A Sol-Gel/Solvothermal Synthetic Approach to Titania Nanoparticles for Raman Thermometry

Abstract

The accurate determination of the local temperature is one of the most important challenges in the field of nanotechnology and nanomedicine. For this purpose, different techniques and materials have been extensively studied in order to identify both the best-performing materials and the techniques with greatest sensitivity. In this study, the Raman technique was exploited for the determination of the local temperature as a non-contact technique and titania nanoparticles (NPs) were tested as nanothermometer Raman active material. Biocompatible titania NPs were synthesized following a combination of sol-gel and solvothermal green synthesis approaches, with the aim of obtaining pure anatase samples. In particular, the optimization of three different synthesis protocols allowed materials to be obtained with well-defined crystallite dimensions and good control over the final morphology and dispersibility. TiO2 powders were characterized by X-ray diffraction (XRD) analyses and room-temperature Raman measurements, to confirm that the synthesized samples were single-phase anatase titania, and using SEM measurements, which clearly showed the nanometric dimension of the NPs. Stokes and anti-Stokes Raman measurements were collected, with the excitation laser at 514.5 nm (CW Ar/Kr ion laser), in the temperature range of 293–323 K, a range of interest for biological applications. The power of the laser was carefully chosen in order to avoid possible heating due to the laser irradiation. The data support the possibility of evaluating the local temperature and show that TiO2 NPs possess high sensitivity and low uncertainty in the range of a few degrees as a Raman nanothermometer material.

Ag/TiO2 Nanocomposites for Nanothermometry in the Biological Environment

“…The results, together with the laser power used for the measurements, are resumed in Table 1. The values found are in agreement with those obtained at a comparable excitation wavelength (514.5 nm) with commercial and properly synthesized TiO 2 NP [5,7], where a high sensitivity and an uncertainty of a few degrees have been demonstrated. This confirms the possibility of using Ag@TiO 2 as a nanothermometer.…”

“…Anatase nanoparticles are also suitable materials for Raman nanothermometry because they have a large Raman scattering cross section. TiO 2 anatase, as a commercial powder [5] and as synthesized nanoparticles [7], has already been tested, using its high-intensity Raman signal with a low Raman shift, at 143 cm −1 , as a reference.…”