Fabrication of Arrays of Plasmonic nanostructures for Biosensor Applications

Abstract

Using interferometric lithography (IL) in a double exposure process a library of different arrays of gold nanostructures was formed. Au nanoarrays were used to study the change in the absorption spectra as a result of the difference in the form of the gold nanodots and the space between them. After annealing, all structures produced absorbance spectra that were significantly changed and exhibited strong plasmon bands. The separation between nanodots is one of the leading factors controlling the energy of the localized surface plasmon resonance (LSPR). The LSPR peak is usually between 500 nm and 750 nm whereas the samples with small mirror angles show a strong plasmon peak. The gold nanowires function as label-free LSPR biosensors, as the LSPR extinction spectra of the immobilized streptavidin and IgG on the gold surface produce a red shift of LSPR wavelengths. For biotin, streptavidin has four binding sites. Additionally, a range of biotinylated molecules are accessible, such as biotinylated DNA. The thickness and absorption shift in the plasmon band of streptavidin are shown by spectroscopic ellipsometry and an optical absorption spectrum. Attachment of light-harvesting proteins (Maquettes) to the gold nanostructures, their surface plasmon resonances were found to split. The splitting in the spectra is due to strong coupling between the localized surface plasmon resonances and excitons in the proteins. It was found that samples of gold nanostructure can be reused many times for the immobilization of proteins to carry out spectroscopy. The thia-selective thia-Michael addition process was used to make a monomer cysteine methacrylate (CysMA), which was then used to grow brushes with the ATRP method. The stimulus-responsive poly cysteine methacrylate (PCysMA) was grown from initiated gold nanostructure arrays. A cysteine methacrylate (CysMA) monomer was prepared by employing a selective thia-Michael addition reaction. This monomer was utilized to prepare PCysMA brushes through an ATRP approach, with varying thickness. The brush thickness collapsed when they deprotonated while brushes demonstrate pH responsive behaviours including the mean brush thickness rising substantially and collapsing when pH <2 and >12. UV-visible absorption and ellipsometry examinations were studied to determine their responsiveness to different conditions and PCysMA brush thickness on gold film and gold nanoarrays. AFM was used to measure the growth of PCysMA from gold nanostructure arrays and nanostructure size of the FWHM particle and it showed that the increased free volume impacts brush morphology by boosting the brush thickness. Also, PCysMA showed a response to temperature, and at lower temperature, the polymer brushes increased by 20 nm compared 50oC.