Mesostructured Silica for Optical Functionality, Nanomachines, and Drug Delivery

Abstract

Silica thin films and nanoparticles prepared using sol-gel chemistry are derivatized with active molecules to generate new functional materials. The mild conditions associated with sol-gel processing allow for the incorporation of a range of dopants including organic or inorganic dyes, biomolecules, surfactants, and molecular machines. Silica nanoparticles embedded with inorganic nanocrystals, and films containing living cells have also been synthesized. Silica templated with surfactants to create mesostructure contains physically and chemically different regions that can be selectively derivatized using defined techniques to create dynamic materials. Using two different techniques, donor-acceptor pairs can be doped into separated regions simultaneously and photo-induced electron transfer between the molecules can be measured. Mesoporous silica materials are also useful supports for molecular machines. Machines including snap-tops and nanoimpellers that are designed to control the release of guest molecules trapped within the pores are described. Mesoporous silica nanoparticles are promising materials for drug delivery and other biomedical applications because they are nontoxic and can be taken up by living cells. Through appropriate design and synthesis, multifunctional mesoporous silica nanoparticles for sophisticated bio-applications are created.

Fig. 1

Transmission electron microscope images of iron oxide (left), silver (middle), and gold (right) nanocrystals embedded within the mesoporous silica nanoparticles.

Fig. 2

Spatial separation of electron transfer pairs is achieved by doping the molecules into different regions of a mesostructured film. Photo-induced electron transfer from the Ru donor to the methyl viologen acceptor occurs through tunneling.

Fig. 3

Snap-tops attached to the surface of mesoporous silica nanoparticles are able to store guest molecules within the pores while intact. Guest molecules are released upon selective cleavage of ester-linked adamantyl stoppers by porcine liver esterase (PLE).

Fig. 4

Azobenzene-derivatized mesostructured silica particles loaded with guest molecules and release of the molecules from the pores by the back-and-forth wagging motion of light-activated azobenzenes.

Fig. 5

Fluorescence microscope images of particle uptake into cells. HFF treated with (a) nanoparticles or (b) folate-modified nanoparticles. PANC-1 treated with (c) nanoparticles or (d) folate-modified nanoparticles. Increased uptake of the folate-modified nanoparticles was observed for the PANC-1 cells (overexpressed folate receptors), but not on the HFF. Red fluorescence: membrane stained with WGA-Alexa Fluor 594; blue fluorescence: nuclei stained with DAPI; green fluorescence: nanoparticles. The fluorescence of DAPI is increased by ~20-fold when it binds to the nucleic acids in the nucleus. WGA-Alexa Fluor 594 binds to the glycoproteins in the cell membrane.

Fig. 6

Confocal fluorescence microscope images of the PANC-1 cancer cells that were treated with a suspension of the nanoimpeller-functionalized particles loaded with the camptothecin (CPT), kept in the dark (left) and 5 min illuminated at 413 nm of a light (right). Photoactivated impellers released the CPT from the particles inducing cell apoptosis (right) while unexcited machines did not cause the CPT release and cells were intact (left). Scale bar: 30 μm.