Gold Nanoparticle Inclusion into Protein Nanotube
as a Layered Wall Component
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Abstract
We
describe the synthesis, structure, and catalytic activity of
human serum albumin (HSA) nanotubes (NTs) including gold nanoparticles
(AuNPs) as a layered wall component. The NTs were fabricated as an
alternating layer-by-layer assembly of AuNP and HSA admixture (a negatively
charged part) and poly-l-arginine (PLA, a positively charged
part) into a track-etched polycarbonate membrane (400 nm pore diameter)
with subsequent dissolution of the template. SEM images showed the
formation of uniform hollow cylinders of (PLA/AuNP-HSA)<sub>3</sub> with a 426 ± 12 nm outer diameter and 65 ± 7 nm wall thickness.
Transmission electron microscopy and energy dispersive X-ray measurements
revealed high loading of AuNPs in the tubular wall. HSAs bind strongly
onto the individual AuNP (<i>K</i> = 1.25 × 10<sup>9</sup> M<sup>–1</sup>), generating a core–shell AuNP-HSA
corona, which is the requirement of the robust NT formation. Calcination
of the (PLA/AuNP-HSA)<sub>3</sub> NTs at 500 °C under air yielded
red solid NTs composed of thermally fused AuNPs. From the mass decrease
by heat treatment, we calculated the weight of the organic components
(PLA and HSA) and thereby constructed a six-layer model of the tube.
The (PLA/AuNP-HSA)<sub>3</sub> NTs serve as a heterogeneous catalyst
for reduction of 4-nitrophenol with sodium borohydrate. Furthermore,
implantation of the stiff (PLA/AuNP-HSA)<sub>3</sub> NTs vertically
onto glass plate produced uniformly cylindrical tube arrays