Desktop Biodetectors

IvyMike writes: "EE Times has an interesting article on the development of desktop biodetectors that could quickly detect the presence of pathogens like anthrax and smallpox. It uses some pretty cool technology to identify the target pathogen's DNA. Too bad we don't have these things today."

Best thing about such a device

[namespan]

The best thing about such a device is that it could justify its cost.

A $500 "detect Anthrax" device wouldn't yield much value for a large portion of the population. But... a $500 device that could detect and identify a wide variety of microorganisms might be very useful -- and worthwhile -- indeed.

Maybe it'd be like running "top" -- instead of giving you information about processes taking up system resources, you could get information about microorganism activity in the environment (or your body, given an appropriate sample...).

ID NAME EST COUNT/CU CENT % OF TOTAL
787 Staphlo 2324572 12.2%
8901 Antrax 253334 1.3%
143 E. Coli 289217 1.4%
1589 Ebola 16333 .035%

Re:Too bad we don't have these things today?

[sam_handelman]

What are there now, somthing like under 30 cases of Anthrax so far? Sent to a few high-profile companies? Sure, that's a MASSIVE INCREASE over previous levels, but statistically you're still in pretty good shape. Don't let the media hype get you worked up.

Very true. Also one of the (many) reasons why these things won't work. I'll stick with the three simplest.

Firstly, in order to detect bacterial DNA you have to lyse (break open) the bacteria. This means you have to filter them out of the air, dissolve them in lysing buffer and apply them to your detector, at the bare minimum. Lysis buffer is expensive, and I doubt there technology actually works without doing more than lyse the cells (removing the cellular protein, much of which binds indiscriminately to DNA, would be a good start. Doing that in reasonable time requires a ~12,000 RPM centrifuge, precipitant compounds and a column, at the minimum.)

Secondly, DNA from other organisms is going to bind to your probe (including these gold bead things) with a certain frequency (this binding is called "base pairing," which is largely driven by hydrogen bonding but is not called a bond.) So, your background noise from that is going to be more than enough to drown out the signal from an anthrax concentration high enough to kill you, especially if you're standing across the room from the detector holding an envelope; the anthrax concentration drops as the square of the distance from the contaminant source unless there's a wind.

Thirdly, the reason the previous poster mentioned. In order for these things to be useful the false positive rate has to be on the same order of magnitude, or smaller, than the actual positive rate. Even if you use practical techniques instead of this absurdity with DNA, that's never going to happen. More practical techniques depend on markers on the bacterial cell walls (so you don't need to lyse the bacteria); when the CDC people report "preliminary results" indicating anthrax this is what they're talking about - these results are preliminary because there are many other, more common and harmless bacteria that have the same factors in their cell walls, and because the experiment to detect the stuff occasionally goes wrong for no apparent reason.

Even in a laboratory setting, if you want to detect the DNA from this stuff you have to *culture* it. The idea of a desktop machine, as opposed to a highly trained scientist with a lab full of sophisticated equipment, being able to detect the DNA from the amount of this stuff that is actually floating in the air is patently and absolutely absurd.

A handheld is even more so, since it wouldn't even be able to dissolve the bacteria it filtered.

These devices are either a pipe dream, a scam, or both. Either they'll just report A-OK all the time or, even worse, they'll periodically start an unjustified anthrax scare by giving off an alarm.

Re:desktop not what you think it means

[sam_handelman]

As I continuously repeat, often hopping up and down and foaming at the mouth, to people who do not (I do) work with DNA:

DNA IS NOT THE MOST EFFICIENT WAY TO DETECT ANYTHING. IT IS INSIDE THE CELLS! THE CELL WALLS ARE STUDDED WITH ANTIGENS (things to make antibodies) AND THEY ARE ON THE OUTSIDE. THE CHOICE IS CLEAR.

I'll wait until I see hard numbers on the technology with the beads; if it really is more sensitive than the photodetection on present day DNA microarrays, than that's very promising. However, I'd like to see an independent group assay the technique's sensitivity before making any judgements on it's utility - I strongly suspect that it will turn out to be actually less sensitive, based on the (scientifically irresponsible) comments made by the crackpots and or sleaze at the company that produces it.

Re:desktop not what you think it means

[myc]

FYI I do work with DNA, I am a postdoc at Harvard Med School. The fact of the matter is, antibodies are a bitch to work with. Unless you make a hybridoma you can't mass produce antibodies, and even if you do have a good antibody the best you can do is an ELISA assay. There is no way that ELISA is more sensitive than PCR. This bead technology is likely to be more sensitive than PCR, faster than PCR, or both. It's also not that hard to extract DNA, usually a simple organic extraction gives you a good enough sample to work with.

IEEE Spectrum Article

[amacek]

The current issue of IEEE Spectrum has a one of its big articles on Biological Warfare Detectors. The article is available at http://www.spectrum.ieee.org/WEBONLY/publicfeature /oct01/bio.html [ieee.org].

A little ironic that they put together this article before September 11th.