LaF3 core/shell nanoparticles for subcutaneous heating and thermal sensing in the second biological-window

Abstract

We report on Ytterbium and Neodymium codoped LaF 3 core/shell nanoparticles capable of simultaneous heating and thermal sensing under single beam infrared laser excitation. Efficient light-to-heat conversion is produced at the Neodymium highly doped shell due to non-radiative deexcitations. Thermal sensing is provided by the temperature dependent Nd 3þ ! Yb 3þ energy transfer processes taking place at the core/shell interface. The potential application of these core/shell multifunctional nanoparticles for controlled photothermal subcutaneous treatments is also demonstrated. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4954170] Photothermal therapy (PTT) is a therapeutic strategy in which photon energy is converted into heat to cause irreversible damage at the cellular level and that could efficiently treat a great variety of diseases including cancer tumors. [1][2][3] In particular, nanoparticle (NP) based PTTs are attracting great attention nowadays. They are based on the use of nanoheaters (NHs), which are NPs with large light-to-heat conversion efficiencies. [4][5][6] The selective incorporation of NHs into cancer cells or tumors provides the means by which a subsequent optical excitation produces a temperature increment that will only affect the tissues aimed to be treated. The net effects caused on cancer tumors during PTTs strongly depend on both the magnitude of the heating as well as the treatment duration. [7][8][9][10] In this regard, in order to achieve an efficient treatment and keep the collateral damage at minimum it is extremely necessary to have a temperature reading during NP based PTTs. As a consequence, there has been an increasing interest in the design of multifunctional luminescent NPs capable of simultaneous heating and thermal sensing under single power excitation as they would constitute significant building blocks toward the achievement of real controlled PTTs as well as subcutaneous studies. 11 Despite the continuously growing list of systems that could operate as simultaneous NHs and nanothermometers (NThs), including polymeric NPs, quantum dots, nanodiamonds, metallic NPs, and rare earth-doped NPs, only a few of them show real potential of working subcutaneously. 12-14 This is so because most of them operate in the visible spectrum domain, where optical penetration into tissues is minimal. To avoid this limitation, it is necessary to shift their operation spectral range from the visible to the spectral infrared ranges where tissues become partially transparent (due to simultaneous attenuation in both tissue absorption and scattering), lying in the so-called biological windows (BWs). 15,16 Traditionally, three biological windows are defined: the first extending from 650 up to 950 nm, the second covering the infrared region about 1000-1350 nm and the third extending from 1500 up to 1750 nm. 17 In particular, the applicability in the second biological window (II-BW) opens up the possibility of not only deep tissue imaging but also of high contrast, autofluorescence free in ...

Physical Background for Luminescence Thermometry Sensors Based on Pr3+:LaF3 Crystalline Particles

“…The luminescent nanothermometry is based on the luminescence features which are analyzed and which are used for the temperature measurement [1,4]. Luminescent nanothermometers are widely applied in the thermal imaging of integrated circuits [7], in vitro and in vivo imagining of biological objects [8], the subtissue thermal sensing [9][10][11], and temperature detecting for harsh environments or fast moving objects [12]. Generally, there are six parameters that define the luminescence emission of a material: intensity, lifetime, band shape, band width, polarization, and spectral position [1].…”

“…Therefore, the luminescent nanothermometers can be grouped into six corresponding subclasses. The most widespread is the subclass of luminescent nanothermometers based on the analysis of relative fluorescence intensity between the different emission bands corresponding to the suitable transitions [1,9,13]. Among the most usable materials for luminescent nanothermometers such as quantum dots (QD) and dye-based luminescent nanothermometers, the rare-earth based materials have a special place mainly because of their excellent photostability, long luminescent lifetimes, sharp emission bands, and low toxicity which is highly important for biomedical application, for example, in photothermal and photodynamic therapies [14].…”

“…For such ions as Pr 3+ and Er 3+ the same approach is used and these ions operate in overlapping temperature ranges of 300-600 K and 300-2000 K, respectively [12,16]. For the biomedical applications and in vitro and in vivo experiments, the luminescent thermometers which can operate in physiological temperature range ∘ C) are highly relevant [9]. [9][10][11]18].…”

“…For the biomedical applications and in vitro and in vivo experiments, the luminescent thermometers which can operate in physiological temperature range ∘ C) are highly relevant [9]. [9][10][11]18]. For example, the active-core/active-shell Nd 3+ /Yb 3+ -doped LaF 3 NPs demonstrate relative thermal sensitivity around 0.41 ± 0.01% ⋅ ∘ C −1 , at 10 ∘ C [9,11].…”

“…[9][10][11]18]. For example, the active-core/active-shell Nd 3+ /Yb 3+ -doped LaF 3 NPs demonstrate relative thermal sensitivity around 0.41 ± 0.01% ⋅ ∘ C −1 , at 10 ∘ C [9,11]. The systems based on Pr 3+ are studied in [19][20][21].…”