How Biosonic Spectroscopy Hears Viruses with Light

Sound has long been used to reveal the properties of materials. The characteristic tones generated when an object is struck arise from its intrinsic mechanical properties, with resonance frequencies determined by its size and shape, density, and elastic response. In condensed matter systems, the same idea appears in the form of phonons, which describe the collective vibrations that govern many thermal and mechanical behaviors.

These principles also apply at the nanoscale. When a short pulse of light is absorbed by a metal nanoparticle, it undergoes a rapid expansion and contraction that produces a well-defined vibrational response. This motion can be detected optically through minute changes in the scattered light as the particle vibrates at its natural frequency. Until recently, it was not clear whether similar vibrational signatures could be observed in soft biological structures where membranes and protein assemblies are far less rigid than metals.

Recent work has shown, using ultrafast pump probe spectroscopy, that individual virus particles support coherent vibrational modes that persist for several nanoseconds after excitation. These vibrations occur billions of times per second (GHz) and show that viruses behave as nanoscopic elastic resonators whose mechanical properties that can be measured optically. In enveloped viruses, shifts in frequency and damping reflect changes in membrane structure, glycoprotein interactions, and the early stages of disassembly.

Because this approach relies entirely on light and does not require labels or chemical modification, it tracks mechanical changes under native aqueous conditions and timescales relevant to viral function. These mechanically encoded optical signatures offer new opportunities in fundamental virology and suggest diagnostic strategies in which the vibrational response of a single virus can provide rapid and reagent free information about its identity and structural integrity.

About the presenter
Elad Harel, Ph.D., is a professor in the Department of Chemistry at Michigan State University, whose research advances ultrafast spectroscopy, nonlinear optical imaging, and coherent acoustic phonon sensing. His work spans biological nanoparticles, quantum and energy materials, and solution-phase chemistry, with applications ranging from label-free viral diagnostics to light-directed materials synthesis.