'Cooking' carbon nanotubes like spaghetti

Scientists from the Pacific Northwest National Laboratory (PNNL) have developed a technique to force a variety of enzymes to self-assemble layer-by-layer on carbon nanotubes (CNTs) with the help of noodle-like polymer molecules. This technique could be used for ultra-precise blood-sugar monitoring or infectious-agent detection.

Scientists from the Pacific Northwest National Laboratory (PNNL) have developed a technique to force a variety of enzymes to self-assemble layer-by-layer on carbon nanotubes (CNTs) with the help of noodle-like polymer molecules. In "A biosensor layered like lasagna," the researchers say that this technique can be applied to a wide range of applications. In particular, it will be possible to build other biosensors "that react specifically with other biological chemicals, environmental agents or even microbes." Read more...

Let's start with the spectacular cover of the April 2006 issue of the Journal of Nanoscience and Nanotechnology which shows the "self-assembly of enzymes on carbon nanotube surfaces through layer-by-layer technique" developed by PNNL scientists Yuehe Lin and Guodong Liu (Credit: DOE/PNNL; Journal of Nanoscience and Nanotechnology). Here is a link to a larger version of this cover (PDF format, 1 page, 953 KB). [And remember to use the zooming features of the PDF format to really enjoy this picture.]

The self-assembly of enzymes on carbon nanotube surfaces

Here is a short description of the technique used to build these biosensors.

Lin and co-author Guodong Liu, a postdoctoral fellow in Lin's group, coaxed electrostatic clinginess in a polymer and an oppositely charged protein-enzyme, in this case glucose oxidase, which reacts in the presence of blood sugar.
The catalyzed products from the reaction ping the carbon nanotube; if the tube is connected to an electrode, the tube will carry a signal that corresponds precisely with the amount of glucose detected. The first polymer binds to the carbon nanotube. Enzymes are attracted to the polymer, leaving an outer layer for the next polymer of opposite charge to cling to, and so on.

Below is an image showing the "schematics of layer-by-layer electrostatic self-assembly of protein-polyion on carbon nanotube template: "A polymer, here labeled PDDA, clings to a carbon nanotube of opposite charge, and an enzyme, GOX, does the same with the polymer. The steps can be repeated to build up a biosensor's layers, enzyme count and sensitivity" (Credit: DOE/PNNL; and EurekAlert! for the second part of the caption).

Building a biosensor's layers

And what could be the usages of such a technique?

Now that the glucose enzyme biosensor has passed the test, Lin said, it should be possible to build a similar sensor using other enzymes that react specifically with other biological chemicals, environmental agents or even microbes and their toxic byproducts.

In a short technical paper, Biosensors Based on Layer-By-Layer Assembly of Enzymes on Carbon Nanotubes (PDF format, 1 page, 287 KB), from which the above diagram has been extracted, the researchers add some details on this subject.

One promising application of carbon nanotubes (CNTs) involves their use in the construction of chemical sensors and biosensors. In the present work, highly sensitive amperometric biosensors for glucose, choline, organophosphate pesticides and nerve agents based on self-assembly of enzymes on CNT electrode have been developed.

This research work has been published by the Journal of Nanoscience and Nanotechnology under the name "Carbon Nanotube-Templated Assembly of Protein" (Volume 6, Number 4, Pages 948-953, April 2006). Here is a link to the abstract of this paper which is available for purchase for $110.00 plus tax.

Sources: Pacific Northwest National Laboratory news release, April 28, 2006; and various web sites

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