Holy Batballs Batman!

Surprisingly, scanning electron microscopy (SEM) isn’t as exciting as it might sound.  I know, I was shocked too.  A lot goes into SEM.  First, you have to coat your samples.  I’ve been coating mine with gold and palladium (not enough to get rich on though).  Then, you have to sit around while the vacuum chamber that your samples will be placed in vents (generally three whole minutes!), put the samples in, and pump it back down (another three minutes!).  After that you have to turn on the electron gun (cool) and align everything.  Just getting ready takes about twenty frickin minutes!

After all of that, you take pictures of your samples.  Here’s one I got yesterday of a silica nanosphere (ok, nanoball) array:

How to Increase Problem Solving Abilities

Melanie Cooper from Clemson University was yesterday’s speaker at the chemistry department colloquium.  Her talk was about research in chemical education about what increases problem solving abilities in general chemistry students, most of which she has published in the J. Chem. Ed. vol. 85, pg 866 (2008) (sorry, not a free article).  I’ll highlight what she and her co-workers found, but for the full story you really should just read the article.

One of the first issues she dealt with was exactly what she meant by problem solving, which she quotes from Anderson as “What you do when you don’t know what to do.”  Her talk, and the JCE paper referenced above, both center on students solving open ended, ill-defined problems (so, not something like, how many Ne atoms are there in 1 g of Ne?).    Students in her study were applying previously acquired knowledge to case-based problems.  The results of the study debunk five common myths about learning and problem solving.

I Love the Smell of Results in the Morning!

Things are looking up in p-(dimethyl)amino cinnamaldehyde (pDMAC) land. Over the last couple summers one of the students I’ve been working with (Diane, that’s you!) has collected enough SERS and Raman data to begin putting together a manuscript! I’ve been working on getting some more spectra over the last couple of weeks, as well as finishing up some calculations using Gaussian 03W.

One question that comes up frequently about our spectra is if we are seeing the cis or trans isomer of pDMAC. As we dug around looking for published spectra and frequencies, we (quite happily) discovered that there aren’t any! So this means that we can write up a nice paper about it. To strengthen it, and to help us assign the vibrations, we decided to do some Gaussian calculations on the optimized geometries (which tell us that trans is more stable than cis) and predict vibrational frequencies and the Raman spectrum. Below the fold are the experimental (normal Raman, solid pDMAC) and theoretical Raman spectra (isolated molecules in gas phase, wavenumbers scaled by 0.9806).

Lab Update – Using Pseudopotentials

I’m trying to finish up some of the work on p-dimethyl aminocinnamaldehyde (DMAC) that started several years ago. My goal is to refine the theoretical calculations that Diane performed last summer by including Ag atoms[1]. Hopefully the calculations will help us understand how DMAC adsorbs at the Ag surface, and maybe support the vibrational assignments that Diane made.

Lysozyme SERS – Different Spectra in Different Pubs?

Our major research goal this summer is to find out what conditions are necessary for reliable SERS of proteins. Lots of people are interested in this for many different reasons. Ours are to further collaborations with some colleagues in the biology department who are interested in finding out some structural information about proteins they are studying. Hopefully as we work on this we’ll be able to get some general information about what one needs to think about in doing SERS with proteins.

We’ve started by trying to reproduce literature results. You’d think that would be easy, but it isn’t turning out to be the case. As an example, consider lysozyme. I have four published reports of lysozyme SERS, and all four have markedly different SERS spectra. Each is reviewed in chronological order below the fold.

What Do “Good” Ag Colloids Look Like?

If you are my faithful reader, then you know that much (all?) of the research that happens here relies on “good” silver colloids. Last week I posted a prep that results in good Ag sols. But what do I mean by good? Well, they have to look good.

Formation of HCl – One Water at a Time

At some point, all students who take General Chemistry learn that acids are species that donate protons in water. For example, hydrochloric acid is formed when hydrogen chloride gas is dissolved in water:

Formation of the hydronium ion (H₃O⁺) results in a decrease of the pH of the solution. Yeah, if you’ve had General Chemistry, you definitely know that. But did you know that until recently, we didn’t know how many water molecules it took to make this happen?

What Happened in Lab: 6/15 – 6/16, 2009

Dylan is getting closer (we hope) to figuring out some of the conditions necessary for SERS of lysozyme and bovine serum albumin (BSA). On Monday we figured out that a lot of what we were seeing in our spectra were bands from the phosphate buffer [1]. That’s what happens when you do control experiments! Since then, we decided to stop using the buffer and use DI water as our solvent.

Now Dylan has several (ok, lots) of spectra with broad bands that match up with the solid state lysozyme Raman spectrum we have (which matches up exactly with all the published spectra except one!). We aren’t sure why the bands are as broad as they are. One hypothesis is that our colloids have broad size distribution and we are observing a bulk average of many different SERS active sites. We plan to make more colloids and aim for a narrower extinction spectrum, which would indicate a more monodisperse colloid. Failing that, we may try core-shell nanoparticles, starting with an Au seed.

Dylan has also tried making Ag colloids using borohydride as the reducing agent [2]. The initial results looked good, but after storing them they aggregated. With colloids, cleanliness is very important.

[1] I think this is also in some published spectra too, not necessarily assigned correctly. More on that later.
[2] This is one of the several “Lee and Meisel” preps. Moral – if a paper says “Lee and Meisel method”, it could be one of up to four different preps for silver colloids. Reviewers need to tell authors to be more specific.

What Happened in Lab: 6/12/09

Yesterday we learned how to make silver colloids (well, re-learned for me). I read through the notebooks of several former students, and concocted the following protocol for making 200 mL of Ag colloid via citrate reduction (essentially one of the Lee & Meisel preps):

What Are the Rules of the Game?

Richard Feynman on science: