68
K. Illath et al.
absorption corresponds to the plasmonic peak of 537 nm increased with reaction
time 10 min to 20 min. Beyond 20 min, the intensity of absorption is decreased.
Hence, the optimum reaction time of 20 min is needed in autoclaving the reaction
mixture. Effect of concentration of bioreductant LBG is also investigated; An increase
in the intensity of absorption is observed with increase in LBG. With 0.1% LBG,
the amount of bioreductant is not sufficient to reduce all the gold ions. Hence the
obtained spectrum is broad, and the peak is very weak (~579 nm). 0.2–0.5% of LBG
is found to be the optimum amount for producing spherical nanoparticles with a
narrow absorption band and sharp peak.
3.4.4 Miscellaneous Synthesis of MNPs
Apart from microorganisms and plant extracts, higher organisms can also be used to
synthesize MNPs. It has been reported that products from higher organisms such as
insects, birds, and mammals can be used to produce Pt NPs with controlled size and
shapes. As an example, protein from sheep milk, honey from the bee, and egg yolk
of quail were used to synthesize Pt NPs [92]. Table 2 summarizes the synthesis of
MNPs using biological methods along with the type of microorganism, location of
synthesis for specific metal, its shape, and size.
All the methods of synthesizing MNPs discussed above involve the use of conical
flask in a laboratory set up, which are known as conventional batch reactor-based
synthesis or macrosystems. Tuning the parameters to achieve the desired size, shape,
and crystallinity of NPs is technically challenging and difficult to attain in a batch
reactor. These difficulties can be overcome with the help of microfluidic technology.
3.5 Microfluidic Technology-Based Synthesis
Microfluidics is a part of micro-electro-mechanical system technology, which
involves the flow of fluid of 10
−9 to 10
−18 litres through micron-sized channels. Since
the dimension of the channel becomes very small, fluid flowing through a microfluidic
channel shows some fascinating features, which are different from those of macrosystems. Flow-through microfluidics is laminar, electro-osmotic flow is observed for
charged particles flow, and microfluidics has the ability to control water in channels,
the dimensions of which match with the Debye layer [131]. The key feature of the
microfluidic device is a high surface-area-to-volume ratio. It allows abrupt heat and
mass transfer, results in rapid cooling and heating of reagents, and maintains an
isothermal condition. Consumption of reagent in microfluidics is minimum, hence
the cost of synthesis is low, making transportation and storage safer. It also helps to
protect while handling toxic and inflammable solvents. The evolution of reactions in
the spatial and temporal domain is possible in microfluidics. At any point of time, the
reaction can be modified by controlling the reactant flow rate. Scaling up of products
can be performed by conducting parallel experiments at the same time. Further, it is
K. Illath et al.
absorption corresponds to the plasmonic peak of 537 nm increased with reaction
time 10 min to 20 min. Beyond 20 min, the intensity of absorption is decreased.
Hence, the optimum reaction time of 20 min is needed in autoclaving the reaction
mixture. Effect of concentration of bioreductant LBG is also investigated; An increase
in the intensity of absorption is observed with increase in LBG. With 0.1% LBG,
the amount of bioreductant is not sufficient to reduce all the gold ions. Hence the
obtained spectrum is broad, and the peak is very weak (~579 nm). 0.2–0.5% of LBG
is found to be the optimum amount for producing spherical nanoparticles with a
narrow absorption band and sharp peak.
3.4.4 Miscellaneous Synthesis of MNPs
Apart from microorganisms and plant extracts, higher organisms can also be used to
synthesize MNPs. It has been reported that products from higher organisms such as
insects, birds, and mammals can be used to produce Pt NPs with controlled size and
shapes. As an example, protein from sheep milk, honey from the bee, and egg yolk
of quail were used to synthesize Pt NPs [92]. Table 2 summarizes the synthesis of
MNPs using biological methods along with the type of microorganism, location of
synthesis for specific metal, its shape, and size.
All the methods of synthesizing MNPs discussed above involve the use of conical
flask in a laboratory set up, which are known as conventional batch reactor-based
synthesis or macrosystems. Tuning the parameters to achieve the desired size, shape,
and crystallinity of NPs is technically challenging and difficult to attain in a batch
reactor. These difficulties can be overcome with the help of microfluidic technology.
3.5 Microfluidic Technology-Based Synthesis
Microfluidics is a part of micro-electro-mechanical system technology, which
involves the flow of fluid of 10
−9 to 10
−18 litres through micron-sized channels. Since
the dimension of the channel becomes very small, fluid flowing through a microfluidic
channel shows some fascinating features, which are different from those of macrosystems. Flow-through microfluidics is laminar, electro-osmotic flow is observed for
charged particles flow, and microfluidics has the ability to control water in channels,
the dimensions of which match with the Debye layer [131]. The key feature of the
microfluidic device is a high surface-area-to-volume ratio. It allows abrupt heat and
mass transfer, results in rapid cooling and heating of reagents, and maintains an
isothermal condition. Consumption of reagent in microfluidics is minimum, hence
the cost of synthesis is low, making transportation and storage safer. It also helps to
protect while handling toxic and inflammable solvents. The evolution of reactions in
the spatial and temporal domain is possible in microfluidics. At any point of time, the
reaction can be modified by controlling the reactant flow rate. Scaling up of products
can be performed by conducting parallel experiments at the same time. Further, it is