Plasmonic sensors on 2D ordered structures

Colloidal lithography with polystyrene spheres allows for the fabrication of hybrid polymer/metal two-dimensional ordered surfaces. They consist of a hexagonal lattice of plasma-polymerized acrylic acid (ppAA) or poly(methyl methacrylate) (PMMA) pillars embedded in an optically thick gold film deposited on a glass substrate. Such a kind of nanostructured system has been shown to support either propagating Surface Plasmon Polaritons or “Mie-like” localized resonances, and appears to be particularly interesting for sensing applications. Tuning the structural parameters, a strong interaction among delocalized and localized plasmonic modes can be obtained together with a good coupling with light. This opens the way towards an optical biomolecular sensor system in which a modification/adhesion on the free nanostructured surface can be easily detected by a simple, near normal reflectance measurement performed from the substrate side, despite the relatively large gold thickness. The simple configuration allows for a surface plasmon resonance (SPR) imaging configuration and enables the real-time multiplexed detection of several analytes. The sensing performance of the surfaces (sensitivity to refractive index change and to the adhesion of molecular monolayers) has been tested using standard spectroscopic techniques. The electromagnetic field’s spatial distribution within the nanostructures and its intensity enhancement have been numerically calculated by finite difference time domain (FDTD) simulations. The results, including the calculated reflectance spectra, are in good agreement with the experimental data

Oligomerization Profile of Human Transthyretin Variants with Distinct Amyloidogenicity

One of the molecular hallmarks of amyloidoses is ordered protein aggregation involving the initial formation of soluble protein oligomers that eventually grow into insoluble fibrils. The identification and characterization of molecular species critical for amyloid fibril formation and disease development have been the focus of intense analysis in the literature. Here, using photo-induced cross-linking of unmodified proteins (PICUP), we studied the early stages of oligomerization of human transthyretin (TTR), a plasma protein involved in amyloid diseases (ATTR amyloidosis) with multiple clinical manifestations. Upon comparison, the oligomerization processes of wild-type TTR (TTRwt) and several TTR variants (TTRV30M, TTRL55P, and TTRT119M) clearly show distinct oligomerization kinetics for the amyloidogenic variants but a similar oligomerization mechanism. The oligomerization kinetics of the TTR amyloidogenic variants under analysis showed a good correlation with their amyloidogenic potential, with the most amyloidogenic variants aggregating faster (TTRL55P > TTRV30M > TTRwt). Moreover, the early stage oligomerization mechanism for these variants involves stepwise addition of monomeric units to the growing oligomer. A completely different behavior was observed for the nonamyloidogenic TTRT119M variant, which does not form oligomers in the same acidic conditions and even for longer incubation times. Thorough characterization of the initial steps of TTR oligomerization is critical for better understanding the origin of ATTR cytotoxicity and developing novel therapeutic strategies for the treatment of ATTR amyloidosis

A multiplexed label free plasmonic nano-device for near infrared applications

The development of a new surface plasmon resonance (SPR) imaging biosensor is reported. The biosensor exploits the optical properties of a nano-structured gold-polymer chip, which allows for the coupling of the SPR with the incident light. The spectral characterization of the chip permits to analyze the plasmonic response to a refractive index change near its free surface. The nano-structured surface features are presented together with an exemplifying biological tests which demonstrate the multiplexing label-free detection capability of the proposed device

Multiplexed label-free optical biosensor for medical diagnostics

This paper describes a new multiplexed label-free biosensor. The detection technology is based on nanostructured gold-polymer surfaces. These surfaces support surface plasmon resonance modes that can be probed by a miniaturized optical setup. The optical characterization of the sensing chip shows the sensitivity and the limit-of-detection to refractive index changes. Moreover, by studying the progressive adhesion of molecular monolayers of polyelectrolytes, the decay of the plasmonic mode electric field above the surface has been reconstructed. A multiplexed label-free biosensing device is then described and characterized in terms of sensitivity, lateral resolution, and sensitivity to a model biological assay. The sensitivity in imaging mode of the device is of the order of 10-6 refractive index units, while the measured lateral resolution is 6.25 μm within a field of view of several tenths of mm2, making the instrument unique in terms of multiplexing capability. Finally, the proof-of-concept application of the technology as a point-of-care diagnostic tool for an inflammatory marker is demonstrated

Simultaneous detection of multiple biomarkers by means of SERS on polymer nanopillar gold arrays

The detection of biomarkers by means of Surface Enhanced Raman Spectroscopy (SERS) is foreseen to became a very important tool in the clinical practice because of its excellent sensitivity and potential for the simultaneous detection of multiple biomarkers. In the present paper we describe how it was possible to build a sensor for the detection of genetic biomarkers involved in acute myeloid leukemia. The assay is based on the use of a specifically designed SERS substrate made of a 2D crystal structure of polymeric pillars embedded in a gold layer. This substrate is characterized by good enhancing properties coupled with an excellent homogeneity. The SERS substrate was conjugated with DNA probes complementary to a target sequence and used in a sandwich assay with gold nanoparticles labeled with a second DNA probe and a Raman reporter. The so developed assay allowed the detection of a leukemia biomarker (WT1 gene) and an housekeeping gene with low picomolar sensitivity. At last, we optimized the assay in order to tackle one of the main limitations of SERS based assay: the loss of signal that is observed when the Raman spectra are collected in liquid. Combining a preferential functionalization on the polymeric pillars with a different height of the polymer pillars from the gold layer the assay demonstrated its effectiveness even when measured in buffer