Polyethylenimine-Encapsulated InP-Based Quantum Dots for Living Cell Bioimaging

InP-based quantum dots (QDs) provide an environmentally friendly and feasible substitute for Cd-based QDs with comparable performance in biological applications. The high-quality InP-based QDs made currently with hydrophobic surface ligands are insoluble in aqueous solutions and limit their biomedical applications. Thus, phase transfer to aqueous solutions is crucial for their biological applications. Numerous studies mainly focus on the ligand exchange of QDs, while efficient polymer encapsulation methods are rarely mentioned. In this study, water-soluble InP-based QDs were prepared via a surface modification technique using alkylated polyethylenimine (PEI) as an amphiphilic polymer encapsulant. We have characterized the fundamental physical, chemical, and biological characteristics of water-soluble PEI-encapsulated InP/ZnSe/ZnS QDs (InP/ZnSe/ZnS@PEI). This encapsulation approach can preserve the inherent hydrophobic ligands on the surfaces of the QDs and realize the aqueous solubility. The InP/ZnSe/ZnS@PEI QDs retain their original photoluminescence quantum yield and photon emission characteristics of pristine QDs in organic solvents, ensuring an optimal performance. Furthermore, these water-soluble QDs show potential biocompatibility, low toxicity, and photostability. Notably, they were successfully employed to label HeLa, HepG2 liver cancer cells and HL-7702 healthy liver cells, exhibiting outstanding performance. These findings demonstrate that the InP/ZnSe/ZnS@PEI QDs can serve as a secure and nontoxic probe for bioimaging and other biological applications.