Visiting Louis Haber’s lab in the Department of Chemistry at LSU is like visiting a neighborhood lit up for the holidays. In the lab, a long table is adorned with hundreds of small metal stands holding mirrors of various shapes. Laser beams bend their way around the table like reflections in a miniature House of Mirrors. But it’s when solutions of silver and gold nanoparticles are placed in the path of these lasers that we get light like we’ve never seen it before.
Haber’s lab is home to a pulsed ultrafast laser system. This laser system produces light that pulses on the order of less than a single picosecond, or one trillionth of a second.
Ultrafast lasers are used in a wide range of experiments to study details about how light interacts with atoms, chemicals and materials. One such experiment, ultrafast spectroscopy, is used to understand what happens after a molecule or material absorbs light. This can help in developing new materials for solar panels, biological imaging technologies and a wide range of other light-based technologies, including light-triggered drug delivery inside the human body.
Researchers in Haber’s lab, including chemistry Ph.D. candidate Raju Kamal, are currently using the lab’s pulsed ultrafast laser system to investigate the properties of nanomaterials – tiny materials that interact with different colors of light in special ways – for drug delivery and other applications. A Christmas tree has nothing on a gold or silver nanoparticle interacting with light from a laser in Haber’s lab.
“Light interacts with gold and silver nanoparticles in a very interesting way,” Haber said. These metal nanoparticles have free electrons at their surface that can resonate, or bounce up and down in synchrony, when a particular color of light hits them. When these free electrons in gold and silver nanoparticles resonate, they can create plasmons or coherent oscillations of electrons that lead to enhanced optical fields and large signals in ultrafast spectroscopy experiments. In other words, gold and silver nanoparticles can practically enhance light at their surfaces. This enhanced light can be a powerful tool for light-triggered release of drugs attached to the surface of nanoparticles, including cancer-treating drugs that need to be delivered to specific locations of tumors inside the human body.
In collaboration with other researchers including Daniel Hayes, an associate professor of biomedical engineering at Penn State who previously conducted research in the LSU Department of Biological Engineering, Haber’s lab studies light-triggered or light-activated drug delivery using gold and silver nanoparticles. A gold or silver nanoparticle is a very small particle of either silver or gold with size dimensions ranging from about 1-100 nanometers. A nanometer is the length of one billionth of a meter. If you took a meter-long measuring stick and cut it into a billion equal pieces, each piece would be on the scale of the nanoparticles Haber’s lab works with.
On the surface of these particles, researchers can attach drug molecules that only break away when a particular color or wavelength of laser light irradiates the surface of the particles. This process is called photocleavage.
“The idea is that drug molecules attached to nanoparticles can be injected to a certain part of the body and will then only release from the nanoparticles into the body or into specific cells upon irradiation with light,” Haber said. “We have attached drug molecules to nanoparticle surfaces using linkers that cleave [break apart] upon irradiation with ultraviolet light.”
Using a pulsed ultrafast laser system, Haber and researchers working in his lab can practically watch the drug molecules breaking away from the nanoparticle surface after being hit with a beam of light. Using a surface-sensitive nonlinear spectroscopy process called second harmonic generation, researchers in Haber’s lab can determine how quickly the drug molecules break away from the nanoparticle surface under different conditions.
Haber’s lab has compared how quickly the photocleavage happens on silver nanoparticles, gold nanoparticles and polystyrene or polymer nanoparticles. “We find that the silver nanoparticles have fastest and most efficient photocleaving kinetics corresponding to approximately three times faster than the gold nanoparticles and approximately six times faster than the polystyrene nanoparticles,” Haber said.
How can the drug molecules break away from the surface of the silver nanoparticles so quickly? It turns out that silver nanoparticles interact with light in a very special way, enhancing the optical field or the light hitting their surface. This plasmon enhancement means that the available light can do more work in breaking the light-sensitive linkers that hold the drug molecules to the silver nanoparticles. Gold nanoparticles don’t enhance light at the ideal color or wavelength for this improved photocleavage, and polystyrene nanoparticles don’t enhance light at all.
“It's very exciting to do this type of research that may lead to improved techniques for using nanoparticles for drug delivery,” Haber said. “This work is part of a larger field of nanomedicine, where nanoparticles can be used for the treatment of different diseases for the benefit of society. It's also very interesting to do research that studies fundamental properties of nanoparticles relating to interactions with molecules and light, since the work can lead towards new discoveries that are sometimes wide-ranging or unexpected.”
Check out papers published by Haber and his research group here.
In the future, Haber hopes to improve how drug carrying nanoparticles release drugs inside the human body using light as a trigger. One idea is to use a new type of layered nanoparticle made of both silver and gold to convert infrared light into heat that could be used to trigger the release of drug molecules inside the human body. Infrared light is better than ultraviolet light for drug delivery applications in the body because infrared light can travel deeper into biological tissue. Haber’s lab is already testing such nanoparticles with temperature-triggered linkers that hold drug molecules onto the surface of the particles. “We are getting very encouraging preliminary data on this work, so we are very excited to finish this study and publish this work soon for drug delivery applications using these near-infrared wavelengths,” Haber said.
So - how about some nanoparticles and laser beams for your holiday decorations next year?!