PHYS01200704032 Debes Ray - Homi Bhabha National Institute

this method is limited by the longer synthesis time which increases as the number of steps
increased to increase the yield. In the second method (additional reductant method), the
presence of additional reductant (e.g. trisodium citrate) is utilized to enhance the reduction
and hence yield. The nanoparticle yield has been found to increase drastically with gold salt
concentration in presence of additional reductant and has been synthesized up to two order
higher gold salt concentrations than earlier works. This method can be viewed as the additive
effect of the enhanced reduction by trisodium citrate with control and stabilization by the
block copolymers. The size of the nanoparticles also increases with the nanoparticle
concentration. The time-dependent decrease in the concentration of nanoparticles observed at
higher gold salt concentrations is related to the increased surface coating of gold
nanoparticles.
Chapter 7 presents optimization of high yield synthesis of gold nanoparticle for
probing their interaction with proteins [19, 20]. The stable and high-yield gold nanoparticles
have been synthesized at very low block copolymer concentration (decrease of 3 orders) to
minimize any direct interaction of proteins with the block copolymer. The faster formation
rate of gold nanoparticles is found with higher value of block copolymer concentration in
these systems. The stability and yield of nanoparticle remain same irrespective of the large
decrease in block copolymer concentration. The nanoparticle structure is also found identical
irrespective of block copolymer concentration. The interaction of these gold nanoparticles
with two model proteins, lysozyme and bovine serum albumin (BSA) has been examined. It
has been found that gold nanoparticles form stable solutions over a wide concentration range
of BSA whereas phase separate even with small amount of lysozyme protein at physiological
conditions. These results can be explained on the basis of that citrate ions are adsorbed on the
gold nanoparticles make it negative, as a result their complex with positively charged
lysozyme phase separates whereas it remains stable with similarly charged BSA. The
complexes of gold nanoparticles with BSA have been studied using UV-visible spectroscopy,
zeta potential and SANS. The presence of BSA shows a red shift in the SPR peak and is
believed to be due to the changes in the dielectric nature surrounding the nanoparticles
without and with protein conjugation. Further the conjugation of BSA with gold
nanoparticles is supported by the zeta potential measurements of nanoparticles in presence of
varying protein concentration. SANS data of nanoparticle-protein conjugates have been
found to be significantly different than that of addition of individual contributions from gold
nanoparticles and BSA. The build-up of scattering intensity in the low-Q region for the
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