C O MMU N I C A T I O N S
column. Consistent with this, we also found that Au-S-EG
4
particles do not bind to either total cellular RNA or chromosomal
DNA, both of which are highly negatively charged.14
In conclusion, we discovered that with the water content
optimized in the range of 9-18% in the reaction mixture, di-, tri-,
and tetra(ethylene glycol) protected gold nanoparticles Au-S-EG
n ) 2, 3, and 4) could be directly synthesized. These gold
n
(
nanoparticles that are bonded with a uniform monolayer with
defined length varying from 0.8 to 1.6 nm (from molecular
modeling) have great stability in aqueous solutions with a high
concentration of electrolyte and organic solutions. Using ion-
exchange chromatography and gel electrophoresis, we first dem-
Figure 1. Gel image of protein binding assay. Eleven microliters of protein/
particle binding reaction mixture was loaded onto a 1% agarose gel, and
electrophoresis was run for 20 min at 90 V constant voltage. Lane 1: 10
µL of Au-Tp at ∼100 µM. Lanes 2 and 3 are the same amount of Au
particles mixed with 1 µL of lysozme and BSA, respectively. Protein
concentrations are all 10 mg/mL. Lanes 4-6 are similar to lanes 1-3, except
that Au-EG4 particles were used.
onstrated that these Au-S-EG (n ) 2, 3, or 4) nanoparticles with
n
neutral and hydrophilic surfaces have complete resistance to protein
nonspecific interactions. These types of nanoparticles provide a
fundamental starting material for designing hybrid materials
composed of metallic nanoparticles and biomolecules. One of the
advantages for the direct synthesis method is that it allows the
synthesis of a mixed monolayer of ethylene glycol and a functional
ligand to eliminate nonspecific interactions and provide specific
interactions in the same time.15 From the aspect of industrial
applications, these biologically inert gold nanoparticles will have
commercial utilities in electronic and biomedical applications. Some
of these works are underway.
Supporting Information Available: Synthesis of EG
, 3, or 4), synthesis of the Au-EG nanoparticle, synthesis of Au-
S-EG (n ) 2, 3, or 4) through replacement with the tiopronin protected
Au nanoparticle, gel electrophoresis experiment, ion exchange chro-
n
-SH (n )
2
4
Figure 2. Strong cation exchange chromatography for Au-Tp and Au-
EG4 binding with lysozyme. (a) Au-EG4; (b) Au-EG4 + lysozyme; (c)
lysozyme; (d) Au-Tp; and (e) Au-Tp + lysozyme.
n
1
matography, H NMR spectra of free EG
nanoparticle, TEM image of Au-EG , and gel electrophoresis assay
of Au-EG binding with DNA and RNA (PDF). This material is
4
-SH and the Au-S-EG
4
results clearly showed that the Au-S-EG4 does not bind to either
the very basic protein lysozyme or the very acidic protein BSA.
The most dramatic contrast was provided by the binding between
Au particles and lysozyme. Addition of lysozyme into the Au-Tp
particle solution causes an immediate color change from pinkish
red to blue, indicating that Au particles form aggregates, presumably
because the positively changed lysozyme (pI ) 11) molecules cross-
link negatively charged Au-Tp particles (-COOH). Centrifugation
of the Au-Tp/lysozyme reaction mixture resulted in a clear/
colorless supernatant, indicating that no soluble Au-Tp particles
remained in the supernatant. The cation exchange column chro-
matography confirmed that only lysozyme proteins were present
in the supernatant, as shown in Figure 2. However, when lysozyme
4
4
available free of charge via the Internet at http://pubs.acs.org.
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1
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(
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4
was mixed with Au-S-EG solutions, no color change happened
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EG4/lysozyme mixture. The reaction mixture was eluted from the
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(
9) (a) Prime, K. L.; Whitesides G. M. J. Am. Chem. Soc. 1993, 115, 10714.
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lysozyme and Au-S-EG
is no binding reaction occurring between Au-S-EG
4
particles. This result indicates that there
and the
(
10) (a) Wuelfing, W. P.; Gross, S. M.; Miles, D. T.; Murray, R. W. J. Am.
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4
lysozyme protein. Also tested were cytochrome C, ribonuclease
A, and myoglobin. In all cases, no binding was observed between
(
(
12) Bartz, M.; Kuther, J.; Nelles, G.; Weber, N.; Seshadri, R.; Tremel, W. J.
Mater. Chem. 1999, 9, 1121.
Au-S-EG
between Au-Tp and those proteins was seen. The Au-EG
nanoparticle was also run through an anion exchange column. The
Au-S-EG nanoparticles were eluted at the void volume from
both cation and anion exchange columns, indicating that the surface
of Au-S-EG particles is charge neutral and does not bind to either
4
and the tested proteins, but a varying degree of binding
(13) (a) Brust, M.; Walker, M.; Bethell, D.; Schiffrin, D. J.; Whyman, R. J.
Chem. Soc., Chem. Commun. 1994, 801. (b) Templeton, A. C.; Chen, S.;
Gross, S. M.; Murray, R. W. Langmuir 1999, 15, 66.
4
4
(14) See Supporting Information.
(15) Manuscript in preparation.
4
JA0350278
J. AM. CHEM. SOC.
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VOL. 125, NO. 26, 2003 7791