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Characterization of Silver Nanoparticle Plasmon Effects on Systems of Free and
Bound Chromophores
19TH ANNUAL ARGONNE SYMPOSIUM FOR UNDERGRADUATES
IN SCIENCE, ENGINEERING AND MATHEMATICS
November 7th, 2008
Undergraduate Researcher: Will Boyd
Faculty Mentor: Dr. Joseph Perry
Graduate Student Mentor: Wojciech Haske
I. Project Background
Why Silver Nanoparticles?
The Plasmon Effect: A Strongly Localized Electric Field
Incident Electromagnetic Radiation at Plasmon Resonance Frequency
Oscillations of Nanoparticle Conduction Band Electrons
[1]
The Chromophore: TPD
Incident electromagnetic radiation at chromophore resonance frequency
Oscillating molecular dipole
TPD-thiolN
N
O
(CH2)12SH
Δ+Δ-
Theoretical Predictions
Modeling of Excited State Chromophore – AgNP Interactions a. Theoretical expression for molecules near spheroids derived by Gersten and Nitzan [2]
b. Enhanced and suppressed fluorescence radiative and non-radiative constants, kr and knr, depending on chromophore orientation
c. kr is inversely related to fluorescence lifetime:
d. Already reports of shorter lifetimes for chromophores on silver nanoparticles [3], [4], [5]
II. Physical Characterization of Chromophore-Coated AgNPs
Synthesis of AgNPs
Silver Acetate (AgAc)
NH2Oleylamine (OLA)
Ave. Diam.: 4.5 nm Std. Dev.: 18.8%
AgAc + OLAo-Xylene
145°C
AgOLA NP
Ag
Chromophore Exchange Reaction
Exchange Reactiona. Thiolated chromophores replace OLA
on surface of AgNPs
b. Thiol “footprint” (~20 Å2) used to estimate relative concentrations of AgNPs to chromophores
Purificationb. Aggregation in hexane
c. Precipitation following centrifugation
c. Extraction of supernatant
d. Dissolution of chromophore-coated AgNPs in toluene (TPD)
Est. Surface Coverage TPD((CH2)12SH): ~70%
III. Optical Characterization of Chromophore-Coated AgNPs
Stability of AgNP-TPD((CH2)12SH)
Time-Based Fluorimetry
a. Silver strongly quenches chromophore fluorescence
b. Increasing fluorescence intensity: desorption of chromophores
c. Stability was found to be highly solvent-dependent
Time-Based Fluorimetry of AgNPs-TPD((CH2)12SH) in Toluene/DMF (5:1)
UV-vis of AgNPs-TPD((CH2)12SH) in Toluene/DMF (5:1)
UV-vis Spectroscopy
a. Taken before and after time-based
fluorimetry
b. AgNPs stained cuvette in toluene
c. DMF and other organic solvents
strongly quenched fluorescence
Measuring Fluorescence Lifetimes
Time Correlated Single Photon Counting (TC/SPC)
TC/SPC generates ahistogram of the decay times for single photons from fluorescence emission
An analysis of the histogram finds the best fit exponential decay lifetimes
Mea
sure
d
Ph
oto
ns
Time
TC/SPC Results
TC/SPC Results: Exponential Decay Lifetimes
System TPD((CH2)12SH)AgNPs-
TPD((CH2)12SH)
Solvent Toluene/DMF (5:1) Toluene/DMF (5:1)
τ1 [ns] 1.599 < 0.070
A1 [%] 100.00 2.70
τ2 [ns] - 0.919
A2 [%] - 33.16
τ3 [ns] - 2.86
A3 [%] - 64.13
Mono-exponential decay of free TPD demonstrated
Tri-exponential decay of bound TPD
a. Ultra-short component too fast to resolve with TCSPC
b. Long component could represent TPD bound in parallel orientation
IV. Conclusions and Future Work
Physical Characterization of AgNP-Chromophore Systemsa. OLA-coated AgNPs can be synthesized with relatively small size distribution
b. Thiolated chromophores can be attached via a ligand exchange reaction
c. Relatively high chromophore coverage can be achieved
Optical Characterization of AgNP-Chromophore Systemsa. More work needed to fully characterize fluorescence lifetimes
b. Difficulty resolving short fluorescence lifetimes with small error
c. Utilization of femtosecond transient absorption to measure ultra-fast component of the excited state lifetimes
V. References
[1] Kelly, K. Lance; Coronado, Eduardo; Zhao, Lin Lin; Schatz, George C. J. Phys. Chem. B 107(3): 668-677 (2003)
[2] J. Gersten, A. Nitzan, J. Chem. Phys. 75(3): 1139-1152 (1981)
[3] Tovmachenko, Oleg G.; Graf, Christina; van den Heuvel, Dave J.; van Blaaderen, Alfons; Gerritsen, Hans C., Advanced Materials 18(1): 91-95 (2006)
[4] Fu, Yi; Zhang, J.; Lakowicz, J. R., J. Fluorescence 17: 811-816 (2007)
[5] Viger, M. L.; Live, L. S.; Therrien, O. D.; Boudreau, D., Plasmonics 3: 33-40 (2008)
VI. Acknowledgements
Special thanks to the following individuals and organizations for making this research possible:
National Science Foundation
MDITR REU Grant # 0120967
Georgia Tech President’s Undergraduate Research Award
Dr. Joseph Perry
Wojciech Haske
Michal Malicki
Zac Heacker
Matteo Cuzzuol
Sarah Chi
Dr. Matthew Sartin
Dr. Joel Hales
Questions?