1. Ekaterina N. Lazareva1,2 and Valery V. Tuchin1,2,3
Measurements of refractive index of hemoglobin in the visible and NIR spectral ranges
Ekaterina N. Lazareva1,2 and Valery V. Tuchin1,2,3
1Research Education Institute of Optics & Biophotonics, Saratov National Research State University, 83 Astrakhanskaya str., Saratov, Russia
2Interdisciplinary Laboratory of Biophotonics, National Research Tomsk State University, Tomsk, Russia
3Laboratory of Laser Diagnostics of Technical and Living Systems, Institute of Precision Mechanics and Control RAS, Saratov, Russia

2. Motivation Refractometry can be used to study different interactions.
Hemoglobin, contained in erythrocytes, is responsible for the absorption properties of blood in visible and near infrared spectral ranges, so it is important to know its optical properties.
There is little literature data on the refractive index of biological environments for a wide range of wavelengths.

3. ABSTRACT
This study is focused on the determination of the refractive index of hemoglobin in the visible and NIR range at room temperature. Measurements were carried out using the multi-wavelength Abbe refractometer (Atago, Japan). Were investigated in solutions of different concentrations of hemoglobin obtained from human whole blood.
The refractive index of hemoglobin solutions was measured at wavelengths of 480, 486, 546, 589, 644, 656, 680, 930, 1100, and 1550 nm.
Calculated specific increment of refractive index of hemoglobin and the coefficients for the representation of the dispersion based on the formula of Sellmeier.

4. Dispersion of light ñ(λ)=n(λ)-ik(λ) ñ(λ)=n(λ)-ik(λ)
N - number of molecules, m – molecular weight, q – molecular charge,
ω – frequency of oscillation, ω0 - natural frequency, γ=g/m – damping factor.
normal dispersion
k = 0
Cauchy formula:
А, В, С – empirical constants

5. The dependence of the refractive index of the solution concentration
n(C) = n0 + K C
where n - index of refraction of the solution,
n0 - index of refraction of the solvent,
C - the concentration of the solute,
K - specific refractive index increment substance, that is the value of the refractive index increase with increasing solution concentration of 1%.

6. Materials and methods
Measurements were carried out using the multi-wavelength Abbe refractometer (Atago, Japan).
The refractive index was measured at wavelengths of 480 nm and 1550 nm.
Samples of hemoglobin hemoglobin obtained from human whole blood (96, 146, 219 and 292 g/l) were investigated.
The temperature was 25 °C.
Fig. 1. Multi-wavelength Abbe Refractometer (Atago, Japan): 1 - refractometer; 2 - supply; 3 - light source; 4 - the attachment for measurements in the near IR region; 5 - interference filter; 6 – sample.

7. The dispersion dependence of the refractive index of hemoglobin solution
Fig 2. The dispersion dependence of the refractive index of hemoglobin solution: 1 – for hemoglobin 292 g/l, 2 - for hemoglobin 219 g/l, 3 - for hemoglobin 146 g/l, 4 - for hemoglobin 96 g/l

8. The dependence of the refractive index of the concentration of hemoglobin
Fig 4. The dependence of the refractive index of the concentration of hemoglobin for visible range: 1 – 930 nm, 2 – 1100 nm, 3 – 1300 nm, 4 – 1550 nm (black symbol - experimental data, red lines - approximation of data).
Fig 3. The dependence of the refractive index of the concentration of hemoglobin for visible range: 1 – 480 nm, 2 – 546 nm, 3 – 589 nm, 4 – 680 nm (black symbol - experimental data, red lines - approximation of data).

9. The absolute refractive index and specific refraction increment of Hemoglobin
Fig 6. The dependence of specific temperature increments of hemoglobin solution from wavelength (black symbol - experimental data, red lines - approximation of data).
Fig 5. The dispersion dependence of the absolute refractive index of hemoglobin solution (black symbol - experimental data, red lines - approximation of data).

10. Conclusions
A dispersion dependence and dependence of refractive index of hemoglobin concentration in visible and near infrared regions.
Calculation of coefficients for submission of hemoglobin in refractive index by formula Sellmeier in visible and near infrared regions.
Calculated absolute index of refraction and specific refraction coefficients for the temperature dependence of the refractive index of hemoglobin. For example, (dn/dC) λ=589, T=+24 о С= 0,197±0,007 ml g-1.