Roadmap for optical tweezers

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAMOptical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects, ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in the life sciences, physics, and engineering. These include accurate force and torque measurement at the femtonewton level, microrheology of complex fluids, single micro- and nano-particle spectroscopy, single-cell analysis, and statistical-physics experiments. This roadmap provides insights into current investigations involving optical forces and optical tweezers from their theoretical foundations to designs and setups. It also offers perspectives for applications to a wide range of research fields, from biophysics to space explorationEuropean Commission (Horizon 2020, Project No. 812780

Identification of water content in nanocavities

A tapered dielectric waveguide that scans, at constant height, a sample containing a viral capsid is studied by combining a lattice gas model to simulate water meniscus formation and a finite difference time domain algorithm for light propagation through the media involved. Our results show different contrasts related to different water contents and different meniscus orientations. We propose this method as a way to study water content and evaporation process in nanocavities being either biological, like viral capsides, or nonbiological, like photonic crystalsThis work has been funded through projects FIS2009-13403-C02-01 (MINECO), S2009-MAT-1467 (CAM), and CSD2010-00024 (MINECO

Giant enhanced diffusion of gold nanoparticles in optical vortex fields

We study the diffusion of a metal nanoparticle in the nonconservative force field of an optical vortex lattice. Radiation pressure in the vortex array is shown to induce a giant enhancement over the free thermal diffusion. Langevin dynamics simulations show that the diffusion coefficient of (50 nm radius) gold particles at room temperature is enhanced by 2 orders of magnitude at power densities of the order or smaller than those used to trap nanoparticles with optical tweezers

Scattering forces from the curl of the spin angular momentum of a light field

Light forces on small (Rayleigh) particles are usually described as the sum of two terms: the dipolar or gradient force and the scattering or radiation pressure force. The scattering force is traditionally considered proportional to the Poynting vector, which gives the direction and magnitude of the momentum flow. However, as we will show, there is an additional nonconservative contribution to the scattering force arising in a light field with nonuniform helicity. This force is shown to be proportional to the curl of the spin angular momentum of the light field. The relevance of the spin force is illustrated in the simple case of a 2D field geometry arising in the intersection region of two standing wavesThis work was supported by the Spanish MEC through the Consolider NanoLight (CSD2007-00046), FIS2005-05137 and FIS2006-11170-C02-02 projects, Microseres-CM and by the Spanish-French PICASSO program (HF2007- 0068

Test of cold denaturation mechanism for proteins as a function of water's structure

In a recent paper [PRL 91, 138103 (2003)] a new mechanism to explain the cold denaturation of proteins, based on the loss of local low-density water structure, has been proposed. In the present paper this mechanism is tested by means of full atom numerical simulations. In good agreement with this proposal, cold denaturation resulting in the unfolded state was found at the High Density Liquid (HDL) state of water, at which the amount of open tetragonal hydrogen bonds decreases at cooling.Comment: 5 pages, 5 figure

Evolution of the universality class in slightly diluted (1>p>0.8) Ising systems

The crossover of a pure (undiluted) Ising system (spin per site probability p=1) to a diluted Ising system (spin per site probability p<0.8) is studied by means of Monte Carlo calculations with p ranging between 1 and 0.8 at intervals of 0.025. The evolution of the self averaging is analyzed by direct determination of the normalized square widths for magnetization and susceptibility as a function of p. We find a monotonous and smooth evolution from the pure to the randomly diluted universality class. The p-dependent transition is found to be independent of the size (L). This property is very convenient for extrapolation towards the randomly diluted universality class avoiding complications resulting from finite size effects.Comment: 15 pages, 6 figures, RevTe

The quantum paraelectric behavior of SrTiO_{3} revisited: relevance of the structural phase transition temperature

It has been known for a long time that the low temperature behavior shown by the dielectric constant of quantum paraelectric $SrTiO_{3}$ can not be fitted properly by Barrett's formula using a single zero point energy or saturation temperature ($T_{1}$). As it was originally shown [K. A. M\"{u}ller and H. Burkard, Phys. Rev. B {\bf 19}, 3593 (1979)] a crossover between two different saturation temperatures ($T_{1l}$=77.8K and $T_{1h}$=80K) at $T\sim10K$ is needed to explain the low and high temperature behavior of the dielectric constant. However, the physical reason for the crossover between these two particular values of the saturation temperature at $T\sim10K$ is unknown. In this work we show that the crossover between these two values of the saturation temperature at $T\sim10K$ can be taken as a direct consequence of (i) the quantum distribution of frequencies $g(\Omega)\propto\Omega^{2}$ associated with the complete set of low-lying modes and (ii) the existence of a definite maximum phonon frequency given by the structural transition critical temperature $T_{tr}$.Comment: 8 pages, 3 figure

Optical forces at the nanoscale: Size and electrostatic effects

“This document is the Accepted Manuscript version of a Published Work that appeared in final form in Nano Letters copyright © American Chemical Society after peer review and technical editing by publisher. To acces final work see Optical Forces at the Nanoscale: Size and Electrostatic Effects, Nano Letters, 18.1 (2018), pags. 602-609. http://doi.org/10.1021/acs.nanolett.7b04804"The reduced magnitude of the optical trapping forces exerted over sub-200 nm dielectric nanoparticles complicates their optical manipulation, hindering the development of techniques and studies based on it. Improvement of trapping capabilities for such tiny objects requires a deep understanding of the mechanisms beneath them. Traditionally, the optical forces acting on dielectric nanoparticles have been only correlated with their volume, and the size has been traditionally identified as a key parameter. However, the most recently published research results have shown that the electrostatic characteristics of a sub-100 nm dielectric particle could also play a significant role. Indeed, at present it is not clear what optical forces depend. In this work, we designed a set of experiments in order to elucidate the different mechanism and properties (i.e., size and/or electrostatic properties) that governs the magnitude of optical forces. The comparison between experimental data and numerical simulations have shown that the double layer induced at nanoparticle’s surface, not considered in the classical description of nanoparticle’s polarizability, plays a relevant role determining the magnitude of the optical forces. Here, the presented results constitute the first step toward the development of the dielectric nanoparticle over which enhanced optical forces could be exerted, enabling their optical manipulation for multiples purposes ranging from fundamental to applied studiesThis work has been supported by the Spanish Ministerio de Economia y Competitividad (project Nr.MAT2016-75362-C3-1-R), FIS2015-69295-C3-3-P and the “María de Maeztu” Program Ref: MDM-2014-0377. P.R.S. thanks MINECO and the Fondo Social Europeo (FSE) for the “Promoción del talento y su Empleabilidad en I+D+i” statal program (BES-2014-069410). K.P. acknowledges financial support from the National Science Center Poland (NCN) under the ETIUDA doctoral scholarship on the basis of decision number DEC-2014/12/T/ST5/00646. A.B. acknowledges the statutory financial support from ILT&SR PAS. P.H.G. thanks MINECO for the Juan de la Cierva program (IJCI-2015- 24551). The European Upconversion Network (COST Action CM1403) is acknowledge

Thermoresponsive Polymeric Nanolenses Magnify the Thermal Sensitivity of Single Upconverting Nanoparticles

Lanthanide-based upconverting nanoparticles (UCNPs) are trustworthy workhorses in luminescent nanothermometry. The use of UCNPs-based nanothermometers has enabled the determination of the thermal properties of cell membranes and monitoring of in vivo thermal therapies in real time. However, 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, it is shown how these problems can be elegantly solved using a thermoresponsive polymeric coating. Upon decorating the surface of NaYF4:Er3+,Yb3+ 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 °C). This optical force improvement is accompanied by a significant enhancement of the thermal sensitivity— a maximum value of 8% °C+1 at 32 °C induced by the collapse of PNIPAM. Numerical simulations reveal that the enhancement in thermal sensitivity mainly stems from the high-refractive-index polymeric coating that behaves as a nanolens of high numerical aperture. The results in this work demonstrate how UCNP nanothermometers can be further improved by an adequate surface decoration and open a new avenue toward highly sensitive single-particle nanothermometryThis work was supported by the Ministerio de Ciencia e Innovación de España (PID2019-106211RB-I00 PID2019-105195RA-I00 and MAT2017- 83111R), by the Comunidad de Madrid (S2017/BMD-3867 RENIM-CM), co-financed by European Structural and Investment Fund and by the Universidad Autónoma de Madrid and Comunidad Autónoma de Madrid (SI1/PJI/2019-00052 and PR38/21-36 ANTICIPA-CM). D.L. acknowledges a scholarship from the China Scholarship Council (201808350097). J.R.B. acknowledges the support from Carl Tryggers Foundation (CTS18:229). M.I.M acknowledges financial support from the Spanish Ministerio de Ciencia e Innovación, through the “María de Maeztu” Programme for Units of Excellence in R&D (CEX2018-000805-M) and the MELODIA PGC2018-095777-B-C22 proje

Universality Class of Thermally Diluted Ising Systems at Criticality

The universality class of thermally diluted Ising systems, in which the realization of the disposition of magnetic atoms and vacancies is taken from the local distribution of spins in the pure original Ising model at criticality, is investigated by finite size scaling techniques using the Monte Carlo method. We find that the critical temperature, the critical exponents and therefore the universality class of these thermally diluted Ising systems depart markedly from the ones of short range correlated disordered systems. Our results agree fairly well with theoretical predictions previously made by Weinrib and Halperin for systems with long range correlated disorder.Comment: 7 pages, 6 figures, RevTe