(a) Scheme showing synthesis of Au–Pt core–shell
structure (PtNC), where 15 nm gold nanoparticles are used as seeds
for subsequent platinum overgrowth in the presence of polyvinylpyrrolidone
(PVP) as a stabilizer and l-ascorbic acid as a reducing agent.
Influence of PVP molecular weight on PtNC catalytic activity, measured
by the absorbance at 652 nm corresponding to the oxidation of TMB
by H2O2 (n = 3). In the absence
of PVP, significant aggregation occurred. (b) Catalytic activity of
PtNCs incubated in serological and protein-rich environments up to
24 h (n = 6). (c) Transmission electron micrographs
of PtNCs synthesized with varying AuNP seed concentrations to control
size: (i) 5 nM seeds and (ii) 0.3 nM seeds. (iii) High-resolution
TEM image of an individual PtNC formed from 0.3 nM seed concentration.
Inset shows the lattice fringes corresponding to platinum (111) and
(200). (iv) Selected area electron diffraction (SAED) pattern taken
from a single PtNC (ca. 120 nm) with diffraction
spots consistent with polycrystalline platinum with an FCC lattice.
(d) Number distribution of the hydrodynamic diameter of PtNCs formed
by varying [Au]:[Pt] measured by dynamic light scattering. Batches
were synthesized in the presence of different gold nanoparticle seed
concentrations: A, 5 nM; B, 1.2 nM; C, 0.6 nM; D, 0.3 nM; E, 0.15
nM; F, 0.08 nM; G, 75 pM ca. 120 nm PtNCs as seeds;
H, 40 pM ca. 120 nm PtNCs as seeds. (e) Intensity
of test line for antibody modified PtNCs (150 pM) varying in size
from ca. 50 to 280 nm (mean number distribution by
DLS) for detection of 100 pg·mL–1 p24 in FBS
with 5 min development in CN/DAB and H2O2. All
data are averaged from ≥3 independent measurements where error
bars represent the standard deviation from the mean.