NSF Award
0933531
0933531<br/>Arnold<br/><br/>Virus particles are a major cause for human disease, and their early detection and identification is of increasing importance as air travel allows these infectious agents to spread rapidly to populations across the globe. A fast detector that is sensitive to a single virus particle by determining its genus and size would answer the demand for early detection. The present proposal is to continues the investigation into microsphere whispering gallery mode (WGM) biosensors for early detection of viruses in human fluids as we utilize a recently discovered phenomenon of light trapping of nanoparticles within the WGM evanescent volume. The sensing is based on the extremely narrow photonic resonances of microspheres that shift their frequencies as a result of an environmental change. Within the reach of the WGM?s evanescent field (~ 200 nm) nanoparticles are drawn toward the surface by gradient forces, similar to those present in optical tweezers. A trapping potential-well is formed by an attractive evanescent polarization potential, repulsive electrostatic potential, and van der Waals potential. In the case of a low binding-affinity or a low density of binding sites, nanoparticles are propelled around in orbit by radiation pressure. This trapping mechanism (WGM Carousel) along with controlled binding-affinity adds additional functionality and assures high sensitivity and specificity to the WGM biosensor. The ultimate goal is to build microfluidic biosensors that are sensitive to a single viral particle and can differentiate virions according to their size/mass and affinity to specific antibodies. The small size of these bio-particles demands micrometer-size sensors3. However Brownian diffusion of ultra-low concentration analytes crossing the boundary layer is considered a major hurdle4 for miniature sensors. Preliminary results show that the WGM Carousel sensor can have significantly enhanced transport rates (> 50×) of particles to the sensing region, compared to other miniature sensors. In addition the carousel mechanism provides a means for investigating forces arising near the surface. Understanding these forces is of great importance for the design of microfluidic devices and micro-fabrication. Nanoparticles trapped in a WGM carousel can be used to quantitatively measure surface interactions from their stochastic radial motion. By proper choice of the interacting surfaces and the liquid medium it will be possible to screen the electrostatic repulsion and reveal short range interactions such as van der Waals. There are challenges for the DLVO (the theory of colloidal stability) to properly describe the interactions at very short range (<5nm) for various aqueous solutions, where repulsive solvation forces are observed. WGM Carousel will help address these challenges.
