Quantitative detection of eryptosis in human erythrocytes using tunable resistive pulse sensing and annexin-V-beads.

Toxicological assessments of human red blood cells (RBCs) are important in human health because RBCs are the most abundant cell type in our body. Erythrotoxicology testing guidelines using hemolysis have been established as a standard (e.g. by the ASTM International). However, many xenobiotics promote eryptosis (apoptosis in human RBCs) without causing hemolysis. Based on the major features of eryptosis, i.e. cell shrinkage and translocation of phosphatidylserine (PS) to the outer lipid bilayer of the plasma membrane, we report here a novel approach utilizing the quantitative tunable resistive pulse sensing (TRPS) technology, a widely adopted technique for characterizing nanoparticles in the field of nanotechnology, to measure the degree of eryptosis in a non-optical manner. With the TRPS system, we were able to determine PS externalization with microbeads functionalized with annexin-V for PS binding, cell swelling and shrinkage in physiological buffers (cell volume: 86 ± 12 fL) and solutions of different osmolarities with or without apoptotic trigger. After setting these standards, we then evaluated the toxicity of Polyphyllin D (PD), a potential anti-cancer drug that kills more liver cancer cells with multi-drug resistance, in erythrocytes to prove our concept. Data revealed that PD induced PS externalization and shrinkage in RBCs in a dose-dependent manner. Moreover, another feature of eryptosis, as small as 5 fL, was detected thus showing the PD-induced erythrotoxicity in human cells. Taken together, our results indicate that our approach using annexin-V-beads and TRPS is simple, safe and convenient, using only a small volume (35 µL) to evaluate the erythrotoxicity of xenobiotics.

Two-component mixed and patterned films on carbon surfaces through the photografting of arylazides.

Organic films have been grafted to glassy carbon surfaces by the photolysis of arylazides. Atomic force microscopy and electrochemical measurements reveal that the films are loosely packed. The methodology was expanded to prepare two-component thin films incorporating either a reactive tether species and a nonreactive background film or two different reactive tethers. Strategies were developed to generate both continuous mixed films and surfaces presenting patterns of two components. For patterning, the arylazide derivative was grafted onto previously modified glassy carbon surfaces. In this case, the first modification step is not limited to photografting, which increases the scope of the methods. For all grafted surfaces, the reactivity of tether species was confirmed by coupling electroactive targets to the tethers, followed by electrochemical monitoring. The ease of preparing surfaces with spatially controlled functionality offers promise for the design of sensing platforms on graphitic carbon substrates.

An electrochemical and XPS study of reduction of nitrophenyl films covalently grafted to planar carbon surfaces.

Nitrophenyl (NP) films were grafted to glassy carbon and pyrolyzed photoresist films by electroreduction of the corresponding diazonium salt. The as-prepared, multilayered films were examined using electrochemistry and X-ray photoelectron spectroscopy (XPS). Electrochemical analysis confirmed the absence of electrooxidizable groups whereas XPS showed approximately 35% of N was present in a reduced form. The reduced N is assigned to azo groups, which are known to be electroinactive in the film environment. NP films were reduced electrochemically in three media and also by chemical reduction in ethanolic disodium sulfide. The concentrations of aminophenyl and hydroxylaminophenyl groups produced by each method were estimated electrochemically, and the relative amounts of unreacted NP groups were established from XPS measurements. Aminophenyl is the major product for all reduction methods, and Na2S gives the cleanest and most complete conversion to aminophenyl groups, with less than 5% residual NP. Reduced NP films were reacted with carboxylic acid and acid chloride derivatives; the highest yield of electroactive-coupled product was obtained for a film electroreduced in H2SO4 and reacted with acid chloride. The detailed electrochemical and XPS analysis reveals the limitations of electrochemistry for determining the composition of these films.

Photochemical grafting and activation of organic layers on glassy carbon and pyrolyzed photoresist films.

Organic films have been grafted to polished glassy carbon (GC) and as-prepared pyrolyzed photoresist film (PPF) by photolysis of alkenes and an alkyne. The alkene or alkyne is spin-coated onto the carbon surface and photolyzed in air at 254 nm. Characterization by water contact angle measurements, depth profiling and surface roughness measurements using atomic force microscopy (AFM), and electrochemistry reveal that for most modifiers a loosely packed monolayer is grafted to the surface. Grafted layers of 1-decene were further reacted by drop-coating with oxalyl chloride and photolyzing at 254 nm in air. The procedure adds acid chloride groups to the film. Amines were attached to these films via amide bond formation, and were characterized by electrochemistry and assembly of citrate-capped gold nanoparticles. Amines were also coupled to photografted 1-undecylenic acid layers and to carboxyphenyl layers prepared by electroreduction of the corresponding diazonium salt. Quantitative analysis using electrochemistry established that the highest concentration of amines was attached to the oxalyl chloride treated film, and that a higher concentration of amines was attached via reaction with the photografted 1-undecylenic acid layer than the electrografted carboxyphenyl layer. Thus photografting and photoreaction with oxalyl chloride are simple methods for generating amine-reactive tethers on GC and PPF surfaces.

Effect of applied potential on arylmethyl films oxidatively grafted to carbon surfaces.

Arylmethyl films have been grafted to glassy carbon surfaces and to pyrolyzed photoresist films (PPFs) by electrochemical oxidation of 1-naphthylmethylcarboxylate and 4-methoxybenzylcarboxylate. Atomic force microscopy (AFM) and electrochemistry were used to characterize the as-prepared films and to monitor changes induced by post-preparation treatments. Film thickness was measured by depth profiling using an AFM tip to remove film from the PPF surface. Surface coverage of electroactive modifiers was estimated from cyclic voltammetry, and monitoring the response of a solution-based redox probe at grafted surfaces gave a qualitative indication of changes in film properties. For preparation of the films, the maximum film thickness increased with the potential applied during grafting, and all films were of multilayer thickness. The apparent rate of electron transfer for the Fe(CN)(6)3-/Fe(CN)(6)4- couple was very low at as-prepared films. After film-grafted electrodes were transferred to pure acetonitrile-electrolyte solution and subjected to negative potential excursions, the response of the Fe(CN)(6)3-/Fe(CN)(6)4- couple changed and was consistent with faster electron-transfer kinetics, the film thickness decreased and the surface roughness increased substantially. Applying a positive potential to the treated film reversed changes in film thickness, but the voltammetric response of the Fe(CN)(6)3-/Fe(CN)(6)4- couple remained kinetically fast. After as-prepared films were subjected to positive applied potentials in acetonitrile-electrolyte solution, the apparent rate of electron transfer for the Fe(CN)(6)3-/Fe(CN)(6)4- couple remained very slow and the measured film thickness was the same or greater than that before treatment at positive potentials. Mechanisms are considered to explain the observed effects of applied potential on film characteristics.