Non-invasive continuous monitoring of pro-oxidant effects of engineered nanoparticles on aquatic microorganisms

Paul Bowen, Volodymyr Koman, Olivier Martin, Christian Santschi, Nadia Rachel Von Moos
2017
Journal paper

Abstract

Engineered nanomaterials (ENMs) are key drivers for the development of highly sophisticated new technologies. As all new attainments, the rapidly increasing used of ENMs raise concerns about their safety for the environment and humans. There is growing evidence showing that if engineered nanomaterials are released into the environment, there is a possibility that they could cause harm to aquatic microorganisms. Among the divers effects triggering their toxicity the ability of ENMs to generate reactive oxygen species (ROS) capable of oxidizing biomolecules is currently considered a central mechanism of toxicity. Therefore, development of sensitive tools for quantification of the ROS generation and oxidative stress are highly sought. After briefly introducing ENMs-induced ROS generation and oxidative stress in the aquatic microorganisms (AMOs), this overview paper focuses on a new optical biosensor allowing sensitive and dynamic measurements of H2O2 in real-time using multiscattering enhanced absorption spectroscopy. Its principle is based on sensitive absorption measurements of the heme protein cytochrome c whose absorption spectrum alters with the oxidation state of constituent ferrous Fe-II and ferric Fe-III. For biological applications cytochrome c was embedded in porous random media resulting in an extended optical path length through multiple scattering of light, which lowers the limit of detection to a few nM of H2O2. The sensor was also integrated in a microfluidic system containing micro-valves and sieves enabling more complex experimental conditions. To demonstrate its performance, abiotic absorption measurements of low concentrations of dye molecules and 10 nm gold particles were carried out achieving limits of detection in the low nM range. Other biologically relevant reactive oxygen species can be measured at sub-mu M concentrations, which was shown for glucose and lactate through enzymatic reactions producing H2O2. In ecotoxicological investigations H2O2 excreted by aquatic microorganisms exposed to various stressors were measured. Pro-oxidant effects of nano-TiO2 and nano-CuO towards green alga Chlamydomonas reinhardtii were explored in various exposure media and under different light illuminations. Dynamics of Cd2+ induced effects on photosynthetic activity, sensitisation and recovery of cells of C. reinhardtii was also studied.

Official source

https://infoscience.epfl.ch/record/227164?ln=en

About this result

This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.

Related concepts

Related publications

Paul Bowen, Volodymyr Koman, Olivier Martin, Christian Santschi, Nadia Rachel Von Moos
2017
Journal paper

Abstract

Official source

https://infoscience.epfl.ch/record/227164?ln=en

About this result

Related concepts (13)

Related concepts

Related publications (6)

Related publications

Since the first inductively coupled plasma (ICP) torch was developed in the 60's, RF thermal plasmas have found a variety of applications in material processing such as crystal growth, thermal spray coatings, spheroidization and vaporization of refractory materials. In recent decades, inductively coupled thermal plasmas have been used for the synthesis of high purity nanoparticles, thank to their remarkable advantages such as high energy density, variable operating pressures and low product contamination. The formation of nano-sized particles in thermal plasmas particularly using solid refractory precursor is a complex process. Hereby the injected precursor powders are heated by the high temperature of the thermal plasma. The heated powders are vaporized and decomposed into vapor species. During the following cooling, the vapor species are condensed to nano-sized particles. In this synthesis process, characterized by evaporation-condensation, the properties of the synthesized particles such as particle size, size distribution, phases and morphology are affected by various process parameters. Gas pressure, flow rates of the different torch gases, size of the precursor powders and powder loading in the plasma are considered as the influencing process parameters. In order to optimize and control the process for tailor-made nanoparticle synthesis, it is necessary to understand the effects of the process parameters on plasma properties and on the particle-plasma interactions resulting in final properties of the synthesized powders. In the present work, firstly, the enthalpy probe technique, a well-established plasma diagnostic tool for high pressure thermal plasma, has been applied to characterize the inductively coupled Ar-H2 thermal RF plasma used for alumina nanoparticle synthesis at different operating conditions. The plasma enthalpy has been determined, and the plasma temperature under a given gas pressure could subsequently be calculated assuming local thermodynamic equilibrium (LTE), once the gas composition has been determined by mass spectrometry. The gas velocity of the plasma jet could also be obtained by using the Bernoulli equation and stagnation pressure. Secondly, the influence of flow rates of central gas and precursor feed rates on the Al2O3 precursor evaporation has been investigated by process monitoring. Optical emission spectroscopy (OES) and laser light extinction (LE) measurements have been carried out to monitor in-situ the injection of the alumina precursors and to obtain information on the ongoing precursor evaporation. The emission line intensities of the aluminum vapor were used to determine the dependence of process parameters on precursor evaporation. Furthermore, the laser light extinction was used to calculate the number density of non plasma-treated powders, from which the number fraction of evaporated powders could be deduced. The size and morphology of the synthesized particles have been characterized ex-situ. Finally, the influence of quenching conditions on the condensation and formation of the nano-sized alumina particle has been studied by process analysis of the gas phase reactions of alumina. Optical emission spectroscopic was performed at different axial positions to monitor the gas phase reactions of the vaporized particles. Axial profiles of the emission line intensities of the main vapor species of alumina, Al(g) and AlO(g), were compared with the results of the enthalpy probe measurements and the thermal decomposition reactions of alumina found in literature. The results allow explanation of the alumina reactions in the thermal plasma as well as gives indications for the optimal axial position of the quenching gas injection. In addition to the determination of the optimal quenching position, the influence of the flow rates of quenching gas on the nanoparticle formation has been investigated. The synthesis of the submicron alumina using vapor-condensation principle predominantly leads to various thermodynamically metastable crystal structures called transition alumina. Therefore, the occurrence of different transition aluminas is discussed with regards to the flow rates of the quenching gas. The results presented in this thesis show that the synthesis process of the nanoparticle can be described on the basis of experimental results and basic information on the powder materials. The explanation of the influence of process parameters on powder evaporation and nanoparticle formation shows the usefulness of the in-situ plasma process monitoring, and the large potential for optimizing and controlling the nanopowder synthesis process in an inductively coupled RF thermal plasma.

EPFL2006

Carbon nanotubes functionalized with dye molecules and metal nanoparticles

Tilman Assmus

Single-walled carbon nanotubes are highly interesting quasi one-dimensional nanostructures. They possess a multitude of fascinating optical, mechanical and electrical properties, which can be even further expanded through appropriate functionalization strategies. This thesis covers a number of functionalization strategies and their effects on the nanotube's optical and electrical properties. The first part deals with the functionalization of carbon nanotubes with dye molecules and the characterization of the functionalized system. Both covalent and noncovalent approaches were investigated with the goal of modifying the nanotubes' photoelectrical properties. Upon excitation with light of the appropriate wavelength, a clear electrical response could be observed on some functionalized individual nanotubes. Depending on the attached dye molecule, the conductivity change is either induced by a light-induced conformational change or by a charge transfer between the nanotube and the excited dye molecule. The perspectives of constructing an optoelectronic nanoswitch based on these effects are discussed. The second part of the thesis addresses carbon nanotubes functionalized by a low density of electrodeposited gold nanoparticles with sizes in the range between 10 and 100nm. In this case, the functionalization is targeted on amplifying the nanotube's Raman response (SERS effect). The novel sample preparation technique developed in this thesis allowed for an investigation of SERS on the level of individual molecule / nanoparticle hybrids. The optical emission spectra of the nanotube-nanoparticle hybrid structure disclosed Raman peaks associated with the nanotubes, which are superimposed on a broad luminescence background originating from the metal particles. Wavelength dependent experiments revealed maximum Raman intensity when both the nanotube and the metal particle are in optical resonance. In well-prepared samples the Raman signals collected over isolated particles exhibited an intensity enhancement by at least one order of magnitude, as compared to bare sections on the same tube, without appreciably interfering with polarization dependent Raman measurements.

EPFL2008

Couches minces nanoporeuses pour la réalisation de dispositifs optiques

Gaëtan Wicht

The physical-chemical properties of polymer films can be modified by embedding inorganic materials (e. g. inorganic nanoparticles) into the polymer matrix. Depending both on the material properties (e. g. nanoparticles concentration) and on the fabrication procedure, air pores can appear into such hybrid organic-inorganic matrices, thus creating nanoporous layers. At the end of the 90's, Ilford Imaging Switzerland GmbH was a pionner in the field with the development of a unique "roll-to-roll" process to coat such layers on large surfaces and on an industrial scale. First used as absorbing layers in the ink-jet printing of high quality photographs, the interest for such nanoporous films as optical films has been rapidly growing. In particular, the possibility of introducing air nanopores on demand in a polymer matrix make these layers the perfect candidates for the fabrication of optical films with a very low refractive index (n < 1.2). In optical devices based on thin film multilayers, such nanoporous materials can guarantee an excellent index matching between the air and a plastic substrate, thus acting as very good antireflection coatings. On the other hand, in a different approach, these nanoporous layers cans also yield a good index contrast between a guiding layer and its claddings, thus allowing the fabrication of good polymer waveguides. The goal of this thesis was then to demonstrate the optical potential of the industrial nanoporous layers fabricated by Ilford on flexible plastic substrates. First, both the morphology and the optical response of different nanoporous layers were thoroughly characterised with respect to the fabrication parameters. The impact of the fabrication process as well as of the nanoparticle type (silica (SiO2), bohemite (AlOOH) and titania oxyde (TiO2)), size and concentration were studied. While reflectance and transmittance measurements revealed the highly transparent nature of all these layers, ellipsometry measurements showed the large range of achievable refractive indices (1.15 < n < 2.0). With the possibility of coating several nanoporous layers one on top of the other, with independently adjusted thicknesses and indices, we designed and fabricated antireflection multilayers with graded-index, that, once coated on a plastic substrate successfully reduce its surface reflectance from 10 % to few 0.1 %. Besides the measurements, a theoretical model based on the transfer matrix method allowed us to analyse in details the response of our samples. We could thus show that the residual interface roughness is responsible for the loss of coherence of the light reflected at each interface, thus reducing the amplitude of the interference fringes in the reflectance spectrum and yielding an optical response almost constant over the entire visible spectrum. Finally, the nanoporous layers were also used as optically isolating layers for the fabrication of polymer optical waveguides. An original measurement method, based on the emission of a fluorescent dye dispersed inside the guiding layer, allowed us to clearly demonstrate the feasability of such guides. Propagation loss in the order of 1.5 dB/cm were measured, a very promising value that, after optimisation of both the material and the optical design, is likely to be further reduced in order to reach better performances than standard polymer waveguides and, eventually, to approach those of inorganic devices. Having highlighted the optical properties of our polymer nanoporous layers with the fabrication of two complementary optical devices based on polymer-nanoporous multilayers, this thesis clearly demonstrates their potential that, combined with their industrial nature, can guarantee them a very promising future, even brighter than that for similar prototype layers fabricated at a lab scale.

EPFL2010