Potential Application of Nanoparticles as Antipathogens - Advanced Materials for Agriculture, Food and Environmental Safety - page 349

12.10 Types of Nanoparticles

Nanoparticles exist in several forms, shapes and morphology such as:

• Nanocrystals: h ey are any crystalline nanomaterial with

at least one dimension ≤ 100nm. Nanocrystals can provide
ei cient light emission even while bulk material does not
[50, 75-76].

• Quantum dots: Semiconductor nanocrystals having all the

three dimensions in nano-range are ot en referred to as quan-
tum dots. h ese are zero-dimensional structures [77-78].

• Nanowires: Nanowires are the structures that have a thick-

ness or diameter constrained to tens of nanometers or less
and an unconstrained length. Nanowires can be used to link
tiny components into extremely small circuits. h ese are
1-dimensional structures.

• Nanoribbons: h ese are strips of graphene or silicate with

ultrathin width (<50nm).h ey can be produced by unzip-
ping or cutting open nanotubes.

12.11 Synthesis of Nanoparticles by Conventional

Methods

For the synthesis of nanoparticles, the i rst priority is to achieve large-scale
production in an economical manner [79]. h ere are two main methods
for the preparation of nanoparticles:

1. Top-down approach via milling
2. Bottom-up approach via chemical processes

12.11.1 Top-down approach

h is method is solely based on physical and microlithographic philosophy,
in contrast to the other approach, where atomic or molecular units are used
to assemble molecular structure, ranging from atomic dimensions up to
supramolecular structure in nanometer range. It mainly involves mechani-
cal/thermal cycle and yields:

• Broad size distribution (10-1000nm)
• Varied particle shape or geometry
• Impurities