Multiplexed Remote SPR Detection of Biological Interactions through Optical Fiber Bundles

Abstract

The development of sensitive methods for in situ detection of biomarkers is a real challenge to bring medical diagnosis a step forward. The proof-of-concept of a remote multiplexed biomolecular interaction detection through a plasmonic optical fiber bundle is demonstrated here. The strategy relies on a fiber optic biosensor designed from a 300 µm diameter bundle composed of 6000 individual optical fibers. When appropriately etched and metallized, each optical fiber exhibits specific plasmonic properties. The surface plasmon resonance phenomenon occurring at the surface of each fiber enables to measure biomolecular interactions, through the changes of the retro-reflected light intensity due to light/plasmon coupling variations. The functionalization of the microstructured bundle by multiple protein probes was performed using new polymeric 3D-printed microcantilevers. Such soft cantilevers allow for immobilizing the probes in micro spots, without damaging the optical microstructures nor the gold layer. We show here the potential of this device to perform the multiplexed detection of two different antibodies with limits of detection down to a few tenths of nanomoles per liter. This tool, adapted for multiparametric, real-time, and label free monitoring is minimally invasive and could then provide a useful platform for in vivo targeted molecular analysis.

Keywords: SPR; biomolecular detection; biosensor; functionalization; label-free; microstructuration; multiplexed detection; optical fiber; surface plasmon resonance.

Figure 1

Scanning Electron Microscopy (SEM) pictures of a polymeric microcantilever used to perform the antibodies immobilization at different magnifications. (See electronic Supplementary Materials for more information on its conception).

Figure 2

(A) multifunctionalization of the microstructured gold coated surface according to i. Spotting map, and ii. Scheme of the deposition, with the image corresponding to iii. Rabbit-IgG spot formation, iv. Rat IgG spots formation. Insert in (A) ii. Scanning Electron Microscopy (SEM) image of the microstructured gold coated surface. (B). Surface Plasmon Resonance (SPR) view of the droplets deposition with i. Spotting map on subtracted image, ii. Image of the retro-reflected light; (C) confirmation of the immobilization and antibodies detection by fluorescence microscopy with streptavidin-Phycoerythrin after addition of the biotinylated antibodies: i. Anti-rabbit and ii. Anti-rat.

Figure 3

SPR signal (i(t), in gray level) monitoring on the different spots of the bundle for the detection of (A) anti-rabbit IgG and (B) anti-rat IgG; (C) Surface Plasmon Resonance (SPR) images of the light retro-reflected on the fibers after injection of i. anti-rabbit IgG and ii. anti-rat IgG followed by coupling with streptavidin-phycoerythrin. (D) response range of the SPR signal on the different spots as a function of the corresponding specific antibodies concentration. Insert in A. zoom in one concentration of the curve, showing signal stabilization and rinsing in Phosphate-Buffered Saline (PBS).