There are two approaches for the manufacturing of nanomaterials: The “top-down” approach, which involves the breaking down of large pieces of material to generate the required nanostructures from them. The “bottom-up” approach, which implies assembling single atoms and molecules into larger nanostructures. Bottom-Up includes:- Sol gel method Template Assisted Synthesis Chemical Precipitation Microwave Assisted Synthesis Self Assembly Top-Down Includes:- Mechanical Milling High Pressure Torsion Laser Ablation Chemical Etching Sputtering

1. TOP-DOWN AND BOTTOM-UP APPROACH IN
SYNTHESIS OF NANOPARTICLES
Presented By-Lubhanshi Raje Shisodia
ROLL NUMBER-221240
MSc Biotechnology

2. Introduction
 The synthesis of nanoparticles can be approached using either a top-down or
bottom-up approach, each with its own advantages and limitations. These
approaches are used in nanotechnology to create nanoparticles with specific
properties and characteristics.

3. Top-Down Approach:
In the top-down approach, larger bulk
materials are broken down into smaller
nanoparticles through various
mechanical, chemical, or physical
methods. This method is used for
carving or sculpting a larger piece of
material into a desired shape at the
nanoscale.

4. Mechanical Milling:
Mechanical milling is usually
done using a planetary ball mill.
A refractory or steel ball's
energy transmission to a
powder relies on the rotating
(vibration) speed, size and
quantity of balls, ball-to-powder
mass ratio, duration and milling
environment. The shear action
of grinding produces
nanoparticles. Mechanical
milling is used to change the
properties of silver powders,
including disintegration of
particle aggregates, particle
shape, and particle surface
characteristics.

5. Laser Ablation:
Laser ablation or photoablation is
the process of removing material
from a solid surface by irradiating
it with a laser beam. At low laser
flux, the material is heated by the
absorbed laser energy and
evaporates or sublimates. At high
laser flux, the material is typically
converted to a plasma.

6. High Pressure Torsion:
In this the material sample is
subjected to very high pressure
typically in the gigapascals with the
help of equipment such as
hydraulic press machine along with
high pressure then sample is
subjected to torsion or shear this
means the material is twisted or
rotated along with pressure. Atoms
arrange themselves into regular,
repeating patterns to form a crystal
lattice The grain size is a measure
of how large or small these
individual crystalline structures are
within a given material

7. Chemical Etching:
In this technique chemical is used
for the synthesis of nanoparticles
materials like metals and ceramics
.In this technique basically the
metal is first coated with masking
material like wax – this material
protect the areas that should not be
etched, then the masked sample is
submerged or exposed to the
chemical which ultimately helps in
breaking down the molecular bonds
which helps in the synthesis of
nanomaterials

8. Sputtering
The sputtering process involves the removal of
atoms or molecules from a solid target material and
their deposition onto a substrate to form a thin film.
The sputtering process takes place in a vacuum
chamber to eliminate the interference of air or other
gases. To initiate the sputtering process, a low-
pressure inert gas (commonly argon) is introduced
into the chamber. The gas is ionized and accelerated
by an electric field, forming positively charged ions.
These ions are then directed toward the target
material. When the accelerated ions strike the target
material, they transfer energy to the target atoms.
This energy causes the atoms in the target to be
dislodged from the target's surface. These dislodged
atoms are ejected with sufficient energy to become
vaporized. The vaporized target atoms travel through
the vacuum chamber and are deposited onto the
substrate, creating a thin film.

9. Bottom-Up Approach:
A bottom-up approach to the synthesis of
nanoparticles involves building or growing
nanoparticles from individual atoms or
molecules. This approach allows for
precise control over the size, shape, and
composition of nanoparticles and is
commonly used in nanotechnology and
materials science.

10. The sol–gel method
This method is based on the transformation of a sol (a colloidal suspension of
nanoparticles) into a gel-like network and the subsequent conversion of the
gel into solid nanoparticles. It consist of the metal cations called precursors is
added in the solvent to create a sol, then hydrolysis is done which helps in
breaking down the precursors into hydroxides then the hydrolysed particles
are condensed and form gel. Then the gel is carefully dried to remove solvent
leaving behind the nanopowder

11. Template-Assisted Synthesis:
In this technique templates or you
can say moulds are used for the
synthesis of nanoparticles, in these
templates precursor material is filled
. The precursor may be a metal salt or
a chemical compound depending on
the desired nanoparticle composition.
It is a technique used to produce
nanoparticles with controlled size,
shape, and properties by using
templates as scaffolds or molds for
the nanoparticles to form around.

12. Chemical Precipitation:
In this method, nanoparticles are
formed by the precipitation of ions
from a solution to create solid
particles. A reagent, often a
reducing agent or a precipitating
agent, is added to the precursor
solution. The reagent induces a
chemical reaction, causing the
metal ions to undergo a
precipitation reaction and form
solid nanoparticles. As the reaction
proceeds, solid nanoparticles form
and precipitate out of the solution.
The nanoparticles are then
separated from the solution
through processes like
centrifugation or filtration.

13. Microwave-Assisted Synthesis:
:
The reaction vessel containing the
precursor solution is placed in the
microwave cavity. When
microwaves are applied, the
molecules in the reaction mixture
absorb energy and become highly
energized. This localized and rapid
heating initiates the nanoparticle
synthesis. The tiny building blocks
in the liquid come together to form
the tiny particles. This is like
building a tiny LEGO structure
using the right pieces.

14. Self-Assembly:
Self-assembly is a fascinating process
where nanoparticles spontaneously
arrange themselves into organized
structures or patterns. This method is
widely used in nanotechnology to
create well-ordered and functional
materials.Nanoparticles are put down
in the liquid like water . Nanoparticles
as we know have the property of
magnet so they stick to each other like
magnets

15. Reference
 https://pubs.rsc.org/en/content/articlelanding/2016/me/c6me00016a
 https://www.semanticscholar.org/paper/Synthesis-and-Characterization-of-
ZnS-Nanoparticles-Hamed-
Ahmed/57810d96935cccd2b01aa7509ddc257eba6bec02
 https://pubs.rsc.org/en/content/articlehtml/2021/ma/d0ma00807a
 https://chat.openai.com/c/e91a929e-4bcb-492d-9247-75aec3fb463c