualitative detection of tannins, carbohydrates, alkaloids, flavonoids, saponins, anthraquinones, steroids, glycosides, reducing sugars, and volatile oils in selected medicinal-plant extracts. The strip classifications were compared directly with standard procedures. Additional analyses included extraction yield, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity using FRAP, ABTS, thiocyanate, and DPPH assays. Results: For the samples evaluated, the paper strips reproduced the positive or negative classifications obtained with the corresponding conventional procedures. In Limnophila aromatica, extraction yield was highest with 100% methanol (26.06 ± 1.64%), whereas TPC and TFC were highest with 100% ethanol (40.50 ± 0.88 mg GAE/g and 31.11 ± 0.43 mg QCE/g, respectively). TPC and TFC were strongly correlated (R = 0.923). The tested medicinal-plant extracts showed solvent-dependent FRAP and ABTS responses, and aqueous Cetraria islandica showed strong antioxidant activity in the thiocyanate and DPPH assays. Conclusion: The paper-based format provides a rapid, inexpensive, and visually interpretable approach for qualitative phytochemical screening. The findings support further optimization of reagent stability, standardized color interpretation, analytical validation, and image-assisted readout before wider routine application.