Mireia Baeza

Ceramic microsystem incorporating a microreactor with immobilized biocatalyst for enzymatic spectrophotometric assays.

Low-temperature cofired ceramics (LTCC) technology is a versatile fabrication technique used to construct microflow systems. It permits the integration of several unitary operations (pretreatment, separation, (bio)chemical reaction, and detection stage) of an analytical process in a modular or monolithic way. Moreover, because of its compatibility with biological material, LTCC is adequate for analytical applications based on enzymatic reactions. Here we present the design, construction, and evaluation of a LTCC microfluidic system that integrates a microreactor (internal volume, 24.28 microL) with an immobilized beta-galactosidase from Escherichia coli (0.479 activity units) and an optical flow cell to measure the product of the enzymatic reaction. The enzyme was immobilized on a glyoxal-agarose support, maintaining its activity along the time of the study. As a proof of concept, the LTCC-beta-galactosidase system was tested by measuring the conversion of ortho-nitrophenyl beta-D-galactopyranoside, the substrate usually employed for activity determinations. Once packed in a monolithically integrated microcolumn, the miniaturized flow system was characterized, the operational conditions optimized (flow rate and injection volume), and its performance successfully evaluated by determining the beta-galactosidase substrate concentration at the millimolar level.

Operational aspects, pH transition and microbial shifts of a H2S desulfurizing biotrickling filter with random packing material.

Pall rings, a common random packing material, were used in the biotrickling filtration of biogas with high H2S. Assessment of 600d of operation covered the reactor start-up, the operation at neutral pH and the transition from neutral to acid pH. During the start-up period, operational parameters such as the aeration rate and the trickling liquid velocity were optimized. During the steady-state operation at neutral pH, the performance of the random packing material was investigated by reducing the gas contact time at both constant and increasing H2S loads. The random packing material showed similar elimination capacities and removal efficiencies in comparison with previous studies with a structured packing material, indicating that Pall rings are suitable for biogas desulfurization in biotrickling filters. The diversity of Eubacteria and the structure of the community were investigated before and after the pH transition using the bacterial tag-encoded FLX amplicon pyrosequencing. The pH transition to acid pH drastically reduced the microbial diversity and produced a progressive specialization of the sulfur-oxidizing bacteria community without any detrimental effect on the overall desulfurizing capacity of the reactor. During acidic pH operation, a persistent accumulation of elemental sulfur was found.

Flow injection analysis system based on amperometric thin-film transducers for free chlorine detection in swimming pool waters

This work reports on the performance of a user-friendly flow injection analysis (FIA) system for the monitoring of free chlorine. A methacrylate flow cell integrating a gold thin-film microelectrode, together with an on-chip gold counter electrode, both fabricated by microfabrication technology, provided robustness, low output impedance, rapid response and low cost to the proposed flow system. An external Ag/AgCl reference electrode placed downstream the chip completes the electrochemical cell. Amperometric detection of chlorine was carried out at a set potential of +350 mV, without oxygen interference. The proposed flow system responded linearly to chlorine concentrations in a range from 0.2 to 5 mgl(-1), with a sensitivity of 0.23 microAlmg(-1), the estimated limit of detection being 0.02 mgl(-1). In addition, the system response was kept stable for at least 10 days (+/-3sigma criterion), by keeping the flow system in an inert atmosphere when not in use. Fifteen samples of swimming pool waters were analyzed and no matrix effects were detected. Also, results were in good agreement with those obtained by a standard method. The excellent analytical performance of the system together with its good working stability would also enable its application for the detection of chlorine in other matrices such as tap water or chlorine stock solutions.

Composite planar electrode for sensing electrochemical oxygen demand

This work reports on the development of a graphite-polystyrene composite electrode of planar configuration, containing silver(II) oxide and copper(II) oxide catalysts (AgO-CuO), for the measurement of electrochemical oxygen demand (EOD). Optimisation studies of the composite composition as well as conditions for its processing on planar substrates and generation of an appropriate electrochemical active area resulted in the scalable fabrication of robust composite electrodes. These were evaluated with glucose as target analyte. They showed competitive low limits of detection in a linear concentration range from 5 mgL(-1) to 1400 mgL(-1) of O(2). Besides, they were stable for at least one year. The determination of EOD in wastewater samples coming from production lines of parenteral food and winemaking was successfully carried out.

Highly sensitive CNT composite amperometric sensors integrated in an automated flow system for the determination of free chlorine in waters.

We report the benefit of using an optimized composite electrode, based on a multiwall carbon nanotubes and epoxy resin, as working electrode in an automated flow system. The optimal composite electrode composition consists in a 10% carbon nanotubes and 90% epoxy resin. This composition provides lower limit of detection and increases the stability and reproducibility of the analytical signal compared to the 20% conventional composition electrodes. Moreover, the standard solutions are on-line prepared with an automated flow system. The integration of the developed carbon nanotube electrodes in the proposed flow system provides a highly sensitive analyzer for free chlorine determination in water down to the 20microgL(-1). The working range was found to be 0.02-4mgL(-1) with an analysis time of 60s. The system sensitivity was maintained into the control limits (+/-2sigma) for one month, with a mean value of -0.146 (+/-0.008) microALmg(-1). Validation of the analytical system has been performed by the successful determination of free chlorine in tap water and swimming pools water samples.

Aerobic desulfurization of biogas by acidic biotrickling filtration in a randomly packed reactor

Biotrickling filters for biogas desulfurization still must prove their stability and robustness in the long run under extreme conditions. Long-term desulfurization of high loads of H2S under acidic pH was studied in a lab-scale aerobic biotrickling filter packed with metallic Pall rings. Reference operating conditions at steady-state corresponded to an empty bed residence time (EBRT) of 130s, H2S loading rate of 52gS-H2Sm(-3)h(-1) and pH 2.50-2.75. The EBRT reduction showed that the critical EBRT was 75s and the maximum EC 100gS-H2Sm(-3)h(-1). Stepwise increases of the inlet H2S concentration up to 10,000 ppmv lead to a maximum EC of 220gS-H2Sm(-3)h(-1). The H2S removal profile along the filter bed indicated that the first third of the filter bed was responsible for 70-80% of the total H2S removal. The oxidation rate of solid sulfur accumulated inside the bioreactor during periodical H2S starvation episodes was verified under acidic operating conditions. The performance under acidic pH was comparable to that under neutral pH in terms of H2S removal capacity. However, bioleaching of the metallic packing used as support and chemical precipitation of sulfide/sulfur salts occurred.

Highly sensitive electrochemical immunosensor for IgG detection based on optimized rigid biocomposites.

In this work we present the construction of immunosensors based on graphite-epoxy which incorporate RIgG to the composite matrix. In order to improve the electrochemical properties of the immunocomposite electrodes, characterization and optimization was carried out in terms of electrochemical impedance spectroscopy and cyclic voltammetry. Consequently, taking into the account the properties required by a sensitive electrode such as high electron-transfer rate, high signal-to-noise ratio and suitable sensitivity; the optimal proportion of the transducer material (graphite-epoxy ratio) was chosen using constant amount of RIgG. The optimum composition range values, which provide these requirements, were from 16% to 17% of graphite loading. Then, the analytical properties of these immunosensors were evaluated measuring RIgG by using a competitive assay and using alkaline phosphatase-labeled antibody. Amperometric measurements were performed using hydrogen peroxide as substrate. Moreover, it has been the first time that it has been performed an optimization of the antigen-antibody ratio used in the assay, being this reduced significantly.

Simple green routes for the customized preparation of sensitive carbon nanotubes/epoxy nanocomposite electrodes with functional metal nanoparticles

In this communication, we report novel, simple and effective methodologies for the incorporation of functional metal nanoparticles in carbon nanotubes/epoxy nanocomposite electrodes. The incorporation of nanoparticles was obtained by three different routes: (a) in situ functionalization of carbon nanotube surfaces, (b) incorporation and dispersion into a composite matrix and (c) composite surface modification by drop-attachment. These techniques offer a customized route for the preparation of sensitive amperometric sensors. Independent of the route of noble metal nanoparticle incorporation, the final result is a significant enhancement of the electroanalytical response.

Autoadaptative sequential injection system for nitrite determination in wastewaters

A novel autoadaptative sequential injection system for the analysis of nitrite is described. The automatic determination uses a direct spectrophotometric method, based on the Griess-Ilosvay reaction. In this method the absorbance of the purple azo dye formed is measured at 555nm. In the sequential injection operation, the sample and the reagent are aspirated and mixed by reverse flow. The sequencing and overlapping of stacked (reagent) zones as well as selection of volumes have been studied in detail. The proposed analytical system is intelligent, simple and robust, allowing for nitrite determination in a double concentration range, by a simple and automatic programmable operation change. These two ranges are 0.0-3.0 and 0.0-20.0ppm with detection limits being 0.048 and 0.4ppm, respectively. Next surroundings have been developed allowing autocalibration and independent monitoring of nitrite concentration. The experimental set-up has been evaluated applying it to real samples analysis of very diverse concentration samples coming from a WWTP. The throughput of the method was 12 samples per hour.

CdS quantum dots as a scattering nanomaterial of carbon nanotubes in polymeric nanocomposite sensors for microelectrode array behavior

This work is focused on evaluating the direct electrochemical effect of semi-conducting nanocrystals when they are integrated in bulky nanocomposite sensors based on multiwalled carbon nanotubes (MWCNTs). For this aim, MWCNTs have successfully been functionalized with CdS quantum dots (CdS–QDs@MWCNTs) and then dispersed within an insulating polymeric matrix, as epoxy resin, for electroanalytical sensing purposes. After an accurate voltammetric and impedimetric characterization, some electrochemical parameters were surprisingly enhanced regarding the non-modified sensors, such as peak current height, electroactive area, and emphasizing the double-layer capacitance. These results can be explained since CdS–QDs confer to the nanocomposite sensor a microelectrode array behavior, dispersing the conductive microzones through the polymeric matrix, as revealed by morphological experiments. The feasibility of this approach was amperometrically evaluated for ascorbic acid and hydrogen peroxide, both used as reference analytes. Electroanalytical results demonstrated that this approach provides to the CdS–QDs-modified nanocomposite sensors the capability to determine low concentrations of analytes and improved sensitivities.