Microauscultation devices via acoustic coupling with near-field light-matter interactions

Sound waves are crucial in communication and imaging, including medical ultrasound, sonar, and seismography. Auscultation—listening to the sounds of the body—is one of the first things a physician does to assess the health of a patient. Heart activity, blood flow, and pulmonary gas exchange all have unique sounds that to a trained physician’s ear can be used to quickly identify problems in bodily functions.

It is also conceivable that cells, bacteria, and viruses all generate distinct acoustic signals. Being able to eavesdrop on this acoustic world would not only be a significant scientific breakthrough but would also transform our ability to monitor our health, diagnose disease, particularly at an early stage, and help answer fundamental biological questions.

However, detecting the subtle acoustic signatures from small biological objects while surrounded by a cacophony of other sounds will require a new approach to listening: devices that can approach the size of the sound source, have exceptional sensitivity over a broad range of acoustic frequencies, and have a strong directional and distance-limited sensory capability. Current mechanoelectrical stethoscopes and hydrophones are not engineered to push the limits of auscultation nor be scaled down to operate extremely close to acoustic sources.

To address these shortcomings, this proposal seeks to engineer small nanoscale fiber optics that can efficiently convert weak sound waves into an optical signal that can be measured with a photodetector or camera. The working principle of the design involves metal nanoparticles decorating a soft polymer coating that moves in response to extremely low amplitude sound waves, creating a modulated optical signal unique to the detected acoustic signature.

This project will have a major impact on student learning and achievement. For example, “Summer of Nano” workshops will be developed to increase student enrollment numbers in STEM degree programs at UC San Diego, and other higher education institutes, by galvanizing cross-border relationships between UC San Diego and Mexico as well as local San Diego high schools.

Through teaching about how cross-disciplinary science can be used to accelerate scientific discovery and innovation, this project will also be pivotal in recruiting and retaining a broad range of students in engineering degree programs at UCSD.

This proposal aims to design, fabricate, and evaluate acoustic-to-optical nanoscale transducers that leverage strong near-field plasmon-dielectric coupling effects to detect and interpret sound signatures never heard before by other local nano-ears. Impedance-optimized acousto-compressible polymer nanofiber cladding layers will be synthesized that enable strong, acoustic modulation of plasmonic nanoparticles embedded in, or attached to, the polymer layer.

It will be demonstrated that these cladding layers can be tuned to be modulated by weak sound waves in the optical near field with a broad range of frequencies and amplitudes. Through laser Doppler vibrometry and high-speed digital holographic microscopy, the acoustic resonance and response of the plasmomechanical transduction mechanism will be fully correlated to the cladding deformation studies, providing a deep understanding of how to leverage various parameters (light wavelength, nanoparticle size/shape, polymer composition/thickness, etc.) to control the performance and response of the nanofiber microauscultation devices.

The directional response pattern and frequency-dependent sensitivity will be quantified using custom lithium niobate transducers, which will help fill the intellectual gap on how the acoustic near field couples to the far field, and it will be demonstrated that the nanofiber microauscultation devices are sensitive enough to detect and transduce acoustic signatures from nanobiomechanical systems (e.g., genome ejection from viral capsids) for the first time.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.