Ultrasensitive torque sensing and optomechanical measurements of spider silks in high vacuum

Abstract

For centuries, the torsion pendulum (ToP) has stood as an extraordinary instrument, facilitating groundbreaking discoveries such as the first detection of the gravitational constant, first measurements of radiation pressure, the discovery of Coulomb’s law etc. Torsion pendulum force sensors are invaluable tools for precise force measure ment across a wide range of applications. However, the detection of these ultra-low forces requires long period, high Q oscillators which employ complicated detection mechanisms demanding high angular precision and long integration times. We intro duce a new class of optical silk torsion pendulum showing wide range of sensitivity from pNm down to few hundred zeptoNm achieved by exploiting hitherto unknown ultra-soft twist response of tough spider silk fibers in ultrahigh vacuum. We demonstrate several macroscopic micro-gram ToPs using three different silk types showing six orders of magnitude wide range of sensitivity and show modulation of silk properties in different types of silk. Remarkably, a nanoscale diameter capture silk exhibits about 20 fNm/rad torsion constant with low damping and responds to sub-400 zNm impulses in quantitative agreement with model simulations. We demonstrate rapid response single-cycle radiation pressure torque measurements using silk ToP within one oscillation cycle of a few seconds. This results in a rapid quantitative measurement in real time that has an automatic reset for the next mea surement without any relaxation time. As a unique application, we show detection of a direct exposure of sunlight, rendering a fast and precise determination of local push of solar radiation. We present a thorough investigation of mechanical properties and tensile behavior of spider silk in vacuum. We report a phenomenon of supercon traction observed in different types of spider silk fibers when introduced in vacuum. We present a direct comparison of the mechanical properties of spider silk in air and vacuum by performing stress-strain tests using an optically readable customized cantilever setup calibrated for force measurement