Next week, over ten thousand people will converge on the Boston Convention & Exhibition Center for the fall 2015 meeting of the American Chemical Society (ACS). The ACS was founded in 1876 and has grown to 158,000 members, making it the largest scientific society in the world. Attending such a big conference can seem a little daunting the first time, so Sustainable Nano is here to help you make the most of your ACS (or other conference) experience! The following is a handy list of conference tips and suggestions compiled from students, faculty, and friends of the Center for Sustainable Nanotechnology.
Scientists have known for some time that nanomaterials can stick to cell membranes and, in some cases, damage the membrane in the process. But what exactly do nanomaterials stick to on the cell membrane? A particular type of molecule called lipopolysaccharides (LPS) may provide a key to answering this question.1
Many of us take notice of bacteria only when they make us sick. In reality, bacteria are always working behind the scenes, sometimes making us sick, but more often performing tasks that are beneficial to humans and the broader environment, like helping us to digest our food and supplying nutrients to plants.
As Vivian Feng mentioned in her recent post, there are two ways that bacteria are likely to encounter nanomaterials: when the bacteria are being directly targeted by nanomaterials (as in nanoparticle-based antibiotics), or when they randomly encounter nanomaterials that humans release into the environment.
In either case, it is imperative that we understand how bacteria interact with the nanomaterials that we make: this will help us increase the effectiveness of nanomaterials that are designed to kill bacteria, and decrease the killing-power of nanomaterials that enter the environment as nano-waste, where beneficial bacteria are hard at work. (For more on this, take a look at Part 1 and Part 2 of our series on how nanoparticles get into the environment.)
As I mentioned at the beginning of this post, scientists have known for a while that some nanomaterials can stick to and potentially damage cell membranes.2,3 But knowing that isn’t always enough to give us control over which nanomaterials will be antibiotics and which will be harmless to bacteria in the environment. The cell membrane is not a single uniform entity, but is composed of a sea of molecules including lipids and proteins. We need to identify which of these components is sticky for nanomaterials in order to control how those materials interact with bacteria.
To do this, we (meaning myself and a number of collaborators within the Center for Sustainable Nanotechnology) recently studied how gold nanoparticles interacted with both living bacterial cells (using a bacterium called Shewanella oneidensis) and artificial cell membranes that we made in the lab using the same kinds of molecules found in real cell membranes. Specifically, we varied the amount of one molecule, called lipopolysaccharides (LPS), and observed the impact this had on how sticky the membranes were for the nanoparticles.1
Why did we focus on lipopolysaccharides? This question is best addressed with a picture. As shown below, gram-negative bacteria have two lipid membranes (drawn as sandwiched structures composed of red/pink heads and white/yellow tails). The outer one contains LPS molecules (orange curved lines) that stick out from the cell membrane, kind of like the hooks on Velcro. We hypothesized that this would make the LPS molecules more available than other components of the membrane to stick to things that pass by the cell, like nanoparticles.
Our results suggest that our hypothesis was correct. When we removed LPS molecules from live bacterial cell membranes, fewer nanoparticles stuck to them. Similarly, when we incorporated fewer LPS molecules into artificial membranes, fewer nanoparticles stuck to them. Bacterial species differ not only in how much LPS is present in their cell membranes, but also in how long those molecules are. We used a type of laser spectroscopy to show that gold nanoparticles that stuck to longer LPS molecules were held farther away from the membrane than nanoparticles stuck to shorter LPS molecules.
So what does all of this mean in the long run? Our work suggests that bacterial membranes richer in LPS molecules may be stickier for some types of nanomaterials, and that those with longer LPS molecules may trap nanomaterials farther away from the membrane, where we think the nanomaterials can do less damage to the cell. We expect that this work will help us (and other scientists) design better nanomaterials, whether for the purpose of killing bacteria or leaving them alone.
This post is part of our ongoing series of public-friendly summaries describing research articles that have been published by members of the Center for Sustainable Nanotechnology. Ian Gunsolus, a doctoral student at the University of Minnesota, was a co-first author on this paper. The article was first published online in July 2015 in Environmental Science & Technology.1
- Jacobson, K., Gunsolus, I., Kuech, T.; Troiano, J., Melby, E., Lohse, S., Hu, D., Chrisler, W., Murphy, C., Orr, G., Geiger, F., Haynes, C., & Pedersen, J. Lipopolysaccharide density and structure governs the extent and distance of nanoparticle interaction with actual and model bacterial outer membranes. Environmental Science & Technology, in press. doi: 10.1021/acs.est.5b01841
- de Planque, M., Aghdaei, S., Roose, T., and Morgan, H. Electrophysiological Characterization of Membrane Disruption by Nanoparticles. ACS Nano, 2011, 5 (5), 3599–3606. doi: 10.1021/nn103320j
- Liu, S., Wei, L., Hao, L., Fang, N., Chang, M., Xu, R., Yang, Y., & Chen, Y. Sharper and Faster “Nano Darts” Kill More Bacteria: A Study of Antibacterial Activity of Individually Dispersed Pristine Single-Walled Carbon Nanotube. ACS Nano, 2009, 3(12), 3891–3902. doi: 10.1021/nn901252r
Last month we posted “Light Can Do Way More Than Bend: Part 2,” in which we talked about using lasers to create a particular type of metamaterial from gold nanoparticles. One exciting application for metamaterials research is the development of invisibility technology, and now the ACS Reactions team has produced a great little video explaining more about this topic: “Are Invisibility Cloaks Possible?”
Another recent video relevant to our blog is the very first episode of Chem-Lapsed, a new time-lapse video series from C&E News. In “How the Fruits Got Their Colors,” we described the importance of the molecule lycopene in the red color we see in tomatoes. In their “Tomato Juice Rainbow” demo, Chem-Lapsed shows how the interaction between bromine water and lycopene can produce a rainbow of colors:
Videos like these can help illuminate (ha!) how we perceive light and color, which involves phenomena that are much too small to see with the naked eye. Molecules like lycopene are even smaller than a nanometer, and visible light wavelengths are about 400-700 nanometers, which is why nanoscience research is so relevant to the development of metamaterials and other cutting-edge technologies.
Do you have any favorite videos or activities for demonstrating how we see light and color?
This post is part of our ongoing series of public-friendly summaries describing research articles that have been published by members of the Center for Sustainable Nanotechnology. Vivian Feng, a chemistry professor at Augsburg College, is the first author of this paper, which was a collaboration with undergraduate and graduate students as well as other CSN faculty members. Vivian says, “Understanding the impact of nanomaterial toxicity on the environment is a highly interdisciplinary task. I really valued the team effort while working on this manuscript, especially for my undergraduate students to experience it. The boundaries between disciplines of chemistry, biology and physics were blurred when we all put our heads together to solve the same problem – that’s the beauty of a collaboration.”
Let’s face it, staying in a hotel can be pretty wasteful. All those take-out containers for food, those little soaps in cardboard boxes (or plastic wrap!) that get used three times before they’re replaced with a new one, and hard-to-control thermostats that lead to ice-box air conditioning even when no people are around to enjoy it.
This week the Center for Sustainable Nanotechnology had one of our rare in-person meetings where we gathered from all around the country to talk science (and blogging!). We met at the University of Wisconsin-Madison, and many of us stayed at the Wisconsin Union Hotel, just down the road from the Chemistry Department. It turned out to be a good fit philosophically as well as geographically for our CSN meeting: the hotel had the most comprehensive approach to sustainability that I personally have ever experienced.
You literally cannot walk into your room at the hotel without noticing their sustainability efforts: the lights won’t operate unless you put your room key in a slot by the door!
It’s Sunday night and I am watching one of my favorite shows, which of course revolves around food. In this particular episode, competitors were challenged to incorporate blue into their baked delights without using artificial coloring. That may not seem to be much of a challenge, but there are actually very few naturally occurring blue foods. Many challengers reached for blueberries as their blue ingredient, but blueberries seem to be closer to purple than blue to me. (I guess because blue is in the name, we can just consider it close enough to blue to pass. But how many other blue fruits or vegetables can you think of?) Fruit and vegetable colors seem to be dominated by greens, yellows, oranges and reds. With my interest piqued, I set out to explore and better understand how the fruits (and vegetables) got their colors.
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When you’re done, you may enjoy celebrating the U.S. Fourth of July holiday by re-reading our post about nanomaterials making their way into fireworks; or check out this infographic from Compound Interest about the Chemistry of Sparklers:
Thanks so much for reading Sustainable Nano – we look forward to hearing from you!