Fiorenzo Vetrone

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.

Synthesis of Ligand-Free Colloidally Stable Water Dispersible Brightly Luminescent Lanthanide-Doped Upconverting Nanoparticles

The synthesis using the thermal decomposition of metal trifluoroacetates is being widely used to prepare oleate-capped lanthanide-doped upconverting NaYF(4):Er(3+)/Yb(3+) nanoparticles (Ln-UCNPs). These nanoparticles have no inherent aqueous dispersibility and inconvenient postsynthesis treatments are required to render them water dispersible. Here, we have developed a novel and facile approach to obtain water-dispersible, ligand-free, brightly upconverting Ln-UCNPs. We show that the upconversion luminescence is affected by the local environment of the lanthanide ions at the surface of the Ln-UCNPs. We observe a dramatic difference of the integrated upconverted red:green emission ratio for Ln-UCNPs dispersed in toluene compared to Ln-UCNPs dispersed in water. We can enhance or deactivate the upconversion luminescence by pH and H/D isotope vibronic control over the competitive radiative and nonradiative relaxation pathways for the red and green excited states. Direct biofunctionalization of the ligand-free, water-dispersible Ln-UCNPs will enable myriad new opportunities in targeting and drug delivery applications.

Significance of Yb3+ concentration on the upconversion mechanisms in codoped Y2O3:Er3+, Yb3+ nanocrystals

The optical properties of five different nanocrystalline Y2O3:Er3+, Yb3+ samples are presented and discussed. Green and red emission was observed following excitation with 488 nm and attributed to 2H11/2, 4S3/2→4I15/2, and 4F9/2→4I15/2 transitions, respectively. Striking red enhancement was observed in the upconversion spectra when exciting the Y2O3:Er3+, Yb3+ samples with 978 nm, and it became more pronounced with an increase in Yb3+ concentration. A cross relaxation mechanism (4F7/2→4F9/2 and 4F9/2←4I11/2) was responsible for directly populating the 4F9/2 state but did not explain the difference in the magnitude of red enhancement between identically doped bulk and nanocrystalline Y2O3:Er3+, Yb3+ samples. The 4F9/2 level was populated via a nonresonant mechanism that involved the 4F9/2←4I13/2 transition that is more prevalent in the nanocrystals, which is due to the high energy phonons inherent in this type of material. In nanocrystalline Y2O3:Er3+, Yb3+, we observe a change in the upconversion mechanis...

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.

980 nm excited upconversion in an Er-doped ZnO–TeO2 glass

In this letter, we investigate the upconversion properties of 19ZnO–80TeO2–1Er2O3 glass after excitation into the 4I11/2 level using 980 nm radiation. At an excitation power density of 880 W/cm2, green emission [(2H11/2, 4S3/2)→4I15/2] dominates the upconversion spectrum with an efficiency of 0.16%. Temporal studies reveal that the 4I11/2 level is the intermediate state by which the two-step upconversion process occurs. Excited-state absorption and phonon-assisted energy transfer are discussed as possible mechanisms for the upconversion.

Improving biocompatibility of implantable metals by nanoscale modification of surfaces: an overview of strategies, fabrication methods, and challenges.

The human body is an intricate biochemical-mechanical system, with an exceedingly precise hierarchical organization in which all components work together in harmony across a wide range of dimensions. Many fundamental biological processes take place at surfaces and interfaces (e.g., cell-matrix interactions), and these occur on the nanoscale. For this reason, current health-related research is actively following a biomimetic approach in learning how to create new biocompatible materials with nanostructured features. The ultimate aim is to reproduce and enhance the natural nanoscale elements present in the human body and to thereby develop new materials with improved biological activities. Progress in this area requires a multidisciplinary effort at the interface of biology, physics, and chemistry. In this Review, the major techniques that have been adopted to yield novel nanostructured versions of familiar biomaterials, focusing particularly on metals, are presented and the way in which nanometric surface cues can beneficially guide biological processes, exerting influence on cellular behavior, is illustrated.

Water dispersible ultra-small multifunctional KGdF4:Tm3+, Yb3+ nanoparticles with near-infrared to near-infrared upconversion

Ultra-small multifunctional KGdF4:Tm3+,Yb3+ nanoparticles with near-infrared to near-infrared upconversion are synthesized. The average sizes of KGdF4:Tm3+ 2%, Yb3+ 20% core-only and KGdF4:Tm3+ 2%, Yb3+ 20%/KGdF4 core–shell nanoparticles are ∼3.7 nm and ∼7.4 nm, respectively, which fall within the reported optimal sizes (<10 nm) for bioimaging probes. The excitation and emission at 980 and 803 nm are favorable to deeper tissue penetration and reduced autofluorescence. The weak upconversion luminescence of the ultra-small core-only nanoparticles is overcome by the use of the core–shell approach. The magnetic mass susceptibility and magnetization of the ultra-small core-only and core–shell nanoparticles were determined, and are close to those of large nanoparticles (26 and 50 nm) used for magnetic resonance imaging and bio-separation. There is no variation in the magnetic properties with the nanoparticles’ sizes between the core-only (∼3.7 nm) and core–shell (∼7.4 nm) nanoparticles, which differs from the size-dependent luminescence. The oleate-capped core–shell nanoparticles were further encapsulated with a PEG-phospholipid shell to endow them with dispersibility in water, which is indispensable for future biological applications.

Visible upconversion of Er3+ doped nanocrystalline and bulk Lu2O3

Abstract We report the luminescence and upconversion spectra of nanocrystalline and bulk Lu1.98Er0.02O3. After direct excitation at 488 nm or using the upconversion wavelengths (804 and 650 nm), blue, green and red emissions were observed for both samples under investigation. A temperature study of the bulk sample showed that the upconversion of the 4 F 9/2 → 4 I 15/2 and the 4 S 3/2 → 4 I 15/2 emission show maxima at 140 and 180 K, respectively, which is due to the competition of two different phonon-assisted processes. We have shown that upconversion occurs via a sequential absorption of three photons and via a phonon-assisted energy transfer (PET) process, with the latter being more efficient at higher Er3+ concentrations.

Optical spectroscopy of nanocrystalline cubic Y2O3:Er3+ obtained by combustion synthesis

We report the emission and upconversion spectra and the lifetimes of Er3+ doped Y2O3 nanocrystalline and bulk samples. We found that when the nanocrystal and bulk samples of Y1.80Er0.20O3 were excited at 815 nm, the overall emission intensity was stronger for the bulk sample. However, the relative intensity of the (2H11/2, 4S3/2)→4I15/2/4F9/2→4I15/2 transitions is 2:3 and 3:2 for the nanocrystal and bulk sample, respectively. The decay times obtained for the nanocrystalline samples are in general significantly faster than those observed for the bulk sample. We attribute this to the adsorption of CO2 on the surface of the nanocrystalline samples. The effect of Er3+ concentration on the decay time of the nanocrystalline samples is also discussed.

Nanoscale Oxidative Patterning of Metallic Surfaces to Modulate Cell Activity and Fate

In the field of regenerative medicine, nanoscale physical cuing is clearly becoming a compelling determinant of cell behavior. Developing effective methods for making nanostructured surfaces with well-defined physicochemical properties is thus mandatory for the rational design of functional biomaterials. Here, we demonstrate the versatility of simple chemical oxidative patterning to create unique nanotopographical surfaces that influence the behavior of various cell types, modulate the expression of key determinants of cell activity, and offer the potential of harnessing the power of stem cells. These findings promise to lead to a new generation of improved metal implants with intelligent surfaces that can control biological response at the site of healing.