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. 2022 Mar 4;12(3):163.
doi: 10.3390/bios12030163.

Effect of Graphene vs. Reduced Graphene Oxide in Gold Nanoparticles for Optical Biosensors-A Comparative Study

Ana P G Carvalho  1 , Elisabete C B A Alegria  1   2 , Alessandro Fantoni  3   4 , Ana M Ferraria  5   6 , Ana M Botelho do Rego  5   6 , Ana P C Ribeiro  2
Affiliations

Effect of Graphene vs. Reduced Graphene Oxide in Gold Nanoparticles for Optical Biosensors-A Comparative Study

Ana P G Carvalho et al. Biosensors (Basel). .

Abstract

Aiming to develop a nanoparticle-based optical biosensor using gold nanoparticles (AuNPs) synthesized using green methods and supported by carbon-based nanomaterials, we studied the role of carbon derivatives in promoting AuNPs localized surface plasmon resonance (LSPR), as well as their morphology, dispersion, and stability. Carbon derivatives are expected to work as immobilization platforms for AuNPs, improving their analytical performance. Gold nanoparticles (AuNPs) were prepared using an eco-friendly approach in a single step by reduction of HAuCl4·3H2O using phytochemicals (from tea) which act as both reducing and capping agents. UV-Vis spectroscopy, transmission electron microscopy (TEM), zeta potential (ζ-potential), and X-ray photoelectron spectroscopy (XPS) were used to characterize the AuNPs and nanocomposites. The addition of reduced graphene oxide (rGO) resulted in greater dispersion of AuNPs on the rGO surface compared with carbon-based nanomaterials used as a support. Differences in morphology due to the nature of the carbon support were observed and are discussed here. AuNPs/rGO seem to be the most promising candidates for the development of LSPR biosensors among the three composites we studied (AuNPs/G, AuNPs/GO, and AuNPs/rGO). Simulations based on the Mie scattering theory have been used to outline the effect of the phytochemicals on LSPR, showing that when the presence of the residuals is limited to the formation of a thin capping layer, the quality of the plasmonic resonance is not affected. A further discussion of the application framework is presented.

Keywords: AuNPs; Mie theory; biosensors; metal–graphene hybrid; simulations.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
LSPR of AuNP samples synthesized with 5% tea extract (Thea sinensis) at t1w (after 1 week) and t2w (after 2 weeks).
Figure 2
Figure 2
LSPR of AuNPs synthesized with 5% tea (w/w) extract and after the addition of G, GO, and rGO, one week after their synthesis (t1w).
Figure 3
Figure 3
TEM images. (a) AuNPs in 5% tea extract. (b) rGO-supported AuNPs in 5% tea extract.
Figure 4
Figure 4
Schematic illustration of AuNPs anchored on the surface of reduced graphene oxide (rGO).
Figure 5
Figure 5
TEM image. GO supported on AuNPs synthesized with 5% tea extract.
Figure 6
Figure 6
C 1s regions of (a) AuNPs/G and G; (b) AuNPs/rGO and rGO; (c) G with fitting (similar to rGO and AuNPs/rGO and AuNPs/G); and (d) GO and AuNPs/GO.
Figure 7
Figure 7
Au 4f XPS regions.
Figure 8
Figure 8
AuNP samples stability (t1w–t2w). Carbon-based nanomaterials added after AuNP formation.
Figure 9
Figure 9
Simulated LSPR intensity for AuNPs with increasing dimensions (radius between 10 and 50 nm). Gold nanospheres are immersed in pure water and have a capping layer of EGCG with a thickness between 1 and 30 nm.
Figure 10
Figure 10
Simulated LSPR intensity for AuNPs with fixed dimensions (radius 30 nm). Gold nanospheres are immersed in pure water and have a capping layer of EGCG with thickness between 0 and 100 nm.
Figure 11
Figure 11
(a) Variation of the central wavelength for the LSPR resonance as a function of the medium refractive index for different thickness of the EGCG capping layer. (b) Sensitivity of the NPs’ LSPR as a function of the EGCG capping layer thickness.
Figure 12
Figure 12
Preparation of samples by SQ1-AuNPs/rGO (a) or SQ2-rGO/AuNPs (b).
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