A multimodal colorimetric biosensor for bisphenol A based on DNA walker signal amplification and the formation of a molybdophosphoric acid-brilliant green complex

Aptamer combined with DNA walker and ALP enables sensitive indirect detection of BPA. • Brilliant green binds molybdophosphoric acid to generate yellow-green color shifts. • Three modes (UV–Vis, RGB, swab sensor) satisfy lab, field and house testing demands. Bisphenol A (BPA) is a ubiquitous contaminant prevalent in food and environmental matrices. Herein, a smartphone-assisted multichannel colorimetric biosensor for BPA detection is constructed by integrating BPA aptamer-activated DNA walker, alkaline phosphatase (ALP)-catalyzed hydrolysis, and the molybdophosphoric acid assay. The DNA walker is immobilized on magnetic beads through biotin-streptavidin interaction, which enables target-triggered DNAzyme release and cyclic cleavage reactions. This autonomous cyclic amplification process efficiently releases substantial ALP into the supernatant. The liberated ALP further catalyzes the hydrolysis of 4-nitrophenyl phosphate (4-NPP) to produce phosphate ions (Pi), which react with ammonium molybdate under acidic conditions to form 12-molybdophosphoric acid (12-MPA). The introduction of brilliant green (BG) induces a distinct solution color transition from yellow to green, and the color variation exhibits a positive correlation with BPA concentration. Based on the above sensing mechanism, three versatile detection modes are established, including laboratory-grade UV–Vis spectrophotometry, smartphone-based RGB colorimetry, and a portable cotton swab sensor. The proposed biosensor displays superior selectivity against BPA structural analogs, excellent reproducibility, and satisfactory spiked recovery in real milk sample detection. Leveraging low-cost commercial commodities (cotton swabs and smartphones) and cascaded signal amplification strategy, this work provides a cost-effective, user-friendly, and multi-scenario adaptable platform for BPA detection. Download: Download high-res image (148KB) Download: Download full-size image