News & Events
Jianjun Wei, Ph.D.
Posted on February 3, 2017
Date - February 3, 2017
The Department of Nanoscience, Joint School of Nanoscience and Nanoengineering (JSNN)
Title: “Nanoscale Interactions and Applications: Integrated Nanoplasmonic Sensing & A Fluorescence-Electrochemical Study of Carbon Nano-Dots (CNDs)”
In this lecture, I will present our recent progress and results of two research programs.
Integrated Nanoplasmonic Sensing: Nano-plasmonics, an emerging branch field of nanophotonics concerning properties of collective electronic excitations (surface plasmon, SP) in nanostructures of noble metals (e.g. silver and gold), has attracted intense attention due to its versatility for optical sensing and chip-based device integration. Since understanding the underlying physics and developing applications of nanoplasmonic devices with desirable optical properties, e.g. intensity of light scattering, high refractive index (RI) sensitivity and reproducibility, is crucial for practical uses in physics, biomedical detection, and environmental monitoring, a semi-analytical model that enables decomposition and quantitative analysis of SP under plane-wave illumination is used to generate a new nanoledge aperture structure, directing to design such plasmonic devices for optimal optical transmission and RI sensitivity. In concert with the analytical treatment, a finite-difference time-domain (FDTD) simulation and testing of the fabricated devices were performed to validate the optical responses as a function of the nanoledge device’s geometric parameters. Furthermore, we tried to address the challenge of efficient delivery of bio-molecules to the subwavelength nanoledge cavity by using near-field fluorescence correlation spectroscopy (FCS) of labeled proteins and visualize the transportation of molecules and migration in nanoscale. Finally, a cancer protein biomarker, f-PSA, is demonstrated for detection in an integrated nanoplasmonic chip prototype.
A Fluorescence Origin Study of Carbon Nano-Dots (CNDs): Carbon nanodots (CNDs) have attracted great attention due to their superiority in good solubility, biocompatibility, tunable photoluminescence, and optic-electronic properties. While CNDs have experienced tremendous growth and strongly impacted research since its discovery since its discovery, it remains debatable and controversial on photoluminescence (PL) origins. This work proposes a new combined fluorescence spectroelectrochemistry technique to obtain both spectral and electrochemical information about the microwave synthesized CNDs. In addition, corresponding to the optical band gap by UV-vis absorption spectrum calculation by assuming CND as a molecule, the energy gap (about 2.09 eV) of CNDs has been calculated by both experimental electrochemical measurement and simulated Hückel method, which bridges between the band (VBM and CBM) energy and molecular orbital (HOMO and LUMO) energy level, and is further used to illustrate that the carbon region (of C=C) and functionalized region (C=O, C-O, and O=C-OH) associated with surface-state transitions are the dominant factors on excitation-dependence emission of CNDs. This work may provide a new way to understand the underlying physics, specifically the origin of photoluminescence from CNDs, and benefit practical uses in biomedicine, chemical sensor, and photoelectric devices.