Early detection of tumors is one of the Holy Grails of cancer research, an achievement that would greatly improve cancer therapy and prognosis. Two new reports describe different but promising approaches to solving this problem.
At the University of Florida, Weihong Tan, Ph.D., and colleagues used gold nanoparticles linked to aptamers, which are short, synthetic molecules of deoxyribonucleic acid (DNA) that bind to specific targets much like antibodies. In work published last year, Dr. Tan’s group described the methods it developed to create aptamers that bind specifically to cancer cells. The current paper, published in the journal Analytical Chemistry, shows how the combination of these aptamers with gold nanoparticles produces a diagnostic optical signal when they cover targeted cancer cells.
Gold nanoparticles are efficient optical beacons whose light-absorbing properties depend strongly on the size of the nanoparticle. In this work, the investigators used gold nanoparticles that show peak absorption of light with a wavelength of about 500 nanometers when linked to an aptamer. However, when these same aptamer-conjugated nanoparticles bind in large numbers to a targeted cell, their absorption spectrum changes dramatically, producing a visible shift in color from green to red. Although this change is visible to the human eye, the researchers used a microplate spectrophotometer to increase the sensitivity of the assay to a lower limit of 90 malignant cells.
Taking a different approach, Gary Maki, Ph.D., and collaborators at the University of Idaho have developed a nanowire transistor capable of detecting very low levels of DNA methylation. DNA methylation plays a critical role in silencing tumor suppressor genes and thus could serve as a very early indicator of tumor development.
Conventional methods of detecting DNA methylation are complex and time-consuming, two limitations that Dr. Maki and his team set out to address. The heart of their device is a nanowire transistor, formed using standard electron-beam photolithography, that is coated with a antibody that binds to methylated cytosine, one of the four bases of DNA. When DNA containing methylated cystein passes over the nanowires, the antibodies bind the DNA, generating a measurable electrical signal.