Have you ever seen a nanoparticle? You probably haven’t ‘SEEN’ one since you could fit about 600 nanoparticles within the diameter of a single human hair, but you’d be surprised to learn that nanoparticles are everywhere. There are two types of nanoparticles, naturally-occurring and manmade. Naturally-occurring nanoparticles come in the form of volcanic ash and sea spray; manmade nanoparticles are formed as byproducts of car exhaust and mining, can be used in medicine, and are made in labs like ours. This summer the Nano lab incorporates three different projects, all dealing with a different aspect of gold nanoparticles: medicine, toxicity, and fundamental properties.
Why Gold Nanoparticles?
So why did we choose to work with nanoparticles, and more specifically, why gold nanoparticles? Well, nanoparticles are interesting to study because they exhibit properties that are very different from their bulk substances. For instance, a gold necklace will react and respond differently to physical and chemical changes than a gold nanoparticle will. One of the easiest differences to observe is the change in the way nanoparticles absorb light. Bulk gold all looks, well, gold. However, as the size of a nanoparticle changes, so does the way it responds to light.
Nanospheres in solution appear red (far left), while long nanorods appear brown (far right), and short nanorods appear green (middle).
This same difference in properties can be seen in nanoparticles of other metals, such as silver or iron. We work specifically with gold because we have the ability to synthesize them in our very own lab using the process shown below. The ability to synthesize the nanoparticles in lab allows us to choose what size (and therefore, color) of particle we would like to make. We simply vary the amount of silver added in the scheme outlined below, and the size changes. The smallest amount of silver produces spheres, and as the silver is increased, the length of rods increases as well. Making the nanoparticles in our own lab also ensures that we have the particles we want, when we want them, which means no waiting for shipments of particles to arrive before our research can take place.
An outline for the seed-mediated growth of gold nanoparticles we use in our lab.
Who Are We and What Do We Do?
My name is Ida DiMucci. I am a rising senior Chemistry major and have done research in Dr. Thompson’s lab for two summers and one school semester in between. I am also an active member of Residence Life and will be the Residence Coordinator for Paul Hall this upcoming year. In addition to research, I also act as a Peer Science Mentor for the general chemistry classes and am currently the president of the Chemistry club on campus known as Sceptical Chymists. In my free time, you will find me climbing at the rock wall in the Den, running on the battlefields, or at Mr. G’s getting ice cream. After graduation, I plan to attend graduate school and receive a Ph. D in Chemistry, eventually returning to a small school like Gettysburg and becoming a professor with adorable children like Professor Frey.
In the Lab
While the study of nanoparticles may seem like new up-and-coming research, they have actually been around since the creation of stained glass windows during the medieval period.
The different colors in stained glass are caused by differences in nanoparticle size and shape.
Obviously, in the last 2000 years, many advances in the study of nanoparticles have been made, from using them in facial cream to using them in photothermal therapy to destroy cancer cells. My work with gold nanoparticles follows this trend and utilizes their unique structure and optical properties for the potential of drug delivery. While a nanoparticle may seem small when compared to a human hair, when thinking about them from a chemistry point of view they are actually gigantic. As seen in the picture below, about 30 benzene rings could fit across the diameter of one nanosphere.
A typical gold nanosphere has a diameter 30 times that of a benzene ring.
This raises the question: Could small molecule (in particular, medicinal molecules) be somehow attached to a nanoparticle, allowing the particle to act as a drug delivery device in the body? My work involves preliminary studies on what types of molecules could be attached to gold nanoparticles and how that attachment would take place. When synthesis is completed, the gold nanoparticle core is surrounded by a layer of CTAB, which is a surfactant or soapy molecule which consists of a long hydrophobic tail and a hydrophilic head. As shown below, this hydrophobic tail makes it possible for small hydrophobic (non-polar) molecules to be placed into that layer, a process referred to as partitioning.
Hydrophobic organic molecules partition into the hydrophobic region of the CTAB bilayer surrounding a gold nanoparticle.
I have specifically studied the partitioning of the four molecules shown below.
Different naphthol compounds have polar (hydroxy and methoxy) and nonpolar (naphthalene ring) groups.
The main goal is to quantify how differences in the molecular structure – such as size, polarity, and structure – could affect this partitioning. Hopefully, this will provide insight into how different drug molecules can be utilized to treat tumors and diseases in the medical field.
My name is Laura Lee, and I am a rising senior Chemistry major. This is my first summer doing research in Dr. Thompson’s Lab. My project investigates environmental toxicity. The nanoparticle industry is continually growing and has implemented its technology to enhance products people use every day. This is especially true with athletic clothing: silver nanoparticles can now be found in some athletic t-shirts and socks because of their unique antibacterial and odor neutralizing properties. While this can be seen as beneficial to the wearer and those around them, many researchers are looking ahead to the potential consequences of this technology. Think about it: This athletic clothing will still end up in the laundry even if the silver is helping to control the odor. Some amount of the particles will be removed from the clothing after every wash cycle and make their way to a waste water treatment facility. Unfortunately, these facilities are not equipped to filter out such tiny particles (remember: about 600 nanoparticles could fit along the diameter of a human hair). Thus, nanoparticles are washed away into nearby rivers, streams, and other water systems. What happens when these nanoparticles enter the environment and encounter plants, animals, and other chemicals? This is a question Dr. Thompson and many other researchers are trying to answer.
Nanoparticles enter the environment in many different ways from many different sources.
My research this summer is a part of Dr. Thompson’s on-going Tadpole Project. Last year, he studied developmental changes in tadpoles exposed to gold nanoparticles and preliminary research on tadpole uptake of gold nanoparticles. This year, we are solely focusing on quantifying gold uptake. Professor Fong in the Biology department raised two types of tadpoles, bullfrogs and woodfrogs, in two variable tanks – a gold nanoparticle solution and CTAB solution (the coating around the particles) – and a control tank. After the 25-day exposure period, the tadpoles were graciously sacrificed and preserved until I was able to process them. The bulk of my time in the lab has been spent processing the tadpoles and working with Professor Andresen in the Physics department to run samples using ICP-OES. This machine is able to detect and quantify the amount of specific metals – in my case gold – in a given solution. We will use the data to see how much gold is being taken up by the two types of tadpoles and if we can relate it to the size of the species or other characteristics of the tadpole.
Bullfrog tadpoles are just one example of creatures that are susceptible to nanoparticles in the environment.
My name is Michael Counihan, and I am a rising junior Chemistry and Music double major at Gettysburg College. I am interested in graduate school and doing research in the field of analytical chemistry. This summer is my first research experience, and I am splitting my time between the Frey and Thompson labs investigating lipid monolayers and nanoparticle surface-enhanced Raman spectroscopy, respectively.
Our Raman setup: a 785 nm (NIR) laser, Raman spectrometer, computer, and state-of-the-art dark box and cuvette holder.
Raman spectroscopy is a unique type of spectroscopy that utilizes inelastic (Raman) light scattering to give information about bonds in molecules. However, Raman signals are very weak since only about 1 in 1,000,000 electrons experience this inelastic scattering (the wavelength of light exciting the electron is different from the wavelength the electron emits as it jumps back down to a different lower energy state). To enhance this Raman scattering up to a million times, molecules can be brought close (within 5 nm) to the surface of certain substrates (in this case, gold nanoparticles); this is known as surface-enhanced Raman spectroscopy (SERS).
Raman signal intensities increase dramatically and a new Au-Br band appears when nanoparticles are introduced to a CTAB solution.
In Dr. Thompson’s lab, I am synthesizing gold nanorods of different lengths and concentrations to see which particles will give us the best signal enhancement. These particles are surrounded by a CTAB bilayer which keeps them stable. However, the bilayer will begin to collapse when the concentration of CTAB in the solution is too low (around 2-5 mM; aggregation occurs at less than 1 mM). When the bilayer collapses, it is brought closer to the surface of the particle, and signals from the aliphatic tails of the CTAB experience enhancement. My goal is to investigate how adding other molecules into the bilayer (right now, dihydroxynaphthalenes) affects the SERS signals of the CTAB as it collapses and use this data to gain information about this surfactant bilayer.
Bilayer stability is dependent on the concentration of CTAB in the solution.
Life in the Lab applied Outside the Lab
While working in a research lab over the summer is obviously focused on learning about the research, there are many other things that happen when a summer is spent working in a scientific community. We have learned a great deal about communication skills and how to present my research to a broad range of audiences. In addition, the faculty we work with act largely as mentors, providing us with insight on graduate schools and our future endeavors, and bake us cookies once a week to help us make it through the struggles of research. The connections and skills gained this summer will prove useful as we continue on in our studies and in our lives.