Ultrasound contrast agents (UCAs) can significantly improve the imaging quality in ultrasonic diagnosis. A common form of UCA is the microbubble (MB), which nowadays has being developed as a novel carrier for targeted gene or drug delivery by ultrasound-targeted microbubble destruction (UTMD) technique. On the other hand, quantum dots (QDs) have become ideal diagnostic agents for cell and tissue imaging because of their excellent fluorescent properties. In addition, it has been suggested recently that QDs have the potential to serve as photosensitizers in photodynamic therapy (PDT) through QD-based energy transfer.
To obtain a kind of novel bi-mode diagnostic agents, we combined ST68 MBs and CdTe QDs together via layer by layer assembly (LBL) technique. Through fluorescent spectra and confocal laser scanning microscopy, it was confirmed that CdTe nano-particles were successfully deposited on the outer surface of the MBs. We also measured the size distribution of MBs before and after the absorption of CdTe QDs by static light scattering, and it showed that after modification the MBs got a little smaller in size but no significant differences were found. Besides, in vitro and in vivo ultrasound imaging indicated that QD modified MBs still maintained as good properties of contrast enhancement as ST68 MBs. Not only did the QD modified MBs reserve both ultrasound and fluorescent imaging properties to act as bi-mode diagnostic agents, but they may have the potential to be used for targeted PDT through UTMD technique.