Sensitive localized surface plasmon resonance multiplexing protocols.

Herein are reported two new protocols to obtain different zones of localized surface plasmon resonance (LSPR) gold nanostructures on single glass substrate by using a vacuum evaporation technique followed by a high-temperature annealing (550 °C). The thickness of the gold film, considered as the essential parameter to determine specific LSPR properties, is successfully modulated. In the first protocol, a metal mask is integrated onto the glass substrate during vacuum evaporation to vary the gold film thickness by a "shadowing effect", while in the second protocol several evaporation cycles (up to four cycles) at predefined areas onto the single substrate are performed. The resulting gold-modified samples are characterized using a transmission UV-vis extinction optical setup and scanning electron microscopy (SEM). The size distribution histograms of nanoparticles are also acquired. By employing the first protocol, thanks to the presence of different zones of gold nanoparticles on a single substrate, optimized LSPR responses to different (bio)functionalization zones are rapidly screened. Independently, the second protocol exhibited an excellent correlation between the nominative evaporated gold film thickness, gold nanoparticle sizes, and plasmonic properties (resonant wavelength and peak amplitude). Such substrates are further used in the construction of LSPR immunosensors for the detection of atrazine herbicide.