Noble metal nanoparticles for assay development

Noble metal nanoparticles exhibit a unique optical property known as localized surface plasmon resonance (LSPR), which occurs when interacting light couples to the collective oscillations of the surface electrons. This work investigates the use of various nanoparticles for biosensing based on LSPR. Triangular silver nanoplates (TSNPs), synthesized using two different methods, and their derivatives, gold-coated TSNPs (AuTSNPs), were investigated for use in refractive index sensitivity-based solution assays. Refractive index sensitivities of these nanoplates were determined and benchmarked against the theoretical calculation predicted by Miller et al.. The first generation TSNPs and AuTSNPs were used for the detection of human C-reactive protein (CRP) and cardiac troponin I (cTnI) and the second generation AuTSNPs were used for the detection of human CRP. In order to address the complex assay design, a simpler aggregation-based assay for the detection of human IgG was implemented using spherical gold nanoparticles. Furthermore, a preliminary study on incorporating the AuTSNPs into a surface plasmon resonance (SPR) sensor was carried out to explore the enhancement effect of the nanoplates on SPR detection. Nobel metal nanoparticles are found to enhance fluorescence-based biosensing due to a phenomenon known as metal-enhanced fluorescence (MEF) when the nanoparticles are in the vicinity of fluorophores. In this work, the enhancement effects of the AuTSNPs and spherical silver nanoparticles (AgNPs) on the fluorescence were evaluated. A significant enhancement was observed for AgNPs whereas no enhancement was observed for AuTSNPs. Further MEF studies were conducted using various dyes and gold-coated AgNPs. AgNPs were used for enhancing the fluorescence-based assays for human IgG and CRP detection. The limits of detection (LODs) of the IgG and CRP assays were improved by ~ 9-fold and ~ 19-fold, respectively. This work establishes the potential of plasmonic nanoparticles for highly sensitive biosensing and holds much promise for the improvement of biomedical diagnostics