CAMP Professor Igor Sokolov Makes Ultrabright Fluorescent Silica Particles
CAMP Professor Igor Sokolov, in collaboration with Ph.D. student Kievsky (now in NRC , Canada), and undergraduate Physics major Kaszpurenko discovered a way of making the brightest ever synthesized fluorescent silica particles. Organic fluorescent molecules are physically entrapped inside a nanoporous silica matrix. Fluorescence of such particles is approximately 170 times brighter than the brightest so far micron-size particles, assembled from aqueous compatible quantum dots embedded in polymeric particles of similar size. The Clarkson team’s work will soon be published in one of the upcoming issues of Small, a new popular scientific journal that has already been ranked as number two in the IRS "Nanoscience and Nanotechnology" category.
The synthesized particles are complex nanostructured objects that can be described as tightly packed arrays/bundles of silica nanotubes. The increase in fluorescence is because of the following two reasons: 1. Attaining higher concentrations of the organic fluorescent dye molecules inside the tubes without the dye dimerization (which would quench fluorescence); 2. Physical entrapment of the dye inside the silica nanotubes.
Maintaining a high concentration of the dye without dimerization can presumably be explained by one-dimensional confinement of the molecules inside the tubes (the silica walls between the tubes/channels naturally do not let the dye molecules dimerize in a direction perpendicular to the channels) and the presence of surfactant molecules inside the tubes, which can act as dispersants. See Figure 4.
Figure 4. Schematics of location of the dyes inside the synthesized shapes. Right side of the image presents a “zoomed” in area of the tubes with the dye encapsulated inside ~ 3 nm channels. Alkane chains of surfactant molecules (shown as zigzag vertical lines with the headgroups adjacent to silica walls) act as separators between the dye molecules, preventing dimerization of the dye molecules in the direction along the channels. In the perpendicular directions, silica walls play the role of the separator to prevent dimerization.
Figure 5. This is a fluorescent image of a physical mixture of fluorescent silica particles of different shapes having different dyes.