Nd3+ and Nd3+/Yb3+-incorporated complexes as optical thermometer working in the second biological window

Luminescent Properties of Phosphonate Ester-Supported Neodymium(III) Nitrate and Chloride Complexes

This study examines the synthesis of two geminal bisphosphonate ester-supported Ln³⁺ complexes [Ln(L3)₂(NO₃)₃] (Ln = Nd³⁺ (5), La³⁺ (6)) and optical properties of the neodymium(III) complex. These results are compared to known mono-phosphonate ester-based Nd³⁺ complexes [Nd(L1/L2)₃X₃]_n (X = NO₃^-, n = 1; Cl^-, n = 2) (1-4). The optical properties of Nd³⁺ compounds are determined by micro-photoluminescence (µ-PL) spectroscopy which reveals three characteristic metal-centered emission bands in the NIR region related to transitions from ⁴F_3/2 excited state. Additionally, two emission bands from ⁴F_5/2, ²H_9/2 → ⁴I_J (J = 11/2, 13/2) transitions were observed. PL spectroscopy of equimolar complex solutions in dry dichloromethane (DCM) revealed remarkably higher emission intensity of the mono-phosphonate ester-based complexes in comparison to their bisphosphonate ester congener. The temperature-dependent PL measurements enable assignment of the emission lines of the ⁴F_3/2 → ⁴I_9/2 transition. Furthermore, low-temperature polarization-dependent measurements of the transitions from R₁ and R₂ Stark sublevel of ⁴F_3/2 state to the ⁴I_9/2 state for crystals of [Nd(L3)₂(NO₃)₃] (5) are discussed.

Lanthanide doped luminescence nanothermometers in the biological windows: strategies and applications

The development of lanthanide-doped non-contact luminescent nanothermometers with accuracy, efficiency and fast diagnostic tools attributed to their versatility, stability and narrow emission band profiles has spurred the replacement of conventional contact thermal probes. The application of lanthanide-doped materials as temperature nanosensors, excited by ultraviolet, visible or near infrared light, and the generation of emissions lying in the biological window regions, I-BW (650 nm-950 nm), II-BW (1000 nm-1350 nm), III-BW (1400 nm-2000 nm) and IV-BW (centered at 2200 nm), are notably growing due to the advantages they present, including reduced phototoxicity and photobleaching, better image contrast and deeper penetration depths into biological tissues. Here, the different mechanisms used in lanthanide ion-doped nanomaterials to sense temperature in these biological windows for biomedical and other applications are summarized, focusing on factors that affect their thermal sensitivity, and consequently their temperature resolution. Comparing the thermometric performance of these nanomaterials in each biological window, we identified the strategies that allow boosting of their sensing properties.

Upconversion nanoparticles modified by Cu2S for photothermal therapy along with real-time optical thermometry

Highly effective photothermal conversion performance coupled with high resolution temperature detection in real time is urgently needed for photothermal therapy (PTT). Herein, ultra-small Cu₂S nanoparticles (NPs) were designed to absorb on the surface of NaScF₄: Yb³⁺/Er³⁺/Mn²⁺@NaScF₄@SiO₂ NPs to form a central-satellite system, in which the Cu₂S NPs play the role of providing significant light-to-heat conversion ability and the Er³⁺ ions in the NaScF₄: Yb³⁺/Er³⁺/Mn²⁺ cores act as a thermometric probe based on the fluorescence intensity ratio (FIR) technology operating in the biological windows. A wavelength of 915 nm is used instead of the conventional 980 nm excitation wavelength to eliminate the laser induced overheating effect for the bio-tissues, by which Yb³⁺ can also be effectively excited. The temperature resolution of the FIR-based optical thermometer is determined to be better than 0.08 K over the biophysical temperature range with a minimal value of 0.06 K at 298 K, perfectly satisfying the requirements of biomedicine. Under the radiation of 915 nm light, the Cu₂S NPs exhibit remarkable light-to-heat conversion capacity, which is proved by photothermal ablation testing of E. coli. The results reveal the enormous potential of the present NPs for PTT integrated with real-time temperature sensing with high resolution.