INTRODUCTION

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INTRODUCTION

1.1 Nanotechnology

Nanotechnology is the study, investigation, and creation process of functional and

useful materials, devices, and systems through control of matter at the nanometer (nm) scale,

generally between 1 to 100 nm in at least one dimension. The study of physical properties of

nanoscale materials has led to numerous new applications. The word “Nanotechnology” was

originated from a Greek world which means "dwarf" i.e. one billionth of a meter (1nm = 10-9

m). The nanoscale is unique because nothing solid can be made any smaller. It is also unique

because many of the mechanisms of the biological and physical world operate on length

scales from 1 to 100 nm. At these dimensions materials exhibit different physical properties,

thus scientists expect that many novel effects at the nanoscale will be discovered and used for

breakthrough technologies.

A number of important breakthroughs have already occurred in nanotechnology.

These developments are discovered in materials and products used throughout the world.

Some examples are devices in computers that read from and write to the hard disk, catalytic

converters in automobiles that help to remove air pollutants, certain sunscreens, and

cosmetics that transparently block harmful radiation from the sun. Still, many scientists

believe that they have only scratched the surface of nanotechnology’s potential and it will

have a major impact on medicine and health care; energy production and conservation;

environmental cleanup and protection; electronics, computers, and sensors; and world

security and defense.

To grasp the size of the nanoscale, consider the diameter of an atom, the basic

building block of the matter. The hydrogen atom, one of the smallest naturally occurring

atoms, is only 0.1 nm in diameter. In fact, nearly all atoms are roughly 0.1 nm in size, too

small to be seen by human eyes. We know that atoms bond together to form molecules, the

smallest part of a chemical compound. Molecules that consist of about 30 atoms are only

about 1 nm in diameter. Molecules, in turn, compose cells, the basic units of life. Human

cells range from 5,000 to 200,000 nm in size, which means that they are larger than the

nanoscale. However, the proteins that carry out the internal operations of the cell are just 3 to

20 nm in size and so have nanoscale dimensions. Viruses that attack human cells are about 10

to 200 nm, and the molecules in drugs used to fight viruses are less than 5 nm in size.

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1.2 Synthetic Strategies

There are two different approaches to synthesize nanocrystals (NCs): the top-down

physical processes and the bottom-up chemical methods (Figure 1.1). In the "bottom-up"

approach, materials and devices are built from molecular components which assemble

themselves chemically by principles of molecular recognition. The term molecular

recognition refers to the specific interactions between two or more molecules through

noncovalent bonding such as hydrogen bonding, metal coordination, hydrophobic forces, van

der Waals forces, pi-pi interactions, electrostatic and electromagnetic effects. The host and

guest involved in molecular recognition exhibit molecular complementary. In the "top-down"

approach, the nanoobjects are constructed from larger entities without atomic-level control.

Figure 1.1. Top-down and bottom-up

approaches of nanoparticle synthesis.

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The size or shape control of semiconductor NCs can be accomplished by adjusting the space

in which the NCs grow (e.g., in templates).

Creating nanostructured materials based on bottom-up method is a fast-growing field

of research. Of particular interest are two-dimensional arrays of NCs, which have been

shown to display unique optoelectronic, magnetic, or catalytic properties that can be tuned by

varying their size and/or interparticle separation distance1-5

. Advanced functional materials

incorporating well-defined NCs architectures have potential for practical applications in

many areas, including miniaturized nanoelectronics6, ultrafast quantum computing

7, high-

density memory/data storage media8, ultrasensitive chemical sensing/biosensing

9, generation

of high-efficiency catalytic substrates10

, and high-throughput templating for the growth/

attachment of other types of bio- or inorganic nanomaterials11,12

.

Synthesis of protein protected NCs are of particular interest to understand the

protein’s specificity and binding capabilities. One of the most widely used proteins is Bovine

Serum Albumin (BSA)13

(Figure 1.2). Serum albumin is the most abundant protein in blood

plasma and it serves as a vehicle for intracellular transportation14

. Serum albumin is of great

importance in pharmacology as the conjugation of drugs to albumin decreases their toxicity15

.

BSA

Figure 1.2. Structure of BSA showing its

three homologous domains.

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It has also been reported that BSA conjugated NCs show improved stability against

flocculation, increased quantum yield, and low toxicity. BSA can then be conjugated for the

targeting purpose16

. Typically, bioconjugation of NC is a multistep process. This requires the

modification of NC surface with a linker that can recognize the biomolecule and can also

protect the NC from uncontrolled growth and aggregation17,18

.

The synthesis of NCs of metals and metal alloys by biological molecules is known as

biomineralization19

. Over millions of years of evolution, nature has evolved mechanisms to

produce such NCs for a wide variety of purposes. Diatoms produce exquisitely intricate

porous silica shells with nanoscaled spikes (Figure 1.3, left panel), pores and valleys20,21

and

sponges produce spicules22

that are utilized for structure and protection. Bacteria synthesize

crystalline magnetic NCs for navigation and orientation23,24

. Algae, plants and bacteria

produce metal NCs (Figure 1.3, right panel) as a consequence of detoxification pathways25

. In

Figure 1.3. Porous silica structure (left); magnetic crystals (shown as black particles)

in magnetotactic bacteria act as tiny compasses that guide these organisms to move

vertically in river bed sludge. MV indicates empty vesicles.

many cases, the NCs are produced under genetic control, resulting in specific morphologies,

sizes, and crystallinities of the structures and particles22

.

For appropriate biocompatible applications of bioconjugated chalcogenides26-30

,

carefully designed synthetic routes involving biological molecules such as amino acids,

proteins, and biopolymers are required. Colloidal synthesis of nanochalcogenides is an

exciting branch of synthetic inorganic chemistry in which surface active compounds provide

charge and steric stabilizations for the growing nucleating centers in order to attain desired

morphologies. Many groups31-34

have followed this route to obtain fine morphologies at

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relatively much elevated temperatures. However, in order to synthesize biomaterials

involving biomolecules, it is desirable to have relatively low temperature (<100 oC) synthesis

where biofunctionalities could be retained.

Bioconjugated NCs35-38

have become the focus of intensive research due to their

applications in drug delivery, biological labeling, luminescence tagging, etc. Semiconductor

chalcogenides have been widely used as optical filters, optical recording materials,

thermoelectric cooling materials, sensors, solar cells, superionic materials, and laser

materials39-42

. Lead selenide (PbSe) is an attractive semiconducting material that has been

employed to produce photoresistors, photodetectors, photovoltaic absorbers, photographic

plates, and so forth. PbSe has been the subject of particular attention because of its narrow

band gap (in bulk) of 0.28 eV (at room temperature) and strong quantum confinement effects

due to its large Bohr radius (rB ≈ 46 nm)43-54

. Many recent reports55-62

have focused on the

synthesis of various shapes, and physics of PbSe NCs. Cadmium selenide (CdSe), another

calcogenide, has a much lower rB in comparison to PbSe. It is equally important material to

use in opto-electronic devices, laser diodes, nanosensing, biomedical imaging and high-

efficiency solar cells63-65

. Considering the rapid miniaturization of technology in all fields, we

have synthesized important chalcogen-based materials, i.e. PbSe and CdSe at the nanoscale

using aqueous solution phase synthesis at relatively mild temperature of 85 oC with particular

emphasis on their biocompatible applications.

Bovine Serum Albumin (BSA) has been chosen due to its important characteristic

features. It is an important blood protein with molecular weight of 66500 Da and is composed

of 580 amino acid residues66,67

(Figure 1.2). BSA contains one single cysteine and eight

disulfide bonds. The overall shape of BSA is oblate ellipsoid which contains three

structurally homologous domains І, II, and III. It is a water soluble and weak reducing agent

and has already been used as a capping/stabilizing agent for the synthesis of semiconductor

nanomaterials and various noble metals68-70

. BSA binds endogenous as well as exogenous

substrates in its hydrophobic pockets71

. It is well- known that protein denaturation is often

followed by a massive "unfolding" of the protein. Native BSA is a globular protein which

undergoes structural changes and transforms into its unfolded or tertiary configuration. This

secondary structure consists of hydrogen bonded α-helices and β-sheets, and is called the

large-scale structure. The latter structure even proved to be a better capping/stabilizing agent.

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Figure 1.4. Dependence of PbS NCs morphology on the native and

denatured state of BSA with temperature.

We have recently observed72

that (Figure 1.4), there is a significant capping/stabilizing

difference between the native and denatured states of BSA. The unfolded or denatured BSA

is much efficient in controlling the crystal growth.

1.3 The Importance and Use of Biomolecules in the Synthesis of Nanomaterials

Now-a-days, people are becoming more and more interested in materials with

recognition properties toward biological macromolecules, such as protein and nucleic acids.

Biomolecules are the subject of particular attention due to their nanoscale dimensions, their

various and distinctive molecular structures and functionalities, and their specificities and

versatility in recognition and assembly. The conjugation of nanoparticles (NPs) with

biomolecules could provide electronic or optical transduction of biological phenomena in the

development of novel biosensors73,74

. A nanometer scale has significant relevance to the

biological systems, where many proteins are in the nm size similar to those of NPs, thus the

two classes of materials are structurally compatible. Enzymes, antigens and antibodies, and

biomolecular receptors have dimensions in the range of 3-20 nm. Because of several

fundamental features, biomaterials are the important future building blocks for NP

architectures. For example, biomaterials display specific and strong complementary

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recognition interactions and thus to self-assembly. Various biomolecules contain several

binding sites and this allows the multidirectional growth of NP structures. Proteins may be

genetically engineered and modified with specific anchoring groups. This facilitates their

aligned binding to NPs or the site-specific linkage of the biomaterial to surfaces.

Consequently, the directional growth of NP structures may be dictated. Deoxyribonucleic

acid (DNA) may be synthetically prepared in complex rigidified structures that act as

templates for the assembly of NPs by electrostatic binding to phosphate groups. Enzymes are

catalytic tools for the manipulation of biomaterials. For example, the ligation process of

nucleic acids provides effective tools for controlling the shape and structure of biomolecule-

NP hybrid systems. In this context, it has been found that Mother Nature has developed

unique biocatalytic replication processes and the use of these biomolecule-NP conjugates

may provide an effective system for the formation of nanostructures of specific shapes and

compositions.

The importance of functionalized NPs for biomedical applications cannot be

overestimated. For example, targeted entry into cells is an increasingly important area of

research75

. The nucleus is a desirable target because the genetic information of the cell and

transcription machinery resides there. Gold (Au) NPs76

(20 nm) were modified with shells of

BSA which were conjugated to various cellular targeting peptides to provide functional NPs

that penetrate the biological membrane and target the nuclei. Various NPs are applied as

drug-delivery agents to tumors in the analysis and medical treatment of cancers77

. The

functionalization of NPs with biomolecules effects the change in the shape and hence the

properties of the NPs. Upon adsorption of vitamin C on TiO2 NPs, the optical properties of

the particles were red-shifted by 1.6 eV as a result of charge transfer that originates from the

specific binding of the electron-donating modifier to corner defects on the surface of the

NPs78

. The solubility of NPs in water can be greatly improved by the functionalization of

their surfaces with highly hydrophilic biomolecules79

. A biomolecule can speed up or slow

the rate at which a monomer is generated, changing its concentration and, in turn, its

solubility equilibria or crystal nucleation and growth rates. Au NPs modified with long chain

alkanethiols are only soluble in low-polarity organic solvents. Furthermore, Au NPs that are

modified with biomolecules such as tiopronin or coenzyme A give excellent solubility in

water79

.

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Biomolecule-directed mineralization can lead to the formation of biomineralized

hybrid structures with improved performance in nature. The presence of a biomolecule can

also change the course of crystal nucleation or growth. A biomolecule that coordinates

strongly to a metal centre could, of course, prevent crystallization altogether. Alternatively, a

biomolecule can bind selectively to certain facets, speeding or slowing monomer addition to

that facet relative to others, which results in non-thermodynamic and often highly anisotropic

crystal shapes. Biomacromolecule surface recognition by NPs as artificial receptors provides

a potential tool for controlling cellular and extracellular processes for numerous biological

applications such as transcription regulation, enzymatic inhibition, delivery and sensing. The

size of NP cores can be tuned from 1.5 nm to more than 10 nm depending on the core

material, providing a suitable platform for the interaction of NPs with proteins and other

biomolecules80-82

. The conjugation of NPs with biomolecules such as proteins and DNA can

be done by using two different approaches, direct covalent linkage and non-covalent

interactions between the particle and biomolecules83-88

. The most direct approach to the

creation of integrated biomolecule-NP conjugates is through covalent attachment89

. Direct

covalent linkage can be achieved either through chemisorptions of the biomolecule to the

particle surface or through the use of heterobifunctional linkers. Chemisorption of proteins

onto the surface of NPs can be done through cysteine residues that are present in the protein

surface90

. The combination of one-dimentional (1D) NCs with biomolecules paves the way to

novel nanobioelectronic elements that could, for instance, transport bioelectronic signals

along that 1D nanowires. The combination of nanoobjects, nanotools, and nanotemplates91-93

with biomolecules gives new ideas of bioelectronics94

to open new doors of

nanobioelectronics. This is the reason to synthesize and to see the properties of biomolecule–

nanoparticle/nanorod hybrid systems as well as the organization of these systems as

functional devices (Figure 1.5).

1.4 Review of Literature

Gao et al.95

used a simple biomolecule-mediated process to the direct growth and

assembly of CdS nanorods. Many kinds of biomolecules such as amino acids (glycine,

serine), peptides (glycyl-glycine, glutathione), protein (gelatin, lysozyme), protein

metabolism product (guanidine), RNA base (uracil), and pyrimidine (uridine) have been

utilized. A series of complex CdS nanorod-based structures have been synthesized in high

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Figure 1.5. The schematic presentation of biomolecule-

nanoparticle/ nanorod conjugates to yield functional

devices.

yields, including three-dimensional (3D) and two-dimensional (2D) leaflike structures and

flower-like structures by assembly of CdS nanorods. The product’s morphology and structure

have been confirmed to correspond to the used biomolecule’s type and structure. By

controlling biomolecule’s structure and type, reactant’s concentration, ratio of inorganic

compound to biomolecule, heating method, and reaction temperature, CdS nanorod-based 3D

leaves, 2D leaves, or flowers could be obtained with predominantly single morphology. This

study shows that the structures of biomolecules appear to direct the morphology of complex

nanostructures of inorganic materials such as CdS and could theoretically lead to more

complex and useful nanostructures of many other materials. Yang et al.96

described the small-

biomolecule (glycyl glycine)-directed synthesis of single-crystalline Ag nanoplates. It was

found that the ratio of glycyl glycine to AgNO3 was the key to forming Ag nanoplates. The

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nanoplates were characterized by X-ray diffraction (XRD), scanning electron microscope

(SEM) and transmission electron microscopy (TEM). Zhou et al.97

reported the preparation of

a compact, functional quantum dot (QD)-DNA conjugate, where the capturing target DNA is

directly and covalently coupled to the QD surface.

Bakshi et al.72

first reported the PbS NCs synthesized in aqueous phase within a

temperature range of 40-80 oC in the presence of native and denatured states of BSA as the

capping/stabilizing agent. The purpose of this study was to design bio-nanomaterials whose

shape and structure depend on the nature of protein biomacromolecules. Due to the water

soluble nature of BSA, it acts as a capping as well as stabilizing agent for colloidal PbS NCs,

while thermal denaturation of BSA effectively alters this property. An important dependence

of NC morphology on the native to denatured states of BSA has been observed where latter

state proves to be quite effective in controlling the NC shape and size. At 40 oC, large

spherical PbS NCs are obtained and their size decrease as temperature is increased to 80 oC.

Tong et al.98

reported a simple biomolecule-assisted synthesis of ZnS nanostructured spheres

assembled from ZnS NCs with the controllable crystal phase and morphology. L-Cysteine, a

biomolecule, was used as the sulfur source and played a key role in the formation of ZnS

nanostructured spheres. Wu et al.99

studied a biomolecule-assisted hydrothermal route for

generating SnO2 with diameters <10 nm. SnO2 is an n-type semiconductor with the free

exciton Bohr radius of 2.7 nm. The degradation of rhodamine B (RhB), an organic dye in

aqueous suspension is selected as a probe reaction to evaluate the catalytic activity of

semiconductor photocatalytic performance. Zheng et al.100

reported the nanocrystalline ZrO2

with narrow size distribution and mean size of about 8 nm by the L-lysine assisted

hydrothermal method. The structural and morphological characterizations were studied by

XRD and TEM, and physicochemical characterizations were carried out by using infrared

spectra (IR), UV-visible spectra, and photoluminescence (PL) spectra.

Sarkar et al.101

studied the development of semiconductor CdS NCs (QDs of average

diameter less than 2 nm) directly conjugated to a transporter protein human serum albumin

(HSA) as fluorescent biological labels. This study is likely to attract widespread attention as a

powerful tool for the study of protein folding. Liu et al.102

prepared PbS fishbone-like

architectures by using a biomolecule (L methionine)-assisted approach in a mixture solvent

made of ethanolamine (EA) and distilled water. The as-prepared PbS products were

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examined by using XRD, field emission scanning electron microscope (FESEM), TEM, high

resolution transmission electron microscopy (HRTEM), selected area electron diffraction

(SAED) and PL. Chen et al.103

reported well-defined hexangularly faced CdS nanorod arrays

which were fabricated via a facile one-step and non template hydrothermal approach in large

scale by using biomolecules of glutathione as capping agents. Structural and morphological

evolutions of CdS nanorod arrays were studied by SEM, TEM, and XRD. A formation

mechanism of CdS nanorod arrays via this one-step synthesis was tentatively studied by

investigating the effects of synthesis parameters on the nanorod arrays. The growth process

of CdS nanorod arrays was discussed further from the absorption spectra of CdS nanorod

arrays obtained at different reaction times.

Zuo et al.104

prepared nanocube-based pagoda-like PbS hierarchical architectures

which were fabricated by hydrothermal treatment of Pb(Ac)2 and L-cysteine solution. It was

suggested that a biomimetic mineralization process happened during the growth of the

hierarchical architectures. The biomolecule, L-cysteine, exerts coordination, oriented

nucleation of crystals, and the morphology modulating effect. By studying the intermediates

of the reaction, they observed that 4-fold symmetric star-shaped microcrystals were formed at

first, and a second nucleation process resulted in the generation of nanocube-based pagoda-

like hierarchical architectures. Xiang et al.105

reported Ag2S nanospheres which were

synthesized by a hydrothermal reaction using L-cysteine as the sulfur source and chelating

reagent. The XRD and X-ray photoelectron spectroscopy (XPS) confirmed that the products

were monoclinic α-Ag2S. The optical absorption spectra of the Ag2S nanospheres showed

very broad absorption peaks centred at about 515 nm in wavelength. PL spectra exhibited

emission peaks centered at about 637 nm in wavelength accompanied by weaker shoulder

peaks at nearly 590 nm in wavelength when the sample was excited with a wavelength of 490

nm. Mi et al.106

designed a novel “green” chemical route to prepare nanostructured Bi2Te3 in

near-critical water using the biomolecule alginic acid as reductant.

Zhao and Qi 107

have also carried out synthesis of star-shaped PbS NCs by the

thermal decomposition of thioacetamide (TAA) in aqueous solutions of lead acetate in the

presence of the cationic surfactant (CTAB) and the anionic surfactant sodium dodecyl sulfate

(SDS). A low-magnification SEM image of the PbS product obtained after a reaction time of

5h, indicates the exclusive formation of uniform star-like NCs. The related XRD pattern

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shows sharp peaks corresponding to cubic PbS with a rock salt structure, confirms the

formation of pure PbS NCs. Reaction temperatures of 190-250 °C and multicomponent

surfactant mixtures result in a nearly defect-free crystal lattice and high uniformity of

nanowire diameter along the entire length. In addition to straight nanowires, zigzag, helical,

branched, and tapered nanowires as well as single-crystal nanorings can be prepared in one-

pot reactions by careful adjustment of the reaction conditions. Wang et al.108

gave a novel

and simple one-step solid-state reaction in the presence of a suitable surfactant. They have

synthesized PbS NPs with the diameters of 10-15 nm by using the above method. The PbS

NPs were characterized by XRD, TEM, HRTEM, UV-visible absorption, and XPS. The role

of surfactant C18H37O(CH2CH2O)10H (abbreviated as C18EO10) in the formation of PbS NPs

was discussed, and the results indicated that C18EO10 played an important role in the

preparation of PbS NPs. Gautam and Seshadri109

employed a new solvothermal route for the

preparation of NCs of PbS and PbSe, involving a reaction of lead stearate with sulfur or

selenium and tetralin (tetrahydronaphthalene) in toluene solvent. The NCs were characterized

by powder XRD and electron microscopy. The use of surfactant Triton X-100 resulted in

both nanorods and nanoparticles of PbSe. Wang et al.110

prepared cross-shaped PbS crystals

composed of six pods by refluxing. Parameters affecting the morphology of PbS have been

investigated systematically. Results reveal that various PbS structures including cubic,

truncated octahedral, flower-shaped and dendritic crystals were obtained by changing the

sulfur and lead source, the solvent or the surfactant.

Zhu et al.111

reported the PbSe NPs of about 12 nm in size. They have prepared them

by a pulse sonoelectrochemical technique from an aqueous solution of sodium selenosulfate

and lead acetate. The PbSe NPs were characterized by TEM, XRD, absorption spectroscopy,

diffuse reflection spectrum, and energy-dispersive X-ray (EDX). Bierman et al.112

studied a

chemical vapor deposition (CVD) synthesis of hyperbranched single-crystal nanowires of

both PbSe and PbS using PbCl2 and S/Se as precursors under hydrogen flow. Multiple

generations of nanowires grow perpendicularly from the previous generation of nanowires in

an epitaxial fashion to produce dense clusters of a complex nanowire network structure. The

flow rate and duration of the hydrogen co-flow in the argon carrier gas during the CVD

reactions are found to have a significant effect on the morphology of the PbSe/PbS grown,

from hyperbranched nanowires to micrometer-sized cubes. Pietryga et al.113

reported the

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synthesis of PbSe colloidal QDs with efficient, particle-size-tunable, narrow band width mid-

IR photoluminescence at energies as low as 0.30 eV. Bulk PbSe has a band gap of 0.26 eV at

room temperature, so PbSe QDs have the potential to provide PL in the mid-IR energy range.

All QDs were characterized by PL and absorption spectroscopy, as well as by TEM. Pietryga

et al.114

had synthesized and further used PbSe QDs to produce heterostructured NCs

(PbSe/CdSe/ZnS core/shell) with bright, stable infrared emission. PbSe QDs, provide

efficient emission over a large spectral range in the infrared, but their application has been

limited by instability in emission quantum yield and peak position on exposure to ambient

conditions and hence this is overcome by making these core shell structures.

Ren et al.115

synthesized the hexagonal selenium (Se) nanowires by using a simple

vapor-phase growth with the assistance of the silicon powder as a source material, which

turned out to be very important in the growth of the Se nanowires. The morphology,

microstructure, and chemical compositions of the nanowires were characterized using various

means such as XRD, SEM, TEM, XPS, and Raman spectroscopy. XRD patterns of the

samples demonstrate that the nanowires have a pure hexagonal Se phase. EDS and XPS

results confirmed that the nanowires consist of Se, while a small amount of Se is in the state

of Se-O bonds sheathing the nanowires. TEM and SEM revealed that the length of nanowires

is up to several micrometers and the diameter of nanowires can be as thin as 20 nm. HRTEM

analysis depicted the detailed crystalline structures of the Se nanowires. Raman spectra of Se

nanowires were compared with that of the bulk Se powder. High-yield synthesis of bamboo-

raft-like single-crystalline Se superstructures had been realized for the first time by Song et

al.116

via a facile solvothermal approach by reducing SeO2 with ethylene alcohol in the

presence of cellulose acetate. The formation of a raftlike superstructure with various forms is

strongly dependent on the temperature, amount of cellulose acetate, reaction time, and even

preheating treatment. The suitable amount of cellulose acetate is essential for the formation

of elegant and uniform raft Se. The morphology, microstructure, optical properties, and

chemical compositions of bamboo-raft-like Se were characterized using the following

techniques as XRD, FESEM, TEM, HRTEM, XPS, UV-visible spectroscopy, Fourier

Transform Infrared spectroscopy (FTIR) and Raman spectroscopy. Single-crystalline

nanobelts and nanowires of trigonal selenium (t-Se) have been selectively synthesized by Ma

et al.117

in micellar solutions of nonionic surfactants. In particular, t-Se nanobelts about 30

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nm in thickness were obtained in micellar solutions of poly(oxyethylene(20)) octadecyl ether

(C18EO20), whereas t-Se nanowires were obtained in micellar solutions of

poly(oxyethylene(10)) dodecyl ether (C12EO10). Elemental t-Se microrods have been

synthesized by Mondal et al.118

using a facile solution-phase biomolecule approach in the

presence of L-cysteine being used as both the ligand for the formation of the complex and a

capping agent under hydrothermal conditions. The phase analysis, purity, and morphology of

the product have been studied by XRD, SEM and Raman spectroscopy. Xiong et al.119

have

carried out synthesis of Se nanoneedles with the stem diameter ranging from 100-500 nm and

lengths up to tens of micrometers, gradually becoming thinner to form a sharp tip, which

were fabricated by reduction of sodium selenite (Na2SeO3)with poly(vinyl alcohol) (PVA).

An interesting feature of the nanoneedles is their tendency to form branches and junctions.

The morphology of Se nanoneedles were characterized by using various methods such as

XRD, FESEM, TEM, and HRTEM, indicating that the nanoneedles were single crystalline

with high purity, structurally uniform, and dislocation-free. Nath et al.120

have described the

synthesis of Se NPs through the reduction of aqueous selenious acid solution by sodium

borohydride. To prevent aggregation of the particles and to offer stability, a non-ionic

micelle, Triton X-100, has been introduced into the reaction medium. The NPs were

characterized by UV-visible spectroscopy, atomic force microscopy (AFM), and XPS

studies. The characteristic catalytic behavior of the Se particles is established by studying the

decolorization of methylene blue in the presence of UV light. It has been authenticated from

the study that the NPs afforded a complete mineralization process and the rate of dye

decolorization varies linearly with the NP concentration. Song et al.121

have reported Se/C

nanocables through the reduction of Na2SeO3 with glucose in the presence of CTAB under

hydrothermal conditions. In the process, glucose acts as a reducing agent and carbon source,

and the final morphology of the product was determined by the CTAB concentration. The

products are characterized in detail by XRD, EDX, SEM, and TEM. The results show that the

obtained products are coaxial nanocables with lengths of 2-6 µm, about 300-500 nm in

diameter, and a surrounding sheath about 20-30 nm in thickness. It is of great importance and

wide application that the obtained Se/C coaxial nanocables could be tailored freely by an

electron beam of TEM. Zhang et al.122

have reported solution-phase approach to the large-

scale synthesis of faceted single-crystalline Se nanotubes, in the presence of CTAB. Shah et

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al.123

gave a new simple wet chemical method to synthesize Se NPs (50-100 nm), by reaction

of sodium selenosulphate precursor with acrylonitrile monomer, under ambient conditions.

PVA has been used to stabilize the Se NPs.

Bakshi et al.124

reported Au nanoribbons in aqueous phase under ambient conditions

by using dimethylene bis(tetradecyldimethyl-ammonium bromide) (abbreviated as 14-2-14)

as a capping agent as well as a soft template. A two steps seed-growth (S-G) method was

used. The first step of S-G method mainly gave nanorods of high aspect ratio along with NPs

of other shapes, but the next step produced mainly fine Au nanoribbons of several

micrometers long, 50-150 nm wide, and ≈ 5 nm thick. They were characterized by TEM,

XPS, EDX, and XRD. Sau et al.125

reported the short Au nanorods of average lengths ranging

between 20 and 100 nm (with corresponding aspect ratios of 2 and 4). These nanorods were

characterized by dark-field microscopy, UV-visible spectroscopy, and TEM. Jana et al.126

followed S-G method to produce Au NPs of diameters 5-40 nm. The particle size can be

controlled by varying the ratio of seed to metal salt, and thus any size in the range 5-40 nm

can be prepared. Shi et al.127

gave a method to produce core-shell structures consisting of

monodisperse polystyrene latex nanospheres as cores and Au NPs as shells. Use of

polystyrene spheres as the core in these structures is advantageous because they are readily

available commercially in a wide range of sizes, and with dyes or other molecules doped into

them. Au NPs, ranging in size from 1-20 nm, are prepared by reduction of a Au precursor

with sodium citrate or tetrakis(hydroxymethyl)phosphonium chloride (THPC). Wei and Qian

128 also reported the fabrication of Au NPs by UV photoactivation in the presence of

biopolymeric chitosan and the tracing of the Au salt solution aging. Detailed UV-visible

spectroscopy study witnessed the evolution of the surface plasma resonance (SPR) absorption

during the Au NPs growth. The effect of chitosan in aqueous solution for the Au NPs

preparation was investigated in detail. The results indicated the size and distribution of Au

NPs could be controlled over by altering the concentration of chitosan, and the Au NPs

growth during aging was a chitosan-mediated autocatalytic process. FTIR showed that the

hydroxyl in molecular chitosan was oxidized to carbonyl groups in the fabrication of Au NPs

after aging and nitrogen atoms are the main sites for the complexation of chitosan with Au

atoms. Huang and Yang129

studied that the Au NPs were prepared by reducing Au salt with

chitosan, in the absence/presence of tripolyphosphate (TPP). Here, chitosan acted as a

INTRODUCTION

16

reducing/stabilizing agent. Sarma and Chattopadhyay 130

reported the synthesis of Au NPs

with tunable longitudinal plasmon band and shape selectivity, mediated by starch in the

presence of ultrasonic waves. The synthesis was carried out by reduction of HAuCl4, at

various concentrations, using H2O2 as the reducing agent. The conformational changes of

BSA in the albumin : Au NP bioconjugates were investigated in detail by Shang et al.131

by

using various spectroscopic techniques including UV-visible absorption, fluorescence,

circular dichroism, and FTIR spectroscopies.

Nanocrystalline CdS particles directly conjugated BSA protein were prepared by

Meziani et al.132

by applying the supercritical fluid processing technique, rapid expansion of

a supercritical solution into a liquid solvent. The direct conjugation takes advantage of the

unique features of the process for NPs formation. The BSA-conjugated CdS NPs in stable

aqueous suspension or in the solid state were characterized by using microscopy, XRD, and

optical spectroscopy methods. The results show that well-dispersed CdS NPs are coated with

BSA in a core-shell-like arrangement and that the protein species associated with the NPs

remain functional according to the modified Lowry assay. Highly water soluble and

biocompatible L-cysteine-capped CdS NPs having narrow size distribution were synthesized

by Chatterjee et al.133

for the first time by γ -irradiation technique without using any

additional stabilizer. FTIR study shows that CdS NPs are capped through mercapto-group of

cysteine amino acid while its free amino and carboxylate groups make it amenable to

bioconjugation. Size and luminescence of the NPs can be well controlled by varying the

parameters like radiation dose, pH and concentration of cysteine. He and Urban134

gave a

communication which outlines a simple two-step approach of modification of 1 nm diameter

Au NPs using an aqueous solution of (1,2-dipalmitoyl-sn-glycero-3-phosphothio-ethanol)

phospholipid. TEM as well as particle size analysis show that, as a result of phospholipid

reactions with Au particles, the initial Au NP size increases to 5 nm. Considering the size of

the phospholipid and their ability to form liposomes, 5 nm diameter spheres indicate that the

phospholipid bilayer was attached to the surface of Au particles and the phospholipid-Au

interactions are facilitated by the presence of thiol functionality.

1.5 Research Plan

In view of all these studies, a systematic and comprehensive work to synthesize and

characterize metal and semiconductor NPs by using a series of biomolecules such as BSA,

INTRODUCTION

17

zein protein, phospholipids, DNA, and chitosan has been carried out. The main goal of this

study was to achieve the shape controlled synthesis by utilizing the stabilizing as well as

surface active properties of these complex molecules which range from high molecular

weight proteins to small phospholipids. Various factors such as folding/unfolding of proteins,

hydrophilic/hydrophobic properties, and their interfacial adsorption have been compared and

discussed to achieve the shape controlled morphologies at nanoscale. Likewise, the material’s

properties related to the nucleation and subsequent growth of NPs under the capping and

stabilizing effects of these biomolecules have been explored and discussed on the basis of

crystal structures of various semiconducting and noble metal NPs. Keeping in view of the

film making properties of zein protein, zein conjugated Au NPs have further been used in the

environmental friendly biodegradable protein film formation for their industrial applications

especially in the food and pharmaceutical industries. It has been shown that Au NPs

incorporated zein films have much stronger tensile strength and flexibility than pure zein

protein films normally used for such applications. Finally, all reactions have been carried out

and standardized in aqueous phase so as to preserve the biofunctionalities of biomaterials in

view of environmental concerns and green chemistry. We have carried out the above work to

achieve the following objectives:

1. Synthesis and characterization of metal chalcogenides and noble metal nanocrystals

by using various biomolecules as capping or stabilizing agents.

2. Evaluation and influence of molecular and structural factors of different kinds of

biomolecules on the shape directed synthesis of biomaterials at nanoscale.

3. Use of bioconjugated nanomaterials for the synthesis of biodegradable protein films

for their industrial applications.

INTRODUCTION

18

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