We propose the combination of polyN-isopropylacrylamide (PNIPAM) particles and optical coherence tomography (OCT) to overcome the main limitations of current nanothermometry for medical purposes. We demonstrate that PNIPAM particles can behave as temperature-sensitive contrast agents in OCT thanks to their structural phase transition at 32 °C, resulting in changes in the refractive index that make their OCT contrast temperature-dependent. Simple experiments have been conducted to demonstrate the feasibility of this approach for three-dimensional imaging of phantom tissues subjected to photothermal processes. The results included in this work constitute an alternative route towards facile incorporation of nanothermometry into the clinical world.
Lanthanide-based upconverting nanoparticles (UCNPs) boast low thermal sensitivity and brightness, which, along with the difficulty in controlling individual UCNP remotely, make them less than ideal nanothermometers at the single-particle level. In this work we show how these problems can be elegantly solved using a thermoresponsive polymeric coating. Upon decorating the surface of NaYF4:Er,Yb UCNPs with poly(N-isopropylacrylamide) (PNIPAM), a >10-fold enhancement in optical forces is observed, allowing stable trapping and manipulation of a single UCNP in the physiological temperature range (20-45 ºC). This optical force improvement is accompanied by a significant enhancement of the thermal sensitivity reaching a maximum value of 7 % °C-1 at 31.5 ºC caused by the temperature-induced collapse of PNIPAM.
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