Person:

Hong, Wooyoung

Fluorescent labeling techniques have been widely used in live cell studies; however, the labeling processes can be laborious and challenging for use in non-transfectable cells, and labels can interfere with protein functions. While label-free biosensors have been realized by nanofabrication, a method to track intracellular protein dynamics in real-time, in situ and in living cells has not been found. Here we present the first demonstration of label-free detection of intracellular p53 protein dynamics through a nanoscale surface plasmon-polariton fiber-tip-probe (FTP).

Fluorescent-labeling imaging techniques have been widely used in live cell studies; however, the labeling processes can be laborious and challenging for non-transfectable cells and clinical cells, and labels can interfere with protein functions. In this thesis, we present the first demonstration of label-free detection and quantification of intracellular biomarker dynamics with a nanoscale localized-surface-plasmon fiber-tip-probe (LSP-FTP). Our results have established the FTP technique as a new tool to study the time dynamics of proteins and protein phosphorylations in single live cell, and could be generalized to study other types of primary cells in response to external triggers, including drugs.

Chapter 2 focuses on the fabrication methods of fiber tip probes (FTPs). FTP is a lab-on-a-fiber probe wet-etched at nanoscale dimensions. The base material of FTPs may comprise any solid materials as long as they have matching etchants. FTPs take various configurations and may comprise of single-ended fiber, double-ended fiber, or an end-portion or mid-portion nanowire with various aspect ratios. Structures of FTPs can be tuned at nanoscale accuracy with extreme surface smoothness. These FTPs can be mass-fabricated and multiplexed at a single fabrication step and at low cost.

Chapter 3 discusses the procedures and results on measuring intracellular biomarker dynamics in intact live cells. We demonstrated label-free detection of tumor suppressor p53 dynamics in single HeLa cells under ultraviolet radiation and under treatment with neocarzinostatin (NCS). Also, we employed the FTP technique to prove that \textbeta -Amyloid generation precedes Tau phosphorylation by continually monitoring intracellular levels of \textbeta -Amyloid and phosphorylated Tau in live human neuroblastoma cells (SY5Y).

Chapter 4 discusses other potential applications of FTPs. An FTP with a nanodiamond at its tip can be used to measure various intracellular properties such as electromagnetic fields, temperature, or pressure. Manipulation of electron spins at nitrogen-vacancy centers in a nanodiamond allows these measurements. An FTP with a plasmonic particle at its tip can be used for surface-enhanced Raman spectroscopy (SERS) and potentially allow single molecular detection. A mechanical FTP with an end-portion nanowire (a few hundred micrometers long and sub-micron thick) functions as a cantilever sensor, and we can detect changes in its vibration modes induced by binding of analytes to a reaction entity immobilized relative to the nanowire. Free-standing FTP waveguides with a sub-micron portion in diameter can be used for efficient light coupling and device characterizations.

Single-crystal diamond, with its unique optical, mechanical and thermal properties, has emerged as a promising material with applications in classical and quantum optics. However, the lack of heteroepitaxial growth and scalable fabrication techniques remains the major limiting factors preventing more wide-spread development and application of diamond photonics. In this work, we overcome this difficulty by adapting angled-etching techniques, previously developed for realization of diamond nanomechanical resonators, to fabricate racetrack resonators and photonic crystal cavities in bulk single-crystal diamond. Our devices feature large optical quality factors, in excess of 105, and operate over a wide wavelength range, spanning visible and telecom. These newly developed high-Q diamond optical nanocavities open the door for a wealth of applications, ranging from nonlinear optics and chemical sensing, to quantum information processing and cavity optomechanics.