Single-walled carbon nanotubes (SWNTs) have been considered as nearly ideal luminescent probes for deep-tissue bioimaging because of their photoluminescence in near-infrared range known as the second optical window of biological tissues [1]. Moreover, efficient phonon-assisted up-conversion photoluminescence (UCPL) in SWNTs, for which the excitation light wavelength can be longer than the emission one, has recently been discovered [2, 3]. The UCPL phenomena enable SWNTs excited at wavelengths longer than ~1050-1200 nm to emit PL shorter than 1000 nm in which standard Si-based detectors have finite sensitivity. The availability of the UCPL thus potentially enhances the usefulness of SWNTs as luminescent probes in their bioimaging applications. We will report our recent progress in whole-body imaging of living mice with negligible autofluorescence using UCPL of SWNTs. We will also discuss application of the UCPL phenomena of SWNTs for near-infrared optical thermometry.

[1] K. Welsher, Z. Liu, S. P. Sherlock, J. T. Robinson, Z. Chen, D. Daranciang, and H. Dai, Nat. Nanotechnol. 4, 773 (2009). [2] N. Akizuki, S. Aota, S. Mouri, K. Matsuda, and Y. Miyauchi, Nat. Commun. 6, 8920 (2015). [3] S. Aota, N. Akizuki, S. Mouri, K. Matsuda, and Y. Miyauchi, Appl. Phys. Express 9, 045103 (2016).

Part of this study was supported by the Research Foundation for Opto-Science and Technology, the Nakatani Foundation, and by JSPS KAKENHI Grant Number JP15H05408.