Coalescence of Nanoclusters and Formation of
Submicron Crystallites Assisted by
Binoj Nair and T. Pradeep*
Department of Chemistry and Regional Sophisticated Instrumentation Centre,
Indian Institute of Technology, Madras 600 036, India
Received April 6, 2002; Revised Manuscript Received May 13, 2002
strains, common in buttermilk, assist the growth of gold, silver, and gold
crystals of submicron dimensions upon exposure to the precursor ions. Several well-defined crystal morphologies
are observed. Crystal growth occurs by the coalescence of clusters, and tens of crystals are found within the bacterial
contour. Crystal growth does not affect the viability of the bacteria. Crystals are presumably nucleated through
nanoclusters, which are formed within as well as transported into the bacteria. Biomass with the crystals can be
harvested completely. Results point to potential applications in analytical chemistry, nanotechnology, medicine,
and metal ion recovery. Coalescence appears to be a route by which surface area of the crystal is reduced so that it
can be effectively protected to avoid biological damage.
Tomorrow’s technology is going to depend on nano-
It is predicted
that the impact of this technology will be felt greatly at
the interface of chemistry and biology.
The desire to
synthesize materials using efficient and green chemistry
approaches is considerable, which has led to the use of
microorganisms. Although efforts directed toward nano-
materials are recent, metal ion interaction with prokary-
otic species has been one of the focal points of research
for a long time.
Bacteria have been known to enrich
synthesize magnetite crystals,
as well as octa-
containing S and P, and recently, prepare
ceramic to metal composites
(cermets). Formation of
minerals by unicellular and multicellular organisms has
long been recognized; the synthesis of siliceous materi-
by diatoms and the preparation of gypsum and
by S-layer bacteria are some of the
examples. Single-crystalline semiconducting particles
such as CdS have been synthesized in algae.
recent addition into this biosynthesis approach is the
reduction of gold and silver by fungi.
Variety and diversity of this chemistry suggest nu-
merous possibilities with other, more common micro-
organisms. Herein we report the growth of gold, silver,
silver alloy crystals with well-defined mor-
phologies assisted by most common
found in buttermilk, when exposed to appropriate ions.
Accumulation of metals occurs to such an extent that