Biomedical Engineering Reference
In-Depth Information
4.4 Nanoparticles
Nanoparticles are a class of materials with properties distinctively dif erent
from their bulk and molecular counterparts. Colloidal dispersions of metal
nanoparticles having size much smaller than wavelength of visible radia-
tion exhibit intense colours. Art of making coloured glass is known over
thousand years. Small amount of metal nanoparticles such as gold, silver,
copper etc. doped in glass give rise to beautiful colours [9]. Windows of
churches, palaces etc. are ot en decorated with such glasses. One such win-
dow of Milan cathedral, having small gold particles as colorant. Although
technique of making coloured glass had been known since long time, it was
not known that it is because of the presence of the metal nanoparticles in
glass, until Michael Faraday in 1857 synthesized gold nanoparticles. He got
ruby red and pink colour dispersion of gold particles.
Nanoparticles can be synthesized by growing, shaping or assembling the
materials by:
Physical
methods
Synthesis of
nanoparticles
Hybrid
methods
Chemical
methods
Biological
methods
Broadly speaking synthesis of nanomaterials can be divided in to two cat-
egories viz. top down and bottom up approach [11]. In “top-down” approach,
macroscopic particles can be reduced to the nanosize by removal of material.
h is approach involves milling, machining and lithography techniques. On
the other hand “bottom up” approach involves aggregation of atoms to form
particles of dei nite size, shape or structure. Bottom up approach consists
of physical as well chemical methods. h e advantages of chemical methods
over physical methods are that they are relatively simple, inexpensive, low
temperature techniques and do not require sophisticated equipment. h e
materials can be synthesized in various shapes, sizes and structures [12].
