Characterization of polymer-coated CdSe/ZnS quantum dots and investigation of their behaviour in soil solution at relevant concentration by asymmetric flow field-flow fractionation – multi angle light scattering – inductively coupled plasma - mass spectrometry

Asymmetric flow field-flow fractionation for comprehensive characterization of hetero-aggregates made of nano-silver and extracellular polymeric substances

The present study explores the capability of asymmetrical flow field-flow fractionation (AF4) coupled online with diode array (DAD), fluorescence detectors (FLD), multi-angle light scattering (MALS) and dynamic light scattering (DLS) to characterize silver nanoparticles (nAg) hetero-aggregates formed with diatoms derived extracellular polymeric substances (EPS). The content of EPS varied from 10.5 to 105 mgC L-1 and nAg were dispersed at 4 mg L-1 in a freshwater medium. Good recoveries (∼ 76.9 ± 8.4 %) of nAg-EPS were obtained from AF4-DAD signals, but an anomalous elution was observed as EPS concentration increased: AF4 retention times decreased despite average gyration radii measured by MALS for nAg-EPS increased (from 16 nm to 24 nm), which suggests a change in the aggregation state, as evaluated by UV-Vis scans obtained from DAD. A regular Brownian relaxation of nAg-EPS was proven for each EPS concentration using these 2 detectors. The comparison of on-line and batch DLS measurements validated in addition, that no (dis)aggregation occurs upon injections. After a thorough comparison with classical AF4 using standards, the frit-inlet-AF4 was used. Slightly higher recovery (79.6 ± 4.6 %) was obtained but similar deviation of nAg-EPS elution occurred, excluding the implication of membrane differential fouling of nAg-EPS /conditioning effects of EPS. The investigation of physico-chemical parameters controlling the Brownian relaxation of nAg-EPS suggests the influence of nAg-EPS structure and EPS loading. This study demonstrates the suitable use of AF4 coupled to multiple detectors to probe-out eco-corona formation and characterize polydisperse systems containing NPs, EPS and their hetero-aggregates in freshwaters, even under a non-ideal size-fractionation scenario.

Field-Flow Fractionation in Molecular Biology and Biotechnology

Field-flow fractionation (FFF) is a family of single-phase separative techniques exploited to gently separate and characterize nano- and microsystems in suspension. These techniques cover an extremely wide dynamic range and are able to separate analytes in an interval between a few nm to 100 µm size-wise (over 15 orders of magnitude mass-wise). They are flexible in terms of mobile phase and can separate the analytes in native conditions, preserving their original structures/properties as much as possible. Molecular biology is the branch of biology that studies the molecular basis of biological activity, while biotechnology deals with the technological applications of biology. The areas where biotechnologies are required include industrial, agri-food, environmental, and pharmaceutical. Many species of biological interest belong to the operational range of FFF techniques, and their application to the analysis of such samples has steadily grown in the last 30 years. This work aims to summarize the main features, milestones, and results provided by the application of FFF in the field of molecular biology and biotechnology, with a focus on the years from 2000 to 2022. After a theoretical background overview of FFF and its methodologies, the results are reported based on the nature of the samples analyzed.

Size characterization of nanomaterials in environmental and biological matrices through non-electron microscopic techniques

Engineered nanomaterials (ENs) can enter the environment, and accumulate in food chains, thereby causing environmental and health problems. Size characterization of ENs is critical for further evaluating the interactions among ENs in biological and ecological systems. Although electron microscope is a powerful tool in obtaining the size information, it has limitations when studying nanomaterials in complex matrices. In this review, we summarized non-electron microscope-based techniques, including chromatography-based, mass spectrometry-based, synchrotron radiation- and neutron-based techniques for detecting the size of ENs in environmental and biological matrices. The advantages and disadvantages of these techniques were highlighted. The perspectives on size characterization of ENs in complex matrices were also presented.

Selective quantification of nanoplastics in environmental matrices by asymmetric flow field-flow fractionation with total organic carbon detection

Nanoplastics are of rapidly emerging concern as ubiquitous environmental pollutants. However, fate and transport assessments are currently hindered by a need for new analytical methods that can selectively quantify nanoplastics in environmental matrices. This study presents the first proof of principle to hyphenate asymmetric flow field-flow fractionation (AF4) with total organic carbon (TOC) detection for nanoplastics analysis, as evaluated on mixtures of multimodal polystyrene nanoplastics in the presence of dissolved organic matter and clay colloids. The AF4-TOC method enables more robust, size-resolved quantification of nanoplastics over other AF4 detection modes, including UV-vis, refractive index, and fluorescence tagging. This method development can fill a critical gap in analytical methodology for environmental nanoplastics research.

Field-flow fractionation for nanoparticle characterization

This review presents field-flow fractionation: The elements of theory enable the link between the retention and the characteristics of the nanometer-sized analytes to be highlighted. In particular, the nature of force and its way of being applied are discussed. Four types of forces which determine four types of techniques were considered: hydrodynamic, sedimentation, thermal, and electrical; this is to show the importance of the choice of technique in relation to the characterization objectives. Then the separation performance is presented and compared with other separation techniques: field-flow fractionation has the greatest intrinsic separation capability. The characterization strategies are presented and discussed; on the one hand with respect to the characteristics needed for the description of nanoparticles; on the other hand in connection with the choice of the nature of the force, and also of the detectors used, online or offline. The discussion is based on a selection of published study examples. Finally, current needs and challenges are addressed, and as response, trends and possible characterization solutions.

Characterization of volcanic ash nanoparticles and study of their fate in aqueous medium by asymmetric flow field-flow fractionation-multi-detection

Dimensional and elemental characterization of environmental nanoparticles is a challenging task that requires the use of a set of complementary analytical methods. Asymmetric flow field-flow fractionation coupled with UV-Vis, multi-angle laser light scattering and ICP-MS detection was applied to study the nanoparticle fraction of a volcanic ash sample, in a Milli-Q water suspension at pH 6.8. It has been shown that the separated by sedimentation nanoparticle fraction of the Klyuchevskoy volcano ash suspension contains 3 polydisperse populations for which size ranges (expressed in gyration radius, rG), hydrodynamic behaviours (evaluated via shape index) and elemental compositions are different. These 3 populations did not dissolve over the 72-h study but aggregated and settled out differently. Thus, the population of particles with gyration radii <140 nm (P1), which contained 6% Al₂O₃ and represented approximately 20% by mass of the nanoparticle fraction, remained in suspension without observable aggregation. The populations P2 and P3, which represented 67% and 13% by mass in the initial suspension, covered the rG range 25-250 nm and contained 17% and 15% Al₂O₃, respectively. Over time, populations P2 and P3 aggregated and their concentration in suspension at 72 h decreased by approximately 40% compared with the initial suspension. The decrease of these nanoparticle populations occurred either from the beginning of the temporal monitoring (P2) or after 30 h (P3). Aggregation generated a new population (P4) in suspension with rG up to 300 nm and mostly consisting of P2. This population represented only up to 6 to 7% of the nanoparticle fraction and decreased beyond 50 h. As a result, the trace elements present in the nanoparticle fraction and monitored (Cu and La) were also no longer found in the suspension. The results obtained can offer additional insights into the fate of volcanic ash nanoparticles in the environment.

Mobility and transformation of CdSe/ZnS quantum dots in soil: Role of the capping ligands and ageing effect

The increasing application of Quantum Dots (QDs) is cause of concern for the potential negative effects for the ecosystem, especially in soils that may act as a sink. In this study, soil leaching experiments were performed in quartz sand packed columns to investigate the behavior of core-shell CdSe/ZnS QDs coated with either small ligands (TGA-QDs) or more complex polymers (POAMA-QDs). Fluorescence emission was compared to mass spectrometric measurements to assess the nanoparticles (NPs) state in both the leachate (transported species) and porous media (deposited amounts). Although both QDs were strongly retained in the column, large differences were observed depending on their capping ligand stability. Specifically, for TGA-QDs elution was negligible and the retained fraction accumulated in the top-columns. Furthermore, 74% of the NPs were degraded and 38% of the Se was found in the leachate in non-NPs state. Conversely, POAMA-QDs were recovered to a larger extent (78.1%), and displayed a higher transport along the soil profile. Further experiments with altered NPs showed that homo-aggregation of the QDs prior injection determined a reduced mobility but no significant changes in their stability. Eventually, ageing of the NPs in the column (15 days) caused the disruption of up to 92% of the original QDs and the immobilization of NPs and metals. These results indicate that QDs will accumulate in top-soils, where transformations phenomena will determine the overall transport, persistency and degradation of these chemicals. Once accumulated, they may act as a source for potentially toxic Cd and Se metal species displaying enhanced mobility.

Inorganic nanoparticle synthesis in flow reactors – applications and future directions

The use of flow technologies for obtaining nanoparticles can play an important role in the development of ecological and sustainable processes for obtaining inorganic nanomaterials, and the continuous methods are part of the Flow Chemistry trend.

Separation of nanoparticles from polydisperse environmental samples: comparative study of filtration, sedimentation, and coiled tube field-flow fractionation

Nanoparticles (NPs) in the environment have a potential risk for human health and the ecosystem due to their ubiquity, specific characteristics, and properties (extreme mobility in the environment, abilities to accumulate of toxic elements and penetrate into living organisms). There is still a gap in studies on the chemical composition of natural NPs. The main reason is the difficulty to recover NPs, which may represent only one-thousandth or less of the bulk environmental sample, for further dimensional and quantitative characterization. In the present study, a methodology for the recovery of the nanoparticle fraction from polydisperse environmental samples was developed taking as example volcanic ashes from different regions of the world. For the first time, three separation methods, namely, filtration through a 0.45-μm membrane, sedimentation, and coiled tube field-flow fractionation (CTFFF), were comparatively studied. The separated fractions were characterized by laser diffraction and scanning electron microscopy and then analyzed by inductively coupled plasma atomic emission and mass spectrometry. It has been shown that all three methods provide the separation of NPs less than 400 nm from the bulk material. However, the fraction separated by sedimentation also contained a population (5% in mass) of submicron particles (~ 400-900 nm). The filtration resulted in low recovery of NPs. The determination of most trace elements was then impossible; the concentration of elements was under the limit of detection of the analytical instrument. The sedimentation and CTFFF made it possible to determine quantifiable concentrations for both major and trace elements in separated fractions. However, the sedimentation took 48 h while CTFFF enabled the fractionation time to be decreased down to 2 h. Hence, CTFFF looked to be the most promising method for the separation of NPs followed by their quantitative elemental analysis.