Abstract
Silver nanoparticles (AgNPs) have a large number of applications in
technology and physical and biological sciences. These nanomaterials can
be synthesized by chemical and biological methods. The biological
synthesis using fungi represents a green approach for nanomaterial
production that has the advantage of biocompatibility. This work studies
silver nanoparticles (AgNPs) produced by fungi Rhodotorula glutinis and
Rhodotorula mucilaginosa found in ordinary soil of the Universidade
Federal do Ceara campus (Brazil). The biosynthesized AgNPs have a
protein-capping layer involving a metallic Ag core. The focus of this
paper is to investigate the size and structure of the capping layer, how
it interacts with the Ag core, and how sensitive the system (core +
protein) is to visible light illumination. For this, we employed SEM,
AFM, photoluminescence spectroscopy, SERS, and dark-field spectroscopy.
The AgNPs were isolated, and SEM measurements showed the average size
diameter between 58 nm for R. glutinis and 30 nm for R. mucilaginosa.
These values are in agreement with the AFM measurements, which also
provided the average size diameter of 85 nm for R. glutinis and 56 nm
for R. mucilaginosa as well as additional information about the average
size of the protein-capping layers, whose found values were 24 and 21 nm
for R. mucilaginosa and R. glutinis nanoparticles, respectively. The
protein-capping layer structure seemed to be easily disturbed, and the
SERS spectra were unstable. It was possible to identify Raman peaks that
might be related to alpha-helix, beta-sheet, and protein mixed
structures. Finally, dark-field microscopy showed that the silver cores
are very stable, but some are affected by the laser energy due to
heating or melting.
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