WGM ultrasound probe with a DFB laser tuning system for ultrasensitive solution concentration detection

Accurate liquid concentration detection is vital for medical, industrial, and environmental applications, yet conventional methods still face limitations.We propose an ultrasound probe with a self-assembled polymer whispering-gallery-mode (WGM) microcavity, leveraging the photoacoustic (PA) effect and a distributed feedback (DFB) laser tuning system for ultrasensitive quantification.The probe achieves 13.5 Pa sensitivity and 42 MHz bandwidth (-6 dB), ensuring broad applicability in diverse liquids.Overcoming traditional WGM sensors' instability, our integrated platform demonstrates a recordlow detection limit of 10 -7 g/mL for crystal violet among substrate-free, real-time methods.Unifying the microcavity, laser, and electronics into a portable architecture, this system enables high-fidelity, nondestructive liquid analysis with strong anti-interference and endoscope-deployable sensing in complex environments.