Nonlinear optical and photoacoustic properties of aqueous crystalline hemoglobin. Towards facile detection of hemoglobin concentration in blood

In this work, nonlinear optical properties of hemoglobin are studied under the irradiation of a blue LED laser beam. The z-scan setup is applied in order to determine nonlinear optical responses. Photoacoustic waves are created in a hearable sound region. Sounds are recorded by a microphone and analyzed by using Fourier transform to evaluate the sonic frequencies. The suspensions of hemoglobin in water are prepared in the range of 120-160 mg/mL that is in the range of hemoglobin concentration in blood. It is found that the amplitude of photoacoustic (PA) signals and nonlinear absorption coefficients depend directly to the hemoglobin concentration. On the other hand, blood of rabbit is studied using this method and results are compared with the crystalline hemoglobin findings. It is concluded that the frequency domain of photoacoustic waves created by hemoglobin is similar to that observed for the blood sample. It means that the main portion of photoacoustic response in blood is due to its hemoglobin content and amplitude of the sonic signals is directly related to the concentration of hemoglobin. FT-IR studies confirmed that the vibrational levels of hemoglobin had no a significant effect on the recorded PA signals and the main PA effect has been originated from explosion of the micro- and nano-bubbles. Moreover, from the UV-Vis spectrum of hemoglobin, it can be conferred that absorption of the blue photons by the porphyrin ring leads to the evaporation of water molecules and generation of the mentioned bubbles responsible for the created sonic waves after explosion. This study would be considered as a fast and simple method to determine hemoglobin concentration in the real blood samples using nonlinear optical and photoacoustic characterizations. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the nonlinear optical properties of hemoglobin under blue LED laser irradiation, using z-scan setup to determine nonlinear optical responses. It is found that the amplitude of photoacoustic signals and nonlinear absorption coefficients depend directly on hemoglobin concentration. Furthermore, the study of rabbit blood reveals similarities in frequency domain of photoacoustic waves with crystalline hemoglobin, indicating the main portion of photoacoustic response in blood is due to its hemoglobin content.