# An optically driven microstructure for torque measurement in rotary molecular motors

## TL;DR

Researchers developed a light-powered microstructure to measure torque in bacterial flagellar motors, enabling precise control and measurement at the nanoscale.

## Contribution

A 3D chiral light-mill is introduced as a tunable torque clamp for live E. coli flagellar motors.

## Key findings

- The 3D microstructure couples selectively to E. coli flagellar motors for torque measurement.
- A calibration protocol allows absolute quantification of torque in both natural and reverse rotation directions.
- The device expands optical tools for studying biomechanics of rotary molecular motors.

## Abstract

‘Light-mills’ are optically driven microstructures that can exchange orbital angular momentum with light and thus rotate around a central axis with a controlled applied torque. Although many studies have explored the employment of light momentum for torque generation, only a few convincing applications in cellular and molecular biology have been demonstrated. Here, we design a 3D chiral structure that can be selectively coupled to a target nanometric flagellar motor in a live E. coli cell, functioning as an external, tunable torque clamp. We optimize our 3D microstructures for torque conversion efficiency and mechanical stability, and propose a calibration protocol that enables absolute quantification of the torque generated by the flagellar motor during rotation in both its natural and reverse directions. Our results demonstrate that microfabricated light-mills expand the optical toolbox for biomechanical study of individual rotary motors by enabling controlled torque application and measurement at the nanoscale.