Low-Bandgap Conjugated Polymer Dots for Near-Infrared Fluorescence Imaging

Low-bandgap conjugated polymers attract significant research interests because of their broad light absorption spectra in the red and near-infrared regions, making them desirable materials for solar photovoltaics. To date, low-bandgap conjugated polymers yield some of the best power conversion efficiencies offered by polymer solar cells. In addition to their applications as solar photovoltaic materials, nanoparticles of these polymers may be potentially beneficial for cell imaging because of their red and near-infrared absorption features, which are required for significant light penetration into biological samples. In this work, conjugated polymer dots (CPdots) of PCPDTBT, PSBTBT, PTB7, PCDTBT, and PBDTTPD are prepared in aqueous solution using nanoprecipitation. The maximum fluorescence wavelengths of these CPdots range from 800 to 1000 nm. The CPdots exhibit an average zeta potential of −30 mV, giving rise to colloidal stability of these nanoparticles. Dynamic light scattering results show that the CPdots have a hydrodynamic diameter of approximately 100 nm. Furthermore, analyses of atomic force microscopy images of the low-bandgap donor–acceptor CPdots show an average height of approximately 20 nm. The CPdots are introduced to live THP-1 cells, a human monocytic cell line, and the internalization of CPdots by these cells is observed. Confocal fluorescence microscopy images of cells labeled with the low-bandgap CPdots show the presence of these bright nanoparticles in the cells. In short, we demonstrate the preparation of low-bandgap CPdots as an aqueous dispersion and their applications in cell imaging.