Quantification of fast molecular adhesion by fluorescence footprinting

Abstract

Rolling adhesion is a unique process in which the adhesion events are short-lived and operate under highly non-equilibrium conditions. These characteristics pose a challenge in molecular force quantification, where in situ measurement of such forces cannot be achieved with most molecular force sensors that probe near equilibrium. In this report, we demonstrated a quantitative adhesion footprint assay combining DNA-based non-equilibrium force probes and modelling to measure the molecular force involved in fast rolling adhesion. We were able to directly profile the ensemble molecular force distribution during rolling adhesion with a dynamic range between 0 – 18 pN. Our results showed that the shear stress driving bead rolling motility directly controls the molecular tension on the probe-conjugated adhesion complex. Furthermore, the shear stress can steer the dissociation bias of components within the molecular force probe complex, favouring either DNA probe dissociation or receptor-ligand dissociation.

Quantitative interpretation of cell rolling velocity distribution

“…This includes the limited force dynamic range of existing probes and high sensitivity detection because of each bond's short adhesion time (29). A recent study measuring the molecular force of bead rolling might potentially offer a solution to this (30). Although not measuring native P-selectin/ PSGL-1 interactions, similar direct in vivo measurements of molecular force could help validate existing models and provide new insights into mechanisms regulating their behavior.…”

Optothermal rotation of micro-/nano-objects

“…Compared to in-plane rotation, out-of-plane rotation finds a variety of unique applications in fields such as single-cell mechanics, 3D bio-imaging, and micro-/nano-surgery. 16,[106][107][108][109][110][111][112] However, out-of-plane rotation is known to be more challenging to accomplish especially for highly symmetric or isotropic targets. 113 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.…”

“…Rotation of single cells is important for the identification of cellular phenotypes, cell-cell communication, and, particularly, single-cell mechanics. 106,129 Among different measurements of single-cell mechanics, 130 cell adhesion has attracted a lot of attention as it is highly involved in many biological processes such as viral infections.…”

Universal optothermal micro/nanoscale rotors

“…It becomes more challenging to achieve light-driven out-ofplane rotation (i.e., rotation of an object around an axis parallel to the substrate) (24,25). By enabling three-dimensional (3D) interrogation of objects such as biological particles, out-of-plane rotation techniques would improve rolling cell adhesion measurements (26,27), single-cell engineering (28), organism identification (29), and microsurgery (30)(31)(32)(33). Recently, light-driven out-of-plane rotation has only been realized using multiple-beam optical tweezers (10,34) or combining light with a microfluidic field (35) or an external electric field (36).…”