Size-Fluorescence Correlation of Organic Fluorescent Nanoparticles

A diverse range of fluorescent nanoparticles, including quantum dots, silicon nanoparticles, carbon dots, and conjugated polymer nanoparticles, have been developed and can be used for imaging and analytical purposes. Establishing a quantitative relationship between the size and the fluorescence of organic fluorescent nanoparticles would be useful for exploring their behavior. However, the prepared organic nanoparticles usually have a broad distribution of sizes, shapes, and defects, which hinders the investigation of size-fluorescence correlations. In addition, organic fluorescent nanoparticles can be affected by aggregation-caused quenching (ACQ), causing a lowered fluorescence signal sensitivity.

Bin Liu, Hui-Qing Peng, Beijing University of Chemical Technology, China, Xiaoyan Zheng, Beijing Institute of Technology, China, and colleagues have performed a quantitative investigation of the size-fluorescence correlation for supramolecular polymeric fluorescent nanoparticles prepared from tetraphenylethylene-based bis-ureidopyrimidinone monomers (bis-UPys). The team used three different monomers to fabricate organic nanoparticles with different sizes. The bis-UPys can assemble into hydrogen-bonded supramolecular polymers for constructing nanoparticles with well-defined shapes, and nanoparticles of different sizes can be easily obtained by adjusting the bis-UPy concentration in the precursor solution. In addition, the aggregation-induced emission (AIE) features of TPE derivatives eliminate the ACQ effect, providing bright fluorescence signals.

The team found a logarithmic relationship between the fluorescence intensity and the size of the fluorescent nanoparticles. They successfully utilized the established fluorescence intensity-size correlation to estimate the sizes of nanoparticles by measuring their fluorescence intensity. The work provides a new way for the simple and real-time determination of nanoparticle dimensions and could be useful for the optimization of size-dependent nanoparticle properties.