Light-driven single-cell rotational adhesion frequency assay

Abstract

The interaction between cell surface receptors and extracellular ligands is highly related to many physiological processes in living systems. Many techniques have been developed to measure the ligand-receptor binding kinetics at the single-cell level. However, few techniques can measure the physiologically relevant shear binding affinity over a single cell in the clinical environment. Here, we develop a new optical technique, termed single-cell rotational adhesion frequency assay (scRAFA), that mimics in vivo cell adhesion to achieve label-free determination of both homogeneous and heterogeneous binding kinetics of targeted cells at the subcellular level. Moreover, the scRAFA is also applicable to analyze the binding affinities on a single cell in native human biofluids. With its superior performance and general applicability, scRAFA is expected to find applications in study of the spatial organization of cell surface receptors and diagnosis of infectious diseases.

Optothermal rotation of micro-/nano-objects

“…116 In the past five years, a few groups have proposed diverse strategies for out-of-plane rotation under broken symmetries generated in light-driven temperature fields. 44,72,75,[117][118][119][120] Opto-thermo-electrokinetic rotation techniques. Historically, the main issue in achieving light-driven out-of-plane rotation has centered on generating torque about an axis perpendicular to the optical axis for rotation while simultaneously forming a trap well to overcome Brownian motion for stable rotation.…”

“…118 More recently, we reported a new strategy for the out-ofplane rotation of single cells using opto-thermo-osmotic flows generated from light-absorbing substrates. 117 The experimental setup is shown in Fig. 7a.…”

“…(d) Time-resolved optical images of a rolling yeast cell. (a-c) Adapted with permission 117. Copyright 2022, Springer Nature.…”

Creating stable trapping force and switchable optical torque with tunable phase of light

“…Optical rotation is easily affected when the motor is repelled from the optical field by perturbations, such as fluidic flow. The flow can sometimes be useful though; e.g., rotation of small objects can also be achieved through thermophoresis, shear flow, or harmonic acoustics (29)(30)(31).…”

Light-driven high-precision cell adhesion kinetics

“…This method integrates optical trapping, rotation, imaging, and spectroscopy on a single platform. ScRAFA exploits a microfluidic platform integrated with versatile optothermal manipulation and optical imaging capabilities to stably trap and rotate any specific single cell, continuously monitor the complete cell adhesion process from initiation of bonding with the substrate to formation of permanent attachment (response time <0.1 s), and precisely control the interaction distance between substrate ligands and cell receptors (resolution ±0.1 nm), which control cannot be achieved in a conventional flow chamber assay 32 . More specifically, a focused 785 nm laser beam was first applied to trap the cell with optical force, then the temperature gradient field produced by a focused 532 nm laser beam was used to rotate the cell.…”