Microbubbles have been used for many years now in clinical practice as
contrast agents in ultrasound imaging. Recently, their therapeutic applications have also attracted more attention. However, the short circulation time (minutes) and relatively large size (two to ten micrometers) of currently used commercial
microbubbles do not allow effective extravasation into
tumor tissue, preventing efficient
tumor targeting. Fortunately, more multifunctional and
theranostic nanoparticles with some special advantages over the traditional
microbubbles have been widely investigated and explored for biomedical applications. The way to synthesize an ideal ultrasound
contrast agent based on nanoparticles in order to achieve an expected effect on contrast imaging is a key technique. Currently a number of nanomaterials, including
liposomes,
polymers,
micelles,
dendrimers,
emulsions,
quantum dots, solid nanoparticles etc., have already been applied to pre or clinical trials. Multifunctional and
theranostic nanoparticles with some special advantages, such as the
tumor-targeted (passive or active), multi-mode
contrast agents (magnetic resonance imaging, ultrasonography or fluorescence), carrier or enhancer of drug delivery, and combined chemo or thermal
therapy etc., are rapidly gaining popularity and have shown a promising application in the field of
cancer treatment. In this mini review, the trends and the advances of multifunctional and
theranostic nanoparticles are briefly discussed.