The availability of a real-time assay of apoptosis would provide a critically useful tool for oncologists, who would then have the means to determine whether a given therapeutic approach was working soon after that therapy was started. Cancer drug development would also benefit from a real-time apoptosis assay if such an assay could be used to provide rapid and sensitive results in high-throughput drug screening experiments.
A research team headed by Dae Hong Jeong, Ph.D., Yoon-Sik Lee, Ph.D., and Myung-Haing Cho, D.V.M., Ph.D., Seoul National University, created their fluorescent surface enhanced Raman spectroscopic (F-SERS) nanodots to boost the optical signal generated by typical, biocompatible fluorescent dyes. The nanodots consist of silver nanoparticles embedded in a silica sphere. Attached to the silica core are fluorescent dye molecules and molecules known as Raman labels that enhance the electronic interactions between the silver nanoparticles and the dye molecules. The researchers also linked annexin-V, a molecule that binds specifically to a chemical that appears on cells undergoing apoptosis, to the silica-silver nanoparticle construct.
Toxicity tests showed that the silica-silver nanodots were not toxic to various human cells growing in culture. The investigators then added the nanodots to cells triggered to undergo apoptosis and were able to image those cells as they went through programmed cell death. Based on these results, the researchers prepared other nanodots containing antibodies that bind to other molecules involved in apoptosis. They then added these antibody-linked nanodots and the annexin-V-linked nanodots to cultured human lung cancer cells. The investigators were able to track the appearance of all three molecules simultaneously, which has been difficult to do using conventional cell staining techniques.