Ratiometric Afterglow Nanothermometer for Simultaneous in Situ Bioimaging and Local Tissue Temperature Sensing

Simultaneous in situ bioimage tracing and temperature sensing have been two of the foci of modern biomedicine that have given birth to designing novel luminescent nanothermometers with dual functions. To minimize the disadvantages of existing approaches, like the surface effect of nanoparticles, autofluorescence, and/or the thermal effect described herein, a bifunctional (simultaneous in vivo bioimaging and local tissue temperature sensing) ratiometric afterglow nanothermometer has been realized in the physiological temperature range (298–325 K) based on persistent luminescent Cr³⁺ (with d electron configuration)-doped zinc gallogermanate nanoparticles. The contributions of the radiative ²E → ⁴A₂ and ⁴T₂ → ⁴A₂ transitions of surface and interior Cr³⁺ to the near-infrared afterglow dual emissions are modeled, and the measured thermal sensitivities (0.043–0.047 K^–1) for detecting the temperature of a human serum albumin solution are 1 order of magnitude higher than those using an upconverting luminescent nanoparticle strategy. For a local tissue with various thicknesses (0–15 mm), a similar detection sensitivity can be obtained because of the use of the near-infrared wavelength. Meanwhile, in situ temperature sensing can recur after near-infrared light (808 nm) re-excitation.