Wan Omar, Wan Ibtisam (2023) Synthesis, characterization and simulation of fluorescent graphene quantum dots for three-dimensional cell imaging. Doctoral thesis, Universiti Tun Hussein Onn Malaysia.

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Abstract

In the search for staining dyes for three-dimensional cell imaging, graphene quantum dots (GQDs) that are nanometers in scale, photoluminescent (PL), and dispersible in water may be investigated. The doping of graphene-based materials with nitrogen heteroatoms has demonstrated the ability to control the optical, electrical and opto-electronic properties of nitrogen-doped GQDs (N-GQDs). However, the characteristics of the energy-state and the properties of the N-GQDs are still unclear and require more study. This thesis designed and synthesised nanometer-sized GQDs using the hydrothermal technique. In addition, theoretical model based from experimental results of N-GQDs was execute by electronic structure calculations via the density function theory (DFT) using the GAUSSIAN 09 and GAMESS software. The sterilised N-GQDs after hydrothermal synthesis produce a high-crystalline form of N-GQDs with aspect (100) with lattice distance of 0.21 nm. The synthesis also produced one-layer or multiple-layer N-GQDs with an average diameter of 3.2 nm. The N-GQDs also highly soluble in water. It also exhibited high fluorescence emission ranging from 500 to 600 nm with green-coloured PL with highest peak at 525 nm contributed to electronic energy gap of 3.38 eV. In terms of bio-compatibility, the study shows cell viability ranging from 80%–90%, non-toxic. Moreover, this is the first study using GQDs for 3D cell imaging to display stained 3D cells with scattered individual cells in a multi-layered structure. For the DFT simulations, calculation shows that the range of electronic energy from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) of the GQDs depended on graphitic nitrogen doping and edge functionality. In conclusion, this research shows a novel optoelectronic properties extract from the energy levels of N-GQDs derived from experimental and theoretical calculations for 3D cell imaging applications

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