Actuated plasmonic nanohole arrays for sensing and optical spectroscopy applications.

Herein, we report a new approach to rapidly actuate the plasmonic characteristics of thin gold films perforated with nanohole arrays that are coupled with arrays of gold nanoparticles. The near-field interaction between the localized and propagating surface plasmon modes supported by the structure was actively modulated by changing the distance between the nanoholes and nanoparticles and varying the refractive index symmetry of the structure. This approach was applied by using a thin responsive hydrogel cushion, which swelled and collapsed by a temperature stimulus. The detailed experimental study of the changes and interplay of localized and propagating surface plasmons was complemented by numerical simulations. We demonstrate that the interrogation and excitation of the optical resonance to these modes allow the label-free SPR observation of the binding of biomolecules, and is applicable for in situ SERS studies of low molecular weight molecules attached in the gap between the nanoholes and nanoparticles.

High-Affinity α5ß1-Integrin-Selective Bicyclic RGD Peptides Identified via Screening of Designed Random Libraries.

We report the identification of high-affinity and selectivity integrin α5ß1-binding bicyclic peptides via "designed random libraries", that is, the screening of libraries comprising the universal integrin-binding sequence Arg-Gly-Asp (RGD) in the first loop in combination with a randomized sequence (XXX) in the second loop. Screening of first-generation libraries for α5ß1-binding peptides yielded a triple-digit nanomolar bicyclic α5ß1-binder (CT3RGDcT3AYGCT3, IC50 = 406 nM). Next-generation libraries were designed by partially varying the structure of the strongest first-generation lead inhibitor and screened for improved affinities and selectivities for this receptor. In this way, we identified three high-affinity α5ß1-binders (CT3RGDcT3AYJCT3, J = d-Leu, IC50 = 90 nM; CT3RGDcT3AYaCT3, IC50 = 156 nM; CT3RGDcT3AWGCT3, IC50 = 173 nM), of which one even showed a higher α5ß1-affinity than the 32 amino acid benchmark peptide knottin-RGD (IC50 = 114 nM). Affinity for α5ß1-integrin was confirmed by SPFS analysis showing a Kd of 4.1 nM for Cy5-labeled RGD-bicycle CT3RGDcT3AYJCT3 (J = d-Leu) and a somewhat higher Kd (9.0 nM) for Cy5-labeled knottin-RGD. The α5ß1-bicycles, for example, CT3RGDcT3AYJCT3 (J = d-Leu), showed excellent selectivities over αvß5 (IC50 ratio α5ß1/αvß5 between <0.009 and 0.039) and acceptable selectivities over αvß3 (IC50 ratios α5ß1/αvß3 between 0.090 and 0.157). In vitro staining of adipose-derived stem cells with Cy5-labeled peptides using confocal microscopy revealed strong binding of the α5ß1-selective bicycle CT3RGDcT3AWGCT3 to integrins in their natural environment, illustrating the high potential of these RGD bicycles as markers for α5ß1-integrin expression.

Tunable laser interference lithography preparation of plasmonic nanoparticle arrays tailored for SERS.

The facile preparation of arrays of plasmonic nanoparticles over a square centimeter surface area is reported. The developed method relies on tailored laser interference lithography (LIL) that is combined with dry etching and it offers means for the rapid fabrication of periodic arrays of metallic nanostructures with well controlled morphology. Adjusting the parameters of the LIL process allows for the preparation of arrays of nanoparticles with a diameter below hundred nanometers independently of their lattice spacing. Gold nanoparticle arrays were precisely engineered to support localized surface plasmon resonance (LSPR) with different damping at desired wavelengths in the visible and near infrared part of the spectrum. The applicability of these substrates for surface enhanced Raman scattering is demonstrated where cost-effective, uniform and reproducible substrates are of paramount importance. The role of deviations in the spectral position and the width of the LSPR band affected by slight variations of plasmonic nanostructures is discussed.