Emma Martín Rodríguez

Temperature sensing using fluorescent nanothermometers.

Acquiring the temperature of a single living cell is not a trivial task. In this paper, we devise a novel nanothermometer, capable of accurately determining the temperature of solutions as well as biological systems such as HeLa cancer cells. The nanothermometer is based on the temperature-sensitive fluorescence of NaYF(4):Er(3+),Yb(3+) nanoparticles, where the intensity ratio of the green fluorescence bands of the Er(3+) dopant ions ((2)H(11/2) --> (4)I(15/2) and (4)S(3/2) --> (4)I(15/2)) changes with temperature. The nanothermometers were first used to obtain thermal profiles created when heating a colloidal solution of NaYF(4):Er(3+),Yb(3+) nanoparticles in water using a pump-probe experiment. Following incubation of the nanoparticles with HeLa cervical cancer cells and their subsequent uptake, the fluorescent nanothermometers measured the internal temperature of the living cell from 25 degrees C to its thermally induced death at 45 degrees C.

CdSe Quantum Dots for Two-Photon Fluorescence Thermal Imaging

The technological development of quantum dots has ushered in a new era in fluorescence bioimaging, which was propelled with the advent of novel multiphoton fluorescence microscopes. Here, the potential use of CdSe quantum dots has been evaluated as fluorescent nanothermometers for two-photon fluorescence microscopy. In addition to the enhancement in spatial resolution inherent to any multiphoton excitation processes, two-photon (near-infrared) excitation leads to a temperature sensitivity of the emission intensity much higher than that achieved under one-photon (visible) excitation. The peak emission wavelength is also temperature sensitive, providing an additional approach for thermal imaging, which is particularly interesting for systems where nanoparticles are not homogeneously dispersed. On the basis of these superior thermal sensitivity properties of the two-photon excited fluorescence, we have demonstrated the ability of CdSe quantum dots to image a temperature gradient artificially created in a biocompatible fluid (phosphate-buffered saline) and also their ability to measure an intracellular temperature increase externally induced in a single living cell.

Hybrid Nanostructures for High‐Sensitivity Luminescence Nanothermometry in the Second Biological Window

Hybrid nanostructures containing neodymium-doped nanoparticles and infrared-emitting quantum dots constitute highly sensitive luminescent thermometers operating in the second biological window. They demonstrate that accurate subtissue fluorescence thermal sensing is possible.

Nanoparticles for highly efficient multiphoton fluorescence bioimaging

In this paper, we demonstrate for the first time that the new class of fluoride-based inorganic upconverting nanoparticles, NaYF4:Er3+, Yb3+, are the most efficient multiphoton excited fluorescent nanoparticles developed to date. The near-infrared-to-visible conversion efficiency of the aforementioned nanoparticles surpasses that of CdSe quantum dots and gold nanorods, which are the commercially available inorganic fluorescent nanoprobes presently used for multiphoton fluorescence bioimaging. The results presented here open new perspectives for the implementation of fluorescence tomography by multiphoton fluorescence imaging.

Bio-functionalization of ligand-free upconverting lanthanide doped nanoparticles for bio-imaging and cell targeting

We report on the functionalization of ligand-free NaGdF(4):Er(3+), Yb(3+) upconverting nanoparticles with heparin and basic fibroblast growth factor (bFGF). These upconverting nanoparticles are used to obtain high-contrast images of HeLa cells. These images reveal that the heparin-bFGF functionalized nanoparticles show specific binding to the cell membrane.

Fluorescent nanothermometers for intracellular thermal sensing

The importance of high-resolution intracellular thermal sensing and imaging in the field of modern biomedicine has boosted the development of novel nanosized fluorescent systems (fluorescent nanothermometers) as the next generation of probes for intracellular thermal sensing and imaging. This thermal mapping requires fluorescent nanothermometers with good biocompatibility and high thermal sensitivity in order to obtain submicrometric and subdegree spatial and thermal resolutions, respectively. This review describes the different nanosized systems used up to now for intracellular thermal sensing and imaging. We also include the later advances in molecular systems based on fluorescent proteins for thermal mapping. A critical overview of the state of the art and the future perspective is also included.

Neodymium-doped nanoparticles for infrared fluorescence bioimaging: The role of the host

The spectroscopic properties of different infrared-emitting neodymium-doped nanoparticles (LaF3:Nd3+, SrF2:Nd3+, NaGdF4: Nd3+, NaYF4: Nd3+, KYF4: Nd3+, GdVO4: Nd3+, and Nd:YAG) have been systematically analyzed. A comparison of the spectral shapes of both emission and absorption spectra is presented, from which the relevant role played by the host matrix is evidenced. The lack of a “universal” optimum system for infrared bioimaging is discussed, as the specific bioimaging application and the experimental setup for infrared imaging determine the neodymium-doped nanoparticle to be preferentially used in each case.

High Resolution Fluorescence Imaging of Cancers Using Lanthanide Ion-Doped Upconverting Nanocrystals

During the last decade inorganic luminescent nanoparticles that emit visible light under near infrared (NIR) excitation (in the biological window) have played a relevant role for high resolution imaging of cancer. Indeed, semiconductor quantum dots (QDs) and metal nanoparticles, mostly gold nanorods (GNRs), are already commercially available for this purpose. In this work we review the role which is being played by a relatively new class of nanoparticles, based on lanthanide ion doped nanocrystals, to target and image cancer cells using upconversion fluorescence microscopy. These nanoparticles are insulating nanocrystals that are usually doped with small percentages of two different rare earth (lanthanide) ions: The excited donor ions (usually Yb3+ ion) that absorb the NIR excitation and the acceptor ions (usually Er3+, Ho3+ or Tm3+), that are responsible for the emitted visible (or also near infrared) radiation. The higher conversion efficiency of these nanoparticles in respect to those based on QDs and GNRs, as well as the almost independent excitation/emission properties from the particle size, make them particularly promising for fluorescence imaging. The different approaches of these novel nanoparticles devoted to “in vitro” and “in vivo” cancer imaging, selective targeting and treatment are examined in this review.

The near-IR photo-stimulated luminescence of CaS:Eu2+/Dy3+ nanophosphors

We report on the synthesis, the characterization and the optical properties of CaS:Eu2+/Dy3+ nanophosphors. We demonstrate the generation of strong red light emission following NIR excitation of the CaS:Eu2+/Dy3+ nanophosphors.

Overcoming Autofluorescence: Long-Lifetime Infrared Nanoparticles for Time-Gated In Vivo Imaging.

The always present and undesired contribution of autofluorescence is here completely avoided by combining a simple time gating technology with long lifetime neodymium doped infrared-emitting nanoparticles.