Vibrational Spectroscopy and Morphological Studies on Protein-Capped Biosynthesized Silver Nanoparticles

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 Cearácampus (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 α-helix, β-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.

Green Route Synthesis and Characterization Techniques of Silver Nanoparticles and Their Biological Adeptness

“… 118 , 121 Finally, the lower signal-to-noise ratio and spatial resolution are the major drawbacks of SEM in comparison to transmission electron microscopy (TEM). 112 Agressott et al 122 described the manufacture of AgNPs using fungus, with SEM pictures showing AgNPs of various sizes and spherical forms, as seen in Figure 14 .…”

“… (a) R. glutinis AgNP SEM image and (c) size histogram. (b) R. mucilaginosa AgNP SEM image and (d) size histogram (reprinted with permission from ref ( 122 )). …”

Streptomyces catenulae as a Novel Marine Actinobacterium Mediated Silver Nanoparticles: Characterization, Biological Activities, and Proposed Mechanism of Antibacterial Action

“…One drop was put onto a 0.2 mm-thick glass substrate using a micropipette and covered for 48 h at room temperature. The optical microscope was equipped with a 100/NA = 0.90 objective lens and was coupled to a Raman spectrometer (WITec alpha 300) ( Agressott et al, 2020 ).…”

Dark-Field Microscopy: Recent Advances in Accurate Analysis and Emerging Applications

“…By rotational tracking of a single anisotropic nanoprobe under DFM, spatiotemporal heterogeneous gelation was directly observed (Figure A) . During spectroscopy and morphology studies of protein-capped silver nanoparticles, although the silver cores were found to be quite stable, laser energy-induced heating or melting still affected some of them . The three-dimensional defect distribution of the transparent optical components (TOCs) could be detected by coaxial transmission DFM .…”

“…119 During spectroscopy and morphology studies of protein-capped silver nanoparticles, although the silver cores were found to be quite stable, laser energy-induced heating or melting still affected some of them. 120 The threedimensional defect distribution of the transparent optical components (TOCs) could be detected by coaxial transmission DFM. 121 The iDFM exhibited a better imaging performance in the optical imaging of the high aspect ratio nanostructures, leading to a substrate, which further led to improved segmentation during image analysis.…”