Entrapment of live microbial cells in electropolymerized polyaniline and their use as urea biosensor

Conductive Polymers and Their Nanocomposites: Application Features in Biosensors and Biofuel Cells

Conductive polymers and their composites are excellent materials for coupling biological materials and electrodes in bioelectrochemical systems. It is assumed that their relevance and introduction to the field of bioelectrochemical devices will only grow due to their tunable conductivity, easy modification, and biocompatibility. This review analyzes the main trends and trends in the development of the methodology for the application of conductive polymers and their use in biosensors and biofuel elements, as well as describes their future prospects. Approaches to the synthesis of such materials and the peculiarities of obtaining their nanocomposites are presented. Special emphasis is placed on the features of the interfaces of such materials with biological objects.

A Sustained-Release Nanosystem with MRSA Biofilm-Dispersing and -Eradicating Abilities Accelerates Diabetic Ulcer Healing

Introduction

Drug-resistant bacterial infections and biofilm formation play important roles in the pathogenesis of diabetic refractory wounds. Tea tree oil (TTO) exhibits antimicrobial, antimycotic, and antiviral activities, especially against common clinically resistant strains, such as methicillin-resistant Staphylococcus aureus (MRSA), making it a potential natural antimicrobial for the treatment of acute and chronic wounds. However, TTO is insoluble in water, volatile, light-sensitive, and cytotoxic. While previous macroscopic studies have focused on sterilization with TTO, none have sought to alter its structure or combine it with other materials to achieve sustained release.

Methods

Electrospun TTO nanoliposomes (TTO-NLs), arranged linearly via high-pressure homogenization, could stabilize the structure and performance of TTO to achieve slow drug release. Herein, we established a composite nano-sustained release system, TTO-NL/polyvinyl alcohol/chitosan (TTO-NL@PCS), using high-voltage electrospinning.

Results

Compared with the control, TTO-NL@PCS exhibits higher concentrations of the active TTO drug components, terpinen-4-ol and 1,8-cineole. Owing to its increased stability and slow release, early exposure to TTO-NL@PCS increases the abundance of reactive oxygen species in vitro, ultimately causing the biofilm to disperse and completely killing MRSA without inducing cytotoxic effects to the host. Moreover, in BKS-Leprem2Cd479/Gpt mice with a whole-layer skin infection, untargeted metabolomics analysis of wound exudates reveals upregulated PGF2α/FP receptor signaling and interleukin (IL)-1β and IL-6 expression following application of the composite system. The composite also ameliorates the chemotaxis disorder in early treatment and attenuates the wound inflammatory response during the repair stage of diabetic inflammatory wounds, and upregulates VEGF expression in the wound bed.

Conclusion

TTO-NL@PCS demonstrates the remarkable potential for accelerating diabetic and MRSA-infected wound healing.

Methods of Encapsulation of Biomacromolecules and Living Cells. Prospects of Using Metal–Organic Frameworks

The review discusses different methods of encapsulation and biomineralization of macromolecules and living cells. Main advantages and disadvantages of most commonly used carriers, matrices, and materials for immobilization of proteins, enzymes, nucleic acids, and living cells are briefly surveyed. Examples of delivery vehicles for multifunctional encapsulation of protein-like substances are presented. Particular attention is paid to prospects of using metal–organic frameworks in medicine and biotechnology.

Electrochemical Biosensors Based on Conducting Polymers: A Review

Conducting polymers are an important class of functional materials that has been widely applied to fabricate electrochemical biosensors, because of their interesting and tunable chemical, electrical, and structural properties. Conducting polymers can also be designed through chemical grafting of functional groups, nanostructured, or associated with other functional materials such as nanoparticles to provide tremendous improvements in sensitivity, selectivity, stability and reproducibility of the biosensor’s response to a variety of bioanalytes. Such biosensors are expected to play a growing and significant role in delivering the diagnostic information and therapy monitoring since they have advantages including their low cost and low detection limit. Therefore, this article starts with the description of electroanalytical methods (potentiometry, amperometry, conductometry, voltammetry, impedometry) used in electrochemical biosensors, and continues with a review of the recent advances in the application of conducting polymers in the recognition of bioanalytes leading to the development of enzyme based biosensors, immunosensors, DNA biosensors, and whole-cell biosensors.

Fast fabrication of reusable polyethersulfone microbial biosensors through biocompatible phase separation

In biosensors fabrication, entrapment in polymeric matrices allows efficient immobilization of the biorecognition elements without compromising their structure and activity. When considering living cells, the biocompatibility of both the matrix and the polymerization procedure are additional critical factors. Bio-polymeric gels (e.g. alginate) are biocompatible and polymerize under mild conditions, but they have poor stability. Most synthetic polymers (e.g. PVA), on the other hand, present improved stability at the expense of complex protocols involving chemical/physical treatments that decrease their biological compatibility. In an attempt to explore new solutions to this problem we have developed a procedure for the immobilization of bacterial cells in polyethersulfone (PES) using phase separation. The technology has been tested successfully in the construction of a bacterial biosensor for toxicity assessment. Biosensors were coated with a 300  μm bacteria-containing PES membrane, using non-solvent induced phase separation (membrane thickness ≈ 300 μm). With this method, up to 2.3 × 10⁶ cells were immobilized in the electrode surface with an entrapment efficiency of 8.2%, without compromising cell integrity or viability. Biosensing was performed electrochemically through ferricyanide respirometry, with metabolically-active entrapped bacteria reducing ferricyanide in the presence of glucose. PES biosensors showed good stability and reusability during dry frozen storage for up to 1 month. The analytical performance of the sensors was assessed carrying out a toxicity assay in which 3,5-dichlorophenol (DCP) was used as a model toxic compound. The biosensor provided a concentration-dependent response to DCP with half-maximal effective concentration (EC₅₀) of 9.2 ppm, well in agreement with reported values. This entrapment methodology is susceptible of mass production and allows easy and repetitive production of robust and sensitive bacterial biosensors.

Modification of Aspergillus niger by conducting polymer, Polypyrrole, and the evaluation of electrochemical properties of modified cells

The enhancement of bioelectrochemical properties of microorganism by in situ formation of conducting polymer within the cell structures (e.g. cell wall) was performed. The synthesis of polypyrrole (Ppy) within fungi (Aspergillus niger) cells was achieved. Two different Aspergillus niger strains were selected due to their ability to produce glucose oxidase, which initiated the Ppy formation through products of enzymatic reaction. The evolution of Ppy structural features was investigated by absorption spectroscopy, cyclic voltammetry and Fourier transform infrared spectroscopy.

Functional Micrococcus lysodeikticus layers deposited by laser technique for the optical sensing of lysozyme

Whole cell optical biosensors, made by immobilizing whole algal, bacterial or mammalian cells on various supports have found applications in several fields, from ecology and ecotoxicity testing to biopharmaceutical production or medical diagnostics. We hereby report the deposition of functional bacterial layers of Micrococcus lysodeikticus (ML) via Matrix-Assisted Pulsed Laser Evaporation (MAPLE) on poly(diallyldimethylamonium) (PDDA)-coated-glass slides and their application as an optical biosensor for the detection of lysozyme in serum. Lysozyme is an enzyme upregulated in inflammatory diseases and ML is an enzymatic substrate for this enzyme. The MAPLE-deposited bacterial interfaces were characterised by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Fourier-Transformed Infrared Spectroscopy (FTIR), Raman and optical microscopy and were compared with control interfaces deposited via layer-by-layer on the same substrate. After MAPLE deposition and coating with graphene oxide (GO), ML-modified interfaces retained their functionality and sensitivity to lysozyme's lytic action. The optical biosensor detected lysozyme in undiluted serum in the clinically relevant range up to 10μgmL^-1, in a fast and simple manner.

Electro-Active Polymers (EAPs): A Promising Route to Design Bio-Organic/Bioinspired Platforms with on Demand Functionalities

Through recent discoveries and new knowledge among correlations between molecular biology and materials science, it is a growing interest to design new biomaterials able to interact-i.e., to influence, to guide or to detect-with cells and their surrounding microenvironments, in order to better control biological phenomena. In this context, electro-active polymers (EAPs) are showing great promise as biomaterials acting as an interface between electronics and biology. This is ascribable to the highly tunability of chemical/physical properties which confer them different conductive properties for various applicative uses (i.e., molecular targeting, biosensors, biocompatible scaffolds). This review article is divided into three parts: the first one is an overview on EAPs to introduce basic conductivity mechanisms and their classification. The second one is focused on the description of most common processes used to manipulate EAPs in the form of two-dimensional (2D) and three-dimensional (3D) materials. The last part addresses their use in current applications in different biomedical research areas including tissue engineering, biosensors and molecular delivery.

Conducting polymer based electrochemical biosensors

Conducting polymer (CP)-based electrochemical biosensors have gained great attention as such biosensor platforms are easy and cost-effective to fabricate, and provide a direct electrical readout of the presence of biological analytes with high sensitivity and selectivity.

Enzymatic electrochemical biosensor for urea with a polyaniline grafted conducting hydrogel composite modified electrode

A new conducting polymer hydrogel (CPH) comprising polyaniline grafted polyvinyl alcohol–polyacrylamide ensured high enzyme loading and urea sensitivity.

One-pot and one-step synthesis of bioactive urease/ZnFe₂O₄ nanocomposites and their application in detection of urea

This communication describes a novel environmentally friendly method to prepare bioactive urease/ZnFe2O4 nanocomposites through a one-pot and one-step process. The synthetic procedure is triggered through a biological mineralization process of decomposition of urea catalyzed by urease. During the growth of ZnFe2O4, urease molecules are immobilized by original ZnFe2O4 nanoparticles. As a consequence, the bioactive urease/ZnFe2O4 nanoparticle composites are assembled. This simple route is expected to endow the bioactive nanocomposites with new properties for various interesting fields.

A paper strip based non-invasive glucose biosensor for salivary analysis

In our present study, we developed an optical biosensor for direct determination of salivary glucose by using immobilized glucose oxidase enzyme on filter paper strip (specific activity 1.4 U/strip) and then reacting it with synthetic glucose samples in presence of co-immobilized color pH indicator. The filter paper changed color based on concentration of glucose in reaction media and hence, by scanning this color change (using RGB profiling) through an office scanner and open source image processing software (GIMP) the concentration of glucose in the reaction medium could be deduced. Once the biosensor was standardized, the synthetic glucose sample was replaced with human saliva from donors. The individual's blood glucose level at the time of obtaining saliva was also measured using an Accuchek(™) active glucometer (Roche Inc.). In this preliminary study, a correlation of nearly 0.64 was found between glucose levels in saliva and blood of healthy individuals and in diabetic patients it was nearly in the order of 0.95, thereby validating the importance of salivary analysis. The RGB profiling method obtained a detection range of 9-1350 mg/dL glucose at a response time of 45 s and LOD of 22.2 mg/dL.

Conductive polymers: towards a smart biomaterial for tissue engineering

Developing stimulus-responsive biomaterials with easy-to-tailor properties is a highly desired goal of the tissue engineering community. A novel type of electroactive biomaterial, the conductive polymer, promises to become one such material. Conductive polymers are already used in fuel cells, computer displays and microsurgical tools, and are now finding applications in the field of biomaterials. These versatile polymers can be synthesised alone, as hydrogels, combined into composites or electrospun into microfibres. They can be created to be biocompatible and biodegradable. Their physical properties can easily be optimized for a specific application through binding biologically important molecules into the polymer using one of the many available methods for their functionalization. Their conductive nature allows cells or tissue cultured upon them to be stimulated, the polymers' own physical properties to be influenced post-synthesis and the drugs bound in them released, through the application of an electrical signal. It is thus little wonder that these polymers are becoming very important materials for biosensors, neural implants, drug delivery devices and tissue engineering scaffolds. Focusing mainly on polypyrrole, polyaniline and poly(3,4-ethylenedioxythiophene), we review conductive polymers from the perspective of tissue engineering. The basic properties of conductive polymers, their chemical and electrochemical synthesis, the phenomena underlying their conductivity and the ways to tailor their properties (functionalization, composites, etc.) are discussed.

Development and initial testing of a novel slime mould biosensor

A plurality of whole cell biosensors have been developed using many different cell types. Biosensors incorporate biomolecular components or whole cells to facilitate specific analyte interaction; research documented here presents a novel whole cell biosensor based on the slime mould Physarum polycephalum (PP). The electrical response of PP when exposed to multiple chemicals are measured and quantified in terms of amplitude and frequency response. The PP biosensor is capable of detecting the tested chemicals and individually identifying a large number in terms of a specific shift in either oscillation frequency or amplitude. However, it does exhibit a sensitivity to environmental changes such as light level and temperature which may interfere with the detection of the target analyte but could also be used for wider sensing applications. It is proposed that this novel biosensor is capable of detecting many organic chemicals beyond those presented in this work and that the biosensor may be used for environmental monitoring and toxicity evaluation.

Conductive PANi/PEGDA macroporous hydrogels for nerve regeneration

Only recently polymers with intrinsic conductive properties have been studied in relation to their incorporation into bioactive scaffolds for use in tissue engineering. The reason for this interest is that such scaffolds could electrically stimulate cells and thus regulate specific cellular activities, and by this means influence the process of regeneration of those tissues that respond to electrical impulses. In our work, macroporous hydrogels are developed with controlled pore morphology and conductive properties to enable sufficient cell signaling to supply events inherent to nerve regeneration. A hybrid material has been prepared by in situ precipitation of polyaniline (PANi) in polyethyleneglycol diacrylate (PEGDA) solution, followed by crosslinking via UV irradiation. A porous architecture, characterized by macropores from 136 μm to 158 μm in size, has been achieved by sodium chloride particle leaching. In this work, we demonstrate that PANi synthesis and hydrogel crosslinking combine to enable the design of materials with suitable conductive behaviour. The presence of PANi evidently increased the electrical conductivity of the hybrid material from (1.1 ± 0.5) × 10(-3) mS/cm with a PANi content of 3wt%. The hydrophilic nature of PANi also enhanced water retention/proton conductivity by more than one order of magnitude. In vitro studies confirmed that 3 wt% PANi also improve the biological response of PC12 and hMSC cells. Hybrid PANi/PEGDA macroporous hydrogels supplement new functionalities in terms of morphological and conductive properties, both of which are essential prerequisites to drive nerve cells in regenerative processes.

Biosensors in clinical chemistry - 2011 update

Research activity and applications of biosensors for measurement of analytes of clinical interest over the last eight years are reviewed. Nanotechnology has been applied to improve performance of biosensors using electrochemical, optical, mechanical and physical modes of transduction, and to allow arrays of biosensors to be constructed for parallel sensing. Biosensors have been proposed for measurement of cancer biomarkers, cardiac biomarkers as well as biomarkers for autoimmune disease, infectious disease and for DNA analysis. Novel applications of biosensors include measurements in alternate sample types, such as saliva. Biosensors based on immobilized whole cells have found new applications, for example to detect the presence of cancer and to monitor the response of cancer cells to chemotherapeutic agents. The number of research reports describing new biosensors for analytes of clinical interest continues to increase; however, movement of biosensors from the research laboratory to the clinical laboratory has been slow. The greatest impact of biosensors will be felt at point-of-care testing locations without laboratory support. Integration of biosensors into reliable, easy-to-use and rugged instrumentation will be required to assure success of biosensor-based systems at the point-of-care.

Immobilization of microbial cells on inner epidermis of onion bulb scale for biosensor application

Inner epidermis of onion bulb scales was used as a natural support for immobilization of microbial cells for biosensor application. A bacterium Sphingomonas sp. that hydrolyzes methyl parathion into a chromophoric product, p-nitrophenol (PNP), has been isolated and identified in our laboratory. PNP can be detected by electrochemical and colorimetric methods. Whole cells of Sphingomonas sp. were immobilized on inner epidermis of onion bulb scale by adsorption followed by cross-linking methods. Cells immobilized onion membrane was directly placed in the wells of microplate and associated with the optical transducer. Methyl parathion is an organophosphorus pesticide that has been widely used in the field of agriculture for insect pest control. This pesticide causes environmental pollution and ecological problem. A detection range 4-80 μM of methyl parathion was estimated from the linear range of calibration plot of enzymatic assay. A single membrane was reused for 52 reactions and was found to be stable for 32 days with 90% of its initial hydrolytic activity. The applicability of the cells immobilized onion membrane was also demonstrated with spiked samples.

Microbial biosensor for detection of methyl parathion using screen printed carbon electrode and cyclic voltammetry

Whole cells of recombinant Escherichia coli were immobilized on the screen printed carbon electrode (SPCE) using glutaraldehyde. Recombinant E. coli was having high periplasmic expression of organophosphorus hydrolase enzyme, which hydrolyzes the methyl parathion into two products, p-nitrophenol and dimethyl thiophosphoric acid. Cells immobilized SPCE was studied under SEM. Cells immobilized SPCE was associated with cyclic voltammetry and cyclic voltammograms were recorded before and after hydrolysis of methyl parathion. Detection was calibrated based on the relationship between the changes in the current observed at +0.1 V potential, because of redox behavior of the hydrolyzed product p-nitrophenol. As concentration of methyl parathion was increased the oxidation current also increased. Only 20 μl volume of the sample was required for analysis. Detection range of biosensor was calibrated between 2 and 80 μM of methyl parathion from the linear range of calibration plot. A single immobilized SPCE was reused for 32 reactions with retention of 80% of its initial enzyme activity.

A whole-cell amperometric herbicide biosensor based on magnetically functionalised microalgae and screen-printed electrodes

We report the fabrication of an amperometric whole-cell herbicide biosensor based on magnetic retention of living cells functionalised with magnetic nanoparticles (MNPs) on the surface of a screen-printed electrode. We demonstrate that Chlorella pyrenoidosa microalgae cells coated with biocompatible MNPs and retained on the electrode with a permanent magnet act as a sensing element for the fast detection of herbicides. The magnetic functionalisation does not affect the viability and photosynthesis activity-mediated triazine herbicide recognition in microalgae. The current of ferricyanide ion was recorded during alternating illumination periods and biosensor fabricated was used to detect atrazine (from 0.9 to 74 µM) and propazine (from 0.6 to 120 µM) (the limits of detection 0.7 and 0.4 µM, respectively). We believe that the methodology presented here can be widely used in fabrication of a number of whole cell biosensors since it allows for efficient and reversible cells immobilisation and does not affect the cellular metabolism.

Interfacing living unicellular algae cells with biocompatible polyelectrolyte-stabilised magnetic nanoparticles

Green algae are a promising platform for the development of biosensors and bioelectronic devices. Here we report a reliable single-step technique for the functionalisation of living unicellular green algae Chlorella pyrenoidosa with biocompatible 15 nm superparamagnetic nanoparticles stabilised with poly(allylamine hydrochloride). The magnetised algae cells can be manipulated and immobilised using external permanent magnets. The distribution of the nanoparticles on the cell walls of C. pyrenoidosa was studied by optical and fluorescence microscopy, TEM, SEM and EDX spectroscopy. The viability and the magnetic properties of the magnetised algae are studied in comparison with the native cells. The technique may find a number of potential applications in biotechnology and bioelectronics.

An optical microbial biosensor for detection of methyl parathion using Sphingomonas sp. immobilized on microplate as a reusable biocomponent

Organophosphorus pesticides such as methyl parathion have been widely used in the field of agriculture for insect pest control. These pesticides and their degradation products cause environmental pollution and ecological problem. With a view to monitor these pesticides biosensors are being developed. A bacterium Sphingomonas sp. from field soil has been isolated and identified in our laboratory that hydrolyzes the methyl parathion upto a chromophoric product, p-nitrophenol (PNP). PNP can be detected by electrochemical and colorimetric methods, which can be exploited to develop a biosensor for detection of the organophosphate pesticide. Whole cells of Sphingomonas bacteria were immobilized directly onto the surface of the wells of polystyrene microplates (96 wells) using glutaraldehyde as the cross-linker. SEM study confirmed the immobilization of Sphingomonas sp. Immobilized bacterial microplate was associated directly with the optical transducer, microplate reader. The microplate-based biosensor is having advantages as it has 96 reaction vessels and therefore it provides a convenient system for detecting multiple numbers of samples in a single platform. Detection range of the biosensor from the linear range was determined to be 4-80 μM methyl parathion. Cells-immobilized microplates were having reusability upto 75 reactions. Present study reports an innovative concept where the microplate can be used as immobilizing support for development of reusable microbial biocomponent.