SWNT/SDS aqueous dispersions as photoluminescent nanothermometers

Temperature is one of the basic parameters often required to characterize a system. A great demand has arisen for local measurements, especially in liquids or complex biological environments. Various approaches have been proposed to study the temperature at the nano-scale level. Some of them are based on the spectroscopic properties of carbon nanotubes (CNT) used as sensors. Raman spectroscopy is indeed a powerful technique to identify single-walled carbon nanotubes (SWNT) and to study their structure, defects and electronic properties through the measurement of specific Raman signatures (RBM, D, G and 2D bands). On the other hand, individual SWNT or small bundles emit light in the near infrared and the photoluminescence (PL) spectra is very sensitive to the quality of the dispersion and the dielectric environment of the nanotubes. In particular, when SWNT are dispersed in aqueous solutions, the PL energies are sensitive to the nature of the surfactants or polymers, to their concentration, and to the way they adsorb on/wrap around the nanotubes. In this work we show that the PL/Raman spectra of SWNT dispersed with sodium dodecyl sulfate (SDS) is very sensitive to the temperature (figure 1) in a large range of SDS concentrations. We discuss the influence of the chiral angle of the SWNT on these PL changes, and the origin of the changes in terms of SDS reorganization at the surface of the nanotubes. Similar changes are obtained with increasing laser power (figure 2), showing the local heating of the nanotubes. These results pave the way for the development of SWNT-based nano-thermometers.