Walter Scott, Jr. College of Engineering

Graduate Exam Abstract

Sanaz Sadegh
Ph.D. Final
Feb 22, 2017, 10:00 am - 1:00 pm
LSC room 300
Single Molecule Fluorescent Measurements of Complex Systems
Abstract: Single molecule methods are powerful
tools for investigating the properties of
complex systems that are generally
concealed by ensemble
measurements. Here we use single
molecule fluorescent measurements to
study two different complex systems:
1/f noise in quantum dots and diffusion
of the membrane proteins in live cells.

The power spectrum of quantum dot
(QD) fluorescence exhibits 1/f noise,
related to the intermittency of these
nanosystems. As in other systems
exhibiting 1/f noise, this power
spectrum is not integrable at low
frequencies, which appears to imply
infinite total power. We report
measurements of individual QDs that
address this long-standing paradox.
We find that the level of 1/f noise for
QDs decays with the observation time.
We show that the traditional
description of the power spectrum with
a single exponent is incomplete and
three additional critical exponents
characterize the dependence on
experimental time.

A broad range of membrane proteins
display anomalous diffusion on the cell
surface. Different methods provide
evidence for obstructed subdiffusion
and diffusion on a fractal space, but
the underlying structure inducing
anomalous diffusion has never been
visualized due to experimental
challenges. We addressed this
problem by imaging the cortical actin
at high resolution while simultaneously
tracking individual membrane proteins
in live mammalian cells. Our data
show that actin introduces barriers
leading to compartmentalization of the
plasma membrane and that membrane
proteins are transiently confined within
actin fences. Furthermore,
superresolution imaging shows that
the cortical actin is organized into a
self-similar meshwork.
Adviser: Diego Krapf
Co-Adviser: N/A
Non-ECE Member: Dr. Michael Tamkun, Biomedical Sciences
Member 3: Dr. Edwin Chong, Electrical & Computer Engineering
Addional Members: Dr. Ashok Prasad, Chemical & Biological Engineering
1. Sadegh, Sanaz, Eli Barkai, and Diego Krapf. "1/f noise for intermittent quantum dots exhibits non-stationarity and critical exponents." New Journal of Physics 16.11 (2014): 113054.

2. Sadegh, Sanaz, et al. "Visualizing the Compartmentalization of the Surface of Mammalian Cells by Cortical Actin with Superresolution." Biophysical Journal 108.2 (2015): 452a.
Program of Study: