Synthesis of 3D hydrogel graphene quantum dots nanocomposites modified fibre optic for biosensors application / Muhammad Haziq Noor Akashah

In this study, a novel fibre optic sensor towards biosensing application was developed by introducing polymeric supporting membranes of hybrid hydrogels (HH) and nanomaterials of graphene quantum dots (GQDs) as coating materials. HH was formed by introducing chitosan (CH) as an additive that would further aid in introducing the amide group that was lacking in agarose (AG) hydrogel. GQDs were synthesised using a chemical reduction method transforming the precursor graphene oxide (GO) into GQDs nanostructures. GO was synthesised prior to that using a modified Hummers' method. GQDs were optimised by varying the parameters in the chemical reduction method with the optimum condition for synthesis ~2 nm of GQDs was obtained by using 25 uL of dispersed in 5 mL of sulfuric acid, 0.014 g of potassium permanganate and 0.1 mL of hydrogen peroxide. The optimum GQDs were found to be having an average size of 2.481 ± 0.649 nm as confirmed by transmission electron microscopy, subtle x-ray diffraction peak at around 29=26°, loaded with hydroxyl (OH), carbonyl (C=0) and carbon bonds found from Fourier transform infrared analysis reflect that GQDs have many oxygenated functional groups making them soluble in water and stable fluorescence stability for up to 90 days with a quantum yield of 48%. A conventional fibre optic cable was used and exposed its core region made from silica by using mechanical etching via a fibre optic cable stripper. Before that, signal validation for the uncladded region (1, 2 and 3 cm) was performed with 2 cm of uncladded and was found to give the signal of 1660.74 a.u. and efficient uncladded length to be spliced. The fibre optic core coated HH was then let to be coated with the optimum coating thickness of HH on fibre optic was found at 122.18 ± 0.3 um by 2% total concentration of HH (2% w/v of AG with 2% v/v of CH) with confirmation by signal validation from the spectrometer with laser as a light source.