MIT researchers have developed a group of gold nanoparticles that may soon be used by oncologists to find, locate, and kill tumors. By resonating when near-infrared light is introduced, the nanoparticles can heat up enough to cook surrounding tumor cells out of existence.
From MIT news office:

Gold nanoparticles can absorb different frequencies of light, depending on their shape. Rod-shaped particles, such as those used by von Maltzahn and Bhatia [Geoffrey von Maltzahn and Sangeeta Bhatia, graduate student and MIT professor respectively], absorb light at near-infrared frequency; this light heats the rods but passes harmlessly through human tissue.
In a study reported in the team’s Cancer Research paper, tumors in mice that received an intravenous injection of nanorods plus near-infrared laser treatment disappeared within 15 days. Those mice survived for three months with no evidence of reoccurrence, until the end of the study, while mice that received no treatment or only the nanorods or laser, did not.
Once the nanorods are injected, they disperse uniformly throughout the bloodstream. Bhatia’s team developed a polymer coating for the particles that allows them to survive in the bloodstream longer than any other gold nanoparticles (the half-life is greater than 17 hours).
In designing the particles, the researchers took advantage of the fact that blood vessels located near tumors have tiny pores just large enough for the nanorods to enter. Nanorods accumulate in the tumors, and within three days, the liver and spleen clear any that don’t reach the tumor.
During a single exposure to a near-infrared laser, the nanorods heat up to 70 degree Celsius, hot enough to kill tumor cells. Additionally, heating them to a lower temperature weakens tumor cells enough to enhance the effectiveness of existing chemotherapy treatments, raising the possibility of using the nanorods as a supplement to those treatments.
The nanorods could also be used to kill tumor cells left behind after surgery. The nanorods can be more than 1,000 times more precise than a surgeon’s scalpel, says von Maltzahn, so they could potentially remove residual cells the surgeon can’t get.
The nanorods’ homing abilities also make them a promising tool for diagnosing tumors. After the particles are injected, they can be imaged using a technique known as Raman scattering. Any tissue that lights up, other than the liver or spleen, could harbor an invasive tumor.
In the Advanced Materials paper, the researchers showed they could enhance the nanorods’ imaging abilities by adding molecules that absorb near-infrared light to their surface. Because of this surface-enhanced Raman scattering, very low concentrations of nanorods – to only a few parts per trillion in water [gf1]- can be detected.
Another advantage of the nanorods is that by coating them with different types of light-scattering molecules, they can be designed to simultaneously gather multiple types of information – not only whether there is a tumor, but whether it is at risk of invading other tissues, whether it’s a primary or secondary tumor, or where it originated.

Press release: Targeting tumors using tiny gold particles …
Abstract in Cancer Research: Computationally Guided Photothermal Tumor Therapy Using Long-Circulating Gold Nanorod Antennas
Abstract in Advanced Materials: SERS-Coded Gold Nanorods as a Multifunctional Platform for Densely Multiplexed Near-Infrared Imaging and Photothermal Heating