Fiber optics photoacoustic generation using gold nanoparticles as target

Abstract

Ultrasound transducers have been used in various applications such as nondestructive testing, acoustic response analysis of vascular tissues, and medical imaging. Most recent applications lead to a demand of more advanced ultrasound generators featuring higher central frequency, wider bandwidth and miniature size. In this paper, a novel ultrasound generator on an optical fiber tip is designed, fabricated and characterized. The ultrasound generator was fabricated by coating several layers of gold nanoparticles (Au NPs) on the end face of a piece of commercially available optical fiber via a layer-by-layer (L-b-L) technique. The Au NPs were synthesized by a traditional sodium citrate reduction method and the diameter of Au NPs was controlled at 20 nm. The ultrasound is generated through photoacoustic procedure. By introducing excitation laser pulses on the Au NPs layer, the energy of laser is converted into the heat through photothermal mechanism. Then, the heat transforms into kinetic energy through thermalelastic mechanism. Thus, ultrasound can be generated. The experiment results showed that this kind of ultrasound generator shows wide bandwidth, high frequency and miniature size. By comparing to the conventional energy absorption material such as graphite, the Au NPs show high energy absorption efficiency and high thermal expansion rate. Therefore, the generator exhibits great potentials in intravascular imaging due to its miniature size.