Ag/Ag₂S Nanocrystals for High Sensitivity Near‐Infrared Luminescence Nanothermometry

Abstract

control, [4] luminescence thermometry (LTh) is rapidly expanding. In this case, thermal sensing is based on the appropriate analysis of temperature-dependent luminescence, leading to the appearance of Luminescent Nanothermometers (LNThs). [5] The main limitations of LNThs include: (i) the reading of temperatureinduced changes in the luminescence intensity from single emission lines and (ii) the short penetration depths of LNThs operating in the visible range [6] for in vivo applications along with autofluorescence background signals. [7] The former can be overcome by the use of ratiometric-based LNThs (hereafter RLNThs), [5a] in which the readout is extracted from the ratio between their photoluminescence (PL) intensity at different wavelengths, and the latter requires the use of NPs working in the near-infrared range (NIR), in particular in the second biological window (II-BW), expanding from 1000 to 1350 nm. [6b,8] Some examples of RLNThs working in the II-BW include singly and doubly rare earth doped NPs (RE-NPs) or the combination, in a single structure, of both RE-NPs and semiconductor quantum dots (QDs). [5c,9] In the case of rare earth doped NPs, their thermal sensitivity is lower than 0.5% °C −1 and the reduced absorption cross sections per NP leads to low signal-to-noise ratios during in vivo experiments. The combination of these two factors results in thermal Temperature sensing in biological media (cells, tissues, and living organisms) has become essential in the development of the last generation of diagnostics and therapeutic strategies. Thermometry can be used for early detection of different diseases, such as cancer, stroke, or inflammation processes, one of whose incipient symptoms is the appearance of localized temperature singularities. Luminescence nanothermometry, as a tool to accurately provide temperature sensing in biological media, requires the rational design and development of nanothermometers operating in the second biological window. In this work, this is achieved using Ag/Ag 2 S nanocrystals as multiparametric thermal sensing probes. Temperature sensing with remarkably high sensitivity (4% °C −1 ) is possible through intensity-based measurements, as their infrared emission is strongly quenched by small temperature variations within the biological range (15-50 °C). Heating also results in a remarkable redshift of the emission band, which allows for concentrationindependent temperature sensing based on infrared ratiometric measurements, with thermal sensitivity close to 2% °C −1 . These results make Ag/Ag 2 S nanocrystals the most sensitive among all noncomposite nanothermometers operating in the second biological window reported so far, allowing for deeptissue temperature measurements with low uncertainty (0.2 °C).

Recent Advances of Low Biological Toxicity Ag2S QDs for Biomedical Application

“…Afterward, the addition of CA125 induced obvious NIR PL recovery (“on” state), exhibited a good linear relationship between the relative NIR PL intensities (I/I0) and Log[CA125] in the [CA125] range of 0.1–106 ng mL −1 , together with a low LOD of 0.07 ng mL −1 , and a high linear coefficient ( R 2 ) of 0.9961. Using Ag/Ag 2 S nanocrystals as multiparametric thermal sensing probes for deep tissue temperature measurements was of low uncertainty (0.2 °C) . The Ag/Ag 2 S NCs were synthesized by thermal decomposition route and the TEM revealed the presence of a rich Ag core and a stoichiometric Ag 2 S shell.…”

In Vivo Early Tumor Detection and Diagnosis by Infrared Luminescence Transient Nanothermometry

“…From the data in Figure b, we determined that the Ag 2 S nanocrystals showed an intensity‐based thermal sensitivity of 3% °C −1 , in good agreement with recently published results. [20a] The thermal calibration curves obtained for Ag 2 S nanocrystals in aqueous dispersion and in a tumor tissue sample (see Figure S1, Supporting Information) showed no effects of the environment in their thermal sensitivity, highlighting the reliability of these NPs as temperature sensors in biological media. To achieve intratumoral thermometry, Ag 2 S nanocrystals were injected either together with the cancer cells used to induce tumor growth or at later stages of the tumor development.…”

“…In this work, we evaluate the impact of tumor development in tissue thermal relaxation dynamics using a murine model of melanoma, a highly aggressive form of skin cancer . To measure the in vivo thermal relaxation dynamics, we relied on intratumorally injected Ag 2 S NPs, chosen because of their demonstrated minimal in vivo toxicity and their high thermal sensitivity in NIR‐II, which grants deep tissue temperature sensing . We studied the evolution of the thermal dynamics of the tumor throughout its development from induction (day 0) until necrosis was visually evident (around day 14), while also keeping track of its size and surface temperature.…”

Beyond Phototherapy: Recent Advances in Multifunctional Fluorescent Nanoparticles for Light‐Triggered Tumor Theranostics

“…These nanopyramids enabled in vivo tumor labeling via NIR‐II imaging with minimal background noise, as seen in Figure i, and successful PTT with complete tumor ablation. Considering that Ag 2 S QDs show a temperature‐dependent emission, these NPs could also be used for PTT with real‐time temperature feedback, although this possibility has not been demonstrated yet.…”