Markus Pesonen

Biocomposites of Nanofibrillated Cellulose, Polypyrrole, and Silver Nanoparticles with Electroconductive and Antimicrobial Properties

In this work, flexible and free-standing composite films of nanofibrillated cellulose/polypyrrole (NFC/PPy) and NFC/PPy-silver nanoparticles (NFC/PPy-Ag) have been synthesized for the first time via in situ one-step chemical polymerization and applied in potential biomedical applications. Incorporation of NFC into PPy significantly improved its film formation ability resulting in composite materials with good mechanical and electrical properties. It is shown that the NFC/PPy-Ag composite films have strong inhibition effect against the growth of Gram-positive bacteria, e.g., Staphylococcus aureus. The electrical conductivity and strong antimicrobial activity makes it possible to use the silver composites in various applications aimed at biomedical treatments and diagnostics. Additionally, we report here the structural and morphological characterization of the composite materials with Fourier-transform infrared spectroscopy, atomic force microscopy, and scanning and transmission electron microscopy techniques.

An impedimetric study of DNA hybridization on paper-supported inkjet-printed gold electrodes

In this study, two different supramolecular recognition architectures for impedimetric detection of DNA hybridization have been formed on disposable paper-supported inkjet-printed gold electrodes. The gold electrodes were fabricated using a gold nanoparticle based ink. The first recognition architecture consists of subsequent layers of biotinylated self-assembly monolayer (SAM), streptavidin and biotinylated DNA probe. The other recognition architecture is constructed by immobilization of thiol-functionalized DNA probe (HS-DNA) and subsequent backfill with 11-mercapto-1-undecanol (MUOH) SAM. The binding capacity and selectivity of the recognition architectures were examined by surface plasmon resonance (SPR) measurements. SPR results showed that the HS-DNA/MUOH system had a higher binding capacity for the complementary DNA target. Electrochemical impedance spectroscopy (EIS) measurements showed that the hybridization can be detected with impedimetric spectroscopy in picomol range for both systems. EIS signal indicated a good selectivity for both recognition architectures, whereas SPR showed very high unspecific binding for the HS-DNA/MUOH system. The factors affecting the impedance signal were interpreted in terms of the complexity of the supramolecular architecture. The more complex architecture acts as a less ideal capacitive sensor and the impedance signal is dominated by the resistive elements.

Anionic polysaccharides as templates for the synthesis of conducting polyaniline and as structural matrix for conducting biocomposites.

A green chemoenzymatic pathway for the synthesis of conducting polyaniline (PANI) composites is presented. Laccase-catalyzed polymerization in combination with anionic polysaccharides is used to produce polysaccharide/PANI composites, which can be processed into flexible films or coated onto cellulose surfaces. Different polysaccharide templates are assessed, including κ-carrageenan, native spruce O-acetyl galactoglucomannan (GGM), and TEMPO-oxidized cellulose and GGM. The resulted conducting biocomposites derived from natural materials provide a broad range of potential applications, such as in biosensors, electronic devices, and tissue engineering.

Dispersible composites of exfoliated graphite and polyaniline with improved electrochemical behaviour for solid-state chemical sensor applications

We report here the in situ polymerization of aniline in the presence of exfoliated graphite of two different grades (graphene and graphite) resulting in composite materials which are readily dispersible in N-methylpyrrolidone. Compared to polyaniline (PANI) prepared without graphene/graphite which becomes electrically non-conducting at pH > 3, the PANI–graphene/graphite composites showed significantly improved pH stability and electrochemical behaviour in aqueous electrolyte solutions at pH ≤ 8, without any further need of surface functionalization of the graphene/graphite flakes to stabilize the conducting form of polyaniline (PANI). The improved electroactivity is ascribed to the synergistic effect of graphene/graphite and PANI, and the network formation of the electrically conducting exfoliated graphites in the PANI matrix, which was electrochemically confirmed by simple cyclic voltammetric measurements at pH = 9.5 in the presence of the Ru(NH3)62+/3+ and Fe(CN)63−/4− redox couples. Due to the dispersibility of the composites, thin films possessing stability in water can easily be prepared by solution casting for different types of solid-state chemical sensor and ion-selective electrode applications operating at neutral pH. By using sodium ascorbate as a model substance, we show that its amperometric detection at pH = 7.3 with the PANI–graphite films results in a current amplification of 1.3–10.2 times in the concentration range of 10−4–10−2 M, compared to conventional PANI, which clearly demonstrates the advantage of incorporating exfoliated graphites in the PANI films. The materials reported in this paper were systematically characterized with cyclic voltammetry, FTIR, Raman and X-ray photoelectron spectroscopy, scanning electron microscopy, X-ray diffraction and electrical conductivity measurements.

Sub-ppm electrical detection of hydrogen sulfide gas at room temperature based on printed copper acetate–gold nanoparticle composite films

This paper presents the sub-ppm level electrical detection of H2S gas at room temperature using printed copper acetate–gold nanoparticle composite films. The excellent sensitivity of these films towards H2S can be attributed to the catalytic activity of gold nanoparticles in combination with the plasma oxidation of copper acetate films.

Conducting ink based on cellulose nanocrystals and polyaniline for flexographical printing

A water-based environmentally friendly electrically conducting ink composed of cellulose nanocrystals (CNC) and polyaniline (PANI) was prepared. PANI was synthesized by the emulsion polymerization approach using dodecylbenzenesulfonic acid (DBSA) as the dopant to induce spherical nanoparticulate formation. Glycerol was used to adjust the viscosity of the ink. The CNC–PANI ink was characterized by transmission electron microscopy, UV-visible spectroscopy and viscosity measurements. The ink was successfully printed on multilayer curtain coated paper by the flexographical printing method. The printed layers were characterized by optical and atomic force microscopy techniques and cyclic voltammetry. A stable nanoparticulate CNC–PANI ink with an electrical conductivity of the printed films between 30 and 60 S cm−1 was obtained which was more than an order of magnitude higher than for the corresponding film without CNC.

Synthesis and characterization of polypyrrole/H-Beta zeolite nanocomposites

Different amounts of polypyrrole (PPy) were synthesized in aqueous solution on zeolite frameworks by chemical oxidation using FeCl3 as the oxidizing agent at ambient temperature (22 ± 1 °C). The proton form of BEA zeolites with SiO2/Al2O3 ratios of 25, 150 and 300 were used as the host for PPy in this study. Both the anionic groups in the zeolite structures and the chloride ions from the oxidant functioned as the dopants during the polymerization. For comparison, parallel experiments were carried out with only purified pyrrole and FeCl3 in water solution in order to obtain the bulk PPy powder. The nitrogen adsorption–desorption technique, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) were used to characterize the composites. PPy was formed both in the inner and outer surface of the zeolite structures. The composites showed electrical conductivity at ambient temperature in the range from 6.2 × 10−6 to 1.3 S cm−1 depending on the ratio between pyrrole and H-Beta zeolite. Electrochemical behavior of the synthesized samples was investigated by cyclic voltammetry.

Reduced graphene oxide as a water, carbon dioxide and oxygen barrier in plasticized poly(vinyl chloride) films

Herein, we report the incorporation of a 10 μm thick reduced graphene oxide (RGO) barrier layer in a plasticized poly(vinyl chloride) (PVC) film as the main constituent in ion-selective membranes used in potentiometric solid-contact ion-selective electrodes (SCISE). Fourier transform infrared attenuated total reflection (FTIR-ATR) and oxygen transmission rate (OTR) measurements showed that the embedded RGO barrier efficiently impedes the diffusion of liquid water, carbon dioxide and oxygen (O2) through the 400 μm thick PVC film, which causes potential instability and irreproducibility of the SCISEs. The measurements revealed that the RGO layer completely blocks the carbon dioxide diffusion, while it fully blocks the water diffusion for 16 h and reduced the OTR by 85% on average. The μm-thick RGO films used in this study were easier to handle and incorporate into host polymers, and form more efficient and robust barriers compared to the mono-, few- and multilayer graphene commonly applied as barrier layers for liquids and gases. We also demonstrated that the FTIR-ATR technique employed in the permeability measurements is a versatile and very sensitive technique for studying the diffusion of small amounts of water and carbon dioxide through graphene-based thin films.