Optical imaging and gene transfection potential of linear polyethylenimine-coated Ag2S near-infrared quantum dots.

Background/aim: The application of biocompatible heavy metal-free and cationic Ag₂S NIR quantum dots (QDs), which have intense luminosity in the 700-900 nm medical range, as a nonviral gene delivery system paves the way to overcome autofluorescence and easily track the delivery of genes in real time.

Materials and methods: The newly developed small and colloidally stable 2-mercaptopropionic acid (MPA)-capped Ag₂S aqueous quantum dots electrostatically complexed with linear polyethyleneimine (Ag₂S@2MPA/LPEI) were investigated for the first time both as a strong fluorescent probe and as a vector for nonviral gene delivery for the highest tracking of the system and delivery of genes into the nuclei of different cancer cells. The synthesized Ag₂S@2MPA/LPEI quantum dots demonstrated strong optical imaging properties and were used to deliver a green fluorescent protein (GFP) plasmid as a standard gene.

Results: For Ag₂S@2MPA/LPEI-pDNA nanoparticles, an N/P ratio of 20 was the ideal transfection efficiency. Ag₂S@2MPA/LPEI was substantially more compatible with HEK 293T cells than the free 25-kDa linear polyethylenimine (LPEI). Next, the transfection efficiency evaluation of pGFP genes with synthesized Ag₂S@2MPA/LPEI and LPEI in different cancer cells demonstrated their high potential as a theranostic cancer gene delivery system.

Conclusion: This is the first instance of gene transfection and optical imaging carried out in vitro using Ag₂S@2MPA/LPEI QDs. Overall, the newly synthesized highly biocompatible and trackable Ag₂S@2MPA/LPEI QDs can be an effective and biocompatible theranostic system for cancer gene therapy.