Universal Parameter Optimization of Density Gradient Ultracentrifugation Using CdSe Nanoparticles as Tracing Agents

Hybrid modeling of an ultracentrifugation process for separation of full and empty adeno-associated virus particles

Ultracentrifugation is an attractive method for separating full and empty capsids, exploiting their density difference. Changes of the serotype/capsid, density of loading material, or the genetic information contained in the adeno-associated viruses (AAVs) require the adaptation of the harvesting parameters and the density gradient loaded onto the centrifuge. To streamline these adaptations, a mathematical model could support the design and testing of operating conditions.Here, hybrid models, which combine empirical functions with artificial neural networks, are proposed to describe the separation of full and empty capsids as a function of material and operational parameters, i.e., the harvest model. In addition, critical quality attributes are estimated by a quality model which is operating on top of the harvest model. The performance of these models was evaluated using test data and two additional blind runs. Also, a "what-if" analysis was conducted to investigate whether the models' predictions align with expectations.It is concluded that the models are sufficiently accurate to support the design of operating conditions, though the accuracy and applicability of the models can further be increased by training them on more specific data with higher variability.

Analytical separation techniques: toward achieving atomic precision in nanomaterials science

The size- and shape-dependence of the properties are the most characteristic features of nanoscale matter. In many types of nanomaterials, there is a size regime wherein every atom counts. In order to fully realize the idea of 'maneuvering things atom by atom' envisioned by Richard Feynman, synthesis and separation of nanoscale matter with atomic precision are essential. It is therefore not surprising that analytical separation techniques have contributed tremendously toward understanding the size- as well as shape-dependent properties of nanomaterials. Fascinating properties of nanomaterials would not have been explored without the use of these techniques. Here we discuss the pivotal role of analytical separation techniques in the progress of nanomaterials science. We begin with a brief overview of some of the key analytical separation techniques that are of tremendous importance in nanomaterials research. Then we describe how each of these techniques has contributed to the advancements in nanomaterials science taking some of the nanosystems as examples. We discuss the limitations and challenges of these techniques and future perspectives.

Glutathione Disulfide as a Reducing, Capping, and Mass-Separating Agent for the Synthesis and Enrichment of Gold Nanoclusters

Water-soluble nanoclusters, which are facilely enrichable without changes in the original properties, are highly demanded in many disciplines. In this contribution, a new class of gold nanoclusters (AuNCs) was synthesized using glutathione disulfide (GSSG) as a reducing and capping agent under intermittent heating mode. The as-prepared GSSG–AuNCs had a higher quantum yield (4.1%) compared to the conventional glutathione-protected AuNCs (1.8%). Moreover, by simply introducing the GSSG–AuNC solution to acetonitrile at a volume ratio of 1:7, a new bottom phase was formed, in which GSSG–AuNCs could be 400-fold enriched without changes in properties, with a percentage recovery higher than 99%. The enrichment approach did not need additional instruments and was potentially suitable for large-scale enrichment of nanoclusters. Further, density functional theory calculations indicated that the hydrogen bonding between GSSG and acetonitrile plays a key role for the bottom phase formation. Our work suggests that the highly emissive GSSG–AuNCs possess great potential not only in fluorescent measurements but also in other scenarios in which high-concentration AuNCs may be needed, such as catalysis, drug delivery, and electronic and optical industries.

Detailed analysis of size-separation of silver nanoparticles by density gradient centrifugation method

In this research, silver nanoparticles were synthesized by chemical precipitation method and stabilized by chitosan biopolymer in the range of 15 to 235 nm. Then, the silver nanoparticles were separated by density gradient centrifugation method at different gradients and centrifuged at various duration and speed. The best separation was done with the gradient chosen at 10%, 20%, 30% and 40% for a duration of 2 h at 6000 rpm. The UV-visible spectra demonstrated the proper synthesis of silver nanoparticles, while FTIR spectrum and XRD data revealed the structure of prepared Ag-NPs. The FESEM and TEM analysis were used to check for the exact shape and size of Ag-NPs, respectively. However, the separation of silver nanoparticles was assessed making use of DLS analysis.

Density gradient ultracentrifugation for colloidal nanostructures separation and investigation

In this article, we review the advancement in nanoseparation and concomitant purification of nanoparticles (NPs) by using density gradient ultracentrifugation technique (DGUC) and demonstrated by taking several typical examples. Study emphasizes the conceptual advances in classification, mechanism of DGUC and synthesis-structure-property relationships of NPs to provide the significant clue for the further synthesis optimization. Separation, concentration, and purification of NPs by DGUC can be achieved at the same time by introducing the water/oil interfaces into the separation chamber. We can develop an efficient method "lab in a tube" by introducing a reaction zone or an assembly zone in the gradient to find the surface reaction and assembly mechanism of NPs since the reaction time can be precisely controlled and the chemical environment change can be extremely fast. Finally, to achieve the best separation parameters for the colloidal systems, we gave the mathematical descriptions and computational optimized models as a new direction for making practicable and predictable DGUC separation method. Thus, it can be helpful for an efficient separation as well as for the synthesis optimization, assembly and surface reactions as a potential cornerstone for the future development in the nanotechnology and this review can be served as a plethora of advanced notes on the DGUC separation method.

Purification technologies for colloidal nanocrystals

Almost all applications of colloidal nanocrystals require some type of purification or surface modification process following nanocrystal growth. Nanocrystal purification - the separation of nanocrystals from undesired solution components - can perturb the surface chemistry and thereby the physical properties of colloidal nanocrystals due to changes in solvent, solute concentrations, and exposure of the nanocrystal surface to oxidation or hydrolysis. For example, nanocrystal quantum dots frequently exhibit decreased photoluminescence brightness after precipitation from the growth solvent and subsequent redissolution. Consequently, purification is an integral part of the synthetic chemistry of colloidal nanocrystals, and the effect of purification methods must be considered in order to accurately compare and predict the behavior of otherwise similar nanocrystal samples. In this Feature Article we examine established and emerging approaches to the purification of colloidal nanoparticles from a nanocrystal surface chemistry viewpoint. Purification is generally achieved by exploiting differences in properties between the impurities and the nanoparticles. Three distinct properties are typically manipulated: polarity (relative solubility), electrophoretic mobility, and size. We discuss precipitation, extraction, electrophoretic methods, and size-based methods including ultracentrifugation, ultrafiltration, diafiltration, and size-exclusion chromatography. The susceptibility of quantum dots to changes in surface chemistry, with changes in photoluminescence decay associated with surface chemical changes, extends even into the case of core/shell structures. Accordingly, the goal of a more complete description of quantum dot surface chemistry has been a driver of innovation in colloidal nanocrystal purification methods. We specifically examine the effect of purification on surface chemistry and photoluminescence in quantum dots as an example of the challenges associated with nanocrystal purification and how improved understanding can result from increasingly precise techniques, and associated surface-sensitive analytical methods.

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.