Silver nanoparticles (AgNPs) were selectively concentrated from environmental water samples without disturbing their sizes and shapes by cloud point extraction (CPE) with Triton X-114 (TX-114). The highest extraction efficiency for AgNPs was obtained at about their zero point charge pH (pH PZC ), which was ∼3.0-3.5 for the studied AgNPs. Addition of salts such as 35 mM NaNO 3 or 10 mM Na 2 S 2 O 3 enhanced the phase separation and thus increased the extraction efficiency of AgNPs. Furthermore, Na 2 S 2 O 3 efficiently eliminated the interference of Ag + due to the formation of a complex between Ag + and S 2 O 3 2-that was not extracted into the TX-114-rich phase. The presence of humic acid at an environmentally relevant level (0-30 mg/L dissolved organic carbon) had no effect on the extraction of AgNPs. An enrichment factor of 100 was obtained with 0.2% (w/v) TX-114, and the recoveries of AgNPs from various environmental samples were in the range of 57-116% at 0.1-146 µg/L spiked levels. The AgNPs preconcentrated into the TX-114-rich phase were identified by transmission electron microscopy/scanning electron microscopy-energy dispersive spectrometer/UV-vis spectrum and quantified after microwave digestion by inductively coupled plasma mass spectrometry with a detection limit of 0.006 µg/L (34.3 fmol/L particles of AgNPs). As the proposed CPE procedure preserves the sizes and shapes of AgNPs, the original morphology of AgNPs in environmental waters can be obtained by characterizing the preconcentrated analytes in the TX-114-rich phase. This proposed method provides an efficient approach for the analysis and tracking of AgNPs in the environment.Given their large quantity of production and widespread applications, engineered nanomaterials (NMs) will inevitably be released into the environment during production, handling, and disposal. The unique properties of NMs, such as high surfaceto-volume ratio, mobility and catalytic activity, could cause adverse effects on the eco-environmental system. Evaluation of the risk of NMs to human health and the environment relies on the understanding of their fate, transport, and exposure, as well as their effects on the fate, transport, and exposure of other toxic substances. However, little is known about the occurrence, fate, and toxicity of NMs, partly due to the lack of quantitative methodology for NMs in environmental and biological matrixes. 1-6A variety of methods have been developed for characterization and quantitative analysis of NMs in simple matrixes, as well as natural NMs in a complex matrix such as environmental waters and soils. [7][8][9][10][11][12] Characterization was mainly conducted with microscopy and microscopy-related techniques (e.g., scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM)), whereas quantification was mainly based on the coupling of size separation techniques (e.g., size-exclusion chromatography, 13-15 field flow fractionation, [16][17][18] hydrodynamic chromatography, 19,20 and capill...

The rapid growth in commercial use of silver nanoparticles (AgNPs) will inevitably increase silver exposure in the environment and the general population. As the fate and toxic effects of AgNPs is related to the Ag(+) released from AgNPs and the transformation of Ag(+) into AgNPs, it is of great importance to develop methods for speciation analysis of AgNPs and Ag(+). This study reports the use of Triton X-114-based cloud point extraction as an efficient separation approach for the speciation analysis of AgNPs and Ag(+) in antibacterial products and environmental waters. AgNPs were quantified by determining the Ag content in the Triton X-114-rich phase with inductively coupled plasma mass spectrometry (ICPMS) after microwave digestion. The concentration of total Ag(+), which consists of the AgNP adsorbed, the matrix associated, and the freely dissolved, was obtained by subtracting the AgNP content from the total silver content that was determined by ICPMS after digestion. The limits of quantification (S/N = 10) for antibacterial products were 0.4 μg/kg and 0.2 μg/kg for AgNPs and total silver, respectively. The reliable quantification limit was 3 μg/kg for total Ag(+). The presence of Ag(+) at concentrations up to 2-fold that of AgNPs caused no effects on the determination of AgNPs. In the cloud point extraction of AgNPs in antibacterial products, the spiked recoveries of AgNPs were in the range of 71.7-103% while the extraction efficiencies of Ag(+) were in the range of 1.2-10%. The possible coextracted other silver containing nanoparticles in the cloud point extraction of AgNPs were distinguished by transmission electron microscopy (TEM), scanning electron microscopy (SEM)- energy dispersive spectroscopy (EDS), and UV-vis spectrum. Real sample analysis indicated that even though the manufacturers claimed nanosilver products, AgNPs were detected only in three of the six tested antibacterial products.

Diverse applications of nanoparticles (NPs) have revolutionized various sectors in society. In the recent decade, particularly magnetic nanoparticles (MNPs) have gained enormous interest owing to their applications in specialized areas such as medicine, cancer theranostics, biosensing, catalysis, agriculture, and the environment. Controlled surface engineering for the design of multi-functional MNPs is vital for achieving desired application. The MNPs have demonstrated great efficacy as thermoelectric materials, imaging agents, drug delivery vehicles, and biosensors. In the present review, first we have briefly discussed main synthetic methods of MNPs, followed by their characterizations and composition. Then we have discussed the potential applications of MNPs in different with representative examples. At the end, we gave an overview on the current challenges and future prospects of MNPs. This comprehensive review not only provides the mechanistic insight into the synthesis, functionalization, and application of MNPs but also outlines the limits and potential prospects.

No abstract

Ubiquitous natural organic matter (NOM) plays an important role in the aggregation state of engineered silver nanoparticles (AgNPs) in aquatic environment, which determines the transport, transformation, and toxicity of AgNPs. As various capping agents are used as coatings for nanoparticles and NOM are natural polymer mixture with wide molecular weight (MW) distribution, probing the particle coating-dependent interaction of MW fractionated natural organic matter (M f -NOM) with various coatings is helpful for understanding the differential aggregation and transport behavior of engineered AgNPs as well as other metal nanoparticles. In this study, we investigated the role of pristine and M f -NOM on the aggregation of AgNPs with Bare, citrate, and PVP coating (Bare-, Cit-, and PVP-AgNP) in mono-and divalent electrolyte solutions. We observed that the enhanced aggregation or dispersion of AgNPs in NOM solution highly depends on the coating of AgNPs. Pristine NOM inhibited the aggregation of Bare-AgNPs but enhanced the aggregation of PVP-AgNPs. In addition, M f -NOM fractions have distinguishing roles on the aggregation and dispersion of AgNPs, which also highly depend on the AgNPs coating as well as the MW of M f -NOM. Higher MW M f -NOM (>100 kDa and 30−100 kDa) enhanced the aggregation of PVP-AgNPs in mono-and divalent electrolyte solutions, whereas lower MW M f -NOM (10−30 kDa, 3−10 kDa and <3 kDa) inhibited the aggregation of PVP-AgNPs. However, all the M f -NOM fractions inhibited the aggregation of Bare-AgNPs. For PVP-and BareAgNPs, the stability of AgNPs in electrolyte solution was significantly correlated to the MW of M f -NOM. But for Cit-AgNPs, pristine NOM and M f -NOM has minor influence on the stability of AgNPs. These findings about significantly different roles of M f -NOM on aggregation of engineered AgNPs with various coating are important for better understanding of the transport and subsequent transformation of AgNPs in aquatic environment.

Based on the "coffee-ring effect", we developed a highly efficient SERS platform which integrates the fabrication of SERS-active substrates and the preconcentration of analytes into one step. The high sensitivity, robustness, reproducibility and simplicity make this platform ideal for on-site analysis of small volume samples at low concentrations in complex matrices.Since its invention in the 1970s, 1,2 surface-enhanced Raman spectroscopy (SERS) has been receiving growing interest in a variety of areas due to its inherent merits such as a high signalto-noise ratio, non-photobleaching features and the use of single photoexcitation. 3 These features make SERS one of the most powerful techniques for non-destructive, on-site and in vivo analysis of chemical and biological substances. 4 However, the utilization of SERS in determination of trace analytes is restricted by the sophisticated and expensive nanofabrication of highly SERS-active substrates, as well as its limited sensitivity and selectivity for trace substances in complex matrices due to the swamping of the analyte signal in background molecule signals. For example, while the concentrations of PAHs in the environment are commonly in the range of 10 À12 to 10 À9 g L À1 , the lowest detection limits available with a well-designed SERS substrate are in the range of 3 Â 10 À6 to 1.78 Â 10 À4 g L À1 . 5 To meet the requirements for analysis of trace analytes in complex matrices, metallic substrates were tailored to increase the signal strength, and analytes were preconcentrated before SERS analysis. As these two approaches are very complicated and timeconsuming, it is highly desired to develop a fast, simple and robust approach to simultaneously perform the self-assembling of SERS substrates and preconcentration of trace analytes.One technique that holds great promise in this regard is the "coffee-ring effect", which refers to the accumulation of a ringlike dense array on the border by evaporating a droplet of aqueous solution containing nonvolatile solutes such as organic small molecules, biomacromolecules, polymers, and nanoparticle microspheres on solid surfaces. In this process, the three-phase contact line among the atmosphere, droplet and solid substrate is pinned, and a remarkable capillary ow happens because of the evaporation of solvents, driving solutes to move outward from the inner side to the rim of the droplet. Consequently, solutes are highly concentrated along the original droplet edge. It was found that the coffee-ring effect is applicable for enriching both chemical and biological substances. 6-11 One example is its application in normal Raman spectrometry that is termed as drop coating deposition Raman (DCDR). 10 In recent years, the coffee-ring effect has become a powerful tool for self-structuring of nanomaterials. [12][13][14][15] Herein, we report the development of a novel SERS platform by integrating the generation of SERS substrates and the enrichment of analytes into one step. We demonstrate the benets of the coffee-ring effect in co...

No abstract

Association with Hg 2+ enhances the hydrophobicity and triggers the cloud point extraction of B4 nm-diameter gold nanoparticle probes functionalized with mercaptopropionic acid and homocystine, which results in the color change of the TX-114-rich phase from colorless to red, and therefore provides a novel approach for visual and colorimetric detection of Hg 2+ with ultrahigh sensitivity and selectivity.The high toxicity of Hg 2+ has resulted in ever-growing demand for sensitive detection methods, especially rapid and field detection of Hg 2+ in environmental samples. 1 In recent years, gold nanoparticles (AuNPs) functionalized with DNA, 2 alkylthiol ligand, 3 and other species 4 have emerged as a new generation of probes for Hg 2+ determination. 5 AuNPs-based methods for visual or colorimetric sensing of Hg 2+ have become of great interest because the intense red color arising from surface plasmon absorption should allow highly sensitive detection, and the simple colorimetric approach, eliminating the usage of complex and expensive instruments, could facilitate rapid field detection. Most of these methods involve a color change from red to blue through the analyte-triggered aggregation of AuNPs, giving rise to the reduction of sensitivity due to the interference from background colors. 6 Another restriction of these methods is the limited tolerance to the interference of coexisting heavy metals, which was reported to be between 1 and 150-fold of the Hg 2+ concentration. 2b,e,3c To overcome these drawbacks, we demonstrate here, for the first time, that cloud point extraction (CPE) of small sized AuNPs can be used for sensing trace Hg 2+ in water with excellent selectivity and sensitivity.Scheme 1 illustrates the concept of this proposed procedure, which was based on the Hg 2+ -triggered CPE of the AuNP probe. In the absence of Hg 2+ , the functionalized B4 nmdiameter AuNP probe were hardly extracted into the Triton X-114 (TX-114)-rich phase, which remained colorless after CPE. In the presence of Hg 2+ , however, the TX-114-rich phase changed from colorless to red due to the enrichment of the AuNP probe from the aqueous solution. Therefore, upon the completion of the CPE process, visual and colorimetric detection of Hg 2+ can be conducted by sensing the color of the TX-114-rich phase with the naked eye and measuring the absorbance of the TX-114-rich phase at 520 nm, respectively.It is noteworthy that the CPE procedure can also serve to enrich the Hg 2+ associated AuNPs probe and eliminate the interference of coexisting metals, which markedly improves the sensitivity and selectivity, relative to other methods. The preparation of the AuNP probe and CPE procedure are detailed in ESI.wIn order to improve the method selectivity toward Hg 2+ , the 4 nm-diameter AuNPs, prepared by NaBH 4 reduction of HAuCl 4 , 3c were modified with mercaptopropionic acid (MPA) and homocystine (HCys), and 2,6-pyridinedicarboxylic acid (PDCA) was introduced into the system. The larger stability constants of MPA and PDCA with Hg 2+ in com...