Thesis sumarization: Synthesis and optical properties of gold nanostructures spherical, rod and core/shell SiO2/Au shape for biomedical applications

The objectives of research contents of the thesis: (i) to synthesize and investigate the optical properties of gold nanostructures spherical, rod and core/shell SiO2/Au shape with controlled sizes; (ii) to try application of synthesized gold nanostructures in imaging and in photothermal.

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VIETNAM ACCADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY

INTITUTE OF PHYSICS -*** -

DO THI HUE

SYNTHESIS AND OPTICAL PROPERTIES OF GOLD NANOSTRUCTURES SPHERICAL, ROD AND CORE/SHELL SIO2/Au SHAPE FOR BIOMEDICAL APPLICATIONS

Speciality : Solid State Physics Code : 944 01 04

THESIS SUMARIZATION

Ha Noi – 2018

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The work was completed at the Center for Quantum Electronics, Institute of Physics, Vietnam Academy of Science and Technology

Supervisor:

1 Dr Nghiem Thi Ha Lien

2 Assoc Prof Dr Tran Hong Nhung

Referee 1: Dr.Nguyen Cao Khang

Referee 2: Prof Dr Nguyen Nang Dinh

Referee 3: Dr Nguyen Tran Thuat

The thesis will be presented and defended at the Scientific Committee of Institute of Physics held in:

at The thesis can be found at the library:

- National Library of Hanoi

- Library of Institute of Physics, VAST

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1 Origin of thesis title

The gold nano structures are one in the nano physical types used more in the biomedical applications for increasing sensitivity of the diagnostic and the targeted therapy These are the research directions that many labs in the world and in Viet Nam are interested in developing Gold nanospheres show an extinction sccross-section (absorption and scattering) 4-5 orders higher than conventional absorbing dyes In particular, the plasmon resonance of the gold or silver nanostructures can be tuned to specific wavelengths across the visible and infrared range of the electromagnetic spectrum, for applications ranging from the construction of photonic crystals to biophotonics Moreover, the superior properties of gold nanostructures are stability structural, non-toxic, highly biocompatible, and they are easily surface function to bind to biomolecules such as amino acids, enzymes, DNA and drug molecules through the -SH group With these unique surface-chemistry properties, the applied studies of gold nanostructures are more and more developed and promising great achievements in biomedical applications For example: (i) gold nanoparticles are capable of carring drugs, delivering drugs and photoluminescence in tissue; (ii) core / shell nanostructures with strong

light scattering from visible to near infrared (NIR) are applied to in vivo

imaging in the body (10 cm) to present cancer cells At the same time, with the ability to absorb light intensively in the near-infrared region, gold nanoshells are used to destroy cancer cells by phototherapy without compromising healthy cells also do not affect the genetic factors

Based on the actual exigency and the ability to response those exigencies of the gold nanostructures, as well as from the research situation in the world

and in Viet Nam, we chose and study the topic: “Synthesis and optical

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properties of gold nanostructures spherical, rod and core/shell SiO 2 /Au shape for biomedical applications”

2 The objectives of research contents of the thesis: (i) to synthesize and

investigate the optical properties of gold nanostructures spherical, rod and core/shell SiO2/Au shape with controlled sizes; (ii) to try application of synthesized gold nanostructures in imaging and in photothermal

3 Usefulness of the thesis:

The thesis is a basic research to orientate application of gold nanostructures that are and will be promising many applications in nanotechnology, especially bioapplications The thesis has found a simple process for synthesising gold nanoparticles at room temperature by the seeded growth with particle size be controlled in a wide range from 2nm to over 200nm The thesis has controlled minutely the gold film thickness of nanoshells from 10-30 nm by control of seed concentration At the same time, the use

of uniform and small size Duff-Baiker gold particles creates a thinner, less rugged gold film, which is better than today's Simultaneously, we have created small nanoshells less than 100 nm with plasmon absorption peaks about 700 nm

Thesis structure

The thesis consists of 158 pages arranged into 5 chapters

Chapter 1: OVERVIEW OF RELATED MATTERS AND THEORY 1.1 Optical properties of metallic nanoparticles

1.1.1 Surface plasmon resonance (SPR)

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Surface plasmon polaritons are electromagnetic excitations propagating at the interface between a dielectric and a conductor Metals as Au, Ag and Cu have plasmon frequencies in the visible light region, so their nanostructures have color effects The colour of the colloidal solutions is the result of the scattering and absorbing of light by the surface plasmon The optical properties of metallic nanostructures are explained by the theory of Mie and Gans

1.1.2 The Mie theory - the dependence of optical properties on particle size

From the Mie theory can calculate scattering sca and the absorption cross section abs of a particle as follows:

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The above formulas show that when the particle size is small, the scattering

efficiency is smaller than the absorption efficiency Absorption A of a

sample of dispersed nanoparticles is given by:

𝐴(𝜆) = 𝑙𝑜𝑔𝐼𝜆

𝐼𝜆 = 1

2.303𝑁 𝜎𝑒𝑥𝑡𝜆 𝑙 where ext is the extinction cross section of the sample at wavelength  and

N number of particles in a liter, l is the thickness of the absorbing medium

(cm)

1.1.3 Optical characteristics of gold nanostructures

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As a result of the Mie theory, it is possible to see the plasmon absorption spectra of the metal nanoparticles depending on the particle size

1.1.3.1 Gold nanoparticle

Optical properties depend on the size of the particle: particles less than 20

nm in diameter scatter negligible As the particle diameter increases, the contribution of surface plasmon scattering increases significantly So large particles are suitable for imaging applications based on scattering of light Depending on the purpose of application, gold nanoparticles with suitable dimensions will be selected

1.1.3.2 Gold nanorod

Figure 1 The distribution of charge on a nanorod below the

excitation of the light

The optical properties of the gold nanorods depend on the ratio of the aspect ratio of gold nanorods, particularly, the longitudinal surface plasmon resonance (LSPR) red – shifts when the aspect ratio increases

1.1.3.3 Nano core/shell SiO2/Au

Relative thickness of core-to-shell layer is sensitive towards the position of the SPR band

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Figure 2 Variation in SPR band with shell thickness

Figure 3 Hybridization model describing interaction between sphere and

cavity plasmons to give rise to nanoshell plasmon

Plasmon excitation from nanoshell particles can be viewed as an interaction between plasmon response from a nanosphere and a nanocavity (fig 3) The frequencies of these modes (bonding and antibonding) can be expressed as

where, R 1 is the inner radius of the shell, R 2 the outer radius of the shell, n

the order of spherical harmonics, p the bulk plasmon frequency, n+ the antisymmetric plasmon and n- the symmetric plasmon

1.2 Methods for synthesising of gold nanostructures

1.2.1 Seeded growh method

This method has the advantage of synthesizing at room

temperature, easy to control particle size, uniform size and less byproducts However, to obtain the results that this method requires:

- Creating seeds are single dispersed, uniform in shape and size

- Controlling pH of growth solution

1.2.2 Methods for making gold nanoparticles

1.2.3 Synthesis of gold nanorods

1.2.4 Synthesis of nano core/shell SiO2/Au

1.3 Application of gold nanostructures

1.3.1 Bio-marking and imaging

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Figure 4: Transmission electron microscopy images of Au seed particles –

scale 20 nm (left); absorption spectra of seed gold colloid

TEM image shows that gold nanoparticles are formed with an average size

of 2 nm The absorption spectra of the seed solution is characterized spectra

of small gold nanoparticles (less than 10 nm): broad spectrum with

resonant peak in the range of 505 nm - 510 nm

2.3 Synthesis of gold nanospheres by seed growth method

2.3.1 Role of Gold plating solutions (GPS) in the growth of Au seeds

Figure 5 Absorption spectra of the solutions with varied pH values

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We chose to use a pH 9.4 hydroxyde solution as a seeded growth solution

2.3.2 Effect of Seed Concentration

Figure 6 Effect of seed concentration Transmission electron microscopy images of Au particles obtained using different concentrations of seed while

keeping the amount of Au precursor added constant

The results showed that the larger the [Au3+] / [seed Au ), the larger the seed was and when the ratio was greater than 12.5, the particles lost

symmetry This can be explained by the La Mer mechanism

2.3.3 Seeded Growth Synthesis of Au NPs of Up to 200 nm

2.3.3.1 Using the Duff-Baiker gold particles

2.3.3.2 Using the citrate gold particles

Figure 7 Seeded growth with the dilution of the seed solution

Transmission electron microscopy images of nanoparrticles obtained after

different growth steps, scale 100 nm

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Dimensions obtained from calculations, TEM images, and DLS measurements are relatively consistent This again shows that by using the seeded growth method with the pH 9,4 growth solution, we can completely controlled synthesis the good quality gold nanoparticles at the room temperature

Figure 8 Plasmon resonance spectra of small gold nanoparticles obtained

from step 1 to step 3 (A), normalized plasmon resonance spectra of solutions obtained from step 5 to step 16 (B) and plasmon resonance spectra of large gold nanoparticles obtained from step 17 to step22 (C)

After each step of the growth, the gold nanoparticles are larger, the plasmon absorption peak shift toward the long wave At the same time, it is also possible to see that the spectral widths of these spectra are much narrower than that of small particle sizes (less than 10nm) and in this size range the

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spectral width increases with the increase in particle size This is the result

of the interaction between electromagnetic waves and large metal nanoparticles

Chapter 3: Synthesis and optical properties of gold nanoshell SiO2/Au 3.1 Materials and methods

3.2 Synthesis of amino-functionalized silica nanoparticles

Figure 9 TEM images of silica NPs prepared by sol–gel with the

increasing amounts of ammonia and corresponding sizes of (a) 40 ± 3 nm, (b) 65 ± 4 nm,(c) 110 ± 5 nm, (d )130 ± 5 nm, and (e) 150 ± 5 nm, before functionalization with APTES, and f– j the respective silica NPs obtained after functionalization with APTES The same scale bar (100 nm) applies to

all images

The sizes of the spherical particles were regulated by the amount of

ammonia used during the synthesis: a corresponding increase in the average diameter from 40 to 150 nm was obtained with the increasing amounts of ammonia from 0,9 ml to 1,3 ml

Results of the zeta potential and infrared absorption spectra showed that silica nanoparticles functioned successfully with APTES molecules

3.3 Seed particles: THPC–gold-decorated APTES- functionalized silica NPs

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Figure 10 TEM images of THPC–gold-decorated on (a) bare silica NPs, in

citrate buffer solution, (b) APTES-functionalized silica NPs, in citrate

buffer solution Scale bars are 100 nm for all images

TEM images show that gold nanoparticles adsorpt very little and uneven on the surface silica nanoparticles are only groups -OH Whereas, the Duff-Baiker gold nanoparticles adsorpt uniformly on the surface of the silica nanoparticles are –NH2 groups due to the electrostatic interaction between the amino - NH2 functional groups on the nano silica and -COO groups on Duff-Baiker gold nanoparticles

3.4 Gold–silica core–shell formation

3.4.1 Effect of HCHO concentration

The minimum HCHO required for the reduction reaction to form the core / shell structure is determined to be a molar ratio of HCHO to Au3+ in the growth solution to 2.5

3.4.2 Gold nanoshell SiO2/Au

3.4.2.1 SiO 2 / Au nanoshells with varying shell thickness

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Figure 11 HTEM and corresponding EDX analysis image of silica

core in diameter following the gold-plating process Yellow corresponds to

Au, red corresponds to O; Green corresponds to Si; scale bar of 100 nm

3.4.2.2 Synthesis nanoshell on the silica core with a diameter of 40-150

nm

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Figure 12 TEM images of silica NPs with varying sizes of a 40 ± 3 nm, b

65 ± 4 nm, c 100 ± 5 nm, d 110 ± 5 nm, e 130 ± 5 nm, and f 150 ± 5 nm coated with gold shells Each frame shows the development of the nanoshells at different stages of the deposition process: (i) bare APTES- functionalized silica, (ii) gold-decorated APTES-functionalized silica, (iii) partial gold shell growth, and (iv) complete gold shell formation

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Figure 13 Normalized plasmon resonance spectra of SiO 2 / Au with the

same shell thickness and varying core diameters

Chapter 4: Synthesis and optical properties of gold nanorods (GNRs) 4.1 Materials and methods

Gold nanorods are synthesised by seeded growth methods This method consists of two stages: preparation of the gold seed and preparation of gold nanorod of various aspect ratios By analyzing the role of forming factors,

we found that many factors influence the formation and development of gold nanorods, such as: Ag+, CTAB, AA, Au3+ concentration

4.2 Synthesizing of GNRs

4.2.1 Effect of Ag + concentration

In order to consider role of Ag+ in the formation of GNRs, 7 different samples of GNRs were prepared Firstly, 150 µl HAuCl4 0.023 mM was put into 10 ml of the mixture CTAB 0.1M and BDAC 0.00 5M in 7 different reactions Then, various volumes of AgNO3 corresponding to the Ag+

concentrations of 0.0 mM; 0.024 mM; 0.040 mM; 0.048 mM; 0.064 mM;

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0.080 mM; 0.107 mM; 0.134 mM were added in the above reaction solutions Next, 25 µl AA 0.25M reductant reaction agent was added Finally, 100 µl of the gold seed solution was put into each reaction solution under vigorous stirring at room temperature The growth process of GNRs was maintained in 2 hours

4.2.3 Effect of Ag + concentration

The amount of 0.25 M AA was varied from 0 - 40 μl and the ratio of

concentration [AA] to [Au3+] was observed from insufficient 0,92 to excess 2.45

4.3 Results

4.3.1 The shape and composition of the gold nanorods

Figure 14 XRD spectra of gold nanorods

4.3.2 The influence of factors on the formation and development of the GNRs

4.3.2.1 Ratio of molar concentration [Ag + ] to [Au 3+ ]

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Figure 15 TEM images of the GNR solutions upon changing of the

Ag + concentrations at scale bare of 20 nm

Figure 15 shows TEM images of the GNRs prepared under different Ag+ concentrations as: 0 mM; 0.04 mM; 0.064 mM; 0.08 mM; 0.107 mM, and 0.134 mM We can easily see that the yield of the rod and their uniformity increase while the diameter of the particles decreases as the

Ag+ concentration increases from 0.04 mM to 0.107 mM.Without Ag+ ions, TEM image indicates that the obtained sample contains different shapes, including spherical, triangle and a few high aspect ratio rod-like particles This is consistent with results published in the ref

Figure 16 The absorption spectra of the GNR solutions prepared

under different Ag + concentrations