Al3+-induced far-red fluorescence enhancement of conjugated polymer nanoparticles and its application in live cell imaging

Fluorescent nanoparticles (NPs) for Al3+ sensing with high selectivity were developed from a type of carbazole-based conjugated polymer with a two-dimensional donor-pi bridge-acceptor (D-pi-A) structure. These NPs are characterized by their small particle diameter (similar to 18 nm), far-red fluorescence emission (centered similar to 710 nm), and Al3+-induced fluorescence enhancement with high selectivity owing to an Al3+-triggered inhibition on the intramolecular charge transfer (ICT) processes between the conjugated backbone and the pendant acceptors. This type of nanoparticle is easily suspended in aqueous solutions, indicating their practical applicability in physiological media, and their ability for intracellular Al3+ sensing was confirmed. As compared to other types of conjugated polymer based probes showing metal ion mediated fluorescence quenching, these as-prepared NPs possess analyte-enhanced fluorescence emission, which is analytically favored in terms of sensitivity and selectivity. Fluorescence emission with wavelengths in the biological window of maximum optical transparency (similar to 700 to 1000 nm) is expected to impart a salient advantage for biological detection applications to these as-prepared probes. The superior features of merit of this new type of fluorescent probe, together with the validation of practicability for intracellular Al3+ ion sensing, are indicative of their potential for application in fluorescence-based imaging and sensing, such as investigations on Al3+-related physiological and pathological processes.