Gold nano-islands on FTO as plasmonic nanostructures for biosensors

Metal nanoislands (NIs) deposited on transparent surfaces can be a convenient plasmonic material for bio/organic sensors, under the condition that a stable morphology is reached.Plasmonic materials suitable for the fabrication of low cost biosensors based on localized surface plasmon resonance (LSPR) UV-Vis spectroscopy, are fabricated by a simple methodology based on thermal evaporation of Au on commercially available, transparent fluorine-doped tin oxide (FTO) surfaces. The LSPR UV-Vis spectroscopy performed in transmittance mode reveals: (i) a small energy shift, Δλ_max, of the LSPR band under immersion both in organic solvent, and significantly in aqueous media, and (ii) a sensible and reproducible Δλ_max under formation of organic SAMs on the NIs surface. These data indicate that the Au NIs when deposited on FTO substrate exhibit (i) strong adhesion and a high stability, and (ii) a good sensitivity to molecular interaction. The samples also show that the LSPR bands recover the original feature after being exposed to different type of SAMs. Significantly, the absorption maximum, λ_max of the Au-NIs LSPR spectra shows a red shift when SAMs incorporating single strands DNA are exposed to the complementary strands. The plasmonic system based on Au NI deposited on FTO surfaces because of (i) the inexpensive fabrication of stable NIs, (ii) the easy way to detect the molecular interaction occurring at their surface, and (iii) the sensitivity of their LSPR to molecular interaction represents a convenient platform for biosensors.