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We report a simple one-pot strategy to prepare surface-function-alized, water-dispersible iron oxide nanoparticles. Small organic molecules that have desired functional groups such as amines, carboxylics, and thiols are chosen as capping agents and are injected into the reaction medium at the end of the synthesis. A diversity of functionalities are effectively introduced onto the surface of the nanoparticles with a minimal consumption of solvents and chemical resources by simply switching the capping ligand to form the ligand shell. The resulting nanocrystals are quasi-spherical and narrowly size-distributed. Energy-dispersive X-ray analysis and Fourier transform infrared spectroscopy studies suggest a successful surface modification of iron oxide nanoparticles with selected functionalities. The colloidal stabilities are characterized by dynamic light scattering and zeta potential measurements. The results imply that functionalized nanoparticles are very stable and mostly present as individual units in buffer solutions. The pedant functional groups of the capping ligand molecules are very reactive, and their availabilities are investigated by covalently linking fluorescent dyes to the nanoparticles through the cross-linking of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. The quenched quantum yield and shortened lifetime of the dyes strongly indicate a direct bonding between the functional group of the nanoparticles and the fluorescent molecules.

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Due to the increasing use of engineered nanomaterials in consumer products, regulatory agencies and other research organizations have determined that the development of robust, reliable, and accurate methodologies to characterize nanoparticles in complex matrices is a top priority. Of particular interest are methods that can separate and determine the size of nanomaterials in samples that contain polydisperse and/or multimodal nanoparticle populations. Asymmetric-flow field flow fractionation (AF4) has shown promise for the separation of nanoparticles with wide size range distributions; however, low analyte recoveries and decreased membrane lifetimes, due to membrane fouling, have limited its application. Herein, we report straightforward strategies to minimize membrane fouling and improve nanoparticle recovery by functionalizing the surface of the nanoparticles, as well as that of the AF4 membranes. Gold nanoparticles (AuNP) were stabilized through functionalization with a phosphine molecule, whereas the surface of the membranes was coated with a negatively charged polystyrenesulfonate polymer. Improved nanoparticle separation, recoveries of 99.1 (±0.5) %, and a detection limit of 6 μg/kg were demonstrated by analyzing AuNP reference materials of different sizes (e.g., 10, 30, and 60 nm), obtained from the National Institute of Standards and Technology (NIST). Furthermore, the stability of the polymer coating and its specificity toward minimizing membrane fouling were demonstrated.

We report the development and optimization of a system consisting of capillary electrophoresis (CE) interfaced with inductively coupled plasma mass spectrometry (ICPMS) for rapid and high resolution speciation and characterization of metallic (e.g., gold, platinum, and palladium) nanoparticles in a dietary supplement. Multiple factors, including surfactant type and concentration, pH of running buffer, and applied voltage, were investigated to optimize the separation conditions. It was found that by using the anionic surfactant sodium dodecyl benzenesulfonate (SDBS) in the running buffer the separation resolution was significantly improved, allowing for easy distinction of adjacent size fractions in a gold nanoparticle mixture with very small size differences (e.g., 5, 15, 20, and 30 nm). The type and concentration of the surfactant was found to be critical in obtaining sufficient separation while applied voltage and pH values of the running buffers largely affected the elution times by varying the electroosmotic flow. Quantum dots were used as mobility markers to eliminate the run-to-run variation. The diameters of the nanoparticles followed a linear relationship with their relative electrophoretic mobility, and size information on unknown samples could be extrapolated from a standard curve. The accuracy and precision of this method was confirmed using 10 and 30 nm gold nanoparticle standard reference materials. Furthermore, the method was successfully applied to the analysis of commercially available metallic nanoparticle-based dietary supplements, as evidenced by good agreement between the particle sizes calculated by CE/ICPMS and transmission electron microscopy (TEM).

The surface of superparamagnetic silica coated iron oxide (Fe3O4@SiO2) nanoparticles was functionalized with a disulfide bond linked N-hydroxysuccinimidyl (NHS) ester group in order to develop a method for labeling primary amines in peptides/proteins. The nanoparticle labeled proteins/peptides formed after NHS ester reaction with the primary amine groups were isolated using a magnet without any additional purification step. Nanoparticle moieties conjugated to peptides/proteins were then trimmed by cleavage at the disulfide linker with a reducing agent. The labeled peptides were analyzed by LC-MS/MS to determine their sequences and the sites of NHS ester labeling. This novel approach allowed characterization of lysine residues on the solvent accessible surface of native bovine serum albumin. Low cost, rapid magnetic separation, and specificity towards primary amine groups make NHS ester coated Fe3O4@SiO2 nanoparticles a potential labeling probe to study proteins on living cell surfaces.

Production and application of nanoparticles in consumer products is at an all-time high due to the emerging field of nanotechnology. Direct detection and quantification of trace levels of nanoparticles within consumer products is very challenging and problematic. Although multiple methodologies are available for this purpose, each method has its own set of limitations. Herein, we developed an analytical platform consisting of asymmetric flow-field flow fractionation (AF4) coupled with inductively coupled plasma mass spectroscopy (ICP-MS) for the speciation and quantification of silver ions and silver nanoparticles at the ng/kg level (ppt). AF4 is utilized to concentrate the nanoparticles, and ICP-MS acts as the detector. The protein corona that forms upon exposure of nanoparticles to bovine serum albumin was utilized as a nanoparticle stabilization and AF4 recovery enhancement mechanism. Speciation of silver ions and nanoparticles was achieved with the assistance of penicillamine as a complexation ligand. The effect of nanoparticle size, surface coating, and ionization state toward the detection and quantification of the developed methodology was evaluated. The detection limit was found to be 4 ng/kg with the application of a 5 mL sample loop. Further application of this developed methodology on environmentally relevant samples was demonstrated by the analysis of Arkansas River water spiked with silver nanoparticles and nanoparticle spiked into humic acid solution (50 mg/L) at an environmentally relevant level.