ABSTRACT
In the present work, the standard monometallic localized surface plasmon resonance (LSPR) biosensing sensitivity is highly improved when using a new system based on glass substrates modified with high-temperature annealed gold/silver bimetallic nanoparticles (Au/Ag bimetallic NPs) coated with polydopamine films before biomolecule specific immobilization. Thus, different zones of bimetallic NPs are spatially created onto a glass support thanks to a commercial transmission electron microscopy (TEM) grid marker in combination with two sequential evaporations of continuous films of gold (4 nm) and silver (2 nm) and followed by annealing at 500 °C for 8 h. By using the scanning electron microscopy (SEM), it is found that annealed Au/Ag bimetallic NPs have uniform size and shape distribution that exhibited a sharper well-defined LSPR resonant peak when compared with that of monometallic Au NPs and thereby contributing to an improved sensitivity in LSPR biosensor application. The controlled micropatterns consisting of bimetallic particles are used in the construction of LSPR biochips for high-throughput detection of different concentrations of a model antigen named bovine serum albumin (BSA) on a single glass sample, with a lower limit of detection of 0.01 ng/mL under the optimized conditions.
ABSTRACT
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.
