The impact of different gold nanoparticles (GNPs) structures on the plasmonic enhancement for DNA detection is investigated on a few-layer graphene (FLG) surface plasmon resonance (SPR) sensor. Two distinct structures of gold nanourchins (GNu) and gold nanorods (GNr) were used to bind the uniquely designed single-stranded probe DNA (ssDNA) of Mycobacterium tuberculosis complex (MTBC) DNA. The two types of GNPs-ssDNA mixture were adsorbed onto the FLG-coated SPR sensor through the π-π stacking force between the ssDNA and the graphene layer. In the presence of the complementary single-stranded DNA (cssDNA), the hybridization process took place and gradually removed the probes from the graphene surface. From SPR sensor preparation, the annealing process of the Au layer of the SPR sensor effectively enhanced the FLG coverage leading to a higher load of the probe DNA onto the sensing interface. The FLG was shown effective in providing a larger surface area for biomolecular capture due to its roughness. Carried out in the DNA hybridization study with SPR sensor, GNu, with its rough and spikey structures, significantly reinforced the overall DNA hybridization signal than the GNr with smooth superficies, especially in capturing the probe DNA. The DNA hybridization detection assisted by GNu reached the femtomolar range limit of detection (LoD). An optical simulation validated the extreme plasmonic field enhancement at the tip of the GNu spicules. The overall integrated approach of graphene-based SPR sensor and GNu-assisted DNA detection provided the proof-of-concept for the possibility for Tuberculosis disease screening using a low-cost and portable system potentially applied in a remote or the third world countries.
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