Acoustic detection of laser induced optical breakdown in dendrimer nanocomposites: implications for site targeted molecular diagnostics and therapeutics

Laser-induced optical breakdown (LIOB) attained at the focus of a femtosecond laser leads to nonlinear energy absorption and measurable secondary effects that include shock-wave emission, heat transfer, and bubble formation. A real-time acoustic technique has been developed to characterize LIOB thresholds in tissue-like materials regardless of their optical transparency. With LIOB, a bubble forms resulting in a high velocity shock-wave propagating spherically outward from the effective point source. This wave can be detected acoustically. In addition, the optical focal zone is actively probed with acoustic pulse-echo measurements to monitor formed bubbles. The power of 50-100 MHz acoustic waves reflected from the bubbles can quantify differences between non-breakdown and breakdown events. Using this technique, two dendrimer nanocomposites (DNC) have been evaluated as potential site targeted diagnostic/therapeutic agents. The LIOB threshold was 50 mW (200 nJ/pulse) for a bare DNC system and a reduced threshold of 4 mW (15 nJ/pulse) for an Ag-loaded DNC system. These results suggest that metal-loaded DNC systems may be efficient site targeted diagnostic/therapeutic agents. In addition, their action can be sensitively monitored using high frequency ultrasound imaging.