July 31, 2006
Nanoscale Devices Advance Biomedical Sensing and Screening Applications
One of the hopes for nanotechnology is that researchers will be able to harness the power of the nanoscale to develop faster, more sensitive and less expensive assay techniques for use in diagnostic and drug discovery applications. New results from Gil Lee, Ph.D., and his colleagues at Purdue University and from Iuliana Lazar, Ph.D., and her collaborators at Virginia Polytechnic demonstrate two promising approaches that researchers are taking in this area.
Writing in the journal Langmuir, the Purdue team describes a method for using arrays of fabricated nanoscale reaction vessels to detect trace levels of delicate proteins and protein assemblies. The device that this team built uses a modified ink jet printer to add small amounts of sample and analytical fluids, or reagents, to the reactor vessels, which hold between 1 and 100 nanoliters of liquid. Because the inkjet head does not contact the reactors, there is no chance of cross-contamination among the reactors. Also, the process by which an inkjet print head creates droplets has been shown to be compatible with sensitive biomolecules and even cells.
To demonstrate the utility of this device, the investigators conducted a standard antibody-based immunoassay. Each nozzle of the inkjet print head dispensed one reagent solution into the nanoreactors. The immunoassay was designed to generate an optical signal that could be detected and recorded by a standard optical microscope. The researchers found in conducting this assay that it was sensitive to drying. To maintain constant humidity over each nanoreactor, the investigators modified the device design by building a chamber surrounding the array. This simple design change enabled the researchers to control humidity to within 1% tolerance.
Since controlling the amount of reagent added to each plate is as simple as changing the color of a sentence in a word processing program, this device should enable researchers to study the behavior of cells and proteins under a variety of conditions. The researchers note that the small amount of material used in each nanoreactor should make this device useful for array-based sensing of trace biomarkers.
Another approach to biomarker screening involves injecting small biospecimen samples onto microfluidic chips and separating the various trace components in the nanoscale channels etched onto such a chip. That’s the approach that Lazar and her team took in creating a system for high-throughput proteomic analyses that separate trace protein components and feed them directly into a mass spectrometer for identification. To accomplish this task, the Virginia Tech team developed an integrated system containing all of the pumps, valves, separation columns and electrospray interface to a mass spectrometer needed to conduct six analyses simultaneously on a single 3-inch-square glass slide. The small size, ease of construction, and fully integrated nature of these chips should keep manufacturing and per-assay costs low.
Reporting their work in the journal Analytical Chemistry, the investigators conducted a proteomic analysis of breast cancer cells and compared the results to those obtained using conventional desktop liquid chromatography systems and larger samples. The microfluidic system was capable of identifying 77 different proteins, similar to the results obtained using the larger desktop system. Among the proteins detected were three different keratin proteins that are overproduced by many cancers; PCNA, a protein involved in cell proliferation and associated with breast, lung and pancreatic cancers; and cathepsin D, a protein involved in metastasis and whose presence correlates with poor prognosis in breast cancer patients.
The work on nanoscale reactors is detailed in a paper titled, “Nanoliter-scale reactor arrays for biochemical sensing.” This paper was published online in advance of print publication. An abstract is available at the journal’s website.
The work developing microfluidic devices for proteomics is detailed in a paper titled, “Microfluidic liquid chromatography system for proteomic applications and biomarker screening.” This paper was published online in advance of print publication. An abstract is available at the journal’s website.