Shape Analysis of DNA-Au Hybrid Particles by Analytical Ultracentrifugation

Effect of protein adsorption on the dissolution kinetics of silica nanoparticles

Nanoparticulate systems in the presence of proteins are highly relevant for various biomedical applications such as photo-thermal therapy and targeted drug delivery. These involve a complex interplay between the charge state of nanoparticles and protein, the resulting protein conformation, adsorption equilibrium and adsorption kinetics, as well as particle dissolution. SiO₂ is a common constituent of bioactive glasses used in biomedical applications. In this context, the dissolution behavior of silica particles in the presence of a model protein, bovine serum albumin (BSA), at physiologically relevant pH conditions was studied. Sedimentation analysis using an analytical ultracentrifuge showed that BSA in the supernatant solution is not affected by the presence of silica nanoparticles. However, zeta potential measurements revealed that the presence of the protein alters the particles' charge state. Adsorption and dissolution studies demonstrated that the presence of the protein significantly enhances the dissolution kinetics via interactions of positively charged amino acids in the protein with the negative silica surface and interaction of BSA with dissolved silicate species. Our study provides comprehensive insights into the complex interactions between proteins and oxide nanoparticles and establishes a reliable protocol paving the way for future investigations in more complex systems involving biological solutions as well as bioactive materials.

Structural and Optical Sensing Properties of Nonthermal Atmospheric Plasma-Synthesized Polyethylene Glycol-Functionalized Gold Nanoparticles

Polyethylene glycol-functionalized gold nanoparticles (Au@PEG NPs) were prepared by a simple plasma-assisted method without additional reducing chemicals. After irradiating tetrachloroauric acid (HAuCl₄) and polyethylene glycol (PEG) in aqueous medium with an argon plasma jet, the gold precursor transformed into an Au@PEG NP colloid that exhibited surface plasma resonance at 530 nm. When the plasma jet entered the water, additional reactive species were induced through interactions between plasma-generated reactive species and aqueous media. Interaction of the gold precursor with the plasma-activated medium allowed the synthesis of gold nanoparticles (AuNPs) without reductants. The plasma-synthesized Au@PEG NPs had a quasi-spherical shape with an average particle diameter of 32.5 nm. The addition of PEG not only helped to stabilize the AuNPs but also increased the number of AuNPs. Au@PEG NP-loaded paper (AuNP-paper) was able to detect the degradation of rhodamine B, therefore, indicating that AuNP-paper can act as a surface-enhanced Raman scattering platform. Dye degradation by plasma treatment was investigated by optical absorption and Raman spectroscopy. The method proposed for the fabrication of Au@PEG NPs is rapid, low-cost, and environment-friendly and will facilitate the application of plasma-synthesized nanomaterials in sensors.

Revealing the Formation of Well-Dispersed Polystyrene@ZIF-8 Core-Shell Nanoparticles by Analytical Ultracentrifugation

Significant progress has been made in the synthesis and application of core-shell nanoparticles in the past decade. But particle agglomerations are hard to avoid as the formation mechanisms of core-shell nanoparticles are still vague and not clear even for the simplest and most straightforward hard-templating method. Here, analytical ultracentrifugation (AUC) is applied to investigate the formation of polystyrene@ZIF-8 core-shell nanoparticles, as a model to understand the hard-templating method. It has been found that the concentration of the ZIF-8 precursor influences both the ZIF-8 shell formation and the agglomeration of the polystyrene (PS) template. An overdiluted ZIF-8 precursor is not suitable for ZIF-8 shell formation, while a highly concentrated ZIF-8 precursor causes strong aggregation of the PS core. By applying the optimal precursor concentration identified by AUC, well-dispersed polystyrene@ZIF-8 core-shell nanoparticles can be obtained.

Moving analytical ultracentrifugation software to a good manufacturing practices (GMP) environment

Recent advances in instrumentation have moved analytical ultracentrifugation (AUC) closer to a possible validation in a Good Manufacturing Practices (GMP) environment. In order for AUC to be validated for a GMP environment, stringent requirements need to be satisfied; analysis procedures must be evaluated for consistency and reproducibility, and GMP capable data acquisition software needs to be developed and validated. These requirements extend to multiple regulatory aspects, covering documentation of instrument hardware functionality, data handling and software for data acquisition and data analysis, process control, audit trails and automation. Here we review the requirements for GMP validation of data acquisition software and illustrate software solutions based on UltraScan that address these requirements as far as they relate to the operation and data handling in conjunction with the latest analytical ultracentrifuge, the Optima AUC by Beckman Coulter. The software targets the needs of regulatory agencies, where AUC plays a critical role in the solution-based characterization of biopolymers and macromolecular assemblies. Biopharmaceutical and regulatory agencies rely heavily on this technique for characterizations of pharmaceutical formulations, biosimilars, injectables, nanoparticles, and other soluble therapeutics. Because of its resolving power, AUC is a favorite application, despite the current lack of GMP validation. We believe that recent advances in standards, hardware, and software presented in this work manage to bridge this gap and allow AUC to be routinely used in a GMP environment. AUC has great potential to provide more detailed information, at higher resolution, and with greater confidence than other analytical techniques, and our software satisfies an urgent need for AUC operation in the GMP environment. The software, including documentation, are publicly available for free download from Github. The multi-platform software is licensed by the LGPL v.3 open source license and supports Windows, Mac and Linux platforms. Installation instructions and a mailing list are available from ultrascan.aucsolutions.com.

Stepwise assembly of nanoclusters guided by DNA origami frames with high-throughput

We contrive two strategies to assemble well-defined nanoclusters with high-throughput guided by DNA origami frames either by (1) introducing a micro-sized surface to fabricate patchy particles for binding with DNA structures or (2) restricting the assembly process of free nanoparticles and DNA origami frames on the fixed sites. Both the strategies can omit the process of gel purification of the final products.

Spectroscopic and Hydrodynamic Characterisation of DNA-Linked Gold Nanoparticle Dimers in Solution using Two-Photon Photoluminescence

Two-photon photoluminescence (TPPL) emission spectra of DNA-gold nanoparticle (AuNP) monoconjugates and the corresponding DNA-linked AuNP dimers are obtained by photon time-of-flight spectroscopy. This technique is combined with two-photon photoluminescence fluctuation correlation spectroscopy (TPPL-FCS) to simultaneously monitor the optical and hydrodynamic behaviour of these nano-assemblies in solution, with single-particle sensitivity and microsecond temporal resolution. In this study, the AuNPs have an average core diameter of 12 nm, which renders their dark-field plasmonic light scattering too weak for single-particle imaging. Moreover, as a result of the lack of plasmonic coupling in the dimers, the optical extinction, scattering and photoluminescence spectra of the DNA-AuNP complexes are not sufficiently different to distinguish between monomers and dimers. The use of TPPL-FCS successfully addresses these bottlenecks and enables the distinction between AuNP monomers and AuNP dimers in solution by measurement of their hydrodynamic rotational and translational diffusion.

Structural studies of RNA-protein complexes: A hybrid approach involving hydrodynamics, scattering, and computational methods

The diverse functional cellular roles played by ribonucleic acids (RNA) have emphasized the need to develop rapid and accurate methodologies to elucidate the relationship between the structure and function of RNA. Structural biology tools such as X-ray crystallography and Nuclear Magnetic Resonance are highly useful methods to obtain atomic-level resolution models of macromolecules. However, both methods have sample, time, and technical limitations that prevent their application to a number of macromolecules of interest. An emerging alternative to high-resolution structural techniques is to employ a hybrid approach that combines low-resolution shape information about macromolecules and their complexes from experimental hydrodynamic (e.g. analytical ultracentrifugation) and solution scattering measurements (e.g., solution X-ray or neutron scattering), with computational modeling to obtain atomic-level models. While promising, scattering methods rely on aggregation-free, monodispersed preparations and therefore the careful development of a quality control pipeline is fundamental to an unbiased and reliable structural determination. This review article describes hydrodynamic techniques that are highly valuable for homogeneity studies, scattering techniques useful to study the low-resolution shape, and strategies for computational modeling to obtain high-resolution 3D structural models of RNAs, proteins, and RNA-protein complexes.