An ultra-thin MXene film with high conversion efficiency for broadband ultrasonic photoacoustic transducer

High-pressure, broadband, and miniatured ultrasound emitters are urgently needed in biomedical imaging and treatment as well as non-destructive detection. In this work, we report a laser generated ultrasonic photoacoustic transducer (LGUPT) based on an ultra-thin layer of MXene (Ti₃C₂T_x) nanosheets. Under the excitation of 532nm nanosecond laser pulses, the amplitude of the generated sound pressure can reach 8.7MPa, with a bandwidth of 17.4MHz at the irradiation intensity of 17.72mJ/cm². The photoacoustic conversion efficiency of the 1.2μm-thick MXene film/PDMS transducer was found to be 1.21×10^-2, which is among the highest values reported to date. The MXene thin film can also be drop-casted on the curved surface of a focusing lens. The amplitude of the sound pressure signal can reach 25.3 MPa and the bandwidth 19.7MHz at a pulse laser energy of 28.12mJ/cm². The width of the focal spot at -3 dB of maximum amplitude was found in the range of 0.14mm for the optical lens based LGUPT under the condition of a laser spot diameter of 15mm by theoretical simulation. The water processable focusing LGUPT demonstrated excellent ultrasonic cavitation effect on the tissue mimicking agar plate. Our experimental and theoretical work highlights the potential of ultra-thin MXene film based LGUPTs for high precision photoacoustic therapy, integrated imaging and sensing instruments.