Colorimetric paper-based device by enzymatic reaction for detecting allopurinol in traditional medicine

The paper-based device for allopurinol detection was developed by an enzymatic reaction. The concept is that allopurinol will act by blocking the xanthine oxidase enzyme to produce uric acid and H2O2, resulting in a color change from purple to pale purple until it is colorless. The concept was proofed by spectrophotometry and was applied in four types of filter paper including Whatman Qualitative No. 1, No. 4, and No. 6, and Whatman 1 chromatography. The application of this system was observed using ImageJ analysis. The performance of the paper reveals that each Whatman has different characteristics with LOD and LOQ range were 1.62-2.24 ppm and 4.91-6.80 ppm, respectively. The stability study shows that all of the paper was stable for 3 days both at room temperature (around 24°C–26°C) and 4°C. The presence of another drug like paracetamol did not prevent allopurinol detection. The real traditional medicine sample was also analyzed to confirm the applicability of this paper, and the result showed good agreement with spectrophotometry data.