Pythagoras' initial discovery of enhanced vibrations in strings at specific frequencies laid the foundation for our tone system. These natural vibrations exist universally in objects, aiding in species, composition, and morphology identification. For instance, terahertz molecular vibrations serve as common chemical fingerprints. Recently, focus shifted to mesoscopic particle vibrations, encompassing functional particles, cells, and viruses. Yet, these vibrations remained concealed due to current limitations.
A Nature Photonics article, “Single-particle photoacoustic vibrational spectroscopy using optical microresonators,” led by Professor Xiao Yunfeng from Peking University, introduces a breakthrough. They employed optical microresonators for real-time measurement of natural vibrations in single mesoscopic particles, expanding vibrational spectroscopy's scope.
Dr. Tang Shuijing explains the microresonator-based approach: Mesoscopic particles vibrate subtly at MHz to GHz rates, challenging traditional detection methods. To address this, a new spectroscopy leverages a brief laser pulse to induce particle vibrations. Placing particles on a high-Q optical microresonator causes vibrations to generate acoustic waves, perturbing its optical mode.
In experiments, researchers placed mesoscopic particles on a silica microspherical resonator (radius ~30 μm, quality factor ~106). Using a 532 nm, 200 ps pulsed laser, they stimulated vibrations (incident energy density ~2 pJ μm−2). This innovation opens a new spectral window for vibrational spectroscopy.
Utilizing a continuous-wave probe laser, the microresonator's optical mode was activated, enabling real-time detection of particle vibrations by tracking the transmitted laser's power. Through Fourier transformation of temporal responses, the particles' vibrational spectra were extracted.
The effectiveness of this vibrational spectroscopy was validated using diverse mesoscopic particles, varying in constituents, sizes, and internal structures. Remarkably, results displayed an unparalleled 50 dB signal-to-noise ratio and a detection bandwidth surpassing 1 GHz.
This groundbreaking technology additionally showcased the capability for biomechanical fingerprinting of microorganisms at the single-cell level, discerning species and living conditions. The unique bunching of natural frequencies in microbial cells of the same species yielded distinct fingerprints, attributed to stable morphologies of specific biological species.
Dr. Xiao Yunfeng, a Boya Professor at Peking University, emphasized, “This vibrational spectroscopy allows non-destructive examination of particle structures and mechanical traits. It can deduce crucial biomechanical features in cells, tied to species and living states.”
He further noted, “The wide applicability of this technology for various mesoscopic particles could potentially revolutionize our understanding of this realm with unparalleled precision.”
Given the complexity of living cells and the significance of their mechanical properties in function, development, and disease, this research introduces a novel fingerprinting technique to analyze biological systems at the individual cell level. It's anticipated to bring forth fresh insights and discoveries across scientific domains.
Source: Peking University