Highly precise FIR thermometer based on the thermally enhanced upconversion luminescence for temperature feedback photothermal therapy

Abstract

A highly precise temperature-feedback photothermal therapy platform in deep tissue is proposed based on all-fiber fluorescence intensity ratio (FIR) thermometry, which provides a promising route to realize real-time temperature monitoring in the minimally invasive treatment of tumors. Highly disordered double perovskite Li₂Zn₂Mo₃O₁₂ (LZMO) phosphors doped with rare earth ions were prepared and intense green upconversion emissions were observed with an ultra-low excitation power. The thermal enhancement of the upconversion luminescence was achieved up to 423 K, which is very beneficial to achieve a good signal-to-noise performance during the temperature-rise period. Superior temperature sensing performance was demonstrated with the maximum absolute sensitivity of 89.9 × 10^-4 at 423 K. The strong upconversion emissions and high temperature sensitivity result in a small temperature error (±0.4 K). The integrated bifunctional needle could simultaneously realize temperature measurement and laser heating, which was exhibited in the denaturation of egg white and laser ablation of the porcine liver in vitro.

Fig. 1. (a) The diagram of the integrated temperature-feedback photothermal therapy platform. (b) The interior structure of the integrated probe. (c) The photogram of the green upconversion luminescence at the end-face of optical fiber.

Fig. 2. (a) XRD results of LZMO:0.1Eu³⁺ and LZMO:0.02Er³⁺/0.5Yb³⁺. (b) Rietveld refinement of XRD pattern for LZMO:0.02Er³⁺/0.5Yb³⁺ phosphor. (c) Crystal structure of LZMO phosphors. (d) SEM micrograph of LZMO:0.02Er³⁺/0.5Yb³⁺ phosphor.

Fig. 3. (a) The photoluminescence emission spectrum of LZMO:0.1Eu³⁺ phosphor. (b) The chromaticity coordinates of LZMO:0.1Eu³⁺ phosphor.

Fig. 4. (a) Upconversion luminescence. (b) The energy-level diagram and possible upconversion mechanism in LZMO:Er³⁺/Yb³⁺ phosphor.

Fig. 5. (a) Upconversion luminescence spectra versus temperature in LZMO:0.02Er³⁺/0.5Yb³⁺ phosphor. (b) Relationship between integral upconversion emission intensities and temperature. (c) XRD images of LZMO:0.02Er³⁺/0.5Yb³⁺ at different temperature. (d) Weight loss curve of LZMO:0.02Er³⁺/0.5Yb³⁺ phosphor.

Fig. 6. (a) The dependence of ln(FIR) on 1/T. (b) Temperature sensitivities S_a and S_r as a function of temperature. (c) Response of the sensor to step-tuned temperatures. (d) The difference ΔT at 318 K.

Fig. 7. (a–j) The amplified integrated probe heating phenomenon in egg white. The diameters of glass tube and stainless steel needle are 3 mm and 0.9 mm, respectively.

Fig. 8. (a) The temperature of FIR thermometer in the pig liver tissue under irradiation with 980 nm laser at 300 mW and 800 mW. (b) Cross-section view of pig liver after heating.