Can cloud point-based enrichment, preservation, and detection methods help to bridge gaps in aquatic nanometrology?

Dynamic Phosphorus: Thiolate Exchange Cascades with Higher Phosphorothioates

In this study, we introduce phosphorus, a pnictogen, as an exchange center for dynamic covalent chemistry. Cascade exchange of neutral phosphorotri- and -tetrathioates with thiolates is demonstrated in organic solvents, aqueous micellar systems, and in living cells. Exchange rates increase with the pH value, electrophilicity of the exchange center, and nucleophilicity of the exchangers. Molecular walking of the dynamic phosphorus center along Hammett gradients is simulated by the sequential addition of thiolate exchangers. Compared to phosphorotrithioates, tetrathioates are better electrophiles with higher exchange rates. Dynamic phosphorotri- and -tetrathioates are non-toxic to HeLa Kyoto cells and participate in the dynamic networks that account for thiol-mediated uptake into living cells.

Surfactant stabilized gold nanomaterials for environmental sensing applications - A review

Surfactant stabilized Gold (Au) nanomaterials (NMs) have been documented extensively in recent years for numerous sensing applications in the academic literature. Despite the crucial role these surfactants play in the sensing applications, the comprehensive reviews that highlights the fundamentals associated with these assemblies and impact of these surfactants on the properties and sensing mechanisms are still quite scare. This review is an attempt in organizing the vast literature associated with this domain by providing critical insights into the fundamentals, preparation methodologies and sensing mechanisms of these surfactant stabilized Au NMs. For the simplification, the surfactants are divided into the typical and advanced surfactants and the Au NMs are classified into Au nanoparticles (NPs) and Au nanoclusters (NCs) depending upon the complexity in structure and size of the NMs respectively. The preparative methodologies are also elaborated for enhancing the understanding of the readers regarding such assemblies. The case studies regarding surfactant stabilized Au NMs were further divided into colorimetric sensors, surface plasmonic resonance (SPR) based sensors, luminescence-based sensors, and electrochemical/electrical sensors depending upon the property utilized by the sensor for the sensing of an analyte. Future perspectives are also discussed in detail for the researchers looking for further progress in that particular research domain.

From Impure to Purified Silver Nanoparticles: Advances and Timeline in Separation Methods

AgNPs have exceptional characteristics that depend on their size and shape. Over the past years, there has been an exponential increase in applications of nanoparticles (NPs), especially the silver ones (AgNPs), in several areas, such as, for example, electronics; environmental, pharmaceutical, and toxicological applications; theragnostics; and medical treatments, among others. This growing use has led to a greater exposure of humans to AgNPs and a higher risk to human health and the environment. This risk becomes more aggravated when the AgNPs are used without purification or separation from the synthesis medium, in which the hazardous synthesis precursors remain unseparated from the NPs and constitute a severe risk for unnecessary environmental contamination. This review examines the situation of the available separation methods of AgNPs from crude suspensions or real samples. Different separation techniques are reviewed, and relevant data are discussed, with a focus on the sustainability and efficiency of AgNPs separation methods.

Non-Conventional Fluorescence and Cytotoxicity of Two Aliphatic Hyperbranched Polymer Dots Having Poly(amic acid) Structures: Implications for Labeling Nanodrug Carriers

In this study, we used one-pot A2 + B3 polymerizations to synthesize two aliphatic + alicyclic polymer dots (PDs) having non-conjugated hyperbranched structures, employing two types of dianhydrides as the A2 components, possessing bridged bicyclic alkene (PD-BT) and non-alkene (PD-ET) units, and Jeffamine T403 polyetheramine (T403) as the B3 components. We prepared PD-ET from commercially available ethylenediaminetetraacetic dianhydride (EDTAD, A2) and T403 (B3) and PD-BT from bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCDA, A2) and T403 (B3). These two types of PDs possessed non-conjugated hyperbranched poly(amic acid) structures with terminal amino functional groups. PD-BT and PD-ET exhibited non-conventional fluorescence with emissions at 435 and 438 nm, respectively, and quantum yields of 12.8 and 14.0%, respectively. The fluorescence intensity of PD-ET was influenced by the pH, but PD-BT was less affected because of its rigid aliphatic bridged bicyclic structure. In aqueous solutions, the sizes of the PD-BT and PD-ET nanoparticles were 3-5 nm, and their net charges can be adjusted by varying the pH. These PDs were non-cytotoxic toward human MCF-7 breast cancer cells and human keratinocyte HaCaT cells at concentrations of 50 μg mL-1 for PD-BT and 500 μg mL-1 for PD-ET. Confocal microscopic bioimaging revealed that the PDs were located within the cells after treatment for 6 h. These PDs were easy to prepare, highly water-soluble, and possessed a large number of peripheral functional groups for further modification. Combined with their non-conventional fluorescence, they appear to have potential uses in bioimaging and as drug-labeling carriers.

Separating dissolved silver from nanoparticulate silver is the key: Improved cloud-point-extraction hyphenated to single particle ICP-MS for comprehensive analysis of silver-based nanoparticles in real environmental samples down to single-digit nm particle sizes

Investigating silver-based nanoparticles (Ag-b-NPs) in environmental samples is challenging with current analytical techniques, owing to their low concentrations (ng L^-1) in the presence of high quantities of dissolved Ag(I) species. sp-ICP-MS is a promising technique able to simultaneously determine the concentration and particle sizes of Ag-b-NPs even at concentrations of several ng L^-1. However, sp-ICP-MS suffers from the coexistence of dissolved analyte species causing high background signals. These background signals cover particle signals and therefore limit the size detection limit (SDL) in sp-ICP-MS. Ag-b-NPs in environmental samples exhibit diameters of < 20 nm, whereas the current sp-ICP-MS approaches barely reach an SDL as low as 20 nm. Using a surfactant-mediated sample pre-treatment (improved cloud point extraction, iCPE), we were able to separate Ag-b-NPs in aqueous samples from dissolved Ag(I) species and enrich the NPs in the extract. By hyphenating iCPE to sp-ICP-MS, we were able to reach SDL values as low as 4.5 nm, thus paving the way for the successful monitoring of Ag-b-NPs in the environment.

Natural TiO2-Nanoparticles in Soils: A Review on Current and Potential Extraction Methods

The monitoring of anthropogenic TiO2-nanoparticles in soils is challenged by the knowledge gap on their characteristics of the large natural TiO2-nanoparticle pool. Currently, no efficient method is available for characterizing natural TiO2-nanoparticles in soils without an extraction procedure. Considering the reported diversity of extraction methods, the following article reviews and discusses their potential for TiO2 from soils, focusing on the selectivity and the applicability to complex samples. It is imperative to develop a preparative step reducing analytical interferences and producing a stable colloidal dispersion. It is suggested that an oxidative treatment, followed by alkaline conditioning and the application of dispersive agents, achieve such task. This enables the further separation and characterization through size or surface-based separation (i.e., hydrodynamic fractionation methods, filtration or sequential centrifugation). Meanwhile, cloud point extraction, gel electrophoresis, and electrophoretic deposition have been studied on various nanoparticles but not on TiO2-nanoparticles. Furthermore, industrially applied methods in, for example, kaolin processing (flotation and flocculation) are interesting but require further improvements on terms of selectivity and applicability to soil samples. Overall, none of the current extraction methods is sufficient toward TiO2; however, further optimization or combination of orthogonal techniques could help reaching a fair selectivity toward TiO2.

Looking at Silver-Based Nanoparticles in Environmental Water Samples: Repetitive Cloud Point Extraction Bridges Gaps in Electron Microscopy for Naturally Occurring Nanoparticles

The growing use of silver-based nanoparticles (Ag-b-NPs) in everyday products goes hand in hand with their release into the environment, resulting in ng L^-1 traces in natural water bodies. In order to assess their fate, possible transformations and ecotoxicology-essential information to proper risk assessment-particle size, shape, and chemical composition have to be determined. Transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (TEM-EDX) is a powerful tool for determining these particle characteristics, but it requires high particle concentrations in order to produce statistically reliable results. In this study, we will present the extraction of Ag-b-NPs at environmentally relevant concentrations down to 5 ng L^-1 from artificial as well as environmental water samples via cloud point extraction on a repetitive basis. The combination with an on-grid centrifugation technique ensures an efficient concentration and deposition of the extracted particles onto the TEM grid for subsequent TEM-EDX measurements. Furthermore, electron microscopy investigations were supplemented by single particle inductively coupled plasma mass spectrometry (sp-ICP-MS) measurements. Ag-b-NPs were successfully visualized and characterized at environmentally relevant concentrations of 5 ng L^-1 with TEM-EDX and sp-ICP-MS measurements. Their size, shape, and chemical composition were not affected by the sample preparation.

What happens to silver-based nanoparticles if they meet seawater?

Silver based nanoparticles (Ag-b-NPs) in the environment are of current concern as they may pose risks to human and environmental health, even at low concentration levels. It is widely known that Ag-b-NPs, once released from products containing these particles for antimicrobial reasons, can pass through wastewater treatment plants to some extent. These particles are transported via running waterways and eventually reach the sea. However, the fate of environmentally relevant ng L^-1 traces of Ag-b-NPs in seawater has not yet been sufficiently studied. Analytical techniques capable of determining these ultratraces of Ag-b-NPs in seawater are scarce and struggle furthermore with the high chloride content in highly saline matrices, such as seawater. In this study, we extracted Ag-b-NPs from matrices with varying salinity via cloud point extraction (CPE) and determined concentration and size of Ag-b-NPs in extracts with single particle inductively coupled plasma mass spectrometry (sp-ICP-MS). Applying this extraction and measurement technique, we were able to investigate the fate of Ag-b-NPs with different coatings (citrate and the predominant coatings in nature, silver sulfide and silver chloride) in matrices with increasing salinity and real seawater. All types of Ag-b-NPs were dissolved in all matrices almost independently of the chemical composition of the nanoparticles (NPs), whereas dissolution rates increased with increasing salinity due to the formation of soluble Ag(I) species and - in the presence of chloride - AgCl_x^1-x (x > 1) complexes. After an incubation time of not more than 72 h, Ag-b-NPs were dissolved almost completely. During the dissolution process, NP shrinkage could be clearly observed by sp-ICP-MS. Supplementary electron microscopy measurements revealed that the sulfur content in silver sulfide nanoparticles (Ag₂S-NPs) increased during the dissolution process. Finally, we were able to investigate the dissolution process of real Ag-b-NPs in wastewater after increasing the salinity to seawater levels.

Copper Drinking Water Pipes as a Previously Undocumented Source of Silver-Based Nanoparticles

Wastewater streams are widely known to release silver-based nanoparticles (Ag-b-NPs) into the environment with a plethora of unknown consequences. Until recently, studies have commonly associated Ag-b-NP sources with products that contain these NPs for antimicrobial reasons, such as fabrics, cosmetics, and medical products. However, our study reveals that there is a thus far completely undocumented source of Ag-b-NPs: copper drinking water pipes. We applied cloud point extraction hyphenated to electrothermal atomic absorption spectrometry or single-particle inductively coupled plasma mass spectrometry to analyze the concentration and perform size-selective quantification of Ag-b-NPs in tap water passing through copper pipes. Up to 83 ng of total silver and 25 ng of Ag-b-NPs were present in tap water samples per liter, which resulted in an NP proportion of approximately 30% of total silver. In total, 96% of the measurable particle sizes ranged from 10 to 36 nm. Additionally, 53 μg of copper was released per liter tap water on average. The measurements included tap water from different sampling days and from four different buildings with varying ages, whereas Ag-b-NPs could be detected in the tap water of two buildings. Silver traces in the copper pipe material of 27.5 ± 4.4 μg g^-1 were found to be responsible for the release of nanoparticulate silver into the tap water.

Characterization of Nanoparticles: Advances

Over the past two decades, the unique properties of engineered nanoparticles (NPs) have placed them at the centre of revolutionary advancements in many sectors of science, technology and commerce. Multi-technique and multi-disciplinary analytical approaches are required to identify, quantify, and characterize the chemical composition, size and size distribution, surface properties and the number and concentration of NPs. In this chapter, an overview of the recent advances in the characterization of NPs will be presented.

A highly sensitive fluorescent sensor for Zn2+ based on diarylethene with an imidazole unit

A new sensitive sensor for Zn²⁺ based on diarylethene with an imidazole unit has been synthesized. Its photochromic and fluorescent behaviors have been systematically investigated by the stimulation of UV/vis lights and Zn²⁺ ion in THF solution. It displayed a dual-mode with a "turn on" fluorescence and color response to Zn²⁺. With the addition of Zn²⁺, the emission intensity enhanced 26-fold, accompanied by the fluorescent color changed from dark red to bright yellow. The 1:1 stoichiometry between the sensor and Zn²⁺ was verified by Job's plot and MS. The LOD for Zn²⁺ was determined to be 6.12 × 10^-9 mol L^-1. Furthermore, a logic circuit was designed by using the fluorescence at 578 nm as output and the combinational stimuli of UV/vis and Zn²⁺/EDTA as inputs.

Low risk posed by engineered and incidental nanoparticles in drinking water

Natural nanoparticles (NNPs) in rivers, lakes, oceans and ground water predate humans, but engineered nanoparticles (ENPs) are emerging as potential pollutants due to increasing regulatory and public perception concerns. This Review contrasts the sources, composition and potential occurrence of NNPs (for example, two-dimensional clays, multifunctional viruses and metal oxides) and ENPs in surface water, after centralized drinking water treatment, and in tap water. While analytical detection challenges exist, ENPs are currently orders of magnitude less common than NNPs in waters that flow into drinking water treatment plants. Because such plants are designed to remove small-sized NNPs, they are also very good at removing ENPs. Consequently, ENP concentrations in tap water are extremely low and pose low risk during ingestion. However, after leaving drinking water treatment plants, corrosion by-products released from distribution pipes or in-home premise plumbing can release incidental nanoparticles into tap water. The occurrence and toxicity of incidental nanoparticles, rather than ENPs, should therefore be the focus of future research.

Developing and interpreting aqueous functional assays for comparative property-activity relationships of different nanoparticles

It is difficult to relate intrinsic nanomaterial properties to their functional behavior in the environment. Unlike frameworks for dissolved organic chemicals, there are few frameworks comparing multiple and inter-related properties of engineered nanomaterials (ENMs) to their fate, exposure, and hazard in environmental systems. We developed and evaluated reproducibility and inter-correlation of 12 physical, chemical, and biological functional assays in water for eight different engineered nanomaterials (ENMs) and interpreted results using activity-profiling radar plots. The functional assays were highly reproducible when run in triplicate (average coefficient of variation [CV]=6.6%). Radar plots showed that each nanomaterial exhibited unique activity profiles. Reactivity assays showed dissolution or aggregation potential for some ENMs. Surprisingly, multi-walled carbon nanotubes (MWCNTs) exhibited movement in a magnetic field. We found high inter-correlations between cloud point extraction (CPE) and distribution to sewage sludge (R²=0.99), dissolution at pH8 and pH4.9 (R²=0.98), and dissolution at pH8 and zebrafish mortality at 24hpf (R²=0.94). Additionally, most ENMs tend to distribute out of water and into other phases (i.e., soil surfaces, surfactant micelles, and sewage sludge). The activity-profiling radar plots provide a framework and estimations of likely ENM disposition in the environment.

Micellization and Partition Equilibria in Mixed Nonionic/Ionic Micellar Systems: Predictions with Molecular Models

In practical applications, surfactant solutions are mostly used in mixtures of nonionic and ionic surfactants because they have improved characteristics compared to those of single surfactant solutions. By adjusting the composition of the micelles and the pH value, the solubilization of solutes can be enhanced. Nevertheless, the partitioning of solutes between nonionic/ionic mixed micelles and the aqueous phase is studied to a much lesser extent than for single surfactant solutions. Theoretical methods to predict partition equilibria in mixed micelles are of interest for screening studies. For those, the composition of the mixed micelle has to be known. Here we investigate mixtures of TX-114 (Triton X-114), Brij35 (C12E23), SDS (sodium dodecyl sulfate), and CTAB (cetyltrimethylammonium bromide). First, to investigate the surfactant compositions in the micelles, molecular dynamics (MD) self-assembly simulations were applied. Thereafter, the predictive COSMO-RS model, which applies the pseudophase approach, and its extension to anisotropic systems termed COSMOmic were compared for the prediction of partition equilibria in mixed micelles, where various molar ratios of the surfactants were considered. It could be demonstrated that both methods are applicable and lead to reasonable predictions for neutral molecules. However, taking into account the three-dimensional structure of the micelle is beneficial because the calculations with COSMOmic are in better agreement with experimental results. Because the partitioning behavior of ionizable molecules in mixed micelles is of particular interest, the partitioning of ionized isovanillin in mixed Brij35/CTAB micelles at different micelle compositions was calculated with COSMOmic. Using a thermodynamic cycle, the position-dependent pK_a of isovanillin within the micelle is calculated on the basis of COSMOmic free energy profiles. As a result, the protolytic equilibrium of isovanillin within the micelles can be taken into account, which is crucial for the reliable prediction of partition coefficients.

Metal and Metalloid Size-Fractionation Strategies in Spatial High-Resolution Sediment Pore Water Profiles

Sediment water interfaces (SWIs) are often characterized by steep biogeochemical gradients determining the fate of inorganic and organic substances. Important transport processes at the SWI are sedimentation and resuspension of particulate matter and fluxes of dissolved materials. A microprofiling and micro sampling system (missy), enabling high resolution measurements of sediment parameters in parallel to a direct sampling of sediment pore waters (SPWs), was combined with two fractionation approaches (ultrafiltration (UF) and cloud point extraction (CPE)) to differentiate between colloidal and dissolved fractions at a millimeter scale. An inductively coupled plasma-quadrupole mass spectrometry method established for volumes of 300 μL enabled the combination of the high resolution fractionation with multi-element analyzes. UF and CPE comparably indicated that manganese is predominantly present in dissolved fractions of SPW profiles. Differences found for cobalt and iron showed that the results obtained by size-dependent UF and micelle-mediated CPE do not necessarily coincide, probably due to different fractionation mechanisms. Both methods were identified as suitable for investigating fraction-related element concentrations in SPW along sediment depth profiles at a millimeter scale. The two approaches are discussed with regard to their advantages, limitations, potential sources of errors, further improvements, and potential future applications.