Z-scan as a hemoglobin sensor: A simple and sensitive optical tool for measuring hemoglobin concentration in human blood

Over the last few years, sensitive, prototype, and cost-effective devices have been in high demand to measure various biological parameters. Determining these parameters is highly essential to understand the associated diseases. Therefore, in the present study, we have proposed and demonstrated one of the simple and sensitive nonlinear optical tools (Z-scan technique) as a hemoglobin sensor. For demonstration, we have taken different human blood samples (variation in groups and Rh factors) with varying hemoglobin concentrations. Specifically, we have implemented the closed-aperture (CA) Z-scan technique and observed that all blood samples exhibit thermo-optical nonlinearity due to the self-defocusing effect, and the strength of nonlinearity is directly proportional to the hemoglobin concentration. The calculated values of nonlinear refractive indices show a linear relationship with different hemoglobin concentrations in all blood types. Further evidence that hemoglobin is the primary contributor to the nonlinearity observed in these blood samples comes from the CA Z-scan results of pure hemoglobin. The nonlinear refractive indices of pure hemoglobin at various concentrations also display a linear relationship with hemoglobin concentration, similar to that observed in blood samples. Hence, we propose that the CA Z-scan technique could measure the hemoglobin concentration in human blood by following the linear relationship between the nonlinear refractive index and hemoglobin concentration. The findings of this study may contribute to a better understanding of various diseases in which hemoglobin levels play a critical physiological role.