Ester Segal

Oxidation-triggered release of fluorescent molecules or drugs from mesoporous Si microparticles

The fluorescent dye Alexa Fluor 488 or the anticancer drug doxorubicin is attached to the surface and inner pore walls of mesoporous Si particles by covalent attachment, and the oxidation-induced release of each molecule is studied. The molecules are bound to the Si matrix using a 10-undecenoic acid linker, which is attached by thermal hydrosilylation. Loading capacity of the microparticles using this method is approximately 0.5 and 45 mg/g of porous Si microparticle for Alexa Fluor 488 and doxorubicin, respectively. The Si-C-bound assembly is initially stable in aqueous solution, although oxidation of the underlying Si matrix results in conversion to silicon oxide and slow release of the linker-molecule complex by hydrolysis of the Si-O attachment points. When the attached molecule is a fluorophore (Alexa Fluor 488 or doxorubicin), its fluorescence is effectively quenched by the semiconducting silicon matrix. As the particle oxidizes in water, the fluorescence intensity of the attached dye increases due to growth of the insulating silicon oxide layer and, ultimately, dye release from the surface. The recovery of fluorescence in the microparticle and the release of the molecule into solution are monitored in real-time by fluorescence microscopy. Both processes are accelerated by introduction of the oxidizing species peroxynitrite to the aqueous solution. The oxidation-triggered release of the anticancer drug doxorubicin to HeLa cells is demonstrated.

Polymerization of aniline in the presence of DBSA in an aqueous dispersion

Abstract This paper describes a unique process of polymerization in an aqueous medium of an anilinium–dodecyl benzene sulfonic acid (DBSA) complex obtained by reacting aniline with DBSA prior to polymerization. The typical properties of the complex, appearing as fine needles, have been characterized and its polymerization behavior in the presence of DBSA upon addition of ammonium peroxydisulfate in an aqueous medium was investigated by visual color inspection, UV-VIS spectroscopy and pH measurements. The polymerization process was interrupted at different stages and polyaniline (PANI) powders were obtained by precipitation with methanol. The powders morphology was investigated using scanning electron microscopy (SEM) and their electrical conductivity was measured on compression molded strips. UV-VIS and pH measurements show that the average oxidation state of the formed PANI chains vary during polymerization from doped pernigraniline to doped emeraldine and correlate with the dispersions color. In the beginning of the polymerization course, the SEM studies show agglomerates consisting of spherical PANI particles. As polymerization proceeds, the voids among these particles are filled, forming a smooth surface of the PANI agglomerates. Simultaneously, the conductivity of the PANI powders increases with the polymerization time.

Polyaniline–DBSA/polymer blends prepared via aqueous dispersions

Abstract Stable polyaniline–dodecyl benzene sulfonic acid (PANI–DBSA) aqueous dispersions were obtained by a unique method of aniline polymerization in the presence of DBSA, through an anilinium–DBSA complex appearing as solid needle-like particles, in an aqueous medium. The average size of the PANI primary particles, determined by small angle X-ray scattering (SAXS), is 18.7 nm. These primary particles form aggregates, which further cluster into ∼50 μm agglomerates. PANI–DBSA/polymer blends were obtained by mixing an aqueous PANI–DBSA dispersion with an aqueous emulsion of the matrix polymer, followed by water evaporation. These blends exhibit electrical conductivity already at a very low PANI–DBSA content (0.5 wt.%). The conductivity level of the various blends depends on the PANI content, on the surfactant present in the polymer matrix emulsion, and it is practically independent of the polymer matrix nature. Thus, a similar structuring mechanism prevails in these blends, irrespective of the polymer matrix (contrary to solution and melt blends). The PANI–DBSA particles strongly segregate within the polymer matrix, already in the combined aqueous dispersion, and upon drying, a very fine conductive network is formed. This strong segregation tendency leads to a conductive network formation already at low PANI–DBSA contents, thus generating the conductive blends.

Electrically conductive composites based on epoxy resin with polyaniline-DBSA fillers

A conductive epoxy-anhydride system containing polyaniline (PANI)-dodecylbenzenesulfonic acid (DBSA) has been developed and characterized. Two forms of PANI-DBSA, powder and paste (containing excess DBSA), have shown that excess DBSA in the paste contributes to improved dispersion of PANI-DBSA in the resin, and thus a lower percolation threshold is found. Excess DBSA, however, retards the curing reaction of epoxy/hardener system, but this deficiency can be remedied by using higher accelerator concentrations. Similar trends were found by incorporation of PANI-DBSA coated mica particles, however, the PANI-DBSA engulfed mica particles result in a much lower percolation threshold compared to the PANI-DBSA powder or paste. SEM observation provides useful information for understanding the conductivity behavior of the conductive epoxy systems. Significantly different morphologies are observed for the PANI-DBSA powder and paste dispersed in the epoxy matrix.

Mechanism of erosion of nanostructured porous silicon drug carriers in neoplastic tissues

Nanostructured porous silicon (PSi) is emerging as a promising platform for drug delivery owing to its biocompatibility, degradability and high surface area available for drug loading. The ability to control PSi structure, size and porosity enables programming its in vivo retention, providing tight control over embedded drug release kinetics. In this work, the relationship between the in vitro and in vivo degradation of PSi under (pre)clinically relevant conditions, using breast cancer mouse model, is defined. We show that PSi undergoes enhanced degradation in diseased environment compared with healthy state, owing to the upregulation of reactive oxygen species (ROS) in the tumour vicinity that oxidize the silicon scaffold and catalyse its degradation. We further show that PSi degradation in vitro and in vivo correlates in healthy and diseased states when ROS-free or ROS-containing media are used, respectively. Our work demonstrates that understanding the governing mechanisms associated with specific tissue microenvironment permits predictive material performance.

Label-free optical biosensors based on aptamer-functionalized porous silicon scaffolds.

A proof-of-concept for a label-free and reagentless optical biosensing platform based on nanostructured porous silicon (PSi) and aptamers is presented in this work. Aptamers are oligonucleotides (single-stranded DNA or RNA) that can bind their targets with high affinity and specificity, making them excellent recognition elements for biosensor design. Here we describe the fabrication and characterization of aptamer-conjugated PSi biosensors, where a previously characterized his-tag binding aptamer (6H7) is used as model system. Exposure of the aptamer-functionalized PSi to the target proteins as well as to complex fluids (i.e., bacteria lysates containing target proteins) results in robust and well-defined changes in the PSi optical interference spectrum, ascribed to specific aptamer-protein binding events occurring within the nanoscale pores, monitored in real time. The biosensors show exceptional stability and can be easily regenerated by a short rinsing step for multiple biosensing analyses. This proof-of-concept study demonstrates the possibility of designing highly stable and specific label-free optical PSi biosensors, employing aptamers as capture probes, holding immense potential for application in detection of a broad range of targets, in a simple yet reliable manner.

Picking up the pieces: a generic porous Si biosensor for probing the proteolytic products of enzymes.

A multifunctional porous Si biosensor that can both monitor the enzymatic activity of minute samples and allow subsequent retrieval of the entrapped proteolytic products for mass spectrometry analysis is described. The biosensor is constructed by DNA-directed/reversible immobilization of enzymes onto a Fabry-Pérot thin film. We demonstrate high enzymatic activity levels of the immobilized enzymes (more than 80%), while maintaining their specificity. Mild dehybridization conditions allow enzyme recycling and facile surface regeneration for consecutive biosensing analysis. The catalytic activity of the immobilized enzymes is monitored in real time by reflective interferometric Fourier transform spectroscopy. The real-time analysis of minute quantities of enzymes (concentrations at least 1 order of magnitude lower, 0.1 mg mL(-1), in comparison to previous reports, 1 mg mL(-1)), in particular proteases, paves the way for substrate profiling and the identification of cleavage sites. The biosensor configuration is compatible with common proteomic methods and allows for a successful downstream mass spectrometry analysis of the reaction products.

On the structure and electrical conductivity of polyaniline/polystyrene blends prepared by an aqueous‐dispersion blending method

This article describes electrically conductive polymer blends containing polyaniline-dodecyl benzene sulfonic acid (PANI-DBSA) dispersed in a polystyrene (PS) matrix or in crosslinked polystyrene (XPS). Melt blending of previously mixed, coagulated, and dried aqueous dispersions of PANI-DBSA and PS latices lead to high conductivities at extremely low PANI-DBSA concentrations (∼0.5 wt % PANI-DBSA). In these blends, the very small size of the PANI-DBSA particles and the surface properties (with surfactants used) of both the PANI and polymer particles play a major role in the PANI-DBSA particle structuring process. The PANI-DBSA behavior is characteristic of a unique colloidal polymeric filler with an extremely high surface area and a strong interaction with the matrix, evidenced by a significantly higher glass-transition temperature of the matrix. The effect of the shear level on the conductivity and morphology of the PS/PANI-DBSA blends was studied by the production of capillary rheometer filaments at various shear rates. An outstanding result was found for XPS/PANI-DBSA blends prepared by the blending of aqueous XPS and PANI-DBSA dispersions. Some of these blends were insulating at low shear levels; however, above a certain shear level, smooth surface filaments were generated, with dramatically increased and stable conductivities.

Engineering porous silicon nanostructures as tunable carriers for mitoxantrone dihydrochloride

Nanostructured porous silicon (PSi) thin films, fabricated by the electrochemical anodization of single crystalline Si wafers, are studied as delivery systems for the anticancer drug mitoxantrone dihydrochloride (MTX). The surface chemistry of the PSi carriers was tailored by surface alkylation using thermal hydrosilylation of 1-dodecene and undecylenic acid, followed by physical adsorption or covalent attachment of MTX to the Si scaffold. The nanostructure and the physiochemical properties of the different carriers were characterized by attenuated total reflectance Fourier transform infrared spectroscopy, nitrogen adsorption-desorption and contact angle measurements, demonstrating that surface alkylation results in a pronounced effect on the hydrophobicity/hydrophilicity of the scaffolds and a volumetric gain in pore wall, which in turn results in a decrease in pore diameter (>23%) and available porous volume (>40%). The effect of these key parameters on MTX loading efficacy, release profile, Si scaffold erosion kinetics and in vitro cytotoxicity on human breast carcinoma (MDA-MB-231) cells was studied and compared to the behavior of neat PSi carriers. We show that the chemically modified PSi carriers exhibit sustained release for several days to weeks with minimal to no burst effect, while for the native PSi MTX release was completed within 5h with a substantial burst release of ~40%. Moreover, our in vitro cytotoxicity experiments have clearly demonstrated that the MTX released from all PSi carriers maintained its cytotoxic effect towards MDA-MB-231 cells, in comparison to the low toxicity of the PSi carriers.

Structured electrically conductive polyaniline/polymer blends

This paper describes electrically conductive polymer blends consisting of polyaniline (PANI) dispersed in a polymer matrix. Melt blending of previously mixed, coagulated and dried aqueous dispersions of PANI and the polymer matrix lead to high conductivities at extremely low PANI concentrations (∼0.5 wt% PANI). In these blends the surface properties (surfactants used) of the PANI and the polymer particles play a major role in the structuring process, in addition to the very small size of the PANI particles. In another approach, i.e. conventional melt blending of PANI powder with a given polymer powder, the success of generating an efficient conductive network depends on the PANI/polymer interaction level. A high interaction level (for example, similar solubility parameters) leads under dynamic hot blending conditions to the formation of conductive networks, but still at relatively high PANI concentration (>10 wt% PANI). To further reduce the PANI conductivity threshold concentration, ternary PANI/polymer/polymer blends can be designed, in which PANI is selectively attracted to the minor polymer component, thus generating double-percolation structures. The threshold PANI concentration in the ternary blends may be reduced by a factor of ∼2 compared to the binary blends. Further reduction can be expected in special ternary blends designed so that the PANI particles will mostly locate at the interfaces, rather than within the dispersed minor polymer particles. The blending method of aqueous dispersions is limited to matrix polymers which can be synthesized by emulsion polymerization. Thus, the conventional melt blending procedure and also the formation of ternary blend systems are particularly beneficial for condensation-type polymers, whereas melt blending of PANI/polymer powders prepared by the aqueous dispersions method is beneficial for the addition-type polymers. Copyright