X-Ray Nanothermometry of Nanoparticles in Tumor-Mimicking Tissues under Photothermia

Abstract

Temperature plays a critical role in regulating body mechanisms and indicating inflammatory processes. Local temperature increments above 42 °C are shown to kill cancer cells in tumorous tissue, leading to the development of nanoparticle-mediated thermo-therapeutic strategies for fighting oncological diseases. Remarkably, these therapeutic effects can occur without macroscopic temperature rise, suggesting localized nanoparticle heating, and minimizing side effects on healthy tissues. Nanothermometry has received considerable attention as a means of developing nanothermosensing approaches to monitor the temperature at the core of nanoparticle atoms inside cells. In this study, a label-free, direct, and universal nanoscale thermometry is proposed to monitor the thermal processes of nanoparticles under photoexcitation in the tumor environment. Gold-iron oxide nanohybrids are utilized as multifunctional photothermal agents internalized in a 3D tumor model of glioblastoma that mimics the in vivo scenario. The local temperature under near-infrared photo-excitation is monitored by X-ray absorption spectroscopy (XAS) at the Au L₃ -edge (11 919 eV) to obtain their temperature in cells, deepening the knowledge of nanothermal tumor treatments. This nanothermometric approach demonstrates its potential in detecting high nanothermal changes in tumor-mimicking tissues. It offers a notable advantage by enabling thermal sensing of any element, effectively transforming any material into a nanothermometer within biological environments.

Keywords: X-ray absorption spectroscopy; nanomedicines; nanothermal therapy; nanothermometry; photothermia; plasmonic nanoparticles.

Figure 1

Gold iron‐oxide hybrids as magneto‐photothermal agents in 3D tumor spheroids. A) TEM images of synthesized gold‐iron oxide nanohybrids. B) Cell viability of gold‐iron oxide nanohybrids in U87 glioblastoma cells incubated at 12.5, 25, 50, and 100 µg_TOTAL mL⁻¹ for 24 h internalized in U87 cells (n = 3). C) TEM micrographs of gold‐iron oxide nanohybrids in U87 cells. Nanohybrids are inside endosomal compartments. D) Images of control and labeled (with nanohybrids) spheroids. E) Confocal images of a spheroid stained with actin (cytoskeleton, red) and with DAPI (nucleus, blue) at different orientation planes: 3D reconstruction (left), plane bottom (central), and border surface (right) of the spheroid. F) Spheroid section stained with hematoxylin/eosin (viable cells in pink, nucleus in purple, and extracellular matrix in light pink). G) Magnetization hysteresis loop at 300 K of Au/Fe₃O₄ synthesized nanohybrids (dark blue) and in cells (light blue). H) UV–vis–NIR spectra of previous samples in solution (on top) and in cells (down), which display a plasmon resonance at the NIR region.

Figure 2

A) Scheme of the experimental set‐up to obtain X‐ray absorption nanothermal spectroscopy inside cells measurements applying simultaneously X‐rays and NIR laser irradiation on systems based on nanoheaters within 3D tumor spheroids. A thermographic camera is positioned in place to monitor the macroscopic temperature achieved under photothermal excitation. B) XANES at both (B) Au L₃‐edge (11 919 eV) and C) Fe K‐edge (7112 eV) at 300 K of Au/Fe₃O₄ nanohybrids as‐synthesized and in cells. D) Au L₃‐edge EXAFS oscillation functions χ(k)·k² in the calibration range from 100 to 375 K and subjected to photothermal excitation at different density powers (0.05–0.6 W). E,F) Fourier transformed EXAFS signal (FT) in the calibration range (100–375 K) and under photothermal excitation (0.05–0.6 W). G) Temperature‐dependent curve of Debye–Waller factor (σ²) for nanohybrids (calibration fit curve) (open symbols). The solid symbols correspond to calculated values under photothermal excitation. The solid lines represent the fitting following the Debye‐Einstein model in the linear approximation (100–375 K). Inset: Local temperatures attained under laser excitation (0.05–0.6 W).

Figure 3

A) Temperature elevations for Au/Fe₃O₄ subjected to different laser powers (0.05–0.6 W), reaching the thermal steady state, measured with the EXAFS technique (local temperature) and with the infrared thermal camera. The macroscopic temperature increase of control cells (unlabeled) has been also measured upon laser excitation. B,C) Infrared thermal images and temperature curves of Au/Fe₃O₄ nanohybrids under laser irradiation at different laser powers (0.05–0.6 W).