a 4:1 nanoparticle:Con A complex at neutral pH. The
complex can be dissociated by the disaccharide isomaltose
which competitively binds to Con A. In another report, the
importance of solution pH was mentioned [41]. In alkaline
pH (pH 12) an aminodextran solution yields spherical
uniform AuNPs (20 nm) while acidic pH favours the
formation of large Au crystals of other shapes. Dextran was
also used as a reducing agent and surface coating material
for the synthesis of stable, biocompatible AuNPs [42]. In
this case, dextran was cross-linked using epichlorohydrin
and aminated by ammonium hydroxide. The resulting
nanoparticles exhibited colloidal stability at elevated
temperatures, extreme pH, high salt concentration and in
common biological buffers.
2.7 Alginic acid
Alginic acid is a polysaccharide widely distributed in the cell
walls of brown algae. It has homopolymeric blocks of (1,4)-
linked b-D-mannuronic acid (M) and a-L-glucuronic acid (G)
where they are C-5 epimers of each other (Fig. 1g). These
homopolymeric blocks are made of several types, including
G-block regions, M-block regions and alternating regions
[43]. Alginic acid has many applications, including use as a
pharmaceutical excipient in drug products and contributions
to drug delivery systems [44]. It is used in the food industry
as a stabiliser and as a thickener [43]. AgNPs and AuNPs
were synthesised with calcium alginate via a photochemical
approach using a UV light source (365 nm wavelength) and
were evaluated as a solid-phase heterogeneous catalyst for
industrial applications [45]. Calcium alginate gel served as
both a reducing agent and stabiliser and the resulting
nanoparticles were spherical and crystalline with a size of
less than 10 nm. Their catalytic activity was assessed by
the reduction of 4-nitrophenol to 4-aminophenol, and was
found to be very efficient.