Optical Manipulation of Erythrocytes via Evanescent Waves: Assessing Glucose-Induced Mobility Variations

TL;DR

The study addresses how near-surface evanescent waves can non-invasively propel red blood cells and how glucose concentration modulates this interaction. Using a dual-chamber prism and a 1064 nm evanescent field, the authors quantify RBC velocities with automated TrackMate tracking under 5 mM and 50 mM glucose. They find a significant reduction in mean velocity from $11.8 \pm 2.1~\mu$m/s$ to $8.8 \pm 1.8~\mu$m/s$ (p = 0.019), suggesting glucose-induced biomechanical changes influence near-surface optical coupling. The work demonstrates a sensitive, non-invasive platform for probing cell mechanics and points to potential micro-rheology-based clinical applications for vascular health assessment.

Abstract

This study investigates the dynamics of red blood cells (RBCs) under the influence of evanescent waves generated by total internal reflection (TIR). Using a 1064 nm laser system and a dual-chamber prism setup, we quantified the mobility of erythrocytes in different glucose environments. Our methodology integrates automated tracking via TrackMate\c{opyright} to analyze over 60 trajectory sets. The results reveal a significant decrease in mean velocity, from 11.8 μm/s in 5 mM glucose to 8.8 μm/s in 50 mM glucose (p = 0.019). These findings suggest that evanescent waves can serve as a non-invasive tool to probe the mechanical properties of cell membranes influenced by biochemical changes.

Figures (6)

• Figure 1: The experimental setup consists of a. laser source 1064 nm CW laser (Ventus) operated at 1.8 W. A series of prisms fabricated with dual-region chamber to allow simultaneous measurement of control (polystyrene) and RBC samples. Imaging with 60x objective (NA 0.85) coupled with a CMOS camera at 25 fps. b. Red blood cell visualization. c. Major and minus axis of EW-area on prism surface. d. Two-chamber method on a single prism for simultaneous experiment with polystyrene micro-particles and erythrocytes (RBC). This method avoid misalignment and artifacts instead of single samples on different prisms.e. EW-scheme: a micro-particle of radius $a$ and refractive index $n_3$ located at a height $h$ above the interface, immersed in the evanescent field (EW) generated by a laser with an angle of incidence $\theta_1$.
• Figure 2: Probability densities for the velocity of microparticles, measured for samples on two different prisms.
• Figure 3: Measurement (in pixels) of laser beam area at prism surface area using formula of ellipse area $\pi ab$, where $a,b$ are major and minus axis, respectively. Software used was Thorcam installed with the CMOS monochrome sensor camera.
• Figure 4: Predicted velocities of spherical micro-particles using $Matlab$ according to Stokes law $F_{drag}=\gamma v_{part}$ where $\gamma = 6\pi\eta R$. Assuming equal forces, then $v_{particle}=F_{EW}/3\pi\mu D$, where $D$ is particle diameter for different refractive indices of the microparticles. a. Linear scale. b. Logarithmic scale.
• Figure 5: a. Representation of all paths traveled by the micro-particles generated in TrackMate©. b. Comparison of probability distributions for micro-particle velocities for two regions on the same prism (two-chamber method). c. Trajectories described by the erythrocytes, generated in $TrackMate$. d. Violin plot for red blood cell measurements at different glucose concentrations and their respective controls (with respect to micro-polystyrene particles); the gray bars correspond to the respective mean and standard deviation, while the colored dots indicate the medians of the data set.