Characterizing how platinum metallocomplexes bind to human serum albumin (HSA) is essential in evaluating anticancer drug candidates. Using cisplatin as a reference complex, the application of capillary electrophoresis (CE) to reliably assess drug/HSA interactions was validated. Since this complex is small compared to the size of the protein, the binding response could only be recognized when applying CE coupled to a (platinum) metal-specific mode of detection, namely inductively coupled plasma-mass spectrometry (ICP-MS). This coupling allowed for confirmation of a specific affinity of cisplatin and novel Pt complexes to HSA, measurement of the kinetics of binding reactions, and determination of the number of drug molecules attached to the protein. As the cisplatin/HSA molar ratio increased, the reaction rate became faster with a maximum on the kinetic curve appearing at about 50 h of incubation at 20 times excess of cisplatin. The reaction was characterized as a pseudo-first order reaction with the rate constant k = 0.003 min(-1) at 37 degrees C. When incubated with a 20-fold excess of cisplatin, HSA bound up to 10 mol of Pt per mol of the protein. This is indicative for a strong metal-protein coordination occurring at several HSA sites other than the only protein cysteine residue. Structural analogs of cisplatin, bearing aminoalcohol ligands, showed comparable protein binding reactivity and stoichiometry but a common equilibrium was not reached even after one week of incubation. Also apparent was a two-step mechanism of the binding reaction. Results demonstrated the suitability of CE-ICP-MS as a rapid assay for high-throughput studying of drug/HSA interactions.

In the present work, CdSe nanocrystals (NCs) synthesized with a trioctylphosphine surface passivation layer were modified using amphiphilic molecules to form a surface bilayer capable of providing stable NCs aqueous solutions. Such modified nanocrystals were used as a test solute in order to analyze new electrophoretic phenomena, by applying a micellar plug as a separation tool for discriminating nanocrystals between micellar and micelle-free zones during electrophoresis. The distribution of NCs between both zones depended on the affinity of nanocrystals towards the micellar zone, and this relies on the kind of surface ligands attached to the NCs, as well as electrophoretic conditions applied. In this case, the NCs that migrated within a micellar zone can be focused using a preconcentration mechanism. By modifying electrophoretic conditions, NCs were forced to migrate outside the micellar zone in the form of a typical CZE peak. In this situation, a two-order difference in separation efficiencies, in terms of theoretical plates, was observed between focused NCs (N ~ 107) and a typical CZE peak for NCs (N ~ 105). By applying the amino-functionalized NCs the preconcentration of NCs, using a micellar plug, was examined, with the conclusion that preconcentration efficiency, in terms of the enhancement factor for peak height (SEFheight) can be, at least 20. The distribution effect was applied to separate CdSe/ZnS NCs encapsulated in silica, as well as surface-modified with DNA, which allows the estimation of the yield of conjugation of biologically active molecules to a particle surface.FigureMicellar plug as a tool to separate nanoparticles: nanocrystals coated with an ionic surfactant form a pseudomicellar system with a non-ionic surfactant. Appling this system in the form of a plug, in capillary electrophoresis, nanocrystals preconcentration within a plug or release from a plug, depending on applied conditions, were observed. This was used to discriminate particles vs. particles bioconjugated with aptamerElectronic supplementary materialThe online version of this article (doi:10.1007/s00216-011-4650-y) contains supplementary material, which is available to authorized users.

Metal-based nanoscale particles possess unique optoelectronic or magnetic properties that make them highly promising as imaging agents in cancer therapy research. The fate of nanoparticles in vivo and particularly, the delivery to tumours are closely related to their interactions with plasma proteins. Furthermore, proteins can be used to modify the nanoparticle surface in order to facilitate active targeting to tumours. Therefore, there is an ongoing need for new and more capable analytical methodologies to characterize the protein-nanoparticle binding. Due to the small-sample volume requirement, high degree of resolution and, most importantly, mild, species-friendly separation conditions, capillary electrophoresis (CE) is gaining increasing popularity in the analysis of protein-nanoparticle interaction. This perspective article highlights the potential of CE in studying reactions associated with protein-mediated transformations of nanoparticles, with the focus on quantum dots, gold and iron oxide nanoparticles. Different ways by which CE can be applied to such monitoring are summarized and critically assessed using a representative coverage of recent publications.

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The feasibility of using gold electrodes modified with short-chain ssDNA oligonucleotides for determination of uranyl cation is examined. Interaction between UO22+ and proposed recognition layer was studied by means of voltammetric and quartz crystal microbalance measurements. It was postulated that ssDNA recognition layer functions via strong binding of UO22+ to phosphate DNA backbone. The methylene blue was used as a redox marker for analytical signal generation. Biosensor response was based on the difference in electrochemical signal before and after subjecting it to sample containing uranyl ion. The lower detection limit of 30 nmol L−1 for UO22+ was observed for a sample incubation time of 60 min. Proposed ssDNA-modified electrodes demonstrated good selectivity towards UO22+ against common metal cations, with only Pb2+ and Ca2+ showing considerable interfering effect.

We have developed a capillary electrophoresis method to characterize the QD surface ligand interactions with various surfactant systems. The method was demonstrated with 2-5 nm CdSe nanoparticles surface-passivated with trioctylphosphine oxide (TOPO).Water solubility was accomplished by surfactant-assisted phase transfer via an oil-in-water microemulsion using either cationic, anionic, or non-ionic surfactants. Interaction between the QD surface ligand (TOPO) and the alkyl chain of the surfactant molecule produces a complex and dynamic surface coating that can be characterized through manipulation of CE separation buffer composition and capillary surface modification. Additional characterization of the QD surface ligand interactions with surfactants was accomplished by UV-VIS spectroscopy, photoluminescence, and TEM. It is anticipated that studies such as these will elucidate the dynamics of QD surface ligand modifications for use in sensors.

The CdSe quantum dots (QDs) with bidentate ligands: a-diimine (NN) and dihydrolipoic acid (DHLA) were synthesized and characterized by UV-Vis, particle size and capillary electrophoretic techniques. Two systems were analyzed: CdSe with one ligand (CdSe/ligand) and CdSe with two different ligands (CdSe//ligand1/ligand2), where ligand = α-diimine or DHLA. Hydrodynamic features of functionalized QDs were characterized by zone capillary electrophoretic (CZE), and particle size techniques and these methods were consistent. It was established that CZE, micellar (MEKC) and microemulsion (MEEKC) modes were suitable for separating charged CdSe QDs and that no peaks were obtained for QDs passivated with electrically neutral ligands. For CdSe QDs with neutral (NN) ligands, a preconcentration method with the use of a micellar plug was introduced for visualizing these QDs. A sharp peak representing neutral QDs was obtained within the zone of micellar plug of a non-ionic surfactant, Here, a ligand character used for CdSe modification and the type of the electrophoretic method applied were the determining factors for the QDs peak visualization. Moreover, examples of visualization of charged and neutral QDs on the same run were presented, and for this purpose, dual mechanism (separation/preconcentration) was proposed.

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