Effect of Graphene Characteristics on Morphology and Performance of Composite Noble Metal-Reduced Graphene Oxide SERS Substrate.

Tajana Kostadinova,Radmila Tomovska,Nikolaos Politakos,Ana Trajcheva,Jadranka Blazevska-Gilev

doi:10.3390/molecules26164775

Abstract

Graphene/noble metal substrates for surface enhanced RAMAN scattering (SERS) possess synergistically improved performance, due to the strong chemical enhancement mechanism accounted to graphene and the electromagnetic mechanism raised from the metal nanoparticles. However, only the effect of noble metal nanoparticles characteristics on the SERS performance was studied so far. In attempts to bring a light to the effect of quality of graphene, in this work, two different graphene oxides were selected, slightly oxidized GOS (20%) with low aspect ratio (1000) and highly oxidized (50%) GOG with high aspect ratio (14,000). GO and precursors for noble metal nanoparticles (NP) simultaneous were reduced, resulting in rGO decorated with AgNPs and AuNPs. The graphene characteristics affected the size, shape, and packing of nanoparticles. The oxygen functionalities actuated as nucleation sites for AgNPs, thus GOG was decorated with higher number and smaller size AgNPs than GOS. Oppositely, AuNPs preferred bare graphene surface, thus GOS was covered with smaller size, densely packed nanoparticles, resulting in the best SERS performance. Fluorescein in concentration of 10−7 M was detected with enhancement factor of 82 × 104. This work demonstrates that selection of graphene is additional tool toward powerful SERS substrates.

Highlights

Because of the graphene unique features, such as high electron mobility and high surface area, followed by exceptional mechanical, thermal, and electrical properties, it attracts a huge interest in various research fields, including materials science and engineering
The reduction of neat Graphene oxide (GO) in aqueous dispersion was performed with AsA reducing agent in presence of PVP (Mw of 10.000 Da) that sterically stabilized the reduced graphene oxide (rGO) platelets in dispersions
Elemental composition of all rGO-based materials was determined by EDX and the chemical composition by FTIR spectroscopy

Summary

Introduction

Because of the graphene unique features, such as high electron mobility and high surface area, followed by exceptional mechanical, thermal, and electrical properties, it attracts a huge interest in various research fields, including materials science and engineering. One of the important applications of graphene is its utilization as a substrate for surfaceenhanced Raman scattering (SERS) [1] that allows detection of a very low concentration of chemical or biological molecules. Raman signals are inherently weak, especially when the visible light excitation is used and a small number of scattered photons are used for the detection of the investigated molecules. By insertion of the investigated molecules onto the surface of the SERS substrate, a largely increased Raman scattering is induced because of two simultaneous effects. In case of metal substrate, such as nano-cast gold (Au) or silver (Ag) surface, resonantly enhanced field allows an electromagnetic enhancement effect that much strongly enhances the Raman signal [9,10,11,12,13,14]. It has been stated that single-layer graphene shows higher SERS signal enhancement in contrast to few-layer graphene [19]

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