Conjugation and fluorescence quenching between bovine serum albumin and L-cysteine capped CdSe/CdS quantum dots

Water-soluble, biological-compatible, and excellent fluorescent CdSe/CdS quantum dots (QDs) with L-cysteine as capping agent were synthesized in aqueous medium. Fluorescence (FL) spectra, absorption spectra, and transmission electron microscopy (TEM) were employed to investigate the quality of the products. The interactions between QDs and bovine serum albumin (BSA) were studied by absorption and FL titration experiments. With addition of QDs, the FL intensity of BSA was significantly quenched which can be explained by static mechanism in nature. When BSA was added to the solution of QDs, FL intensity of QDs was faintly quenched. Fluorescent imaging suggests that QDs can be designed as a probe to label the Escherchia coli (E. coli) cells. These results indicate CdSe/CdS/L-cysteine QDs can be used as a probe for labeling biological molecule and bacteria cells.     

Fluorescence quenching investigation on the interaction of glutathione‐CdTe/CdS quantum dots with sanguinarine and its analytical application

Water‐soluble glutathione (GSH)‐capped core/shell CdTe/CdS quantum dots (QDs) were synthesized. In pH 5.4 sodium phosphate buffer medium, the interaction between GSH‐CdTe/CdS QDs and sanguinarine (SA) was investigated by spectroscopic methods, including fluorescence spectroscopy and ultraviolet‐visible absorption spectroscopy. Addition of SA to GSH‐CdTe/CdS QDs results in fluorescence quenching of GSH‐CdTe/CdS QDs. Quenching intensity was in proportion to the concentration of SA in a certain range. Investigation of the quenching mechanism, proved that the fluorescence quenching of GSH‐CdTe/CdS QDs by SA is a result of electron transfer. Based on the quenching of the fluorescence of GSH‐CdTe/CdS QDs by SA, a novel, simple, rapid and specific method for SA determination was proposed. The detection limit for SA was 3.4 ng/mL and the quantitative determination range was 0.2–40.0 µg/mL with a correlation coefficient of 0.9988. The method has been applied to the determination of SA in synthetic samples and fresh urine samples of healthy human with satisfactory results. Copyright © 2013 John Wiley & Sons, Ltd.     

CdSe and CdSe/CdS core–shell QDs: New approach for synthesis,investigating optical properties and application in pollutant degradation

In this work, CdSe quantum dots (QDs) were synthesized by a simple and rapid microwave activated approach using CdSO₄, Na₂SeO₃ as precursors and thioglycolic acid (TGA) as capping agent molecule. A novel photochemical approach was introduced for the growth of CdS QDs and this approach was used to grow a CdS shell around CdSe cores for the formation of a CdSe/CdS core–shell structure. The core–shells were structurally verified using X‐ray diffraction, transmission electron microscopy and FTIR (Fourier‐transform infrared (FTIR)) spectroscopy. The optical properties of the samples were examined by means of UV–Vis and photoluminescence (PL) spectroscopy. It was found that CdS QDs emit a broad band white luminescence between 400 to 700 nm with a peak located at about 510 nm. CdSe QDs emission contained a broad band resulting from trap states between 450 to 800 nm with a peak located at 600 nm. After CdS shell growth, trap states emission was considerably quenched and a near band edge emission was appeared about 480 nm. Optical studies revealed that the core–shell QDs possess strong ultraviolet (UV) ? visible light photocatalytic activity. CdSe/CdS core–shell QDs, showed an enhancement in photodegradation of Methyl orange (MO) compared with CdSe QDs.     

Near Infrared,Highly Efficient Luminescent Solar Concentrators

The fabrication of a low reabsorption emission loss, high efficient luminescent solar concentrator (LSC) is demonstrated by embedding near infrared (NIR) core/shell quantum dots (QDs) in a polymer matrix. An engineered Stokes shift in NIR core/shell PbS/CdS QDs is achieved via a cation exchange approach by varying the core size and shell thickness through the refined reaction parameters such as reaction time, temperature, precursor molar ratio, etc. The as‐synthesized core/shell QDs with high quantum yield (QY) and excellent chemical/photostability exhibit a large Stokes shift with respect to the bare PbS QDs due to the strong core‐to‐shell electrons leakage. The large‐area planar LSC based on core/shell QDs exhibits the highest value (6.1% with a geometric factor of 10) for optical efficiency compared to the bare NIR QD‐based LSCs and other reported NIR QD‐based LSCs. The suppression of emission loss and the broad absorption of PbS/CdS QDs offer a promising pathway to integrate LSCs and photovoltaic devices with good spectral matching, indicating that the proposed core/shell QDs are strong candidates for fabricating high efficiency semi‐transparent large‐area LSCs.     

Aqueous synthesis of CdTe/CdS/ZnS quantum dots and their optical and chemical properties

In this paper, we described a strategy for synthesis of thiol‐coated CdTe/CdS/ZnS (core–shell–shell) quantum dots (QDs) via aqueous synthesis approach. The synthesis conditions were systematically optimized, which included the size of CdTe core, the refluxing time and the number of monolayers and the ligands, and then the chemical and optical properties of the as‐prepared products were investigated. We found that the mercaptopropionic acid (MPA)‐coated CdTe/CdS/ZnS QDs presented highly photoluminescent quantum yields (PL QYs), good photostability and chemical stability, good salt tolerance and pH tolerance and favorable biocompatibility. The characterization of high‐resolution transmission electron microscopy (HRTEM), X‐ray powder diffraction (XRD) and fluorescence correlation spectroscopy (FCS) showed that the CdTe/CdS/ZnS QDs had good monodispersity and crystal structure. The fluorescence life time spectra demonstrated that CdTe/CdS/ZnS QDs had a longer lifetime in contrast to fluorescent dyes and CdTe QDs. Furthermore, the MPA‐stabilized CdTe/CdS/ZnS QDs were applied for the imaging of cells. Compared with current synthesis methods, our synthesis approach was reproducible and simple, and the reaction conditions were mild. More importantly, our method was cost‐effective, and was very suitable for large‐scale synthesis of CdTe/CdS/ZnS QDs for future applications. Copyright © 2010 John Wiley & Sons, Ltd.     

Application of CdS quantum dots modified carbon paste electrode for monitoring the process of acetaminophen preparation

In this research article, a novel, selective, and sensitive modified carbon paste electrode (CPE) using CdS quantum dots (QDs) is presented. The highly stable CdS QDs were successfully synthesized in an in situ process using Na₂S₂O₃ as a precursor and thioglycolic acid as a catalyst and capping agent. The synthesis of CdS QDs was studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The synthesized CdS QDs were used for preparation of a modified carbon paste electrode (CdS/CPE). The electrochemical behavior of the electrode toward p-aminophenol (PAP) and acetaminophen (Ac) was studied, and the results demonstrated that the CdS/CPE exhibited good electrocatalytic performance toward PAP and Ac oxidation. The oxidation peak potential of each analyte in the mixture was well separated. As a result, a selective and reliable method was developed for the determination of PAP and Ac simultaneously without any chemical separations. Application of the fabricated electrode for monitoring the process of Ac preparation from PAP was investigated. The obtained results show that CdS/CPE has satisfactory analytical performance; it could be a kind of attractive and promising nanomaterial-based sensor for process monitoring via the electrochemical approach.     

Molecular spectroscopic studies on the interactions of rhein and emodin with thioglycolic acid‐capped core/shell CdTe/CdS quantum dots and their analytical applications

Water‐soluble thioglycolic acid (TGA)‐capped core/shell CdTe/CdS quantum dots (QDs) were synthesized. The interactions of rhein and emodin with TGA‐CdTe/CdS QDs were evaluated by fluorescence and ultraviolet‐visible absorption spectroscopy. Experimental results showed that the high fluorescence intensity of TGA‐CdTe/CdS QDs could be effectively quenched in the presence of rhein (or emodin) at 570 nm, which may have resulted from an electron transfer process from excited TGA‐CdTe/CdS QDs to rhein (or emodin). The quenching intensity was in proportion to the concentration of both rhein and emodin in a certain range. Under optimized conditions, the linear ranges of TGA‐CdTe/CdS QDs fluorescence intensity versus the concentration of rhein and emodin were 0.09650–60 µg/mL and 0.1175–70 µg/mL with a correlation coefficient of 0.9984 and 0.9965, respectively. The corresponding detection limits (3σ/S) of rhein and emodin were 28.9 and 35.2 ng/mL, respectively. This proposed method was applied to determine rhein and emodin in human urine samples successfully with remarkable advantages such as high sensitivity, short analysis time, low cost and easy operation. Based on this, a simple, rapid and highly sensitive method to determine rhein (or emodin) was proposed. Copyright © 2014 John Wiley & Sons, Ltd.     

Controlled surface trap state photoluminescence from CdS QDs impregnated in poly(methyl methacrylate)

A method of microwave (MW) assisted synthesis was employed to prepare cadmium sulfide (CdS) quantum dots (QDs) in dimethylformamide in the presence of poly(methyl methacrylate) (PMMA). The MW irradiation was carried out for a fixed time of 20-30 s and the size of QDs varied from 2.9-5.5 nm. Before each irradiation the solution was cooled down to ambient temperature and the irradiation process was repeated six times. An increase in the intensity and red shift of the characteristic UV-vis absorption peak originating from CdS QDs were observed with repeated MW irradiation, suggesting that the amount of generated CdS QDs increased within the PMMA network and aggregated with repeated MW irradiation. MW irradiation could influence selectively the nucleation and growing rates of PMMA-CdS QDs systems. The broadness and large Stokes shift of the emission from Cd(2+)-rich PMMA-CdS QDs was due to the surface trap state photoluminescence. The recombination of shallow trapped electrons and shallow trapped holes has been considered as the primary source of the surface trap state photoluminescence in Cd(2+)-rich PMMA-CdS QDs. The photoluminescence lifetime was observed to be decreased sharply when the amount of QDs was less, showing the emission decay was dependent on the surface property of PMMA-CdS QDs. The origin of the longer lifetime was due to the involvement of surface trap states and dependent on the amount of CdS QDs present within PMMA and its environment. The effect of the concentration of Cd(2+), S(2-) and PMMA on the generation of CdS QDs within PMMA and the effect of repeated MW irradiation on the optical properties was studied and the results are discussed in this article.     

Synthesis of glutathione-capped CdS quantum dots and preliminary studies on protein detection and cell fluorescence image.

A series of glutathione (GSH)-capped aqueous CdS quantum dots (QDs) with strong photoluminescence (PL) were prepared by changing the reaction temperatures and times on the basis of optimization of the mole ratio of S to Cd. The reaction time was shortened to about 1/10 compared with that reported previously by increasing the reaction temperature. The absorption and fluorescence spectra indicated good optical properties with PL full width of half-maximum (FWHM) of about 100 nm. The excitation spectrum was broad and continuous in the range 200-480 nm. The PL quantum efficiency (QE) of the prepared QDs was about 36% compared with rhodamine 6G (95%). The shape and size of the CdS QDs were characterized using high-resolution transmission electron microscopy (HRTEM). The prepared QDs were conjugated with bovine serum albumin (BSA) and onion inner pellicle cells and used as fluorescence probes for the first time. The results demonstrated that the fluorescence of CdS can be enhanced by BSA and the enhanced fluorescence intensity is proportional to the concentration of BSA in the range 1.0-10 mg/L. The aggregation of CdS in onion inner pellicle cells and its fluorescence images indicated that the QDs can aggregate around cells soaked for 8 h in CdS solution but enter the interior of cells and become aggregated to the nucleus when they are soaked in CdS solution for longer, e.g. 98 h.     

MULTIPLEX DETECTION OF ESCHERICHIA COLI AND SALMONELLA ENTERITIDIS BY USING QUANTUM DOT-LABELED ANTIBODIES

In this study, we demonstrated the simultaneous detection of Escherichia coli and Salmonella enteritidis, by coupling immunomagnetic separation (IMS) with quantum dots (QDs) labeling. QDs having different emission wavelengths were conjugated with anti- E. coli and anti- Salmonella antibodies. QD–antibody conjugates were used to label immunomagnetically separated bacteria and the fluorescence intensities were measured for enumerations of both species. The concentrations of primary antibodies used in IMS, the ratio of QDs to antibodies during the conjugation and the concentration of QD–antibody conjugates used in labeling were optimized to enhance the sensitivity of the assay. After labeling bacteria with QDs, the quenching observed between bead–bacteria complex and QDs was eliminated by separating QDs from the complex using sodium dodecyl sulfate solution. The fluorescence intensities due to the capturing of different concentrations of bacteria were measured and the working ranges were found to be 5 × 10² to 5 × 10⁵ cfu/mL for E. coli and 4  ×  10² to 4  ×  10⁵ cfu/mL for S. enteritidis .

PRACTICAL APPLICATIONS

In this study, antibody-conjugated multicolor quantum dots (QDs) were used for simultaneous detection of Escherichia coli and Salmonella enteritidis . The results of this study indicate that QD labels can be used in multiplex, rapid and selective detection of bacteria with detection limits comparable with those of many novel methods in cases where the assay conditions are optimized. Furthermore, the assay can be modified for the simultaneous detection of more than two species through using QD labels having different emission wavelengths.     

“Use of acidophilic bacteria of the genus Acidithiobacillus to biosynthesize CdS fluorescent nanoparticles (quantum dots) with high tolerance to acidic pH”

The use of bacterial cells to produce fluorescent semiconductor nanoparticles (quantum dots, QDs) represents a green alternative with promising economic potential. In the present work, we report for the first time the biosynthesis of CdS QDs by acidophilic bacteria of the Acidithiobacillus genus. CdS QDs were obtained by exposing A. ferrooxidans, A. thiooxidans and A. caldus cells to sublethal Cd²⁺ concentrations in the presence of cysteine and glutathione. The fluorescence of cadmium-exposed cells moves from green to red with incubation time, a characteristic property of QDs associated with nanocrystals growth. Biosynthesized nanoparticles (NPs) display an absorption peak at 360 nm and a broad emission spectra between 450 and 650 nm when excited at 370 nm, both characteristic of CdS QDs. Average sizes of 6 and 10 nm were determined for green and red NPs, respectively. The importance of cysteine and glutathione on QDs biosynthesis in Acidithiobacillus was related with the generation of H₂S. Interestingly, QDs produced by acidophilic bacteria display high tolerance to acidic pH. Absorbance and fluorescence properties of QDs was not affected at pH 2.0, a condition that totally inhibits the fluorescence of QDs produced chemically or biosynthesized by mesophilic bacteria (stable until pH 4.5–5.0). Results presented here constitute the first report of the generation of QDs with improved properties by using extremophile microorganisms.     

Using bacteria to express and display anti-Plasmodium molecules in the mosquito midgut

Bacteria capable of colonizing mosquito midguts are attractive vehicles for delivering anti-malaria molecules. We genetically engineered Escherichia coli to display two anti-Plasmodium effector molecules, SM1 and phospholipase-A(2), on their outer membrane. Both molecules significantly inhibited Plasmodium berghei development when engineered bacteria were fed to mosquitoes 24h prior to an infective bloodmeal (SM1=41%, PLA2=23%). Furthermore, prevalence and numbers of engineered bacteria increased dramatically following a bloodmeal. However, E. coli survived poorly in mosquitoes. Therefore, Enterobacter agglomerans was isolated from mosquitoes and selected for midgut survival by multiple passages through mosquitoes. After four passages, E. agglomerans survivorship increased from 2 days to 2 weeks. Since E. agglomerans is non-pathogenic and widespread, it is an excellent candidate for paratransgenic control strategies.     

Survival differences among freeze-dried genetically engineered and wild-type bacteria.

Because the death mechanisms of freeze-dried and air-dried bacteria are thought to be similar, freeze-drying was used to investigate the survival differences between potentially airborne genetically engineered microorganisms and their wild types. To this end, engineered strains of Escherichia coli and Pseudomonas syringae were freeze-dried and exposed to air, visible light, or both. The death rates of all engineered strains were significantly higher than those of their parental strains. Light and air exposure were found to increase the death rates of all strains. Application of death rate models to freeze-dried engineered bacteria to be released into the environment is discussed.     

Synthesis of highly luminescent and biocompatible CdTe/CdS/ZnS quantum dots using microwave irradiation: a comparative study of different ligands

We compared the effects of several ligands frequently used in aqueous synthesis, including L‐cysteine, L‐cysteine hydrochloride, N‐acetyl‐L‐cysteine (NAC), glutathione and 3‐mercaptopropionic acid, for microwave synthesis of CdTe quantum dots (QDs) in a sealed vessel with varied temperatures and times, and then developed a rapid microwave‐assisted protocol for preparing highly luminescent, photostable and biocompatible CdTe/CdS/ZnS core–multishell QDs. The effects of molecular structures of these ligands on QD synthesis under high temperatures were explored. Among these ligands, NAC was found to be the optimal ligand in terms of the optical properties of resultant QDs and reaction conditions. The emission wavelength of NAC‐capped CdTe QDs could reach 700 nm in 5 min by controlling the reaction temperature, and the resultant CdTe/CdS/ZnS core–multishell QDs could achieve the highest quantum yields up to 74% with robust photostability. In addition, the effects of temperature, growth time and shell–precursor ratio on shell growth were examined. Finally, cell culturing indicated the low cytotoxicity of CdTe/CdS/ZnS core–multishell QDs as compared to CdTe and CdTe/CdS QDs, suggesting their high potential for applications in biomedical imaging and diagnostics. Copyright © 2014 John Wiley & Sons, Ltd.     

Compound 800, a natural product isolated from genetically engineered Pseudomonas: proposed structure, reactivity, and putative relation to heme d1

Genetically engineered strains of Escherichia coli and Pseudomonas aeruginosa were prepared harboring the gene cluster nirFDLGH from Pseudomonas stutzeri substrain ZoBell on a high copy plasmid. These genes have been previously implicated as being essential for the biosynthesis of heme d(1), the prosthetic group of dissimilatory nitrite reductases in anaerobic, denitryfying bacteria. Tetrapyrroles detectable at steady-state levels were identified from both organisms, and cell-free extracts from each were also used to transform uroporphyrinogen in vitro. E. coli does not naturally produce d(1), and the engineered strain failed to produce d(1) or any tetrapyrrole foreign to E. coli. Therefore, while nirFDLGHmay be necessary for d(1) biosynthesis, it is not sufficient. In the denitrifier P. aeruginosa, the results were more positive. The presence of the plasmid led to increased levels of d(1). In addition, a previously unidentified tetrapyrrole was detected. This compound was characterized by visible absorption spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, mass spectrometry, and NMR, and a tentative structure was proposed for this compound. The tetrapyrrole has structural features similar to sirohydrochlorin (as precorrin-2 or sirotetrahydrochlorin, a known intermediate of d(1)) and d(1) itself. The most unusual substituents are epoxide and sulfoxide moieties. When this tetrapyrrole was treated with strong mineral acid and heat, it was converted into natural d(1).     

A urea electrochemical sensor based on molecularly imprinted chitosan film doping with CdS quantum dots

An improved imprinted film-based electrochemical sensor for urea recognition was developed using CdS quantum dots (QDs) doped chitosan as the functional matrix. The microstructure and composition of the imprinted films depicted by scanning electron microscopy (SEM), attenuated total reflection infrared (ATR-IR), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS) indicated the fabricated feasibility of the nanoparticle doped films via in situ electrodeposition. Differential pulse voltammetric responses under the optimal fabrication conditions showed that the sensitivity of CdS QDs-MIP (molecularly imprinted polymer) electrochemical sensor was enhanced from the favorable electron transfer and magnified surface area of CdS QDs with a short adsorption equilibrium time (7 min), wide linear range (5.0 × 10(-12) to 4.0 × 10(-10) M and 5.0 × 10(-10) to 7.0 × 10(-8) M), and low detection limit (1.0 × 10(-12) M). Meanwhile, the fabricated sensor showed excellent specific recognition to template molecule among the structural similarities and coexistence substances. Furthermore, the proposed sensor was applied to determine the urea in human blood serum samples based on its good reproducibility and stability, and the acceptable recovery implied its feasibility for practical application.     

Interaction properties of biosynthesized cadmium sulphide quantum dots with human serum albumin: further investigation of antibacterial activities and sensing applications

The synthesis of small-sized quantum dots (QDs) (1–10 nm) via the green route has garnered great interest regarding their prospective use in many biological applications (diagnosis, drug delivery and in vivo sensing); this is difficult to achieve using chemical synthesis methods, which produce larger size QD particles and also require hazardous reagents. Here, we synthesized biogenic cadmium sulphide (CdS) QDs using green tea extract as the reducing agent to produce particles that were homogeneous and a smaller size of 2–4 nm. We also elucidated the (a) protein binding, (b) antibacterial use and (c) sensing applications of biogenic CdS QDs in this present work. The biosynthesized CdS QDs were found to have extensive antibacterial activity against both Gram-negative Escherichia coli and Gram-positive Enterococcus faecalis bacterial strains. The introduction of QDs in biological medium can lead to the formation of protein–QD complexes; therefore we investigated the binding interaction of CdS QDs with the carrier protein human serum albumin (HSA) in vitro. The synthesized CdS QDs quenched the intrinsic fluorescence of HSA through a static quenching mechanism and the binding constant (K_b) was in the order of 10⁴ M⁻¹. It was also observed that the presence of biogenic CdS QDs affected the HSA–ligand interactions in vitro. The synthesized CdS made highly effective sensors for tetracycline, rifampicin, and bilirubin with limit of detection (LOD) values of 99, 141 and 29 ng/ml, respectively.     

Study on the fluorescence resonance energy transfer between CdS quantum dots and Eosin Y

Water‐soluble CdS quantum dots (QDs) were prepared using mercaptoacetic acid (TGA) as the stabilizer in an aqueous system. A fluorescence resonance energy transfer (FRET) system was constructed between water‐soluble CdS QDs (donor) and Eosin Y (acceptor). Several factors that impacted the fluorescence spectra of the FRET system, such as pH (3.05–10.10), concentration of Eosin Y (2–80 mg/L) and concentration of CdS QDs (2–80 mg/L), were investigated and refined. Donor‐to‐acceptor ratios, the energy transfer efficiency (E) and the distance (r) between CdS QDs and Eosin Y were obtained. The results showed that a FRET system could be established between water‐soluble CdS QDs and Eosin Y at pH 5.0; donor‐to‐acceptor ratios demonstrated a 1: 8 proportion of complexes; the energy transfer efficiency (E) and the distance (r) between the QDs and Eosin Y were 20.07% and 4.36 nm,respectively. Copyright © 2014 John Wiley & Sons, Ltd.     

Space mutagenesis of genetically engineered bacteria expressing recombinant human interferon α1b and screening of higher yielding strains

The aim of this study was to investigate the space mutagenesis of genetically engineered bacteria expressing recombinant human interferon α1b. The genetically engineered bacteria expressing the recombinant interferon α1b were sent into outer space on the Chinese Shenzhou VIII spacecraft. After the 17 day space flight, mutant strains that highly expressed the target gene were identified. After a series of screening of spaceflight-treated bacteria and the quantitative comparison of the mutant strains and original strain, we found five strains that showed a significantly higher production of target proteins, compared with the original strain. Our results support the notion that the outer space environment has unique effects on the mutation breeding of microorganisms, including genetically engineered strains. Mutant strains that highly express the target protein could be obtained through spaceflight-induced mutagenesis.     

Preparation and in vitro analysis of microencapsulated genetically engineered E. coli DH5 cells for urea and ammonia removal

This article describes a novel method of urea and ammonia removal using microencapsulated, genetically engineered Escherichia coli DH5 cells. Optimization of bacterial cell encapsulation was carried out. The optimal method consists of alginate 2.00% (w/v) at a flow rate of 0.0724 mL/min and a coaxial air flow rate of 2.00 L/min. This produces spherical, alginate-poly-L-lysine-alginate (APA) microcapsules of an average 500 +/- 45 mum diameter. Increasing the concentration of alginate from 1.00% to 1.75% improves the quality of the microcapsules, while cell viability remains unaffected. The APA microcapsules are mechanically stable up to 210-rpm agitation with no bacterial cell leakage. The in vitro performance of urea and ammonia removal by encapsulated bacteria is assessed. One hundred milligrams of bacterial cells in APA microcapsules, in their log phase state of growth, can lower 87.89 +/- 2.25% of the plasma urea within 20 min and 99.99% in 30 min. The same amount of encapsulated bacteria can also lower ammonia from 975.14 +/- 70.15 muM/L to 81.151 +/- 7.37 muM/L in 30 min. There are no significant differences in depletion profiles by free and encapsulated bacteria for urea and ammonia removal. This novel approach using microencapsulated, genetically engineered E. coli cells is significantly more efficient than presently available methods of urea and ammonia removal. For instance, it is 30 times more efficient than the standard urease-ammonium adsorbent system. (c) 1995 John Wiley & Sons, Inc.