Intracellular Temperature Sensing: An Ultra-bright Luminescent Nanothermometer with Non-sensitivity to pH and Ionic Strength

Abstract

Luminescence thermometry usually suffer from cellular complexity of the biochemical environment (such as pH and ionic strength), and thus the accuracy and reliability of the determined intracellular temperature are directly affected. Herein, a photoluminescent nanothermometer composed of polymer encapsulated quantum dots (P-QD) has been developed. And the prepared nanothermometer exhibits some advantages: such as non-sensitivity to pH and ionic strength, as well as high detection sensitivity and ultrahigh reversibility. The intracellular temperature was accurately determined under physiological conditions with different pH and ionic strength, and direct measurement of thermogenesis in individual cells has been achieved.

Figure 1

(a) Photograph of P-QD in water taken under natural light (left) and 365 nm light (right). (b) UV-vis absorption and photoluminescence spectra (λ_ex = 400 nm) of P-QD in water and initial QDs in THF. (c) Photoluminescence spectra of P-QD under various temperatures. (d) The PL intensity of P-QD as a function of temperature. Error bars represent standard deviations obtained from three parallel experiments.

Figure 2

(a) Top: Photograph of P-QD in solutions with various pH, under 365 nm light. Bottom: The PL intensity as a function of pH. Error bars represent standard deviations obtained from three parallel experiments. (b) Top: Photograph of P-QD in solutions with different KCl, under 365 nm light. Bottom: The PL intensity as a function of the concentration of KCl. Error bars represent standard deviations obtained from three parallel experiments. (c) The PL intensity of P-QD under 25 °C (top panel) and 37 °C (bottom panel). The heating-cooling cycles were repeated 100 times. (d) The temperature determined by P-QD temperature probes and the values measured with a thermocouple thermometer. Error bars represent standard deviations obtained from three parallel experiments.

Figure 3. The temperature experiment controlled by infrared laser.

(a) Schematic of the experimental setup, illustrating the essential optical pathways in a Zeiss LSM 780 confocal microscope. (b) Representative snapshot of P-QD treated HepG2 cells. Scale bar:100 μm. (c) The PL intensity of P-QD as a function of time for the region 1–3 shown in Fig. 3b. (d) Local temperature variations (ΔT) and simulation results as a function of time for the region 1 shown in Fig. 3b. (e) Location-dependent temperature changes within a live cell as a function of time for the region 1 shown in Fig. 3b. The time points at which IR laser was on/off are marked by an arrow. The uncertainties of position localization as estimated from the Gaussian fitting are represented as shades of the temperature colour; the more intense and the narrower the vertical distribution, the more accurately the location is.

Figure 4

(a) The PL intensity of P-QD as a function of temperature in solution and live cells. Error bars represent standard deviations obtained from three parallel experiments. (b) Statistics of temperature variations for the 24 P-QD treated cells, showing a bigger variation value of 13.7 ± 0.44 °C than that of environment (9 °C). The red line is the Gaussian fitting curve.