Selective Colorimetric Determination of Phenylephrine Using a Prussian Blue Nanoparticle-Modified Paper-Based Sensor

Phenylephrine is a widely used α1-adrenergic agonist employed as a decongestant and vasoconstrictor in numerous pharmaceutical formulations. Considering its widespread use and its relevance in biological monitoring and anti-doping control, the development of rapid, sensitive, and reliable analytical methods for its determination has attracted significant attention. A paper-based colorimetric sensor based on Prussian blue nanoparticles was developed for the determination of phenylephrine. Prussian blue nanoparticles were synthesized by the precipitation method, and their structural, morphological, and surface properties were systematically characterized using complementary analytical techniques. The sensing mechanism is based on the reduction in Prussian blue to its colorless form in the presence of phenylephrine, resulting in a decrease in absorbance intensity. Under optimized conditions (pH 6.5 and 5 min incubation time), the colorimetric sensor exhibited a linear response toward phenylephrine over the concentration range of 5–150 µg mL−1, with a limit of detection of 1.56 µg mL−1 (R2 = 0.9986). The sensing system was further integrated into a paper-based platform, enabling visual detection of phenylephrine. Digital image analysis using ImageJ showed a linear response over 5–150 µg mL−1 (R2 = 0.9884) and a detection limit of 5.37 µg mL−1. The sensor’s practical applicability was validated using artificial urine samples, yielding recovery values of 95.87–97.5% and relative standard deviations of 1.15–2.13%. Unlike conventional methods requiring multi-step reactions, this study introduces, for the first time, a simple paper-based colorimetric sensor for phenylephrine detection based on the direct Prussian blue–Prussian white redox transition integrated with digital image analysis.