Wavelength dependent photothermal conversion efficiency of photosensitizers for photothermal therapy

Today, cancer treatment is one of the most important research fields since it is the second most lethal disease worldwide. Among the current treatment methods that have strong potential for future cancer therapies is photothermal therapy (PTT). Nanoparticles have become popular photosensitizers for photothermal therapy (PTT), as they can be targeted to specific cancer tissues and deliver a chemotherapeutic drug, providing a multimodal therapeutic approach. Photothermal conversion efficiency of nanoparticles is critical in the assessment of their therapeutic use in PTT. In this thesis, we describe an accurate calorimetric method for the determination of the photothermal conversion efficiency of nanoparticles in solution. A tightly focused continuous wave laser beam was used to irradiate a cuvette containing a solution of silver sulfide-glutathione quantum dots (Ag2S-GSH QDs), and the maximum steady-state temperature rise was measured with an infrared camera. The data were analyzed using two different photothermal conversion efficiencies, the intrinsic and external conversion efficiencies, to relate the induced heating power of the nanoparticles to the absorbed and incident optical powers, respectively. Measurements with a tunable Ti3+:sapphire laser showed that the intrinsic photothermal conversion efficiency of Ag2SGSH QDs exceeded 91% over the 720−810 nm wavelength range. The method was also used to analyze poly (acrylic acid)-coated superparamagnetic iron oxide nanoparticles (PAA/SPIONs), and the intrinsic photothermal conversion efficiency was determined to be 83.4% at 810 nm. At 640nm, PAA/SPIONs with 600 µg/ml of iron had intrinsic and extrinsic photothermal conversion efficiency of 76% and 63%, respectively. This approach is useful for the evaluation of various potential nanoparticles for photothermal therapy applications. In additional in vivo experiments, Ag2S-GSH Herceptin QDs were injected into mice grown with tumor SKBR3. Cisplatin was used as chemotherapeutic drug with the QDs. Both Cisplatin and Ag2S-GSH Herceptin QDs were injected subcutaneously into the mouse and investigated for different drug dozes of 10 mg/kg and 20 mg/kg. The mice were then irradiated with a fiber-coupled diode laser at 793 nm. 10 mg/kg of QDs gave 6.2℃ temperature rise whilst 20 mg/kg of QDs raised the surface temperature by almost 9 ℃ at 1.49 W/cm2 of laser intensity. When the laser intensity was increased to 1.59 W/cm2 and applied for 10 minutes, the temperature rise was recorded as 15℃. The experimental methods described in this thesis work should be useful in the characterization of new potentially important nanoparticles for photothermal therapy applications.