Ihor Tokarev

Stimuli-responsive hydrogel thin films

In this brief review we address a range of interesting applications and prospects of responsive hydrogel thin films for the fabrication of “smart” responsive surfaces, membranes, sensors with various transduction mechanisms, micro/nanoactuators, and capsules. We show that hydrogel thin films compete with grafted polymers and demonstrate strong advantages for the fabrication of robust multifunctional and multiresponsive surfaces. This article reviews recent publications on the synthesis of responsive hydrogel thin films and hybrid films with entrapped nanoparticles and reagents by the chemical crosslinking of reactive polymers, layer-by-layer deposition, and block-copolymer self-assembly, as well as examining those publications to determine a range of applications.

Stimuli‐Responsive Porous Hydrogels at Interfaces for Molecular Filtration, Separation, Controlled Release, and Gating in Capsules and Membranes

A continuously growing area of controlled and tunable transport and separation of biomolecules and drugs has recently attracted attention to the structures which can be referred to as stimuli-responsive porous hydrogel thin films. Because of spatial constraints, swelling/shrinking of the hydrogel films results in closing/opening (or vice versa) of the films pores. Such responsive systems can be used in the configuration of plane films or capsules. The combination of a low thickness (translating into a low hydrodynamic flow resistance and rapid response) with well-defined size and shape of pores (translating into better control of transport and separation), which can be closed, opened, or tuned by an external signal (allowing a large amplitude of changes in diffusivity of solutes in the thin film and a precise control of the pore size), makes these materials very attractive for a range of applications, such as molecular filtration, separation, drug delivery, sensors, and actuators.

Molecular-engineered stimuli-responsive thin polymer film: a platform for the development of integrated multifunctional intelligent materials

The area of stimuli-responsive thin polymer films (brushes, layer-by-layer multilayered structures, networks, and hybrid systems with inorganic particles) is discussed in this article with the major focus on the properties and potential applications for sensors, smart coatings, miniaturized devices, and hierarchically assembled multifunctional systems. We suggest directions for further expansion of this area using all aspects of the mechanism of response (transduction, dynamics, selectivity, sensitivity, and amplifications) and combinations of different thin film structural designs.

Electrochemically controlled drug-mimicking protein release from iron-alginate thin-films associated with an electrode.

Novel biocompatible hybrid-material composed of iron-ion-cross-linked alginate with embedded protein molecules has been designed for the signal-triggered drug release. Electrochemically controlled oxidation of Fe(2+) ions in the presence of soluble natural alginate polymer and drug-mimicking protein (bovine serum albumin, BSA) results in the formation of an alginate-based thin-film cross-linked by Fe(3+) ions at the electrode interface with the entrapped protein. The electrochemically generated composite thin-film was characterized by electrochemistry and atomic force microscopy (AFM). Preliminary experiments demonstrated that the electrochemically controlled deposition of the protein-containing thin-film can be performed at microscale using scanning electrochemical microscopy (SECM) as the deposition tool producing polymer-patterned spots potentially containing various entrapped drugs. Application of reductive potentials on the modified electrode produced Fe(2+) cations which do not keep complexation with alginate, thus resulting in the electrochemically triggered thin-film dissolution and the protein release. Different experimental parameters, such as the film-deposition time, concentrations of compounds and applied potentials, were varied in order to demonstrate that the electrodepositon and electrodissolution of the alginate composite film can be tuned to the optimum performance. A statistical modeling technique was applied to find optimal conditions for the formation of the composite thin-film for the maximal encapsulation and release of the drug-mimicking protein at the lowest possible potential.

Gold‐Nanoparticle‐Enhanced Plasmonic Effects in a Responsive Polymer Gel

Localized surface plasmon resonance excited in gold nanoparticles coupled with a responsive polymer gel is explored. A specially designed structure (vertically aligned cylindrical pores decorated with gold nanoparticles) of responsive polymer gel thin films allows for the transduction of external signal/ stimuli into a strong optical effect enhanced by interactions of gold nanoparticles.

Tunable plasmonic nanostructures from noble metal nanoparticles and stimuli-responsive polymers

The review describes the progress in the field of tunable plasmonic nanostructured materials based on the combination of noble metal (typically gold or silver) nanoparticles and stimuli-responsive polymers acting as interparticle linkers. This combination enables the transduction of chemical and physical forces into an optical signal, arising from the localized surface plasmon resonance (LSPR) and plasmon coupling effects in metal nanoparticles and their aggregates. We briefly overview the existing designs of such tunable plasmonic nanostructures, discuss their advantages and shortcomings, demonstrate possible applications in optical sensors, biosensors, and various miniaturized devices and systems, and conclude with future prospects.

Specific Biochemical-to-Optical Signal Transduction by Responsive Thin Hydrogel Films Loaded with Noble Metal Nanoparticles

2010 WILEY-VCH Verlag Gmb This Communication concerns the combination of three distinct phenomena—a biocatalytic process, localized surface plasmon resonance (LSPR) effects in noble metal nanoparticles, and the swelling–shrinking transition in a stimuli-responsive hydrogel— with the aim to create a novel sensing platform for two important applications: analysis of biomolecules (biosensors) and probing (monitoring) of local properties of biomaterials. The above combination allowed us to realize an efficient biochemicalto-optical signal transduction scheme, possessing high specificity and diminishing the impact of nonspecific interactions. LSPR effects in noble metal nanoparticles are observed through a color by the naked eye or in a transmission visible spectrum that reveals characteristic absorbance bands. The LSPR absorption is much more pronounced compared to organic dyes. Furthermore, LSPR spectra are sensitive to the immediate particle environment. In particular, changes in the refractive index of the environment in the close vicinity to the particle surface or in the interparticle plasmon coupling result in the alternation of the spectrum (i.e., changes in position, width, and intensity of the extinction bands). The sensitivity of LSPR spectra to the immediate environment has been recently explored for bioanalytical applications. In these studies, biomolecules (DNA or antibodies) were immobilized onto noble metal nanoparticles. Then, the biorecognition events were detected through changes in the chemical composition occurring on the surfaces of colloidal nanoparticles or supported nanoparticle arrays (nanoislands). In some studies, the hybridization events were detected through the reversible aggregation of dispersed noble metal nanoparticles capped with the complementary oligonucleotides; the aggregation was accompanied by plasmon coupling among the particles and led to noticeable changes in the color of the dispersion. One of the most important advantages of LSPR spectroscopy is the high stability and biocompatibility of the noble metal nanoparticles compared to organic dyes and quantum dots. Alternatively, the changes in LSPR spectra of the nanoparticles can be tuned by a stimuli-responsive polymeric material. For example, swelling–shrinking of a polymer network (gel) or a monolayer of polymer chains tethered to a transparent substrate may lead to changes in the local refractive index of gold or silver nanoparticles entrapped in the polymeric material or/and in the average interparticle distance. In previous studies, the swelling transitions in responsive polymeric materials were initiated by changes in the pH and temperature of aqueous media. Hence, the transformations of chemical and physical signals into the optical effect were used for analytical applications. In this work, we extend the analytical potential of plasmonic sensing devices based on the combination of noble metal nanoparticles and stimuli-responsive polymeric materials by coupling them with highly specific enzymatic reactions. To date, numerous sensing platforms have been demonstrated on the basis of biocatalytic processes. Many of them were realized for measuring glucose levels in blood by using catalytic oxidation of glucose in the presence of glucose oxidase (GOx) and detecting the pH changes produced in the course of this enzymatic reaction. Here, we explore this approach in a novel plasmonic sensing platform. One of the major issues in biosensors is that, being applied for analysis of biological fluids, such as blood, they produce a false response caused by fouling of the sensing elements with proteins. We overcome this problem in the proposed material. Besides biosensing, another important application of the developed approach is in situ probing of materials, where the changes in optical properties are used to extract the information about local changes in the material structure or properties (e.g., the degree of swelling). The latter is especially important for biomaterials used in nonequilibrium conditions. For example, biodegradable implants or scaffolds for tissue engineering may experience local changes in the pH or concentrations of various ions. In particular, this may happen when pH changes induced by products of degradation (e.g., lactic acid) are too rapid to be equilibrated by physiological mechanisms. Measuring changes in the local structure and properties of responsive materials coupled with LSPR effects provides valuable information for understanding their dynamic behavior and can also be used to remotely and noninvasively monitor the material’s state. The plasmonic sensing platform, depicted in Figure 1, consists of a transparent glass support decorated with silver nanoislands ca. 12–14 nm thick (3), a 20–25 nm, pH-responsive, hydrogel thin film (1), and silver nanoparticles (2) encapsulated in the film. The film thickness is chosen in such a way that the Ag nanoparticles are confined in the immediate vicinity to the nanoislands, thus enabling their efficient plasmon coupling. The particles are completely encapsulated by the hydrogel in the sense that they are

Superomniphobic Magnetic Microtextures with Remote Wetting Control

Universal remote control of wetting behavior enabling the transition from a superomniphobic to an omniphilic wetting state in an external magnetic field via the alternation of reentrant curvature of a microstructured surface is demonstrated. This reconfigurable microtexture made of Ni micronails repels water, water-surfactant solutions, and practically all organic liquids, whereas it gets wetted by all of these liquids after a magnetic field pulse is applied.

Ultrathin molecularly imprinted polymer sensors employing enhanced transmission surface plasmon resonance spectroscopy

An ultrathin novel nanosensor (31.5 +/- 4.1 nm thick in the absence of analytes), employing a molecularly imprinted polymer as a recognition element for cholesterol and gold nanoparticle enhanced transmission surface plasmon resonance spectroscopy for detection, was constructed.

Field-Directed Self-Assembly with Locking Nanoparticles

A reversible locking mechanism is established for the generation of anisotropic nanostructures by a magnetic field pulse in liquid matrices by balancing the thermal energy, short-range attractive and long-range repulsive forces, and dipole-dipole interactions using a specially tailored polymer shell of nanoparticles. The locking mechanism is used to precisely regulate the dimensions of self-assembled magnetic nanoparticle chains and to generate and disintegrate three-dimensional (3D) nanostructured materials in solvents and polymers.