Biosynthesis of Metallic Nanoparticles and Their Applications - Intracellular Delivery: Fundamentals and Applications - page 377

Biosynthesis of NPs is becoming an emerging consequence of overlap between
nano- and biotechnology. In the last few years it has received attention due to its
potential to develop environmentally benign technologies in material science. But
in fact, this type of NP synthesis method is also a “chemical” approach. Living cells
are extremely complex system with thousands of molecules. These molecules have
varied functional groups (such as hydroxyl, amine etc.) which each can possibly
facilitate metal reduction. Therefore, it is very difficult to describe a specific place
or process responsible directly for NP growth. This can result in certain drawbacks
for biosynthesis methods. The resulting matter is usually mixture of cells (cell
debris) and NPs, accompanying with thousands of metabolic products and other
molecules. Frequently it is very complicated to separate the tiny product particles
from the cell debris. Moreover, surrounding matrix and capping proteins contribute
to NP stability (Lynch and Dawson 2008 ) and can influence their properties.
Among the other disadvantages of precursors (such as AgNO 3 ) is their toxicity to
the target organisms. Therefore, this does not allow the usage of higher concentra-
tions of the salts.
In this article, we provide a brief overview of the current research worldwide on
the use of organisms such as bacteria, cyanobacteria and actinomycetes (both
prokaryotes), as well as algae, yeast, fungi and plants (eukaryotes) in the biosyn-
thesis of metal NPs with emphasize on their applications.

3 Applications of Metallic Nanoparticles

Although current research results show a wide field for biosynthesized NPs, we can
segment these applications into several groups. The following division is based
primarily on the purpose of biofabricated NPs (even though the chemical composi-
tion, shape and source organisms will be mentioned too).

3.1 Biosorption

Different organisms have ability to change metal oxidation state and concomitantly
deposit resulting metal compounds and zero-valent metals on the cell surface or
inside their cells. A variety of biomaterials have been known for a long time to bind
the precious metals (including algae, fungi, bacteria, actinomycetes, yeast etc.).
along with some biopolymers and biowaste materials (Table 1 ).
In particular, recovery of precious metals like gold, silver, palladium, and plati-
num is interesting due to their increasing market prices and various industrial appli-
cations. Conventional technologies (e.g. ion exchange, chemical binding, surface
precipitation) which been have been developed for the recovery of such metals are
neither efficient nor economically attractive. Biosorption represents a biotechnologi-
cal innovation as well as a cost effective tool for recovery of precious metals from