https://doi.org/10.15407/jopt.2018.53.220

K.V. Kostyukevych, Yu.M. Shirshov, R.V. Khristosenko, A.V. Samoylov, Yu.V. Ushenin, S.A. Kostyukevych, A.A. Koptiukh

ANGULAR SPECTRUM PECULIARITIES OF SURFACE PLASMON-POLARITON RESONANCE UNDER INVESTIGATION OF LATEX WATER SUSPENSION IN THE KRETSCHMANN GEOMETRY

In this work, the possibility of description of the turbid medium (suspension of the light-scattering spherical particles in water) at the interface with glass and gold surface, based on simultaneous measurement of total internal reflection (TIR) and surface plasmon resonance (SPR) angles, and aimed to increase the informativity of optical methods when studying samples of biological origin and to facilitate creation of new sensor systems, is investigated theoretically and experimentally. Proposed theoretical approach takes into account the excess of particles at the surface caused by sedimentation, and the presence of transitional layer near the surface with continuous change of refraction index in the direction from the surface toward the suspension bulk. The near-surface area is defined as a set of thin layers, each characterized by its specific thickness and refraction index, calculated according to the Bruggeman effective medium theory. For the simulated “glass — gold film — latex suspension of spherical particles” system, TIR (FTIR) and SPR (FSPR) angle values were calculated. An unambiguous relationship between the measured angles and the particles concentration and size is demonstrated, as well as possibility to determine the degree of surface excess of the particles. The presence of intermediate layer with reduced refraction is proven, explained by the restriction of molecular movement of the opaque particles by the surface. Simulation of the refraction gradient has shown that the TIR angle increases linearly with the increasing concentration of particles in suspension regardless of their size in accordance with the Bruggeman’s rule. The rate of SPR angle increase with the increasing concentration of particles lags behind the rate of TIR angle increase, and the lag increases systematically with the increasing concentration. The peculiarities of internal reflection of light R(F) in Kretschmann geometry for aqueous suspension of polystyrene spherical particles 200 nm and 920 nm in size were investigated using a compact computerized “Plasmon” series instrument; qualitative agreement of the experimental results with model simulations was observed.

Keywords: surface plasmon resonance, effective medium, suspension, polystyrene spheres, sedimentation.