Yevgeniya Kalachyova

Polymethylmethacrylate doped with porphyrin and silver nanoparticles as light-activated antimicrobial material

Light-activated antimicrobial materials based on polymethylmethacrylate doped with porphyrin and silver nanoparticles were prepared and studied. The inspiration for the material design originates from photodynamic therapy where light is used to destroy pathogen microbes. Antimicrobial response of the materials is controlled by blue light illumination. Porphyrin molecules serve as light absorbers with dual antimicrobial response under illumination they produce reactive oxygen and affect the kinetics of silver release from the polymer. Silver is responsive for the antimicrobial effect, for the protection of porphyrin against photobleaching and for the conservation of energy through suppression of porphyrin luminescence. Triggerable and enhanced antimicrobial response of the material is activated through several possible mechanisms, including local heating of the polymer matrix, transfer of the excited state from porphyrin to silver and the synergetic effect of reactive oxygen and silver. In a passive state the material exhibits weak antimicrobial response against Gram-negative bacteria. In an active state, however, it is fatal for both Gram negative and Gram positive bacteria.

Silver nanostructures: From individual dots to coupled strips for the tailoring of SERS excitation wavelength from near-UV to near-IR

In this paper, we report the preparation of silver nanostructures with plasmon absorption peaks tuned by the metal arrangement. Silver nanostructures were prepared by sputtering onto a patterned polymer surface. A surface polymer grating was achieved by modification with an excimer laser. Depending on the amount of deposited silver, randomly distributed silver dots or coupled silver wires were obtained. The plasmon absorption shifted from 500 to 800 nm for a configuration of random dots to that of coupled wires, respectively. Prepared samples were used as substrates for surface enhanced Raman scattering (SERS) excited by near-UV and near-IR wavelengths. The absorption peak position and SERS response strongly depended on the silver arrangement.

One-step preparation of antimicrobial silver nanoparticles in polymer matrix

Simple one-step procedure for in situ preparation of silver nanoparticles (AgNPs) in the polymer thin films is described. Nanoparticles (NPs) were prepared by reaction of N-methyl pyrrolidone with silver salt in semi-dry polymer film and characterized by transmission electron microscopy, XPS, and UV–Vis spectroscopy techniques. Direct synthesis of NPs in polymer has several advantages; even though it avoids time-consuming NPs mixing with polymer matrix, uniform silver distribution in polymethylmethacrylate (PMMA) films is achieved without necessity of additional stabilization. The influence of the silver concentration, reaction temperature and time on reaction conversion rate, and the size and size-distribution of the AgNPs was investigated. Polymer films doped with AgNPs were tested for their antibacterial activity on Gram-negative bacteria. Antimicrobial properties of AgNPs/PMMA films were found to be depended on NPs concentration, their size and distribution. Proposed one-step synthesis of functional polymer containing AgNPs is environmentally friendly, experimentally simple and extremely quick. It opens up new possibilities in development of antimicrobial coatings with medical and sanitation applications.

Surface morphology and optical properties of porphyrin/Au and Au/porphyrin/Au systems

Porphyrin/Au and Au/porphyrin/Au systems were prepared by vacuum evaporation and vacuum sputtering onto glass substrate. The surface morphology of as-prepared systems and those subjected to annealing at 160°C was studied by optical microscopy, atomic force microscopy, and scanning electron microscopy techniques. Absorption and luminescence spectra of as-prepared and annealed samples were measured. Annealing leads to disintegration of the initially continuous gold layer and formation of gold nanoclusters. An amplification of Soret band magnitude was observed on the Au/meso-tetraphenyl porphyrin (TPP) system in comparison with mere TPP. Additional enhancement of luminescence was observed after the sample annealing. In the case of sandwich Au/porphyrin/Au structure, suppression of one of the two porphyrins’ luminescence maxima and sufficient enhancement of the second one were observed.

Synthesis, Characterization, and Antimicrobial Activity of Near-IR Photoactive Functionalized Gold Multibranched Nanoparticles

Abstract Surface‐modified gold multibranched nanoparticles (AuMs) were prepared by simple chemical reduction of gold chloride aqueous solution followed by in situ modification by using water‐soluble arenediazonium tosylates with different functional organic groups. Chemical and morphological structures of the prepared nanoparticles were examined by using transmission electron and scanning electron microscopies. The covalent grafting of organic compounds was confirmed by scanning electron microscopy with energy dispersive X‐ray spectroscopy (SEM‐EDX) and Raman spectroscopy techniques. Covalent functionalization of nanoparticles significantly expands the range of their potential uses under physiological conditions, compared with traditional non‐covalent or thiol‐based approaches. The antibacterial effect of the surface‐modified AuMs was evaluated by using Escherichia coli and Staphylococcus epidermidis bacteria under IR light illumination and without external triggering. Strong plasmon resonance on the AuMs cups leads to significant reduction of the light power needed kill bacteria under the mild conditions of continuous illumination. The effect of the surface‐modified AuMs on the light‐induced antibacterial activities was founded to be dependent on the grafted organic functional groups.

Preparation of ordered silver angular nanoparticles array in block copolymer film for surface-enhanced Raman spectroscopy

We report a single-step method of preparation of ordered silver nanoparticles array through template-assisted nanoparticles synthesis in the semidried block copolymer film. Ordered nanoparticles were prepared on different substrates by the proper choice of solvents combination and preparation procedure. In particular, block copolymer and silver nitrate were dissolved in the mix of tetrahydrofuran, toluene, and n-methylpyrolidone. During short spin-coating procedure ordering of block copolymer, evaporation of toluene and preferential silver redistribution into poly(4-vinylpyridine) block occurred. Rapid heating of semidry film initiated silver reduction, removing of residual solvent and creation of ordered silver array. After polymer removing silver nanoparticles array was tested as a suitable candidate for subdiffraction plasmonic application–surface-enhanced Raman scattering. Enhancement factor was calculated and compared with the literature data.

Reversible switching of PEDOT:PSS conductivity in the dielectric–conductive range through the redistribution of light-governing polymers

One of the biggest challenges in the field of organic electronics is the creation of flexible, stretchable, and biofavorable materials. Here the simple and repeatable method for reversible writing/erasing of arbitrary conductive pattern in conductive polymer thin film is proposed. The copolymer azo-modified poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) was synthesized to achieve reversible photo-induced local electrical switching in the insulator–semimetal range. The photoisomerization of the polymer was induced by grafting nitrobenzenediazonium tosylate to the PSS main chains. While the as-deposited PEDOT:PSS thin films showed good conductivity, the modification procedure generated polymer redistribution, resulting in an island-like PEDOT distribution and the loss of conductivity. Further local illumination (430 nm) led to the azo-isomerization redistribution of the polymer chains and the creation of a conductive pattern in the insulating polymer film. The created pattern could then be erased by illumination at a second wavelength (470 nm), which was attributed to induction of reverse azo-isomerization. In this way, the reversible writing/erasing of arbitrary conductive patterns in thin polymer films was realized.

Design and optimization of the silver nanograting structure utilizing surface plasmon-polariton for increase of SERS sensor response

This paper reports on the design of the surface enhanced Raman spectroscopy (SERS) structures that were optimized through computation and simulation to obtain the best enhancement of the surface plasmon-polariton (SPP) response on these structures. The structure of the silver nano-grating was designed, fabricated, optimized and measured. The enhancement factor and the increase in the absorption capabilities associated with SPP were evaluated. The rigorous coupled wave analysis (RCWA) and finite-difference time-domain (FDTD) computational/simulation methods were utilized. The comparison between the computation simulation outputs and the measured outputs of the fabricated samples was performed.