Credit: © 2006 ACS

Mesoporous silica nanoparticles (MSNs) have large surface areas and pores that may be capped at will. They can also be taken up into mammalian cells. Therefore, MSNs have the potential to deliver large quantities of drugs, genes or disease-detection molecules to specific cellular targets.

Now, Victor S.-Y. Lin and co-workers1 from Iowa State University in the US have shown that chemically modifying the surface of MSNs alters the extent to which they are taken up by cells. Fluorescent MSNs with an average diameter of 150 nm were reacted with one of four different small organic compounds and their uptake by human cervical cancer cells was monitored by flow cytometry. The concentration of functionalized MSN particles at which 50% of cells take them up, known as ED50, was correlated with the effective charge of the particles. Moreover, escape of the nanoparticles from endosomes (compartments inside cells), which is essential for drug delivery, was also dependent on their charge.

Receptors for folate, a vitamin molecule that is essential for the production and maintenance of new cells, are abundant on human cancer cell membranes. Consequently, a higher uptake was observed for MSNs coated with folate groups, but these nanoparticles were also trapped inside endosomes most readily. Tests with inhibitor molecules showed that different mechanisms were responsible for the uptake of the other functionalized MSNs.