Abstract
Long-range surface plasmon Y-junctions are demonstrated as sensors for the detection of bulk refractive index changes in solution and for protein binding. Using a fully-cladded Au stripe waveguide as a reference channel, common drift and noise in the system can be eliminated, relaxing the need for precise optical alignments. The performance of the structure is discussed theoretically, then bulk sensing is carried out experimentally with five solutions of different refractive indices, and protein sensing is demonstrated through physisorption of bovine serum albumin on a carboxyl-terminated Au stripe. The Y-junction biosensor demonstrated a very good ability to perform drift and noise suppression for fast and accurate biosensing.
Highlights
Long-range surface plasmon polaritons (LRSPPs) are optical surface waves excited by transverse magnetic (TM) polarized incident light propagating along a thin metal stripe or slab bounded by symmetric dielectrics [1]
We previously demonstrated the ability of straight LRSPP waveguides to detect small changes in the bulk refractive index of solutions and the adsorption of bovine serum albumin (BSA) [13], to perform immunological blood typing of human red blood cells [14], to detect dengue antibody and antigen in infected patient blood plasma [15, 16], to selectively detect gram negative or gram positive bacteria in human urine [17], and to detect leukemic markers in patient blood serum [18]
2-Isopropanol semiconductor grade (IPA), 16-Mercaptohexadecanioc acid (16-MHA), acetone HPLC grade ≥ 99.9%, glycerol, bovine serum albumin (BSA), heptane and phosphate buffered saline (PBS) 0.01 M, pH 7.4 were obtained from Sigma-Aldrich
Summary
Long-range surface plasmon polaritons (LRSPPs) are optical surface waves excited by transverse magnetic (TM) polarized incident light propagating along a thin metal stripe or slab bounded by symmetric dielectrics [1]. The ease of excitation of LRSPPs by butt-coupling a polarisation-maintaining single-mode optical fibre (PM-SMF) to the input waveguide allows miniaturization. LRSPP waveguides are sensitive to bulk and surface changes because the mode is bound to the surface of the metal, has fields that peak thereon, and propagates mostly in the background dielectric. LRSPPs on metal slabs have been demonstrated in sensing experiments using prism-coupled geometries [5,6,7,8]. Au is a preferred sensing surface and is most studied [9], but dielectric waveguides in integrated geometries have been tested for biosensing applications [10,11,12]
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