Polydopamine-coated carbon nanodots are a highly selective turn-on fluorescent probe for dopamine

Carbon nanodots (CDs) were prepared by the pyrolysis of lactose in hot alkali solution for 5 min. The resulting CDs possess spherical and monodisperse shape with an average diameter of ∼3 nm. The blue fluorescence of the CDs, with excitation/emission peaks at 414/470 nm, can be turned-on in the presence of very low concentrations of dopamine (DA) due to the formation of a poly-DA shell on the CDs. Fluorescence is only enhanced by DA, while other chemically related compounds do not interfere. Fluorescence increases linearly in the 1.0–10.0 μM DA concentration range, with a 0.22 μM lower detection limit. The nanoprobe was applied to the determination of DA in injections and in spiked urine samples, and the results compared well with those obtained by HPLC. The nanoprobe has a fast response, is inexpensive and highly selective.