Abstract
Plasmonic biosensors are a powerful tool for studying molecule adsorption label-free and with high sensitivity. Here, we present a systematic study on the optical properties of strictly regular nanostructures composed of metallodielectric cuboids with the aim to deliberately tune their optical response and improve their biosensing performance. In addition, the patterns were tested for their potential to eliminate spurious effects from sensor response, caused by refractive index changes in the bulk solution. Shifts in the plasmonic spectrum are exclusively caused by the adsorbing molecules. For this purpose, nanopatterns of interconnected and separated cubes with dimensions ranging from 150 to 600 nm have been fabricated from poly(methyl methacrylate) using electron-beam lithography followed by metallization with gold. It is shown that a small lateral pattern size, a high aspect ratio, and short connection lengths are favorable to generate extinction spectra with well-separated and pronounced peaks. Furthermore, for selected nanostructures, we have been able to identify reflection angles for which the influence of the bulk refractive index on the position of the plasmonic peaks is negligible. It is shown that sensor operation under these angles enables monitoring of in situ biomolecule adsorption with high sensitivity providing a promising tool for high-throughput applications.
Highlights
In recent decades, plasmonic sensors have been established as a powerful tool for label-free studies of molecular binding processes [1,2,3]
The use of chromium as an adhesion promotor turned out to be essential in the electron beam lithography (EBL) fabrication process as otherwise, the nanoarrays were destroyed upon contact liquid contact
The adsorption process takes tuned.1 hWith optical response, small lateral pattern ratio, about and respect yields a to final wavelength shift of about. This size, valueaishigh moreaspect than three and short connection lengths appear to be favorable in order to obtain extinction spectra times higher than for our standard core-shell nanoparticle sensors under comparable conwith well-separated andthat pronounced peaks.shift
Summary
Plasmonic sensors have been established as a powerful tool for label-free studies of molecular binding processes [1,2,3]. The underlying mechanism is based on the detection of refractive index changes in the sensor environment by resonant coupling of electromagnetic waves to collective oscillations of free electrons in metals leading to localized surface plasmons in metal nanoparticles or propagating surface plasmons in the case of plain metal films [4]. This can be achieved by the reflection of light from the sensor surface, yielding specific adsorption bands at wavelengths, where the dispersion curves of plasmon and photon intersect [5,6,7]. Refractive index changes in the vicinity of the sensor surface result in wavelength shifts of the plasmonic spectrum. 4.0/).
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