Light Interactions with Gold Nanorods and Cells: Implications for Photothermal Nanotherapeutics

Abstract

Gold nanorods (AuNR) can be tailored to possess an intense and narrow longitudinal plasmon (LP) absorption peak in the far-red to near-infrared wavelength region, where tissue is relatively transparent to light. This makes AuNRs excellent candidates as contrast agents for photoacoustic imaging, and as photothermal therapeutic agents. The favorable optical properties of AuNR which depend on the physical parameters of shape, size and plasmonic coupling effects, are required to be stable during use. We investigate the changes that are likely to occur in these physical parameters in the setting of photothermal therapeutics, and the influence that these changes have on the optical properties and the capacity to achieve target cell death. To this end we study 3 sets of interactions: pulsed light with AuNR, AuNR with cells, and pulsed light with cells incubated with AuNR. In the first situation we ascertain the threshold value of fluence required for photothermal melting or reshaping of AuNR to shorter AuNR or nanospheres, which results in drastic changes in optical properties. In the second situation when cells are exposed to antibody-conjugated AuNR, we observe using transmission electron microscopy (TEM) that the particles are closely packed and clustered inside vesicles in the cells. Using dark-field microscopy we show that plasmonic interactions between AuNRs in this situation causes blue-shifting of the LP absorption peak. As a consequence, no direct lethal damage to cells can be inflicted by laser irradiation at the LP peak. On the other hand, using irradiation at the transverse peak (TP) wavelength in the green, at comparative fluences, extensive cell death can be achieved. We attribute this behavior on the one hand to the photoreshaping of AuNR into spheres and on the other hand to clustering of AuNR inside cells. Both effects create sufficiently high optical absorption at 532 nm, which otherwise would have been present at the LP peak. We discuss implications of these finding on the application of these particles in biomedicine.

Emerging nanotechnological research for future pathways of biomedicine

“…Gold NPs and gold nanorods, 6 due to their electronic structure, heat themselves when exposed to strong electromagnetic radiations, like those emitted by lasers (Ratto et al, 2011;Ungureanu et al, 2011). This biomedical procedure uses heat to kill cancer cells (El-Sayed et al, 2006).…”

Photothermolysis mediated by gold nanorods modified with EGFR monoclonal antibody induces Hep-2 cells apoptosis in vitro and in vivo

“…Gold nanorods (AuNRs) are a nontoxic nonmaterial and are thought to be a promising tool for use in clinical diagnosis and treatment of diseases. 1,2 AuNRs have a characteristic surface plasmon resonance, [2][3][4][5] with two distinctive absorption peaks: a longitudinal plasmon absorption peak and transverse plasmon peak (at around 520 nm). The longitudinal plasmon peak locates in the far-red and near-infrared (NIR) region of the electromagnetic spectrum.…”

“…The light absorbed by AuNRs can subsequently convert into heat. 2,3 Therefore, AuNRs have a great potential to be used in plasmonic photothermal therapy.…”

“…42 Cell death mediated by EGFRmAb-AuNRs+Laser treatment is closely associated with thermal production after NIR laser irradiation. 2 In our study, the thermal production with EGFRmAb-AuNRs+Laser treatment was measured by the temperature change during the NIR laser irradiation. It is noted that the temperature of the EGFRmAb-AuNRs+Laser solution stabilized after continuous NIR irradiation for a certain time (Figure 2 International Journal of Nanomedicine 2014:9 Figure 5 (A-C) effects of egFrmab-auNrs+laser treatment on xenograft tumors of hep-2 cells (student's t-test, *P,0.05).…”

Microspectroscopic characterisation of gold nanorods for cancer detection

“…Although the applied laser power may still be increased, care has to be taken not to exceed the threshold for particle reshaping which already can occur at very short laser pulses. 290,294,295 In addition, the 3D contour plotting could be improved by optimizing the thresholding routine. Currently, thresholds are set manually and are rather arbitrary.…”