Fiber-tip photoacoustic probe with MoS₂-PDMS composite coating for temperature and density-induced ultrasonic speed tuning

We demonstrate here a miniature broadband (up to ~12.8 MHz) fiber-tip photoacoustic probe with ~68.32-μm thick MoS₂-polydimethylsiloxane (PDMS) composite coating for ultrasound velocity adjustment by the regressive dependence on the temperature and density of saline solution. The composite was applied to the tip of a double-clad fiber with an outer diameter of 125 μm using drop casting. Under a 5-ns pulsed laser excitation, the developed probe sensitivities to temperature and density in the range of 20-50 °C and 0.99-1.10 g/cm³ were investigated in terms of the change in velocity and attenuation of ultrasonic wave transmitting in the saline solution. An excellent goodness of fit (R²>0.99) and significance of the binary linear regression (F>>F_0.01) were achieved with the corresponding mean relative errors of 0.38% and 0.12% for measured temperatures and densities, along with a tunable range of 1478.51 to 1679.13 m/s. The proposed technique could therefore be extended for in situ matching ultrasound velocity of coupling liquid at the transducer-tissue boundary in optoacoustic imaging.