Dielectric functionalization for differential phase detecting localized surface plasmon resonance biosensor

Abstract In this paper, a novel dielectric functionalization approach is introduced for differential phase detecting localized surface plasmon resonance (LSPR) immunoassay biosensor, which exhibits high sensitivity. The plasmonic “hot spots” at the nanoscale dielectric gaps among self-assembly gold nanoislands were first functionalized. These “hot spots” are believed to be highly sensitive to localized refractive index change and the phase response induced by the binding event at these functionalized “hot spots” is monitored by our common-path spectral interferometer during biosensing. Its performance was compared with that from conventional gold functionalization protocol. It was found that the dielectric functionalization approach attained limit of detection of the same order as that from conventional gold functionalization, i.e. 1 pM of human IgG antigen. The novel protocol was also applied to detection of the antigen in serum samples. To our knowledge, these are two orders of magnitude improvement over existing label-free SPR biosensors. In view of the myriad of emerging plasmonic materials in the foreseeable future, the dielectric functionalization approach would provide a convenient protocol for label-free LSPR biosensing, as it would be generally applicable to any plasmonic material on glass substrate.