On-Chip Optical Sensing Technique Detects Multiple Flu Strains

The ability to simultaneously detect and identify multiple biomarkers is one of the key requirements for molecular diagnostic tests that are becoming even more important as personalized and precision medicine place increased emphasis on such capabilities.

Integrated optofluidic platforms can help create such highly sensitive, multiplexed assays on a small, dedicated chip and a method for multiplex fluorescence detection of single bioparticles by creating color-dependent excitation spot patterns from a single integrated waveguide structure has been developed.

Biophysicists at the University of California, Santa Cruz (CA, USA) have described a novel method to perform diagnostic assays for multiple strains of influenza virus on a small, dedicated chip. They demonstrated a novel application of a principle called wavelength division multiplexing, which is widely used in fiber-optic communications. By superimposing multiple wavelengths of light in an optical waveguide on a chip, they were able to create wavelength-dependent spot patterns in an intersecting fluidic channel. Virus particles labeled with fluorescent markers give distinctive signals as they pass through the fluidic channel depending on which wavelength of light the markers absorb.

The team tested the device using three different influenza subtypes labeled with different fluorescent markers. Initially, each strain of the virus was labeled with a single dye color, and three wavelengths of light were used to detect them in a mixed sample. In a second test, one strain was labeled with a combination of the colors used to label the other two strains. Again, the detector could distinguish among the viruses based on the distinctive signals from each combination of markers. This combinatorial approach is important because it increases the number of different targets that can be detected with a given number of wavelengths of light. For these tests, each viral subtype was separately labeled with fluorescent dye. For an actual diagnostic assay, fluorescently labeled antibodies could be used to selectively attach distinctive fluorescent markers to different strains of the influenza virus.

Holger Schmidt, PhD, a professor of Optoelectronics and lead author of the study, said, “A standard flu test checks for about ten different flu strains, so it's important to have an assay that can look at 10 to 15 things at once. We showed a completely new way to do that on an optofluidic chip. Each color of light produces a different spot pattern in the channel, so if the virus particle is labeled to respond to blue light, for example, it will light up nine times as it goes through the channel, if it's labeled for red it lights up seven times, and so on.” The study was published on October 6, 2015, in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).

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