Highly sensitive and rapid detection of resorcinol by forming fluorescent azamonardine with dopamine

We propose a sensitive, selective, and rapid fluorescent assay for detecting resorcinol (RC) based on its specific chemical reaction with dopamine. Under alkaline condition, RC would react with dopamine to yield fluorescent azamonardine, which emits strong blue fluorescence and has a superior excitation wavelength at 416 nm and an emission wavelength at 461 nm. The azamonardine with a molecular weight of 258.1 confirmed by ICP-MS has a quantum yield of 71.3%. The reaction is completed within 1 min showing great potential for point-of-care testing. This assay showed high sensitivity and had a good relationship between fluorescent intensity at 461 nm and RC concentration (I₄₆₁ = 106.4 + 93.6*C_RC; R² = 0.9904) over the range of 0-40 μM. More importantly, the assay showed a prominent anti-interference from various substances and even can distinguish RC from its isomers, o-dihydroxybenzene and p-dihydroxybenzene. Finally, our assay successfully quantified RC contents in wheat powder and hair dyes with high accuracy.