We propose the combination of polyN-isopropylacrylamide (PNIPAM) particles and optical coherence tomography (OCT) to overcome the main limitations of current nanothermometry for medical purposes. We demonstrate that PNIPAM particles can behave as temperature-sensitive contrast agents in OCT thanks to their structural phase transition at 32 °C, resulting in changes in the refractive index that make their OCT contrast temperature-dependent. Simple experiments have been conducted to demonstrate the feasibility of this approach for three-dimensional imaging of phantom tissues subjected to photothermal processes. The results included in this work constitute an alternative route towards facile incorporation of nanothermometry into the clinical world.
The precise and non-invasive control over single particles is key for an array of physical and bio-medical
applications, such as microfluidics and biophysics. In particular, the three-dimensional manipulation of
single rare-earth-doped luminescent particles is of great interest due to their biocompatibility and the
sensitivity of their luminescent properties to environmental conditions, which stand out among other
dielectric luminescent particles. The analysis of the damped rotation dynamics of an optically trapped
microparticle is a novel and powerful tool that allows not only the controlled and remote manipulation of
the sensor, but also an improved characterization of the medium and fast recording of its content.
Here, an optically trapped and rotated rare-earth-doped β-NaYF 4 :RE 3+ microparticle is presented as a novel
sensor to characterize the properties of a liquid medium at the microscale (temperature, viscosity and
detection of bio-objects).
Precise and non-invasive control over single particles is key for a range of physical and bio-medical applications, such as microfluidics and biophysics. The analysis of the rotation dynamics of an optically trapped dielectric microparticle is presented as a novel tool to characterize the properties of a liquid medium at the microscale (temperature, viscosity and bio-objects). In this work, single dielectric β-NaYF4:Ln3+ microparticles are used as optical sensors and the analysis of its damped rotational dynamics allowed not only the controlled and remote manipulation of the sensor, but also an improved characterization of the medium and fast recording of its content.
Lanthanide-based upconverting nanoparticles (UCNPs) boast low thermal sensitivity and brightness, which, along with the difficulty in controlling individual UCNP remotely, make them less than ideal nanothermometers at the single-particle level. In this work we show how these problems can be elegantly solved using a thermoresponsive polymeric coating. Upon decorating the surface of NaYF4:Er,Yb UCNPs with poly(N-isopropylacrylamide) (PNIPAM), a >10-fold enhancement in optical forces is observed, allowing stable trapping and manipulation of a single UCNP in the physiological temperature range (20-45 ºC). This optical force improvement is accompanied by a significant enhancement of the thermal sensitivity reaching a maximum value of 7 % °C-1 at 31.5 ºC caused by the temperature-induced collapse of PNIPAM.
In this work we demonstrate laser cooling in liquids on a micrometric scale by using colloidal microparticles doped with ytterbium ions. These microparticles behave as cooling elements thanks to their anti-stokes luminescence. The novel point of our work is that laser radiation produces laser refrigeration and linear and angular transfer of momentum that allows cooling during remote particle manipulation and rotation. This dual function of laser radiation opens the door to new applications based on the use of portable micro-refrigerants. In addition, we demonstrate for the first time how analyzing rotation dynamics is a new and simpler way to determine, in real time, the magnitude of cooling. In other words, we show how laser light can heat, cool, move and rotate our particles simultaneously. All this without requiring complicated experimental systems.
An optical system based on a photonic nanojet created by an optically trapped microsphere is proposed for enhanced trapping and remote manipulation of upconverting nanoparticles. The nanojet-induced enhancement in the optical forces acting on a 8 nm single upconverting nanoparticle are compared to those achievable by the traditional approach based on the use of high numerical aperture optics. The results presented in this work prove that this is a simple and effective method to remotely trap, manipulate, and detect single upconverting nanoparticles. This is an innovative approach to overcome the current challenges in the remote manipulation of probes in biosensing or in single particle studies.
Temperature at the mesoscale is important in many fields due to its key role in, e.g., cell mechanics, quantum ground state studies and hydrodynamics. In levitated optomechanics, measuring temperature is challenging at the same time as necessary to understand the dynamics of the optically trapped particle. Generally, the particle’s temperature has been directly correlated to its centre-of-mass (CoM) motion (i.e. translational dynamics). This, together with the rotational dynamics, encompasses the particle’s external degree of freedom which is affected by the external temperature. However, the particle presents an internal structure that is at another internal temperature. Generally, the CoM temperature is experimentally measured and compared to a theoretically calculated internal temperature. The rotation rate (i.e. rotational dynamics) has also been correlated to an experimentally measured internal temperature for thermometric studies. Despite its importance, the temperature of these three degrees of freedom had never been simultaneously measured and correlated. We developed a tripartite method able to independently measure both the internal temperature of the particle (through temperature-dependent luminescence) and the external temperature (through the rotational rate and trap stiffness). We found that, even though they are strongly coupled, the external and internal degrees of freedom present distinct temperatures. This study gives new insight into thermometry at the mesoscale where the appropriate parameter should be carefully chosen for an accurate characterisation of temperature. Moreover, experiments attempting to cool levitated particles to the quantum ground state, in which all degrees of freedom must be independently controlled and characterised, will also benefit from this advance.
Luminescence of a single upconverting particle (NaYF4:Er3+,Yb3+) can be used to determine the optical trap temperature due to the partial absorption of the trapping beam either by the medium (water) or the optically trapped particle itself. This fact is an important drawback can be reduced by shifting the trapping wavelength out of the water absorption band, or by using time-modulated laser trapping beams. Both approaches have been studied and the results have shown that the thermal loading due to the trapping radiation can be minimized.
Rheological parameters (viscosity, creep compliance and elasticity) play an important role in cell function and viability. For this reason different strategies have been developed for their study. In this work, two new microrheometric techniques are presented. Both methods take advantage of the analysis of the polarized emission of an upconverting particle to determine its orientation inside the optical trap. Upconverting particles are optical materials that are able to convert infrared radiation into visible light. Their usefulness has been further boosted by the recent demonstration of their three-dimensional control and tracking by single beam infrared optical traps. In this work it is demonstrated that optical torques are responsible of the stable orientation of the upconverting particle inside the trap. Moreover, numerical calculations and experimental data allowed to use the rotation dynamics of the optically trapped upconverting particle for environmental sensing. In particular, the cytoplasm viscosity could be measured by using the rotation time and thermal fluctuations of an intracellular optically trapped upconverting particle, by means of the two previously mentioned microrheometric techniques.
We have studied different strategies of use of luminescence thermometry with upconverting nanoparticles in the biological range of temperatures, among them, the thermal sensing ability of fluoresncent lifetime of Er,Yb:NaY2F5 nanoparticles. Er,Yb:NaY2F5O nanocrystals show great potentiality as thermal sensors at the nanoscale for biomedical applications due to the incorporation of additional non-radiative relaxation mechanisms that shorten the emission lifetime generated by the oxygen present in the structure. Here we report ex-vivo temperature determination by laser induced heating in chicken breast using lifetime-based thermometry in these up-conversion nanoparticles.
Strong ion migration in shown to enable the production of high refractive index contrast waveguides by fs-laser writing
in a commercial (Er,Yb)-doped phosphate based glass. Waveguide writing was performed using a high repetition rate fslaser
fibre amplifier operated at 500 kHz and the slit shaping technique. Based on measurements of the NA of
waveguides, the positive refractive index change (Δn) of the guiding region has been estimated to be ∼1-2 x10-2. The
compositional maps of the waveguides cross-sections performed by X-ray microanalysis evidenced a large increase of
the La local concentration in the guiding region up to ~25% (relative to the non-irradiated material). This large
enrichment in La was accompanied by the cross migration of K to a neighbouring low refractive index zone. The
refractive index of the La-phosphate glass increases linearly with the La2O3 content (Δn per mole fraction increase of
La2O3 ≈ 5x10-3) mainly because of the relative mass of the La3+ ions. The density increase without substantial
modification of the glass network was confirmed by space-resolved micro-Raman spectroscopy measurements showing
minor variations in the (PO2)sym vibration Raman band. These results provide evidence for the feasibility of adapting the glass composition for enabling laser-writing of high refractive index contrast structures via spatially selective
modification of the glass composition.
B. del Rosal, P. Haro-González, W. Ramsay, L. Maestro, K. Santacruz-Gómez, M. C. Iglesias-de la Cruz, F. Sanz-Rodríguez, J. Y. Chooi, P. Rodríguez-Sevilla, D. Choudhury, A. Kar, J. García Solé, L. Paterson, D. Jaque
Laser-induced thermal effects in optically trapped microspheres and single cells have been investigated by Luminescence
Thermometry. Thermal spectroscopy has revealed a non-localized temperature distribution around the trap that extends
over tens of microns, in agreement with previous theoretical models. Solvent absorption has been identified as the key
parameter to determine laser-induced heating, which can be reduced by establishing a continuous fluid flow of the
sample. Our experimental results of thermal loading at a variety of wavelengths reveal that an optimum trapping
wavelength exists for biological applications close to 820 nm. This has been corroborated by a simultaneous analysis of
the spectral dependence of cellular heating and damage in human lymphocytes during optical trapping. Minimum
intracellular heating, well below the cytotoxic level (43 °C), has been demonstrated to occur for optical trapping with 820 nm laser radiation, thus avoiding cell damage.
Continuous wave red, green and blue laser light have been generated under infrared pumping crystals of Nd3+:YAl3(BO3)4 by a Ti:Sapphire laser. The red (669 nm) and green (532 nm) radiations were obtained by self-frequency doubling of the fundamental laser lines at 1338 nm (4F3/2 yields 4I13/2 channel) and 1062 nm (4F3/2 yields 4I11/2 channel) respectively. Blue laser radiation (458 nm) was achieved by self-sum- frequency mixing of the main laser line at 1062 nm and the pumping radiation at 807 nm. The main spectroscopic and nonlinear properties of this crystal are included. In addition, a simple model devoted to optimize the blue radiation is given.
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