Tumor cell membranes often have an abnormally high number of receptor sites to capture molecules of folic acid, or folate, a form of vitamin B that many tumor cells crave. The Purdue researchers attached folate to the gold nanorods, enabling them to target the receptors and attach to the tumor cell membranes.
"The cells are then illuminated with light in the near-infrared range," said Ji-Xin Cheng (pronounced Gee-Shin), an assistant professor in Purdue's Weldon School of Biomedical Engineering. "This light can easily pass through tissue but is absorbed by the nanorods and converted rapidly into heat, leading to miniature explosions on the cell surface."
Scientists have recently determined that gold nanorods and other nanostructures can be used to target and destroy tumor cells, but it was generally assumed that cell death was due to the high heat produced by the light-absorbing nanoparticles. The Purdue team discovered, however, that a more complex biochemical scenario is responsible for killing the cells.
"We have found that rather than cooking the cells to death, the nanorods first punch holes in the membrane, and cell death is then chemically induced, in this case by an influx of calcium," said Alexander Wei, an associate professor of chemistry at Purdue.
Findings are detailed in a research paper appearing Oct. 19 in the journal Advanced Materials. The paper, which appeared online last week, was written by doctoral students Ling Tong, Yan Zhao, Terry B. Huff and Matthew N. Hansen, along with Wei and Cheng.
The gold rods are less than 15 nanometers wide and 50 nanometers long, or roughly 200 times smaller than a red blood cell. Their small size is critical for the technology's potential medical applications: the human immune system quickly clears away particles larger than 100 nanometers, whereas smaller nanoparticles can remain in the bloodstream far longer.
Shining light on the gold nanorods causes them to become extremely hot, ionizing the molecules around them.
"This generates a plasma bubble that lasts for about a microsecond, in a process known as cavitation," Wei said. "Every cavitation event is like a tiny bomb. Then suddenly, you have a gaping hole where the nanorod was."
The gold nanorods also are ideal for a type of optical imaging known as two-photon luminescence, used by Cheng and his research group to monitor the position of nanorods in real time during tumor-cell targeting. The imaging technique provides higher contrast and brighter images than conventional fluorescent imaging methods.
In experiments with tumor cells in laboratory cultures, the nanorods attached to the cell membranes and were eventually taken up into the cells. The researchers found that it could take far less power to injure cells by exposing the nanorods to near-infrared light while they are still on the membrane surface instead of waiting until the nanorods are internalized.
"This means that if you wait until the nanorods are inside the cell, then you really have to pump up the laser power, so localizing the nanorods on the cell membrane strongly influences their ability to inflict cell damage," Cheng said.
The findings suggest an optimal window of opportunity for applying near-infrared light to the nanorods for cancer treatment.
"We like to believe this opens the possibility of using nanorods for biomedical imaging as well as for therapeutic purposes," Cheng said.
The Purdue researchers observed that light-absorbing nanorods cause the formation of membrane "blebs, " similar to severe blistering. These blisters, however, are not produced directly by the high heat generated by the nanorods.
"The blebbing is triggered by the nanorods, but it's really caused through a complex biochemical pathway - a chemically induced process," Cheng said. "Extra calcium gets into the cell and triggers enzyme activity, which causes the infrastructure inside the cell to become loose, and that gives rise to the membrane blebs."
Researchers used a calcium-sensitive fluorescent dye to back up their argument that calcium influx caused the tumor cell death. When the nanorod-bearing tumor cells were maintained in a calcium-free nutrient medium, no blisters were formed if the nanorods were exposed to near-infrared light. But when the researchers added calcium to the medium, the blebbing took place immediately.
Although the technique offers promise for a new cancer treatment, it is too early to determine when it could be in clinical use, said Wei, who is collaborating with the National Cancer Institute to determine the suitability of the functionalized gold nanorods for future clinical studies.
The research has been supported by the National Science Foundation and the National Institutes of Health. The research also has been supported by Purdue's Oncological Sciences Center and the Purdue Cancer Center.Writer: Emil Venere, (765) 494-4709, email@example.com
Emil Venere | alfa
Cancer diagnosis: no more needles?
25.05.2018 | Christian-Albrechts-Universität zu Kiel
Less is more? Gene switch for healthy aging found
25.05.2018 | Leibniz-Institut für Alternsforschung - Fritz-Lipmann-Institut e.V. (FLI)
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences