Events Calendar

Tian Yang Seminar - Friday, June 10th at 2:00pm in EEB 132

Speaker: Tian Yang, Shanghai Jiao Tong University

Talk Title: Nano-plasmonic sensing: single molecule and single chemical event detection, quantum phonon pumping, and fiber end facet integration

Abstract: Nano-plasmonic sensing devices empower the investigation of chemical structures and dynamic behaviors of molecules, reveal fundamental physics at nanometer scales, and provide key components for advanced analytical instruments.
I will start the talk with an introduction to our peculiar surface enhanced Raman spectroscopy (SERS) measurement method, in which a gold nanosphere-plane junction is excited with the focal spot of a radially polarized laser beam. A SERS electromagnetic enhancement factor of 109~10 has been obtained with a reproducibility of 10+/-0.08, in each hotspot of 9 nm3 volume. The unprecedented simultaneous achievement of ultrahigh SERS enhancement and high reproducibility in deterministic single hotspots opens a path for efficient in-situ investigation of single molecule structures and dynamics. For example, several chemical events on the single molecule level have been observed in real time, including plasmon-driven dimerization of 4-nitrobenzenethiol molecules to dimercaptoazobenzene (DMAB), DMAB desorption, and DMAB trans-cis isomer conformation switching, the last of which has been very difficult to observe even for a collection of molecules in any previous experiments. In addition, by measuring the SERS scattering off a monolayer of malachite green isothiocyanate molecules in a single hotspot, we identify a nonlinear dependence of SERS intensity on the laser power, against the common concept that SERS is a linear process. Further, the nonlinear behavior contains multiple heterogeneous stages, which arises from the quantum nature of molecular vibration and stimulated phonon emission.
In the second part of the talk, I shall show our work on integrating nano-plasmonic sensing devices on single-mode optical fiber end facets. Compared with free-space and chip based devices, single-mode fiber end facet devices have the advantages of simple and flexible light delivery, leveraging fiber-optic communication technologies, and compact systems. A plasmonic crystal cavity structure has been designed to improve the refractive index sensing capability under optical fiber guided mode, and a glue-and-strip method has been developed to transfer the plasmonic nano film from a flat substrate to the fiber end facet. A limit of detection of 3.5x10-6 RIU has been obtained, which is two orders of magnitude lower than any reported plasmonic sensors on (multi-mode) fiber end facets. A prototype instrument has been built to demonstrate real-time monitoring of the kinetic interaction process between Human Immunoglobulin G protein (hIgG) and its binding partner anti-hIgG.

Biography: Tian Yang is currently a tenure-track Associate Professor at the University of Michigan - Shanghai Jiao Tong University Joint Institute. He got the B.S. degree in Electrical Engineering from Tsinghua University in 2000, the Ph.D. degree in Electrical Engineering from the University of Southern California in 2006, took a postdoctoral fellow then research associate position at Harvard University from 2006-2009, and joined Shanghai Jiao Tong University in 2009.
His expertise lies in the areas of optoelectronics and nanotechnology. He has worked on semiconductor nano lasers for photonic integrated circuits, microfluidics integrated nano optical sensors for sensitive biomolecule detection, single molecule and single chemical event detection by enhanced Raman spectroscopy, and fiber-optic integrated biomolecule sensing and chemical trace detection.

Host: EE-Electrophysics

Location: Hughes Aircraft Electrical Engineering Center (EEB) - 132

Audiences: Everyone Is Invited

Contact: Marilyn Poplawski