ANALYSIS OF FORMING BLOOD ELEMENTS USING SURFACE PLASMON-POLARITON RESONANCE: MODEL OF TRANSITION LAYER

Abstract

Despite the great practical importance, the control of blood by optical methods is enormously complicated by the strong scattering of light. This is especially true for formed blood elements (FBEs), which are a compact suspension that remains after plasma removal from blood by centrifugation. The study of the surface plasmon resonance (SPR) in Kretchman’s geometry together with measurement of the angular dependence of the light internal reflection R( φ ) at the glass/ FBEs boundary is one of the few possibilities to obtain additional information about the structure and molecular composition of this complex inhomogeneous object. Measurement of R( φ ) for contact FBEs with the glass surface allows to determine the total internal reflection (TIR) angle and the effective refractive index N of the binary of erythrocytes-blood plasma mixture. At the same time, the comparison of the angles of TIR and SPR makes it possible to establish the presence of a transition layer between gold surface and the volume of FBEs. In addition, a detailed matching of the experimental dependence R( φ ) with one of calculated curve by regression method allows minimize the objective function and allows to establish a detailed model of the transition layer. The paper shows that the value of N is 1.4003...1.4008. According to the formula of the effective Bruggeman's medium, the packing density of erythrocytes in the volume of FBEs is about 85%, which is well matched with the data known from the literature. At the same time, at least two intermediate layers were detected at the gold /FBEs interface. (1) A layer 33–38 nm thick adjacent to the hydrophobic surface of the gold film and with a refractive index of N p = 1.356–1.357. Presumably, it is a binary phase with a liquid part in the form of water, a buffer solution or blood plasma and a hard part in the form of proteins non-specifically related to gold, most likely molecules of albumin and fibrinogen. (2) A thicker, transition-to- volume FBEs layer is most likely related to the edges curvature and marginal packing of erythrocytes; the effective thickness of this layer is d m = 130-200 nm, and the effective refractive index N m = 1.356... 1.369. The details of this transition layer are currently of considerable practical interest because they can reflect the physiological state of blood cells and whole body, and the parameters d m and N m can be useful from a biological or medical point of view.