Search

Highlights • Sonochemical production of smart hospital textiles able to detect live bacteria by changing its own colour. • Sonochemical coating of Prussian Blue nanoparticles in a single-step and scalable ultrasonic process. • Use of Prussian Blue as electrochromic metabolic indicator for live bacterial detection. • Textile colour change is produced by bacterial metabolism, either by Gram-negative or Gram-positive bacteria., In healthcare facilities, environmental microbes are responsible for numerous infections leading to patient’s health complications and even death. The detection of the pathogens present on contaminated surfaces is crucial, although not always possible with current microbial detection technologies requiring sample collection and transfer to the laboratory. Based on a simple sonochemical coating process, smart hospital fabrics with the capacity to detect live bacteria by a simple change of colour are presented here. Prussian Blue nanoparticles (PB-NPs) are sonochemically coated on polyester-cotton textiles in a single-step requiring 15 min. The presence of PB-NPs confers the textile with an intensive blue colour and with bacterial-sensing capacity. Live bacteria in the textile metabolize PB-NPs and reduce them to colourless Prussian White (PW), enabling in situ detection of bacterial presence in less than 6 h with the bare eye (complete colour change requires 40 h). The smart textile is sensitive to both Gram-positive and Gram-negative bacteria, responsible for most nosocomial infections. The redox reaction is completely reversible and the textile recovers its initial blue colour by re-oxidation with environmental oxygen, enabling its re-use. Due to its simplicity and versatility, the current technology can be employed in different types of materials for control and prevention of microbial infections in hospitals, industries, schools and at home.

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.

In biosensors development, alginate hydrogels are a first choice for enabling stable biomolecules entrapment in biocompatible membranes obtained under soft physiological conditions. Although widely exploited, most alginate membranes are isolating and poorly repetitive, which limit their application in biosensing. Significant steps forward on improving repeatability and conductivity have been performed, but to date there is no single protocol for controlled deposition of live cells in replicable conductive alginate layers. Here, cell electrotrapping in conductive alginate hydrogels is examined in order to overcome these limitations. Conductive alginate-coated electrodes are obtained after potentiostatic electrodeposition of graphite-doped alginate samples (up to 4% graphite). The presence of graphite reduces electrode passivation and improves the electrochemical response of the sensor, although still significantly lower than that recorded with the naked electrode. Bacterial electrotrapping in the conductive matrix is highly efficient (4.4 × 10 7 cells per gel) and repetitive (CV < 0.5%), and does not compromise bacterial integrity or activity (cell viability = 56%). Biosensing based on ferricyanide respirometry yielded a four times increase in biosensor response with respect to non-conductive alginate membrane, providing toxicity values completely comparable to those reported. Cell electrotrapping in conductive hydrogels represents a step forward towards in high-sensitive cell-based biosensors development with important influence in environmental analysis, food and beverage industry as well as clinical diagnosis.

In the current work, we study the use of electrodeposited calcium alginate hydrogels in the development of enzymatic biosensors. Alginate electrodeposition involves the rupture of CaCO 3 particles by protons from water electrolysis into Ca 2+ and HCO 3 − . The released calcium ions cross-link alginate forming the hydrogel. Horseradish peroxidase (HRP, used as model enzyme) was electrodeposited on screen printed gold electrode (SPGE) and the activity of the enzyme was analyzed amperometrically using 3,3’,5,5’-Tetramethylbenzidine (TMB) as the mediator. The obtained gels showed good adherence to the electrode surface and stability, and did not extend more than 0.5 mm far from the desired area of deposition, allowing high control of the electrodeposition. The biosensors showed good analytical characteristics to H 2 O 2 determination, with short response times, sensitivity, low limit of detection and long lineal range.

Environmental pollutants determination mostly requires sample collection and transport to the laboratory for analysis. This process delays data acquisition, postponing any action to prevent an environmental catastrophe. This article presents an optical analysis system for in situ determination of environmental pollution, overcoming traditional limitations of optical systems such as cost, robustness, portability, dimensions, complexity or the interference of ambient light. The optical analysis system is composed of a poly(methyl methacrylate) (PMMA) optofluidic structure incorporating discrete auxiliary optical elements (i.e. light emitting diodes, LEDs, and detectors) controlled by an electronic circuit, which enables optical measurement and subtraction ambient light interference. Electronic circuit is based on a simplification of a lock-in amplifier where information is at the level of the received signal (modulus) and the phase is not considered. This configuration allows for simplification of electronic circuit requirements (i.e. mixer and Phase Locked Loop, PLL, systems are not necessary) and important reduction of size and cost. To this end, analytical signal pattern generated with the microcontroller is positioned at a frequency much higher (8 kHz) than potential interfering sources (e.g. house light or sunlight, below 50 Hz), which simplifies filtering. Optical analysis system is applied to general toxicity determination of water samples in situ. Toxicity analysis is based on a quick optical bioassay where bacterial reduction kinetics of ferricyanide is used to determine cell metabolism in less than 10 min. Ferricyanide interacts with bacterial membrane proteins which reduces it with time. Ferricyanide reduction kinetics (as the variation of ferricyanide absorption with time) allows for simple, sensitive and reliable water toxicity determination with a portable, robust, miniaturized and low cost system, insensitive to environmental changes. This optical instrument, here applied to environmental pollution, may be used in the in situ determination of other (bio)molecules of interest, such as biomarkers in biochemical analysis or pathogens in the food and beverage industry.

Materials science offers new perspectives in the clinical analysis of antimicrobial sensitivity. However, a biomaterial with the capacity to respond to living bacteria has not been developed to date. We present an electrochromic iron(III)-complexed alginate hydrogel sensitive to bacterial metabolism, here applied to fast antibiotic-susceptibility determination. Bacteria under evaluation are entrapped –and pre-concentrated- in the hydrogel matrix by oxidation of iron (II) ions to iron (III) and in situ formation of the alginate hydrogel in less than 2 min and in soft experimental conditions (i.e. room temperature, pH 7, aqueous solution). After incubation with the antibiotic (10 min), ferricyanide is added to the biomaterial. Bacteria resistant to the antibiotic dose remain alive and reduce ferricyanide to ferrocyanide, which reacts with the iron (III) ions in the hydrogel to produce Prussian Blue molecules. For a bacterial concentration above 107 colony forming units per mL colour development is detectable with the bare eye in less than 20 min. The simplicity, sensitivity, low-cost and short response time of the biomaterial and the assay envisages a high impact of these approaches on sensitive sectors such as public health system, food and beverage industries or environmental monitoring.

An impedimetric transducer based on an interdigitated electrode array (IDEA) modified with polyethyleneimine was used to study interactions with bacteria present in a sample solution. Bacteria immobilization on the sensor surface affects the surface charge and produces changes in the superficial impedance. The sensor surface was chemically modified by layer-by-layer (LbL) method with oppositely charged polyelectrolyte layers by alternating polyethyleneimine (PEI) and poly(sodium 4-styrenesulfonate) (PSS). Escherichia coli gram-negative bacteria were employed as a model for sensitivity and response time evaluation. Bacteria were immobilized on IDEA with PEI-PSS-PEI multilayer taking into account the ability of PEI to react chemically with outer membrane compounds of gram-negative bacteria and thus improve purely electrostatic interactions. Detection limit of the sensor was found to be as low as 101 cfu/mL in E. coli cultures with response time around 20 minutes. In order to introduce a biorecognition element by bacterial detection, the lectin Concanavalin A (ConA) was deposited on IDEA surface through PEI-ConA interaction, achieving a detection limit of 104 cfu/mL. The strategies developed show the possibility to achieve highly sensitive and rapid detection of bacteria using IDEA transducers.

This work proposes the use of cationic ion exchange resins as a platform for in situ formation and recrystallization of nanoparticles as a way to dynamically modulate their activity by changing their structure/composition. Here applied to Ag@Co-nanoparticles in cationic resins, this protocol may be expanded to other materials, opening the possibility to modulate activity with a simple and economic approach.

Phenolic compounds are one of the main contaminants of soil and water due to their toxicity and persistence in the natural environment. Their presence is commonly determined with bulky and expensive instrumentation (e.g. chromatography systems), requiring sample collection and transport to the laboratory. Sample transport delays data acquisition, postponing potential actions to prevent environmental catastrophes. This article presents a portable, miniaturized, robust and low-cost microbial trench-based optofluidic system for reagentless determination of phenols in water. The optofluidic system is composed of a poly(methyl methacrylate) structure, incorporating polymeric optical elements and miniaturized discrete auxiliary components for optical transduction. An electronic circuit, adapted from a lock-in amplifier, is used for system control and interfering ambient light subtraction. In the trench, genetically modified bacteria are stably entrapped in an alginate hydrogel for quantitative determination of model phenol catechol. Alginate is also acting as a diffusion barrier for compounds present in the sample. Additionally, the superior refractive index of the gel (compared to water) confines the light in the lower level of the chip. Hence, the optical readout of the device is only altered by changes in the trench. Catechol molecules (colorless) in the sample diffuse through the alginate matrix and reach bacteria, which degrade them to a colored compound. The absorbance increase at 450 nm reports the presence of catechol simply, quickly (~10 min) and quantitatively without addition of chemical reagents. This miniaturized, portable and robust optofluidic system opens the possibility for quick and reliable determination of environmental contamination in situ, thus mitigating the effects of accidental spills.

This work reports the results obtained by the development of two types of nanocomposite membranes containing metal nanoparticles prepared by applying the Intermatrix Synthesis technique for the synthesis of silver nanoparticles in the ion-exchange matrices of sulfonated polyethersulfone-Cardo and Nafion membranes. The stability (in terms of silver nanoparticles loss) of the polymer-metal nanocomposites was evaluated by using both ultrasonic and thermostatic baths and appeared to be appropriate for their practical applications. The dual-function nanocomposites were characterized in batch tests, first, by monitoring their catalytic activity in the reduction of p-nitrophenol to p-aminophenol and second, by evaluating their antibacterial efficiency towards E. coli. The results of the catalytic tests have shown that polymer-silver nanocomposites demonstrate remarkably better activity in comparison with their polymer-palladium nanocomposite analogues. The same nanocomposites have been shown to permit the complete disinfection of E. coli containing water within a short period of time.

The intermatrix synthesis (IMS) technique has proven to be an environmentally friendly methodology for the preparation of functional metal nanoparticles (FMNPs) on different reactive matrices. The distribution of these FMNPs is an important feature to control depending on the final application of the nanocomposite: bactericide assays for water treatment, heterogeneous catalysis, electrocatalytic effects and others. IMS offers the feasibility to control the FMNP distribution, taking into account the adequacy of the ion exchange form of the reactive matrix and the chemical nature of the reducing agent used for the synthesis (the Donnan effect). Consequently, AgAu–FMNPs and Au–FMNPs containing nanocomposites have been prepared by coupling a galvanic replacement stage to IMS, with tested bactericide features attributed to the distribution of the nanoparticles on the material. In addition, Ag–FMNPs and Au–FMNPs contained on multiwalled carbon nanotubes have been synthesized and used as conducting nanofillers for the development of amperometric nanocomposite sensors based on epoxy resin. The incorporation of these FMNPs into the nanocomposite sensor has shown significant electrocatalytic effects, obtaining enhanced electrochemical and analytical parameters, such as higher signal-to-noise ratios as well as better detection limits, quantification limits and sensitivities for the oxidation of ascorbic acid in water, which was used as a model analyte.

A poly(dimethylsiloxane) biophotonic lab-on-a-chip (bioPhLoC) containing two chambers, an incubation chamber and a monitoring chamber for cell retention/proliferation and pH monitoring, respectively, is presented. The bioPhLoC monolithically integrates a filter with 3 mu m high size-exclusion microchannels, capable of efficiently trapping cells in the incubation chamber, as well as optical elements for real-time interrogation of both chambers. The integrated optical elements made possible both absorption and dispersion measurements, which were comparable to those made in a commercially available cuvette. The size-exclusion filter also showed good and stable trapping capacity when using yeast cells of variable size (between 5 and 8 mu m diameter). For cell culture applications, vascular smooth muscle cells (VSMC), with sizes between 8 and 10 mu m diameter, were used as a mammalian cell model. These cells were efficiently trapped in the incubation chamber, where they proliferated with a classical spindle-shaped morphology and a traditional hill-and-valley phenotype. During cell proliferation, pH changes in the culture medium due to cell metabolism were monitored in real time and with high precision in the monitoring chamber without interference of the measurement by cells and other (cell) debris.

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 protocol.

This note describes the design and construction of new Virtual Instrumentation implemented in LabView 7.1 for the real time monitoring of the concentration of Escherichia coli cultures using impedance spectroscopy and platinum electrode chips. A hand-made Sequential Injection Analysis system was used for both the transport of microbiological samples from the incubator to the electrochemical cell, where they were measured, and the elimination of residues. The impedimetric approach showed good correlation when compared with a standard method, fluorescence microscopy counting after filtration and staining of bacterial samples, until 107 colony forming units per mL was achieved.

This work describes the resolution of binary mixtures of microorganisms using electrochemical impedance spectroscopy (EIS) and artificial neural networks (ANNs) for the processing of data. Pseudomonas aeruginosa, Staphylococcus aureus and Saccharomyces cerevisiae were chosen as models for Gram-negative bacteria, Gram-positive bacteria and yeasts, respectively. In this study, best results were obtained when entering the imaginary component of the impedance at each frequency (strongly related to the capacitive elements of the electrical equivalent circuit) into backpropagation neural networks made up by two hidden layers. The optimal configuration of these layers respectively used the radbas and the logsig transfer functions with 4 or 6 neurons in the first hidden layer and 10 neurons in the second one. In all cases, good prediction ability was obtained with correlation coefficients better than 0.989 when comparing the predicted and the expected values for a set of six external test samples not used in the training process.

This work presents the construction of a numerical model that is able to show the behaviour of a biofilm-based microrespirometer. The model uses finite element methods to solve the mass transport equations for oxygen as it travels from the bulk of the solution towards the microelectrode array through the biofilm and a protective Nafion® layer, whose main purpose is to avoid electrode fouling. The paper describes some of the issues related to the mass transport at arrays of slightly recessed microelectrodes. It provides further evidence of the validity of the diffusion domain approach as a key resource to model microelectrode arrays. The model is used to interpret amperometric data and provide metabolic rate constants that agree reasonably well with measurements performed in bacterial suspensions under similar experimental conditions.

This paper describes an approach for quantifying low concentrations of bacteria, particularly Escherichia coli, based on the measurement of the initial attachment of bacteria to platinum surfaces, using impedance spectroscopy. The value of the interface capacitance in the pre-attachment stage (before 1 min of attachment) showed correlation with suspended concentration of bacteria from 101 to 107 CFU mL−1 (colony forming units per mL). This method was found to be sensitive to the attachment time, to the applied potential and to the size of the counter electrode. The sensor lifetime was also evaluated.

This paper describes a new method for measuring the attachment of bacteria, specifically Escherichia coli on platinum electrodes using impedance spectroscopy. Impedance spectroscopy measurements showed that the double layer capacitance of the electrode was very sensitive both to the concentration of bacteria in the solution and to the attachment time. Impedance measurements of E. coli were compared with classical measurements of bacterial attachment on identical electrodes such as staining/microscopy and bacterial removal by sonication and plating onto agar. The relationship between the measured impedance of the electrode during attachment and the biophysical processes involved is discussed. Keywords: Impedance spectroscopy, Bacterial attachment, Fluorescence microscopy, Bacterial quantification, Platinum chips

This work presents the first true solid-state microrespirometer. It consists on a naturally developed biofilm of Pseudomonas aeruginosa over a Nafion modified array of gold microdisc electrodes. Such a device can be used to monitor acute toxicity in water streams based on the oxygen reduction current recorded at the microelectrode array. When a healthy biofilm is exposed to a toxic stream the bacteria conforming stop breathing which results in an immediate increase of the oxygen supply reaching the microelectrode array. The fabrication and use of such a microrespirometer is described, and a possible operation mode for a real application is presented. Given that different waters may contain toxic compounds of diverse nature, the respirometer presented here provides qualitative information only.

Starting in July 2000, treated wastewater of urban origin has been used for the "Serres de Pals" golf course irrigation (Girona, Spain). To evaluate if the soil and the aquifer underneath are affected by the utilization of this type of water, samples have been taken along a period of several months from the wastewater treatment plant, the stabilization lagoon, groundwater and soil profiles. Analyses have been performed for total coliforms and aerobic bacteria, soil water pressure and soil water content as well as chemical analyses of the irrigation water, aquifer and water of the vadose zone. Soil profiles taken at several times during the study indicate the absence of coliforms except for a short period during summer. In the vadose zone an increase of more than 1000 mg kg(-1) of NaO(2) in the top 60 cm of soil was observed while Cl(-) concentration in the aquifer reached up to 1200 mg l(-1) ten months after starting the irrigation.

There is evidence that microbial mats are able to degrade petroleum components in polluted environments, but it is still a matter of discussion whether cyanobacteria from these mats participate actively in hydrocarbon biodegradation. In this work, we attempt to evaluate whether cyanobacteria can grow using crude oil as the sole carbon source. We used an illuminated continuous packed-column reactor filled with perlite soaked with crude oil. Our reactor did not contain inorganic carbon, and to rule out possible growth of cyanobacteria on CO2 produced from the degradation of oil by heterotrophic bacteria, oxygen tension was kept low, at around 5% of air saturation. Different microorganisms grew attached to the column filling at the expense of petroleum under microaerophilic conditions. The experiment lasted 78 days, but cell numbers in the effluent increased progressively during the first 10 days until reaching a stable value. We investigated the diversity of the biofilm with molecular tools (denaturing gradient gel electrophoresis, clone library), using 16S rRNA bacterial and archaeal primers and 18S rRNA eukaryotic primers for amplification. No archaeal amplification was observed. On the other hand, we detected the presence of bacteria belonging to different groups, mainly to the alpha and gamma proteobacteria, to the chlorobi, and to the low G+C gram-positive bacteria. In addition, the biofilm included an organism closely related to the diatom Navicula cryptocephala. However, cyanobacteria were not able to grow utilizing hydrocarbons as carbon source. Measurements of aliphatic and aromatic hydrocarbons by gas chromatography before and after the experiment showed that microbial growth probably occurred at the expense of the fraction being leached.

Aquatic microorganisms have the ability to adhere onto any solid surface. They are able to re-organise as biofilms when environmental conditions change and put their life at risk. Biofilms allow bacteria to remain inside water pipes without being eliminated by biocides. Among other properties, biofilms are electrically insulating. Because of this, as they grow on a metal transducer surface, biofilms produce changes in the electrode–solution interface properties. These changes have been monitored using impedance measurements and microchips as electrical transducers. Biofilm formation has been characterised using on-chip gold working electrodes and the various growth phases have been related to specific impedance changes. Measurements employing new and reused chips of bacterial and non-bacterial solutions have been performed. Although differences between new and reused chips have been found, both kinds of electrodes can be used to evaluate biofilm formation. The effect of several biocides on biofilms has also been studied. The disinfecting properties of peroxides, strong acid/bases and alcohols have been compared as well as their ability to remove adhered substances from chip surfaces.

A miniaturized calorimeter, based on silicon integrated thermopile chips, has been developed for the determination of growth-related heat production in microbial cultures. The calorimetric vessels consists of two independent sensors located within a thermostated aluminum frame, the heat sink, and covered by a 0.6 ml reaction chamber made of PTFE for improved thermal insulation. The second sensor was used as a reference to minimize temperature perturbations on the output signal. Baseline stability was better than 0.08 μW h −1 . The Si thin-film membrane which supports the Al–Si thermopiles enabled an excellent dynamic response and a temperature resolution of 50 μK. The sensitivity for the heat power measurement was 0.39 V W −1 . Batch measurements of Escherichia coli activity under different conditions have been performed. The thermal profiles matched the exponential growth kinetics usually found in batch cultures of bacteria. A simplified model based in the Monod equation is used to analyze the influence of oxygen depletion on cell growth.

Global urban and industrial growth, with the associated environmental contamination, is promoting the development of rapid and inexpensive general toxicity methods. Current microbial methodologies for general toxicity determination rely on either bioluminescent bacteria and specific medium solution (i.e. Microtox(®)) or low sensitivity and diffusion limited protocols (i.e. amperometric microbial respirometry). In this work, fast and sensitive optical toxicity bioassay based on dual wavelength analysis of bacterial ferricyanide reduction kinetics is presented, using Escherichia coli as a bacterial model. Ferricyanide reduction kinetic analysis (variation of ferricyanide absorption with time), much more sensitive than single absorbance measurements, allowed for direct and fast toxicity determination without pre-incubation steps (assay time=10 min) and minimizing biomass interference. Dual wavelength analysis at 405 (ferricyanide and biomass) and 550 nm (biomass), allowed for ferricyanide monitoring without interference of biomass scattering. On the other hand, refractive index (RI) matching with saccharose reduced bacterial light scattering around 50%, expanding the analytical linear range in the determination of absorbent molecules. With this method, different toxicants such as metals and organic compounds were analyzed with good sensitivities. Half maximal effective concentrations (EC50) obtained after 10 min bioassay, 2.9, 1.0, 0.7 and 18.3 mg L(-1) for copper, zinc, acetic acid and 2-phenylethanol respectively, were in agreement with previously reported values for longer bioassays (around 60 min). This method represents a promising alternative for fast and sensitive water toxicity monitoring, opening the possibility of quick in situ analysis.

Cation exchange polymeric matrices are widely used in water treatment protocols to reduce the mineral content of hard waters, even for human consumption. However, they are not antibacterial and flowing bacteria can be trapped in their structures and proliferate, thus acting as microbial contamination sources. Here, Ag@Co-nanoparticles (Ag@Co-NPs) with a low-cost superparamagnetic Co0-core and an antibacterial Ag-shell are synthesized on granulated cation exchange polymeric matrices under soft reaction conditions. The presence of these NPs provides the final nanocomposite (NC) with additional functionalities (superparamagnetism and antibacterial activity) making it ideal for water purification applications. Ag@Co-NPs are synthesized in situ on four cation exchange polymeric matrices containing either strong (sulfonic) or weak (carboxylic) acid functional groups homogeneously distributed (C-type) or concentrated on an external shell (SST-type) by the intermatrix synthesis (IMS) method. The NCs are characterized (metal content, NP size and distribution, metal oxidative state, and metal release) and evaluated for water purification applications.

This paper presents the study of the dynamics of the formation of polymer-assisted highly-orientated polycrystalline cubic structures (CS) by a fractal-mediated mechanism. This mechanism involves the formation of seed Ag@Co nanoparticles by InterMatrix Synthesis and subsequent overgrowth after incubation at a low temperature in chloride and phosphate solutions. These ions promote the dissolution and recrystallization in an ordered configuration of pre-synthetized nanoparticles initially embedded in negatively-charged polymeric matrices. During recrystallization, silver ions aggregate in AgCl@Co fractal-like structures, then evolve into regular polycrystalline solid nanostructures (e.g. CS) in a single crystallization step on specific regions of the ion exchange resin (IER) which maintain the integrity of polycrystalline nanocubes. Here, we study the essential role of the IER in the formation of these CS for the maintenance of their integrity and stability. Thus, this synthesis protocol may be easily expanded to the composition of other nanoparticles providing an interesting, cheap and simple alternative for cubic structure formation and isolation.

In this communication, the synthesis of nanoparticles on anionic exchange polymers by the Intermatrix Synthesis method is reported. Monometallic (Ag) and core–shell metal/metal oxide (Ag@Fe3O4) nanocomposites were synthesized and characterized. Their magnetic and bactericidal activities were evaluated

This manuscript describes the synthesis (based on the intermatrix synthesis (IMS) method), optimization, and application to bacterial disinfection of Ag@Co polymer metal nanocomposite materials with magnetic and bactericidal properties. This material showed ideal bactericide features for being applied to bacterial disinfection of water, particularly (1) an enhanced bactericidal activity (when compared with other nanocomposites only containing Ag or Co nanoparticles), with a cell viability close to 0% for bacterial suspensions with an initial concentration below 105 colony forming units per milliliter (CFU/mL) after a single pass through the material, (2) capacity of killing a wide range of bacterial types (from coliforms to Grampositive bacteria), and (3) a long performance-time, with an efficiency of 100% (0% viability) up to 1 h of operation and higher than 90% during the first 24 h of continuous operation. The nanocomposite also showed a good performance when applied to water samples from natural sources with more complex matrices with efficiencies always higher than 80%.

8 pages, 4 figures, 1 table.-- PMID: 18762161 [PubMed].-- Printed version published Dec 1, 2008., Bacteria detection in real samples often involves long and tedious methodologies such as culture enrichment, biochemical screening, and serological confirmation. In this context, the development of biosensors and quick assays for bacteria detection appears as fast growing fields. However, a detailed study of reports in these areas reveals the existence of important differences in bacteria storage, handling, and detection conditions, indicating that authors do not take advantage of the well-established procedures existing for classical techniques such as enzyme-linked immunosorbent assay (ELISA). In the current work, we exploit standard ELISA methodology to identify and study diverse parameters that can be critical along the different steps of bacteria detection and sensing. Among others, we studied in detail the effect of the bacterial strain used and the presence of detergent and glycerol in assay performance, as well as the effects of heat inactivation or storing conditions, on bacteria integrity and thus detectability. Finally, we describe the use of “ready-to-use” frozen bacterial pellets as an excellent alternative to the use of daily prepared fresh cultures during assay optimization and preparation of calibration standards. The results presented are also supported by an extensive bibliography search, giving shape to an important compilation of information that will be useful to authors working in a variety of methodologies and sensing formats.

In this communication we describe the synthesis, characterization and evaluation of the bactericide activity of a superparamagnetic bimetallic Ag/Co polymeric nanocomposite material for the treatment of bacteria contaminated aqueous solutions.

A previously reported methodology is applied to monitor the concentration of bacterial suspensions from an incubator using impedance spectroscopy and platinum electrodes. The interface capacitance, commonly fitted as a constant phase element, CPEi, was found sensitive to the suspended bacteria concentration after short exposure times in a wide range of concentrations (from 102 to 107 colony forming units per mL, CFU mL−1) with a limit of detection of 10 CFU mL−1. The effect of the substances released during bacterial growth (enzymes, toxins, exopolysaccharide, etc.) in the CPEi magnitude was found to be negligible and samples only containing cells washed with saline solutions showed results comparable to those obtained using aliquots directly extracted from the bacterial incubator. This impedimetric approach showed correlation with classical microbiological methods for measuring bacterial concentration such as plating onto agar, optical density and fluorescence microscopy. The impedimetric approach was simplified to a single frequency analysis by selecting the optimal frequency for the measurement.

Impedance-based biosensors for bacterial detection offer a rapid and cost-effective alternative to conventional techniques that are time-consuming and require specialized equipment and trained users. In this work, a new bacteria detection scheme is presented based on impedance measurements with antibody-modified polysilicon interdigitated electrodes (3 μm pitch, IDEs). The detection approach was carried out taking advantage of the E. coli structure which, in electrical terms, is constituted by two insulating cell membranes that separate a conductive cytoplasmatic medium and a more conductive periplasm. Impedance detection of bacteria is usually analyzed using electrical equivalent circuit models that show limitations for the interpretation of such complex cell structure. Here, a differential impedance spectrum representation is used to study the unique fingerprint that arises when bacteria attach to the surface of IDEs. That fingerprint shows the dual electrical behavior, insulating and conductive, at different frequency ranges. In parallel, finite-element simulations of this system using a three-shell bacteria model are performed to explain such phenomena. Overall, a new approach to detect bacteria is proposed that also enables to differentiate viable bacteria from other components non-specifically attached to the IDE surface by just detecting their spectral fingerprints. Keywords: Impedance spectroscopy, Bacterial detection, Interdigitated electrodes, Label-free detection, Immuno-detection, E. coli O157:H7

The development of reusable dual-purpose nanocomposite foams for catalytic and bactericidal water treatment is reported. Small non-aggregated silver nanoparticles were made using Intermatrix Synthesis inside a polyurethane foam, which was chosen as a suitable polymeric matrix due to its high chemical and mechanical stability and industrial applicability. The antibacterial activity of the obtained nanocomposites was evaluated against suspensions of Gram-negative bacteria (E. coli), showing ideal bactericidal features for being applied to water disinfection. The catalytic activity of nanocomposites was also evaluated through a model reaction carried out under flow conditions. The possibility of reusing the catalytic material was evaluated in 3 consecutive cycles and, for all of them, no significant loss of efficiency was found. Moreover, the leakage of the active species to the media was evaluated under accelerated ageing conditions (3 h in an ultrasonic bath) and a negligible amount of silver was found outside the matrix. The chemical stability of the as-prepared nanoparticles was also evaluated by XANES and any modification in the chemical structure of silver nanoparticles was detected, even after storing the samples for two years under dry conditions.