Gold nanoparticles (AuNPs) possess desirable features for nanotechnology applications. Recent advancements in fabrication techniques have enabled precise control over light-matter interactions at the subwavelength scale, particularly in the visible light range. These nanoparticles are well-suited for high-sensitivity biological and chemical sensing. Localized surface plasmon resonance (LSPR) is an optical phenomenon where nanostructures resonate at specific frequencies when excited by electromagnetic waves. The resonance is confined to the surface of the nanostructures, making it sensitive to environmental changes. Plasmonic nanomaterial arrays, specifically self-assembled gold nanoislands (AuNIs) on glass substrates, have been developed for highly sensitive sensing applications. The fabrication of AuNIs involves a two-step process of thin-film deposition followed by annealing. These randomly distributed nanostructures exhibit a significant phase transition when subjected to polarized light via total internal reflection in the Kretschmann configuration. This phase transition occurs at the extinction wavelengths and is driven by variations in refractive index. As a result, AuNIs serve as an excellent platform for achieving highly sensitive opti-biochemical sensing.

The other major part of the thesis reports on the development of different approaches to enhance the LSPR sensing performance of nanostructured LSPR sensors.

In order to enhance LSPR effect, the effects of connecting AuNPs and AuNIs together to create electromagnetic coupling among them were investigated for sensing applications. However, AuNPs tend to conglomerate, making it difficult to effectively apply them onto AuNIs. To address this issue, a procedure similar to that of “functionalization” of a sensing surface before bio-chemical sensing was employed to achieve AuNPs attachment. The coupling effect enhancement was implemented by evaluating the refractive index resolution using different concentrations of sodium chloride solution. Biochemical sensing experiments involving the detection of Lead(II) (Pb(II)) ions in water and the immuno-biosensing of human IgG antibody/antigen biomolecules were conducted to demonstrate the capabilities of the enhanced LSPR sensors. The results showed a significant improvement in performance, with the AuNPs functionalized AuNIs exhibiting approximately 450 % enhancement in the sodium chloride test. Moreover, the Pb(II)-sensing capability exhibited a four times enhancement at a concentration as low as 0.06 ppb. In the case of human IgG antibody detection, the detection limit reached 0.29 pM, with a dynamic range from 0.29 pM to 500 pM, covering four orders of magnitude in concentration.

The creation of an additional plasmonic source through surface plasmon amplification by stimulated emission of radiation (SPASER) using the Rhodamine 6G (R6G) system was studied. The light source worked in collaboration with a laser to the sensing system. R6G, a fluorescent dye, was “functionalized” as aforementioned AuNPs near the AuNIs and was excited by the laser, thereby generating additional plasmons during the quenching process for sensing. The effectiveness of this SPASER effect enhancement was also evaluated using the immuno-biosensing of human IgG antibody/antigen biomolecules. The results showed similar improvements in detection limits and dynamic range as the coupling effect. The detection limit reached 0.8 pM, with a dynamic range from 0.8 pM to 500 pM, covering four orders of magnitude in concentration.

Furthermore, the application of LSPR effect enhanced functionalization in biosensing was examined using riboflavin (vitamin B2) and riboflavin binding protein pair. Riboflavin was detected using riboflavin binding protein functionalized AuNIs alone LSPR biosensor and compared with AuNIs with enhancement configuration LSPR biosensor. The results demonstrated further improvement in detection limit for AuNIs with enhancement configuration LSPR biosensor. The detection limit reached 0.19 pM, with a dynamic range from 0.5 pM to 3,000 pM, covering four orders of magnitude in concentration.

In conclusion, the additional functionalization approach for enhancing LSPR effects provides a convenient protocol for LSPR biosensing, applicable to plasmonic materials on glass substrate with appropriate materials to connect AuNPs or R6G. These approaches hold great potential in enhancing the sensitivity of LSPR sensing platforms and can pave the way for future developments in plasmonic materials and techniques.