Carbon fibre composites: integrated electrochemical sensors for wound management

The applicability of employing a carbon fibre mesh as an electrochemical sensing substructure for assessing urate transformations within wound exudates is evaluated. Prototype sensor assemblies have been designed and their response characteristics towards uric acid and other common physiological components are detailed. Modification of the carbon fibre sensor through surface anodisation and the application of cellulose acetate permselective barriers have been shown to lead to optimized responses and much greater sensitivity (1440% increase) and specificity. These could enable the accurate periodic monitoring of uric acid in wound fluid. The performance characteristics of the composite sensors in whole blood, serum and blister fluid have been investigated

Paper-based chromatic toxicity bioassay by analysis of bacterial ferricyanide reduction

Water quality assessment requires a continuous and strict analysis of samples to guarantee compliance with established standards. Nowadays, the increasing number of pollutants and their synergistic effects lead to the development general toxicity bioassays capable to analyse water pollution as a whole. Current general toxicity methods, e.g. Microtox®, rely on long operation protocols, the use of complex and expensive instrumentation and sample pre-treatment, which should be transported to the laboratory for analysis. These requirements delay sample analysis and hence, the response to avoid an environmental catastrophe. In an attempt to solve it, a fast (15 min) and low-cost toxicity bioassay based on the chromatic changes associated to bacterial ferricyanide reduction is here presented. E. coli cells (used as model bacteria) were stably trapped on low-cost paper matrices (cellulose-based paper discs, PDs) and remained viable for long times (1 month at -20 °C). Apart from bacterial carrier, paper matrices also acted as a fluidic element, allowing fluid management without the need of external pumps. Bioassay evaluation was performed using copper as model toxic agent. Chromatic changes associated to bacterial ferricyanide reduction were determined by three different transduction methods, i.e. (i) optical reflectometry (as reference method), (ii) image analysis and (iii) visual inspection. In all cases, bioassay results (in terms of half maximal effective concentrations, EC50) were in agreement with already reported data, confirming the good performance of the bioassay. The validation of the bioassay was performed by analysis of real samples from natural sources, which were analysed and compared with a reference method (i.e. Microtox). Obtained results showed agreement for about 70% of toxic samples and 80% of non-toxic samples, which may validate the use of this simple and quick protocol in the determination of general toxicity. The minimum instrumentation requirements and the simplicity of the bioassay open the possibility of in-situ water toxicity assessment with a fast and low-cost protocolPostprint (author's final draft

Causes and biophysical consequences of cellulose production by Pseudomonas fluorescens SBW25 at the air-liquid interface

Cellulose over-producing wrinkly spreader mutants of Pseudomonas fluorescens SBW25 have been the focus of much investigation, but conditions promoting the production of cellulose in ancestral SBW25, its effects and consequences have escaped in-depth investigation through lack of in vitro phenotype. Here, using a custom built device, we reveal that in static broth microcosms ancestral SBW25 encounters environmental signals at the air-liquid interface that activate, via three diguanylate cyclase-encoding pathways (Wsp, Aws and Mws), production of cellulose. Secretion of the polymer at the meniscus leads to modification of the environment and growth of numerous micro-colonies that extend from the surface. Accumulation of cellulose and associated microbial growth leads to Rayleigh-Taylor instability resulting in bioconvection and rapid transport of water-soluble products over tens of millimetres. Drawing upon data we build a mathematical model that recapitulates experimental results and captures the interactions between biological, chemical and physical processes.IMPORTANCE This work reveals a hitherto unrecognized behaviour that manifests at the air-liquid interface, which depends on production of cellulose, and hints to undiscovered dimensions to bacterial life at surfaces. Additionally, the study links activation of known diguanylate cyclase-encoding pathways to cellulose expression and to signals encountered at the meniscus. Further significance stems from recognition of the consequences of fluid instabilities arising from surface production of cellulose for transport of water-soluble products over large distances

Application of electro-active biofilms

The concept of an electro-active biofilm (EAB) has recently emerged from a few studies that discovered that certain bacteria which form biofilms on conductive materials can achieve a direct electrochemical connection with the electrode surface using it as electron exchanger, without the aid of mediators. This electro-catalytic property of biofilms has been clearly related to the presence of some specific strains that are able to exchange electrons with solid substrata (eg Geobacter sulfurreducens and Rhodoferax ferrireducens). EABs can be obtained principally from natural sites such as soils or seawater and freshwater sediments or from samples collected from a wide range of different microbially rich environments (sewage sludge, activated sludge, or industrial and domestic effluents). The capability of some microorganisms to connect their metabolisms directly in an external electrical power supply is very exciting and extensive research is in progress on exploring the possibilities of EABs applications. Indeed, the best known application is probably the microbial fuel cell technology that is capable of turning biomass into electrical energy. Nevertheless, EABs coated onto electrodes have recently become popular in other fields like bioremediation, biosynthesis processes, biosensor design, and biohydrogen production

Biofouling of indwelling electrochemical sensors

Provision of clean drinking water is regarded as being the most significant positive intervention in human health and it plays a significant role in supporting global health. Population growth, economic development and climate change all drive urbanisation and increase demand for clean water and the infrastructure for its delivery. As demand for clean water increases, so will the pressure to ensure its safety. Indwelling sensor networks offer real-time, long-term and intelligent monitoring system, and would enable optimisation of networks for quality. Electrochemical sensors are inexpensive and simple to construct and operate. However, prolonged exposure of the sensors to water causes biofouling which compromise their performance even in weeks or days, making early detection of performance failure critical. Fouling of sensors due to biofilm formation is very common in indwelling situations and it is a major drawback in the development of sensor networks. Owing to our incomplete understanding of the chemistry, physics and biology of bacterial cell and surface interaction, solutions become ineffective. Understanding how biofilms affect electrochemical sensor performance is important to enable detection of malfunction in situ and can inform the development of methodology to restore the performance in situ. Networks can consist of hundreds of sensors and automated restoration of function in biofouled sensors is thus essential. Hence, the fundamentals on how biofilms affect electrochemical sensor performance, specifically electrode reactions, should be a starting point in the design of a robust indwelling sensors network. A novel electrochemical rapid biofilm formation protocol has been successfully developed to facilitate this investigation. The electrochemical rapid biofilm can form in just 2 hours, instead of days or weeks, and has been shown to be able to replicate key characteristics !" ⁄# of a naturally forming 3 weeks old biofilm. Physico-chemical effects of ! biofouling to diffusional mass transport towards electrode surface and electron transfer kinetics at the surface of electrode can be quantified by using a combination of electroanalytical techniques such as cyclic voltammetry, chronoamperometry, impedance spectroscopy and hydrodynamic techniques, but hydrodynamic voltammetry and amperometry using rotating disk electrode (RDE) and Koutecký-Levich analysis are particularly robust and useful in assessing these effects. Electrochemical reduction of oxygen, or oxygen reduction reaction (ORR), is used as the paradigm to elucidate the nature of electrochemical sensor biofouling. The oxygen paradigm is also used as a means to assess an electrochemical in situ restoration method for biofouled electrode which is based on electrochemical advanced oxidative processes (EAOPs) and pulsed amperometric detection (PAD).Open Acces

Smart and Safe packaging

In line with the latest innovations in the packaging field, this joint project aims at implementing new and innovative micro- and nanoparticles for the development of active and intelligent packaging solutions dedicated to food and medical packaging applications. More specifically, the project combines two major developments which both falls within the scope of active and intelligent packaging. In this work, a specific focus was given to the development of an antibacterial packaging solution and to the development of smart gas sensors. The antibacterial strategy developed was based on the combination of two active materials - silver nanowires and cellulose nanofibrils - to prepare antibacterial surfaces. The formulation as an ink and the deposition processing has been deeply studied for different surface deposition processes that include coatings or screen-printing. Results showed surfaces that display strong antibacterial activity both against Gram-positive and Gram-negative bacteria, but also interesting properties for active packaging applications such as a highly retained transparency or enhanced barrier properties. Regarding the second strategy, gas sensors have been prepared using a combination of Copper benzene-1,3,5-tricarboxylate Metal Organic Framework and carbon-graphene materials, deposited on flexible screen-printed electrodes. The easy-to-produce and optimized sensors exhibit good performances toward ammonia and toward humidity sensing, proving the versatility and the great potential of such solution to be adapted for different target applications. The results of this project lead to innovative solutions that can meet the challenges raised by the packaging industry

Smart dressings based on bacterial cellulose for chronic wounds healing and monitoring

In recent years, there has been an upward trend for novel biomass based green materials for dressing chronic wounds, which can assist in wound healing and monitoring. This research focuses on candidate components for smart chronic wound dressings based on bacterial cellulose (BC), which is comprised of two parts: antimicrobial BC nanocomposites for wound dressing, and a BC-derived pH sensor for monitoring chronic wounds. This research demonstrates a novel ability to utilise BC and BC-derived nanocomposites in potential applications for smart wound dressings. In the chapter regarding BC production, samples grown in static from four different Acetobacter bacterial strains are characterized and compared for the first time. SEM and BET results demonstrate a large surface area (>100 m2/g) and XRD analysis reveals high crystallinity (>60%). In vitro cell tests indicate potential biocompatibility. In the BC based pH sensor chapter, a pyrolyzed BC (p-BC) aerogel was incorporated with polyaniline (PANI) and polydimethylsiloxane (PDMS), exhibiting near-Nernst pH sensitivity (50.4 mV/pH). In the chapter on antimicrobial BC nanocomposites, the inorganic BC/silver nanoparticle (BC/AgNP) and organic BC/lysozyme, BC/eggshell membrane (BC/ESM), BC/methylglyoxal (BC/MGO) nanocomposites were fabricated and characterized, with BC/ESM and BC/MGO nanocomposites proposed for the first time. The antimicrobial properties were tested via a disk diffusion method, with BC/MGO exhibiting the greatest antimicrobial activity, with diameters of inhibition zone (DIZ) up to 17.1 ± 0.6 mm against S. aureus and 15.5 ± 0.5 mm against E. coli. Tensile tests show the nanocomposites still retain the high tensile strength of plain BC (>2 MPa). These results indicate that BC and BC-derived nanocomposites are promising candidate materials for smart wound dressings. The future work will focus on more detailed in vitro biocompatibility tests and in vivo wound healing assays

A cellulose-based bioassay for the colorimetric detection of pathogen DNA

Cellulose-paper-based colorimetric bioassays may be used at the point of sampling without sophisticated equipment. This study reports the development of a colorimetric bioassay based on cellulose that can detect pathogen DNA. The detection was based on covalently attached single-stranded DNA probes and visual analysis. A cellulose surface functionalized with tosyl groups was prepared by the N,N-dimethylacetamide-lithium chloride method. Tosylation of cellulose was confirmed by scanning electron microscopy, Fourier transform infrared spectroscopy and elemental analysis. Sulfhydryl-modified oligonucleotide probes complementary to a segment of the DNA sequence IS6110 of Mycobacterium tuberculosis were covalently immobilized on the tosylated cellulose. On hybridization of biotin-labelled DNA oligonucleotides with these probes, a colorimetric signal was obtained with streptavidin-conjugated horseradish peroxidase catalysing the oxidation of tetramethylbenzamidine by H2O2. The colour intensity was significantly reduced when the bioassay was subjected to DNA oligonucleotide of randomized base composition. Initial experiments have shown a sensitivity of 0.1 μM. A high probe immobilization efficiency (more than 90 %) was observed with a detection limit of 0.1 μM, corresponding to an absolute amount of 10 pmol. The detection of M. tuberculosis DNA was demonstrated using this technique coupled with PCR for biotinylation of the DNA. This work shows the potential use of tosylated cellulose as the basis for point-of-sampling bioassays.Peer reviewedFinal Accepted Versio

Design and implementation of sensor systems for control of a closed-loop life support system

The sensing and controlling needs for a Closed-Loop Life Support System (CLLSS) were investigated. The sensing needs were identified in five particular areas and the requirements were defined for workable sensors. The specific areas of interest were atmosphere and temperature, nutrient delivery, plant health, plant propagation and support, and solids processing. The investigation of atmosphere and temperature control focused on the temperature distribution within the growth chamber as well as the possibility for sensing other parameters such as gas concentration, pressure, and humidity. The sensing needs were studied for monitoring the solution level in a porous membrane material along with the requirements for measuring the mass flow rate in the delivery system. The causes and symptoms of plant disease were examined and the various techniques for sensing these health indicators were explored. The study of sensing needs for plant propagation and support focused on monitoring seed viability and measuring seed moisture content as well as defining the requirements for drying and storing the seeds. The areas of harvesting, food processing, and resource recycling, were covered with a main focus on the sensing possibilities for regulating the recycling process

Comparison between a direct-flow SPR immunosensor for ampicillin and a competitive conventional amperometric device: analytical features and possible applications to real samples

In this research, we developed a direct-flow surface plasmon resonance (SPR) immunosensor for ampicillin to perform direct, simple, and fast measurements of this important antibiotic. In order to better evaluate the performance, it was compared with a conventional amperometric immunosensor, working with a competitive format with the aim of finding out experimental real advantages and disadvantages of two respective methods. Results showed that certain analytical features of the new SPR immunodevice, such as the lower limit of detection (LOD) value and the width of the linear range, are poorer than those of a conventional amperometric immunosensor, which adversely affects the application to samples such as natural waters. On the other hand, the SPR immunosensor was more selective to ampicillin, and measurements were more easily and quickly attained compared to those performed with the conventional competitive immunosensor