Fluorescence biolabeling using methylated silica nanoparticles containing a lanthanide complex

Abstract

This research demonstrates that fluorescent silica nanoparticles containing a lanthanide picolinate complex can be used as optical biolabels by using Candida albicans cells as the model targeting system. As such, new fluorescent biolabels have been prepared by encapsulation of the picolinate terbium(III) complex K₂[Tb₂(pic)₈]·7H₂O (Tbpic) in silica particles through a reverse microemulsion process. The surfaces of the ensuing core–shell nanoparticles were functionalized with 3-aminopropyltriethoxysilane and then quaternized with methyl iodide in order to increase their water-stability and promote uptake by the cells. Confocal microscopy experiments demonstrated that in comparison to the non-quaternized analogues, the uptake of the functionalized nanoparticles by Candida albicans was improved. Therefore the methylation of silica surfaces as described here appears to be a more general strategy to improve the uptake of functionalized nano-silica particles by these cells. There is evidence from these studies that in this case the nanoparticles penetrated the cell wall but did not penetrate the nuclear membrane, thus allowing selective cell biolabeling.