Linker-induced anomalous emission of organic-molecule conjugated metal-oxide nanoparticles.

Semiconductor nanoparticles conjugated with organic- and dye-molecules to yield high efficiency visible photoluminescence (PL) hold great potential for many future technological applications. We show that folic acid (FA)-conjugated to nanosize TiO(2) and CeO(2) particles demonstrates a dramatic increase of photoemission intensity at wavelengths between 500 and 700 nm when derivatized using aminopropyl trimethoxysilane (APTMS) as spacer-linker molecules between the metal oxide and FA. Using density-functional theory (DFT) and time-dependent DFT calculations we demonstrate that the strong increase of the PL can be explained by electronic transitions between the titania surface oxygen vacancy (OV) states and the low-energy excited states of the FA/APTMS molecule anchored onto the surface oxygen bridge sites in close proximity to the OVs. We suggest this scenario to be a universal feature for a wide class of metal oxide nanoparticles, including nanoceria, possessing a similar band gap (∼3 eV) and with a large surface-vacancy-related density of electronic states. We demonstrate that the molecule-nanoparticle linker can play a crucial role in tuning the electronic and optical properties of nanosystems by bringing optically active parts of the molecule and of the surface close to each other.

Release of liposomal contents by cell-secreted matrix metalloproteinase-9.

Liposomes have been widely used as a drug delivery vehicle, and currently, more than 10 liposomal formulations are approved by the Food and Drug Administration for clinical use. However, upon targeting, the release of the liposome-encapsulated contents is usually slow. We have recently demonstrated that contents from appropriately formulated liposomes can be rapidly released by the cancer-associated enzyme matrix metalloproteinase-9 (MMP-9). Herein, we report our detailed studies to optimize the liposomal formulations. By properly selecting the lipopeptide, the major lipid component, and their relative amounts, we demonstrate that the contents are rapidly released in the presence of cancer-associated levels of recombinant human MMP-9. We observed that the degree of lipid mismatch between the lipopepides and the major lipid component profoundly affects the release profiles from the liposomes. By utilizing the optimized liposomal formulations, we also demonstrate that cancer cells (HT-29) which secrete low levels of MMP-9 failed to release a significant amount of the liposomal contents. Metastatic cancer cells (MCF7) secreting high levels of the enzyme rapidly release the encapsulated contents from the liposomes.