Determining the Size and Shape of Gold Nanoparticles · Determining the Size and Shape of Gold...

Determining the Size and Shape of Gold Nanoparticles

Carthage College

Ashley Wulf 11/17/2011

Determining the Size and Shape of Gold Nanoparticles Ashley Wulf

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Abstract:

Gold nanoparticles (GNPs) are studied because they have unique optical

properties making them very useful for things such as diagnostics. GNPs were

synthesized using cetyltrimethylammonium bromide (CTAB) to create icosahedral

shapes and were then studied based on their Surface Enhanced Raman Scattering

(SERS). Various imaging techniques were used in order to better understand the

structure of GNPs and to prove a high yield for the controlled synthesis. Through the

work by Haiss, et al. spherical gold nanoparticles were also synthesized and size was

determined through UV-Visible spectroscopy (UV-Vis) and surface plasmon resonance

(SPR). In another study by Kwon, et al. transmission electron microscope (TEM),

scanning electron microscope (SEM), X-ray diffraction (XRD), and UV-vis were used to

study the GNPs synthesized to determine the size and shape. Equations were

developed based on the diameter of the particle through SPR and UV-vis spectra data

which allowed one to be able to quickly and easily calculate size and concentration of

GNPs. In conclusion, GNPs were synthesized using two different methods to produce

spherical and icosahedral shapes and then were studied to determine size and their

SERS properties.

Introduction:

Gold nanoparticles (GNPs) are the most stable metal nanoparticle and their

unique optical and electrical properties make many researchers believe that they will be

among the key materials and building blocks for nano-materials in the 21st century 1.

Determining the shape and diameter of nanoparticles is important because their uses in


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optical 2, electronic, magnetic and catalytic applications are dependent upon shape and

size 1 . Nanoparticles can be prepared in numerous shapes such as rods, prisms, and

wires 2, but high yields have never resulted from these syntheses. This thesis will

examine a new high-yield synthesis of icosahedral GNPs and will present a study that

characterizes the size of spherical GNPs.

In the article by Kwon, et al., cetyltrimethylammonium bromide (CTAB) was used

to control particle aggregation in a icosahedral GNPs synthesis 3. CTAB stops the

growing process because it can act as a capping agent. The capping between the

CTAB molecules and GNPs occur due to electrostatic interactions. If the GNPs were not

capped then they could fuse into larger particles because GNPs experience dispersion

interactions which increase their tendency to fuse. CTAB counteracts this fusing

process by overcoming the electrostatic repulsion. Therefore, once the driving forces for

growth by GNPs and the CTAB counteracting interactions are in equilibrium, the GNPs

stop growing 1.

In the article by Kwon, et al. Gold particles of 3.5nm size were used as seeds to

grow larger nanoparticles with CTAB. A controlled synthesis was then preformed to

produce GNPs of 10 to 90nm in size. Five synthesized samples were labeled A-E and

had increasing particle size. Each of the five solutions contained the following: 9.0 mL of

growth solution containing 2.5x10-4 M HAuCl4, 0.10 M CTAB solutions and 50 µL of 0.10

M ascorbic acid. Of the seed solution 1.0 mL was mixed with solution A. Then 1.0 mL

was taken from solution A and added to solution B. Again 1.0 mL of solution B was

added to solution C and the same process was used to solutions D, and E. The


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concentrations of the GNPs were calculated and are listed in Table 1. The five different

samples were then studied using

microscopy and spectroscopy 3.

To examine the five samples,

transmission electron microscopy

(TEM) was used to capture images of

the GNPs. In TEM, an electron beam

interacts with and is transmitted through

a thin sample, and then projected onto

a florescent screen. An image of the

sample is thus produced and the brighter regions of the image represent areas where

more electrons have passed through the sample; whereas the darker regions represent

areas where fewer electrons have been passed through due to higher sample density.

TEM was also used because images are able to be magnified up to 500,000 times thus

producing a high resolution, highly magnified, image.4,5, 6

A scanning electron microscope (SEM) was also used to study the synthesized

GNPs. In SEM, a set of coils moves the electron beam across a sample in a two

dimensional grid. When the electron beam across over the sample, different interactions

occur. Some of the electrons from the surface material kick of their electrons by the

beam thus producing secondary electrons. These secondary electrons can then be

detected by the secondary electron detector on a SEM. An image is then produced at

the surface of the sample and is projected. Similarly to TEM, SEM images can be

magnified up to 100,000 times while maintaining a high resolution. 5,4,6


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Both TEM and SEM are electron microscopes and require an electron source.

The most common electron source used is a tungsten filament. When the filament is

heated, electrons are produced and are attracted by the anode where they are pushed

down the column of the apparatus to interact with the sample. 6 Although SEM and TEM

both use electron beams to produce images of particles, the techniques have a few

important differences. For example, in TEM an electron beam passes through a thin

sample whereas in SEM the electron beam scans the entire surface of the sample.

Also, in TEM the samples are very thin, and in SEM the sample can be of any

thickness. Lastly, TEM images are shown on fluorescent screens and SEM images are

shown on television monitors.

X-Ray diffraction (XRD) was also used to also examine the synthesized GNPs.

In XRD, x-rays that are produced by the x-ray beam get scattered by the atoms in the

sample. Waves are then scattered spherically from the atoms which causes the

intensity of the scattered radiation to show minimum and maximums in different

directions. XRD allows a better visual of the structure of the observed atoms because it

shows axes, shape, size and position of the atoms 7. In the article of Kwon, et al., XRD

was used to show that particle growth occurs through adding more gold atoms down the

preferential plane of the five solutions 3.

Surface-enhanced Raman scattering (SERS) is a more advanced spectroscopic

technique which is a form of Raman spectroscopy. Raman scattering is a type of

molecular vibration that can occur between light and molecules. If the energy of light is

not enough to excite the molecules from the ground state to the lowest electronic state,

the molecule is then instead excited to a virtual state between the two. SERS was


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discovered by accident when a researcher was trying to do Raman scattering and

produced a Raman scattering more intense than expected. This strong signal was then

coined SERS. Therefore, SERS is a technique that enhancing Raman scattering by

molecules adsorbed on a rough surface. SERS can occur when molecules are brought

to the surface of metals and can be observed from silver, gold and copper. Also, if metal

nanoparticles are used in SERS, the particle size needs to be from 20-300 nm. 3,8

Surface plasmon resonance (SPR) was used and involved light being directed

onto a thin surface which contains gold. Some of the lights electric field can leak onto

the surface if the angle of light causes it to be reflected. The electric field excites the

surface plasmon waves in the metal. A surface plasmon is an electron wave that travels

along the surface of the gold film. The wavelength of this plasmon wave is then

detected in the SPR experiment.9,10

Ultraviolet-visible spectroscopy (UV-Vis) involves the absorption of light by

molecules in ultraviolet-visible region. The absorption in the visible range directly

corresponds to the color of the chemicals involved. UV-Vis can be used to determine

the concentration of the solution based on the absorbance. UV-Vis uses a

spectrophotometer which measures the intensity of light that passes through a given

sample (I). The instrument then compares the measurement to the intensity of light

before it passes through the sample (I0). A percent transmittance is then determined by

using I/I0. Next, from the percent transmittance, an absorbance can be calculated by

using Equation 1.

A= -log (%Transmittance / 100%) (1)


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Uv-Vis thus allows a concentration and absorbance to be calculated depending on the

wavelength of the particle or solution studied 11.

In a second study by Haiss, et al. UV-Vis and TEM were used to determine the

size of spherical gold nanoparticles. GNPs in aqueous solutions with diameters of three

to 120 nm were studied. Through UV-Vis spectroscopy and SPR, particle diameters

were determined which are important for depending on the application of GNPs.

Equations are developed that correlate UV-vis absorbance and SPR to particle size

thus yielding a simple and quick method to determine size. 11 In the Haiss, et al. study

Gold hydrosols were studied; a hydrosol is a colloidal system where the dispersion

medium is water. The phase for this dispersion can be a solid, gas or another liquid 12. A

colloidal system is a substance which is dispersed throughout another substance 13.

Michael Faraday a famous chemists known for contributing to electrochemistry

and electromagnetism first noted how to form red solutions when a reduction of

chloroaurate (AuCl4-) occurred 1. In order to synthesis the gold hydrosols used in the

article by Haiss, et al. HAuCl4 was used along with water. GNPs seeds were

synthesized using citrate to reduce Au3+ and had an approximate diameter of 17-20nm.

The synthesized GNP seeds were then used as seed particles for the synthesis of

GNPs larger than 20nm. This method allowed Au3+ to be reduced on the surface. Gold

needs to be reduced on the surface of GNPs because it increases their diameter

depending on the side of the seed particle and the amount of gold reduced. The gold

was then studied using UV-Vis spectroscopy in the wavelength range of 350 to 800

nm.11


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The total amount of gold used for synthesis, measured particle diameter, and

volume of synthesized solutions were all used to then calculate the density of particles.

Commercial GNPs were also used for comparison with the synthesized GNPs. The

manufactures of the commercial GNPs provided the size and density of these GNPs.

Through UV-vis and TEM, the synthesized and manufactured GNPs were compared

and size and concentration were determined 11.

In conclusion, gold nanoparticles were synthesized via two methods to create

two different shaped particles. Spherical gold nanoparticles were synthesized and the

size was characterized. Icosahedral particles were also synthesized in order to study

their SERS properties. Other techniques such as TEM, SEM, XRD, UV-Vis were used

to image the particles and to determine size and shape of GNPs. Therefore, through

these two studies gold nanoparticles were synthesized and their size, and shape we

characterized.

Results and Discussion:

Gold seeds were used in a synthesis to create gold nanoparticles with diameters

ranging from 10 to 90 nm. The synthesis also used cetyltrimethylammonium bromide

(CTAB) and ascorbic acid. The starting oxidation state of gold in the synthesis was Au3+

and the final oxidation state was Au0. As a result, a reducing agent was needed in

order to first reduce gold to Au+ from Au3+. The reducing agent used in this synthesis

was ascorbic acid. It allowed larger sized particles to be grown with the growth seeds 3.

The reduction of gold was confirmed because the color changed when ascorbic acid

was added. For example, before CTAB was added the solution color was orange and


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once ascorbic acid was added, the orange color disappeared. Gold was not reduced to

the Au0 because ascorbic acid is too weak to reduce the gold further because it is a

weak acid, with a pka of 4.2. 14, 15

Gold seeds were also used in the synthesis because they act as nucleation

centers which allow the gold to be reduced. The particle size of the gold seeds were

around 3.5 nm 15. The gold seed particles help the synthesis to reduce Au+ to Au0

because they act as nucleation centers. Growth solution containing HAuCl4 and CTAB

was added to ascorbic acid and in labeled vials a-e. Each of the five solutions

contained the following: 9.0 mL of growth solution containing 2.5x10-4 M HAuCl4, 0.10 M

CTAB solutions and 50 µL of 0.10 M ascorbic acid. One millimeter of the seed solution

was mixed with solution A. Then 1.0 mL was taken from solution A and added to

solution B. Again 1.0 mL of solution B was added to solution C and the same process

was used for solutions D, and E. Therefore, after the reducing agents had been added

gold atoms form in the solution and particles begin to form .3 This nucleation process

allows the remaining gold atoms to attach to these nucleation sites. As a result of the

reducing agent and nucleation process, the growth of large nanoparticles was achieved.

In this experiment, five different solutions labeled a-e were prepared of varying

sizes of gold nanoparticles. Imaging measurements were used to determine the particle

size of each solution of gold nanoparticles. Each solution a-e increased in particle size

as shown through Figure 1 3. TEM images were obtained for the five solutions. TEM

uses electrons as the light source to produce images of the particles examined 5,4 .

Figure 1 shows the TEM images of the CTAB-stabilized gold nanoparticles from

solutions a-e. As seen from Figure 1, hexagonal shapes are seen in all solutions.


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However, in solutions a and e hexagonal shapes are not as visible due to image quality.

Particles in solution a are too small

to determine a shape and particles

in solution e are too large to show

the hexagonal shape. Solutions b-

d have good image quality and

show recognizable hexagonal

shapes 3. Gold particles that are

icosahedral may show hexagonal

shapes under TEM imagining

because the shape of fine gold

seeds in CTAB solutions is faceted

with (111) faces. The differences

between an icosahedron with (111)

faces and a cube with (100) faces

is illustrated in Figure 2 16. Also,

lower CTAB and higher ascorbic

acid concentrations favor faster formation and deposition of neutral gold onto the (111)

faces. This leads to the disappearance and formation of (100) faces and as a result

produces cubic instead of spherical shapes. If the CTAB concentration was similar or

slightly higher and the ascorbic acid concentration was slightly lower, then there would

be a truncated octahedral which would contain both (100) and (111) faces 17. Therefore,


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solutions a and e are

not as visible as

compared to b-d

because TEM only

gives a projected

image of objects.

Next, from the

TEM measurements, nanoparticles diameters were measured for CTAB gold

nanoparticles solutions a-e. Table 2,

shows the mean particle diameters in nm

for the 5 solutions 3. Table 2 and Figure 1,

both show that the particle size increases

greatly from solutions a-e using.

Therefore TEM was successfully used to

study the shape and diameter of the

CTAB-stabilized gold nanoparticles.

Scanning Electron Microscopy, (SEM) was also used in order to further examine

the five solutions and see the definite structure of gold nanoparticles. In SEM, a set of

coils moves the electron beam across a sample. When the electron beam moved

across the sample, different interactions occurred. Some of the electrons from the

surface material kick of their electrons by the beam thus producing secondary electrons

and a image of the sample. 5,4 Solution D was analyzed with TEM and further used to

show the shape of the gold nanoparticles. The SEM image of solution D is displayed in


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Figure 3 3. The image shows that the nanoparticles have an icosahedral shape. Also, in

Figure 3 the inset shows all of

the (111) facets of an

icosahedral GNPs. Solution D

was then examined again using

TEM to obtain a high-resolution

image for better understanding

the shape of the particles.

Solution D was used because it

offered the best images of the

hexagonal shape which is the

most useful for studying the gold nanoparticles icosahedral shape.

Figure 4 shows the TEM images of solution D 3. Images, a and b are of solution

D where b is an enlargement of a. The lines drawn on image b represent the two

boundaries which

intersect the two

neighboring facets. To

further confirm the

icosahedron shape, the

d-spacing was found to

be 2.36 Å which is

consistent with the

(111) planes of face


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centered cubic gold 3. D-spacing is important in the identification process. For example,

each particle has a known value for d-spacing and thus when a d-spacing is known it

can help establish which type of facets are observed 18. Through these further studies of

solution D, it was concluded that the

shape of the GNPs was icosahedron by

using TEM and SEM.

X-Ray diffraction (XRD) was also

used to characterize the nanoparticles.

This experiment involves scattering x-

rays through specifically placed atoms

of crystals. In this study XRD was used

to show that particle growth proceeds

by adding more gold atoms on the

preferential planes for each solution.

Figure 5 shows the XRD measurements

for solutions a-e 3.Three peaks were

obtained from each solution. As seen in

Figure 5, solution E shows the largest

peak for the (111) planes as expected

because sample E has the largest

particles. As a result, the particles grow when more gold atoms are added into the

solutions causing an increase in the XRD patterns. The three peaks were assigned to

diffraction peaks of gold metal of (111), (200), (220). The work by Hyunjoon, et al. also


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produced XRD patterns for Pt nanoparticles at facets of (111), (200) and (220) 19.

Equation 1 was used to calculate the intensities ratios of the 5 solutions 3.

(2)

Next, by examining Figure 5 and using Equation 2, the intensity ratios of the five

solutions were calculated and are shown below in Table 2. Although, solution A was

studied and shows a XRD pattern, the intensity could not be obtained due to poor

spectral quality. Table 2 and Figure

5, clearly show that intensity ratios

decrease as particle size

increases. The peak for the (111)

is always the largest peak

compared to the (200) and (220)

peaks because the ratio is less

than one. The (220) peak is the

smallest in most samples except for solution e because e has the GNPs size 3. From

these ratios it was concluded that the gold nanoparticles are primarily composed of

(111) facets. In other words, the five solutions have the highest intensities of the (111)

peak and thus have an icosahedron shape. Therefore, the XRD, SEM and TEM results

all point to gold nanoparticles with an icosahedral shape.

Next, in order to further study gold nanoparticles, Ultraviolet-visible spectroscopy

(UV-Vis) was used to determine the wavelength maximum of the five solutions. UV-vis


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was used because gold nanoparticles have strong plasmon resonance absorption which

is dependent on size and

shape of the particles 3.

Plasmon resonance

absorption occurs because

of d-d band transitions.

Plasmon excitation occurs

with the whole particle

jumping through transition

bands. Also, the resonance

frequency can be affected

by four factors: density of

electrons, electron mass, mass and size of the charge. The UV-vis spectra of the 5

solutions were then compared to the gold seed used in the growth system. The

literature value for Plasmon bands is

usually a between 520 and 530 nm for

spherical gold nanoparticles 3. Figure

6 shows the visible spectra of the five

solutions (a-e) and the gold seed.

From the data in Figure 5, Table 3

constructed to show the wavelength

maxima for solutions a-e. The data

shows that for solutions a-e,


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wavelength increases, steadily. The wavelengths increase with each sample because

the particle size also increases. Larger particles show plasmon absorbance at longer

wavelengths.

Finally, Surface Enhanced Raman Scattering, (SERS) spectra were used to

study gold nanoparticles and investigate further the spherical and icosahedral shapes 3.

SERS enhances the Raman signal from Raman-active molecules that have been

absorbed on metal surfaces. Spherical gold nanoparticles were compared to the

icosahedral gold nanoparticles through SERS. Noble metallic nanostructures exhibit

SERS in which the scattering

cross-sections are

dramatically enhanced for

molecules adsorbed on.

Figure 7 3, shows the spectra

of two gold nanoparticle

shapes under three different

concentrations. The average

particle size for the spherical

gold nanoparticles was 3.5

nm, the same as the

icosahedral. Figure 6a shows

the spectrum of 1 x 10-4 M 4-

nitrobenzenethiol (4-NBT), Figure6b shows the spectrum of 1 x 10-4 M 2-

mercaptopyridine (2-MP), and lastly Figure 6c shows the spectrum of 1 x 10-6 M


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rhodamine 6G (R6G). Therefore, the three spectras in Figure 6 are of solution c and the

three organic molecules used. Not only is the size important but the morphology or

shape of the particles is also important because it has a great effect on SERS activities

of organic molecules. In each of the three spectra in Figure 7, the upper line refers to

the icosahedral particles and the lower line refers to the spherical particles. The

icosahedral particles used in the SERS experiment were from solution c. Particles from

solution c were used because they produced the strongest Raman shift for the SERS

spectrum of 1 x 10-4 M 4-nitrobenzenethiol (4-NBT). In all the spectra, the icosahedral

particles show intensities nearly four times that of the spherical particles. Icosahedral

particles give higher intensities because they have very well-defined edges and corners

and thus sharper features as compared to spherical particles. The detailed shape

difference between icosahedral and spherical particles could be because of the larger

localized field enhancement 3. Therefore, the SERS studies showed the intensities for

two different shaped nanoparticles of gold. It was concluded that the icosahedral

shapes gives stronger signals for intensities as compared to spherical gold

nanoparticles.

In conclusion, TEM, XRD, SEM, SERS, and UV-Vis spectroscopy techniques

were used to study GNPs. In all experiments the nanoparticles synthesized were

shown to have an icosahedral shape. Also, spherical particles were compared to the

icosahedral particles using SERS. This study is related to the work by Haiss, et al.

which deals with spherical GNPs. Haiss, et al. determined the size and concentration of

spherical GNPs. This work also used UV-Vis and TEM to characterize the GNPs.


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Gold nanoparticles (GNPs) can be used in a number of applications due to their

optical properties. The applications include diagnostics, therapeutics, catalysis, and

optical sensing1. Wolfgang, et al. studied the optical properties of spherical gold

nanoparticles, ranging in size from 3 to 120 nanometers 11. Through this work UV-

Visible spectroscopy allowed the researchers to calculate particle size and to determine

particle concentration.

The Haiss, et al. study investigated particles with diameters ranging from three

to 120 nanometers 11. Transmission electron microscopy (TEM) was used as in the

previous study by Kwon, et al., to record images of gold particles and the gold

hydrosols. In a hydrosol particles

are uniformly dispensed in water

12. In this study, TEM was also

used to image at least 100

particles from each particle size

group. The size distribution of

gold nanoparticles from the TEM

images can be seen in Figure 8

11.The histogram was generated

from 617 measurements of

particle size 11. The inset shows

a representative TEM image of

the spherical gold nanoparticles. From the data in the histogram, the average diameter

of spherical gold nanoparticles was found to be 60±9 nm.


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Spherical GNPs were also studied with surface plasmon resonance or SPR. In

the SPR experiment, light is directed onto a thin surface containing gold. If the angle of

light causes it to

all be reflected,

some of the light’s

electric field leaks

onto the surface.

This electric field

can then excite

surface plasmon

waves in the

metal. A surface

plasmon is an

electron wave that

travels across the surface of the gold film. The wavelength of this plasmon wave is

detected in the SPR experiment. The wavelength has been shown to depend on the

size of the nanoparticles on the surface. Previous work has shown that GNPs produce

surface plasmon waves with wavelengths of 520 nm 9,10. Figure 9 shows a diagram of

the surface plasmon resonance (SPR) experiment.


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The overall goal of this experiment was to correlate the size of GNPs to the

wavelength of the surface plasmon wave. Therefore, the wavelength of SPR (λspr) was

examined as a function of the diameter of the particles. The results are shown in Figure

10 11. The calculated

wavelengths of surface plasmon

peaks are shown as circles and

the experimental data is shown

as triangles. The upward

triangles represent particles that

were synthesized in house and

the downward triangles represent

the commercial gold

nanoparticles 11. The error bars in

this figure are horizontal and

show the errors in the diameters

of the particles used. The error

bars are only shows for the in-house synthesized particles. As seen in the figure, the

calculated and experimental wavelengths are in perfect agreement with one another.

Wavelengths vs. diameters data for particles that were larger than 25nm were fit

to the exponential function shown in Equation (3) 11.

λspr= λo + L1 exp (L2d) (3)


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λspr was the surface plasmon resonance wavelength and d was the diameter. The fit to

the data in Figure 10 gave values for the free parameters to be λ0 = 512, L1= 6.53, and

L2 = 0.0216. The error in the fit was three percent. Next, with the three values

established, Equation (3) was rearranged to solve for d. This expression is shown in

Equation (4). With the relationship between λspr and d now established, Equation (4) can

be used to calculate nanoparticles size (d) from the measurements of SPR

wavelengths.

λ λ

(4)

However, the equation cannot be used for particles smaller than 25nm because

the experimentally observed wavelength is lower than what would be expected 11.

Recall that the SPR wavelength for spherical GNPs is usually around 540 nm 20 and this

experiment had a range of 520-580 nm 11. However, when particles were smaller than

25 nm, the wavelength of SPR was smaller than 520 nm. The wavelength may be

smaller for particles smaller than 25 nm because of the increase of the ratio of surface

atoms to bulk atoms for small particle diameters 11.

Since the data for GNPs smaller than 35 nm did not show an experimental

dependence of λspr on d, the size cannot be estimated by Equation (3). Therefore, UV-

vis spectroscopy had to be used to incorporate particles that are smaller than 35 nm

into the study. UV-Vis spectra were collected for GNPs as a function of size. Data

plotted on Figure 11 (a) 11.


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Figure 11 (a) shows a plot of the ratio of the absorbance at two wavelengths vs. particle

diameter.11 For example, the circles in the image represent the ratio of the absorbance

at the wavelength of SPR wave

to the absorbance at 450.

Unlike the square, diamonds

and triangles, these data points

increase at a steady rate with

increasing diameter. Therefore

the ratio of the absorbance at

the SPR wavelength to the

absorbance at 450 nm may be

useful in measuring particle

sizes less than 35 nm.

Since none of the lines

have a strong linearity, Figure

11 (a) is not very useful

because only one line out of the

five could be used for further

analysis of the ratio of absorbencies to diameters. As a result, the data represented by

the circles in Figure 11 (a) was used to construct, Figure 11 (b) 11. In Figure 11 (b) the

absorbance ratio is plotted vs. the natural log of the GNPs diameter.

Therefore, Figure 11 (b) is more useful in showing agreement between

theoretical and experimental results when the absorbance ratios are in the wavelength


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region below 600 nm. The particle diameters used were in the size range of 5 to 80 nm.

The circles in the graph are the theoretical data points produced and can be fitted to a

line with a R2 value of 0.9999. The triangles in the graph again represent the

experimentally in-house and commercial GNPs. Since a strong linear correlation was

produced in the graph the ratio Aspr/A450 can be used to calculate the particle diameter

with Equation (5). 11

(5)

In the equation, B1 is the inverse slope, and B2=B0/m where B0 is the intercept. The

values obtained for B1 and B2 are shown in Table 4. The equation had an error of 18%

when the theoretical data for B1 and B2 were used to calculate particle diameter.

However, if the experimental values for B1 and B2 were used, the error in determining

particle size was 11%. Table 4 shows a comparison of experimental and theoretical

data for B1 and B2.11 As a result, Equation (5) can be used to determine the particle

diameter of particles between 5 to 80 nm.

In conclusion, the particle diameters can be determined through experimental

techniques. The best technique to use depends on the size of the particles. For

example Equation (3) from SPR can be used to calculate particle diameters for particles


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that are between 35 to 100 nm. Equation (4) from UV-Vis spectroscopy can be used to

calculate diameters of the particles when the absorbance ratio is known. Therefore,

these experiments offered efficient methods to calculate particle diameter for spherical

GNPs. If scientists are thus working with gold hydrosols, a quick method for size

determination can be applied due to this experiment because it offers researchers a

way to determine the size and concentration from either the SPR wavelength or UV-Vis

spectrum.

Conclusion:

This thesis has shown the importance of gold nanoparticles because of their size

and shape. The shape and size of GNPs is important for their uses in optical, electronic,

magnetic and catalytic properties. Therefore, through the work by Kwon, et al., GNPs of

icosahedral shape were synthesized and studied. The GNPs were studied through

TEM, SEM, XRD, UV-Vis to focus on the size of each particle synthesized and their

icosahedral properties. The icosahedral particles were also studied to examine their

surface-enhanced Raman scattering properties. In this thesis spherical GNPs were also

studied through the work of Haiss, et al. to determine the size of spherical particles. The

particles were synthesized and studied through UV-Vis, and TEM to develop equations

to calculate the concentration. In essence, icosahedral and spherical GNPs were

synthesized and studied to determine the size, shape, and their surface-enhanced

Raman scattering properties.

Further research could be done to see if the GNP shape affected the correlation

observed. Since GNPs can form numerous shapes; such as prisms and rods, can


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equation to calculate the diameters of these particles can be developed. Another idea to

focus on for further research could be which shape is better for different applications.

For example, each shape of GNPs have different physical properties thus making it

useful to determine which shape is better in areas such as diagnostics, therapeutics,

catalysis, optical sensing, and in further nanotechnology. Thus, a study could be

conducted to learn how shape affects the application GNPs used.

References:

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