Size Selection and Concentration of Silver Nanoparticles by Tangential Flow Ultrafiltration for SERS-Based Biosensors

Hyper-crosslinked Isoporous Block Copolymer Membranes with Robust Solvent Resistance and Customized Pore Sizes for Precise Separation

Isoporous block copolymer membranes are viewed as the next-generation separation membranes for their unique structures and urgent application in precise separation. However, an obvious weakness for such membranes is their poor solvent-resistance which limits their applications to aqueous solution, and isoporous membranes with superior solvent-resistance and tunable pore size have been rarely prepared before. Herein, self-supporting isoporous membranes with excellent solvent resistance are prepared by the facile yet robust hyper-crosslinking approach which is able to create a rigid network in whole membranes. The hyper-crosslinking is found to be a novel and non-destructive approach that does not change pore size and isoporous structure during the reaction, and the resulting hyper-crosslinked isoporous membranes display superior structural and separation stability to a broad range of solvents with varied polarities for months to years. More importantly, hyper-crosslinking has proved to be a universal strategy that is applicable to isoporous membranes with varied pore size and pore chemistry, offering an important opportunity to prepare solvent-resistant isoporous membranes with customizable pore size and pore functionality that are important to realize their accurate separations in organic solvents. This concept is demonstrated finally by precise and on-demand separation of nanoparticles with the prepared membranes.

Construction of the Au Nanoparticle/Graphene Oxide/Au Nanotube (AuNP/GO/AuNT) Sandwich Membrane for Surface-Enhanced Raman Scattering Sensing

Au nanotube-based composite membrane served as surface-enhanced Raman scattering (SERS) substrate with an ultralarge aspect ratio possesses an excellent flexibility and widely tunable surface plasmon resonance, and by introducing graphene oxide (GO) as a spacer layer, the SERS enhancement of the composite membrane is obviously better than those from the individual blocks of the Au nanotubes (AuNTS) membrane and the Au nanoparticle/graphene oxide (AuNP/GO) membrane. Such a "sandwich" (AuNP/GO/AuNT) structured membrane has a high SERS sensitivity and a wide tunability by controlling the size of Au nanoparticles and the thickness of graphene oxide, and the detection limits of the AuNP/GO/AuNT substrate for R6G and NBA are as low as 10-12 and 10-7 M, respectively; the large enhancement is attributed to the adsorption and chemical mechanism of graphene oxide and the physical mechanism of the Au nanoparticles and nanotubes (the electromagnetic field coupling between them).

Label-Free SERS of Urine Components: A Powerful Tool for Discriminating Renal Cell Carcinoma through Multivariate Analysis and Machine Learning Techniques

The advent of Surface-Enhanced Raman Scattering (SERS) has enabled the exploration and detection of small molecules, particularly in biological fluids such as serum, blood plasma, urine, saliva, and tears. SERS has been proposed as a simple diagnostic technique for various diseases, including cancer. Renal cell carcinoma (RCC) ranks as the sixth most commonly diagnosed cancer in men and is often asymptomatic, with detection occurring incidentally. The onset of symptoms typically aligns with advanced disease, aggressive histology, and unfavorable prognosis, and therefore new methods for an early diagnosis are needed. In this study, we investigated the utility of label-free SERS in urine, coupled with two multivariate analysis approaches: Principal Component Analysis combined with Linear Discriminant Analysis (PCA-LDA) and Support Vector Machine (SVM), to discriminate between 50 RCC patients and 44 healthy donors. Employing LDA-PCA, we achieved a discrimination accuracy of 100% using 13 principal components, and an 88% accuracy in discriminating between different RCC stages. The SVM approach yielded a training accuracy of 100%, a validation accuracy of 99% for discriminating between RCC and controls, and an 80% accuracy for discriminating between stages. The comparative analysis of raw and normalized SERS spectral data shows that while raw data disclose relative concentration variations in urine metabolites between the two classes, the normalization of spectral data significantly improves the accuracy of discrimination. Moreover, the selection of principal components with markedly distinct scores between the two classes serves to alleviate overfitting risks and reduces the number of components employed for discrimination. We obtained the accuracy of the discrimination between the RCC patients cases and healthy donors of 90% for three PCs and a linear discrimination function, and a 88% accuracy of discrimination between stages using six PCs, mitigating practically the risk of overfitting and increasing the robustness of our analysis. Our findings underscore the potential of label-free SERS of urine in conjunction with chemometrics for non-invasive and early RCC detection.

Development of surface-enhanced Raman scattering-sensing Method by combining novel Ag@Au core/shell nanoparticle-based SERS probe with hybridization chain reaction for high-sensitive detection of hepatitis C virus nucleic acid

The ultrasensitive detection of hepatitis C virus (HCV) nucleic acid is crucial for the early diagnosis of hepatitis C. In this study, by combining Ag@Au core/shell nanoparticle (Ag@AuNP)-based surface-enhanced Raman scattering (SERS) tag with hybridization chain reaction (HCR), a novel SERS-sensing method was developed for the ultrasensitive detection of HCV nucleic acid. This SERS-sensing system comprised two different SERS tags, which were constructed by modifying Ag@AuNP with a Raman reporter molecule of 4-ethynylbezaldehyde, two different hairpin-structured HCR sequences (H1 or H2), and a detection plate prepared by immobilizing a capture DNA sequence onto the Ag@AuNP layer surface of the detection wells. When the target nucleic acid was present, the two SERS tags were captured on the surface of the Ag@AuNP-coated detection well to generate many "hot spots" through HCR, forming a strong SERS signal and realizing the ultrasensitive detection of the target HCV nucleic acid. The limit of detection of the SERS-sensing method for HCV nucleic acid was 0.47 fM, and the linear range was from 1 to 105 fM.

Experimental and Theoretical Screening of Core Gold Nanoparticles and Their Binding Mechanism to an Anticancer Drug, 2-Thiouracil

This study demonstrated the capability of two readily available optical spectroscopy tools, namely UV-Vis absorption spectrophotometry and Raman/surface-enhanced Raman spectroscopy, to select in a rapid and noninvasive manner the most homogenous gold nanoparticle (AuNP) models and to identify their chemical binding mechanism to 2-thiouracil (2-TU). 2-TU is an anticancer drug of great promise in the antiproliferative and photothermal therapies of cancer. The citrate-capped AuNPs emerged as the most stable as well as time- and cost-effective AuNP model out of the three widely used colloidal nanocores (citrate-, borohydride-citrate-, and sodium dodecyl sulfate (SDS)-capped AuNPs) that were examined. 2-TU chemically attached to the relatively monodispersed AuNPs via a chemisorption mechanism. The 2-TU-AuNPs complex formed through the covalent bonding of the S atom of 2-TU to the nanosurface in a vertical orientation. The spectroscopic results were then confirmed with the help of density functional theory (DFT) calculations and other physicochemical characterization tools for nanomaterials such as transmission electron microscopy (TEM), dynamic light scattering (DLS), and zeta potential. Overall, the purified 2-TU-AuNPs were found to be spherical, had an average diameter of 25 ± 2 nm, a narrow size distribution (1-30 nm), a sharp localized surface plasmon resonance (LSPR) peak at 525 nm, and a negative surface charge (-14 mV).

High-Accuracy Renal Cell Carcinoma Discrimination through Label-Free SERS of Blood Serum and Multivariate Analysis

Renal cell carcinoma (RCC) represents the sixth most frequently diagnosed cancer in men and is asymptomatic, being detected mostly incidentally. The apparition of symptoms correlates with advanced disease, aggressive histology, and poor outcomes. The development of the Surface-Enhanced Raman Scattering (SERS) technique opened the way for investigating and detecting small molecules, especially in biological liquids such as serum or blood plasma, urine, saliva, and tears, and was proposed as a simple technique for the diagnosis of various diseases, including cancer. In this study, we investigated the use of serum label-free SERS combined with two multivariate analysis tests: Principal Component Analysis combined with Linear Discriminate Analysis (PCA-LDA) and Supported Vector Machine (SVM) for the discrimination of 50 RCC cancer patients from 45 apparently healthy donors. In the case of LDA-PCA, we obtained a discrimination accuracy of 100% using 12 principal components and a quadratic discrimination function. The accuracy of discrimination between RCC stages was 88%. In the case of the SVM approach, we obtained a training accuracy of 100%, a validation accuracy of 92% for the discrimination between RCC and controls, and an accuracy of 81% for the discrimination between stages. We also performed standard statistical tests aimed at improving the assignment of the SERS vibration bands, which, according to our data, are mainly due to purinic metabolites (uric acid and hypoxanthine). Moreover, our results using these assignments and Student's t-test suggest that the main differences in the SERS spectra of RCC patients are due to an increase in the uric acid concentration (a conclusion in agreement with recent literature), while the hypoxanthine concentration is not statistically different between the two groups. Our results demonstrate that label-free SERS combined with chemometrics holds great promise for non-invasive and early detection of RCC. However, more studies are needed to validate this approach, especially when combined with other urological diseases.

Biodistribution and toxicity of antimicrobial ionic silver (Ag+) and silver nanoparticle (AgNP+) species after oral exposure, in Sprague-Dawley rats

Although antimicrobial nanosilver finds numerous applications in the health and food industries, the in vivo toxicity of positively charged silver nanoparticles (AgNPs⁺) and relevant controls are largely unexplored. This study investigates the relationship between the biodistribution and toxicity of the well-known cetyltrimethylammonium bromide (CTAB)-capped AgNPs⁺ in 6-weeks old female Sprague-Dawley rats, at sublethal doses. Amounts comparative to those leaked from food products or considered for animal feed were administered through daily water intake, for an 18-day period: AgNPs⁺ (40 μg mL^-1), Ag⁺ (40 μg mL^-1), antimicrobial CTAB⁺ (24 μg mL^-1) and tap water. All exposures except for the water control had adverse effects on the health and systemic functions of rats (e.g., lethargy, hepatomegaly, splenomegaly, impediment of bone development, and/or heightened immune response). Although the total Ag accumulation in tissues (1.4-1.6 μg of Ag/g of liver, spleen, jejunum, and brain) was comparable for the two Ag species, AgNPs⁺ were generally more toxic than Ag⁺, particularly in spleen (0.8 μg Ag/g). Significantly reduced euthanasia time, alopecia, inflammatory responses in spleen, fragile veins, and enhanced lymphocytosis were observed only for AgNPs⁺. Overall, this study raises health concerns about the ingestion of capped-AgNPs⁺ or Ag⁺ by first-hand consumers and industry workers.

Proving Nanoscale Chiral Interactions of Cyclodextrins and Propranolol Enantiomers by Means of SERS Measurements Performed on a Solid Plasmonic Substrate

Chiral separation is an important issue for the pharmaceutical industry. Over the years, several separation methods have been developed, mainly based on chromatography. Their working principle is based on the formation of transient diastereoisomers, but the very subtle nanoscale interactions responsible for separation are not always understood. Recently, Raman and surface-enhanced Raman (SERS) spectroscopy have provided promising results in this field. Here we present Raman/SERS experimental data that provide useful information concerning the nanoscale interactions between propranolol enantiomers and α, β, and γ cyclodextrins. Raman spectroscopy was used to prove the formation of host–guest intermolecular complexes having different geometries of interaction. The occurrence of new vibrational bands and a change in the intensities of others are direct proofs of complexes’ formation. These observations were confirmed by DFT calculations. By performing SERS measurements on a new type of plasmonic substrate, we were able to prove the intermolecular interactions responsible for PRNL discrimination. It turned out that the interaction strength between the substrate and the intermolecular complexes is of paramount importance for SERS-based chiral discrimination. This approach could represent a very good starting point for the evaluation of molecular interactions manifesting between other pharmaceutical compounds and different classes of chiral selectors.

Solid Plasmonic Substrates for Breast Cancer Detection by Means of SERS Analysis of Blood Plasma

Surface enhanced Raman spectroscopy (SERS) represents a promising technique in providing specific molecular information that could have a major impact in biomedical applications, such as early cancer detection. SERS requires the presence of a suitable plasmonic substrate that can generate enhanced and reproducible diagnostic relevant spectra. In this paper, we propose a new approach for the synthesis of such a substrate, by using concentrated silver nanoparticles purified using the Tangential Flow Filtration method. The capacity of our substrates to generate reproducible and enhanced Raman signals, in a manner that can allow cancer detection by means of Multivariate Analysis (MVA) of Surface Enhanced Raman (SER) spectra, has been tested on blood plasma samples collected from 35 healthy donors and 29 breast cancer patients. All the spectra were analyzed by a combined Principal Component-Linear Discriminant Analysis. Our results facilitated the discrimination between healthy donors and breast cancer patients with 90% sensitivity, 89% specificity and 89% accuracy. This is a direct consequence of substrates’ ability to generate diagnostic relevant spectral information by performing SERS measurements on pristine blood plasma samples. Our results suggest that this type of solid substrate could be employed for the detection of other types of cancer or other diseases by means of MVA-SERS procedure.

High-Level Extraction of Recyclable Nanocatalysts by Using Polyphosphazene Microparticles

Improper disposal of metal nanoparticles has caused serious environmental and pathological problems because of their active nanotoxicity. Therefore, there is an urgent need to develop a strategy for efficiently removing redundant metal nanoparticles from water, while also permitting restoration of their catalytic activities to those of pristine particles for reapplication. Herein, we present intrinsically nitrogen-rich cross-linked polyphosphazene microparticles to capture silver nanoparticles (AgNPs) from aqueous media by a simple one-step method. The described microparticles exhibit an outstanding adsorption capacity for AgNPs of approximately 59.35 mg/g, exceeding those of other adsorbents. The adsorption kinetics of AgNPs on these microparticles obeyed a pseudo-second-order kinetic model. More importantly, the recovered AgNPs maintained good catalytic activity in the reduction of methylene blue by sodium borohydride. Based on their simple preparation, high adsorption efficiency, and nondestructive effect on the catalytic activity of the recovered AgNPs, the described polyphosphazene microparticles display promising potential for the removal and recovery of AgNPs from water.

Activated charcoal as a capture material for silver nanoparticles in environmental water samples

Silver nanoparticles (AgNPs), due to their antibacterial activity, have been incorporated into numerous consumer products. Their environmental impact however, is currently unclear. Uncertainties surround the concentration, fate, and effects of AgNPs in aquatic environments. This study examined the suitability of activated charcoal as a capture material for AgNPs from water. Samples of 100 ppb AgNPs were initially generated and exposed to activated charcoal for 24 h to examine the ability of charcoal to capture AgNPs. The decrease in Ag concentration was measured using ICP-MS. Following initial investigations, the surface area of the charcoal was increased firstly with a pestle and mortar and secondly by milling the charcoal using a ball mill. The increased surface area of the milled charcoal increased the capture of the AgNPs from 11.9% to 63.6% for the 100 ppb samples. Further investigations were carried out examining the effect on the capture of AgNP concentration (with concentration ranging from 10 to 100 ppb), particle coating and the effect of exposure time to the activated charcoal. The capture of AgNP increased with decreasing concentration. A hydrochloric acid (HCl) leaching procedure was also developed which successfully removed the captured silver allowing the fraction captured by the charcoal to be quantified with an average of 94.8% recovery. The results show that milled activated charcoal, can successfully capture AgNPs from water samples, and that therefore, activated charcoal may prove to be a cost effective material for the remediation of waters impacted by AgNP or other nano-wastes.

A Droplet-Reactor System Capable of Automation for the Continuous and Scalable Production of Noble-Metal Nanocrystals

Noble-metal nanocrystals with well-controlled shapes or morphologies are of great interest for a variety of applications. To utilize these nanomaterials in consumer products, one has to produce the colloidal nanocrystals in large quantities while maintaining good control over their physical parameters and properties. Droplet reactors have shown great potential for the continuous and scalable production of colloidal nanocrystals with controlled shapes. However, the efficiencies of most previously reported systems are still limited because of the complex post-treatment procedures. For example, the mixture of silicone oil and an aqueous suspension of solid products has to be separated by leveraging their miscibility and difference in density, while the solid products often need to be purified and concentrated by centrifugation. Herein, we report the design and construction of a droplet-reactor system that include new features such as a homemade unit for the automatic separation of silicone oil from the aqueous phase as well as a cross-flow filtration unit for the effective purification and concentration of the nanocrystals. Using various types of Pd nanocrystals as examples, we have demonstrated the feasibility of using this system to automatically produce and collect samples with uniform sizes and well-controlled shapes.

Study of the presence of micro- and nanoparticles in drinks and foods by multiple analytical techniques

A variety of food and drink samples (n = 21) were analyzed to evaluate the presence of (nano-) particles in their composition. After assessment of the sample pre-treatment step, a fast screening analysis was performed for drinks by Dynamic Light Scattering showing particles from 10 to 300 nm that could correspond to organic or metallic NPs. Metallic NPs were identified in foods by Single-Particle mode Inductively Coupled Plasma Mass Spectrometry and Asymmetrical Flow Field-Flow Fractionation coupled to Multiangle Laser Light Scattering and Inductively-Coupled Plasma Mass Spectrometry. The determination of Ti, Si and Ag concentration in the initial food suspensions, after filtration and centrifugal ultrafiltration enabled to estimate the ionic and nanoparticles content. Si-containing particles can be present in cappuccino powder as large aggregates and Si- and Al-containing particles in hot chocolate. Ti-containing NPs (80-200 nm) were found in chewing gum and Ag NPs in silver pearls (50-150 nm) used for decoration pastry.

Nanocolloids in Natural Water: Isolation, Characterization, and Toxicity

Nanocolloids are widespread in natural water systems, but their characterization and ecological risks are largely unknown. Herein, tangential flow ultrafiltration (TFU) was used to separate and concentrate nanocolloids from surface waters. Unexpectedly, nanocolloids were present in high concentrations ranging from 3.7 to 7.2 mg/L in the surface waters of the Harihe River in Tianjin City, China. Most of the nanocolloids were 10-40 nm in size, contained various trace metals and polycyclic aromatic hydrocarbons, and exhibited fluorescence properties. Envelopment effects and aggregation of Chlorella vulgaris in the presence of nanocolloids were observed. Nanocolloids entered cells and nanocolloid-exposed cells exhibited stronger plasmolysis, chloroplast damage and more starch grains than the control cells. Moreover, nanocolloids inhibited the cell growth, promoted reactive oxygen species (ROS), reduce the chlorophyll a content and increased the cell permeability. The genotoxicity of nanocolloids was also observed. The metabolomics analysis revealed a significant ( p < 0.05) downregulation of amino acids and upregulation of fatty acids contributing to ROS increase, chlorophyll a decrease and plasmolysis. The present work reveals that nanocolloids, which are different from specific, engineered nanoparticles (e.g., Ag nanoparticles), are present at high concentrations, exhibit an obvious toxicity in environments, and deserve more attention in the future.

A Raman-Based Imaging Method for Characterizing the Molecular Adsorption and Spatial Distribution of Silver Nanoparticles on Hydrated Mineral Surfaces

Although minerals are known to affect the environmental fate and transformation of heavy-metal ions, little is known about their interaction with the heavily exploited silver nanoparticles (AgNPs). Proposed here is a combination of hitherto under-utilized micro-Raman-based mapping and chemometric methods for imaging the distribution of AgNPs on various mineral surfaces and their molecular interaction mechanisms. The feasibility of the Raman-based imaging method was tested on two macro- and microsized mineral models, muscovite [KAl₂(AlSi₃O₁₀)(OH)₂] and corundum (α-Al₂O₃), under key environmental conditions (ionic strength and pH). Both AgNPs^- and AgNPs⁺ were found to covalently attach to corundum (pH_pzc = 9.1) through the formation of Ag-O-Al- bonds and thereby to potentially experience reduced environmental mobility. Because label-free Raman imaging showed no molecular interactions between AgNPs^- and muscovite (pH_pzc = 7.5), a label-enhanced Raman imaging approach was developed for mapping the scarce spatial distribution of AgNPs^- on such mineral surfaces. Raman maps comprising of n = 625-961 spectra for each sample/control were rapidly analyzed in Vespucci, a free open-source software, and the results were confirmed via ICP-OES, AFM, and SEM-EDX. The proposed Raman-based imaging requires minimum to no sample preparation; is sensitive, noninvasive, cost-effective; and might be extended to other environmentally relevant systems.

Polyvinylidene Fluoride Micropore Membranes as Solid-Phase Extraction Disk for Preconcentration of Nanoparticulate Silver in Environmental Waters

Efficient separation and preconcentration of trace nanoparticulate silver (NAg) from large-volume environmental waters is a prerequisite for reliable analysis and therefore understanding the environmental processes of silver nanoparticles (AgNPs). Herein, we report the novel use of polyvinylidene fluoride (PVDF) filter membrane for disk-based solid phase extraction (SPE) of NAg in 1 L of water samples with the disk-based SPE system, which consists of a syringe pump and a syringe filter holder to embed the filter membrane. While the PVDF membrane can selectively adsorb NAg in the presence of Ag⁺, aqueous solution of 2% (m/v) FL-70 is found to efficiently elute NAg. Analysis of NAg is performed following optimization of filter membrane and elution conditions with an enrichment factor of 1000. Additionally, transmission electron microscopy (TEM), UV-vis spectroscopy, and size-exclusion chromatography coupled with ICP-MS (SEC-ICP-MS) analysis showed that the extraction gives rise to no change in NAg size or shape, making this method attractive for practical applications. Furthermore, feasibility of the protocol is verified by applying it to extract NAg in four real waters with recoveries of 62.2-80.2% at 0.056-0.58 μg/L spiked levels. This work will facilitate robust studies of trace NAg transformation and their hazard assessments in the environment.

Analytical-Based Methodologies for Examining the In Vitro Absorption, Distribution, Metabolism, and Elimination (ADME) of Silver Nanoparticles

The clinical applications of silver nanoparticles (AgNPs) remain limited due to the lack of well-established methodologies for studying their nanokinetics. Hereby, the primary goal is to adapt a suite of analytical-based methodologies for examining the in vitro absorption, distribution, metabolism, and elimination of AgNPs. Vero 76 and HEK 293 cells are exposed to ≈10-nm spherical AgNPs⁺ and AgNPs^- at relevant concentrations (0-300 µg mL^-1 ) and times (4-48 h). Absorption: Inductively coupled plasma optical emission spectroscopy (ICP-OES) demonstrates that the two AgNP formulations are not bioequivalent. For example, different bioavailabilities (C_maximum < 20.7 ± 4% and 6.82 ± 0.4%), absorption times (T_maximum > 48 and ≈24 h), and absorption rate laws (first- and zeroth-order at 300 µg mL^-1 ) are determined in Vero 76 for AgNPs⁺ and AgNPs^- , respectively. Distribution: Raman and CytoViva hyperspectral imaging show different cellular localizations for AgNPs⁺ and AgNPs^- . Metabolism: Cloud point extraction (CPE)-tangential flow filtration (TFF) reveal that ≤ 11% ± 4% of the administered, sublethal AgNPs release Ag⁺ and contribute to the observed cytotoxicity. Elimination: ICP-OES-CPE suggests that AgNPs are cleared via exocytosis.

Nanomaterials in Food Products: A New Analytical Challenge

This chapter focuses on the problem of detecting, characterizing, and determining the concentration of nanomaterials in foods and other biological matrices. After providing an overview of the unique challenges associated with nanoparticle metrology in complex media, sample pretreatment methods (including extraction, digestion, and inline chromatographic separation), imaging analysis, and nanomaterial quantification methods are presented in detail. The chapter also addresses numerous methods under development, including atmospheric scanning electron microscopy, single-particle inductively coupled plasma mass spectrometry, immunological detection methods, and optical techniques such surface plasmon resonance. The chapter concludes with an overview of the research needs in this area.

In situ SERS study of surface plasmon resonance enhanced photocatalytic reactions using bifunctional Au@CdS core-shell nanocomposites

Surface plasmon resonance (SPR) has been utilized in many fields, such as surface-enhanced Raman spectroscopy (SERS) and solar energy conversion. Here we developed an Au@CdS core-shell nanostructure, a bifunctional nanoparticle, used as an efficient catalyst for SPR enhanced photocatalytic degradation, and as a substrate for in situ SERS detection of methylene blue (MB) and p-nitrophenol (pNTP). With integration of an Au nanoparticle into a CdS shell, the degradation process was significantly accelerated under 500 nm long-pass (λ > 500 nm) visible light irradiation, which was caused by the injection of hot electrons. Moreover, a highly uniform, monolayer film of Au@CdS nanoparticles (NPs) has been prepared and used as both a SERS substrate and catalyst. The decomposition of MB molecules and nitrogen coupling reaction of pNTP were observed during the 638 nm laser illumination. We demonstrate that a plasmonic core-semiconductor shell nanocomposite can be a promising material for photocatalysis and in situ SERS study.

Elemental Mass Size Distribution for Characterization, Quantification and Identification of Trace Nanoparticles in Serum and Environmental Waters

Accurate characterization, quantification, and identification of nanoparticles (NPs) are essential to fully understand the environmental processes and effects of NPs. Herein, the elemental mass size distribution (EMSD), which measures particle size, mass, and composition, is proposed for the direct size characterization, mass quantification, and composition identification of trace NPs in complex matrixes. A one-step method for the rapid measurement of EMSDs in 8 min was developed through the online coupling of size-exclusion chromatography (SEC) with inductively coupled plasma mass spectrometry (ICP-MS). The use of a mobile phase with a relatively high ionic strength (a mixture of 2% FL-70 and 2 mM Na₂S₂O₃) ensured the complete elution of different-sized NPs from the column and, therefore, a size-independent response. After application of a correction for instrumental broadening by a method developed in this study, the size distribution of NPs by EMSD determination agreed closely with that obtained from transmission electron microscopy (TEM) analysis. Compared with TEM, EMSD allows a more rapid determination with a higher mass sensitivity (1 pg for gold and silver NPs) and comparable size discrimination (0.27 nm). The proposed EMSD-based method was capable of identifying trace Ag₂S NPs and core-shell nanocomposite Au@Ag, as well as quantitatively tracking the dissolution and size transformation of silver nanoparticles in serum and environmental waters.

Removal of silver nanoparticles by mussel-inspired Fe3O4@ polydopamine core-shell microspheres and its use as efficient catalyst for methylene blue reduction

The removal of silver nanoparticles (AgNPs) from water is highly needed because of their increasing use and potential risk to the environment due to their toxic effects. Catalysis over AgNPs has received significant attention because of their highly catalytic performance. However, their use in practical applications is limited due to high cost and limited resources. Here, we present for the first time that the mussel-inspired Fe3O4@polydopamine (Fe3O4@PDA) nanocomposite can be used for efficient removal and recovery of AgNPs. Adsorption of AgNPs over Fe3O4@PDA was confirmed by TEM, FT-IR, XRD, TGA and magnetic property. The adsorption efficiency of AgNPs by Fe3O4@PDA was investigated as a function of pH, contact time, ionic strength and concentration of AgNPs. The kinetic data were well fitted to a pseudo-second order kinetic model. The isotherm data were well described by Langmuir model with a maximum adsorption capacity of 169.5 mg/g, which was higher than those by other adsorbents. Notably, the obtained AgNPs-Fe3O4@PDA exhibited highly catalytic activity for methylene blue reduction by NaBH4 with a rate constant of 1.44 × 10-3/s, which was much higher than those by other AgNPs catalysts. The AgNPs-Fe3O4@PDA promised good recyclability for at least 8 cycles and acid resistant with good stability.

Evolution of a high local strain in rolling up MoS2 sheets decorated with Ag and Au nanoparticles for surface-enhanced Raman scattering

We report that a high local strain was obtained for multilayer MoS₂ nanoscrolls decorated with noble nanoparticles (Ag and Au NPs) using a rolling process beyond breaking or slipping of MoS₂. The local strain was estimated through the bending strain in the nanoscrolls and the extent of coverage of Ag and Au NPs decorated on MoS₂, exhibiting magnified surface-enhanced Raman scattering. TEM images showed that the MoS₂-Ag and MoS₂-Au nanoscrolls have a tube-like morphology decorated with NPs on the inner and outer sides of the MoS₂ nanoscrolls. In the Raman spectra, we confirmed the red shift and broadness of the FWHM for nanoscrolls in the eigenvectors of the [Formula: see text] and [Formula: see text] modes. From the Grüneisen parameter γ and the shear deformation potential β, we obtained peak shifts of ∼4.9 cm^-1/% at [Formula: see text] and ∼1.1 cm^-1/% strain at [Formula: see text] for free-standing MoS₂. According to the obtained relationship of the Raman shift and the induced uniaxial tensile strain, the [Formula: see text] and [Formula: see text] peaks shifted upwards to around -12.8 cm^-1 and -2.9 cm^-1, respectively, and can be converted to an induced uniaxial tensile strain of about 2.6% for MoS₂-Ag nanoscrolls.

Silver nanoparticles in the environment: Sources, detection and ecotoxicology

The environmental impact of silver nanoparticles (AgNP) has become a topic of interest recently, this is due to the fact that AgNPs have been included in numerous consumer products including textiles, medical products, domestic appliances, food containers, cosmetics, paints and nano-functionalised plastics. The production, use and disposal of these AgNP containing products are potential routes for environmental exposure. These concerns have led to a number of studies investigating the release of particles from nano-functionalised products, the detection of the particles in the aquatic environment and the potential environmental toxicology of these AgNPs to aquatic organisms. The overall aim of this review is to examine methods for the capture and detection of AgNPs, potential toxicity and transmission routes in the aquatic environment.

Acetylcholinesterase (AChE)-mediated immobilization of silver nanoparticles for the detection of organophosphorus pesticides

We report an enzyme-mediated biosensor with the immobilization of silver nanoparticles (AgNPs) for the detection of organophosphorus (OP) pesticides.

Potential Health Impact of Environmentally Released Micro- and Nanoplastics in the Human Food Production Chain: Experiences from Nanotoxicology

High concentrations of plastic debris have been observed in the oceans. Much of the recent concern has focused on microplastics in the marine environment. Recent studies of the size distribution of the plastic debris suggested that continued fragmenting of microplastics into nanosized particles may occur. In this review we assess the current literature on the occurrence of environmentally released micro- and nanoplastics in the human food production chain and their potential health impact. The currently used analytical techniques introduce a great bias in the knowledge, since they are only able to detect plastic particles well above the nanorange. We discuss the potential use of the very sensitive analytical techniques that have been developed for the detection and quantification of engineered nanoparticles. We recognize three possible toxic effects of plastic particles: first due to the plastic particles themselves, second to the release of persistent organic pollutant adsorbed to the plastics, and third to the leaching of additives of the plastics. The limited data on microplastics in foods do not predict adverse effect of these pollutants or additives. Potential toxic effects of microplastic particles will be confined to the gut. The potential human toxicity of nanoplastics is poorly studied. Based on our experiences in nanotoxicology we prioritized future research questions.

Rapid Aluminum Nanoparticle Production by Milling in NH₃ and CH₃NH₂ Atmospheres: An Experimental and Theoretical Study

Ball milling of aluminum in gaseous atmospheres of ammonia and monomethylamine (MMA) was found to produce particles in the 100 nm size range with high efficiency. A combination of mass spectrometry, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis with mass spectrometric product analysis (TGA-MS), scanning electron microscopy (SEM), infrared spectroscopy, and dynamic light scattering (DLS) was used to study the particles and the chemical interactions responsible for particle production. To help understand the nature of the surface chemistry, high level quantum chemical calculations were performed to predict the structures and energetics for binding and reactions of NH3 and MMA on aluminum surfaces. Both NH3 and MMA react with aluminum under milling conditions, producing H2 and other gaseous products, and leaving the surfaces functionalized. The surface functionalization enhances size reduction by reducing the surface free energy and the tendency toward mechanochemical welding. For both NH3 and MMA, the particle cores are metallic aluminum, but the surface chemical properties are quite different. The ammonia-milled particles are capped by an AlNxOyHz layer ∼10 nm thick, which passivates the particles. The MMA-milled particles are capped with a thinner passivating layer, such that they are pyrophoric in air and react with N2 at elevated temperatures.

Facile preparation of highly electrically conductive films of silver nanoparticles finely dispersed in polyisobutylene-b-poly(oxyethylene)-b-polyisobutylene triblock copolymers and graphene oxide hybrid surfactants

The melted morphologies revealed that the AgNPs possessed mobility, and melted on the film surface, giving a high electrical conductivity of 5.2 × 10⁻² Ω sq⁻¹ when heat-treated at 350 °C.

Impact of storage conditions and storage time on silver nanoparticles' physicochemical properties and implications for their biological effects

A multi-parametric assessment of the impact of storage time/conditions and capping agent charge on the stability and toxicity of AgNPs showed agglomeration, dissolution, oxidation, capping agent degradation and attachment of Ag⁺ ions all play a role.

Rapid chromatographic separation of dissoluble Ag(I) and silver-containing nanoparticles of 1-100 nanometer in antibacterial products and environmental waters

Sensitive and rapid methods for speciation analysis of nanoparticulate Ag (NAg) and Ag(I) in complex matrices are urgently needed for understanding the environmental effects and biological toxicity of silver nanoparticles (AgNPs). Herein we report the development of a universal liquid chromatography (LC) method for rapid and high resolution separation of dissoluble Ag(I) from nanoparticles covering the entire range of 1-100 nm in 5 min. By using a 500 Å poresize amino column, and an aqueous mobile phase containing 0.1% (v/v) FL-70 (a surfactant) and 2 mM Na2S2O3 at a flow rate of 0.7 mL/min, all the nanoparticles of various species such as Ag and Ag2S were eluted in one fraction, while dissoluble Ag(I) was eluted as a baseline separated peak. The dissoluble Ag(I) was quantified by the online coupled ICP-MS with a detection limit of 0.019 μg/L. The NAg was quantified by subtracting the dissoluble Ag(I) from the total Ag content, which was determined by ICP-MS after digestion of the sample without LC separation. While the addition of FL-70 and Na2S2O3 into the mobile phase is essential to elute NAg and Ag(I) from the column, the use of 500 Å poresize column is the key to baseline separation of Ag(I) from ∼ 1 nm AgNPs. The feasibility of the proposed method was demonstrated in speciation analysis of dissoluble Ag(I) and NAg in antibacterial products and environmental waters, with very good chromatographic repeatability (relative standard deviations) in both peak area (<2%) and retention time (<0.6%), excellent spiked recoveries in the range of 84.7-102.7% for Ag(I) and 81.3-106.3% for NAg. Our work offers a novel approach to rapid and baseline separation of dissoluble metal ions from their nanoparticulate counterparts covering the whole range of 1-100 nm.

Rapid on-site TLC-SERS detection of four antidiabetes drugs used as adulterants in botanical dietary supplements

A novel facile method has been established for rapid on-site detection of antidiabetes chemicals used to adulterate botanical dietary supplements (BDS) for diabetes. Analytes and components of pharmaceutical matrices were separated by thin-layer chromatography (TLC) then surface-enhanced Raman spectroscopy (SERS) was used for qualitative identification of trace substances on the HPTLC plate. Optimization and standardization of the experimental conditions, for example the method used for preparation of silver colloids, the mobile phase, and the concentration of colloidal silver, resulted in a very robust and highly sensitive method which enabled successful detection when the amount of adulteration was as low as 0.001 % (w/w). The method was also highly selective, enabling successful identification of some chemicals in extremely complex herbal matrices. The established TLC-SERS method was used for analysis of real BDS used to treat diabetes, and the results obtained were verified by liquid chromatography-triple quadrupole mass spectrometry (LC-MS-MS). The study showed that TLC-SERS could be used for effective separation and detection of four chemicals used to adulterate BDS, and would have good prospects for on-site qualitative screening of BDS for adulterants.

Comparative study of hematological responses to platinum group metals, antimony and silver nanoparticles in animal models

Research was conducted to examine the hematological effects of heavy metals (platinum (Pt ((IV))), palladium (Pd ((II))), rhodium (Rh ((III))), antimony (Sb ((III)) and Sb ((V))), and silver nanoparticles (AgNPs)) on white blood cells in mammalian (rat) and avian (chick embryo) models. These metals are used in many everyday products and are accumulating in our environment. Six-week old Sprague-Dawley female rats were treated daily by gavage and six-day old, fertile, specific pathogen-free white leghorn strain chick embryos' eggs were injected on days 7 and 14 of incubation with 0.0, 1.0, 5.0 or 10.0 ppm concentrations of Pt ((IV)) and a platinum group metal (PGM) mix of Pt ((IV)), Pd ((II)) and Rh ((III)). Chick embryos were also tested with 1.0 or 5.0 ppm of antimony compounds (Sb ((III)) and Sb ((V))) and 0.0, 15.0, 30.0, 60.0, or 100.0 ppm of silver nanoparticles (AgNPs). After 8 weeks of treatment, blood was obtained from the rats by jugular cut down and from chick embryos on day 20 of incubation by heart puncture. Blood smears were made and stained and a differential white cell count was performed on each. Examination of the smears revealed unconventional dose responses, stimulation of the immune response, and decreases in leukocyte production with various metals and concentrations. Chick embryos responded differently than rats to Pt and the PGM mix; suggesting that species differences and/or stage of development are important components of response to heavy metals. Route of administration of the metals might also influence the response. All of the heavy metals tested affected the immune responses of the tested animals as demonstrated by changes in the types and numbers of leukocytes. Our findings warrant further research to determine the mechanism of these effects and to understand and prevent toxicological effects in humans and other living organisms.

Chitosans for delivery of nucleic acids

Alternatives to efficient viral vectors in gene therapy are desired because of their poor safety profiles. Chitosan is a promising non-viral nucleotide delivery vector because of its biocompatibility, biodegradability, low immunogenicity and ease of manufacturing. Since the transfection efficiency of chitosan polyplexes is relatively low compared to viral counterparts, there is an impetus to gain a better understanding of the structure-performance relationship. Recent progress in preparation and characterisation has enabled coupling analysis of chitosans structural parameters that has led to increased TE by tailoring of chitosan's structure. In this review, we summarize the recent advances that have lead to a more rational design of chitosan polyplexes. We present an integrated review of all major areas of chitosan-based transfection, including preparation, chitosan and polyplexes physicochemical characterisation, in vitro and in vivo assessment. In each, we present the obstacles to efficient transfection and the strategies adopted over time to surmount these impediments.

Traveling through the Desalting Column Spontaneously Transforms Thiolated Ag Nanoclusters from Nonluminescent to Highly Luminescent

This letter reports an unexpected observation in the purification of ultrasmall (<2 nm) thiolate-protected Ag nanoclusters (NCs) via a common separation technique (e.g., desalting column and ultrafiltration), where the nonluminescent Ag NCs were spontaneously transformed to highly luminescent NCs during the separation. This interesting finding was then used to develop a facile and fast (<5 min) synthesis method for highly luminescent Ag NCs. The key strategy was to use the separation process to selectively remove small species (e.g., salts and excess protecting ligands) from the Ag NC solution, which induced a size or structure-focusing of Ag NCs in the solution, leading to the formation of highly luminescent Ag NCs. The concurrent synthesis and purification of highly luminescent Ag NCs via a common "physical separation unit" could be further advanced in a continuous mode for large-scale production of luminescent Ag NCs.

Biosensors for immune cell analysis-A perspective

Massively parallel analysis of single immune cells or small immune cell colonies for disease detection, drug screening, and antibody production represents a "killer app" for the rapidly maturing microfabrication and microfluidic technologies. In our view, microfabricated solid-phase and flow cytometry platforms of the future will be complete with biosensors and electrical/mechanical/optical actuators and will enable multi-parametric analysis of cell function, real-time detection of secreted signals, and facile retrieval of cells deemed interesting.