View
4
Download
0
Category
Preview:
Citation preview
Synthesis of Gold and Silica Nanoparticles for development of NanosensorsLeah Sanford and John Kirk*
Carthage College
2001 Alford Park Drive, Kenosha, WI 53140
Department of Chemistry
Abstract
Nanotechnology is applicable to many different fields including electronics, drug
delivery, structural materials, and sensors. The research presented here explores
the development of a nanoparticle-based sensor that will detect small organic
compounds such as fungicides, herbicides, and pesticides. The main component of
these sensors is silicon dioxide nanoparticles due to their ability to self-assemble into
nanoporous crystals, thus effectively creating a filtration system. The device’s
sensing surface consists of gold nanoparticles, which is chosen due to favorable
optical properties and the ease of surface modification. In order to create a uniform
colloidal crystal with consistent pores, the nanoparticles must be similar in size.
Nanoparticle syntheses, however, are very sensitive to reaction conditions, making it
difficult to consistently synthesize size-matched particles. We explore different
variables such as reactant concentrations, mixing conditions, and temperature to
control and achieve size matching between silicon dioxide and gold nanoparticles..
Nanoscience is the study of materials that are 10-9m in size in at least one
dimension. The size of the material leads to physical and chemical properties that
are unique to the nanoscale. Some properties may include: color change,
fluorescent, and different melting points. Nanomaterials are becoming more
commonly used today in items such as cars, phones, and medications. One
common nanomaterial being used today is silica nanoparticles. Silica, in macro
form, is a common material found in glass, sand, and pottery. It is also used often
as a desiccant which absorbs moisture from the environment, and is often seen in
shoe boxes, backpacks, and shipped items. On the nanoscale, Silica is used for
slightly different applications. Silica nanoparticles are often found in sunscreens to
help protect against UV rays. Silica nanoparticles are also used commonly in
nanoscale research due to its easy synthesis, cheap starting materials, and its
ability to form nice colloidal crystal structures.• Continue to perfect recipes for silica and gold nanoparticles
• Collect more data from the DLS and images from the TEM
• Begin the gold embedment process into silica
• Strengthen nanoparticles to form sensor
• Test in Lake Michigan
• Carthage College
• Summer Undergraduate Research Experience (SURE) Program
• Carthage College Chemistry and Biology Department
Figure 1. Red spheres representing gold nanoparticles embedded into silica
nanoparticles (white). In theory, each particle is equal in radius and distance
between one another.
Figure 3. The reaction scheme for synthesis of
silica nanoparticles involves a reduction
mechanism. Tetraethyl orthosilicate (TEOS) reacts
with water to add an alcohol group. This silanol
then reacts with another molecule of TEOS to
create a dimer and a polymer there after .
• Kirk, J. S.; Stransky, J. A. Nanoscale Hardness of Sintered Silica Colloidal Crystals
• Le, T. V.; Ross, E. E.; Velarde, T. R. C.; Legg, M. A.; Wirth, M. J. Langmuir 2007, 23
(16), 8554–8559.
• Russo, Paul. A Practical Course in Dynamic Light Scattering. 2012,
• Hoffmann, F.; Fröba, M. Chem. Soc. Rev. 2011, 40 (2), 608–620.
• Stöber, W.; Fink, A. R.; Bohn, E. JOURNAL OF COLLOID AND INTERFACE
SCIENCE 1968, 26 (1), 62–69.
Nanoparticles are sized using a particle sizer. The particle sizer uses dynamic light
scattering to detect the size of particles. Dynamic light scattering uses a laser that
hits the sample and then light is scattered to a detector that determines the size of
the particles in solution.
Figure 2. Dynamic Light Scattering Apparatus.
Where: BS = beam splitter; M = Mirror; D = detector.(4)
Equation 1. Gold nanoparticle reaction scheme is a standard citrate reduction method. Chloroauric
acid reacts with trisodium citrate in water to reduce Gold from Gold 3+ to Gold 0.
Figure 8. Before and After of
Au nanoparticle synthesis.
Color change results from
gold going from 3+ to 0
Figure 4. the figure represents a three axis graph
depicting how amounts of water and ammonium
affect the size of a silica particles (in microns).
Figure 5. TEM image of silica nanoparticles
~105nm at 50,000 mag.
Figure 7. This figure demonstrates how gold nanoparticles are
synthesized. A seed if first yielded by starting materials in equation 1
and then grown.
Figure 6. Image of silica nanoparticles
after 24 hour synthesis.
2𝐴𝑢𝐶𝑙4 𝑠− + 3𝐶6𝐻5𝑂7 𝑠
3− + 3𝐻2𝑂(𝑙) ⇋ 2𝐴𝑢 𝑎𝑞 + 8𝐶𝑙(𝑎𝑞)− + 3𝐶5𝐻4𝑂5 𝑎𝑞
2− + 3𝐶𝑂2(𝑔) + 3𝐻3𝑂+
The interaction of gold with light is dependent on its size and physical
dimensions. Oscillating electric fields of light interact with the gold’s sea of
electrons (free electrons) in the conduction band. The electric fields cause the
electrons to oscillate in resonance with each other similar to that of a quasi-
particle. As smaller monodisperse gold nanoparticles are exposed to light, the
surface plasmon resonance is localized to a smaller area known as localized
surface plasmon resonance (LSPR). Due to the size confinement, the free
electrons cannot oscillate at larger wavelengths. This phenomenon leads to gold
nanoparticles to absorb light around 450 nm (blue-green) and reflect red light
(~700 nm) giving nanogold its red appearance.
Nanoparticle Sizing
Background
Future Work
Optical Properties of Nano Gold
Acknowledgements
References
Synthesis of Silica
Synthesis of Gold
Figure 10.TEM image of 45
nm gold nanoparticles at
20,000 mag.
Figure 12. (Left) Depiction of oscillating electrons in response to presence of light
(Right) LSPR spectra before (black) and after modification (red) of 25 nm Au
nanoparticles
Silica Nanoparticle Size Dependent on Temperature
Figure 11. Results of temperature controlled reactions
0
5
10
15
20
25
0 100 200 300 400
Re
lative
In
ten
sity
Size (nm)
30 °C
35 °C
40 °C
0
2
4
6
8
10
12
0 10 20 30 40 50 60 70 80
Inte
nsity
Size (nm)
Figure 9. Size results of gold
seed synthesis.
Recommended