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

Abstract

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 Fe³⁺,Cu²⁺, 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 Cu²⁺ ion, and then selectively recovered upon addition of His, providing the possibility of constructing a sensitive Cu²⁺-His off-on fluorescent nanoprobe. The PDs exhibited a linear dynamic range for Cu²⁺ from 0.1 to 630 µmol L^-1 with a limit of detection of 61.7 nmol L^-1, and for Fe³⁺ from 0.1 to 720 µmol L^-1 with a limit of detection of 58.1 nmol L^-1. In addition, the PDs/Cu²⁺ probe showed a linear dynamic range for His from 0.1 to 920 µmol L^-1 with a limit of detection of 79.6 nmol L^-1. Besides, the prepared PDs/Cu²⁺ probe exhibited a promising potential for selective and sensitive sensing of His in blood serum and for intracellular imaging.

Keywords: Cell imaging; Fe(3+) and Cu(2+) ions; Fluorescence; Histidine; Off-on nanoprobe; Semiconducting polymer dots.