Ultrasound-inducible fluorescent particles for internal tattooing

Our objective is to selectively and non-invasively deposits markers under image guidance for internal tattooing. This study describes the production of ultrasound-inducible particles carrying large payloads of fluorescent markers and the in vivo proof of concept of their remote deposit via focused ultrasound. The particles are double emulsions produced in a microfluidic system, consisting of aqueous fluorescein in perfluorocarbon in water. The vaporization threshold of these particles is measured with a 2.25 MHz transducer focused in an Opticell plate and observed under an inverted fluorescence microscope. The composite particles are monodisperse with a diameter of 5 microns. Fluorescein-containing water represents about 70% of the particles content and they are stable for weeks. When submitted to 2.25 MHz pulses, the particles vaporize at 4 MPa peak-negative pressure. During disruption, jets of fluorescein are generated. After several seconds, a brightly fluorescent dot (0.5 mm diameter) is observed at the focus of the transducer. Experiments in the chorioallantoique membrane of chicken eggs demonstrate that sufficient fluorescein can be released allows the observation by the naked eye. This localized internal tattooing could help surgeons identify tissue previously highlighted under image guidance.