Microbubbles (MBs) are currently used as ultrasound (US) contrast agents and as delivery vehicles for site-specific US triggered drug and gene delivery. Multimodal US-based imaging methods have been applied preclinically to assess and validate the effectiveness and fate of MBs as imaging contrast agents and drug delivery vehicles. Here we present the generation of trimodality MBs generated from the dense concentration of porphyrins within a MB shell, enabled by the conjugation of a porphyrin to a phospholipid. These trimodality MBs possess US, photoacoustic and fluorescence properties with potential to expand into other imaging modalities such as MRI and nuclear imaging.
Ultrasound and photoacoustic imaging are highly complementary modalities since both use ultrasonic detection for operation. Increasingly, photoacoustic and ultrasound have been integrated in terms of hardware instrumentation. To generate a broadly accessible dual-modality contrast agent, we generated microbubbles (a standard ultrasound contrast agent) in a solution of methylene blue (a standard photoacoustic dye). This MB 2 solution was formed effectively and was optimized as a dual-modality contrast solution. As microbubble concentration increased (with methylene blue concentration constant), photoacoustic signal was attenuated in the MB 2 solution. When methylene blue concentration increased (with microbubble concentration held constant), no ultrasonic interference was observed. Using an MB 2 solution that strongly attenuated all photoacoustic signal, high powered ultrasound could be used to burst the microbubbles and dramatically enhance photoacoustic contrast (>800 -fold increase), providing a new method for spatiotemporal control of photoacoustic signal generation.