3.2
Water-Based Gold Nanoparticle Synthesis
3.2.1
Advantages
1. Water is a good solvent for a number of metal ions as well as a variety of
capping molecules. The synthesis involves preparation of an aqueous gold salt
solution followed by reduction of the metal ions in a single step. It is therefore
considerably simpler than the multi-step Brust protocol [39].
2. No additional stabilization against aggregation of the gold nanoparticles is
required – surface bound ions (citrate ions, chloroaurate ions etc.) normally
stabilize the nanoparticles electrostatically in solution.
3. Electrostatic layer-by-layer assembly involving, for example, oppositely charged
polyelectrolytes/surfactants and nanoparticles may be readily accomplished on
suitably functionalized surfaces [58–61].
4. Nanoparticle shape control can be easily effected by using self-assembled structures such as micelles (arising due to spontaneous assembly of suitable surfactants in water) as templates [4–6].
5. Perhaps the biggest advantage of a water-based synthesis procedure is that
bioconjugation of the gold and other metal/semiconductor nanoparticles with
DNA [32], enzymes [62], antibodies [63] etc. may be easily accomplished.
3.2.2
Disadvantages
1. Ionic interactions limit the concentration of metal/semiconductor nanoparticles
in the aqueous phase to very dilute levels, a big drawback in biological labeling
of the nanoparticles.
2. Control over the particle size and monodispersity in a particular reduction protocol is not very good.
3. The gold nanoparticles do not spontaneously assemble into a close-packed hexagonal arrangement on solvent evaporation.
4. The nanoparticles synthesized in water are not easily separated from solution in
the form of a powder that would be readily re-dispersible in water after storage
[55–57].
3.3
Organic Solution-Based Synthesis of Gold Nanoparticles
3.3.1
Advantages
1. High degree of control may be exercised over the gold nanoparticle size, monodispersity [34] and chemical nature of the nanoparticle surface (via capping with
terminally functionalized thiols, amines, amino acids etc.) [39, 41–57].
3.3 Organic Solution-Based Synthesis of Gold Nanoparticles 33
Water-Based Gold Nanoparticle Synthesis
3.2.1
Advantages
1. Water is a good solvent for a number of metal ions as well as a variety of
capping molecules. The synthesis involves preparation of an aqueous gold salt
solution followed by reduction of the metal ions in a single step. It is therefore
considerably simpler than the multi-step Brust protocol [39].
2. No additional stabilization against aggregation of the gold nanoparticles is
required – surface bound ions (citrate ions, chloroaurate ions etc.) normally
stabilize the nanoparticles electrostatically in solution.
3. Electrostatic layer-by-layer assembly involving, for example, oppositely charged
polyelectrolytes/surfactants and nanoparticles may be readily accomplished on
suitably functionalized surfaces [58–61].
4. Nanoparticle shape control can be easily effected by using self-assembled structures such as micelles (arising due to spontaneous assembly of suitable surfactants in water) as templates [4–6].
5. Perhaps the biggest advantage of a water-based synthesis procedure is that
bioconjugation of the gold and other metal/semiconductor nanoparticles with
DNA [32], enzymes [62], antibodies [63] etc. may be easily accomplished.
3.2.2
Disadvantages
1. Ionic interactions limit the concentration of metal/semiconductor nanoparticles
in the aqueous phase to very dilute levels, a big drawback in biological labeling
of the nanoparticles.
2. Control over the particle size and monodispersity in a particular reduction protocol is not very good.
3. The gold nanoparticles do not spontaneously assemble into a close-packed hexagonal arrangement on solvent evaporation.
4. The nanoparticles synthesized in water are not easily separated from solution in
the form of a powder that would be readily re-dispersible in water after storage
[55–57].
3.3
Organic Solution-Based Synthesis of Gold Nanoparticles
3.3.1
Advantages
1. High degree of control may be exercised over the gold nanoparticle size, monodispersity [34] and chemical nature of the nanoparticle surface (via capping with
terminally functionalized thiols, amines, amino acids etc.) [39, 41–57].
3.3 Organic Solution-Based Synthesis of Gold Nanoparticles 33