A highly selective two-photon fluorescent probe for the determination of mercury ions

In this work, we developed a new two-photon fluorescent probe, ATD (ATD = amino triphenylamine dendron), by combining a two-photon fluorophore 4-(bis(4-(4-(diphenylamino)styryl)-phenyl)amino) benzaldehyde (TD) with a specific recognition molecule for Hg²⁺-phenyl thiourea (PT)-for the determination of Hg²⁺. The designed fluorescent probe emitted at ∼455 nm upon one-photon and two-photon excitation at 400 nm and 800 nm, respectively. The blue fluorescence obviously dropped with the continuous addition of Hg²⁺, and demonstrated a good linearity with the concentration of Hg²⁺ in a wide dynamic range of 5 nM-1.0 μM. The detection limit achieved was 0.49 nM (∼0.2 ppb), which is much lower than the standard levels required by the U.S. Environmental Protection Agency (EPA) and World Health Organization (WHO). Furthermore, this probe featured high selectivity for Hg²⁺ detection over other metal ions such as Cd²⁺, Ag⁺, Pd²⁺, and so on, due to the specific Hg²⁺ recognition by the PT molecule. Meanwhile, the probe demonstrated long-term stability with respect to pH and illumination. As a result, the developed two-photon fluorescent probe, with high sensitivity and selectivity, was successfully applied for the on-site determination of Hg²⁺ in environmental water samples.