Simple functionalization strategies for enhancing nanoparticle separation and recovery with asymmetric flow field flow fractionation.

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.

A lectin-based gold nanoparticle assay for probing glycosylation of glycoproteins.

We report a glycoanalysis method in which lectins are used to probe the glycans of therapeutic glycoproteins that are adsorbed on gold nanoparticles. A model mannose-presenting glycoprotein, ribonuclease B (RNase B), and the therapeutic monoclonal antibody (mAb) rituximab, were found to adsorb spontaneously and non-specifically to bare gold nanoparticles such that glycans were accessible for lectin binding. Addition of a multivalent binding lectin, such as concanavalin A (Con A), to a solution of the modified gold nanoparticles resulted in cross-linking of the nanoparticles. This phenomenon was evidenced within 1 min by a change in the hydrodynamic diameter, D(H), measured by dynamic light scattering (DLS) and a shift and increase in absorbance of the plasmon resonance band of the gold nanoparticles. By combining the sugar-binding specificity and the cross-linking capabilities of lectins, the non-specific adsorption of glycoproteins to gold surfaces, and the unique optical reporting properties of gold nanoparticles, a glycosylation pattern of rituximab could be generated. This assay provides advantages over currently used glycoanalysis methods in terms of short analysis time, simplicity of the conjugation method, convenience of simple spectroscopic detection, and feasibility of providing glycan characterization of the protein drug product by using a variety of binding lectins.

DNA-functionalized carbon nanotubes for biosensing applications.

Carbon nanotubes (CNTs) have been broadly studied due to their exceptional structural, electronic and mechanical properties, and their use have been proposed for many applications. The number of biosensing applications of CNTs has increased in the past few years. Nevertheless, in order to use CNTs as standard materials in the biosensing field and to take full advantage of their unique properties, several problems must be solved. For example, the solubility of CNTs, especially in aqueous solvents, needs to be improved. Furthermore, reliable methodologies for the easy, reproducible and efficient incorporation of CNTs into solid substrates must be developed. Chemical functionalization of CNTs with biomolecules, and specifically with DNA, provides an alternative to the previous challenges. This review will present a brief overview of the methods available for the chemical functionalization of CNTs with DNA by either covalent or non-covalent means. Moreover, the main scope will be on describing the use of DNA-CNT complexes in biosensing applications. Detection of ions, glucose, peroxide and DNA hybridization using the DNA-CNT hybrids will be discussed.

Bioelectrochemical sensing based on single stranded deoxyribonucleic acid-carbon nanotubes covalently attached on gold electrodes.

A biosensor based on single-stranded deoxyribonucleic acid-functionalized carbon nanotubes covalently attached to a self-assembled monolayer of 11-amino-1-undecanethiol on gold has been prepared. The preparation of the deoxyribonucleic acid sensor was followed using cyclic voltammetry. Single-walled carbon nanotubes, covalently attached to the gold surface present a nanoelectrode array behavior. To confirm the hybridization step between the probe and the target deoxyribonucleic acid, we used methylene blue, which is an indicator capable of distinguishing between single-stranded deoxyribonucleic acid and double-stranded deoxyribonucleic acid. Our results demonstrate that the modification of gold with single-walled carbon nanotubes and single-stranded deoxyribonucleic acid can be used for deoxyribonucleic acid hybridization detection.

Detection and characterization of SiO2 and TiO2 nanostructures in dietary supplements.

Nanomaterials are beginning to enter our daily lives through various consumer products as the result of technology commercialization. The development of methodologies to detect the presence of nanomaterials in consumer products is an essential element in understanding our exposure. In this study, we have developed methods for the separation and characterization of silicon dioxide (SiO2) and titanium dioxide (TiO2) nanostructures in dietary supplements marketed in products specifically targeted for women. A total of 12 commercial products claiming the inclusion of SiO2 and TiO2, but not making any claims regarding the particle size, were randomly selected for purchase through various retailers. To isolate nanostructures from these products, a simple methodology that combines acid digestion and centrifugation was utilized. Once isolated, the chemical composition, size, morphology, and crystal structure were characterized using mass spectroscopy, light scattering, electron microscopy, and X-ray diffraction techniques. SiO2 and TiO2 nanostructures were detected in 11 of 12 products using these methods. Many of the isolated nanoscale materials showed a high degree of aggregation; however, identified individual structures had at least one dimension below 100 nm. These robust methods can be used for routine monitoring of commercial products for nanoscale oxides of silica and titanium.

Rapid determination of silver in nanobased liquid dietary supplements using a portable X-ray fluorescence analyzer.

This paper reports a rapid and straightforward method for the quantitation of total Ag content in nanobased commercially available liquid dietary supplements using a portable X-ray fluorescence (pXRF) analyzer. Figures of merits were evaluated by analyzing a series of AgNO3 standards. This method was shown to have a detection limit of 3 ppm, a quantitation limit of 10 ppm, and a broad linear range from the detection limit to 10000 ppm (1%). Accurate detection and quantitation of Ag content in well-characterized Ag nanoparticle samples and in nanobased liquid dietary supplements were achieved with good correlation (i.e., percentage difference average values under 15%) between the total Ag concentration obtained by the pXRF analyzer and by inductively coupled plasma mass spectrometry (ICP-MS). Furthermore, accurate quantitation of Ag in the presence of high concentrations of potential spectral interferences was also demonstrated.