Speciation of metal-based nanomaterials in human serum characterized by capillary electrophoresis coupled to ICP-MS: a case study of gold nanoparticles

Fe3O4SPIONs in cancer theranostics-structure versus interactions with proteins and methods of their investigation

As the second leading cause of death worldwide, neoplastic diseases are one of the biggest challenges for public health care. Contemporary medicine seeks potential tools for fighting cancer within nanomedicine, as various nanomaterials can be used for both diagnostics and therapies. Among those of particular interest are superparamagnetic iron oxide nanoparticles (SPIONs), due to their unique magnetic properties,. However, while the number of new SPIONs, suitably modified and functionalized, designed for medical purposes, has been gradually increasing, it has not yet been translated into the number of approved clinical solutions. The presented review covers various issues related to SPIONs of potential theranostic applications. It refers to structural considerations (the nanoparticle core, most often used modifications and functionalizations) and the ways of characterizing newly designed nanoparticles. The discussion about the phenomenon of protein corona formation leads to the conclusion that the scarcity of proper tools to investigate the interactions between SPIONs and human serum proteins is the reason for difficulties in introducing them into clinical applications. The review emphasizes the importance of understanding the mechanism behind the protein corona formation, as it has a crucial impact on the effectiveness of designed SPIONs in the physiological environment.

Recent Advances in Metalloproteomics

Interactions between proteins and metal ions and their complexes are important in many areas of the life sciences, including physiology, medicine, and toxicology. Despite the involvement of essential elements in all major processes necessary for sustaining life, metalloproteomes remain ill-defined. This is not only owing to the complexity of metalloproteomes, but also to the non-covalent character of the complexes that most essential metals form, which complicates analysis. Similar issues may also be encountered for some toxic metals. The review discusses recently developed approaches and current challenges for the study of interactions involving entire (sub-)proteomes with such labile metal ions. In the second part, transition metals from the fourth and fifth periods are examined, most of which are xenobiotic and also tend to form more stable and/or inert complexes. A large research area in this respect concerns metallodrug-protein interactions. Particular attention is paid to separation approaches, as these need to be adapted to the reactivity of the metal under consideration.

Identification of Proteins Using Supramolecular Gold Nanoparticle-Dye Sensor Arrays

The rapid detection of proteins is very important in the early diagnosis of diseases. Gold nanoparticles (AuNPs) can be engineered to bind biomolecules efficiently and differentially. Cross-reactive sensor arrays have high sensitivity for sensing proteins using differential interactions between sensor elements and bioanalytes. A new sensor array was fabricated using surface-charged AuNPs with dyes supramolecularly encapsulated into the AuNP monolayer. The fluorescence of dyes is partially quenched by the AuNPs and can be restored or further quenched due to the differential interactions between AuNPs with proteins. This sensing system enables the discrimination of proteins in both buffer and human serum, providing a potential tool for real-world disease diagnostics.

The Potential of ICP-MS as a Complementary Tool in Nanoparticle-Protein Corona Analysis

The prolific applicability of nanomaterials has made them a common citizen in biological systems, where they interact with proteins forming a biological corona complex. These complexes drive the interaction of nanomaterials with and within the cells, bringing forward numerous potential applications in nanobiomedicine, but also arising toxicological issues and concerns. Proper characterization of the protein corona complex is a great challenge typically handled with the combination of several techniques. Surprisingly, despite inductively coupled plasma mass spectrometry (ICP-MS) being a powerful quantitative technique whose application in nanomaterials characterization and quantification has been consolidated in the last decade, its application to nanoparticle-protein corona studies is scarce. Furthermore, in the last decades, ICP-MS has experienced a turning point in its capabilities for protein quantification through sulfur detection, hence becoming a generic quantitative detector. In this regard, we would like to introduce the potential of ICP-MS in the nanoparticle protein corona complex characterization and quantification complementary to current methods and protocols.

Red Flags and Adversities on the Way to the Robust CE-ICP-MS/MS Quantitative Monitoring of Self-Synthesized Magnetic Iron Oxide(II, III)-Based Nanoparticle Interactions with Human Serum Proteins

The growing interest in superparamagnetic iron oxide nanoparticles (SPIONs) as potential theranostic agents is related to their unique properties and the broad range of possibilities for their surface functionalization. However, despite the rapidly expanding list of novel SPIONs with potential biomedical applications, there is still a lack of methodologies that would allow in-depth investigation of the interactions of those nanoparticles with biological compounds in human serum. Herein, we present attempts to employ capillary electrophoresis-inductively coupled plasma tandem mass spectrometry (CE-ICP-MS/MS) for this purpose and various obstacles and limitations noticed during the research. The CE and ICP-MS/MS parameters were optimized, and the developed method was used to study the interactions of two different proteins (albumin and transferrin) with various synthesized SPIONs. While the satisfactory resolution between proteins was obtained and the method was applied to examine individual reagents, it was revealed that the conjugates formed during the incubation of the proteins with SPIONs were not stable under the conditions of electrophoretic separation.

Designing the Surface Chemistry of Inorganic Nanocrystals for Cancer Imaging and Therapy

Inorganic nanocrystals, such as gold, iron oxide and semiconductor quantum dots, offer promising prospects for cancer diagnostics, imaging and therapy, due to their specific plasmonic, magnetic or fluorescent properties. The organic coating, or surface ligands, of these nanoparticles ensures their colloidal stability in complex biological fluids and enables their functionalization with targeting functions. It also controls the interactions of the nanoparticle with biomolecules in their environment. It therefore plays a crucial role in determining nanoparticle biodistribution and, ultimately, the imaging or therapeutic efficiency. This review summarizes the various strategies used to develop optimal surface chemistries for the in vivo preclinical and clinical application of inorganic nanocrystals. It discusses the current understanding of the influence of the nanoparticle surface chemistry on its colloidal stability, interaction with proteins, biodistribution and tumor uptake, and the requirements to develop an optimal surface chemistry.

Metal-Specific Response of High-Resolution ICP-MS for Proteins Binding to Gold Nanoparticles in Human Serum

Metalloproteins have many different functions such as storage and transport of proteins, enzymes, signal transduction proteins, etc. Herein, for a selection of gold nanoparticles differing in shape, size, charge, and surface modification, the binding behavior in human serum was assessed with respect to metal-containing proteins. Our results based on sector-field ICP-MS measurements and a simple calculation algorithm indicate the possible involvement of proteins, incorporating Cu and Fe, in the formation of the biomolecular layer around the particle surface. Given that such binding encompasses a substantial amount of copper and iron within the serum proteome (>50%) at a calculated nanoparticle dose, it may result in depleting their biological functions and should be taken into account when selecting lead candidates with an improved biocompatibility.

Electrokinetic elucidation of the interactions between persistent luminescent nanoprobes and the binary apolipoprotein-E/albumin protein system

The affinity between functional nanoparticles (NPs) and proteins could determine the efficacy of nanoprobes, nanosensors, nanocarriers, and many other devices for biomedical applications. Therefore, it is necessary to develop analytical strategies to accurately evaluate the magnitude of these protein corona interactions in physiological media. In this work, different electrokinetic strategies were implemented to accurately determine the interactions between PEGylated ZnGa_1.995Cr_0.005O₄ persistent luminescent NPs (ZGO-PEG) and two important serum proteins: human serum albumin (HSA), the most abundant serum protein, and apolipoprotein-E (ApoE), associated with the active transport of NPs through the blood-brain barrier. Firstly, the injection of ZGO-PEG in a background electrolyte (BGE) containing individual proteins allowed an affinity study to separately characterize each NP-protein system. Then, the same procedure was applied in a buffer containing a mixture of the two proteins at different molar ratios. Finally, the NPs were pre-incubated with one protein and thereafter electrokinetically separated in a BGE containing the second protein. These analytical strategies revealed the mechanisms (comparative, cooperative or competitive systems) and the magnitude of their interactions, resulting in all cases in notably higher affinity and stability between ZGO-PEG and ApoE (K_a = 1.96 ± 0.25 × 10¹⁰ M^-M) compared to HSA (K_a = 4.60 ± 0.41 × 10⁶ M^-M). For the first time, the inter-protein ApoE/HSA interactions with ZGO-PEG were also demonstrated, highlighting the formation of a ternary ZGO-PEG/ApoE/HSA nanocomplex. These results open the way for a deeper understanding of the protein corona formation, and the development of versatile optical imaging applications for ZGO-PEG and other systemically delivered nanoprobes ideally vectorized to the brain.

Enzyme digestion combined with SP-ICP-MS analysis to characterize the bioaccumulation of gold nanoparticles by mustard and lettuce plants

Plants can absorb and accumulate engineered nanomaterials (ENMs) through water and soil, providing a potential way for nanoparticles to be enriched in humans through the food chain. In this paper, a combination of enzymatic digestion method and SP-ICP-MS analysis was used to quantitatively characterize the enriched AuNPs in mustard and lettuce plants. The results showed that Macerozyme R-10 enzyme can extract AuNPs from plants without obvious aggregation/dissolution. Both mustard and lettuce plants can absorb and enrich the complete AuNPs to the above-ground organs, and the particle number concentrations detected are 1.24 × 107 particles L-1 and 4.39 × 107 particles L-1, respectively. With different exposure level of AuNPs(0.5 mg L-1,), a particle number concentration of 2.32 × 107 particles L-1 was detected in the stems of lettuce plants, while the mustard failed to transport AuNPs to the above-ground organs. The transport efficiency of Au ions by plants is higher than that of AuNPs, and the plants have stronger bioavailability for ions.

[Application of non-stationary phase separation hyphenated with inductively coupled plasma mass spectrometry in the analysis of trace metal-containing nanoparticles in the environment]

环境中金属纳米颗粒的分析检测不仅需要关注其浓度和化学组成,还需要对其形状、粒径和表面电荷等进行表征。此外,环境中金属纳米颗粒的分析需要解决其低赋存浓度以及复杂基质干扰的难题。无固定相分离技术与电感耦合等离子体质谱(ICP-MS)的在线联用,具有较强的颗粒分离能力和较低的元素检出限,能够快速准确地提供金属纳米颗粒的粒径分布、化学组成等信息,在金属纳米颗粒的分离检测方面表现出极大的潜能。但这一联用技术尚无法获得金属纳米颗粒物的颗粒数浓度和单个颗粒的元素信息,难以判断金属纳米颗粒涂层厚度、纯度以及颗粒的均相/异相团聚行为等。新兴的单颗粒-电感耦合等离子体质谱(SP-ICP-MS)与无固定相分离技术的在线联用,可以获得金属纳米颗粒的流体动力学粒径、元素质量计算粒径和颗粒数浓度等信息,进而弥补无固定相分离与ICP-MS在线联用技术的不足。该文介绍了流体动力色谱、毛细管电泳和场流分离3种常用无固定相分离技术的分离机制和适用检测器,着重综述了无固定相分离技术与ICP-MS/SP-ICP-MS在线联用技术的特点及其在环境金属纳米颗粒分析中的应用。关于场流分离,主要介绍了可以与ICP-MS联用的沉降场流分离和流场流分离。该文还对流体动力色谱、毛细管电泳和流场流分离与ICP-MS在线联用技术的特点进行了比较。最后,该文对无固定相分离技术与ICP-MS/SP-ICP-MS在线联用技术的发展提出了展望。

Analysis of selenium nanoparticles in human plasma by capillary electrophoresis hyphenated to inductively coupled plasma mass spectrometry

Nanoparticles (NPs) are increasingly applied in research and development of new therapies. Characterization of NP systems most often include size, shape, size distribution, and charge but information on the chemical stability of NPs and investigation of the presence of dissolved species is most often missing in efficacy studies due to lack of appropriate methods. In this study, a method based on capillary electrophoresis coupled to inductively coupled plasma mass spectrometry (CE-ICP-MS) was established for analysis of selenium (Se) NPs and dissolved Se species in aqueous media. Peak area and migration time precisions (RSD) of 1.4-3.0% and 1.0-2.6%, respectively, were obtained. CE-ICP-MS analysis of a commercially available SeNP suspension (Q-SeNP) revealed large amounts of selenite corresponding to 32% of the total Se content in the suspension, indicating considerable NP degradation upon storage. The CE-ICP-MS method was modified using a coated fused silica capillary in order to analyze SeNPs in human plasma. Peak area and migration time precisions (RSD) in the range of 3.3-10.7% and 0.8-2.8%, respectively, were achieved. Degradation of polyvinyl alcohol (PVA)-coated SeNPs to selenite in human plasma was demonstrated using the modified method. The amounts of SeNP and selenite were estimated based on a correction factor for the ICP-MS signals of PVA-SeNP and dissolved Se. To the best of our knowledge, this is the first study of SeNPs by CE-ICP-MS and highlights the potential of CE-ICP-MS for quantitative characterization of the behavior of SeNPs in biological media.

Contributions of Capillary Electrophoresis in Analytical Nanometrology: A Critical View

An overview on the increasing role of capillary electrophoresis in characterization and direct analysis of nanomaterials is herein presented. The niche of electrophoretic approaches in nanometrology is so relevant that nonmetallic, metal, metal oxide nanoparticles, and quantum dots have been analyzed to be targeted via capillary electrophoresis with conventional detection systems or coupling arrangements aimed at increasing selectivity and sensitivity toward either pristine or conjugated nanoparticles. Moreover, parameters altering intrinsic properties of nanoparticles may be optimized to gather the desired results and identify nanomaterials according to their size, shape, or associations with binding agents. The usefulness and quickness of capillary electrophoresis for quantifying or screening ultrasmall-sized particles enables this technique to set an example for analysis of standards or previously synthesized nanostructures in research or routine laboratories. Abundant evidence of the suitability of electrophoretic approaches for characterization and direct determination of nanomaterials in actual samples has been provided in this review, together with a discussion about hyphenation with state-of-the art detectors and comparison between capillary electrophoresis with other separation approaches. This permits scientific community to be optimistic in the short term.

An ICP-MS-based assay for characterization of gold nanoparticles with potential biomedical use

Most of potential diagnostic and therapeutic nanoparticles fail to reach clinical trials because assessment of their 'drug-like' properties is often overlooked during the discovery stage. This compromises the results of cell culture and animal experiments, making them insufficient to evaluate the lead candidates for testing on patients. In this study, we demonstrate the potential of high-resolution inductively coupled plasma mass spectrometry (ICP-MS) as a nanoparticle qualification tool. Using novel gold nanoparticles stabilized by N-heterocyclic carbenes as test nanoparticles, it was shown that important prerequisites for biomedical applications, such as resistance to the action of human serum milieu or reactivity toward serum biomolecules, can be reliably assessed by recording the signals of gold or sulfur isotopes. Implemented during the screening stage, the method would provide benefits in shortening timelines and reducing cost for selection and initial testing of medicinal nanoparticle candidates.

Inductively coupled plasma mass spectrometry based platforms for studies involving nanoparticle effects in biological samples

The widespread application of nanoparticles (NPs) in recent times has caused concern because of their effects in biological systems. Although NPs can be produced naturally, industrially synthesized NPs affect the metabolism of a given organism because of their high reactivity. The biotransformation of NPs involves different processes, including aggregation/agglomeration, and reactions with biomolecules that will be reflected in their toxicity. Several analytical techniques, including inductively coupled plasma mass spectrometry (ICP-MS), have been used for characterizing and quantifying NPs in biological samples. In fact, in addition to providing information regarding the morphology and concentration of NPs, ICP-MS-based platforms, such as liquid chromatography/ICP-MS, single-particle ICP-MS, field-flow fractionation (asymmetrical flow field-flow fractionation)-ICP-MS, and laser ablation-ICP-MS, yield elemental information about molecules. Furthermore, such information together with speciation analysis enlarges our understanding of the interaction between NPs and biological organisms. This study reports the contribution of ICP-MS-based platforms as a tool for evaluating NPs in distinct biological samples by providing an additional understanding of the behavior of NPs and their toxicity in these organisms.

Joint forces of direct, single particle, CE- and HPLC-inductively coupled plasma mass spectrometry techniques for the examination of gold nanoparticle accumulation, distribution and changes inside human cells

The intracellular localization and transformation of gold nanoparticles (AuNPs) are among the crucial aspects in future applications in cancer therapy. In the context of the study, inductively coupled plasma mass spectrometry (ICP-MS)-based techniques were effectively applied to reveal the fate of AuNPs internalized in cancerous MCF-7 cells. Direct ICP-MS was used to obtain quantitative information about the distribution rate of gold from the AuNPs in the cells, namely their membranes, cytosol as well as nuclei. Moreover, the combination of capillary electrophoresis and reversed-phase liquid chromatography with ICP-MS was used as a tool to probe and compare for the effective monitoring of the speciation changes of the gold-containing forms in the cytosol. The chemical nature (ionic vs. nano) of the metal detected in the cytosol was verified via ICP-MS in a single-particle mode, confirming the stability of the nanomaterials and the absence of ionic gold forms inside the cells.

Capillary electrophoresis-based approaches for the study of affinity interactions combined with various sensitive and nontraditional detection techniques

Nearly all processes in living organisms are controlled and regulated by the synergy of many biomolecule interactions involving proteins, peptides, nucleic acids, nucleotides, saccharides, and small molecular weight ligands. There is growing interest in understanding them, not only for the purposes of interactomics as an essential part of system biology, but also in their further elucidation in disease pathology, diagnostics, and treatment. The necessity of detailed investigation of these interactions leads to the requirement of laboratory methods characterized by high efficiency and sensitivity. As a result, many instrumental approaches differing in their fundamental principles have been developed, including those based on capillary electrophoresis. Although capillary electrophoresis offers numerous advantages for such studies, it still has one serious limitation, its poor concentration sensitivity with the most commonly used detection method-ultraviolet-visible spectrometry. However, coupling capillary electrophoresis with a more sensitive detector fulfils the above-mentioned requirement. In this review, capillary electrophoresis combined with fluorescence, mass spectrometry, and several nontraditional detection techniques in affinity interaction studies are summarized and discussed, together with the possibility of conducting these measurements in microchip format.

Analytical strategy based on asymmetric flow field flow fractionation hyphenated to ICP-MS and complementary techniques to study gold nanoparticles transformations in cell culture medium

An analytical methodology based on asymmetric flow field flow fractionation (AF4) hyphenated to inductively coupled plasma mass spectrometry (ICP-MS) has been developed to study gold nanoparticles (AuNPs) in cell culture medium (Dulbecco's Modified Eagle Medium, DMEM, containing 10% fetal bovine serum, FBS, and antibiotics) used for in vitro toxicological studies. AF4-ICP-MS separation of AuNPs was performed using a regenerated cellulose membrane (molecular weight cut-off, MWCO, of 10 kDa). The carrier composition and the AF4 separation program were optimized. Under the optimum conditions, AuNPs of different types, i.e. phosphate buffered saline (PBS) and citrate stabilized, and sizes (10, 30 and 40 nm), without and with cell culture medium could be separated. The developed method allowed to detect transformations in AuNPs and dissolved gold species (Au³⁺) induced by this medium, such as an increase in the hydrodynamic volume and oxidation. Centrifugal ultrafiltration (CU), transmission electron microscopy (TEM) and Ultraviolet-visible (UV-vis) absorption spectrophotometry have been used as complementary techniques to study these processes. This information is of major interest to have a correct interpretation of the in vitro toxicological studies of NPs, which are more and more demanded due to the increasing concerns about the safe use of these materials and their impacts. This work demonstrates the potential of hyphenated techniques based on AF4 to achieve this relevant information.

Analytical methodology for studying cellular uptake, processing and localization of gold nanoparticles

Interactions of gold nanoparticles (AuNPs) with live cells are known to exert a great impact on their functions, including cell signalling, genomic, proteomic, and metabolomic processes. Modern analytical techniques applied to studying nanoparticle-cell interactions are to improve our understanding of the mode of action of AuNPs, which is essential for their approval in disease therapeutics. Such methods may vary depending on what step of particle internalization is in question, i.e., cellular uptake, intracellular transport (accompanying by changes in the chemical state), translocation to different cell compartments, interaction with relevant subcellular structures and localization. This review focuses on the implementation and critical assessment of advanced analytical methodologies to investigate the cellular processing of AuNPs. Also addressed is a sought-after issue of accounting in in-vitro studies for a chemical form in which the AuNPs enter the cell in vivo.

Quantitation of nonspecific protein adsorption at solid–liquid interfaces for single-cell proteomics

Protein nonspecific adsorption that occurred at the solid–liquid interface has been subjected to intense physical and chemical characterizations due to its crucial role in a wide range of applications, including food and pharmaceutical industries, medical implants, biosensing, and so on. Protein-adsorption caused sample loss has largely hindered the studies of single-cell proteomics; the prevention of such loss requires the understanding of protein–surface adsorption at the proteome level, in which the competitive adsorption of thousands and millions of proteins with vast dynamic range occurs. To this end, we feel the necessity to review current methodologies on their potentials to characterize — more specifically to quantify — the proteome-wide adsorption. We hope this effort can help advancing single-cell proteomics and trace proteomics.

Metallomic study on the metabolism of RAPTA-C and cisplatin in cell culture medium and its impact on cell accumulation

The different extracellular speciation of cisplatin and the organoruthenium developmental anticancer agent RAPTA-C impacts the accumulation in cancer cells.

Cellular processing of gold nanoparticles: CE-ICP-MS evidence for the speciation changes in human cytosol

The cellular uptake of gold nanoparticles (AuNPs) may (or may not) affect their speciation, but information on the chemical forms in which the particles exist in the cell remains obscure. An analytical method based on the use of capillary electrophoresis hyphenated with inductively coupled plasma mass spectrometry (ICP-MS) has been proposed to shed light on the intracellular processing of AuNPs. It was observed that when being introduced into normal cytosol, the conjugates of 10-50 nm AuNPs with albumin evolved in human serum stayed intact. On the contrary, under simulated cancer cytosol conditions, the nanoconjugates underwent decomposition, the rate of which and the resulting metal speciation patterns were strongly influenced by particle size. The new peaks that appeared in ICP-MS electropherograms could be ascribed to nanosized species, as upon ultracentrifugation, they quantitatively precipitated whereas the supernatant showed only trace Au signals. Our present study is the first step to unravel a mystery of the cellular chemistry for metal-based nanomedicines.

CE Separation and ICP-MS Detection of Gold Nanoparticles and Their Protein Conjugates

A full understanding and mediation of nanoparticle-serum protein interactions is key to design nanoparticles with vivid functions within the body, and to solve this problem one needs to differentiate and characterize individual nano-protein conjugates. In this paper, the authors applied capillary electrophoresis combined with inductively coupled plasma mass spectrometry detection to study the behavior of gold nanoparticles of different geometry, size and surface functionalization upon interacting with serum proteins and their mixtures. Due to high-resolution and -sensitivity benefits of this combined technique baseline separations were attained for free nanoparticles (at real-life doses) and different protein conjugates, and the conversion into the protein-bound form was scrutinized in terms of reaction time.

Effects of Gold Salt Speciation and Structure of Human and Bovine Serum Albumins on the Synthesis and Stability of Gold Nanostructures

The present study aimed to investigate the influence of albumin structure and gold speciation on the synthesis of gold nanoparticles (GNPs). The strategy of synthesis was the addition of HAuCl₄ solutions at different pH values (3–12) to solutions of human and bovine serum albumins (HSA and BSA) at the same corresponding pH values. Different pH values influence the GNP synthesis due to gold speciation. Besides the inherent effect of pH on the native structure of albumins, the use N-ethylmaleimide (NEM)-treated and heat-denaturated forms of HSA and BSA provided additional insights about the influence of protein structure, net charge, and thiol group approachability on the GNP synthesis. NEM treatment, heating, and the extreme values of pH promoted loss of the native albumin structure. The formation of GNPs indicated by the appearance of surface plasmon resonance (SPR) bands became detectable from 15 days of the synthesis processes that were carried out with native, NEM-treated and heat-denaturated forms of HSA and BSA, exclusively at pH 6 and 7. After 2 months of incubation, SPR band was also detected for all synthesis carried out at pH 8.0. The mean values of the hydrodynamic radius (RH) were 24 and 34 nm for GNPs synthesized with native HSA and BSA, respectively. X-ray diffraction (XRD) revealed crystallites of 13 nm. RH, XRD, and zeta potential values were consistent with GNP capping by the albumins. However, the GNPs produced with NEM-treated and heat-denaturated albumins exhibited loss of protein capping by lowering the ionic strength. This result suggests a significant contribution of non-electrostatic interactions of albumins with the GNP surface, in these conditions. The denaturation of proteins exposes hydrophobic groups to the solvent, and these groups could interact with the gold surface. In these conditions, the thiol blockage or oxidation, the latter probably favored upon heating, impaired the formation of a stable capping by thiol coordination with the gold surface. Therefore, the cysteine side chain of albumins is important for the colloidal stabilization of GNPs rather than as the reducing agent for the synthesis. Despite the presence of more reactive gold species at more acidic pH values, i.e., below 6.0, in these conditions the loss of native albumin structure impaired GNP synthesis. Alkaline pH values (9–12) combined the unfavorable conditions of denaturated protein structure with less reactive gold species. Therefore, an optimal condition for the synthesis of GNPs using serum albumins involves more reactive gold salt species combined with a reducing and negatively charged form of the protein, all favored at pH 6–7.

A sensitive and versatile method for characterization of protein-mediated transformations of quantum dots

We report the development and application of an analytical system consisting of capillary electrophoresis (CE) interfaced with inductively coupled plasma mass spectrometry (ICP-MS) for sensitive and high-resolution characterization of quantum dots (QDs) interacting with serum proteins. Separation resolution between the intact CdSeS/ZnS QDs and their protein conjugates was optimized by varying the type and concentration of background electrolyte, applied voltage, and sample loading. Special attention was paid to the CE system compatibility with physiological conditions, avoiding aggregation effects, and analyte recovery. Optimization trials allowed for acquiring satisfactory stability of migration times (within 6.0% between different days), peak area precision of 5.2-8.0%, capillary recoveries in the range of 90-96%, and a lower limit of detection of 7.5 × 10(-9) mol L(-1) Cd. With the developed method distinct metal-specific profiles were obtained for the QDs in combination with individual serum proteins, their mixtures, and in human serum. Particularly, it was found that albumin binding to the particle surface is completed after 1 h, without noticeable disruption of the core-shell integrity. The transferrin adsorption is accompanied by the removal of the ZnS shell, resulting in evolving two different metal-protein conjugated forms. On the other hand, proteinization in real-serum environment occurs without binding to major transport proteins, the QDs also lose their the shell (the higher the dose the longer is the time they stay unbroken). The concomitant changes in migration behavior can be attributed to interactions with serum proteins other than albumin and transferrin. Speciation information provided by CE-ICP-MS may shed light on the mechanism of QD delivery to the target regions of the body.