Chapter 1 Gold Nanoparticles Synthesis, Optical Properties...

Chapter 1

Gold Nanoparticles ― Synthesis, Optical

Properties and Applications

Abstract

Nanoparticles with controlled size and shape are important from both

fundamental and technological viewpoints. For a long time there had been

much interest in preparing nanoparticles of various sizes and shapes.

Metallic nanoparticles are an important class of nanomaterials with

fascinating optical, electronic and magnetic properties. Among the metallic

nanomaterials gold nanoparticles are particularly interesting due to their

easy methods of synthesis, the ability to adjust properties through size and

shape and their stability in a wide variety of solvents and pH conditions. This

chapter describes in detail the synthesis, optical properties and applications

of gold nanoparticles.

2 Chapter 1

1.1 Introduction

In recent years nanotechnology has become one of the most important and

exciting forefront fields in Physics, Chemistry, Engineering and Biology. It

shows great promise for providing us with many breakthroughs that will

change the direction of technological advances in a wide range of

applications. The research area of nanotechnology is interdisciplinary,

covering a wide variety of subjects ranging from the chemistry of the

catalysis of nanoparticles, to the physics of the quantum dot laser. As a result

researchers in any one particular area need to reach beyond their expertise in

order to appreciate the broader implications of nanotechnology and learn

how to contribute to this exciting new field. Particles with sizes in the range

of 1-100 nm are called nanoparticles, whether they are dispersed in gaseous,

liquid, or solid media [1-2]. Because the NPs are larger than individual

atoms and molecules but are smaller than the bulk solid, materials in the

nanometer size regime show behavior that is intermediate between that of a

macroscopic solid and that of an atomic or molecular system.

Nanotechnology is based on the recognition that particles less than the size

of 100 nm impart to nanostructures built from them new properties and

behavior. The electronic structure, conductivity, reactivity, melting

temperature and mechanical properties have all been observed to change

when particles become smaller than a critical size. The dependence of the

behavior on the particle sizes can allow one to engineer their properties.

The properties of materials with nanometer dimensions are significantly

different from those of atoms and bulk materials. There are three major

factors that are responsible for these differences: high surface-to-volume

ratio, quantum size effect and electrodynamic interactions. All nanoparticles

regardless of their chemical constituents have surface area to volume ratios

Gold Nanoparticles – Synthesis, Optical Properties … 3

that are extremely high. Thus, many of the physical properties of the

nanoparticles such as solubility and stability are dominated by the nature of

the NP surface. One of the direct effects of reducing the size of materials to

the nanometer range is the appearance of quantization effects due to the

confinement of the movement of electrons. This leads to discrete energy

levels depending on the size of the structure. Following these line, artificial

structures with properties different from those of the corresponding bulk

materials can be created. Control over dimensions as well as composition of

structures thus makes it possible to tailor material properties to specific

applications.

Among different nanomaterials employed in research, metallic NPs have

been proved to be the most convenient and suitable. Metallic NPs possess

unique optical, electronic, chemical and magnetic properties that are

strikingly different from those of the individual atoms as well as their bulk

counterparts. It is known that the intrinsic properties of metal NPs are mainly

governed by their size, shape, composition, crystallinity and structure. In

principle, one could control any one of these parameters to fine-tune the

properties of these NPs. If such tiny particles are allowed to coalesce in a

controlled fashion, their color can be systematically varied [3-4] from pink

through violet to blue. The dimension of the particles in the nanometer size

regime makes them ideal candidates for nanoengineering of surfaces and the

fabrication of functional nanostructures [5-6].

Colloidal gold nanoparticles (AuNPs) are particularly interesting because of

its easy preparation and high stability. For biological applications, gold is an

important candidate due to its chemical inertness. The use of AuNPs has

been predominantly found in the work of artists and craftsman because of its

vivid visible colors. However, through research, the size, shape, surface

4 Chapter 1

chemistry and optical properties of AuNPs are the parameters which are

under control and have opened new doors to some very unique and exciting

capabilities. The interest in gold sols has occurred after innumerable

advances in our understanding of various concepts in physics and chemistry.

It includes: (1) the quantum mechanics and the effects associated with

nanoscopic systems, (2) the nature of interaction between colloidal particles,

(3) the statistical mechanics or thermodynamic behavior of aggregates that

can be formed by colloidal particles, (4) the mathematics and physics

associated with pattern formation, pattern characterization and how interplay

of kinetic and thermodynamic effects creates assemblies, (5) the mechanism

of micelle formation, (6) biological physics and (7) numerical methods and

simulation protocols. The corresponding advances in technology related to

optical and electron microscopy, optics, lasers, computing facilities for data

acquisition and data analysis as well as simulations and instruments designed

with better precision and options imply that the corresponding research for

colloidal metal particles can really become useful for applications to lab on a

chip devices, electronic, photonic and sensing applications based on

plasmonics in the field such as cancer treatment, etc. The latest gold rush is

likely to revolutionize the field of biosensing and chemical sensing by

allowing development of technologies that help in identification of chemical

or biological strains with high accuracy, by using highly environmentally

sensitive nature of plasmon resonance as well as other optical effects

associated with the gold and other noble metal particles.

1.2 A brief history of the advances in gold colloids

The use of colloidal gold as a colorant can be traced back at the least to 5th

B.C. for its use in making ruby glass and providing reddish tinge to ceramics.

The definitive study on the nature of gold particles in hydrosols – their


synthesis by reduction of dilute gold chloride using phosphorus, size

dependent optical properties and coagulation behavior were carried out by

Faraday [7]. He obtained relatively unstable colloidal sols, with colors purple

red to sometimes blue and showed that electrical “collidation” of gold in air

or hydrogen gave a precipitate on glass or quartz with the same red or blue

color as present in the sols. Faraday found that the ruby glass was colored

so, because of the presence of finely dispersed gold particles. He showed

that gold chloride can be reduced by heat alone or by reaction with many

different reagents including organic matter, phosphorus, tartaric acid, etc. He

[7] had used many of the reducing agents of his time to produce gold sols.

He also examined other metals like platinum, palladium, rhodium, silver, tin,

lead, zinc, iron, mercury and arsenic. Faraday provided physical and

chemical arguments to emphasize that in both ruby fluid and ruby glass,

metallic gold was present in finely dispersed state. In the context of his

experiments, he attempted to study the optical properties as well as remarked

on the aggregation and sedimentation [7].

For nearly forty years, Faraday’s work remained unnoticed and even the

scientists who worked on the ruby glass were not aware of it. Thereafter

Zsigmondy [8] began his investigations into the color of ruby glass and

formulated a method for preparing colloidal gold by reducing dilute, slightly

alkaline solution of gold chloride with boiling formaldehyde. Using

Faraday’s methods, especially reduction using phosphorus, he combined

both the synthesis techniques to arrive at a two step synthesis method. This

method is referred to as the seed-mediated method in the contemporary

literature and was called ‘nuclear method’ in the early days [8]. Also the

nanoparticles were typically described as ultramicroscopic particles and in

the place of nanometers (nm) as a unit, the equivalent unit used was

6 Chapter 1

ultramicrons )( µµ . The dependence of optical properties on their shape was

apparent to researchers including Zsigmondy who reported difference in

color observed by using polarized light parallel and perpendicular to the

anisotropic particles oriented by spreading out on a gelatin film [8].

Zsigmondy invented the ultramicroscope [9] which allowed the visualization

of colloidal gold particles (i.e. nanoparticles), showing that colloidal matter

consisted of dispersion of particles of measurable size. Zsigmondy was able

to make some of the first particle tracking studies to determine the diffusion

behavior of the nanoparticles. While new generation transmission electron

microscopy can be employed to determine the size and shape of the

nanoparticles, typically dried onto a substrate, ultramicroscopy presents the

option of looking at the particles in their dispersed state. The advances in

optical techniques that have taken place in the past decades and the

expertise developed in the theoretical and experimental aspects of quantum

dot [10-12], make ultramicroscopy an ideal candidate for revisiting colloidal

dispersions of metallic nanoparticles. For example, in principle one can

follow the growth kinetics of particles in situ by visualization through the

ultramicroscope. Zsigmondy also investigated the stability of colloidal gold

in the presence of ions, biomolecules, gums and gelatin, etc., and noted that

certain proteins and substances displayed a ‘‘protective action’’ [8]. The

color of a red gold sol when coagulated with NaCl, changes to blue.

Zsigmondy used this property to define the so called gold number [8] as the

number of milligrams of the hydrophile colloid per 10 cm3 of gold sol that is

sufficient to prevent the coagulation and hence color change to occur when 1

cm3

of 10 per cent NaCl solution is added. The studies were used in

characterizing different proteins as well as in detecting changes in the

composition of liquids containing different proteins. The role of


supersaturation in determining the nucleation and growth of gold particles,

both in condensation growth from solution and in vapor deposition, was also

reported by Svedberg [13-14] and Zsigmondy [8, 15] in their pioneering

studies. Another scientist who played a central role in early studies of gold

sols was Svedberg. He pioneered the use of electrochemical methods for the

synthesis of gold particles. He used every conceivable reducing agent

available at his time to produce colloidal gold from hydrochloroauric acid

[13]. For the early developments of gold colloid the contributions given by

Ostwald’s is also remarkable. He presented experimental and theoretical

principles through a series of demonstrations and it embodied several

principles useful for the synthesis of gold sols [16]. Ostwald pointed out the

importance of pH in the synthesis and expounded how this is useful in

changing the final product from being a red to blue dispersion.

The properties of colloids depend, to a large extent, on the movement of

particles and this movement consists of translational and rotational Brownian

motion. The advances in theoretical understanding of Brownian motion

brought about by Einstein [17-19] and Langevin [20] in the beginning of

twentieth century provided the requisite understanding to describe the

continuous motion of particles as well to understand the size dependence of

their stability and sedimentation behavior. Einstein [18-19] reasoned that

suspended particles behave quite like solute molecules and therefore an

osmotic pressure should be ascribed to the suspended particles. By applying

van’t Hoff’s law to suspensions and by assuming that dissipative force

described by Stokes law balances the force due to osmotic pressure, Einstein

was able to describe Brownian motion as a diffusion process. Further by

formulating the statistical analysis for Brownian motion, he laid a basis for

testing the reality of ‘molecular kinetic theory’ of matter. Einstein showed

8 Chapter 1

that mean squared displacement of particles scales linearly with time and

postulated that these results could be used to determine molecular

dimensions [17-19]. Langevin [20] outlined a simpler derivation for the time

dependence of the displacement of Brownian particles by introducing a

fluctuating random force and counteracting it with Stokesian drag and the

modern treatment of Brownian motion is typically based on it [21].

Perrin carried out meticulous experiments and also used a distribution

function to calculate Avogadro’s number and to establish the equivalence

between a colloidal particle and a molecule as required by the molecular

kinetic theory [22-23]. Perrin’s careful experiments on translational and

rotational Brownian motion not only led support to the theories of Brownian

motion but also established the reality of molecules and established the

statistical nature of thermodynamics. Brownian motion and thermal forces

set the rules for structure, dynamics and function of soft matter [24-25]

(polymers, liquid crystals, emulsions and colloidal dispersions) and the

analysis or theories of Brownian motion apply to stochastic problems in

systems ranging from single cells to galaxies [21, 26]. Another pioneer

Smoluchowski’s theories for diffusion and coagulation [21, 27] are central to

our understanding of collision and coalescence issues in colloidal sols. He

computed the rate at which a diffusing particle arrives in a ‘sphere of

influence’ of another particle. The assumption is that if the diffusing particle

moves about in the region outside this sphere of influence, it moves

unaffected, but if it enters the region, it sticks to the other particle [21]. Thus

Brownian motion, together with the interparticle attractive and repulsive

forces that form the physico-chemical basis for the sphere of influence,

determines the phase behavior and stability of colloids.


1.3 Nanofluids ― general methods of synthesis

Preparing a stable and durable nanofluid is a prerequisite for optimizing its

thermal and optical properties. Therefore, many combinations of a material is

used for particular applications, namely: nanoparticles of metals, oxides,

nitrides, metal carbides and other nonmetals which can be dispersed into

fluids such as water, ethylene glycol or oils [28]. In the stationary state, the

sedimentation velocity of small spherical particles in a liquid follows the

Stokes law [29]

g)(R

V LP ρρµ

−=9

22

(1.1)

where V is the particle’s sedimentation velocity, R is the spherical

particle’s radius, µ is the liquid medium viscosity, Pρ and Lρ are the

particle and the liquid medium density respectively and g is the acceleration

due to gravity. This equation reveals a balance of the gravity, buoyancy force

and viscous drag that are acting on the suspended nanoparticles. According

to Eq. 1.1, the following measures can be taken to decrease the speed of NPs

sedimentation in nanofluids and henceforth to produce an improvement for

the stability of the nanofluids: (1) reducing R, the NPs size; (2) increasing µ ,

the base fluid viscosity and (3) lessening the difference of density between

the nanoparticles and the base fluid )( LP ρ−ρ . Reducing the particle size

should remarkably decrease the sedimentation speed of the NPs and improve

the stability of nanofluids, since V is proportional to the square of R.

According to the theory in colloid chemistry, when the size of particle

decreases to a critical size, ,R c no sedimentation will take place because of

the Brownian motion of NPs (diffusion). However, smaller NPs have a

higher surface energy, increasing the possibility of the nanoparticle

10 Chapter 1

aggregation. Thus, the stable nanofluids preparation strongly link up with

applying smaller nanoparticles to prevent the aggregation process

concurrently [30]. Two different techniques apply to produce nanofluids

namely: single-step and two-step method.

(i) Single step technique

In this method nanoparticle manufacturing and nanofluid preparation are

done concurrently. The single-step method is a process combining the

preparation of nanoparticles with the synthesis of nanofluids, for which the

NPs are directly prepared by physical vapor deposition (PVD) technique or a

liquid chemical method. In this method drying, storage, transportation and

dispersion of nanoparticles are avoided, so the agglomeration of

nanoparticles is minimized and the stability of the nanofluids is increased. A

disadvantage of this method is that it is impossible to scale it up for great

industrial functions and is applicable only for low vapor pressure host fluids

[31-32].

(ii) Two-step technique

In this method, dry NPs are first produced and then they are dispersed in a

suitable liquid host, but as NPs have a high surface energy, aggregation and

clustering are unavoidable and will appear suddenly. Afterward, the particles

will clog and sediment at the bottom of the container. Thus, making a

homogeneous dispersion by two step method remains a challenge. However,

there exist some techniques like high shear and ultrasound to minimise this

problem. Nanofluids containing oxide particles and carbon nanotubes are

produced by this method. This method works well for oxide NPs and is

especially attractive for the industry due to its simple preparation method.

But its disadvantage due to quickly agglomerated particles brings about


many challenges nowadays. As nanoparticles disperse partially, dispersion is

poor and sedimentation happens, so a high volume concentration is needed

increasing the heat transfer (10 times of single step) and accordingly the cost

would be as much as loading [33]. The two-step method is useful for

application with particle concentrations greater than 20 vol % but it is less

successful with metal NPs. However, some surface treated nanoparticles

showed excellent dispersion [34]. The first materials tried for nanofluids

preparation were oxide particles, mainly because of its easy preparation

methods [35].

1.3.1 Synthesis of gold nanofluids

In the synthesis of AuNPs, or more specifically speaking, gold colloidal

dispersion, various types of precursors, reduction reagents, other chemicals

and methods where used to promote or control the reduction reaction, the

initial nucleation and subsequent growth of initial nuclei. The aim of such

synthesis is the preparation of nanoparticles of controlled composition, shape

and size. The simplest and the most commonly used preparation for gold

nanoparticles (AuNPs) is the aqueous reduction of HAuCl4 by sodium citrate

at reflux [36]. Although sodium citrate is the most common reducing agent,

metal nanoparticles can also be synthesized by the use of borohydride and

other reducing agents [37-40]. Particles synthesized by citrate reduction are

nearly monodisperse spheres of a size, controlled by the initial reagent

concentrations [40]. They have negative surface charge as a consequence of

weakly bound citrate coating and are easily characterized by their plasmon

absorbance. Smaller NPs may be formed in the gas phase [41] or by ablation

using high peak power laser pulses [42-43], electrodeposited [44], or

synthesized directly onto surfaces [45-49]. The following section describes

12 Chapter 1

the synthesis of AuNPs with size ranging from 15–80 nm using citrate

reduction method.

(i) Synthesis of nanofluid having 15 nm gold nanoparticles

The AuNPs having a size of 15 nm are synthesized by the citrate reduction of

HAuCl4 in water [50]. A 250 mL double neck round bottom flask was

cleaned in aqua regia (3 HCl: 1 HNO3) and rinsed with distilled water. 100

ml of 1 mM HAuCl4 solution was heated to boiling refluxed while being

stirred. Then, 10 ml of a 38.8 mM sodium citrate solution is added quickly.

The color of the solution turned from yellow to black and then to deep red.

After the color changed, the solution was refluxed for an additional 15

minutes. Then, the heater was turned off and the solution was stirred until it

reached to room temperature.

(ii) Synthesis of nanofluid having particle size from 30 to 80 nm

50 ml of 0.01% HAuCl4 solution was heated to boiling while being stirred in

a 100 ml conical flask. Then a few hundred µl of 1% sodium citrate solution

is quickly added to the auric solution.

6 Au3+

+ C6H5O7 3-

+ 15 OH- 6 Au + 6 CO2 + 10 H2O (1.2)

The color of the solution changed from yellow to black and then to red or

purple color depending on the sizes of the nanoparticles. After the color

change, the solution was stirred for an additional 15 minutes. The color change

for larger nanoparticles was slower compared to smaller nanoparticles. The

amount of citrate solution determines the size of the nanoparticles

synthesized. The photograph of gold nanofluid having particle size from 30

to 80 nm is shown in Fig. 1.1. This method produces very stable gold

nanoparticles with a quite narrow size distribution.


Increasing Particle size

Fig 1.1 Gold nanofluid having particle size from 30 to 80 nm

The advantage of using trisodium citrate is that it can act both as reducing as

well as stabilizing agent. This method presents, with respect to other routes,

several advantages, mainly related to i) easy synthesis procedure,

ii) reproducibility of the method and iii) stability of the prepared sol. Another

advantage is that the medium (water) solvates both reagents very well.

Turkevich et al. [51] have extensively studied the effect of various

parameters, such as the temperature, amount of citrate added or the dilution

of the solution, on the formation of colloidal gold. The amount of citrate

added or the dilution of the solution can dramatically affect the average size

and size distribution of the AuNPs. The latter is additionally depending on

the relative rates of nucleation and growth [52-54]. Gold colloid solutions are

kept in clean, brown glass bottles away from heat or light (alternately, clear

glass bottles may be wrapped in aluminum foil). If Gold colloid solutions are

to be stored for long periods, they can be kept in the refrigerator to prevent

bacterial and fungal growth.

14 Chapter 1

1.4 Optical properties of gold nanoparticles

Although bulk gold and silver are widely known for their lustrous surfaces

and colors, there is a drastic color difference when the metal reduces in

dimensions. Gold and silver NPs are responsible for transmitting the brilliant

colored light through stained glass windows, yet these colors do not resemble

the characteristic yellow or bluish reflective surfaces of the bulk metals.

Even though the artisans did not know it at that time, the mixing of the metal

chlorides with molten glass led to the formation of metallic NPs of different

shape and size, hence the physical dimensions of the metal nanoparticles had

interesting interactions with light and produced visibly beautiful colors.

One of the most fascinating examples of how colloidal metal particles interact

with light is the famous Lycurgus cup which can be seen in the British

Museum in London. The photograph of the Lycurgus cup is shown in Fig. 1.2.

Fig. 1.2 Lycurgus cup in the British Museum in London

This object, crafted by the Romans in the 4th

century, features an amazing

property of changing color depending on the light shed on it. Reflected

light makes it appear green, whereas in transmission a bright red color can

be seen.


Another excellent example is the stained glass windows from any European

Gothic Cathedral during the 15th

century as shown in Fig. 1. 3. The artisans

of the day achieved the brilliant blues, reds, yellows and greens in the glass

windows by mixing metal chlorides into molten glass before pouring it. The

metal chlorides nucleated and formed nanoparticles in the molten glass

before cooling, making art, one of the first uses for nanotechnology.

Fig. 1.3 Photograph of a stained glass windows from a European Gothic

Cathedral

A light beam passing through a colloidal dispersion of metal NPs gets

attenuated by the combined contribution of absorption and scattering, as

given by

)zCnexp(I)z(I ext00 −= (1.3)

16 Chapter 1

Here I0 is the intensity of the incident beam, I(z) is the intensity of the beam

after traveling path length z within the sample, 0n is the number density of

particles and scaabsext CCC += is the extinction cross section of a single

particle and is the sum total of the absorption and scattering cross sections

respectively. The product ext0Cn is often termed as the extinction coefficient

α and it has units of reciprocal length. The absorption spectrum determined

by UV–Vis spectroscopy is a measure of attenuation caused by a dispersion

of gold nanoparticles and is thus related to the absorption cross section.

1.4.1 The physical phenomenon of plasmons

(i) Plasmons

Plasmons are quantized waves in a collection of mobile electrons that are

produced when large numbers of these electrons are disturbed from their

equilibrium positions [55-56]. Electrons present in classic gaseous plasmas

can support plasmons, hence the name of these waves. The collection of

mobile electrons in metals is referred to as quantum plasma [56]. This is

composed of delocalized electrons that bathe the metal nuclei and their

localized core electrons, as described by the free-electron theory of metals

[55]. This metallic bonding has been used to explain many metallic

properties. Metals that best exhibit this free-electron plasma behavior include

the alkali metals, Mg, Al, and noble metals such as Cu, Ag and Au [55].

Plasmons can exist within the bulk of metals and their existence was used to

explain energy losses associated with electrons beamed into bulk metals [57].

For a bulk metal of infinite size, the frequency of oscillation, pω , of the

plasmons can be described by the expression,

( ) 210

2 /ep meN εω = (1.4)


where N is the number density of mobile electrons, 0ε is the dielectric

constant of vacuum, e is the charge of an electron and em is the effective

mass of an electron. Surface plasmons (SPs) are a type of plasmon associated

with the surfaces of metals. They are significantly lower in frequency (and

energy) than bulk plasmons and can interact, under certain conditions, with

visible light in a phenomenon called surface plasmon resonance (SPR).

A macroscopic physical analogy that has been used to describe surface

plasmons is that of seaweed floating in water near a shoreline. The waves of

water lapping along the shoreline represent the electric fields and the

seaweed sloshed back and forth by these waves represent electrons [58]. SPs

have immense use to physicists and chemists. For example, the electric fields

of SPs amplify optical phenomena such as Raman scattering [55, 59]. There

are at least three types of SPs: propagating SPs, which occur on extended

metal surfaces, localized SPs, which occur in small volumes such as metal

particles, acoustic SPs, which are predicted to exist for some structures and

metal surfaces and are the subject of continued study [57].

(ii) Propagating surface plasmons

The combination of photons and SPs produce electromagnetic excitations on

extended surfaces known as surface plasmon polaritons (SPPs) or

propagating surface plasmons (PSPs) [55, 60]. PSPs have lower frequencies

and energies than bulk plasmons; metal surfaces in contact with a vacuum

have PSPs with a theoretical frequency of 2pω . Figure 1.4 shows a

representation of PSPs.

18 Chapter 1

Fig. 1.4 Schematic representation of propagating surface plasmons

As the waves of electron density travel along the surface, alternating regions

of positive and negative charges are produced. The electric fields, produced

by these regions of differing charge, decay exponentially away from the

metal surface [60].

Though PSPs can be produced with light, simply incidenting light on a

smooth metal surface in air is not sufficient because the momentum of the

light does not match that of the SPs [57]. Various methods are employed to

enable light to produce and to be produced by PSPs. Some methods involve

passing the light through a medium with a higher refractive index than air,

such as glass, before it comes near to the metal surface [57, 60]. To better

explain the role of refractive index, consider a beam of light which passes

from a medium with a higher index into a medium with a lower index. In

many cases, part of the incident beam is reflected from the interface and part

of the incident beam passes into the medium with the lower refractive index

(and is refracted in the process).

However, when the angle of the incident light exceeds a critical angle, no

portion of the light leaves the medium with higher refractive index and is

completely reflected. This is the condition of total internal reflection. Many


fiber optic cables utilize the same principle to transmit light down curved

strands: the refractive index of the core of the optical fiber is higher than that

of its cladding layer, and the condition of total internal reflectance keeps the

light in the fiber [61]. Under the conditions of total internal reflectance, light

waves that strike the interface between two materials with differing

refractive indices produce new light waves that propagate from the interface

a very short distance into the medium with the lower refractive index. The so

called evanescent waves decay exponentially as the distance from the

interface increases. At a particular angle of incident light beyond the critical

angle, evanescent waves can propagate PSPs along a thin layer of metal

placed at the interface between the media with differing refractive indices

[58, 60, 62]. This SP resonance angle is susceptible to the refractive index of

the media near the metal film, making it sensitive to chemical changes that

involve changes in refractive index (or its square, the dielectric constant).

Other methods to enable light to access a metal surface and produce PSPs

involve roughening the surface, thereby changing its momentum. If light

shines on a metal diffraction grating, with parallel, linear features, it can be

diffracted by that grating. At the same time, however, PSPs will be

propagated along the surface of the grating in the direction perpendicular to

the linear features [60, 63].

(iii) Localized surface plasmon resonance

The answer to the question how do the nanoparticles interact with light, lies in

the understanding of surface localized plasmon resonance (LSPR) phenomena,

which are deeply affected by the nanometal shape and environment. Localized

surface plasmons (LSPs) are the collective electron oscillations in small

volumes. LSPs also have lower frequencies and energies than bulk plasmons;

metal particles in contact with a vacuum have LSPs with a theoretical

20 Chapter 1

frequency of 3pω [55, 57]. LSP resonances are produced in a somewhat

different fashion from PSPs. A schematic of the interaction between light and

the electrons of a metal particle is shown in Fig. 1.5 [55, 64].

Fig 1.5 Electronic cloud displacements in metal nanoparticle under the

effect of an electromagnetic wave. Electric fields are represented by

arrows

For this phenomenon to occur, the particle must be much smaller than the

wavelength of incident light. The electric field of the incident light can

induce an electric dipole in the metal particle by displacing many of the

delocalized electrons in one direction away from the rest of the metal particle

and thus producing a net negative charge on one side. Since the rest of the

metal particle is effectively a cationic lattice of nuclei and localized core

electrons, the side opposite the negative charge has a net positive charge.

LSPs have also been referred to as dipole plasmons, but the oscillating field

of the incident light can induce quadrupole as well as dipole resonances,

especially for particles greater than 30 nm in diameter [64-65]. If a particle

with a dipole can be considered to have a positively charged pole and a

negatively charged pole, then a particle with a quadrupole can be considered


to have two positively charged poles and two negatively charged poles.

Smaller nanoparticles, (quantum dimension < 2nm), do not display this

phenomenon, as their electrons exist in discrete energy levels, and bulk has a

continuous absorbance in the UV/ Vis/IR region, which effectively collapsed

into the single plasmon absorbance in the case of the nanoparticle.

1.4.2 Factors affecting the surface plasmon resonance

The energy of light required to produce LSP resonance depends on a number

of factors, including the size, shape and composition of the particles, as well

as the composition of the surrounding media.

(i) Size and shape

The surface plasmon band position, bandwidth and intensity are affected by

the size and shape of the NPs. Many theories have been reported, to correlate

the size to the surface plasmon band position, some predicting a blue shift,

some a red one and others no shift at all. Generally speaking, as the particle

size increases, the plasmon resonant frequency decreases (shifts to longer

wavelengths) [66]. This result was subsequently rationalized by Liebsch

[67]. Small Au particles (with diameters less than 20 nm) exhibit extinction

that is primarily due to absorption; larger particles tend to exhibit much

stronger scattering [55]. Particles of different shapes have different plasmon

properties. For example, rod-shaped Ag or Au particles exhibit two

plasmons: a longitudinal plasmon, corresponding to the long axis of the rod,

and a transverse plasmon, corresponding to the short axis of the rod. Keeping

the diameters of the rods constant while increasing their lengths result in the

transverse plasmon remaining essentially constant in frequency (or energy)

while the longitudinal plasmon decreases in frequency [55, 68]. Hollow

metal particles tend to have lower plasmon resonant frequencies than solid

22 Chapter 1

metal particles [69]. Aggregation of colloidal metal particles can also lower

their plasmon frequencies [70].

(ii) Effect of the dielectric environment

The dielectric constant of the surrounding medium plays a predominant role

in determining both the plasmon peak position and intensity [1, 71].

Changing the medium surrounding the NPs, for another medium having a

different refractive index, strongly alters the plasmon behavior of the NPs.

Typically, a higher refractive index (or dielectric constant) of the medium

produces a lower plasmon frequency. This is, for instance, evidenced by the

strong shifts induced by transferring NPs from water or ethanol to a

transparent oxide matrix [72]. A macroscale physical analogy to this

phenomenon is using an oscillating weighted spring to represent the electric

field of the LSP. A high dielectric medium can be represented by a viscous,

higher-friction medium like oil. A spring in a vacuum will oscillate with a

higher frequency than the spring in the oil.

(iii) Electronic effects

The plasmon band may be displaced upon adding or subtracting electrons to

the overall metallic core. Oxidation processes were generally carried out

chemically [73] by the addition of free radicals [74] or under the action of

dioxygen [75]. Chemical reductions similarly proceeded via the action of

nucleophiles [76] or common reducing agents [77]. In all cases the increase

(respectively, decrease) in electron density resulted in the postulated

hypsochromic (respectively, bathochromic) shifts. Direct oxidation and

reduction using electrochemical methods have been performed more recently

[78-79]. The resulting devices are very promising for electro-optical

applications.


1.4.3 Mie theory

It was the color variation of colloidal gold with particle size that motivated

Mie to frame work on the general solution of the diffraction problem of a

single sphere of arbitrary material and hence to apply the general theory of

light extinction to small particles [80]. This theory predicts, what fraction of

light impinging upon colloidal metal particles will be absorbed and what

fraction will be scattered. The sum of absorption and scattering is the

extinction of light due to the particles. This is what is measured when one

places a colloidal metal suspension into a UV–Vis spectrometer. Mie applied

Maxwell’s equations with appropriate boundary conditions in spherical

coordinates using multipole expansions of the incoming electric and magnetic

fields and offered an exact electrodynamic calculation of the interaction of

light with spherical metallic nanoparticles. The theory describes the extinction

(absorption and scattering) of spherical particles of arbitrary sizes. Most

standard colloidal preparations yield particles that are approximately spherical,

and most of the optical methods for characterizing nanoparticle spectra probe a

large ensemble of these particles. This leads to results that can be modeled

reasonably well using Mie theory. The main assumption of Mie’s theory is that

the particle and its surrounding medium are homogeneous and describable by

their bulk optical dielectric functions [81-82].

Mie attempted to calculate the optical response of large isolated, that is, single,

metal particles following classical electrodynamics. This model gives a

qualitative account of the variation of the optical properties with the size or the

surrounding medium. Moreover, it is assumed that the individual particles are

noninteracting and separated from one another. Therefore, the electric field

created around the particle by the excitation of surface plasmon resonance is

not felt by the other surrounding particles. In general, when the particle size

24 Chapter 1

(2R) is small enough (assumed to be spherical in shape) compared with the

wavelength of light λ )R2( λ< and also when the particle concentration is

very low, an absorption peak would result due to the excitation of dipole

plasma mode (n=1), and the optical extinction spectra can be described well by

Mie theory [82, 83-85]. Thus, although the Mie theory is valid for spheres of

any size, the limitation of the theory is that the dielectric constant of a small

particle is different from that of the bulk [86].

1.4.4 Maxwell Garnett effective medium theory

The surface plasmon oscillation in metallic nanoparticles is drastically

changed if the particles are densely packed in the reaction medium so that the

individual particles are electronically coupled to each other. It has been seen

theoretically and experimentally found that when the individual spherical

gold particles come into close proximity to one another, electromagnetic

coupling of clusters becomes effective for cluster-cluster distances smaller

than five times the cluster radius ( R5d ≤ , where, d is the center-to-center

distance and R is the radius of the particles) and may lead to complicated

extinction spectra depending on the size and shape of the formed cluster

aggregate by a splitting of single cluster resonance [87-88]. As a

consequence, their plasmon resonance is red-shifted by up to 300 nm [89].

This effect is negligible if d > 5R but becomes increasingly important at

smaller distances [90]. Aggregation causes a coupling of the gold

nanoparticle’s plasma modes, which results in a red shift and broadening of

the longitudinal plasma resonance in the optical spectrum [91]. The

wavelength at which absorption due to dipole-dipole interactions occurs may

be varied from 520 nm (effectively isolated particles) through 750 nm

(particles that are separated by only 0.5 nm), and the resulting spectra are a

composite of the conventional plasmon resonance due to single spherical


particles and the new peak due to particle-particle interactions [92-93].

Since the inter particle coupling is stronger than the coupling within the

surrounding medium, the Mie’s theory developed for very dilute solutions

and isolated particles fails to describe the optical absorption spectrum.

However, the effective-medium theories, dating back to 1904, predicted by J.

C. Maxwell Garnett [94] have been successfully applied to this problem to

account for the optical absorbance behavior of the metal nanoparticles

present in a closely packed assembly. The Maxwell Garnett theory is strictly

valid in the quasistatic limit )R2( λ<< along with very small inter particle

distances but can be generalized to various shapes of the particles. The

Maxwell Garnett theory is an effective-medium theory [95-97].

1.5 Applications of gold nanoparticles

AuNPs are highly modifiable in size, shape and surface chemistry. Also they

are stable in a wide variety of environments, are inert, non-toxic and have

controllable optical-electronic properties. The main target of AuNPs is for

their application in catalysts, biomedical applications, nanosensors and drug

delivery which is discussed in detail in the following sections.

(i) Gold nanoparticles as a sensor

AuNPs are a very attractive material for biosensor, chemisensor, genosensor

and immunosensor production. Additionally, the unique physical and

chemical properties of gold nanoparticles provide excellent prospects for the

realization of this aim. AuNPs can be used as passive labels or as active

sensors [98]. Gold nanoparticles have been widely used to construct

biosensors because of their excellent ability to immobilize biomolecules.

Many kinds of biosensors, such as enzyme sensor, immunosensor and DNA

sensor, have been prepared based on the application of AuNPs [99].

26 Chapter 1

Developing rapid DNA-detection method is important for life science

research.

(ii) Catalytic properties of gold nanoparticles

The discovery in 1987 by Haruta and coworkers that AuNPs with size of <5

nm supported on the metal oxides, manifested a high catalytic activity, has

opened a new route in catalytic science [100]. AuNPs participated in a series

of important processes including hydrocarbon selective oxidation,

hydrogenation and water-gas shift reaction. The new gold catalyst system,

consisting of nanoparticulate gold on oxide support, is used for low-

temperature CO oxidation. It was shown that catalytical activity of AuNPs in

CO oxidation is strongly dependent on the support materials. From the

practical point of view, alumina (Al2O3) would be a preferable support for

Au catalyst, because it is cheap and possesses a high and thermally stable

surface area. Extraordinarily high catalytic activity of supported AuNPs for

oxidation of CO at room temperature arises from the reaction of CO

adsorbed on the step, edge and corner sites of metallic gold particles. Many

of the heterogeneous catalysts used in industry today consist of nanoparticles

of a catalytically active material anchored on a support. Modern

nanotechnology methods offer the synthesis of heterogeneous catalysts.

(iii) Utilization of gold nanoparticles in biomedical applications

AuNPs have numerous promising applications in nanomedicine field. These

applications include biosensing, bioimaging and bioassay. Gold nanoparticles

are used to produce thermal tumor ablation and new therapeutic agents. Also,

AuNP can be used for the detection of an antigen in conjugation with an

antibody. Most of these applications use the unique optical properties of


AuNPs such as SPR, photoluminescence and surface-enhanced Raman

scattering (SERS) effect.

AuNPs with a well-controlled size are suitable for a colorimetric indicator

because the color can be changed in terms of SPR, which is strongly

influenced by the particle size and agglomeration. The detection of trace

amounts of biomolecules, critical for early imaging and diagnosis of cancer,

will be facilitated by the imaging molecule-dense AuNPs. For cancer

therapy, selective delivery and targeting of NPs to tumors is a key to

overcome the problems of toxicity and to increase therapeutic effects. For

tumor-selective delivery of gold, nanoparticles–antigens hybrid on tumor

cells can be used [101]. Tumor antigens include growth factors and their

receptors, hormones and glycol conjugates. Antibodies conjugated with

AuNPs were fabricated through modifying AuNPs by cysteamine and

conjugating the amine-functional group with an antibody. Conjugation of

antibody onto AuNP surface induced the increase in average diameter of

nanoparticles. Most biomedical applications of AuNPs and nanorods are

based on the gold conjugates. AuNPs contains hundreds to thousands of

surface active gold atoms that are able to connect through the Au–S dative

bond oligonucleotides, antibodies, peptides, and carbohydrates. Such

nanostructures are called bioconjugates [102-103]. Another important

application of AuNPs in the biomedical field is for photothermal therapy.

The irradiation by laser beam to AuNPs causes the absorption and

conversion of photon energy into thermal energy. As a result, the local

temperature of AuNPs dramatically increases. The dramatic increase in

temperature can cause a sudden release of heat to the surrounding

environment. It can be used for photothermal destruction of cancer cells.

28 Chapter 1

Gold nanocarriers provided a new group of target-specific deliveries of

therapeutic agents. Fig. 1.6 shows the loading of drug on nanoparticle

surface. The therapeutic agent could be small drug molecules or large

biomolecules, such as DNA, RNA and proteins. The AuNPs are essentially

inert and nontoxic. They are able to penetrate the cell to facilitate cellular

internalization and connective tissue permeation, thus enabling the drugs to

be delivered efficiently to the targeted cell without clogging capillaries.

Fig. 1.6 Loading of drug on the nanoparticle surface

There are two main categories of drug delivery systems. The first group

consists of the capsulation. The capsulation has an ability to contain a

relatively large amount of drug within the capsule. The second group of drug

delivery systems involves the attachment of the drugs to the carriers.

Targeting of drugs is a central goal of the delivery system. One way to

achieve it could be the conjugation of the drug delivery particle with a ligand

that specifically recognizes the target (cell). The special protein can be

employed as a targeting ligand [104]. The monodisperse AuNPs with the size

range from 1.5 to 15 nm can form the core. It was recognized that the

accumulation of AuNPs in various tissues was found to be dependent on

particle size. AuNPs having 15 nm showed higher distribution in tissues

compared to larger particles [105]. AuNPs provide attractive candidates for

gene delivery. A more sophisticated approach is to modify the surface of


AuNPs by the addition of either an antibody or ligands with affinity for the

desired target. These involve coating the AuNPs with a self-assembled layer

of a thiolated PEG (poly-ethyleneglycol) or liposome. It may raise the

potential application of these AuNPs in the relative biomedical and

bioengineering areas.

(iv) Surface enhanced Raman spectroscopy

One of the most recognizable applications of LSP resonance shown by

metallic nanoparticles is in the surface enhanced Raman Spectroscopy

(SERS). Resonance of LSPs amplifies electric fields, E, near the particle

surfaces. The |E|2 of the plasmon electric field can be 10

2 to 10

4 of the |E|

2 of

the incident light [106]. The electric fields of plasmons can amplify the

Raman signals of chemical species near the metal surface, thus enabling the

technique of surface-enhanced Raman spectroscopy (SERS) [56]. Raman

spectroscopy is a type of vibrational spectroscopy that is sensitive to

polarizable bonds within molecules [107]. The electric field interacts with

polarizable molecules to produce dipoles, described by the equation [108]

Ep α= (1.5)

where α is polarizability of the molecule, E is the applied electric field

and p is the electric dipole induced in the molecule. As Eq. 1.5 shows, p

can be made larger by increasing either α or E , but plasmons tend to

enhance E . As the intensity of the induced dipoles increases, the intensity of

the Raman signals from those molecules increase. This surface enhancement

of Raman signals was first observed from pyridine adsorbed onto a

roughened Ag substrate [109]. Reproducible control of the degree of

enhancement has been problematic. It appears that many of the roughened

substrates have “hot spots” with exceptionally good signal enhancement

30 Chapter 1

[110]. Precise control of the nature of the surface roughness (e.g., by

patterning techniques) allows for better control of the degree of Raman

enhancement and of the wavelength required to access the surface plasmons

[106]. The Raman signal of the adsorbed species can be dramatically

enhanced with colloids as well. Enhancement of the electric fields of both the

incident and Raman scattered light by 104 produces an overall theoretical

enhancement of 108 [106]. The regions where colloidal particles come into

close proximity appear to be the location of intense plasmon electric fields

[111]. The fields that can arise between two particles that are very close (on

the order of one nanometer) to one another have enabled the detection of

SERS signals from single molecules located between these particles [112].

Conclusions

To conclude the synthesis of nanostructured materials with useful and

tunable properties are central to the development of nanoscale science and

technology. Bottom-up approaches based on self-assembly and self-

organization are especially appealing because of intrinsically low overhead

for large scale production. Gold nanoparticles, which have been known for

years, are the subject of an exponentially growing number of reports and are

full of promises for optical, electronic, magnetic, catalytic and biomedical

applications in the 21st century. The reason for the present excitement in

gold nanoparticle research is due to the stability of gold nanoparticles, the

extraordinary diversity of its modes of preparation, its size and shape

dependent properties and its role in nanoscience and future nanotechnology.

On the one hand we are still fascinated by the colors of metallic colloidal

suspensions, like Faraday, stained glass makers of the middle age and even

Roman craftsmen; on the other hand, they may be a real breakthrough in

prospect. After a long period devoted to understanding the physical


principles rationalizing the surface plasmon resonance phenomenon,

chemists and physicists have started to use surface plasmon resonance for

their own purposes. New breakthroughs are likely to come from the use of

the surface plasmon resonance as a tool for nanosynthesis.

32 Chapter 1

References

[1] U. Kreibig, M. Vollmer, Optical Properties of Metal Clusters,

Springer., Berlin, 1995

[2] G. Schmid, Clusters and Colloids – From Theory to Applications,

VCH. Weinheim, Germany, 1994

[3] J.A. Creighton, C.G. Blatchford, M.G. Albrecht, J. Chem. Soc.

Faraday Trans. 75, 790 (1979)

[4] K.U. Von Raben, R.K. Chang, B.L. Laube, Chem. Phys. Lett. 79, 465

(1981)

[5] A.A. Lazarides, G.C. Schatz, J. Chem. Phys. 112, 2982 (2000)

[6] K. Drukker, G. Wu, G.C. Schatz, J. Chem. Phys. 114, 579 (2001)

[7] M. Faraday, Philosophical Transactions of the Royal Society of

London 147, 36 (1857)

[8] R. Zsigmondy, The Chemistry of Colloids, John Wiley & Sons, Inc.,

New York, 1917

[9] R. Zsigmondy, Colloids and the Ultramicroscope, John Wiley &

Sons, Inc., New York, 1909

[10] X. Michalet, F.F. Pinaud, L.A. Bentolila, J.M. Tsay, S. Doose, J.J. Li,

G. Sundaresan, A.M. Wu, S.S. Gambhir, S. Weiss, Science 307, 538

(2005)

[11] S.M. Nie, S.R. Emery, Science 275, 1102 (1997)

[12] A.P. Bartko, R.M. Dickson, J. Phy. Chem. B 103, 11237 (1999)

[13] T. Svedberg, The Formation of Colloids, D. Van Nostrand Company,

Inc., New York, 1921


[14] T. Svedberg, A. Tiselius, Colloid Chemistry, The Chemical Catalog

Company, Inc., New York, 1928

[15] R. Zsigmondy, Colloids and the Ultramicroscope, John Wiley &

Sons, Inc., New York, 1909

[16] W. Ostwald, An Introduction to Theoretical and Applied Colloid

Chemistry, John Wiley & Sons, Inc., New York, 1917

[17] A. Einstein, Annalen Der Physik 17, 549 (1905)

[18] A. Einstein, Investigation on the Theory of Brownian Movement,

Dover Publications, Inc., New York, 1956

[19] A. Einstein, Annalen Der Physik 19, 371(1906)

[20] P. Langevin, Comptes Rendus Hebdomadaires des Seances de L

Academie des Sciences 146, 530 (1908)

[21] S. Chandrasekhar, Revs. Modern Phys. 15, 1 (1943)

[22] J. Perrin, Annales de Chimie et de Physique 18, 5 (1909)

[23] M.J. Nye, The Question of the Atom, Tomash Publishers, Los

Angeles, 1984

[24] M.E. Cates, M.R. Evans, Soft and Fragile Matter, Institute of Physics

Publishing, Bristol, 2000

[25] T.A. Witten, P.A. Pincus, Structured Fluids: Polymers, Colloids,

Surfactants, Oxford University Press, New York, 2004

[26] H.C. Berg, Random Walks in Biology, Princeton University Press,

Princeton, 1983

[27] M. von Smoluchowski, Kolloid-Zeitschrift 21, 98 (1917)

34 Chapter 1

[28] P. Keblinski, J.A. Eastman, D.G. Cahill, Mater. Today 8, 36 (2005)

[29] P.C. Hiemenz, M. Dekker, Principles of Colloid and Surface

Chemistry, New York, 1986

[30] D. Wu, H. Zhu, L. Wang, L. Liua, Curr. Nanosci. 5, 103 (2009)

[31] L. Godson, B. Raja, D. Mohan Lal, S. Wongwises, Sustain. Energy

Rev. 14, 629 (2010)

[32] Y. Li, J.E. Zhou, S. Tung, E. Schneider, S. Xi, Powder Technol. 196,

89 (2009)

[33] S.K. Das, S.U.S. Choi, W.H. Yu, T. Pradeep, Nanofluid: Science and

Technology, John Wiley & Sons Inc. 2007

[34] E.J. Swanson, J. Tavares, S. Coulombe, IEEE Trans. Plasma Sci. 36,

886 (2008)

[35] S.K. Das, S.U.S. Choi, H.E. Patel, Heat Transfer Eng. 27, 3 (2006)

[36] J. Turkevich, G. Garton, P.C. Stevenson, J. colloid Sci. 9, 26 (1954)

[37] T.S. Ahmadi, Z.L. Wang, T.C. Green, Science 272, 1924 (1996)

[38] C.K. Yee, R. Jordan, A. Ulman, H. White, A. King, Langmuir 15,

3486 (1999)

[39] T. Teranishi, M. Hosoe, T. Tanaka, M. Miyake, J. Phys. Chem. 103,

3818 (1999)

[40] M.J. Hostetler, J.E. Wingate, C.J. Zhong, J.E Harris, Langmuir 14,

17 (1998)

[41] R.P. Andres, J.D. Bielefeld, J.I. Henderson, D.B. Janes, Science 273,

1690 (1996)


[42] G. Chumanov, K. Sokolov, B.W. Gregory, J. Phys. Chem. 99, 9466

(1995)

[43] J. Neddersen, G. Chumanov, T.M. Cotton, Appl. Spectrosc. 47, 1959

(1993)

[44] S.E. Gilbert, O. Cavalleri, K. Kern, J. Phys. Chem. 100, 12123 (1996)

[45] R.S. Urquhart, D.N. Furlong, T. Gengenbach, N.J. Geddes, Langmuir

11, 1127 (1995)

[46] G. Sberveglieri, L.E. Depero, P. Nelli, C. Perego, Adv. Mat. 8, 334

(1996)

[47] M.T. Reetz, M. Winter, J. Am. Chem. Soc. 119, 4539 (1997)

[48] M. Nagteggal, R. Seshadri, W. Tremel, Chem. Commun. 19, 2139

(1998)

[49] J.R. Heath, R. S. Williams, J.J. Shiang, J. Phys. Chem. 100, 3144

(1996)

[50] G. Frens, Nat. Phys. Sci. 241, 20 (1973)

[51] J. Turkevich, J. Hillier, Anal. Chem. 21, 475 (1949)

[52] G. Schmid, Chem. Rev. 92, 1709 (1992)

[53] J. Kimling, M. Maier, B. Okenve, V. Kotaidis, H. Ballot, A. Plech, J.

Phys. Chem. B 110, 15700 (2006)

[54] J. Turkevich, P.C. Stevenson, J. Hillier, Discuss. Faraday Soc. 11, 55

(1951)

[55] Y. Xia, N. Halas, MRS Bull. 30, 338 (2005)

36 Chapter 1

[56] T.L. Ferrell, Plasmon. In Concise Encyclopedia of Physics;

McGraw–Hill: New York, 2005

[57] J.M. Pitarke, V.M. Silkin, E.V. Chulkov, P.M. Echenique, J. Opt. A:

Pure Appl. Opt. 7, S73 (2005)

[58] J. Cuy, Biomaterials Tutorial: Surface Plasmon Resonance (SPR)

http://www.uweb.engr.washington.edu/research/tutorials/

plasmon.html

[59] A. Campion, P. Kambhampati, Chem. Soc. Rev. 27, 241(1998)

[60] A.V. Zayats, I.I. Smolyaninov, J. Opt. A: Pure Appl. Opt. 5, S16

(2003)

[61] A.B. Ellis, M.J. Geselbracht, B.J. Johnson, G.C. Lisensky, W.R.

Robinson, Teaching General Chemistry: A Materials Science

Companion; Oxford University Press: Oxford, 1993

[62] D. Nedelkov, R.W. Nelson, Trends Biotechnol. 7, 301 (2003)

[63] M. Moskovits, Rev. Mod. Phys. 57, 783 (1985)

[64] K.L. Kelly, E. Coronado, L.L. Zhao, G.C. Schatz, J. Phys. Chem. B

107, 668 (2003)

[65] E. Hutter, J. H. Fendler, Adv. Mater. 16, 1685 (2004)

[66] U. Kreibig, C.V. Fragstein, Z. Phys. 224, 307 (1969)

[67] A. Liebsch, Phys. Rev. B, Condens. Matter. 48, 11317 (1993)

[68] C. J. Murphy, T. K. Sau, A. Gole, Orendorff, C. J. MRS Bull. 30, 349

(2005)

[69] N. Halas, MRS Bull. 30, 362 (2005)


[70] T.J. Jr. Norman, C.D. Grant, D. Magana, J.Z. Zhang, J. Liu, D. Cao,

F. Bridges, A.Van Buren, J. Phys. Chem. B. 106, 7005 (2002)

[71] S. Underwood, P. Mulvaney, Langmuir 10, 3427 (1994)

[72] F. Goettmann, A. Moores, C. Boissiere, P. Le Floch, C. Sanchez,

Small 1, 636 (2005)

[73] A. Henglein, J. Phys. Chem. 97, 5457 (1993)

[74] A. Henglein, P. Mulvaney, T. Linnert, Faraday Discuss. 92, 31

(1991)

[75] A. Henglein, Chem. Mater. 10, 444 (1998)

[76] T. Linnert, P. Mulvaney, A. Henglein, J. Phys. Chem. 97, 679 (1993)

[77] V.V. Vodnik, J. M. Nedeljkovic, J. Serb. Chem. Soc. 65, 195 (2000)

[78] R. Chapman, P. Mulvaney, Chem. Phys. Lett. 349, 358 (2001)

[79] G.C. Lica, B.S. Zelakiewicz, M. Constantinescu, Y.Y. Tong, J. Phys.

Chem. B. 108, 19896 (2004)

[80] G. Mie Ann. Phys. 25, 377(1908)

[81] V. Bonacic-Koutecky, P. Fantucci, J. Koutecky, Chem. Rev. 91, 1035

(1991)

[82] K.P. Charl, W. Schulze, Ber. Bunsenges. Phys. Chem. 88, 350 (1984)

[83] P. Mulvaney, Langmuir 12, 788 (1996)

[84] U. Kreibig, U. Genzel, Surf. Sci. 156, 678 (1985)

[85] G.W. Arnold, J.A. Borders, J. Appl. Phys. 48, 1488 (1997)

[86] M. Kubo, S. Nakamura, Bull. Chem. Soc. Jpn. 26, 318 (1953)

38 Chapter 1

[87] M. Quinten, U. Kreibig, Appl. Opt. 32, 6173(1993)

[88] U. Kreibig, A. Althoff, H.Pressmann, Surf. Sci. 106, 308 (1991)

[89] T. Ung, L.M. Liz-Marzan, P. Mulvaney, Colloids Surf. A 202, 119

(2002)

[90] J.M. Gerardy, M. Ausloos, Phys. Rev. B 27, 6446 (1983)

[91] A.N. Shipway, M. Lahav, R. Gabai, I. Willner, Langmuir 16, 8789

(2000)

[92] W.Y. Shih, J. Liu, W.H. Shih, I.A. Aksay, J. Stat. Phys. 62, 961

(1991)

[93] K.S. Mayya, V. Patil, M. Sastry, Bull. Chem. Soc. Jpn. 73, 1757

(2000)

[94] J.C. Maxwell Garnett, Philos. Trans. R. Soc. 203, 805 (1904), J. C.

Maxwell Garnett, Philos. Trans. R. Soc. 205, 237 (1906)

[95] G.L. Hornyak, C.J. Patrissi, C.R. Martin, J. Phys. Chem. B 101,

1458 (1997)

[96] C.A. Foss Jr. , G.L. Hornyak, J.A. Stockert, C.R. Martin, J. Phys.

Chem. B 96, 7497 (1992)

[97] C.A. Foss Jr., G.L. Hornyak, J.A. Stockert, C.R. Martin, J. Phys.

Chem. 98, 2963 (1994)

[98] A.R. Sperling, R.P.Gil, F. Zhang, M. Zanella, J.W. Parak, Chem.

Soc. Rev. 37, 1896 (2008)

[99] Q.A. Huo, Colloids Surf. B 50, 1 (2007)

[100] M. Haruta, K. Tanaka, A. Ueda, M. R. Torres Sanchez, J. Catal. 168,

125 (1997)


[101] H.H Cai, P.H Yang, J.Y. Cai, Sens. Actuators B: Chem. 135, 603

(2009)

[102] B. Khlebtsov, V. Zharov, A. Melnikov, V. Tuchin, N. Khlebtsov,

Nanotechnology 17, 5167 (2006)

[103] G.N. Khlebtsov, A.L. Dykman, J. Quant. Spectrosc. Radiact. Transf.

111, 1 (2010)

[104] G. Han, P. Ghosh, M. De, M.V. Rotello, Nanobiotechnology 3, 40

(2007)

[105] G. Sonavane, K. Tomoda, K. Makino, Surf B: Biointerfaces 66, 274

(2008)

[106] A. J.Haes, C.J. Haynes, A.D. McFarland, G.C. Schatz, R.P.Van

Duyne, S. Zou, MRS Bull. 30, 368 (2005)

[107] P.W. Atkins, Physical Chemistry, 3rd ed.; W. H. Freeman and

Company: New York, 1986

[108] G.C. Weaver, K. Norrod, J. Chem. Educ. 75, 621 (1998)

[109] M. Fleischmann, P.J. Hendra, A. McQuillan, J. Chem. Phys. Lett. 26,

163 (1974)

[110] N. Halas, MRS Bull. 30, 362 (2005)

[111] C.J. Murphy, T.K. Sau, A. Gole, C.J. Orendorff, MRS Bull. 30, 349

(2005)

[112] J. Jiang, K. Bosnick, M. Mallaird, L. Brus, J. Phys. Chem. B 107,

9964 (2003)

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