Biosensing With A DNA-Diamond-Silicon Sandwich

Makarand writes "A unique diamond film with DNA attached to it coupled with sensitive microelectronics might be the sensor needed to sniff out harmful biological agents. If DNA is attached to diamond it is possible to electronically detect the electrical response when biomolecules bind to the DNA-diamond surface. A DNA-Diamond interface deposited on a silicon surface can act as a sensitive biosensor. These inexpensive and compact sensors can make it possible to continuously scan public places like airports and subways and send out security alerts to agencies if required."

Comments

I smell vapour...

[Garridan]

That article was extremely lacking in details, says nothing about how it works; especially how it should be able to tell the difference between a biological weapon and a natural virus/bacteria/fungus...

Re:I smell vapour...

[Anonymous Coward]

well, just a few quick answers to your post...

YOu in a sense "program" the sensor to sense whatever you want. In this case, you use DNA that is complimentary to the DNA that you wish to sense. Thus, if you wanted to make a sensor for lets say antrax (since it is such a hot topic) then you just attach DNA that is complimentary to anthrax DNA. By wisely choosing your sequence of DNA, you can (to a high degree of certainty) assure that the sensor will bind anthrax DNA and only anthrax DNA. That is how the sensor would tell the difference between a biological weapon and a natural virus/bacteria/fungus...

now as to how binding = sensing...
the general idea realies on a single DNA strand (ssDNA) binds its compliment to form double stranded DNA (dsDNA). The electrochemical properties of ssDNA are different than dsDNA and these differences are observable. There are many ways that the electrochemical properties change and how they change and which ones you measure depends on the total system on teh sensor. But just to give you a few examples...
You can observe a color change in the sample, visible to the naked eye. You can observe a change in the absorbance spectrum of the sensor, which could be observed with a simple small piece of lab equipment. Or you can observe a changein the conductivity of the sensor. THese are just a few of the means available to monitor the binding of the target DNA, and thus the sensing of the target DNA.

Anywayz, i hope that clarifies a few things :)

Re:inexpensive...diamond

[Goldsmith]

Diamond films are inexpensive, in fact, if you have a decent watch, or glasses you already have one. That's what they use as a scratch resistant coating on a lot of things.

They generally make them from a slab of graphite, which is then heated, sputtered (hit it with high energy gas particles) or otherwise made to vaporize. Then you place what you want to have the film over it above the slab and if you've set the conditions properly (temerpature, pressure, how hot is your carbon vapor), you get a diamond film. All in all, it's relatively inexpensive, but produces nothing like a gem.

The Nature Materials Article & Sensing Propert

[reverseengineer]

This press release is rather short on information (read: no information), but the Nature Materials article itself is a bit more helpful. Now, my university is shelling out a bunch of cash for a site license, and I'm sure neither they nor Nature would like me to post that article here, so I will not do that. The abstract is free though:


Diamond, because of its electrical and chemical properties, may be a suitable material for integrated sensing and signal processing. But methods to control chemical or biological modifications on diamond surfaces have not been established. Here, we show that nanocrystalline diamond thin-films covalently modified with DNA oligonucleotides provide an extremely stable, highly selective platform in subsequent surface hybridization processes. We used a photochemical modification scheme to chemically modify clean, H-terminated nanocrystalline diamond surfaces grown on silicon substrates, producing a homogeneous layer of amine groups that serve as sites for DNA attachment. After linking DNA to the amine groups, hybridization reactions with fluorescently tagged complementary and non-complementary oligonucleotides showed no detectable non-specific adsorption, with extremely good selectivity between matched and mismatched sequences. Comparison of DNA-modified ultra-nanocrystalline diamond films with other commonly used surfaces for biological modification, such as gold, silicon, glass and glassy carbon, showed that diamond is unique in its ability to achieve very high stability and sensitivity while also being compatible with microelectronics processing technologies. These results suggest that diamond thin-films may be a nearly ideal substrate for integration of microelectronics with biological modification and sensing.


The method of attachment of DNA to a diamond surface is particularly clever: they use photochemistry to attach a long chain primary amine to the surface of the diamond, and then use a rather curious and complicated sulfur-containing organic molecule called SSMCC to act as a bridge between the diamond/amine and the strand of DNA. Essentially, you get these strands of DNA that point out into the environment like sticky threads. The sensing aspect, presumably (they don't go too much into it in the article - as the press release notes, they plan on discussing that in a meeting of the ACS) takes place as foreign DNAs contact the sensor. As the abstract tells us, the specificity of the attached DNA strands is not compromised by the diamond bonding technique, so the DNA strands can identify a certain complementary DNA sequence present in the enviroment, say, from Bacillus anthracis. Presumably the change induced in the diamond-bonded DNA that occurs when the complement hydrogen bonds with it will then trigger some sort of physically detectable action- you could tag the DNA with a fluorescent dye, for example, and measure how the fluorescence levels change between bonded and unbounded forms. This sort of information can then be translated into an electronic signal. This has a long ways to go before being a practical outside-the-lab type of device, but the results are still pretty exciting.