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then we can expect the concentration of the loaded compound to
eventually become equal to its concentration in bulk solution. This
was found to be true for fluorescent-labeled HSA as quantified by
confocal microscopy [99]. However, in some cases enzymes have
been encapsulated at an internal concentration of over three orders
of magnitude greater than the bulk value [103, 104], and we have
incorporated silver nanoparticles at an effective concentration four
ordersofmagnitudegreaterthanthebulkvalue[105].Thissuggests
anadditionaldrivingforceforencapsulation,possiblyadsorptionto
either the innercapsule wallsor to undissolved core material.
Incorporation of nanoparticles:
Metal nanoparticles were first
incorporated into the shells of hollow capsules [106] in order
to trigger light-assisted opening of the capsules [107-109]. This
technique was directed at the localized delivery of drugs at a
high dosage, the concept being that illumination in the near-IR
wavelength would cause heating of the nanoparticles and thus
degrade the shell walls. So far, hollow shells have been modified
by silver [108, 110, 111], gold [107, 109, 112, 113], and palladium
[110]. The modification has been performed by (a) depositing
(PAH/PSS)
2
onto a latex core, reducing Ag
+
onto the layers, then
depositing a further (PAH/PSS)
2
, followed by core dissolution [106,
108], or (b) forming (PAH/PSS)
n
shells by core dissolution and then
incubating with metal nanoparticles to allow adsorption, followed
by deposition of afurther PSS layer[109].
We have found that Ag nanoparticles can be entrapped con-
veniently in (PAH/PSS)
4
shells by pH manipulation, as shown in
Fig. 8.11 [105]. Because previous research was directed at light-
assistedcapsuleopening,therehasnot,tothebestofourknowledge,
been any attempt to quantify the nanoparticle loading of the
capsules. However, as described below, this can be achieved to an
order of magnitude accuracy via voltammetry, UV absorbance, and
TEM. Using this process we estimated our loading as approximately
78 silver nanoparticles per capsule. From the mean size of the
nanoparticles(diameter
=
15.8nm),thiscorrespondstotherelease
of 9
×
10
6
Ag
+
ions after acid dissolution. To determine the
distribution of the nanoparticles, we applied the same method
of quantification to nanoparticles adsorbed onto glass cover slips
