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Introduction: A simple and inexpensive differential calorimetric sensor for rapid hydrogen peroxide (H2O2) quantification in industrial solutions was developed, characterized, and validated. An earlier method proposed by the authors, on which the developed sensor is based, was enhanced, allowing overcoming the issues with its practical application. Thus, the following goals were achieved: a response time of 195 s from sampling to the analytical result; the elimination of the influence of initial sample temperature on the precision of the result by a differential mode of measurement application; the elimination of the result precision degradation caused by the parasitic heat produced by the sample stirrer. A linear quantification range from 0.05 to 1.5 mol L-1 H2O2 with a limit of detection (LOD) of 0.035 mol L-1 H2O2 was reached by applying disposable catalyst holders with a lifetime of more than 50 quantifications. The catalyst surface area to sample volume ratio adjustment allows the sensor’s analytical characteristics adaptation to the industrial-technological process requirements. Background: Hydrogen peroxide is used as a reagent in the technological processes of several industrial branches, and the simple and fast monitoring of its concentration is critical for the maintenance of technological process stability. The common disadvantages of the existing sensors are the complex and long measuring procedures requiring sophisticated equipment and qualified personnel. Objective: This study’s objective is the development of a simple and inexpensive calorimetric sensor and measuring instrument for rapid H2O2 quantification in industrial solutions by nonqualified personnel. The sensor is based on the significant improvement of the reagent-less calorimetric method proposed by the authors earlier, allowing its simple and precise practical application. Drawbacks such as the result of precision degradation by the initial sample temperature and by parasitic heat production during the measurement were overcome by obtaining an economical, simple, rapid, and precise sensor. Methods: The temperature increase resulting from the heat generated during the catalytic H2O2 decomposition was recorded as a sensor response. A simple and inexpensive disposable acrylic ring covered by MnO2 serves as a specific catalyst for H2O2 decomposition. The sensor analytical characteristics were evaluated, and permanganate approach validation was conducted. Results: The developed sensor showed a linear response to H2O2 from 0.05 to 1.5 mol L-1 with a LOD of 0.035 mol L-1 and LOQ of 0.115 mol L-1 under optimized experimental conditions. The catalyst surface area to sample volume ratio adjustment allows the sensor’s analytical characteristics adaptation to the industrial process requirements. The results were validated using the permanganate approach application, obtaining recovery values of 98.7%–101.4%. Conclusion: A simple and economic calorimetric sensor for quick hydrogen peroxide quantification in industrial solutions was developed, characterized, and validated. Disposable catalyst-loaded rings were employed allowing 50 successive quantifications of 1 mol L-1 H2O2 with a relative error of 1.08%. The sensor construction enables easy catalyst replacement and adjustment of its analytical characteristics to the industrial technology requirements using catalyst rings with various catalyst surface areas.

A low-cost disposable lipase activity sensor was developed and characterized overcoming the main drawbacks of the already existing disposable ones: insufficient reproducibility to be applied for automatic lipase activity quantification and complicated and long manual analytical procedure performed by qualified personnel. The sensor is based on a capacitor formation on an electrode surface by a substrate layer deposition possessing high electrical resistivity and dielectric constant (composite of olive oil mixed with BaTiO3 nanoparticles) serving as both: sensor sensitive layer and capacitor dielectric. Its decomposition by lipase catalyzed hydrolysis causes its thickness decrease resulting in capacitance increase proportional to the lipase activity. The sensor was characterized in terms of limit of quantification, linear quantification range, sensitivity, response time, precision, repeatability, storage time and the results are presented and discussed. The validation experiment showed excellent agreement with the standardized titrimetric method.

A simple and rapid impedimetric sensor applicable for industrial lipase activity quantification was developed and characterized. It is based on the lipase catalyzed degradation by hydrolysis of a thin nanocomposite substrate sensitive layer deposited on a PCB stick electrode usable as disposable or regenerable. The sensitive layer degradation rate was evaluated by the impedance changes registration along time resulting from its thickness diminution applying a small amplitude AC voltage with a constant frequency. The AC current phase shift variations along the time caused by the impedance changes were registered as s sensor response. The sensor was characterized in terms of linear quantification range, LOD, precision and quantification time. The response time was found to be from 80 to 6 s for the linear concentration range from 0.99x10-2 to 1.68 U.S.P. U mL-1 with relative errors from 3.75% to 1.24% respectively and a LOD of 8x10-3 U.S.P. U mL-1. Finally, lipase spiked whey samples taken from milk industry were quantified and the results were validated by a titrimetric method revealing a good agreement (relative error less than 4.5%)

A simple and rapid reagent less nephelometric method for on-line H2O2 quantification in semiconductors etching solutions was developed, optimized, characterized and validated. The intensity of the light scattered by the oxygen gas suspension resulted from H2O2 catalytic decomposition by immobilized MnO2 was registered as analytical response. The influences of the light wave length, the agitation rate, the temperature and the catalyst surface area on the response amplitude were studied and optimization was done. The achieved linear concentration range from 10 to 150mmolL-1 at 0.9835 calibration curve correlation coefficient, precision from 3.65% to 0.95% and response time from 35 to 20s respectively, at sensitivity of 8.01µAmmol-1 L and LOD of 2.9mmolL -1 completely satisfy the semiconductor industry requirements.

An amperometric bi-enzyme sensor for detection of organophosphorus pesticides (OPs) with phenolic leaving groups, which are not electroactive, is presented in this work. The biosensing platform was created by a simple, controllable, and reproducible one-step electrodeposition onto the surface of a glassy carbon electrode of a chitosan bionanocomposite with entrapped carboxylated multi walled carbon nanotubes, organophosphorus hydrolase (OPH), and horseradish peroxidase (HRP). The OPs determination involved a sequence of OPH and HRP-catalyzed reactions resulting in phenolic radicals production, which were quantified by registering the current of their reduction at a potential of −50 mV vs. Ag, AgCl/KClsat.The developed sensor was applied for the determination of prothiofos, as an example. At optimized conditions (pH 7.25 and H2O2 concentration 200 μmol L−1), a LOD as low as 0.8 μmol L−1 was attained, while the linear concentration range was extended from 2.64 μmol L−1 up to 35 μmol L−1. The main advantage of the proposed bi-enzyme sensor is its selectivity toward the OPs with phenolic leaving groups, excluding the interference of the nitrophenyl-substituted OPs.

A simple, rapid, and reagent-less calorimetric method for H2O2 quantification, applicable automatically on-line was developed, analytically characterized and tested with real SC-1 alkaline etching solutions used in the semiconductor technology. Being based on H2O2 catalytic decomposition by immobilized solid catalyst, the proposed method possesses excellent specificity toward the H2O2 without any interference. The total quantification time was found to be less than 60s, RSD lies in the range from 4.7% to 1.8% for the linear concentration range from 2.8 10-2 to 2molL-1 respectively and the LOD was determined to be as low as 9.3 10-3molL-1.

Current outbreaks associated with drug-resistant clinical strains are demanding for the development of broad-spectrum antibacterial agents. The bactericidal materials should be eco-friendly, economical and effective to suppress bacterial growth. Thus, in this work, diameter controlled spherical Cucore-Agshell nanoparticles (Ag@CuNPs) with diameter ranging from 70 to 100 nm by one-step co-reduction approach were designed and synthesized. The Ag@CuNPs were homogenous, stable, and positively charged. The 70 nm Ag@CuNPs showed a consistent and regular Ag shielding. We observed the 100 nm Ag@CuNPs achieved symmetrical doped Ag clusters on the Cu core surface. We used Gram-positive and Gram-negative models strains to test the wide-spectrum antibacterial activity. The Ag@CuNPs showed detrimental microbial viability in a dose-dependent manner; however, 70 nm Ag@CuNPs were superior to those of 100 nm Ag@CuNPs. Initially, Ag@CuNPs attached and translocated the membrane surface resulting in bacterial eradication. Our analyses exhibited that antibacterial mechanism was not governed by the bacterial genre, nonetheless, by cell type, morphology, growing ability and the NPs uptake capability. The Ag@CuNPs were highly tolerated by human fibroblasts, mainly by the use of starch as glucosidic capper and stabilizer, suggesting optimal biocompatibility and activity. The Ag@CuNPs open up a novel platform to study the potential action of bimetallic nanoparticles and their molecular role for biomedical, clinical, hospital and industrial-chemical applications.

The simultaneous voltammetric determination of species with close peak potentials presents some difficulties, because of the overlapping of their redox peaks at conventional solid electrodes. Therefore, two approaches were proposed to overcome this drawback: (i) chemometric resolution of the overlapped peaks by semi-derivative or multivariate analysis and (ii) development of chemically modified electrodes with better electrochemical performances, permitting peaks separation. However, the mathematical treatment habitually results in a precision decrease, while the electrode modification often requires the use of expensive materials and involves sophisticated techniques. Hence, another strategy for the direct simultaneous species determination is suggested in this work. It involves the application of Differential Alternative Pulses Voltammetry (DAPV) [1], which provides the great resolution of the second order voltammetric techniques, as Radio-Frequency Polarography, Second Harmonic AC Voltammetry, and Differential Faradaic Rectification Polarography (DFRP), in combination with the high sensitivity, precision, and instrumental and operational simplicity of the most common voltammetric technique, the differential pulse voltammetry (DPV). The second order voltammetric techniques including DAPV are based on the nonlinearity of the electrochemical system I/E characteristic yielding voltammograms shaped as a derivative of voltammetric peak resulting from small sinusoidal or rectangular bipolar deviations of the DC potential. Two single pulses of small amplitude, one cathodic and one anodic are successively applied in DAPV for every value of the scanned DC potential with delay time between the pulses equal to the delay time between the scan step and the first one (Fig. 1). The sum of the two pulse faradaic current components with opposite polarities is registered vs. the scanned potential as DAPV voltammogram. The experimentally determined half-width of the DAPV peaks (37 mV at 2 electrons reduction) is 1.22 times smaller than that of the most common voltammetric technique DPV (45.3 mV) at the same conditions and equals that obtained by the application of another second order technique, the DFRP. Thus, the DAPV voltammogram’s shape as second derivative of voltammetric wave combined with the small half-widths of the anodic and the cathodic peaks allows simultaneous quantification of species having very small peak potential difference. Taking advantage from the great resolution power of DAPV, it was applied for the simultaneous determination of a range of organic (catechol and hydroquinone [2]; o-nitrophenol, m-nitrophenol and p-nitrophenol [3]) and inorganic species (Cd2+/In3+; Tl+/Pb2+ [1, 4]) with close peak potential difference, as shown in Figs. 2-5. The proposed approach offers a very simple alternative route for the simultaneous determination of a broad range of species and overcomes the disadvantages of the currently applied strategies involving electrode modification or mathematical data processing. References 1. Zlatev, M. Stoytcheva, B. Valdez, J.P. Magnin, P. Ozil. Electrochem. Communications, 2006, 8, 1699-1706. 2. Ayala, M. Stoytcheva, R. Zlatev, Z. Velkova, V. Gochev, B. Valdez, G. Montero. Electroanalysis, 2018, 30, 1913-1917. 3. Stoytcheva, R. Zlatev, Z. Velkova, V. Gochev, A. Ayala, G. Montero, B. Valdez. Electroanalysis, 2019, 31, 652-660. 4. Zlatev, M. Stoytcheva, B. Valdez. Electroanalysis, 2018, 30, 1902-1905. Figures captions Fig. 1. DAPV potential-time waveform. M1-M4 are the current measuring intervals; DT is the wait time for the pulse capacitive current decay. Fig. 2. HQ (30 mmol L-1) and CC (10 mmol L-1) determination by DAPV. PBS 0.1 mol L-1, pH 7; Spectroscopic graphite electrode. Fig. 3. Nitrophenol (NP) isomers simultaneous determination by DAPV (m-NP 125 mmol L-1, p-NP 125 mmol L-1, and increasing o-NP concentrations: 25, 50, 75, 100 and 125 mmol L-1). PBS 0.1 mol L-1; pH 6.5; glassy carbon electrode modified by a nanocomposite of graphite nanopowder and Au nanoparticles. Fig. 4. Cd2+ and In3+ (E1/2 difference 45 mV) simultaneous determination by DAPV, 0.1 mol L-1 HCl; Hanging Mercury Drop Electrode. Fig. 5. Tl+ and Pb2+ (E1/2 difference 50 mV) simultaneous determination at 12:1 concentration ratio by DAPV and DPV. 0.1 mol L-1 HCl; Hanging Mercury Drop Electrode. Figure 1

In this study we describe a sensitive amperometric microbial biosensor that is fast, economic, reliable, and can compete with the existing proposed methods for vitamin B12 determination. Taking advantage of the bacterial strain Tetrasphaera duodecadis which oxidizes vitamin B12 with oxygen consumption, we shaped a promising alternative tool for the direct and specific determination of vitamin B12 in different samples without pre-treatment. For this purpose, a vitamin B12 amperometric microbial biosensor was constructed based on one-step immobilization of the bacterium by filtration of a concentrated bacterial mass through a 0.15 μm pore size cellulose filter and fixed on a Clark-type oxygen probe, serving as a transducer, and exploiting the described processes. The results obtained indicate a sensitive capability with a linear sensor concentration range from 10−7 mol L−1 to 10−5 mol L−1 and the response time of about 700 seconds at 10−6 mol L−1. Furthermore, the Tetrasphaera duodecadis membrane attached to the Clark type oxygen probe has an estimated 1 month lifetime at room temperature. In addition, the developed prototype allowed the assessment of B12 status directly in samples prepared for that purpose. The results were well correlated with those obtained with commercial samples, thus demonstrating that the proposed microbial sensor offers an accurate and useful analytical tool that can be easily applied to prevent diseases caused by the lack of vitamin B12.

A simple and rapid reagent less nephelometric method for on-line H

The authors describe a graphite immobilized bismuth film electrode with enhanced sensitivity for the organophosphorus pesticide paraoxon. The film was formed by ex-situ electroplating of bismuth onto the large surface of a glassy carbon electrode modified with graphite nanopowder (Bi/Gr/GCE). The modified GCE was characterized by chronoamperometry using p-nitrophenol as a model nitro compound. The modification of the GCE results in an increase of the electroactive area (to 27.7 mm2) and of the electrocatalytic activity (the catalytic rate constant being 4140 L·mol−1·s−1). This results in an enhancement of the current for the electroreduction of paraoxon by a factor of 4.3 (compared to a plain GCE). The modified GCE was applied to the sensitive determination of paraoxon by differential pulse voltammetry. At a typical working potential of −0.45 V vs. Ag/AgCl, the LOD is 2 nmol·L−1 of paraoxon, which is comparable to the LOD of some cholinesterases-based electrochemical sensors and is lower than the LOD of the organophosphorus hydrolase-based electrochemical sensors for paraoxon. In addition, the new GCE is more stable than enzyme-based sensors, and it can be renewed.

Electrodes fouling associated with the electroenzymatic phenols determination was characterized in this work, applying various techniques such as cyclic voltammetry, amperometry, EQCM, and optical microscopy. An approach to overcome the fouling effects and hence to improve the precision of the phenolic compounds determination was suggested and tested. This approach consists of pulsed potential waveform application with a cleaning potential step of + 1.4 V vs. Ag, AgCl/KCl sat with a duration of 166.66 ms, while the determination was carried out at 0.0 V vs. Ag, AgCl/KCl sat applied for 66.64 ms. As a result a RSD of 2.97% for 0.6 mmol L −1 o-catechol determination was achieved, compared with 6.53% without the cleaning step application. The method was successfully used for the precise phenolic and triazine pollutants determination.

As known, the dissolved hydrogen undergoes electrochemical oxidation, the mechanism of which depends on the electrolyte pH. In alkaline solutions the OH- participates in the hydrogen oxidation according to the reaction: H+ OH-= H2O+2e-, while in acid solutions the electrochemical oxidation is direct: H2=2H++2e-. In both cases electrolyte acidifying occurs because of the OH- consumption or H+generation, making suitable the application of very acid electrolytes to avoid the sensor characteristics changes caused by a great pH changes over time. A 3-electrode probe similar to the Clark type oxygen probe construction was proposed, elaborated, and characterized as a dissolved hydrogen sensor. Its analytical characteristics such as LOD, sensitivity, response time, and linear response concentration range were determined as a function of the temperature, membranes materials, the electrolytes composition, and pH. Coulometric controlled electrochemical hydrogen generator was applied for standard solution preparation. The sensor characterization results are presented and discussed together with the results obtained from its application for the real time determination of the rate of hydrogen production by the varieties B10 and IR3 of the photosynthetic strain Phodobacter Capsulatus. Acknowledgement. This work was supported by CONACyT Mexico: Research grant No. 152961, CONACYT-SENER “Sustentabilidad Energética” 2010-01.

An approach for precision improvement in organophosphorus pesticide determination was developed, applied and characterized. The enzyme organophosphorus hydrolase was employed as a specific agent for electrode surface modification, and the pulsed amperometric detection for 66.6 ms was applied for the hydrolysis product detection. Pulsed electrochemical cleaning, i.e. oxidation at a very positive potential (+1.4 V vs. Ag, AgCl) was applied every 233 ms for 166.6 ms for elimination of the fouling effect, which degrades the determination precision. By this way a RSD of 0.41% at 40 μmol L−1p-nitrophenol determination was achieved after 10 determinations, instead of 43.93% without the pulsed cleaning application.

The medical diagnostic, the industry, and the biotechnology require rapid, sensitive, and easy to use methods for trypsin activity determination. A simple approach, which meets all these requirements, based on Quartz Crystal Microbalance (QCM) was developed, analytically characterized and described in the present work. QCM application allows rapid trypsin activity evaluation by real time monitoring of the enzymatic degradation of the substrate. The new approach suggested in this work takes advantage of nanoparticles loaded gelatin employment as a trypsin substrate, deposited on the QCM crystal. The heavy nanoparticles leave the substrate layer together with the products of its enzymatic degradation provoking thus a greater decrease of the total QCM crystal mass compared with the non charged substrate. As a result, a higher sensor frequency response occurs. A 10 fold improvement of the LOD was achieved for trypsin activity evaluation applying the proposed method with Ag nanoparticles loaded gelatin (7.5×10 −4 U mL −1 vs. 7.5×10 −3 U mL −1 obtained by the “classic” QCM method). The approach subject of this work can be applied with any substrate degrading enzyme.

The present work discusses the problem of induced external electrical noise as well as its removal from the electrical potential obtained from Scanning Vibrating Electrode Technique (SVET) in the pitting corrosion process of aluminum alloy A96061 in 3.5% NaCl. An accessible and efficient solution of this problem is presented with the use of virtual instrumentation (VI), embedded systems, and the discrete wavelet transform (DWT). The DWT is a computational algorithm for digital processing that allows obtaining electrical noise with Signal to Noise Ratio (SNR) superior to those obtained with Lock-In Amplifier equipment. The results show that DWT and the threshold method are efficient and powerful alternatives to carry out electrical measurements of potential signals from localized corrosion processes measured by SVET., The authors acknowledge the Materials Corrosion Laboratory of the UABC Institute of Engineering for the economic support and facilities provided for the development of electronic instrumentation and testing of the experimental processes. They are grateful for the international collaboration with the National Center of Metallurgical Research (CENIM) Madrid, the Spanish State Council for Scientific Research (CSIC), for the support provided in the research and experimentation process in this work.

Carbon nanohybrid material (CNF/γ-FeO) was obtained via a modified sol-gel technique consisting of two steps: functionalization of carbon nanofibers (CNF) in HSO/HNO followed by synthesis using Fe(NO)·9HO. As a result, the iron content of the CNF/γ-FeO was increased by more than twice from about 40% to about 87% mass percent, compared to the pristine CNF and oxidized CNF specimens, as proved by energy dispersive X-ray fluorescence. Scanning electron microscopy images exhibited >cumulus> on the CNF/γ-FeO specimen surface, which showed the highest iron mass percentage, proved by energy dispersive X-ray spectroscopy. Transmission electron microscopy images confirmed attachment of γ-FeO cumulus to the inner and outer surfaces of the CNF walls after synthesis. The characteristic peaks of Fe 2p and Fe 2p appeared in the XPS spectra obtained on CNF/γ-FeO. In addition, X-ray diffraction (XRD) results indicated formation of γ-FeO during the synthesis process. The Raman spectrum of the CNF/γ-FeO sample displays peaks with positions close to characteristic peaks of highly crystalline and monodisperse maghemite nanocrystallites. The synthesis of CNF/γ-FeO leads to an increase in the hydrophilicity of CNF and magnetic properties at room temperature., The authors acknowledge the support of the Engineering Institute of the Autonomous University of Baja California (UABC), Mexico, and the National Center for Metallurgical Research (CENIM-CSIC), Spain, during the performance of this research. The authors are also thankful to the Center of Nanoscience and Nanotechnology of the National Autonomous University of Mexico (UNAM), for the help with XPS and TEM analysis. Finally, the authors are grateful to theNational Council of Science and Technology of Mexico (CONACYT) for supporting this research through MYDCI Program Scholarship Grant (no. 257875).

Extracellular lipase production by Penicillium chrysogenum, Trichoderma harzianum and Aspergillus flavus was carried out through solid state fermentation using agro-industrial residues as substrates. For all three strains, the growth temperature was 29±1 °C, and 65% w (g/gds) moisture content. The effect of three factors on lipase production rate was investigated: initial pH (6.0 and 7.0), time of fermentation (72 h, 96 h and 120 h), and type of mixed substrate (wheat bran-olive oil, and wheat bran-castor oil cake). The process was optimized applying a mixed level factorial design. Fermentation time and pH were found to have positive effects on lipase production and secretion rates. However, the time effect was larger than initial pH. Type of substrate demonstrated minor effective importance than the other two factors, and Aspergillus flavus showed the larger lipase production among the three strains. Results indicated that the three fungal strains were able to grow and produce lipase in both cult...

The rates of hydrogen production by B10 and the genetically modified IR3 varieties of the bacterial strain R. capsulatus employing DL-sodium lactate as a carbon source and parts of the visible spectrum light as energy source were compared. The influence of parameters such as: light spectrum (blue, green, red, white light), light luminance (from 2500 to 17000 lux), reactor geometry (flat and cylindrical), was studied to maximize the bacterial hydrogen production. Maximal results were achieved in a flat reactor at 700 nm (red light) and 2500 lux light luminance by both varieties, but the hydrogen production obtained by the genetically modified variety IR3 exceeded the B10 production up to 64 % in spite of the superior biomass quantity of the latter.

Electrochemical biosensing, due to its sensitivity and specificity, combined with the low-cost and operation convenience of the equipment, is considered as a promising point-of-care approach in clinical analysis. This review presents the basic principles of operation, the current status, and the trends in the development and the clinical implementation of some selected electrochemical biosensors. These include: electrochemical glucose biosensors successfully applied in diabetes management, and electrochemical biosensors for cholinesterases and trypsin activities determination. The latter, although less common, demonstrate the potential of improving the existing clinical methods in the diagnostics and the treatment of neurotoxic, neurological, and pancreatic diseases.