A Review on Recent Trends in Biological Applications of Non-conjugated Polymer Dots

With the advancement of zero-dimensional carbon materials, carbon dots (CDs) have received immense attention owing to their exceptional optical properties, tailoring of size, and ease of functionalization. They have wide applications in fluorescent sensing, chemical sensing, bioimaging, photocatalysis, etc. Zero-dimensional polymer nanoparticles are called polymer dots (PDs) and are classified into conjugated and non-conjugated PDs based on their conjugated system. Non-conjugated polymer dots (NCPDs) do not have specific conjugated fluorophore groups, but they have superior chemical stability and water solubility than the conjugated PDs. The carbon core of NCPDs is surrounded by polymer chains containing ample functional groups such as C=O, N=O, and C=N, which are responsible for the luminescent PDs. NCPDs are less toxic, photostable, and biocompatible and are relevant in biological explorations in bioimaging, drug delivery, biosensing, etc. This mini-review provides a systematic overview of the inherent properties and the biological applications of NCPDs. It also emphasises the synergistic impacts on the optical performance of modified PDs and significant future research concerns.