Physical Society Colloquium
Interview for Faculty Position
Ultrafast Spectroscopy on Conjugated Polymers:
from Fundamental Photo-physics to Their Applications in Biosensors
Qing-Hua Xu
University of California at Santa Barbara
Conjugated polymers are novel low-dimensional materials that have attracted
the interest of both physicists and chemists. They display many interesting
optical and electric properties due to their unique molecular and electronic
structure. We have used ultrafast spectroscopy to demonstrate a
charge-generation mechanism via a two-step exciton-exciton annihilation
process by capturing the spectral characteristics of the involving transient
species. This charge generation mechanism is crucial to understanding the
photophysics of conjugated polymers. Conjugated polymers also display
exceptional properties such as optical amplification via energy transfer,
which offers potential high sensitivity in detecting analytes. Fluorescence
resonance energy transfer (FRET) from cationic conjugated polymers (CCP) to a
fluorescent dye that is labeled onto a peptide nucleic acid (PNA), has been
used for DNA sequence detection. A single stranded DNA can form duplexes with
the neutral PNA with complementary sequence. The electrostatic interactions
between the positively charged CCP chain and the negatively charged DNA
strand bring the CCP and fluorescein in close contact for efficient FRET.
This mechanism has been used to detect the DNA sequence. Both electrostatic
and hydrophobic interactions have been found to be responsible for bringing
CCP and PNA into proximity. Dilution of the solution or addition of organic
solvents can reduce the hydrophobic interactions, and improve the selectivity
between the complementary and non-complementary PNA/DNA. These effects have
been investigated with ultrafast spectroscopic measurements.
Monday, March 8th 2004, 16:00
Ernest Rutherford Physics Building, R.E. Bell Conference Room (room 103)
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