Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel
Ultrathin gold films prepared by evaporation of sub-percolation layers (typically up to 10 nm nominal thickness) onto transparent substrates form arrays of well-defined metal islands. The gold island films display a characteristic localized surface plasmon (SP) extinction peak in the visible-to-NIR range, conveniently measured by transmission spectroscopy. The SP band intensity and wavelength are sensitive to the island film morphology as well as to the effective refractive index of the contacting medium. The latter changes upon binding of analytes to the surface, forming the basis for chemical and biological sensing in the transmission localized surface plasmon resonance (T-LSPR) mode. The distance sensitivity of T-LSPR spectroscopy was studied using a coordination-based self-assembled multilayer of a variable thickness. Stabilization of the system response was achieved using an ultrathin (1-2 nm) sol-gel derived silica layer on the gold islands. Use of T-LSPR transducers for biosensing and for gas sensing is demonstrated.