Oxidation-controlled synthesis of fluorescent polydopamine for the detection of metal ions

Abstract Polydopamine (PDA) nanoparticles have shown potential application in chemical sensing, bio-imaging and so on. We herein employ four metal ions (Al 3+ , Cu 2+ , Fe 3+ and Fe 2+ ) and H 2 O 2 for the controlled-oxidation of dopamine to produce water-soluble fluorescent oligomeric dopamine at room temperature in acidic conditions. The oxidized products were characterized by transmission electron microscope, UV–vis absorption spectroscopy, Fourier transform infrared spectra, X-ray photoelectron spectroscopy and fluorescence spectrum. The pH, temperature, and concentrations were individually optimized. The possible reaction mechanisms between dopamine and metal ions/H 2 O 2 have been deduced. Finally, Al 3+ can enhance the fluorescence of Cu 2+ -polydopamine, leading to a sensitive light-up sensor with a detection limit of 0.3 μM Al 3+ . Whereas Fe 2+ or Fe 3+ can enhance the fluorescence of Al 3+ -polydopamine, also leading to a sensitive light-up sensor with a detection limit of 3.7 μM Fe 2+ or Fe 3+ . This work has demonstrated not only a novel method for the synthesis of PDA, but also an interesting application for fluorescent PDA.