Imaging the proton concentration and mapping the spatial distribution of the electric field of catalytic micropumps

Catalytic engines can use hydrogen peroxide as a chemical fuel in order to drive motion at the microscale. The chemo-mechanical actuation is a complex mechanism based on the interrelation between catalytic reactions and electro-hydrodynamics phenomena. We studied catalytic micropumps using fluorescence confocal microscopy to image the concentration of protons in the liquid. In addition, we measured the motion of particles with different charges in order to map the spatial distributions of the electric field, the electrostatic potential and the fluid flow. The combination of these two techniques allows us to contrast the gradient of the concentration of protons against the spatial variation in the electric field. We present numerical simulations that reproduce the experimental results. Our work sheds light on the interrelation between the different processes at work in the chemomechanical actuation of catalytic pumps. Our experimental approach could be used to study other electrochemical systems with heterogeneous electrodes. © 2013 American Physical Society.We acknowledge support from the European Union (ERC-carbonNEMS project), the Spanish government (FIS2009-11284, FIS2011-22603, MAT2012-31338), and the Catalan government (AGAUR, SGR).Peer Reviewe

Nanociencia y Nanotecnología: la gran revolución de lo pequeño

1 página.-- Charla divulgativa presentada en la semana de la ciencia 2010 celebrada en Barcelona (España) el 16/11/2010.Peer reviewe

Collective motion of Nafion-based micromotors in water

This article is part of the themed collection: Water at interfaces.Ion exchange is one of the most interesting processes occurring at the interface between aqueous solutions and polymers, such as the well-known Nafion. If the exchanged ions have different diffusion coefficients, this interchange generates local electric fields which can be harnessed to drive fluid motion. In this work, we show how it is possible to design and fabricate self-propelling microswimmers based on Nafion, driven by ion-exchange, and fueled by innocuous salts. These Nafion micromotors are made using colloidal lithography by micro/nanostructuring Nafion in the form of asymmetric rods. These microswimmers exhibit fascinating collective motion in water driven by the interplay of their self-generated chemical/electric fields and their capability to pump matter nearby towards the collective motile structure. The pumping activity of the microswimmers induces the formation of growing mobile clusters, whose velocity increases with size. Such dynamic structures are able to trap nearby micro/nano-objects while purifying the liquid, which acts both as the transport media and as fuel. Such phenomenology opens the door to potential applications in water remediation that are currently under development.This research was supported by the Spanish Ministry of Science and Innovation (MCIN) under Contracts No. PID2021-124568NB-I00 and PID2021-126570NB-I00. The ICN2 is funded by the CERCA program/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence programme, Grant CEX2021-001214-S, funded by MCIN/AEI/10.13039.501100011033. We also acknowledge the scientific exchange and support of the Centre for Molecular Water Science (CMWS).With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001214-S).Peer reviewe

Non-equilibrium thermodynamics of catalytic nanomotors and micropumps

Abstract of Twentieth Symposium on Thermophysical Properties; Boulder, Colorado (USA), June 24–29 (2018).The conversion of chemical energy into directed motion is a key point behind the high efficient operation of biomolecular machines. Inspired by nature, there is a growing interest in engineering novel artificial machines which can self-propel and carry out autonomous work “a la carte,” mimicking the impressive molecular machinery of living organisms. In this context, Janus particles, bimetallic nanomotors and micropumps, which are powered by catalytic reactions at two different metals, stand out as one of the most promising candidates. But how catalytic reactions end up driving particle or fluid motion is a rather complex non-equilibrium process involving the coupling of electrochemical reactions, electrostatics, mass and charge transport, and fluid dynamics. In this context, a theoretical description complemented by numerical simulations becomes a powerful tool to optimize and shed light on the complex chemo-mechanical actuation of catalytic objects. In this talk, we will discuss the non-equilibrium thermodynamics concepts controlling the operation of catalytic micropumps. The results of this study facilitate a better understanding of the whole scenario behind this process and also provide important clues on how to design more efficient catalytic micro/nano motors for future applications.Peer reviewe

Synthesis of polydopamine at the femtoliter scale and confined fabrication of Ag nanoparticles on surfaces

Nanoscale polydopamine motifs are fabricated on surfaces by deposition of precursor femtolitre droplets using an AFM tip and employed as confined reactors to fabricate Ag nanoparticle patterns by in situ reduction of a Ag+ salt.This work was partly funded through grants MAT2012-38318-C03-02 and MAT2012-38319-C02-01 of the Spanish MINECO. M.G. thanks the CSIC for a JAEPre predoctoral grant.Peer Reviewe

Silicon-based chemical motors: An efficient pump for triggering and guiding fluid motion using visible light

We report a simple yet highly efficient chemical motor that can be controlled with visible light. The motor made from a noble metal and doped silicon acts as a pump, which is driven through a light-activated catalytic reaction process. We show that the actuation is based on electro-osmosis with the electric field generated by chemical reactions at the metal and silicon surfaces, whereas the contribution of diffusio-osmosis to the actuation is negligible. Surprisingly, the pump can be operated using water as fuel. This is possible because of the large - Potential of silicon, which makes the electro-osmotic fluid motion sizable even though the electric field generated by the reaction is weak. The electro-hydrodynamic process is greatly amplified with the addition of reactive species, such as hydrogen peroxide, which generates higher electric fields. Another remarkable finding is the tunability of silicon-based pumps. That is, it is possible to control the speed of the fluid with light. We take advantage of this property to manipulate the spatial distribution of colloidal microparticles in the liquid and to pattern colloidal microparticle structures at specific locations on a wafer surface. Silicon-based pumps hold great promise for controlled mass transport in fluids.The authors acknowledge support from MINECO and the “Fondo Europeo de Desarrollo Regional” (FEDER) through Grant MAT2012-31338, the European Union (ERC-carbonNEMS project), and the Catalan government (AGAUR, SGR).Peer Reviewe

Impedimetric genosensing of DNA polymorphism correlated to cystic fibrosis: A comparison among different protocols and electrode surfaces

7 páginas, 5 figuras, 1 tabla.In this work, a genosensor for the impedimetric detection of the triple base deletion in a cystic fibrosis-related DNA synthetic sequence is presented. Screen-Printed Carbon Electrodes containing Carboxyl functionalised multi-walled carbon nanotubes were used for the immobilization of an amino-modified oligonucleotide probe, complementary to the Cystic Fibrosis (CF) mutant gene. The complementary target (the mutant sequence) was then added and its hybridization allowed. The change of interfacial charge transfer resistance (Rct) between the solution and the electrode surface, experimented by the redox marker ferrocyanide/ferricyanide, confirmed the hybrid formation. A non-complementary DNA sequence and a three-mismatch sequence corresponding to the wild DNA gene (present in healthy people) were used as negative controls. A further step employing a signalling biotinylated probe was performed for signal amplification using streptavidin-modified gold nanoparticles (strept-AuNPs). In order to observe by SEM the presence and distribution of strept-AuNPs, a silver enhancement treatment was applied to electrodes already modified with DNA–nanoparticles conjugate. The developed protocol allowed the very sensitive detection of the triple base deletion in a label-free CF-related DNA sequence, achieving a LOD around 100 pM. Results were finally compared with those obtained using different protocols for immobilization of DNA capture probe.Financial support for this work has been provided by the Ministry of Science and Technology (MCyT, Madrid, Spain) trough projects Consolider-Ingenio 2010 CSD2006-00012, and by the Department of Innovation, Universities and Enterprise (DIUE) from the Generalitat de Catalunya.Peer reviewe

Key Parameters Controlling the Performance of Catalytic Motors

The development of autonomous micro/nanomotors driven by self-generated chemical gradients is a topic of high interest given their potential impact in medicine and environmental remediation. Although impressive functionalities of these devices have been demonstrated, a detailed understanding of the propulsion mechanism is still lacking. In this work, we perform a comprehensive numerical analysis of the key parameters governing the actuation of bimetallic catalytic micropumps. We show that the fluid motion is driven by self-generated electro-osmosis where the electric field originates by a proton current rather than by a lateral charge asymmetry inside the double layer. Hence, the surface potential and the electric field are the key parameters for setting the pumping strength and directionality. The proton flux that generates the electric field stems from the proton gradient induced by the electrochemical reactions taken place at the pump. Surprisingly the electric field and consequently the fluid flow are mainly controlled by the ionic strength and not by the conductivity of the solution, as one could have expected. We have also analyzed the influence of the chemical fuel concentration, electrochemical reaction rates, and size of the metallic structures for an optimized pump performance. Our findings cast light on the complex chemomechanical actuation of catalytic motors and provide important clues for the search, design, and optimization of novel catalytic actuators

Electrostatic and hydrophobic interactions involved in CNT biofunctionalization with short ss-DNA

This work is aimed at studying the adsorption mechanism of short chain 20-mer pyrimidinic homoss-DNA (oligodeoxyribonucleotide, ODN: polyC20 and polyT20) onto CNT by reflectometry. To analyze the experimental data, the effective-medium theory using the Bruggemann approximation represents a suitable optical model to account for the surface properties (roughness, thickness, and optical constants) and the size of the adsorbate. Systematic information about the involved interactions is obtained by changing the physicochemical properties of the system. Hydrophobic and electrostatic interactions are evaluated by comparing the adsorption on hydrophobic CNT and on hydrophilic silica and by modulating the ionic strength with and without Mg2+. The ODN adsorption process on CNT is driven by hydrophobic interactions only when the electrostatic repulsion is suppressed. The adsorption mode results in ODN molecules in a side-on orientation with the bases (nonpolar region) toward the surface. This unfavorable orientation is partially reverse by adding Mg2+. On the other hand, the adsorption on silica is dominated by the strong repulsive electrostatic interaction that is screened at high ionic strength or mediated by Mg2+. The cation-mediated process induces the interaction of the phosphate backbone (polar region) with the surface, leaving the bases free for hybridization. Although the general adsorption behavior of the pyrimidine bases is the same, polyC20 presents higher affinity for the CNT surface due to its acid-base properties.Authors acknowledge the financial contributions of FONCyT, SeCyT-UNC, CONICET, the International Exchange Collaboration between CAPES (Brazil) and SPU (Argentine) (Grant No. 025/05), and National Institute of General Medical Sciences (NIGMS)/National Institutes of Health (1SC3GM081085) (C.D.G). M.J.E. thanks the Ministry of Education and Science of Spain (Project NAN2004-093006-C05-03) and the “Ramón and Cajal” Program. M.L.C. thanks CONICET for the fellowship granted.Peer Reviewe

Effect of temperature on the growth of single crystalline monolayer graphene by Chemical Vapor Deposition (CVD)

Resumen del póster presentado a la 6th edition of Graphene Conference series, the largest European Event in Graphene and 2D Materials, celebrada en Genova (Italia) del 19 al 22 de abril de 2016.The ever increasing interest in graphene properties and its applications has motivated the controlled growth of high-quality graphene and fabrication of graphene-based devices. The growth of graphene via CVD using metal catalysts depends on both the intrinsic properties of the metal catalysts and the growth parameters. Here we demonstrate that the structure of single layer graphene flakes grown on a copper substrate by low pressure CVD depends dramatically on the furnace temperature, within a few tens of degrees Celsius. Optical microscope analysis of as-grown and transferred graphene onto SiO2/Si shows that growth at 1000ºC results in dendritic shapes while growth at 1040ºC gives a compact graphene flake. The low temperature growth was extended over a long time (1 hour) in order to check if there was a change in the structure towards a compact flake as the one in Figure b, which was obtained after just 10 minutes of growth time at 1040ºC. However, the size of the dendrites increased without merging. Although still poorly understood, the dendritic growth may be due to the poor smoothening of the copper at the lower annealing temperatures and to the low carbon attachment/detachment kinetics at the graphene growth fronts. We have characterized the charge and spin transport properties of the graphene grown at low temperatures. We have fabricated non-local spin valve devices with 3 μm graphene channel length and found a spin life time of 0.2 ns and spin diffusion length of 2.5 μm at room temperature. The mobility of the device was of 1000 cm2 /Vs, which is typical for CVD grown graphene on SiO2/Si. Future work will focus on comparing these results with the spintronic performance of graphene grown at higher temperatures.Peer Reviewe