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.