Highly stable PEGylated gold nanoparticles in water: Applications in biology and catalysis

Article abstract of DOI:10.1039/c3ra41873a

Here we report the synthesis of well dispersed gold nanoparticles (Au NPs), with diameters ranging between 5 and 60 nm, in water and demonstrate their potential usefulness in catalysis and biological applications. Functionalised polyethylene glycol-based thiol polymers (mPEG-SH) were used to stabilise the pre-synthesised NPs. Successful PEGylation of the NPs was confirmed by Dynamic Light Scattering (DLS) and zeta potential measurements. PEG coating of the NPs was found to be key to their colloidal stability in high ionic strength media, compared to bare citrate-stabilised NPs. Our results show that PEG-Au NPs with diameters <30 nm were useful as catalysts in the homocoupling of arylboronic acids in water. Additionally, PEG-Au NPs were also shown to be stable in biological fluids, non-cytotoxic to B16.F10 and CT-26 cell lines and able to successfully deliver siRNA to CT-26 cells, achieving a significant reduction (p < 0.05) in the expression levels of luciferase protein; making these NPs attractive for further biological studies. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3ra41873a

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DOI: 10.1039/C3RA41873A
Highly Stable PEGylated Gold Nanoparticles in Water: Applications in
Biology and Catalysis
Marie Therese Nolan,d Timothy Doody,e Gerard P. McGlacken,d Michael A.
a,b,c
Kamil Rahme,*
Morris,a,b Caitriona O’Driscoll e and Justin D. Holmes a,b
aMaterials Chemistry and Analysis Group, Department of Chemistry and the Tyndall National Institute,
University College Cork, Cork, Ireland.
bCentre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College Dublin, Dublin 2,
Ireland.
cDepartment of Sciences, Faculty of Natural and Applied Science, Notre Dame University (Louaize), Zouk
Mosbeh, Lebanon
dOrganic and Pharmaceutical Chemistry Group, Department of Chemistry and Analytical and
Biological Chemistry Research Facility, UCC, Cork, Ireland
ePharmocodelivery group, School of Pharmacie, University College Cork, Cork, Ireland.
*To whom correspondence should be addressed: Fax:+961 9 225164; Tel:+961 9 218950
Eꢀmail: kamil.rahme@ndu.edu.lb
†Electronic Supplementary Information (ESI) available: [details of any supplementary information available
should be included here].
1

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DOI: 10.1039/C3RA41873A
ABSTRACT:
Here we report the synthesis of well dispersed gold nanoparticles (Au NPs), with diameters ranging
between 5ꢀ60 nm, in water and demonstrate their potential usefulness in catalysis and biological
applications. Functionalised polyethylene glycolꢀbased thiol polymers (mPEGꢀSH) were used to
stabilise the preꢀsynthesised NPs. Successful PEGylation of the NPs was confirmed by Dynamic Light
Scattering (DLS) and Zeta potential measurements. PEG coating of the NPs was found to be key to
their colloidal stability in high ionic strength media compared to bare citrateꢀstabilised NPs. Our results
show that PEGꢀAu NPs with diameters < 30 nm were useful as catalysts in the homocoupling of
arylboronic acids in water. Additionally, PEGꢀAu NPs were also shown to be stable in biological fluids,
and not cytotoxic on B16.F10 and CTꢀ26 cell lines, and able to successfully deliver siRNA to CTꢀ26
cells, achieving a significant reduction (p < 0.05) in the expression levels of luciferase protein; making
these NPs attractive for further biological studies.
KEYWORDS: Gold nanoparticles, homocoupling, stabilisation, polyethylene glycol (PEG), cytotoxicty,
cell association and siRNA delivery.
2

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DOI: 10.1039/C3RA41873A
Introduction
The increasing progress of nanotechnology in the last few decades has made nanomaterials
indispensable in many areas such as material science, medicals, and cosmetics.1ꢀ3 Nanoparticles
(diameter 1ꢀ100 nm) exhibit particular properties that arise from quantum size effects and also from a
high surface to volume ratio.1, 4, 5 Their small size enable them to interact with biomolecules (such as
enzymes, antibodies, DNA, proteins etc.) and cells.6 As such, they are of appropriate dimensions for
applications in nanobiotechnology and catalysis.7ꢀ9 Noble metal nanoparticles, especially gold, are well
known for their characteristic surface plasmon resonances which form the basis for many biological
1, 4,10ꢀ13
sensing and imaging applications.
Besides their potential applications in biology, the catalytic
application of gold nanoparticles (Au NPs) in organic reactions has also been of considerable interest in
recent years. Important transformations using Au catalysis, such as the selective oxidation of
alcohols,14ꢀ16 CO oxidation in the absence of H2,
chemoselective reduction of nitroarenes,20 and a
17ꢀ19
wide variety of commercially important synthetic protocols have been studied exstensively.21ꢀ23
Researchers have also shown that poly(2ꢀaminothiophenol) (PATP)ꢀsupported Au NPs can be used in
SuzukiꢀMiyaura crossꢀcoupling reactions.24 More recently, the homocoupling of arylhalides has been
accomplished using a catalytic system comprising of Au NPs supported on a bifunctional periodic
mesoporous organosilica.25 Aryl boronic acids have also been homocoupled using Au on solid supports
through apparent heterogeneous conditions. Homocoupling with high selectivity was achieved using Au
supported on CeO2.26 The applications of nanoparticles in biology and catalysis typically requires them
to be well dispersed and stable in solution, which can be difficult due to their high surface energies.27
Due to this instability especially in presence of salts NPs can lose their sizeꢀdependent properties
(catalytic, optical, magnetic etc.) caused by the high tendency of adhesion and aggregation.28
Aggregation of nanoparticles is much more pronounced in solvents with high ionic strengths, i.e.
biological fluids, and in presence of other chemicals such as high concentration of salts that is one of the
main causes of aggregation.12 Therefore, the dispersion of NPs must be controlled to provide a better
platform for the advancement of these materials in catalytic and biological applications.29 In this
3