54
K. Illath et al.
UV-Vis spectrum recorded during the synthesis revealed that as it progresses, the
absorption band for Au and Ag NPs narrowed, absorbance intensity increased, and
the plasmonic peak was shifted to low wavelength in the case of glucose and sucrose.
Prolong heating results in adhering metal particles as a layer on the glass substrate,
which causes a decrease in absorbance. After drying and sonicating, a blue shift was
observed, and it was more prominent with sucrose and glucose. Fructose reduced
NPs were distributed homogeneously concerning the size. Further, it was found that
Ag and Pd NPs were unable to produce with sucrose. Generally, sucrose hydrolyses
to glucose and fructose in the presence of an acid. In the case of HAuCl 4 and H 2 PtCl 6 ,
hydrolysed products take a longer time to reduce the metallic salt. But for Ag and
Pd, even in the lower pH using sucrose as reductant could not produce particles.
Compared to sucrose and fructose, glucose reduced NPs are smaller in size due to its
strong reducing capability, but actual TEM analysis is contradictory; smallest NPs
were obtained with fructose as reducing agent [77]. Table 1 lists the important works
in the synthesis of MNPs with liquid state method along with synthesis type, shape,
size, tuning parameters, and reaction condition.
3.4 Biological Methods
The biological method is an emerging approach to synthesize MNPs. It overcomes the
difficulties associated with traditional methods such as reaction complications, safety
issues, and high cost. Further, it does not utilize high pressure, temperature, energy,
and toxic chemicals. It is also known as biomimetic method or green synthesis. The
biological method of NPs synthesis involves the use of microorganisms and their
enzymes, plant products, or its extracts. In general, the method can be categorized
into two; bioreduction and biosorption. In the bioreduction method, with the help of
microorganisms and their enzymes, metal ions are reduced chemically into a stable
biological form. The formed MNPs can be safely separated from the sample, and
they are found to be inert and stable. In biosorption, metal cations in aqueous media
bind with the organism cell wall, and reaction between the cell wall and peptide
further results in the formation of stable MNPs [34, 78]. A schematic illustration of
the biological synthesis of MNPs is shown in Fig. 15. Biological species can be either
prokaryotic like bacteria or eukaryotic such as fungi, plants or extracts. Extracts are
mixed with precursor solution under controlled reaction condition, and the formation
of NPs are confirmed with the colour.
3.4.1 Nanoparticle Synthesis Using Fungi
Here, metal salts are reduced with the help of protein and enzymes secreted by fungi.
Generally used fungi for this purpose are Fusarium oxysporum, Aspergillus fumigatus, and Trichoderma reesei. Ag NPs can be easily prepared in this manner as
it can bind with cytoplasmic membrane due to electrostatic interaction; hence Ag
K. Illath et al.
UV-Vis spectrum recorded during the synthesis revealed that as it progresses, the
absorption band for Au and Ag NPs narrowed, absorbance intensity increased, and
the plasmonic peak was shifted to low wavelength in the case of glucose and sucrose.
Prolong heating results in adhering metal particles as a layer on the glass substrate,
which causes a decrease in absorbance. After drying and sonicating, a blue shift was
observed, and it was more prominent with sucrose and glucose. Fructose reduced
NPs were distributed homogeneously concerning the size. Further, it was found that
Ag and Pd NPs were unable to produce with sucrose. Generally, sucrose hydrolyses
to glucose and fructose in the presence of an acid. In the case of HAuCl 4 and H 2 PtCl 6 ,
hydrolysed products take a longer time to reduce the metallic salt. But for Ag and
Pd, even in the lower pH using sucrose as reductant could not produce particles.
Compared to sucrose and fructose, glucose reduced NPs are smaller in size due to its
strong reducing capability, but actual TEM analysis is contradictory; smallest NPs
were obtained with fructose as reducing agent [77]. Table 1 lists the important works
in the synthesis of MNPs with liquid state method along with synthesis type, shape,
size, tuning parameters, and reaction condition.
3.4 Biological Methods
The biological method is an emerging approach to synthesize MNPs. It overcomes the
difficulties associated with traditional methods such as reaction complications, safety
issues, and high cost. Further, it does not utilize high pressure, temperature, energy,
and toxic chemicals. It is also known as biomimetic method or green synthesis. The
biological method of NPs synthesis involves the use of microorganisms and their
enzymes, plant products, or its extracts. In general, the method can be categorized
into two; bioreduction and biosorption. In the bioreduction method, with the help of
microorganisms and their enzymes, metal ions are reduced chemically into a stable
biological form. The formed MNPs can be safely separated from the sample, and
they are found to be inert and stable. In biosorption, metal cations in aqueous media
bind with the organism cell wall, and reaction between the cell wall and peptide
further results in the formation of stable MNPs [34, 78]. A schematic illustration of
the biological synthesis of MNPs is shown in Fig. 15. Biological species can be either
prokaryotic like bacteria or eukaryotic such as fungi, plants or extracts. Extracts are
mixed with precursor solution under controlled reaction condition, and the formation
of NPs are confirmed with the colour.
3.4.1 Nanoparticle Synthesis Using Fungi
Here, metal salts are reduced with the help of protein and enzymes secreted by fungi.
Generally used fungi for this purpose are Fusarium oxysporum, Aspergillus fumigatus, and Trichoderma reesei. Ag NPs can be easily prepared in this manner as
it can bind with cytoplasmic membrane due to electrostatic interaction; hence Ag