Chemical telephones

The folks at UCLA have come up with a way to use cell phones to test for allergens in food. And we're not talking looking it up in a database somewhere, we're talking an actual lab test, which tests the actual piece of food in front of you.

Potentially useful if you have a life-threatening allergy, such as to peanuts, the example used in their paper.

While this does use the camera built into the phone, as a lab test, it is more than just taking a picture. Specifically, it uses a colorimetric process to measure how much allergen is in the sample.

I've used colorimeters before, and they are generally quick and handy (and portable, if you buy the portable version of the reader). However, that "generally" is important. While I've used some colorimetric kits that only take 5 minutes, I've used some that take over half an hour, and that's not counting sample preparation time.

And all of those kits require sample preparation of some sort, adding chemicals, and waiting for the reaction to finish before measuring. Most of the stuff I tested required dilution of a water sample to bring it into the testing range. The peanut test described requires the sample to be finely ground and dissolved first, and is described as taking 20 minutes, not including grinding time.

The good kits come with either pre-measured chemicals or easy quantities of liquid chemicals to measure, such as with a standard pipette or a supplied dropper, to minimize test error. The reaction of the compound of interest with the added reagents causes a colour change, which the sensor (or camera) measures. Generally, at least for the kits I've used, the darker the colour, the more of the compound of interest is present. From the paper, it looks like the peanut test turns red.

Realistically, now that the photo processing and colour measurement has been sorted out, any pre-existing colorimetric kit could be adapted for cel phone use. But then, most people who might get these things for personal use would be more interested in allergens than the stuff I have tested for at work. Most people don't care all that much how much calcium is in their water, because it isn't a health issue.

(Ok, technically this one is almost year old, but I don't restrict myself to only talking about new discoveries.)

Seeing at the surface

One of the quirks of chemistry is that we measure the bulk solution, but the reaction often happens on a surface - whether it's precipitation, dissolution, or catalysis.

While we usually calculate reaction rates based on the concentrations found in the bulk solution, in a case of a surface reaction, that's out where no reaction is happening! The equations for reaction rates empirically account for this in the constants, where the reaction rate is rolled together with the rate the reagents diffuse toward the surface to react and the rate the reaction products diffuse away from the surface and out of the way.

But in terms of designing a reaction, controlling it to get, say, the product we want instead of a byproduct if there are two possible reactions, or speeding it up or slowing it down, what happens at the surface can be key. And whether we watch or measure, knowing what happens at the surface is the first step toward changing what happens at the surface.

Nanostamp

Nano-scale devices have been around for a while now, filling functions such as chemical sensors of extraordinary sensitivity and selectivity, your computer's CPU, and the read/write head on the hard drive. There has also been a lot of progress on what people would recognize as nanomachines, too: motors, gears, switches, all on the nano-scale.

In most cases, however, they're still difficult to make, using the same sorts of high-purity, cleanroom processes as for computer CPUs. Yes, those are in mass production as evidenced by how there are computers in everything these days, right down to doorknobs, but it's still an intensive process requiring extreme purity and cleanroom procedures.

Until recently, that is: some nanoscale devices can now be made easily, even with something as crude as a tabletop vise. Plus, the crucial part, a stamp.

The stamp was made using the cleanroom process, and once complete it can stamp out multiple copies of the actual device outside of a cleanroom, which makes them much cheaper and faster to produce.

One thing that is particularly interesting to me as a chemical engineer is how simply changing the coating on the nanostructured surface (for example, a tiny diffraction grating) changes what chemicals it detects (or more specifically, what chemicals stick to it). Then, on shining a light on it, the presence of those stuck chemicals changes the reflection or diffraction pattern in a way that's proportional to the amount of chemical adsorbed. And, moving outside of my field of expertise, biological molecules can be very specific in what will stick together and what will not. There's a lot of work going on to make these sensors to detect specific enzymes or enzyme activity that are characteristic of a disease, antibodies, and even parasites.

Making these sensors faster and cheaper means that development of useful tests for hospitals, and maybe eventually your GP's office, will speed up dramatically.

Hydrophones at depth

Here's a nifty new piece of technology from Stanford University for any ocean-science types: a hydrophone that can be used at any depth which has low-distortion sound detection over a dynamic range of 160dB and a frequency range of 1Hz to 100,000Hz. By contrast, the human ear can hear a range of about 20-20,000Hz, feels immediate and acute pain at about 120dB—chronic damage starts much lower, down about 85dB. (If you want to know what 120dB feels like, stand about 3m in front of an emergency vehicle with its siren sounding.)

Most microphones have a thin diaphragm which vibrates in response to the sound waves hitting it, and this one is no exception. However, when you're detecting tiny pressure changes against the crush of a deep ocean trench, you need something that will not be overwhelmed by the ambient pressure. The answer for this particular microphone was to drill tiny holes in the diaphragm so that the water pressure on both sides of the diaphragm is the same. The holes would have to be small enough that sound waves in the water wouldn't pass right through them without moving the diaphragm, and large enough that the pressure would equalize before damaging the diaphragm as it's brought to depth. The diaphragm itself is about 500nm thick, so it is very fragile. To measure the movement of such a fragile surface, they use a laser. This is highly accurate and also doesn't touch the diaphragm with anything other than light. At the quiet end of the sounds they wanted to measure, and with water resisting the motion of the diaphragm, it moves only about 0.00001nm or so. Fortunately, lasers and mirrors can detect that sort of tiny movement.

Different sizes of diaphragms (and drumskins, and sound boards, and strings, and horn tubes) are most responsive to a particular frequency, so to cover the full range of frequencies they wanted to hear without distortion would be tricky with only one diaphragm. So, they put three different sizes of diaphragm in one microphone to cover the range.