Gold @ silica core-shell nanoparticle for enhanced surface plasmon resonance detection of DNA hybridization in combination with gold nanowire gratings

Metallic nanoparticles have drawn much interest due to their distinct plasmonic characteristics especially in imaging and sensing applications. Surface plasmon resonance (SPR) based biosensors have evolved in many ways, among which sensitivity enhancement towards molecular sensing capability came up with strategies to overcome the hard limit of the intrinsic sensitivity of gold thin film. Recently adoption of signal contrast materials has proven successful in biochemical sensing applications. This study employs gold-SiO2 core-shell nanoparticles (CSNPs) as a strong SPR signal contrast agents. To reveal the underlying physics for the contrast mechanism, the particle characteristics were analytically evaluated in terms of light interaction coefficients. We experimentally demonstrate the effect of the CSNPs by applying them to acquire enhanced signal in DNA hybridization sensing scheme. We also applied gold nanowire grating structure on conventional gold thin film to further amplify the intrinsic sensitivity, where localized surface plasmon and locally amplified evanescent fields take parts. The results suggest that CSNPs and the grating structure cooperatively enhance the sensitivity and the role of nanowire gratings was analyzed with numerical methods to allow optimum sensitivity enhancement in terms of fill factor variations. The effects of field localization, amplification and enlarged signature of CSNPs are also discussed.