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Nanotech News
Nanotechnology Enables New Approaches for Detecting Proteins, DNA Controlling the architecture of materials at the scale of 1 to 100 nanometers is a grand challenge for chemists and engineers and will take a century or more to accomplish. But the payoff from learning how to work at that scale length, said Chad Mirkin, Ph.D., George B. Rathmann Professor of Chemistry at Northwestern University, will be to change the way we diagnose disease and, perhaps more importantly, to give researchers the ability to ask entirely new questions about the etiology of cancer and other diseases. Mirkin, who is also Professor of Medicine, Professor of Materials Science and Engineering, and Director of the International Institute for Nanotechnology at Northwestern, presented some examples of what nanotechnology can do for the research and clinical communities when he spoke at the NIH on April 26, 2005, as part of NCI's Nanotechnology Seminar Series. One example that he discussed was dip-pen lithography, which he pointed out is just the next evolution in human development of writing technology. Utilizing nanoscale atomic force microscope tips of various shapes, dip-pen lithography is capable of creating gene and protein chips containing millions of spots. In just a short time, this technology has become the standard method for creating materials one atomic layer at a time, making it an important tool for developing new nanoscale materials and characterizing their unique chemical and physical properties. The private sector is already commercializing dip-pen lithography equipment and working to develop additional applications. Most of Mirkin's lecture was devoted to the development of new technology for detecting nucleic acids and proteins at levels comparable to PCR-based assays without the need for enzymes and complex machinery. The goal of this work, which started out as an exploration of the chemical properties of nucleic acid-nanoparticle conjugates, is to develop sensitive, low-cost assays that can be performed at the point of care, rather than in centralized diagnostic laboratories. Starting from experiments that determined how to assemble and stabilize conjugates of nucleic acid with gold nanoparticles ranging from 5 to 30 nanometers in diameter, this work quickly evolved into the quest for new diagnostic test technology when a student in Mirkin's laboratory found that adding complementary oligonucleotides to a stabilized solution of oligonucleotides-nanoparticle conjugates turned a red solution blue. Realizing that this process was in essence a simple and sensitive test for DNA - a DNA litmus paper, so to speak - Mirkin's group soon turned this observation into a color-based assay that could detect femtomoles (1 femtomole = 602 million, or 6.02 x 108, molecules) of specific sequences of DNA. While simple to perform and remarkably sensitive for a chemical assay, the one problem with this system was that it needed to be six orders of magnitude more sensitive (capable of detecting about 600 molecules of a given sequence of DNA) to compete with the ability of PCR to detect small numbers of DNA molecules with a defined sequence. The big breakthrough, explained Mirkin, was made possible by the fact that these nanoparticles are not only colored, but they possess catalytic properties, too. In this case, gold nanoparticles can catalyze the conversion of silver salts into silver metal, which when combined with standard photographic processing techniques yields an assay that is sensitive down to the attomole level (1 attomole = 602 thousand, or 6.02 x 105, molecules). This sensitivity gain of five orders of magnitude provides comparable sensitivity to PCR but without the complexities. This technology is also being developed by the private sector now, and is being tested in hospital clinical laboratories. Mirkin and his colleagues were finished developing this system, however. By adding an antibody-labeled magnetic microparticle, DNA barcodes, and conjugating a second antibody to the DNA-conjugated gold nanoparticle, the Northwestern group has created an ELISA-type assay for detecting proteins, but with PCR-like sensitivity. This system, which Mirkin calls the biobarcode assay, opens up entirely new avenues of investigation, for it allows researchers to search for proteins at levels previously unimaginable. In one example, Mirkin and a colleague from Northwestern have used this system to detect a potential marker of Alzheimer's disease present in attomolar concentrations in spinal fluid. Mirkin is also collaborating on a project to determine if a protein known as inhibin can be used to detect ovarian cancer in its earliest stages.
The videocast of Mirkin's talk is available on the NIH videocast website. The following links can provide more information about the work of Chad Mirkin and his collaborators: Chad Mirkin's web page Selected references:
Georganopoulou DG, Chang L, Nam JM, Thaxton CS, Mufson EJ, Klein WL, Mirkin CA. Nanoparticle-based detection in cerebral spinal fluid of a soluble pathogenic biomarker for Alzheimer's disease. Proc Natl Acad Sci U S A. 2005 102(7):2273-6
Ginger DS, Zhang H, Mirkin CA. The evolution of dip-pen nanolithography. Angew Chem Int Ed Engl. 2004 43(1):30-45.
Nam JM, Stoeva SI, Mirkin CA. Bio-bar-code-based DNA detection with PCR-like sensitivity. J Am Chem Soc. 2004126(19):5932-3.
Nam JM, Thaxton CS, Mirkin CA. Nanoparticle-based bio-bar codes for the ultrasensitive detection of proteins. Science. 2003 301(5641):1884-6. |
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