Engineering researchers develop breakthrough technology to measure rotational motion of cells

Mechanics plays a fundamental role in cell biology. Cells navigate these mechanical forces to explore their environments and sense the behaviour of surrounding living cells. The physical characteristics of a cell’s environment in turn impact cell functions. Therefore, understanding how cells interact with their environment provides crucial insights into cell biology and has wider implications in medicine, including disease diagnosis and cancer therapy.

So far, researchers have developed numerous tools to study the interplay between cells and their 3D microenvironment. One of the most popular technologies is traction force microscopy (TFM). It is a leading method to determine the tractions on the substrate surface of a cell, providing important information on how cells sense, adapt and respond to the forces. However, TFM’s application is limited to providing information on the translational motion of markers on cell substrates. Information about other degrees of freedom, such as rotational motion, remains speculative due to technical constraints and limited research on the topic.

Engineering experts at the University of Hong Kong have proposed a novel technique to measure the cell traction force field and tackle the research gap. The interdisciplinary research team was led by Dr Zhiqin Chu of the Department of Electrical and Electronic Engineering and Dr Yuan Lin of the Department of Mechanical Engineering. They used single nitrogen-vacancy (NV) centres in nanodiamonds (NDs) to propose a linear polarization modulation (LPM) method which can measure both, the rotational and translational movement of markers on cell substrates.

The study provides a new perspective on the measurement of multi-dimensional cell traction force field and the results have been published in the journal Nano Letters. The research, entitled ‘All-Optical Modulation of Single Defects in Nanodiamonds: Revealing Rotational and Translational Motions in Cell Traction Force Fields’, is also featured as the supplementary cover of the journal.

The research showed high-precision measurements of rotational and translational motion of the markers on the cell substrate surface. These experimental results corroborate the theoretical calculations and previous results.

Given their ultrahigh photostability, good biocompatibility, and convenient surface chemical modification, fluorescent NDs with NV centres are excellent fluorescent markers for many biological applications. The researchers found that based on the measurement results of the relationship between the fluorescence intensity and the orientation of a single NV centre to laser polarization direction, high-precision orientation measurements and background-free imaging could be achieved.

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