Biomedical Engineering Reference
In-Depth Information
interactions between Au nanoparticles and the aldehyde or ketone groups
present in the extract. Recently, we reported the synthesis of silver nanopar-
ticles using sugar industry waste (bagasse) under microwave treatment
[164]. h e nanoparticles were characterized using UV-Visible spectroscopy,
DLS, TEM and XRD. h e biomolecules attached to the nanoparticles were
characterized using FTIR. h e hydroxyl and aldehydic sugars of the bagasse
reduces the silver ions within 4 minutes. h e nanoparticles formed were
50-150 nm in size and spherical in shape.
8.2.1.5.2 Proteins/Enzymes
Due to the diverse structure of proteins as compared to polyols, the case of
bioreduction by proteins is more complicated. According to the FTIR analy-
sis of biosynthesized nanoparticles, the presence of amide I and amide II as
well as the C-O stretching bands are frequently observed, which indicate
the presence of protein functional groups [104, 105, 165]. h is suggests that
Au nanoparticles can bind to proteins through their free amine groups or
carboxylate ions of the amino acid residues. In fact, amino acid residues such
as arginine, cysteine, lysine and methionine are known to interact with Ag
ions [166]. It was proposed by some researchers that instead of bioreduc-
tion, proteins could act as stabilizing agents as well [160]. Highly stable and
monodispersed Au nanoparticles were obtained by electrostatic stabilization
via surface-bound amino acids [167]. h e roles of peptides as bioreducing
and biocapping agents were demonstrated by Ag nanoparticles synthesized
by cyclic peptides in the latex of
Jatropha curcas
[168] and targeted pep-
tides enriched with proline and hydroxyl-containing amino acid residues
[169]. A systematic study was carried out by Tan
et al.
[170] in which they
screened the reduction and binding capabilities of 20 natural amino acids
to Au ions. It was found that the reduction process was determined by the
extent of complexation between the peptide and metal ions. Wangoo
et al.
[171] demonstrated the preparation of Au nanoparticles in water directly
by complexion with glutamic acid, where the amino acid acted as both the
reducing and the stabilizing agent in a single one-step process. In a subse-
quent study, a well-studied protein-bovine serum albumin (BSA) was used
as a model protein for Au nanoparticle synthesis to investigate the contribu-
tions from its various functional groups [172]. It is an excellent candidate for
the synthesis because BSA contains a large number of Cys, Tyr, and charged
residues [173]. It was found that BSA could synthesize Au nanoplates in high
yield, under acidic conditions at physiological temperature (37 C), by using
its innate reducing and shape directing capabilities [172]. Besides function-
ing as a shape controlling agent under acidic conditions, BSA can also syn-
thesize very small Au nanoparticles (< 1 nm) under alkaline conditions, as
