Dr. Chad Orzel, a physics professor and blogger on ScienceBlogs.com, recently posted an interesting post, Dorky Poll: Non-Abelian Sciences, wherein Orzel pondered the difference between physical chemistry and chemical physics. Of course the standard reply: "If you publish in the Journal of Chemical Physics JCP) you are a chemical physicist, and if you publish in the Journal of Physical Chemistry (JPC) you are a physical chemist" was promptly added to the comment section. But it reminded me that a couple of months ago, I had the pleasure of meeting a few of the editors of JCP, and they assured me that there is something much more distinct about their journal and its authors: rigor.

The word strikes me as one that is only used by those meticulous enough to know exactly what it means. That is a bit of a circular—and maybe a nebulous—argument, but it became clearer to me once I took a look at a few articles.

This article¹, published in JCP in April, takes a look at so-called nanodimer motors. There have been several synthetic molecular motors fabricated with nanoscale dimensions before, and Tao and Kapral discuss a chemical-reaction fueled method of propelling them. They propose that instead of only resulting in enhanced diffusion, the motors can instead be used in targeted dynamics and to perform tasks.

I bring it to the attention of the blog because of the theoretical rigor included in the paper—it's striking how mathematically thorough the paper is. Once again reminding me of what is perhaps the real difference between chemical physicists and physical chemists (no offense to my chemist friends).

Lots of neat-o scientific discoveries were stumbled on by two or more people at about the same time. Sir Isaac Newton and Gottfried Wilhelm Leibniz both invented calculus. The first patent for an integrated circuit was given to Robert Noyce while Jack Kilby's application was still being mulled over by patent clerks. Check out how the solution for the cubic equation came about—it was really more confusion than mutual discovery, but an interesting read nonetheless.

And, just over 30 years ago, Frederick Sanger published a pretty nifty paper on sequencing DNA. Sanger presented his "inhibitor method" to the world in the December, 1977 issue of the Proceedings of the National Academy of Sciences. Apparently, though, he was a few months too late, because Allan Maxam and Walter Gilbert had already published their paper: "A new method for sequencing DNA", in a February issue of PNAS. In the end though, Gilbert and Sanger shared half of the Nobel Prize (Paul Berg got the other half all to himself) in 1980. It seems though that Sanger really made out like a bandit, because the new sequencing method became known as the "Sanger" method and the Wellcome Trust opened the Sanger Institute. My question: where's the Gilbert Institute? The lesson: always publish second. Ok, that doesn't make sense. Maybe the lesson here is really: don't take advice from bloggers.

Oh well. I only bring it up because I just read this article on sequencing: H. Esfandyarpour and friends have published (in my favorite online open-access journal Biomicrofluidics) a description of a novel method for sequencing based on the heat created by the chemical reactions of DNA synthesis¹. Dubbed "thermosequencing," the authors like to think it may replace the Sanger method.

I can't claim to be an expert in sequencing, so I may come across as a bit naïve in my interpretation of the article. That being said, this seems like an amazing advancement. The temperature differences being measured here are only a few thousandths of a degree (~1500 µK). Cool. (My apologies for the lame pun, but honestly, how could I resist?) This kind of "temperature-based" approach to DNA sequencing strikes me as uncannily original. So, yeah, cool.

1. Esfandyarpour, H., Zheng, B., Pease, R.F., Davis, R.W. (2008). Structural optimization for heat detection of DNA thermosequencing platform using finite element analysis. Biomicrofluidics, 2(2), 024102. DOI: 10.1063/1.2901138

I gather that it's challenging constructing microchannels and microdevices. Like building canals and tiny dams, only they are embedded with sorting mechanisms and mixing devices. The analogy between microfluidic devices and systems of rivers, streams, and lakes only goes so far, though. When's the last time you stood on the bank near two converging rivers and watched as barges were distributed to the tributaries based on their response to an optical field?

I'm thinking of rivers and bodies of water, only because I was recently lucky enough to attend the 2008 ACS Spring Meeting in New Orleans. Approaching the city from the air, looking down on the marshland that surrounds it, you quickly realize: there's a lot of water in New Orleans. But after landing, it seems there may be other liquids that the locals prefer to drink, but I digress. If you walk along the boardwalk, the Mississippi River comes only a few feet from touching your feet. It's a little off-putting because you have to climb up several feet of steps to get to that height. All of this is a reminder that the entire city lies beneath sea level. Sorry, there I go again with a digression.

To build a complex system of micro-waterways, experimenters need to utilize some complicated tools. Building high-aspect-ratio micro channels can be facilitated with the use of Deep Reactive Ion Etching (DRIE), or plasma etching, which can be used to create channels, cavities, and sieves in MEMS and other microfluidic devices. DRIE allows for features with aspect ratios of at least 30:1, perfect for building a lot of interesting devices and such. In MEMS, the results can look impressive, especially if you're trying to construct something like this Torsional Ratcheting Actuator (Courtesy of Sandia National Laboratories [www.mems.sandia.gov]).

Two specific technologies—HARPSS (High Aspect Ratio combined with Poly and Single-crystal Silicon) and HEXSIL (HEXagonal honeycomb polySILicon)—employ DRIE to specific ends. HEXSIL—as you might guess from the name—can be used to build deep honeycomb-shaped structures, while HARPSS can be employed to build capacitive, and related, microdevices.

For another interesting look at microfluidics, I suggest this Physics Today article. This kind of information may be more helpful to me as I attempt to learn more about biomicrofluidics, than to experienced researchers or the general public. However, I don’t think there's anything wrong with an open discussion of a topic.

Anyway, I do believe I'm going to need to head back to New Orleans soon for some "research" on "fluid" flow.