Luminescence Dynamics of Silica-Encapsulated Quantum Dots During Optical Trapping

"This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acs.jpcc.6b11867."[EN] The trade-off between photobrightening and photobleaching controls the emission stability of colloidal quantum dots. This balance is critical in optical trapping configurations, where irradiances that confine and simultaneously excite the nanocrystals in the focal region cannot be indefinitely lowered. In this work, we studied the photobrightening and bleaching behaviors of two types of silica-encapsulated quantum dots excited upon two-photon absorption in an optical trap. The first type consists of alloyed CdSeZnS quantum dots covered with a silica shell. We found that the dynamics of these as-prepared architectures are similar to those previously reported for bare surface-deposited quantum dots, where thousands of times smaller irradiances were used. We then analyzed the same quantum dot systems treated with an extra intermediate sulfur passivating shell for the better understanding of the surface traps influence in the temporal evolution of their emission in the optical trap. We found that these latter systems exhibit better homogeneity in their photodynamic behavior compared to the untreated ones. These features strengthen the value of quantum dot preparations in optical manipulation as well as for applications where both long and maximal emission stability in physiological and other polar media are required.The authors thank A. Blanco and D. Granados for fruitful discussion and S. de Lorenzo for technical help. H.R-R. is supported by an FPI-UAM fellowship and M. A. by a contract from Fundacion IMDEA Nanociencia. The research leading to these results has received funding from the Spanish Ministry of Economy and Competitiveness (grant numbers MAT2015-71806-R and FIS2015-67367-C2-1-P), from Comunidad de Madrid (S2013/MIT-2740) and from UAM-Banco Santander (CEAL-AL/2015-15).Rodríguez-Rodríguez, H.; Acebrón, M.; Juárez, B.; Arias-Gonzalez, JR. (2017). Luminescence Dynamics of Silica-Encapsulated Quantum Dots During Optical Trapping. The Journal of Physical Chemistry C. 121(18):10124-10130. https://doi.org/10.1021/acs.jpcc.6b11867S10124101301211

Alliance free and alliance cover sets

A \emph{defensive} (\emph{offensive}) $k$-\emph{alliance} in $\Gamma=(V,E)$ is a set $S\subseteq V$ such that every $v$ in $S$ (in the boundary of $S$) has at least $k$ more neighbors in $S$ than it has in $V\setminus S$. A set $X\subseteq V$ is \emph{defensive} (\emph{offensive}) $k$-\emph{alliance free,} if for all defensive (offensive) $k$-alliance $S$, $S\setminus X\neq\emptyset$, i.e., $X$ does not contain any defensive (offensive) $k$-alliance as a subset. A set $Y \subseteq V$ is a \emph{defensive} (\emph{offensive}) $k$-\emph{alliance cover}, if for all defensive (offensive) $k$-alliance $S$, $S\cap Y\neq\emptyset$, i.e., $Y$ contains at least one vertex from each defensive (offensive) $k$-alliance of $\Gamma$. In this paper we show several mathematical properties of defensive (offensive) $k$-alliance free sets and defensive (offensive) $k$-alliance cover sets, including tight bounds on the cardinality of defensive (offensive) $k$-alliance free (cover) sets

Optical Trapping of Single Nanostructures in a Weakly Focused Beam. Application to Magnetic Nanoparticles

"This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see [insert ACS Articles on Request author-directed link to Published Work, see https://pubs.acs.org/doi/10.1021/acs.jpcc.8b04676."[EN] Optical trapping of individual particles is believed to be only effective under highly focused beams because these conditions strengthen the gradient forces. This is especially critical in the beam propagating direction, where the scattering and absorption forces must be counterbalanced. Here, we demonstrate that optical trapping of nanostructures is also possible in a weakly focused beam. We study the theoretical conditions for effective three-dimensional optical confinement and verify them experimentally on iron-oxide-based nanoparticles with and without a silica coating, for which scattering, absorption, and gradient forces exist. This chemical approach to their all-optical control is, in turn, convenient for making magnetic nanostructures biocompatible. Weakly focused beams reduce the irradiance in the focal region and therefore the photon damage to the samples, which is further important to delay quantum dot quenching in the trap or to prevent artifacts in the study of biomolecular motor dynamics.We are grateful to Dr. Maria Acebron and Dr. Beatriz H. Juarez for their support in the silica encapsulation of the nano particles. This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO, Grant MAT2015-71806-R). IMDEA Nanociencia acknowledges support from the "Severo Ochoa" Programme for Centers of Excellence in R&D (MINECO, Grant SEV-2016-0686). H.R.-R. is supported by an FPI-UAM fellowship.Rodríguez-Rodríguez, H.; De Lorenzo, S.; De La Cueva, L.; Salas, G.; Arias-Gonzalez, JR. (2018). Optical Trapping of Single Nanostructures in a Weakly Focused Beam. Application to Magnetic Nanoparticles. The Journal of Physical Chemistry C. 122(31):18094-18101. https://doi.org/10.1021/acs.jpcc.8b04676S18094181011223

Spatio-temporal adaptive penalized splines with application to Neuroscience

Data analysed here derive from experiments conducted to study neurons' activity in the visual cortex of behaving monkeys. We consider a spatio-temporal adaptive penalized spline (P-spline) approach for modelling the firing rate of visual neurons. To the best of our knowledge, this is the first attempt in the statistical literature for locally adaptive smoothing in three dimensions. Estimation is based on the Separation of Overlapping Penalties (SOP) algorithm, which provides the stability and speed we look for.MTM2014-55966-P MTM2014-52184-P RETICS, Oftared - RD12/0034/001

Identification and evaluation of fungal strains with fucoidan degradation potential

Ten fungal strains isolated of Mexican semi-desert were screened for ability to hydrolyze fucoidan in order to search microorganism capable to produce sulfated fucans-degrading enzymes. Plate assay and liquid fermentation experiments were carried out using Laminaria japonica fucoidan as only carbon source, testing three nitrogen sources. Growth was observed only in Aspergillus niger PSH, Mucor sp., and Penicillum purpurogenum GH2 in fucoidan-urea medium. The activity of fucoidanases was determined by reduced sugars. Aspergillus niger PSH showed the highest activity titles. This research indicate that filamentous fungi, using specific medium, are sources enable to induce active metabolism that act toward this class of polysaccharide

Cortical and trabecular bone at the radius and tibia in male and female adolescents with Down syndrome:a peripheral quantitative computed tomography (pQCT) study

Abstract Summary We aimed to describe the structure and strength of the tibia and radius of adolescents with Down syndrome. We observed that despite higher levels of volumetric bone mineral density in determined skeletal sites, they are at higher risk of developing osteoporotic fractures in the future due to their lower bone strength indexes. Introduction The aims of the study were to describe the cortical and trabecular volumetric bone mineral density (vBMD), bone mineral content (BMC), area, and bone strength in adolescents with Down syndrome (DS) and to compare them with adolescents without disabilities. Methods Thirty adolescents (11 girls) with DS and 28 without disabilities (10 girls) participated in the study. Peripheral quantitative computed tomography measurements were taken at proximal and distal sites of the tibia and radius. Values of total, trabecular, and cortical BMC; vBMD; and area were obtained of each scan. Cortical thickness and endosteal and periosteal circumferences were also measured, and different bone strength indexes were calculated. Student's t tests were applied between groups. Results The DS group showed greater vBMD at distal radius, BMC at proximal radius, and total and cortical vBMD at proximal tibia. The non-DS group showed higher total and trabecular area at the distal radius and total, cortical, and trabecular BMC and area at distal tibia. Higher values of periosteal and endosteal circumference and bone strength were also found in non-DS group. Conclusions From these results, it can be believed that even with higher vBMD in determined skeletal sites, adolescents with DS are at higher risk of suffering bone fractures due to an increased fragility by lower resistance to load bending or torsion

Photoluminescence Activation of Organic Dyes via Optically Trapped Quantum Dots

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Nano, copyright © American Chemical Society after peer review and technical editing by the publisher.[EN] Laser tweezers afford quantum dot (QD) manipulation for use as localized emitters. Here, we demonstrate fluorescence by radiative energy transfer from optically trapped colloidal QDs (donors) to fluorescent dyes (acceptors). To this end, we synthesized silica-coated QDs of different compositions and triggered their luminescence by simultaneous trapping and two-photon excitation in a microfluidic chamber filled with dyes. This strategy produces a near-field light source with great spatial maneuverability, which can be exploited to scan nanostructures. In this regard, we demonstrate induced photoluminescence of dye-labeled cells via optically trapped silica-coated colloidal QDs placed at their vicinity. Allocating nanoscale donors at controlled distances from a cell is an attractive concept in fluorescence microscopy because it dramatically reduces the number of excited dyes, which improves resolution by preventing interferences from the whole sample, while prolonging dye luminescence lifetime due to the lower power absorbed from the QDs.H.R.-R. is supported by an FPI-UAM 2015 fellowship (BES-2009-027909). Authors acknowledge funding from the Spanish Ministry of Economy and Competitiveness through MAT2017-85617-R and MAT2015-71806-R. B.H.J. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness, through the Maria de Maeztu (IFIMAC) and Severo Ochoa (IMDEA Nanoscience) Programmes for Units of Excellence in R&D.Rodríguez-Rodríguez, H.; Acebrón, M.; Iborra, F.; Arias-Gonzalez, JR.; Juárez, B. (2019). Photoluminescence Activation of Organic Dyes via Optically Trapped Quantum Dots. ACS Nano. 13(6):7223-7230. https://doi.org/10.1021/acsnano.9b02835S7223723013

A comparative study of the electrochemical properties of vitamin B-6 related compounds at physiological pH

A comparative study of vitamin B6 group and related compounds in buffered solutions using electrochemical techniques has been performed at neutral pH. Irreversible bi- or tetra-electronic processes are observed for these substances, and the electron transfer coefficient (αn) calculated. It was concluded that either the first or second electron transfer were the rate determining step of the electrode process. The diffusion coefficient of these substances was calculated and the values given follow an inverse tendency to the molecular size. For aldehydes the values obtained were corrected of the hydration reaction. It is important to remark that catalytic waves were reported for the first time for these compounds. Using a model involving the nitrogen of the basic structure the kinetic constants were calculated for most of them