Super Fantastic NanoNerds

What’s up guys!! It’s your group, the NanoLab from the Chemistry Department, back with another X-SIG blog post! We got a couple of old and new faces to show you along with four projects going on in the lab this summer. Before you continue reading, be sure to SMASH that like button down below AND hit the subscribe button to stay updated with what’s going on in the lab (to actually stay updated with the lab, you can visit our lab website: nanolab – @ Gettysburg College). Also, comment down below what your favorite element is!! Now without further ado… let’s get into it. 

From left to right: Khristian Banks, Cole Springer, Dr. Thompson, Yesenia Posada Cruz, and Hana Konno.

Meet the Lab Members

Dr. Thompson: I’m supposedly in charge of the NanoLab but often I feel like I have no idea what I’m doing. I guess that’s part of doing research, right? I’m lucky to have four wonderful students working with me this summer and you’ll get to hear a little about their work below.

Cole Springer: Hi everyone, I’m Cole! I’m a rising senior and a chemistry and German studies major. This is my first summer in the NanoLab, but I’ve worked the past two summers with Dr. Funk on some organic synthesis, which I’ve gotten the chance to do this summer as well! My favorite element is Osmium because of its status as the densest element! I have a couple grams of it, and I find density to be a weirdly fascinating property of elements.

Hana Konno: Hi guys! My name is Hana, and I’m a rising junior and a chemistry major. This is my second summer in the NanoLab, and I am continuing on with the project that I have been working on since last summer. My favorite element is Einsteinium because the name sounds really cool. 

Yesenia Posada Cruz: What’s up everyone! My name is Yesenia, and I’m a rising senior chemistry major, math minor. This is my first summer in the NanoLab, but I have been working in the lab since last semester. My favorite elements are Yttrium and Xenon because they have very unique spellings! 

Khristian Banks: Hi everyone! My name is Khristian, and I am a rising sophomore majoring in chemistry and minoring in German Studies. This is my first summer in the NanoLab, and I’m working on an aquatic toxicology project in tadpoles at different temperatures. My favorite elements are chlorine and platinum! 

The NanoLab Projects

Project 1 (Hana): Polymer Functionalized Self-Assembly of Gold Nanorods using pH Modifications

Alright, so the basic rundown of my project is that I am synthesizing gold nanorods, then adding two different layers of chemicals called polymers onto the nanorods, and then raising the pH of the nanorod solution to get the nanorods to assemble. Gold nanorods look exactly what they sound like (very small rod-shaped pieces of gold). The image to the right is what a single nanorod looks like! What is special about the outer layer polymer (called Poly-l-lysine) that I coat onto my nanorods is that when the pH is near 10.5 (to match the pKa of the polymer), the polymer changes its structure, which is what drives the nanorod assembly. Gold nanorod assembly is important because it has a wide variety of applications including drug delivery, cancer therapy, etc. I am using a couple of different instruments to collect characterization data for my project, but the coolest instrument that I am going to mention is the Transmission Electron Microscope (aka the TEM). It is a very fancy microscope down in the Imaging Suite of the Science Center. Below is one of the images I took using the TEM! If everything goes well this summer, then my project will be published in a journal sometime in the near future!

Project 2 (Cole): Tuning the Adsorption of Polyelectrolytes to Gold Nanospheres

My project is heavily based on the question, “what happens if…?” From past work in the lab, we have been able to “coat” our gold nanospheres with polyelectrolytes (charged polymers) and quantify how much of the polymer adsorbs to each individual nanosphere (which are usually between 1-50 nm in diameter). This student’s work (Celina Harris) was actually published in a scientific journal! However, one question that arose from her work in the NanoLab was how to tune the amount of polyelectrolyte that adsorbs to our nanospheres. This is where my work starts.

Part of my project has been to synthesize a new intermediate layer (which we use to prevent the aggregation of nanospheres and control their size) that will allow us to quantify both how much of the intermediate layer and the polyelectrolyte coating is on the surface of the gold nanosphere. This would grant us insight into the electrostatic interactions that take place at the surfaces of gold nanospheres and how we can harness those interactions to controllably add molecules to our nanospheres. This work is especially useful when considering that gold nanoparticles show promise as drug delivery systems, and of course, the amount of drug delivered is quite important!

My summer started out by simply synthesizing gold nanospheres (which is a really finicky process), and then moved on to trying to polymerize the intermediary layer. We thought that we could reliably quantify the amount of these molecules on the gold surface due to the relative lack of exchange with free molecules in solution compared to a different intermediary layer, where the molecules freely adsorb and desorb from the gold surface.

A depiction of our free molecule versus the polymerizable version.

However, none of my attempts at polymerizing this molecule worked, and so I moved onto synthesizing a new molecule, which will strongly adsorb to the gold surface and allow us to quantify how much is adsorbed without worrying about a fluctuation in the amount of molecules adsorbed.

The molecule I’m synthesizing.

I am just starting to wrap up this synthesis, so I will start using this molecule with our gold nanospheres and accomplish my goal of quantifying not just the polyelectrolyte coating, but also the intermediary layer. I’m hopeful this will lead to cascading effects of learning how to tune the amount of polyelectrolyte that binds to our gold nanospheres, and lead to more discoveries along the way!

Project 3 (Yesenia): Exploration of Gold Nanoparticles and BSA Interactions Through Surface Chemistry

My project is interested in exploring how gold nanoparticles with known surface chemistries interact with a model protein called bovine serum albumin (BSA). Some examples of the surface chemistries I have worked with this summer are positive, positive-neutral mix, neutral, neutral-negative mix, and negative. For most of my experiments, I am pipetting solutions of nanoparticles (with the examples of known surface chemistry) with solutions of BSA then analyzing them using different instruments. It is very important that in my experiments my spheres do not aggregate. So, to characterize and make sure this has not happened, I use ultraviolet visible spectroscopy to determine the state of my particles. Additionally, I use circular dichroism spectroscopy to determine the secondary structure of the BSA on the particles, such as α-helix or β-sheet as a function of nanoparticle surface chemistry. Knowing and bettering our understanding of how the surface charge of gold nanoparticles can influence the way proteins bind is important in applications such as drug delivery and photothermal therapy. I look forward to continuing to work with the surface chemistry of gold nanoparticles and seeing what biological interactions can be discovered! 

Project 4 (Khristian): Analysis of Citrate-Capped Gold Nanoparticle Uptake During Tadpole Metamorphosis at Varying Temperatures

The purpose of my project is to learn more about how gold nanoparticles impact the metamorphosis of tadpoles at different temperatures. Gold nanoparticles are used in a variety of consumer products from clothing and cosmetics to paints. Due to their versatility, gold nanoparticles will inevitably end up in waterways due to dumping and other ways of pollution. Through my project, we are hoping to learn more about how gold nanoparticles, at relatively low concentrations, may impact the growth of aquatic animals. As global warming becomes more of a pertinent issue, it is also valuable to learn about how that may play a role in the growth of the same tadpoles, so I am working with tadpoles that had been exposed to gold nanoparticles at 3 different temperatures: 15, 20, and 25 °C. 

Figure 1: Tadpole School Picture.

The procedure for my project includes obtaining the tadpoles from Dr. Fong’s lab where they have been well taken care of for several months. I weigh each tadpole and dissolve them in concentrated nitric acid in their respective vials. I then use a hot plate to evaporate the acid overnight. After letting the vials cool, I resuspend them in 10% aqua regia, which is made of HCl and HNO₃. Yay, strong acids and bases! I then use the Sonicator named Hedgehog (which has a mustache!) to get all of the solid floating off the sides of the vials and into solution. Lastly, I filter each solution into a conical tube until it is time to use the ICP-OES. During this time, I also make calibration curves, which are useful for finding how much gold was in each sample. Once I find out how much gold was in each sample, I do a few calculations to find the micrograms of gold per gram of frog. At the time of writing this, it looks to me that the tadpoles at 25°C uptake the most gold, but I still have dozens more tadpoles to process. Another interesting note is that many of the tadpoles at 15°C have not reached metamorphosis yet, so they are being exposed to the nanoparticles for an extended period compared to the other temperature groups.  This situation could potentially mean that the tadpoles at the lowest temperature will uptake the most gold, so it will be interesting to see what happens!

One extremely important part of my project is keeping everything clean and reducing the risk of contamination. Since the NanoLab has been working with gold for several years, it is likely that some of the tools and glassware have been exposed to gold. In order to reduce the risk of contamination in the tadpole samples, I have a long cleaning procedure for each vial and other glassware I use.

Lab Shenanigans:

Some of us on the DC Trip featuring the Smithsonian elephant, molecules, and a gold exhibit (to stay on theme of course).

Super Fantastic Golden Graham Nanorods!

The Lab Members:

Professor Thompson

I’m supposedly in charge of the nanolab but often I feel like I have no idea what I’m doing. I guess that’s part of doing research, right? I’m lucky to have three wonderful students working with me this summer and you’ll get to hear a little about their work below.

Isaiah Lares

Hi! My name is Isaiah. I am a rising sophomore pursuing a physics and chemistry major. I am working on a project in Professor Thompson’s lab about how changing the supporting cation of a polymer affects polymer adsorption.

Ziang Wang

Hi! I am Ziang. I am a rising senior, chemistry major and math minor. Me and Hana are working on understanding and finding ways to control gold nanorods assembly by using pH-responsive polyelectrolytes. Confusing right? Let us break it down for you!

Hana Konno

Hi! My name is Hana. I am a rising sophomore and a chemistry major. I love traveling and visiting new places. This summer, I am working on a project with my lab partner Ziang in Professor Thompson’s lab (AKA the Nanolab). We have been synthesizing a lot of cool nanorods in the lab, so we will explain some of it down below!

What is the NANOlab about?

If you were unsure, our lab researches gold nanoparticles, hence the name, NANOlab. Research into nanomaterials has been heightened in the last couple of decades as nanomaterials exhibit unique properties that are typically not found in the regular material. There has been a lot of interest in researching gold nanoparticles for potential uses in drug delivery, biosensors, and solar technology to list a few. 

One of the projects in the NANOlab this summer is to document the effects of pH on the self-assembly of gold nanorods. This project is being done by us (Ziang and Hana). Controlling the assembly of nanorods is important because the applications of gold nanorods requires an efficient way to assemble nanorods as needed. 

I (Isaiah) am conducting the other project being in done in the NANOlab which is to quantitatively analyze the affects of changing the supporting cation of a polymer on adsorption onto gold nanoparticles. This will help us gain insight to the range of electrostatic interactions between gold nanoparticles and applied ligands.

How do we synthesize gold nanorods?

Schematic representation of nanorods synthesis. (Picture of “rainbow” at the end.)

In our lab, we use a two-step method to synthesize gold nanorods. The first step creates a seed solution with all the nanoparticles being spherical. The second step is the growth phase, where the spherical nanoparticles are grown longer. By varying the amount of AgNO₃ in the growth solution, we can control the length of the nanorods that are synthesized. We decided to add five different amounts of AgNO₃ ranging from 10 µL to 100 µL. The resulting rod solutions show color transition from pink to tan, which we call “rainbow”!

What do we do after the gold nanorods are synthesized?

We first clean our nanorod samples! Because excess CTAB and other polyelectrolytes sitting in the solution for a long time will change the shape of our nanorods. Therefore, we need to clean the nanorods after each coating.

The inside of our centrifuge with some of our nanorod samples.

After the cleaning, we coat them with polyelectrolytes (charged polymers)! The method we use is called layer-by-layer (LbL). As you remember from our synthesis of rod solutions, we used CTAB, so the nanorods are coated with CTAB. Since CTAB is positively charged, we can add negatively charged polyelectrolytes to the solution; the opposite charges naturally attract each other, thus the negative polyelectrolytes will wrap around the gold nanorods. (We use four different negatively charged polyelectrolytes.) The rod solution is cleaned in this step as well to remove the excess polyelectrolytes. Then, we coat the rods (now negatively charged) with pH-responsive positively charged polyelectrolytes.

Polymer coating illustration. The blue layer is the negative polyelectrolytes, the black layer is the positive polyelectrolytes.

Ziang using UV-vis spectroscopy.

In each coating step, the nanorods are characterized with UV-vis, dynamic light scattering (DLS), and zeta potential. UV-vis tells us the amount of light the nanorods absorb and the wavelength of the light that they absorb. As the length of the rods increases, the wavelength they absorb increases. DLS simply tells us the diameter, and zeta potential tells us about the surface charge of the rods. Each is important for us to ensure that each step of the nanorod coating process is done successfully!

From left to right: Graphs of the DLS, UV-vis, and Zeta Potential characterization data.

Now to the pH Experiments!

Once we have our coated gold nanorods, we do pH experiments on them. If you are unfamiliar with what pH is, it is a scale that typically goes from 0-14, 0 being the most acidic, and 14 being the most basic. Our coated nanorods are initially in a solution somewhere between a pH of 5 and 6. Our pH experiments involve pipetting sodium hydroxide (NaOH) into the solution to increase the pH of the solution. Sodium hydroxide is a strong base that when added into solutions makes them more basic (so base for basic), which is why we are using it for the pH experiments.

Hana at work as she sets up a pH experiment.

For the pH experiments, we are collecting characterization data (UV-vis and DLS) at 5 different pHs: 9.5, 10, 10.5, 11, and 11.5. The pH at 10.5 is important because this is when the pH matches the pKa of the solution, so chemical things happen that allow the nanorods to assemble. 

Imaging the Nanorods

Now you may be wondering if there is a way to see what the nanorods look like and the answer is yes! Using a fancy microscope called transmission electron microscopy (TEM), we can actually take images of the nanorods. It is quite tedious to prepare a sample for TEM analysis, but all of the preparation is worth the cool images. The TEM images are important because they are a visual indicator of self-assembly. Currently, we have been taking sets of TEM images of the control samples (so at the initial pH) and pH samples (these have a pH of 10.5). This past week, the lab drove up to Penn State to use another cool microscope called scanning electron microscope (SEM). The SEM we used is worth a couple million dollars, so it was a pretty big deal to use.

The photo on the left shows a TEM image of the nanorods. The photo on the right shows Ziang looking at a cluster of gold nanorods using the TEM.

The SEM we used up at Penn State. It was definitely worth the two and a half drive to use.

What Else Have We Been Up to?

During our spare time in the lab, we have been extremely busy doing other things like a cool Lego puzzle that members of Professor Buettner’s lab helped us finish (actually, they finished 90% of the puzzle for us…). On a real note though, there is also a lot of data analysis that we do which involves making lots of graphs and tables. And I mean A LOT. Anyway, here’s a picture of the completed Lego puzzle to end the post! We hope you learned a thing or two about the Nanolab!

Changing the Supporting Cation of Polystyrene Sulfonate (PSS)

So for my project (this is Isaiah), I follow the same procedural steps as Hana and Ziang until the first polymer coating where I use a different polymer called PSS instead of PAA. This polymer is a negatively charged polyelectrolyte that has the following structure:

What we are interested in with this polymer is how the supporting cation, in this case sodium, affects the electrostatic interactions between the gold nanoparticle and the polymer. This is so that we can gain a better understanding of the amount of polymer that stays on the nanoparticle since the layer-by-layer technique depends on electrostatics. The main takeaway is understanding the difference between layers of polymer that are tightly attached and more loosely attached to the nanoparticle. And in order to properly analyze this, consistent polymer packing is needed across the polymer which is why spherical gold nanoparticles are being used for my research as opposed to nanorods due to their constant surface. In order to characterize my particles, I use UV-vis spectroscopy, DLS, and zeta potential.

So how are we going to do this? By using a centrifugal dialysis process as detailed below:

Using this process we are able to separate and collect polymer that is not fully adsorbed on the nanoparticle. Depending on what stage of the process the polymer gets separated in, it gives insight to how tightly adsorbed the polymer was. With these filtration samples, I am able to get concentration information of specific elements using ICP-OES/AES (Inductively Coupled Plasma Optical/Atomic Emission Spectroscopy). This technique of spectroscopy utilizes an argon plasma to superheat a sample. In our case these are the dialysis samples. When the electrons of the sample are excited and return to their ground state, a photon is emitted. The ICP contains an array of sensors that collect light at different wavelengths. Depending on what element and elemental wavelength you specify the ICP to collect, concentration data can be collected.

However in order to use the ICP effectively, accurate and precise calibration curves have to be made to compare our sample to which is what I have been doing as of late. For our calibration curves to be up to standard, they need an R^2 value of about 0.9999. This has posed quite the challenge, but the calibrations I have done are getting closer to the desired value. So far I have done calibrations of gold and sulfur. Here are two of them:

Gold calibration curve from 100-1000 ppb analyzing at the elemental wavelength Au 267.595

Sulfur calibration curve from 100-1000 ppb analyzing at the elemental wavelength S 180.669

The data received from the ICP will allow me to calculate exactly what amount of polymer desorbs from the nanoparticle at which stage of dialysis. This can give a degree of understanding to the electrostatic strength of sodium as the supporting cation of PSS.

So What’s Next?

The next steps of this project are to finish making the calibration curves for the ICP and then analyze the dialysis samples that I have made. This will give us data to firstly reinforce data gained by previous students, and secondly new data on the amount of sodium ions that are in solution at each stage of the dialysis process. Furthermore, traditional dialysis techniques will be used in order to substitute the sodium ions of PSS with the following ions: lithium, potassium, magnesium, and calcium. With these newly formed modifications of PSS, the centrifugal dialysis process and ICP analysis will be performed in order to compare the differences in polymer adsorption between each supporting cation. I hope you enjoyed learning about my research, thank you for reading!