One goal of recent research on plasmonic nanoparticle-based sensors is maximizing nanoparticle sensitivity or shift of resonance peak wavelength per refractive index change. Equally important is a measurement system's peak location uncertainty or shift resolution. We provide systematic analyses and discuss optimization of factors that determine peak location uncertainty, reporting values as low as 0.3 nm for the presented scheme. This type of analysis is important, in part, because it provides a means of evaluating detection thresholds for biosensor applications such as analyte binding. We estimate thresholds of 310 streptavidin molecules for the presented scheme and 20 molecules with system improvements.
The development of truly scalable, multiplexed optical microarrays requires a detection platform capable of simultaneous detection of multiple independent signals in real-time. We present a technique we term dual order snapshot spectroscopic imaging (DOSSI) and demonstrate that it can be effectively used to collect spectrally-resolved images of a full field of view of sparsely located spots in real-time. Resonant peaks of plasmonic gold nanoparticles were tracked as a function of their surrounding refractive index. Measurement uncertainty analysis indicated that the spectral resolution of DOSSI in the described configuration is approximately 0.95 nm. Further, real-time measurements by DOSSI allowed discrimination between optically identical nanoparticles that were functionalized with two homologous small molecule ligands that bound to the same protein, albeit with different affinity, based purely on their different molecular interaction kinetics– a feat not possible with slower raster-type hyperspectral imaging systems, or other darkfield optical detection systems that solely rely on end-point measurements. Kinetic measurements of plasmon bands by DOSSI can be performed with a relatively simple optical system, thereby opening up the possibility of developing low-cost detectors for arrayed plasmonic diagnostics.
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