Zwitterionic Ligands Bound to Cdse/Zns Quantum Dots Prevent Adhesion to Mammalian Cells

Article abstract of DOI:10.1080/10426507.2015.1085049

Zwitterionic materials are useful tools in material science and biology as they provide high water solubility while preventing nonspecific interactions. Quantum dots (QDs) functionalized with zwitterionic and quaternary ammonium ligands were synthesized to investigate their interactions with the outer membrane of HeLa cells. Quaternary ammonium functionalized quantum dots adhered strongly to the cell surface while zwitterionic QDs had no cell adhesion. These results demonstrate that future noninteracting nanoparticles based on this design are possible.

Full text of DOI:10.1080/10426507.2015.1085049

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
Zwitterionic Ligands Bound to CdSe/ZnS Quantum
Dots Prevent Adhesion to Mammalian Cells
Ryan F. Landis, Rui Tang, Singyuk Hou, Mahdieh Yazdania, Yiwei Lee &
Vincent M. Rotello
To cite this article: Ryan F. Landis, Rui Tang, Singyuk Hou, Mahdieh Yazdania, Yiwei Lee &
Vincent M. Rotello (2015): Zwitterionic Ligands Bound to CdSe/ZnS Quantum Dots Prevent
Adhesion to Mammalian Cells, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI:
10.1080/10426507.2015.1085049
To link to this article: http://dx.doi.org/10.1080/10426507.2015.1085049
Accepted online: 02 Oct 2015.
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Date: 07 October 2015, At: 23:44

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Zwitterionic Ligands Bound to CdSe/ZnS Quantum Dots Prevent Adhesion to
Mammalian Cells
Running Head: Zwitterionic Ligands Prevent Adhesion to Mammalian Cells
Ryan F. Landisa†, Rui Tanga† , Singyuk Houa, Mahdieh Yazdania Yiwei Leea, Vincent M.
Rotello*a
a Department of Chemistry, University of Massachusetts Amherst, 710 North Pleasant
Street, Amherst, Massachusetts 01003, United States
*Email: rotello@chem.umass.edu
Abstract:
Zwitterionic materials are useful tools in material science and biology as they
provide high water solubility while preventing non-specific interactions. Quantum dots
(QDs) functionalized with zwitterionic and quaternary ammonium ligands were
synthesized to investigate their interactions with the outer membrane of HeLa cells.
Quaternary ammonium functionalized quantum dots adhered strongly to the cell surface
while zwitterionic QDs had no cell adhesion. These results demonstrate that future non-
interacting nanoparticles based on this design are possible.
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Keywords: Zwitterion, Quantum Dots, Ammonium, HeLa, CHO, Adhesion
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Introduction:
Zwitterions have emerged as useful tools in material science and biology due to
their high water solubility while maintaining an overall neutral charge.1 Sulfobetaines,
carboxybetaines, and phosphobetaines are examples of zwitterions which do not
change their charge in physiological environments such as those found in blood and
plasma.2 In addition to high water solubility, zwitterions provide a large hydration shell;
water molecules surround both polar moieties providing stability.3 This hydration shell is
useful for developing materials designed for anti-fouling applications.4 Furthermore,
zwitterionic materials are useful in biology where preventing undesired adhesions to
growth media and proteins are required.5
Zwitterions are promising materials to develop non-interacting nanoparticles for
biological applications such as drug delivery. We have shown previously that
zwitterionic ligands bound to gold nanoparticles provide a large hydration shell, resulting
in corona free nanoparticles.6 Herein, we have synthesized red fluorescent QDs (RQDs)
functionalized with sulfobetaine zwitterionic (ZW-RQD) ligands to investigate their
interactions with the outer membrane of mammalian cells. In addition, quaternary
ammonium QDs (TTMA-RQD) was used as a positive control. After incubation and
washing, the cationic QDs adhered strongly to the cell surface while the zwitterionic
QDs had no cell adhesion. These results show that future non-interacting nanoparticles
built off this design is possible.
Results and Discussion:
Scheme 1 outlines the synthesis of the TTMA7 and zwitterion6 ligands in addition
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to the functionalization of the RQDs. RQDs were stirred with either TTMA or ZW ligands
(1-RQD:7-ligand mass ratio) in a 4:1 dichloromethane:methanol solution for three days
at 37 °C. The now hydrophilic RQDs were purified through dialysis to obtain pure
TTMA-RQD and ZW-RQD.
Both RQDs were incubated with HeLa cells for 20 minutes and imaged using
confocal microscopy to determine the degree of cell adhesion (Figure 1). Cationic RQDs
show ample adhesion to the HeLa cells while ZW-RQD had no cell adhesion. In
addition, both RQDs show no uptake within the cells after 20 minutes (Figure 1a, b).
Longer incubation times (one hour) results in uptake of the TTMA-RQDs and was
avoided to ensure cell adhesion was only observed. To investigate if similar adhesion is
possible with other mammalian cells, RQDs were incubated with Chinese hamster ovary
(CHO) cells and imaged using confocal microscopy (Figure S3). TTMA-RQDs show
good adhesion to the surface of CHO cells while ZW-RQD had no cell adhesion.
Image analysis of the HeLa cell confocal images (Figure 2) revealed that TTMA-
RQD showed high fluorescence intensity on the surface of the cell. ZW-RQD shows
almost no fluorescence intensity signifying that ZW-RQDs large hydration shell prevents
cell adhesion.
Experimental:
All solvents and reagents were purchased from Fisher Scientific and were used
as received, unless otherwise noted. Milli-Q (MQ, 18.2 MΩ·cm at 25 °C) water was used
in all steps where water was required. Detailed synthesis of TTMA7 and zwitterionic6
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ligands in addition to RQDs8 can be found at their corresponding papers. Additional
electron microscope images are included in the Supplemental Materials (Figures S 1 –
S 2)
Functionalization of RQDs with TTMA and ZW ligands
In a 20 mL scintillation vial equipped with a stirbar was added 0.020 g of RQD.
Then 4.0 mL of nitrogen purged dichloromethane (DCM) was added to dissolve the
RQDs. A sample of 0.140g (1:7 mass ratio) of either TTMA or ZW ligands was dissolved
in nitrogen purged methanol (MeOH, 1 mL) and directly added to the RQD solution and
allowed to stir for three days at 37 °C under a nitrogen atmosphere. Afterwards, DCM
and MeOH were evaporated, the vial washed three times with hexane, residual hexane
evaporated and the now hydrophilic RQDs dissolved in water. Finally dialysis of TTMA-
RQD and ZW-RQD in 10,000 MWCO membrane bags were performed to afford pure
RQDs.
HeLa Cell Growth
HeLa cells were cultured in a humidified atmosphere (5% CO2) at 37 °C and grown in
Dulbecco’s modified eagle’s medium (DMEM, low glucose) supplemented with 10%
fetal bovine serum (FBS) and 1% antibiotics (100 U/ml penicillin and 100 μg/mL
streptomycin).
Incubation and Imaging of Hydrophilic RQDs with HeLa Cells
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20,000 HeLa cells were plated into 1 cm2 confocal chamber 24 h prior to RQD
incubation. To perform the RQD incubation, cells were washed with PBS for 3 times
followed by incubating with DMEM containing 50 nM RQDs for 20 min. After that,
DMEM was discarded and cells were washed with PBS for 3 times. The confocal
chamber was then placed on Zeiss LSM 510 laser scanning confocal microscope for
imaging.
Image Analysis of the Confocal Images
An 8-bit grayscale format containing both fluorescent and bright field channels
were obtained from least squares conformal map (LSCM). ImageJ was used to extract
the fluorescent intensity channels along the cell walls.
Conclusion:
In conclusion, zwitterionic materials are useful tools as they provide high water
solubility while preventing non-specific interactions. We show that non-interacting
nanoparticles are possible with the functionalization of sulfobetaine zwitterionic ligands
onto RQDs. The positive control, TTMA-RQD, is highly positively charged and can
adhere onto the negatively charged mammalian cell membrane while ZW-RQD shows
no adhesion to the surface both qualitatively and quantitatively. Nanoparticles built off
this zwitterionic strategy will afford non-interacting nanoparticles for future biological
applications such as drug delivery.
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References:
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(a) Singh, P.; Singh, V. K.; Singh, M. e-Polymers 2007, 030, 1–34, (b) Taha, M. Ann Chim., 2007, 95, 105–109.
White, A.; Jiang, S. J. Phys. Chem. B 2011, 115, 660–667.
Yang, R.; Xu, J.; Ozaydin-Ince, G.; Wong, S. Y.; Gleason, K. K. Chem. Mater. 2011, 23, 1263–1272.
(a) Keefe, A. J.; Jiang, S. Nat. Chem., 2012, 4, 59–63, (b) Zhan, N.; Palui, G.; Safi, M.; Ji, X.; Mattoussi, H. J. Am.
Chem. Soc. 2013, 135, 13786–13795.
Moyano, D.; Saha, K.; Prakash, G.; Yan, B.; Kong, H.; Yazdani, M.; Rotello, V. M. ACS Nano 2014, 8, 6748–6755.
You, C. C.; Miranda, O. R.; Gider, B.; Ghosh, P. S.; Kim, I. B.; Erdogan, B.; Krovi, S. A.; Bunz, U.; Rotello, V.
M. Nat. Nanotechnol. 2007, 2, 318–323.
Zhu, Z.; Yeh, Y.; Tang, R.; Yan, B.; Tamayo, J.; Vachet, R. W.; Rotello, V. M. Nat. Chem. 2011, 3, 963–968.
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Scheme 1. a) Synthesis of TTMA and zwitterion ligands. b) Functionalization of RQDs with thiol-
terminated TTMA and zwitterion ligands.
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Figure 1. Confocal images of a) TTMA-RQD and b) ZW-RQD
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Figure 2. Fluorescence intensity of RQDs on the surface of HeLa cells. Quantification was determined by
integrating over seven cells at four different points on the cell membrane.
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