Affordable paper-based strips: A breakthrough in phenol detection for water samples

Phenols are pollutants prevalent in industries such as pharmaceuticals, pulp and paper, petrochemicals, coal, agriculture, and plastics, often released untreated. Detecting and measuring phenols is essential, typically achieved through spectrophotometry, chromatography, electrochemical, and immunochemical biosensors. These methods, however, are expensive and require skilled operators. Thus, developing an efficient, user-friendly, affordable, and environmentally sustainable method is crucial. This study introduces inexpensive colorimetric paper-based sensor strips for detecting phenolic contaminants in water samples using the Folin–Ciocalteu (FC) reagent as the chromogenic probe. Whatman #1 and #4 filter papers were used to construct the prototypes, WFP-1 and WFP-4. The limit of detection (LOD) for five phenols (pyrogallol, gallic acid, resorcinol, vanillin, and hydroquinone) was 6.01 mg/L and 9.66 mg/L, respectively. ImageJ software analyzed the color intensity of each phenol, revealing a detection order of pyrogallol > resorcinol > gallic acid > hydroquinone > vanillin, attributed to the reactivity of phenolic hydroxyl groups with FC reagent. Recovery tests with water samples containing resorcinol showed WFP-1 sensors achieving 90 %–98.50 % recovery and WFP-4 sensors achieving 97.50 %–101.69 % recovery. These results highlight the sensor's simplicity, cost-effectiveness, and potential for widespread application in phenolic contaminant detection and quantification.