Impedimetric sensing of cells on polypyrrole-based conducting polymers

Miniaturized Paper-Supported 3D Cell-Based Electrochemical Sensor for Bacterial Lipopolysaccharide Detection

Sensitive detection of lipopolysaccharides (LPSs), which are present on the outer wall of Gram-negative bacteria, is important to reflect the degree of bacterial contamination in food. For indirect assessment of the LPS content, a miniaturized electrochemical cell sensor consisting of a screen-printed paper electrode, a three-dimensional cells-in-gels-in-paper culture system, and a conductive jacket device was developed for in situ detection of nitric oxide released from LPS-treated mouse macrophage cells (Raw264.7). Nafion/polypyrrole/graphene oxide with excellent selectivity, high conductivity, and good biocompatibility functionalized on the working electrode via electrochemical polymerization could enhance sensing. Raw264.7 cells encapsulated in the alginate hydrogel were immobilized on a Nafion/polypyrrole/graphene oxide/screen-printed carbon electrode in paper fibers as a biorecognition element. Differential impulse voltammetry was employed to record the current signal as-influenced by LPS. Results indicated that LPS from Salmonella enterica serotype Enteritidis caused a significant increase in peak current, varying from 1 × 10^-2 to 1 × 10⁴ ng/mL, dose-dependently. This assay had a detection limit of 3.5 × 10^-3 ng/mL with a linear detection range of 1 × 10^-2 to 3 ng/mL. These results were confirmed by analysis of nitric oxide released from Raw264.7 via the Griess method. The miniaturized sensor was ultimately applied to detect LPSs in fruit juice samples. The results indicated that the method exhibited high recovery and relative standard deviation lower than 2.65% and LPSs in samples contaminated with 10²-10⁵ CFU/mL bacteria could be detected, which proved the practical value of the sensor. Thus, a novel, low-cost, and highly sensitive approach for LPS detection was developed, providing a method to assess Gram-negative bacteria contamination in food.

New tetradentate Schiff bases of 2-amino-3,5-dibromobenzaldehyde with aliphatic diamines and their metal complexes: synthesis, characterization and thermal stability

The tetradentate Schiff base ligands (L(1)-L(4)), were synthesized by reaction between 2-amino-3,5-dibromobenzaldehyde and aliphatic diamines. Then, nickel and oxovanadium(IV) complexes of these ligands were synthesized and characterized by (1)H NMR, Mass, IR, UV-Vis spectroscopy and thermogravimetry. The kinetic parameters of oxovanadium(IV) complexes were calculated from thermal studies. According to the results of thermogravimetric data, the thermal stability of oxovanadium(IV) complexes is as follow: [Formula: see text].

A novel copper(ii) complex with an unsymmetrical tridentate-Schiff base: synthesis, crystal structure, electrochemical, morphological and electrocatalytic behaviors toward electroreduction of alkyl and aryl halides

This work describes the synthesis of a new unsymmetrical tetradentate copper(ii) Schiff base complex Cu(L)(Py)(ClO4) containing N₃O donor atoms.

Polypyrrole microcontainer structures and doughnuts designed by electrochemical oxidation: an electrochemical and scanning electron microscopy study

Scanning electron microscopy (SEM) is employed to monitor the surface morphology of polypyrrole films (PPy) grown on different working electrodes (i.e., vitreous carbon and Au (111)) under diverse experimental conditions (i.e., dynamic vs. static potential protocols) and anion dopants (i.e., I- and F-). The morphology of the electrosynthesized films includes rings (doughnuts) and microcontainers, and depends on the synthesis parameters such as the electropolymerization method, the nature of the substrate, the anion dopant, and the sequence of sandwich composite growth. The formation of well-defined rings and microcontainers is attributed to overoxidation occurring during the formation of F--doped PPy. It is possible to design microcontainers by controlling the overoxidation and degradation of the polymer surface.

Biomimetic strategies for sensing biological species

The starting point of modern biosensing was the application of actual biological species for recognition. Increasing understanding of the principles underlying such recognition (and biofunctionality in general), however, has triggered a dynamic field in chemistry and materials sciences that aims at joining the best of two worlds by combining concepts derived from nature with the processability of manmade materials, e.g., sensitivity and ruggedness. This review covers different biomimetic strategies leading to highly selective (bio)chemical sensors: the first section covers molecularly imprinted polymers (MIP) that attempt to generate a fully artificial, macromolecular mold of a species in order to detect it selectively. A different strategy comprises of devising polymer coatings to change the biocompatibility of surfaces that can also be used to immobilized natural receptors/ligands and thus stabilize them. Rationally speaking, this leads to self-assembled monolayers closely resembling cell membranes, sometimes also including bioreceptors. Finally, this review will highlight some approaches to generate artificial analogs of natural recognition materials and biomimetic approaches in nanotechnology. It mainly focuses on the literature published since 2005.

Note: Characterization of electrode materials for dielectric spectroscopy

When measuring the dielectric properties of aqueous samples, the impedance of the electrode/sample interface can limit low frequency measurements. The electrode polarization problem can be reduced by increasing the effective surface area of the electrodes. In this work, impedance spectroscopy was used to characterize and compare three different electrode surfaces that can be used to mitigate this effect: platinum black, iridium oxide, and [polypyrrole/poly(styrenesulphonate)] (PPy/PSS) conducting polymer. All three materials were directly compared with a bright platinum electrode. Equivalent circuit models were used to extract the increase in the effective surface area of the electrodes: platinum black, iridium oxide and PPy/PSS increase the effective capacitance of the electrode by factors of approximately 240, 75, and 790, respectively. The practical aspects of all electrode materials are discussed. These results suggest that iridium oxide and PPy/PSS are good alternatives to the commonly used platinum black, which is prone to mechanical damage (scratches) and is potentially toxic to cells.

Polypyrrole-based conducting polymers and interactions with biological tissues

Polypyrrole (PPy) is a conjugated polymer that displays particular electronic properties including conductivity. In biomedical applications, it is usually electrochemically generated with the incorporation of any anionic species including also negatively charged biological macromolecules such as proteins and polysaccharides to give composite materials. In biomedical research, it has mainly been assessed for its role as a reporting interface in biosensors. However, there is an increasing literature on the application of PPy as a potentially electrically addressable tissue/cell support substrate. Here, we review studies that have considered such PPy based conducting polymers in direct contact with biological tissues and conclude that due to its versatile functional properties, it could contribute to a new generation of biomaterials.