A highly selective semiconducting polymer dots-based "off-on" fluorescent nanoprobe for iron, copper and histidine detection and imaging in living cells.

Semiconducting polymer dots (PDs) hold a great promise as fluorescence nanoprobes, due to their photostability, biocompatibility, and high quantum yield. Herein, the synthesis and characterization of highly fluorescent PDs for selective and sensitive detection of Fe,Cu, and histidine (His) have been reported. First, carboxyl functionalized poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-(2,1',3)-thiadiazole)] (PFBT) PDs were synthesized through a nano-precipitation technique, and then they were functionalized by -COOH groups using 9-anthracenecarboxylic acid. The formation of PDs was proved using transmission electron microscopy, dynamic light scattering, and Fourier transform infrared (FTIR) spectroscopy analyses. The PDs exhibited a yellow fluorescence with a peak centered at 540 nm (photo-excited at 460 nm) with a quantum yield of 25%. The fluorescence of PDs significantly quenched in the presence of Cu ion, and then selectively recovered upon addition of His, providing the possibility of constructing a sensitive Cu-His off-on fluorescent nanoprobe. The PDs exhibited a linear dynamic range for Cu from 0.1 to 630 µmol L with a limit of detection of 61.7 nmol L, and for Fe from 0.1 to 720 µmol L with a limit of detection of 58.1 nmol L. In addition, the PDs/Cu probe showed a linear dynamic range for His from 0.1 to 920 µmol L with a limit of detection of 79.6 nmol L. Besides, the prepared PDs/Cu probe exhibited a promising potential for selective and sensitive sensing of His in blood serum and for intracellular imaging.