Detection of Axitinib Using Multiwalled Carbon Nanotube-Fe2O3/Chitosan Nanocomposite-Based Electrochemical Sensor and Modeling with Density Functional Theory.

In this study, axitinib (AXI), a potent and selective inhibitor of vascular endothelial growth factor receptor (VEGFR) tyrosine kinase and used as a second-generation targeted drug, was investigated electrochemically under optimized conditions using multiwalled carbon nanotubes/iron(III) oxide nanoparticle-chitosan nanocomposite (MWCNT/Fe2O3@chitosan NC) modified on the glassy carbon electrode (GCE) surface. Characterization of the modified electrode was performed using scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The adsorptive stripping differential pulse voltammetric (AdSDPV) technique was used for the sensitive, rapid, and precise detection of AXI. The current peak obtained with the MWCNT/Fe2O3@chitosan NC modified electrode was 23 times higher compared to the bare electrode. The developed modified electrode showed excellent electrocatalytic activity in AXI oxidation. Under optimized conditions, the effect of supporting electrolyte and pH was investigated, and 0.1 M H2SO4 was chosen as the electrolyte with the highest peak current for the target analyte. In the concentration range of MWCNT/Fe2O3@chitosan NC/GCE, 6 × 10-9 and 1 × 10-6 M, the limit of detection (LOD) and limit of quantification (LOQ) values were calculated to be 0.904 and 0.0301 pM, respectively. Tablet and serum samples were used for the applicability of the developed sensor, relative standard deviation (RSD) values for all samples were below 2%, and the recovery results were 99.23 and 101.84%, respectively. The MWCNT/Fe2O3@chitosan NC/GCE designed to determine AXI demonstrated the applicability, selectivity, precision, and accuracy of the sensor. The mechanism of electron transfer from the modified GCE surface to the analyte solution is studied via modeling the modified GCE surface by the density functional theory (DFT) method at B3LYP/6-311+g(d,p) and M062X/6-31g(d,p) levels. We observed that the iron oxide nanoparticles play an important role in channeling electron flow from the analyte solution to the MWCNT-coated GCE electrode surface. Adsorption of the nanocomposite material onto the GCE surface occurs via strong electrostatic interactions, including ionic and hydrogen bond formations. During the adsorption-controlled oxidation process of the axitinib, the electrons are transferred via the highest occupied molecular orbital (HOMO) localized on the iron oxide moiety to the lowest unoccupied molecular orbital (LUMO) of the MWCNT/GCE surface.

Layer-by-layer self-assembled emerging systems for nanosized drug delivery.

New frontiers in the development of stimuli-responsive surfaces that offer switchable properties according to the end-use application have added a new dimension to the design of drug-delivery systems (DDS). In this respect, layer-by-layer (LbL) self-assembled technologies have attracted interest in nano-DDS (NDDS) design due to the advantage of encapsulating different drug types either individually or in multiple formulations as an easy-to-apply and cost-effective strategy. LbL-based microcapsules and core-shell structures in the form of polyelectrolyte multilayers (PEMs) have been proposed as versatile vehicles for NDDS over the last quarter. This review aims to provide a global view of LbL-PEMs used as templates in NDDS for the last 5 years with an emphasis on emerging drug loading and release strategies.

Innovations in stimuli-responsive surfaces, whose properties can be modified according to end-use application, have opened new doors for the design of drug-delivery systems (DDS). In this context, the layer-by-layer (LbL) method has attracted interest in the preparation of nano-sized DDS (NDDS) due to its low cost and ease of application to load individual or multiple drugs. In the last quarter, microcapsules and core-shell structures prepared by the LbL method, in multilayered form of highly charged particles (polyelectrolyte multilayers; PEMs), have been proposed as vehicles in NDDS. This review aims to provide an overview of LbL-PEMs in NDDS with an emphasis on emerging drug loading and releasing strategies in the last five years.

Slow complexation dynamics between linear short polyphosphates and polyallylamines: analogies with "layer-by-layer" deposits.

Polyelectrolyte "complexes" have been studied for almost a century and find more and more applications in cosmetics and DNA transfection. Most of the available studies focused on the thermodynamic aspects of the "complex" formation, mainly to determine phase diagrams and the influence of diverse physicochemical aspects on the formation of "complexes", but conversely less effort has been given to the kinetics of such processes. We describe herein the "complexation" kinetics of a short linear sodium polyphosphate (PSP) with poly(allylamine hydrochloride) (PAH) in the presence of 10 mM, 0.15 M and 1 M NaCl. We find, by using a combination of physicochemical techniques, that mixtures containing a 1 to 1 molar ratio of phosphate and amino groups allow the formation of "complexes" having a few 100 nm in diameter which progressively grow to particles up to 1.5 microns in hydrodynamic diameter, the growth process being accompanied by some progressive sedimentation. During this slow aggregation kinetics, the polyelectrolytes undergo a release of counterions and the zeta potential changes from a positive value to a negative one of -20 mV which is close to the zeta potential of (PSP-PAH)(n) films deposited under identical physicochemical conditions. Even though the complexes have a negative electrophoretic mobility, they contain an equimolar amount of amino and phosphate groups. This allows us to make some assumption about the structure of such "complexes" and to compare them with other published structures. We will also compare them with the aggregates found during the "layer-by-layer" deposition of the same species under the same conditions.

Step-by-step assembly of self-patterning polyelectrolyte films violating (almost) all rules of layer-by-layer deposition.

Because of its versatility, the layer-by-layer (LBL) assembly method has become a popular tool for preparing multimaterial films, yet astonishingly little is known about the fundamental rules governing their deposition. Here we show an unusual case of self-patterning LBL films made from poly(allylamine hydrochloride) and poly(sodium phosphate). In such films, both the film thickness and the film roughness increase linearly with the number of deposition steps up to a thickness of approximately 60 nm. Even more surprising is the fact that the adsorption of individual "layers" of polyanions and polycations proceeds without a regular inversion of the zeta potential and with the occurrence of a growth instability at approximately 75 layers. These findings underline the need to reconsider the fundamentals of polyelectrolyte multilayer film deposition.