CHARACTERIZING UPTAKE, DISTRIBUTION AND FATE OF CdSe/ZnS QUANTUM DOTS IN SYNNECHOCOCCUS ELONGATUS PCC7942 BY SUN MIN KIM THESIS Submitted in partial fulfillment of the requirements for the degree of Master of Science in Agricultural and Biological Engineering in the Graduate College of the University of Illinois at Urbana‐Champaign, 2011 Urbana, Illinois Advisers: Assistant Professor Kaustubh Bhalerao Professor Rashid Bashir
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CHARACTERIZING UPTAKE, DISTRIBUTION AND FATE OF CdSe/ZnS QUANTUM DOTS IN SYNNECHOCOCCUS ELONGATUS PCC7942
BY SUN MIN KIM
THESIS
Submitted in partial fulfillment of the requirements for the degree of Master of Science in Agricultural and Biological Engineering
in the Graduate College of the University of Illinois at Urbana‐Champaign, 2011
Urbana, Illinois
Advisers:
Assistant Professor Kaustubh Bhalerao Professor Rashid Bashir
ii
ABSTRACT
One of the challenges in developing a framework for characterizing nanoparticle
toxicity is that the number of nanoparticles and their superficial derivatives is very large and
continues to expand rapidly. Multiple factors such as size, geometry, surface chemistry,
nanoscale topology, electromagnetic activity, and aggregation and degradation processes
can modify the original nanoparticle and change its behavior significantly. Secondly, the
type of environments and organisms these nanoparticles may be subjected to are also
numerous and complex. Thirdly, the number of analytical and computational techniques
available to the researcher today spans physical, chemical, biomolecular, ecological and ‘‐
omics’ based approaches. Thus any combination of nanoparticle, model organismal system
and analytical technique is a potential route of investigation and can produce important
broad empirical information on the impact of nanomaterials on living systems.
This study is an extension of the analytical framework called DIMER, which involves
characterizing the dispersion, imbibition, metabolism, elimination and recycle of
nanoparticles to study its life cycle of in the environment. Cadmium selenide quantum dots
coated with zinc sulfide were chosen as a model nanoparticle. Similarly the cyanobacterium
Synechococcus elongatus PCC 7942 were chosen as the model host organism.
This study characterizes the uptake, distribution and fate of both water insoluble and
water soluble CdSe/ZnS quantum dots in cyanobacteria. To quantify the toxicological impact
of quantum dots on cells, cell growth rate, membrane destabilization, viability and the
activity of photosynthetic pigments were characterized. For characterization of uptake and
distribution, flow cytometry, laser scanning confocal microscopy and transmission electron
microscopy were used. When quantum dots are dispersed into the environment, their
imbibition, metabolism, degradation and elimination from cells depends on their surface
coating. Consequently, water soluble quantum dots, which are coated with a hydrophilic
coating, showed dramatically reduced degradation rates and resulting hazardous effects on
the cells even when observed directly in contact with the cells. However, water insoluble
quantum dots were immediately toxic to the cells. The observed toxicity was largely
indistinguishable from cadmium toxicity, which is a degradation product of the quantum dot.
The primary impact observed is that the cadmium destroys the photosynthetic machinery of
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the cells. Given the central role of cyanobacteria in many aquatic ecosystems, such damage
has serious implications to an ecosystem. Additionally, the cadmium toxicity is persistent in
the environment. Once contaminated, the growth media continues to inhibit the growth of
new cyanobacteria indicating a long‐lasting, toxic effect on the environment.
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ACKNOWLEDGEMENTS
My graduate study would not have been finished without many people. First and
foremost, I would like to express my gratitude to Dr. Kaustubh Bhalerao for his guidance,
support and patience to successfully complete all my graduate studies at UIUC. He always
encouraged me to have many questions, which helped me to develop critical thinking and
instilled confidence in me. I would also like to express my sincere thanks to co‐advisor, Dr.
Rashid Bashir for introducing me various nanotechnology applications. I deeply thank my
committee, Dr. Prasanta Kalita for his valuable insight and guidance towards completing the
thesis.
I thank Phil, Vaisak, Rekha and Goutam to have great time together in the lab. I have
lots of great memories in Champaign with Jinhae, Yoon Ju, Patricia, Hyun Seung, Jong Min and
SangHoon. Thanks go also to my friends in the Department of Agricultural and Biological
Engineering.
I also want to thank all my friends and family in Korea. My parents, Si Ju Kim and Jung
Hee Kim have always provided encouragement and support.
1.1. DIMER: Need for a framework for understanding the environmental impact of nanotechnology ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 1 1.2 Case for using quantum dots (QDs) ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 6 1.3 Case for using cyanobacteria ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 7 1.4 Objectives of the present study ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 9
Chapter 2. BACKGROUND AND LITERATURE REVIEW ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 10
2.1 Nanomaterial ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 10 2.2 Biology of Cyanobacteria ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 12
3.1 Visualization of nanoparticles ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 17 3.2 Cells exposed to treatments and controls ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 17 3.3 Fate of quantum dots in cyanobacteria∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 19 3.4 Uptake and distribution of quantum dots ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 21 3.5 Media contamination ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 24
Chapter 4. RESULT AND DISCUSSION ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 25
4.1 Characterization of quantum dots ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 25 4.2 Fate of quantum dots in cyanobacteria∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 26 4.3 Degradation rate of quantum dots ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 43 4.4 Uptake and distribution of quantum dots ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 46
Life cycle of nanoparticles in the environment has recycle and redispersion potential,
which differentiates environmental mobility of nanoparticles from that of the life cycle in
the human bodies. Here, we tested recycle and redispersion to elucidate further
information for life cycle and secondary impact in the environment. Damaged cells did not
grow in new fresh media which confirmed results of viability assays. Growth of fresh cells in
contaminated media was inhibited and photosynthesis pigments lost their color, which is
similar to the result of WIQDs treatments or cadmium controls (Figure 4‐16 and 4‐17). Once
cadmium leaked from quantum dots releases to aqueous system, they can have further
harmful effect to new health organisms.
Figure 4‐16. Cells growth for persistent assay. Dead cells did not grow at all and new live
cells die in contaminated media. Fresh BG‐11 media + WIQD treated pellet ▬ Fresh BG‐11
media + Cd treated pellet ▬ WIQD treated media + Se7942 pellet ▬ Cd treated media +
Se7942 pellet ▬.
55
Figure 4‐17. Photographs of flaks for persistence assay.
56
Chapter5.CONCLUSION
In this study, CdSe/ZnS quantum dots and cyanobacterial species were chosen for
evaluating potential fate of nanoparticles in the environment. Surface coating and
degradation rate of quantum dots were two main factors of determining their toxicity to
cyanobacteria. Aggregated WSQDs were self‐assembled to the cell membrane and
continuously taken up by cyanobacteria via passive and active transport mechanisms.
However, WSQDs had no effect to cell growth and viability at the concentration tested since
surface coating of a carboxylic acid group on WSQDs kept quantum dots intact, preventing
cadmium released from a core portion of quantum dots. WIQDs, quantum dots without
protection of surface coating, were vulnerable to light and were easily degraded into
cadmium and selenium. Thus, toxic responses of quantum dots were similar to that of
cadmium, indicating most quantum dots toxicity was governed by leaked cadmium ions.
WIQDs were impacting the photosynthetic machinery of the cyanobacteria resulting in a
shift of auto‐fluorescence spectrum. We also characterized toxicity of toluene, the solvent
to suspend water insoluble quantum dots. Even though cell exposed to only toluene
changed in color observable to the naked eye, their auto‐fluorescence was not different
with respect to untreated Se7942. To characterize elimination/recycle of nanoparticles for
comprehensive understanding quantum dots life cycle in the environment, media
contamination was analyzed. Contaminated media from quantum dots showed further toxic
effect in new health cells. The result indicates that quantum dots have to be handled
carefully to not disperse into environment.
57
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