In Vivo Spectral Distortions of Infrared Luminescent Nanothermometers Compromise Their Reliability

Luminescence nanothermometry has emerged over the last decade as an exciting field of research due to its potential applications where conventional methods have demonstrated to be ineffective. Preclinical research has been one of the areas that have benefited the most from the innovations proposed in the field. Luminescent nanothermometers have starred unimaginable advances such as in vivo intratumoral thermal reading or brain activity monitoring through real-time thermal sensing.  Nevertheless, certain questions concerning the reliability of the technique under in vivo conditions have been continuously neglected by most of the scientific community. In this work, hyperspectral in vivo imaging demonstrates that in vivo luminescent nanothermometry is not as reliable as previously thought.  This work, indeed, reveals how the temperature-dependent optical transmittance of living tissues can induce spectral changes in the measured fluorescence. These changes, in turns, can be wrongly attributed to temperature variations. The next steps that should be taken in the future for a reliable in vivo luminescence nanothermometry are discussed together with a perspective view of the field after the findings that are here reported.