Lanthanide-based ratiometric luminescence nanothermometry

Luminescent nanothermometry can precisely and remotely measure the internal temperature of objects at nanoscale precision,which,therefore,has been placed at the forefront of scientific attention.In particular,due to the high photochemical stability,low toxicity,rich working mechanisms,and superior thermometric performance,lanthanide-based ratiometric luminesencent thermometers are finding prevalent uses in integrated electronics and optoelectronics,property analysis of in-situ tracking,biomedical diagnosis and therapy,and wearable e-health monitoring.Despite recent progresses,it remains debate in terms of the underlying temperature-sensing mechanisms,the quantitative characterization of performance,and the reliability of temperature readouts.In this review,we show the origin of thermal response luminescence,rationalize the ratiometric scheme or thermometric mechanisms,delve into the problems in the characterization of thermometric performance,discuss the universal rules for the quantitative comparison,and showcase the cutting-edge design and emerging applications of lanthanide-based ratiometric thermometers.Finally,we cast a look at the challenges and emerging opportunities for further advances in this field.

Enabling efficient NIR-II luminescence in lithium-sublattice core–shell nanocrystals towards Stark sublevel based nanothermometry

The luminescence in the second near-infrared(NIR-II)spectral region(1,000–1,700 nm)has recently attracted great attention for emerging biological applications owing to its merit of deep tissue bioimaging and high spatiotemporal resolution.However,it still remains a challenge to achieve the highly efficient NIR-II emissions of lanthanides in nanomaterials.Herein,we report an ideal design of sensitizing lithium sublattice core–shell nanocrystals for efficient NIR-II emission properties from a set of lanthanide emitters including Er3+,Tm3+,Ho3+,Pr3+,and Nd3+.In particular,the typical NIR-II emission of Er3+at 1.5μm was greatly enhanced by further manipulating the energy transfer via Er3+–Ce3+cross-relaxation,and the quantum yield can reach up to 35.74%under 980 nm excitation(12.5 W·cm−2),which is the highest value to the best of our knowledge.The 808 nm responsive efficient NIR-II emission was also enabled at the single-particle level through rational core–shell–shell structure design.Moreover,the lithium-sublattice provides an obvious spectral Stark-splitting feature,which can be used in the ultrasensitive NIR-II nanothermometer with relative sensitivity of 0.248%K−1 and excellent thermal cycling stability.These results open a door to the research of new kinds of efficient NIR-II luminescent materials,showing great promise in various frontier fields such as deep tissue nanothermometry and in vivo bioimaging.

Heating of nanoparticles and their environment by laser radiation and applications

This review considers the fundamental dynamic processes involved in the laser heating of metal nanoparticles and their subsequent cooling.Of particular interest are the absorption of laser energy by nanoparticles,the heating of a single nanoparticle or an ensemble thereof,and the dissipation of the energy of nanoparticles due to heat exchange with the environment.The goal is to consider the dependences and values of the temperatures of the nanoparticles and the environment,their time scales,and other parameters that describe these processes.Experimental results and analytical studies on the heating of single metal nanoparticles by laser pulses are discussed,including the laser thresholds for initiating subsequent photothermal processes,how temperature influences the optical properties,and the heating of gold nanoparticles by laser pulses.Experimental studies of the heating of an ensemble of nanoparticles and the results of an analytical study of the heating of an ensemble of nanoparticles and the environment by laser radiation are considered.Nanothermometry methods for nanoparticles under laser heating are considered,including changes in the refractive indices of metals and spectral thermometry of optical scattering of nanoparticles,Raman spectroscopy,the thermal distortion of the refractive index of an environment heated by a nanoparticle,and thermochemical phase transitions in lipid bilayers surrounding a heated nanoparticle.Understanding the sequence of events after radiation absorption and their time scales underlies many applications of nanoparticles.The applicationfields for the laser heating of nanoparticles are reviewed,including thermochemical reactions and selective nanophotothermolysis initiated in the environment by laser-heated nanoparticles,thermal radiation emission by nanoparticles and laser-induced incandescence,electron and ion emission of heated nanoparticles,and optothermal chemical catalysis.Applications of the laser heating of nanoparticles in laser nanomedicine are of particular interest.Significant emphasis is given to the proposed analytical approaches to modeling and calculating the heating processes under the action of a laser pulse on metal nanoparticles,taking into account the temperature dependences of the parameters.The proposed models can be used to estimate the parameters of lasers and nanoparticles in the various applicationfields for the laser heating of nanoparticles.

Luminescence interference-free lifetime nanothermometry pinpoints in vivo temperature

Luminescence nanothermometry makes non-invasive and real-time temperature readings possible in living animals.However,the spectral fluctuation in tissues and fluids,as well as the interaction between fluorophores and environment hinders accuracy of the thermometry.Here,we report a luminescence lifetime-based nanothermometry which specifically addresses this problem.A temporal based calibration(lifetime sensing)in the NIR range,an endogenous thermal response as well as a polymer encapsulation evading environmental factors,altogether help to pinpoint temperature in vivo.Thanks to the highly condensed NdYb ions in a well-protected tiny core-shell nanocrystal(overall 11 nm),a temperature sensitivity about 2.07%K^(-1)(with 5%Yb^(3+)doped nanoparticles)and an accuracy of 0.27 K(with 25%Yb^(3+)doped nanoparticles)in biological fluids are achieved.Hopefully,combining thermally activated energy transfer nanothermometer with anti-interference lifetime thermometry would provide a more accurate temperature measurement for biological and preclinical studies.

Colloidal(Gd0.98Nd0.02)2O3 nanothermometers operating in a cell culture medium within the first and second biological windows

Non-contact,self-referenced and near-infrared luminescent nanothermometers have been recognized as emerging tools in the fields of nanomedicine and nanotechnology due to their great capability of precise temperature readout at the nanoscale and real-time deep-tissue imaging.However,the development of multifunctional and biocompatible luminescent nanothermometers operating within the optically transparent biological windows with high thermal sensitivity(>2.0%/K)remains challenging.Here,we present(Gd0.98Nd0.02)2O3 nanothermometers operated effectively within the first and second biological windows upon continuous-wave laser diode excitation at 808 nm.Ratiometric thermometric parameters are defined by the relative changes in the emission intensities originating from the two Stark components of the 4 F3/2 level(R2 and R1)to the 4 I9/2(900-1000 nm),4 I11/2(1035-1155 nm)and 4 I13/2(1300-1450 nm)multiplets.The thermo metric parameters are evaluated for colloidal samples in a cell culture medium and powder samples,and the highest thermal sensitivity(2.18%/K at 298 K)is attained for the former in the first biological window(both the excitation and emission in the 800-965 nm range).The repeatability and temperature uncertainty are 99%and 1.2 K,respectively.The nanothermometers are biocompatible with human MNT-1 melanoma and HaCaT cells for 24 h of exposure and nanoparticle concentration up to 0.400 mg/mL,showing their potential for applications in nanomedicine,e.g.,intracellular imaging and temperature mapping.