Enhancing laser thermal-therapy using ultrasound–microbubbles and gold nanorods of in vitro cells

Gold nanorods (GNRs) are being exploited for their absorption properties to improve thermal therapy. However, a key challenge is delivering sufficient concentration of GNRs to induce a therapeutic effect. In this study, ultrasound and microbubbles (USMBs) were used to enhance intracellular uptake of GNRs. AML-5 cells in suspension (0.6 mL) were exposed to ultrasound (1.3 and 1.7 MPa peak negative pressure) and definity microbubbles (1.7% v/v) for 1 min at varying GNR concentrations (0–2.5 × 1011 per mL). Following ultrasound–microbubble treatment, cells were centrifuged twice and treated with an 810 nm laser at an average fluence rate of 3.6 W/cm2 for 5 min. In addition, cells were incubated with GNRs for 12 h prior to laser treatment. Following the treatment, cell viability (VPI) was assessed using propidium iodide (PI) and flow cytometry. Cell viability decreased by ∼4-folds with the combined treatment of USMB + GNR + Laser (VPI = 17%) compared to cells incubated with GNR + Laser (VPI = 68%). This effect depended on ultrasound pressure and GNR concentration. Higher cell death was achieved at higher GNR concentration and 1.3 MPa peak negative pressure. Cell viability decreased from 92% to 29% with increasing GNR concentration from 1 × 1011 to 1.5 × 1011 GNR/mL. In addition, higher temperatures were observed using a thermal camera with the combined treatment (USMB + GNR + Laser) of 59 ± 1 °C compared to 54 ± 0.9 °C for cells incubated with GNRs. The combined treatment of ultrasound–microbubble and gold nanorod laser induced thermal-therapy improved treatment response of in vitro cells.

► USMB enhanced therapeutic effect of AuNP and laser therapy by four folds compared to 12 h incubation with AuNP.
► Temperature increased by ∼20 °C in cell treated with AuNP, USMB and laser as measured with thermal camera.
► Effect of combined treatment depended on acoustic pressure and gold nanoparticle concentration.
► The underlying mechanism may be associated with ultrasound–microbubble induced permeabilization of cell membranes.