Multiplexed Clinical Analysis
Many microfluidic technologies are designed with the idea of one device for one application. This can be a problem, according to Vincent Gau, Ph.D., president of Genefluidics. “To assay something else, you would need another type of system. Our approach is different. We developed a universal microfluidic cartridge that can measure DNAs, RNAs, proteins, and small molecules.”
The key to the device is a two-component cartridge system in which the top portion stores reagents, waste, and sample, while the bottom portion houses microfluidic channels, valves, and vents as well as the integrated sensor array. The raw sample is loaded into the top portion and the assembled cartridge is inserted into the instrument that processes and analyzes the sample. Electrochemical detection methods allow ultra-high nontarget amplified sensitivity.
Dr. Gau notes that the gold standard for most types of DNA/RNA analyses is PCR amplification of a sample whose nucleic acid was first extracted and purified. “Our devices differ because we directly take a specimen such as blood and saliva and process that to completion within 10–20 minutes. The read-out has exceeding high sensitivity because we developed our own sensors that detect proportionally to the number of target molecules.”
Another important feature of this new approach is the ability to multiplex. “We are working with VA hospitals in Los Angeles and Palo Alto on urinary tract infection screening and the UCLA hospital on salivary diagnostics for oral cancers, comments Dr. Gau. “There are many cancer and disease biomarkers relating to RNA, DNA mutations, and proteins. Often, these are evaluated singly via PCR or an ELISA if it is a protein biomarker. However, with the universal cartridge system you can characterize any combination of desired markers, not just one biomarker. We anticipate making a custom blend and a universal panel that would be informative to the physician.”
The company will launch its devices in early 2009 for academic researchers and expects to work with strategic partners to develop other specific applications especially for multiplexing.
UV Imaging Detection
Identifying and quantifying sample images in microfluidics technologies can be a challenge and a bottleneck. Paraytec has a solution—an ultraviolet imager for use with microfluidic devices.
“Traditional optical detection technology revolves around the use of microscopes, which suffer from field of view but are excellent at gathering light,” according to Jim Lenke, engineering manager. “Microscopes are frequently connected to digital cameras for collecting and digitizing data. However, these data images take time to be converted directly into absorbance units (AU) and suffer from not having an available reference for absolute AU values. Thus, researchers struggle to get quantitation in microfluidic devices. Additionally, because volumes are exceedingly small other techniques such as fluorescence are often used to collect even more light signal.”
Paraytec offers its ActiPix™ brand of ultraviolet (UV) area imaging detectors that use sophisticated optics and patented signal referencing with Active Pixel area sensors for high sensitivity UV detection in microfluidics and other applications.
How is this new technology used in microfluidics? “Our ActiPix D100 UV area imaging detectors use an Active Pixel Sensor based imaging chip,” Lenke says. “We can view a 9 mm wide by 7 mm high area, which covers a large area of real estate in a microfluidic device. This is unlike a typical microscope arrangement whereby a selected small region of the channel is chosen as a detection area. As the image is an area pixel array, we have the ability to simultaneously measure absorbance in several channels.”
“The imager is part of a family classed as Active Pixel arrays,” he adds. “Modern-day digital cameras expose us to pixel technology. Pixels are really just tiny photon detectors arranged in an array. These are different from the well-known CCD chips where selectively chosen pixel regions or columns are difficult to isolate. Some performances of pixels between the two classes are different as well. Our imager is 1,280 columns wide by 1,024 rows high and each pixel is 7 by 7 micrometers. Only rows needed for sensing are used while other rows are switched off during that operation. Reducing the total number of rows needed vastly increases readout rate and data size.”