Urea Hydrolysis Reaction Research Articles

Structural characterization of an unprecedented mixture of H4Nb2O7 and TT-Nb2O5 phases obtained by hydrothermal synthesis

Several crystal structures of niobium-based materials are currently being studied. In this work, for the first-time a mixture of H4Nb2O7 and Nb2O5 materials was obtained from ammonium niobate oxalate using the urea hydrolysis reaction in a hydrothermal synthesis. The techniques used for characterization, such as X-ray diffraction (XRD), Rietveld refinement, Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), and High-Resolution Transmission Electron Microscopy (HRTEM), confirmed a combination of pyrochlore-type H4Nb2O7 and pseudohexagonal TT-Nb2O5 phases, with distinct nanostructures and anisotropic growth in the TT- Nb2O5 phase, in addition to controlling phase fractions by synthesis time. These discoveries suggest potential applications in various environmental applications due to the material’s adsorptive capacity.

The Characteristics of Urease Enzyme of Green Bean Seeds (Vigna radiata L.) and Its Activity as An Antifungal Against Candida albicans

Urease is an enzyme responsible for catalyzing the hydrolysis reaction of urea into CO2 and NH3. The urease isolated in this study came from green bean seeds. The urease enzyme was then tested for its antifungal activity against Candida albicans. The research aims to extract and characterize the urease enzyme from green bean seeds and explore its potential use as an antifungal agent. Green bean seeds were smoothed with a mortar and pestle, followed by homogenization using a stirrer and cold centrifugation. The crude extract of the urease enzyme was assessed for its activity through the Nessler method and measured by employing a UV-Vis spectrophotometer at a wavelength of 500 nm. The well-diffusion method was conducted to determine the antifungal activity of rough enzyme extracts against C. albicans. Positive controls were 100% ketoconazole, and negative controls used a pH buffer of 7. The characterization of the urease enzyme from green bean seeds revealed the optimum urease activity at a concentration of 0.25 M, pH level of 7, and an incubation temperature of 35°C with a value of 32.115 U/mL. Maximum reaction rate (Vmax) and Michaelis-Menten constant value (KM) were obtained at 56.497 U/mL and 0.215 M, respectively. Antifungal tests of C. albicans resulted in strong inhibitory activity at a concentration of 100% crude urease extract of 12 mm inhibition zone. The inhibitory concentration value grows at least 0.5% by 0.25 mm and positive control of 19.802 mm.

Enzymatic-Induced Calcite Precipitation (EICP) Method for Improving Hydraulic Erosion Resistance of Surface Sand Layer: A Laboratory Investigation

As a bio-inspired calcite precipitation method, bio-grouting via enzymatic-induced calcite precipitation (EICP) uses free urease enzyme to catalyze the urea hydrolysis reaction. This soil stabilization approach is relatively new and insufficiently investigated, especially for applications involving surface layer stabilization of sandy soil deposits for increasing hydraulic erosion resistance. This paper presents a laboratory investigation on the surface erosion resistance improvements for compacted medium-gradation quartz sand specimens mediated using 10 different EICP treatment protocols. They involved single- and two-cycle injections of the urease enzyme (activity of 2400 U/L) and 0.5, 0.75, or 1.0-M urea–CaCl2 cementation solution reagents. The urease enzyme was extracted from watermelon seeds. Erosion rates were determined for various hydraulic shear stresses applied using the erosion function apparatus. The spatial distribution and morphology of precipitated calcite within the pore-void spaces of the crustal sand layer were investigated with a scanning electron microscope. Compared to untreated sand, all 10 investigated EICP treatment protocols produced substantially improved erosion resistance, especially for the higher cementation solution concentration (1.0 M). Of these 10 EICP protocols, a single cycle of enzyme–1.0-M-cementation solutions injections was identified as the more pragmatic option for achieving near-optimum erosion resistance improvements. Highest and lowest amounts (18.8 and 5.0 wt%) of precipitated calcite corresponded to the best and worst performing EICP-treated specimens, although the calcite’s spatial distribution in treated specimens is another important factor.

Immobilization of Cd2+ and Pb2+ by biomineralization of the carbonate mineralized bacterial consortium JZ1.

Microbially induced carbonate precipitation (MICP) has been proven to effectively immobilize Cd2+ and Pb2+ using a single bacterium. However, there is an urgent need for studies of Cd2+ and Pb2+ immobilized by a bacterial consortium. In this study, a stable consortium designated JZ1 was isolated from soil that was contaminated with cadmium and lead, and the dominant genus Sporosarcina (99.1%) was found to have carbonate mineralization function. The results showed that 91.52% and 99.38% of Cd2+ and Pb2+ were mineralized by the consortium JZ1 with 5g/L CaCl2 at an initial concentration of 5mg/L Cd2+ and 150mg/L Pb2+, respectively. The bioprecipitates were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Moreover, the kinetic studies indicated that the urea hydrolysis reaction fit well with the Michaelis-Menten equation, and the kinetic parameters Km and Vmax were estimated to be 38.69mM and 58.98mM/h, respectively. When the concentration of urea increased from 0.1 to 0.3M, the mineralization rate increased by 1.58-fold. This study can provide a novel microbial resource for the biomineralization of Cd and Pb in soil and water environments.

Paper-based analytical device with colorimetric detection for urease activity determination in soils and evaluation of potential inhibitors

Urease is an enzyme associated with the degradation of urea, an important nitrogen fertilizer in agriculture. Thus, this current report describes the use of a paper-based analytical device (UrePAD) designed to contain a microzone array for colorimetric determination of urease activity in soils in the absence/presence of potential enzyme inhibitors. The UrePAD can be used at the point-of-need (point-of-care), and it offers advantages such as low cost, simplicity in handling, low sample/reagent volumes, and no use of toxic reagents. The acid-base indicator phenol red was used to monitor the urea hydrolysis reaction catalyzed by urease in the evaluated systems. The images were digitalized in a bench scanner, and the analysis was performed using Corel Draw X8 software. The device offered a LOD of 0.10 U mL−1 with linearity between 0.25 and 4.0 U mL−1 and a relative standard deviation ≤ 1.38%. UrePAD was tested in four soil samples of different characteristics and with eight urease inhibitors of varied classes. The results obtained through the proposed device did not differ statistically (95% confidence interval) from those employing the classic method based on the Berthelot reaction, thus indicating that UrePAD was effective for determining urease activity and screening inhibitors, besides showing the capacity to simplify fieldwork involving the application of urea in the soil.

Transformation and fate of urea in pit-toilet blackwater after discharge to environment.

Studies on urea transformation reactions in blackwater are limited as urea rapidly hydrolyses under anaerobic condition. Since ammonium content of blackwater mainly originates from urine-urea, studying urea hydrolysis reactions is important to predict potential nitrate loads in aquifers from on-site sanitation facilities. In this study, urea spiked blackwater samples from pour flush pit toilet are used to examine the urea-ammonium pathways at varying initial urea concentrations and temperature. Based on laboratory results, the annual nitrate load imposed by the urea constituent of blackwater in a hard rock aquifer is predicted. Laboratory results illustrated that experimental temperature of 37 °C and pH range of 6.7 to 8.1 facilitated optimum urease enzyme activity at the initial substrate concentration of 500 mg/L. The Q10 value for urea transformation reactions indicated that increase in temperature has positive influence on enzyme activity. The reduction in urea concentration with time followed first-order kinetics. Part of ammonium ions in blackwater oxidises as nitrate ions that travel to the aquifer. Upon mixing and dilution, the nitrate concentration in 1 km2 of hard rock aquifer would annually increase by 0.004 mg/L due to blackwater infiltration from single household pour flush toilet.

Reaction of Ferralsol to Acidifying Effect of Nitrogen Fertilisation

Background: The objective of this study was to determine the short-term effect of urea fertiliser application on soil reactions in a Ferralsol, with particular thrust on P sorption. Methods: Two experiments were conducted for this purpose: 1) a screenhouse pot experiment; and 2) a laboratory P sorption component. The pot (10 litre capacity plastic pots) experiment was conducted at the Makerere University Agricultural Research, Kabanyolo in Uganda, using a Ferralsol. The study comprised of four urea N (46% N) fertiliser treatments, namely, 0, 40, 80 and 120 kg N·ha-1, equivalent to 0, 200, 400 and 600 mg N per pot. A completely randomised design was adopted with three replicates. Urea rates were applied in 50% split doses, one at planting and the other at 19 days after seedling emergence (to simulate farmer practice). This was followed by watering to field capacity using distilled water. Soil samples were taken at three daily intervals until day fourteen; thereafter, soil sampling was at an interval of seven days. The second urea split dose was applied at 21 days followed by soil sampling at an interval of three days till day fourteen. Thereafter, soil was sampled at seven day intervals until the end of experiment. Soil samples were analysed for exchangeable H+, Al3+, NH4+and NO3- ions. The reaction trends of the concentrations of these ions and Bray 1 P were used to structure different response curves representing the instantaneous reactions. As for the laboratory P-sorption study, treatments included the four rates of urea used in the pot experiment (0, 40, 80 and 120 kg N·ha-1) and seven levels of P (2.5, 5, 10, 20, 30, 40 and 50 ppm) as KH2PO4. The setup was incubated under laboratory conditions and soil samples were repeatedly taken at 10 days (after 4 days of urea incubation plus 6 days of P application). The P sorption data were fitted to Langmuir model. Results: The pot experiment revealed an abrupt drop in the concentrations of exchangeable Al3+ and H+ ions (p 0.05) within the first 6 days after urea application, accompanied by a positive surge in the concentration of NH4+ ions. This phase (6 days) was followed by a rise in the levels of exchangeable Al3+, H+ and NO3- ion concentration, which was inversely mirrored by a drop in the concentration of NH4+ ions. Consequently, the patterns displayed by the soil reactions were delineated into four phases, with Phase 1 (6 days) being characterised by urea hydrolysis reactions of deamination and ammonification, Phase 2 (10 days) being dominated by nitrification and its acidifying properties, Phase 3 being a repeat of Phase 1, both occurring immediately after urea application (within 6 days); and Phase 4 being a repeat of Phase 2. As for the P-sorption study, the effects of urea hydrolysis in a Ferralsol markedly increased soil pH and surprisingly P sorption. The contradictory P sorption behavior, despite the drop in exchange acidity was attributed to presence of divalent calcium in the extraction reagent used. Conclusion: The short term insights obtained in response to urea N application in the Ferralsol, are eye openers to future use of N fertilisers as well as strategic management of the associated acidification process which is often more costly and complicated to manage.

Paper chip-based colorimetric assay for detection of Salmonella typhimurium by combining aptamer-modified Fe3O4@Ag nanoprobes and urease activity inhibition.

Arapid and sensitive colorimetric assay is described forSalmonella typhimurium (S. typhimurium) detection using urea/phenol red impregnated test paper. Aptamer-modified Fe3O4@Ag multifunctional hybrid nanoprobes (apt-Fe3O4@Ag NPs) were used to specifically captured S. typhimurium; the nanoprobes were quickly etched by H2O2 to form Ag+. The generated Ag+ can inhibit the urease-catalyzed hydrolysis reaction of urea to produce NH4+. Consequently, the as-prepared test paper displayed a yellow color. In the presence ofS. typhimurium, the target bacteria can cause aggregation of apt-Fe3O4@Ag NPs, and the deposited Ag on the nanoprobe's surface is shielded against H2O2-induced oxidative decomposition leading to reduced Ag+ production. The catalytic activity of urease cannot be inhibited completely by inadequate amount of Ag+. An obvious color change from yellow to pink can be monitored directly using our test paper as a result of increased NH4+. The entire assay procedure could be completed within 1h. A limit of detection of 48cfu/mL is achieved with a linear range of 1×102 to 1×106cfu/mL. The recoveries ofS. typhimurium spiked in pure milk samples were 92.48-94.05%. Graphical abstract Schematic diagram of the proposed colorimetric assay for S. typhimurium detection based on etching of bifunctional apt-Fe3O4@Ag NPs and inhibiting catalytic activity of urease by Ag+. A color change from yellow to pink can be observed and correlated to the concentration of S. typhimurium.

Solvent Effect on the Regulation of Urea Hydrolysis Reactions by Copper Complexes

Abiotic allosterism is most commonly observed in hetero-bimetallic supramolecular complexes and less frequently in homo-bimetallic complexes. The use of hemilabile ligands with high synthetic complexity enables the catalytic center by the addition or removal of allosteric effectors and simplicity is unusually seen in these systems. Here we describe a simpler approach to achieve kinetic regulation by the use of dimeric Schiff base copper complexes connected by a chlorido ligand bridge. The chlorido ligand acts as a weak link between monomers, generating homo-bimetallic self-aggregating supramolecular complexes that generate monomeric species in different reaction rates depending on the solvent and on the radical moiety of the ligand. The ligand exchange was observed by electron paramagnetic resonance (EPR) and conductivity measurements, indicating that complexes with ligands bearing methoxyl (CuIIL2) and ethoxyl (CuIIL5) radicals were more prone to form dimeric complexes in comparison to ligands bearing hydrogen (CuIIL1), methyl (CuIIL3), or t-butyl (CuIIL4) radicals. The equilibrium between dimer and monomer afforded different reactivities of the complexes in acetonitrile/water and methanol/water mixtures toward urea hydrolysis as a model reaction. It was evident that the dimeric species were inactive and that by increasing the water concentration in the reaction medium, the dimeric structures dissociated to form the active monomeric structures. This behavior was more pronounced when methanol/water mixtures were employed due to a slower displacement of the chlorido bridge in this medium than in the acetonitrile/water mixtures, enabling the reaction kinetics to be evaluated. This effect was attributed to the preferential solvation shell by the organic solvents and in essence, an upregulation behavior was observed due to the intrinsic nature of the complexes to form dimeric structures in solution that could be dismantled in the presence of water, indicating their possible use as water-sensors in organic solvents.

Plasma-enhanced hydrolysis of urea and SCR of NOx over V2O5-MoO3/TiO2: Decrease of reaction temperature and increase of NOx conversion

Plasma-enhanced hydrolysis of urea and selective catalytic reduction (SCR) of NOx over V2O5-MoO3/TiO2 were studied by temperature-programmed experiments using a packed-bed dielectric barrier discharge reactor. Urea over TiO2 and V2O5-MoO3/TiO2 could be hydrolyzed at 110–250 °C to NH3 and CO2 with yields of 79.0%–83.6% and 83.8%–88.6%, respectively. The catalyst type and presence of O2 in the carrier gas hardly affected catalytic urea hydrolysis performance. Introducing plasma reduced urea hydrolysis temperature over V2O5-MoO3/TiO2, without changing NH3 yield under O2-free condition while reducing NH3 yield to lower values at higher discharge power under O2-containing condition. Urea hydrolysis and NOx conversion temperatures decreased and NOx conversion increased after introducing plasma into the urea-SCR process. The presence of NO in the feed gas hardly affected and reduced urea hydrolysis temperature in urea-SCR and plasma-enhanced urea-SCR process, respectively. 5% O2 in the reaction gas favored NOx conversion in urea-SCR regardless of the presence of plasma. In the plasma-enhanced O2-containing urea-SCR process, N(-III) species (urea, NH3 and HNCO) were predominantly consumed in the conversion of NOx rather than being oxidized by oxidative plasma species. Minor slip of HNCO was observed at low temperatures during urea hydrolysis and urea-SCR over V2O5-MoO3/TiO2 and low-concentration N2O was detected during plasma-enhanced urea hydrolysis and urea-SCR process. The BET surface area and TiO2 crystal structure of V2O5-MoO3/TiO2 catalyst remained unchanged after urea hydrolysis and NOx conversion reactions no matter plasma was introduced or not. Plasma enhanced the conversion of NOx partially by enriching the catalyst surface with adsorbed oxygen.

Mathematical modelling and simulation of microbial carbonate precipitation: the urea hydrolysis reaction

Microbial carbonate precipitation is expected to play a major role in next-generation soil improvement technologies. To date, research into this method has relied on experimental and/or observational approaches. However, in order to understand the long-term effects of microbial carbonate precipitation and apply these to real environments, it is necessary to employ a predictive approach to determine the future state of the soil when using this soil improvement method. In this work, a mathematical model and numerical simulations based on the reaction–diffusion system for the microbial urea hydrolysis reaction are proposed. These techniques may be used to provide the spatiotemporal precipitation patterns of carbonates between soil particles and the particle surfaces. The simulation results revealed that the characteristic precipitation patterns depend on the diffusion of carbonates caused by the microbial urea hydrolysis reaction, and there was a significant shift in the amount of carbonate from a dissipated state into an equilibrium state.

Theoretical aspects on local alkalinization following hydrolysis of deep-placed urea in paddy soils under transplanting

Urea broadcasting in rice cultivation often leads to ammonia volatilization because the hydrolysis reaction of urea quickly gives ammonium, ammonia and bicarbonate. Particularly ammonia (NH3) is subject to emanation which can be avoided if urea is deep placed. This no loss optimistic scenario is realized by strict positioning of urea supergranules in the anaerobic layer of the paddy soil. In this study, we wanted to verify if the development of alkalinity in the site of placement could be predicted from the chemical equilibria in soil solution, neglecting the effect(s) of the soil matrix. Calculation of pH related to ammoniacal N concentration was performed considering the main acid-basic equilibria taking place within the soil solution. Data were compared to localized pH and ammoniacal N values obtained in two paddy fields following deep placement of urea supergranules. The pH never trespassed 9.25 which is the pKa of ammonia, in theoretical terms as well in the localized point placement sites in the fields. The linear relationship between log of ammoniacal N concentration and pH seems to indicate a strong influence of the cation exchange capacity so far not taken into account by the model. Urea supergranules are compared to mini-bombs of NH3; to prevent any leak to the floodwater (then to the atmosphere) they have to be buried with precision.© 2019 International Formulae Group. All rights reserved.Keywords: Point placement, urea supergranule, generated alkalinity, wetland soil, soil solution, pH

Synthesis of novel cone-shaped CaAl-LDH directly on aluminum alloy by a facile urea hydrolysis method

The urea method is one of the unique approaches to synthesize highly crystalline-layered double hydroxides (LDHs). Herein, we synthesized calcium-based layered double hydroxide (CaAl–LDH) directly on Al AA6082 substrate by using the urea hydrolysis reaction, in an effort to obtain highly potential novel cone-shaped unique LDH structure. The as-prepared CaAl-LDH thin film is characterized by X-ray diffraction, Fourier transform spectroscopy, scanning electron microscopy, transmission electron microscopy and further investigated the thermal properties and electron impedance spectra behavior. That simple in situ synthetic approach will be helpful to design environmentally friendly CaAl-LDH thin films that can be further investigated for numerous potential applications like environmental science, catalysts and biomedical applications.

Modeling of enzymatic chitosan gelation: Tools for monitoring chitosan gelation and urea hydrolysis kinetics

A modeling of urea hydrolysis in chitosan medium and global enzymatic chitosan gelation kinetics was developed to better understand the gelation dynamics. The model was validated using experimental results in batch stirred reactor. Comparison between urea hydrolysis reaction rates in water and chitosan media shows that the chitosan has nearly no influence on the enzymatic kinetics parameters. Modeling results allowed decoupling gelation phenomena and urea hydrolysis reaction and pointing out the limitation of urea hydrolysis reaction by urea concentration depletion in chitosan medium. Monitoring pH and d(pH)/dt was useful for determining (i) the gelation time, (ii) the advanced gelation time, (iii) time of the maximum gelation rate and (iv) time of the maximum urea hydrolysis rate.

Microfluidic water splitting cell using 3D NiFe2O4 hollow spheres

The present research work shows a simple method to synthesize 3D NiFe2O4 hollow spheres by a hydrothermal route and its application as catalyst for water splitting in an alkaline microfluidic system. The NiFe2O4 was developed by a simple mechanism from the urea hydrolysis reaction and later subjected to a hydrothermal process to carry out a single-step synthesis, obtaining novel 3D hollow nanospheres with doubles, triples and quadruples shells. 3D NiFe2O4 with large surface area and stability showed a catalytic activity for the oxygen evolution reaction (OER) comparable with the commercial material commonly employed IrO2. The NiFe2O4-based material was used as an anode and cathode in a microfluidic water splitting device, where the H2 production was 2.5 and 2.7 × 10−5 mg s−1 for 3D NiFe2O4 hollow spheres and IrO2Pt/C, respectively.

Fabrication of Fe3O4/MgAl-layered double hydroxide magnetic composites for the effective removal of Orange II from wastewater.

A facile approach has been developed to construct a composite of magnetic Fe3O4 (MNPs) and regular hexagon Mg-Al layered double hydroxide (MNPs/MgAl-LDH) via a two-step hydrothermal method combined with the urea hydrolysis reaction for the removal of Orange II. The scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy results showed MNPs and MgAl-LDH have been combined successfully, providing the combination of the superior properties of fast separation and high adsorption capacity. The pH values, contact time, initial dye concentration and temperature were investigated in detail. The kinetics and isotherm study showed the adsorption of Orange II on MNPs/MgAl-LDH obeyed the pseudo-second-order and Langmuir model respectively and the adsorption processes were spontaneous and endothermic in nature. Also, some coexisting anions such as Cl-, NO3 -, CO3 - and SO4 2- had no significant effect on the removal of Orange II. The mechanism study revealed that the adsorption of Orange II on MNPs/MgAl-LDH mainly involves surface adsorption through electrostatic force and the layer anion exchange. Moreover, Orange II could be desorbed from MNPs/MgAl-LDH using 100 mg L-1 NaOH and used for four cycles without any adsorption performance loss, demonstrating MNPs/MgAl-LDH prepared in this work could be used as a cost-effective and efficient material for the removal of Orange II.

Amino functionalization of carboxymethyl cellulose for efficient immobilization of urease

Jack bean urease (EC.3.5.1.5) was effectively immobilized onto amino functionalized epichlorohydrin cross-linked carboxymethyl cellulose (ECH-CMC) beads that were fabricated by graft co-polymerization of polyacrylamide (PAm) onto ECH-CMC beads in presence of potassium persulfate (KPS)/thiourea (TU) combined redox initiator followed by Hoffmann degradation. The progress of the synthesis along with immobilization processes was investigated by FTIR spectra. Also, the morphological structures of the beads before and after urease immobilizations were examined using SEM. Immobilization efficiency and immobilized urease amounts were estimated as a function of the amino functionalization degrees. The effects of pH and temperature on urease activity were studied. The results showed that after immobilization the optimum pH and temperature displayed higher shifts to 8 and 45°C, respectively, which reveal a higher structural stability upon immobilization performance. Moreover, the kinetic studies indicated that the urea hydrolysis reaction, which catalyzed by urease enzyme displayed a good fit with Michaelis–Menten equation, and the kinetic parameters Km and vm were estimated to be 14±0.7mM and 2±0.2μmolNH3/min·mg immobilized urease, respectively. Furthermore, the immobilized urease maintained approximately 88% of its initial activity after the 10th reuse cycle.

Mimicking and Inhibiting Urea Hydrolysis in Nonwater Urinals.

Nonwater urinals are critical in the implementation of building-scale water conservation and urine diversion systems. However, because of the composition of urine and the prevalence of the urease enzyme that hydrolyzes urea, minerals readily precipitate in nonwater urinals and pipes. This leads to clogging, malodor, and possible replacement of nonwater urinals with flush urinals. Accordingly, the goal of this research was to provide an improved understanding of the urea hydrolysis process in nonwater urinals to benefit water conservation and phosphate recovery efforts. Acetic acid addition was used in nonwater urinals to inhibit the urea hydrolysis reaction by lowering the pH, thereby making the precipitation of calcium- and magnesium-containing minerals less favorable. Of the acids tested, 2.5 mL of 2500 mequiv/L acetic acid added after every urination event was able to inhibit urea hydrolysis in synthetic urine and real urine as indicated by the pH and conductivity of the effluent urine. Acid addition also allowed for 43% more phosphate recovery via struvite precipitation in the acetic acid addition synthetic urine than the synthetic urine with no acid addition.

Statistical Modeling of Environmental Factors on Microbial Urea Hydrolysis Process for Biocement Production

Calcium carbonate is a widely used raw material by many industries. It can be precipitated through microbial process within soil pores as cementitious bonding agent between grains for geotechnical applications. It is called microbially induced calcium carbonate precipitation (MICP). Designing an appropriate biogrout material for injection into soil is essential for controlling the amount, type, time, and place of the biocement production within pores. For this purpose, understanding the active reactions and the kinetics of bacterial growth and urea hydrolysis is necessary. A conductometric method and spectrophotometry were used in this study to, respectively, monitor the urea hydrolysis reaction progress and bacterial growth inS. pasteurii-inoculated urea-NB-NH4Cl solution at different level of the environmental factors that are initial cell concentration, urea concentration, and temperature. Variation in conductivity of the solution versus logarithmic scale of time was depicted as microbial ureolysis characteristic curve (MUCC) through which lag duration, specific rate, and potential of urea hydrolysis at each condition were obtained. Central composite face-centered (CCF) design, which is one of the response surface methodologies, was employed to statistically fit polynomial models explaining the bacterial growth and the characteristics obtained from MUCCs in terms of the environmental factors and their interactions. An optimization analysis based on the urea-normalized responses was also carried out.

Development of a ratiometric fluorescent urea biosensor based on the urease immobilized onto the oxazine 170 perchlorate-ethyl cellulose membrane

In this work, the oxazine 170 perchlorate (O17)-ethyl cellulose (EC) membrane was successfully applied in the fabrication of a urea-sensing membrane. The urea-sensing membrane was a double layer consisting of the O17-EC membrane and a layer of the enzyme urease entrapped into EC matrix. The sensing principle of urea was based on the hydrolysis reaction of urea under the catalysis of the urease to produce ammonia in water and also on the binding of ammonia with the dye O17 to create the shift in the emission wavelength from λem=630nm to λem=565nm. The data collected from the ratio of the fluorescence intensities at λem=630nm and λem=565nm was proportional to urea concentration. The urea-sensing membrane with the ratiometric method was used to measure the concentrations of urea in the range of 0.01–0.1M with a limit of detection (LOD) of 0.027mM and 0.1–1.0M with LOD of 0.224mM. It showed fast response time, high reversibility and long-term stability in this concentration range. The recovery percentage of urea concentrations of the urea-sensing membrane for two kinds of biological urine solutions (BU1, BU2) was around 85–118%. The measured results were in good agreement with standard urea concentrations in the range of 0.06M to 1.0M.