Facile doping of silica nanoparticles with far-red cyanine dyes using the microemulsion method.

R. Nooney, C. McDonagh
Biomedical Diagnostics Institute, IE

Keywords: Cy5, microemulsion, silica

Summary:

We prepared silica NPs doped with two far-red absorption cyanine dyes, FR670 and Cy5, using the microemulsion method. At these wavelengths there is less autofluorescence from biological molecules, solvents and substrates. The effects of changing surfactant, pH and dye loading on NP morphology and colloidal stability were investigated using transmission electron microscopy and photo correlation spectroscopy. We found that the incorporation of Cy5 and FR670 was only possible using negatively charged surfactants. We propose a method for the facile incorporation of cyanine dye based on the electrostatic repulsion between negatively charged dye molecules and the negatively charged surfactant, present at the water oil interface, which drives the dye into the silica NP forming inside the water phase. The absorption, fluorescence and quantum efficiency of the NPs were also measured and compared against free dye labels. The optimal fluorescences for FR670 and Cy5 dye doped NPs, were 178 and 83 times brighter than the corresponding free dye labels. The change in fluorescence of FR670 NPs with changing concentration of dye added, matched closely with a model calculated using standard analytical expressions of homo Förster resonance energy transfer (HFRET).