Department: NanoEngineering
Faculty Advisor(s): Donald J. Sirbuly

Primary Student
Name: Joshua Tan Villanueva
Email: jtvillan@ucsd.edu
Phone: 858-534-1670
Grad Year: 2016

Student Collaborators
Qian Huang, q4huang@ucsd.edu

The ability to observe, measure, and manipulate molecular interactions and forces is central to our understanding of complex chemical pathways and biological processes. In addition, measuring small forces (< nN) and/or mechanical displacements with high resolution has direct implications on the development of advanced sensing platforms that can respond to acoustic, strain, pressure, and/or chemical signals. Measuring small forces is typically carried out by sophisticated instruments such as optical traps (or optical tweezers) or atomic force microscopes, which act as calibrated transducers that can directly measure the force and displacement of a system. Both techniques offer excellent force sensitivity (pN range), but it would be extremely difficult to integrate these platforms into transportable or embeddable devices that can accurately measure mechanical phenomena. To push the limits of force sensitivity, portability, and tunability, we have been investigating a novel fiber optic sensing geometry that utilizes optical transmitters embedded in the decaying optical field (i.e., evanescent field) to detect forces impinging on the system. We demonstrate that the evanescent field of subwavelength optical waveguides is extremely sensitive to objects moving normal to the propagation of light. The displacement sensitivity is further enhanced by strong dielectric-plasmon coupling effects in which plasmonic nanoparticles are used to transmit information regarding their position within the evanescent field of the fiber. The coupling between a dielectric waveguide and plasmonic nanoparticle enables angstrom level displacement sensitivity and provides an ultrasensitive feedback mechanism for detecting forces acting on the nanoparticle. Simulations were performed to investigate fluid flow profiles around waveguides integrated in microfluidic channels and to study the relationship between hydrodynamic forces and nanoparticle displacement within the evanescent field. To quantitatively measure these forces we have been investigating systems with thin, compressible polymer coatings between the waveguide and nanoparticles. Experimental results will be presented on the development of a thin polyethylene glycol coating which will serve as a model system to calibrate the response of the fiber optic force sensing devices.

Related Links:

  1. http://sirbuly.ucsd.edu/research

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