Optomechanical Detection of Vibration Modes of Single Bacterium

The field of optomechanics has made impressive advances in the last decades, covering a broad range of applications going from ultrasensitive sensing to fundamental quantum studies. The use of optomechanical devices for biosensing has acquired crescent interest in the last years. A very promising optomechanical platform for biosensing applications are semiconductor microdisks. These devices support a family of modes, the radial breathing modes (RBM), which present extremely high mechanical frequencies (&gt; GHz) and low energy losses in liquids. These assets, together with their remarkably low masses (in the pg range), provide them with extremely low mass sensitivities and high speed, notably, while immersed in liquid¹. In addition, semiconductor microdisks can be integrated in collective configurations, thus, improving their sensing efficiency while keeping their individual capabilities².<br/>In this work we demonstrate that optomechanical sensors allows the detection of low frequency-frequency phonon modes of biological particles such as bacteria. These vibration modes carry information on its structure and mechanical properties that play a pivotal role in many relevant biological processes. We show that the vibration modes of an optomechanical sensor hybridize with the ones of the bacteria when their associated frequencies are similar. We develop a general theoretical framework that allows to retrieve the bacterium eigenfrequencies and mechanical loss. Our method is applied for analysis of the effect of hydration on the vibrational properties of a single bacterium. This work opens the door for a new class of vibrational spectrometry based on the use of high frequency mechanical resonators with the unique capability to obtain information on single biological entities³.<br/><br/>[1] E. Gil-Santos et al. High-frequency nano-optomechanical disk resonators in liquids. Nature Nanotechnology. 10, p. 810-817 (2015).<br/>[2] E. Gil-Santos et al. Light-mediated cascaded locking of multiple nano-optomechanical oscillators. Physical Review Letters. 118, p. 063605 (2017).<br/>[3] E. Gil-Santos et. al. “Optomechanical detection of vibration modes of single bacterium”. Nature Nanotechnology, 15, 469-474 (2020).