Optical force-induced nonlinearity and self-guiding of light in human red blood cell suspensions

TL;DR

This study reveals tunable optical nonlinearities in human red blood cell suspensions caused by optical forces, enabling self-guiding of light, with potential applications in biomedical imaging and diagnosis.

Contribution

It demonstrates for the first time optical force-induced nonlinearity and self-guiding in RBC suspensions under various osmotic conditions, supported by a theoretical model.

Findings

Nonlinear optical effects observed in RBC suspensions.

Nonlinearity strength increases with osmotic pressure.

Different behavior in lysed blood due to free hemoglobin.

Abstract

Osmotic conditions play an important role in the cell properties of human red blood cells (RBCs), which are crucial for the pathological analysis of some blood diseases such as malaria. Over the past decades, numerous efforts have mainly focused on the study of the RBC biomechanical properties that arise from the unique deformability of erythrocytes. Here, we demonstrate nonlinear optical effects from human RBCs suspended in different osmotic solutions. Specifically, we observe self-trapping and scattering-resistant nonlinear propagation of a laser beam through RBC suspensions under all three osmotic conditions, where the strength of the optical nonlinearity increases with osmotic pressure on the cells. This tunable nonlinearity is attributed to optical forces, particularly the forward scattering and gradient forces. Interestingly, in aged blood samples (with lysed cells), a notably different nonlinear behavior is observed due to the presence of free hemoglobin. We use a theoretical model with an optical force-mediated nonlocal nonlinearity to explain the experimental observations. Our work on light self-guiding through scattering bio-soft-matter may introduce new photonic tools for noninvasive biomedical imaging and medical diagnosis.