Surface-enhanced Raman spectroscopy on CVD graphene-DNA composites

Surface-enhanced Raman spectroscopy (SERS) is an analytical method that enhances the sensitivity of Raman scattering signals. 1 Researchers have utilized SERS to investigate various chemical and biological systems, including proteins, cells, and DNA. Due to its distinct molecular composition and specific physical and chemical properties, the emergence of graphene provides excellent nanoplatforms for fabricating SERS-active substrates.2,3 In graphene, the remaining one 2pz orbital of each sp2 hybridized carbon atom constitutes a large delocalized π-bond of graphene, which favors the adsorption of DNA on the carbon surface through π − π interactions between the aromatic rings of graphene and the N-containing groups of DNA bases.4 The main objective of this research project is to synthesize a CVD graphene-DNA composite and reveal the SERS response’s existence on graphene. DNA from the Staphylococcus bacteria culture was deposited at different concentrations 376.2 ng/µL, 409.8 ng/µL, and 543.2 ng/µL over graphene on SiO2/Si substrate. Then, a characterization via Raman spectroscopy was conducted using a 532 nm laser. First, it is explained that SERS on graphene mainly relies on the chemical mechanism (CM) due to molecule-substrate interactions and from an effective charge transfer between them, which are depicted by new Raman modes on SERS spectra, mappings and doping effect. Also, it explains how shifts in the position of the 2D and G bands of graphene result from intrinsic effects of charge doping or strain between dsDNA and graphene. Additionally, SERS spectra exhibited overlapping bands from nucleobases of dsDNA because the helical structure limits it through the closest base-pair. A clean DNA sample (409.8 ng/µL) was deposited on SiO2/Si substrate to compare the DNA Raman signal on this substrate to the one obtained in the presence of graphene, which enhances the vibronic response of the molecule in two ways: i) by quenching the fluorescence derived from the biomolecule, leading the main vibrations from a DNA to become evident, and ii) due to the strong electrostatic interaction between DNA and graphene, this interaction results in an enhanced D-line, a redshift of the G-line, and a blueshift of the 2D-line of graphene. On the other hand, an alternative technique, Fourier-transformed infrared Raman spectroscopy (FTIR), was employed to measure the pristine DNA. However, due to the dilution and low concentration of DNA in water( ng/µL), the obtained FTIR spectra hinder the DNA vibrations into the strong ones from water. As a result, in this thesis, we confirmed: i) employing graphene serves as a detection platform and an optimal substrate to measure the presence of ultra-low concentrated biomolecules, ii) the strong interaction of biomolecules with graphene enhances the Raman signal, which presents many advantages, such as easier preparation, lower cost, better biocompatibility, and fluorescence quenching, as it will be shown along this thesis. Keywords: graphene, DNA, SERS, Raman, CVD, and FTIR.

• Hovedforfatter: Arellano Haro, Daniela Estefania (author)
• Format: bachelorThesis
• Sprog: eng
• Udgivet: 2023
• Fag: Grafeno; Ácido desoxirribonucleico (ADN); Graphene; Deoxyribonucleic acid (DNA); Chemical vapor deposition (CVD)
• Online adgang: http://repositorio.yachaytech.edu.ec/handle/123456789/679