Surface expression of carbonic anhydrase on E. coli as a sustainable approach for enzymatic CO2 capture

The utilisation of carbonic anhydrase (CA) in CO2 sequestration is becoming prominent as an efficient, environment friendly and rapid catalyst for capturing CO2 from industrial emissions. However, the application of CA enzyme in soluble form is constrained due to its poor stability in operational conditions of CO2 capture and also production cost of the enzyme. Addressing these limitations, the present study focuses on the surface display of CA from Bacillus halodurans (BhCA) on E coli aiming to contribute to the cost-effectiveness of carbon capture through CA technology. This involved the fusion of the BhCA-encoding gene with the adhesion molecule involved in diffuse adherence (AIDA-I) autotransporter, resulting in the efficient display of BhCA (595 ± 60 U/gram dry cell weight). Verification of the surface display of BhCA was accomplished by conjugating with FITC labelled anti-his antibody followed by fluorescence-activated cell sorting (FACS) and cellular fractionation in conjunction with zymography. Biochemical characterisation of whole-cell biocatalyst revealed a noteworthy enhancement in thermostability, improvement in the thermostability with T1/2 of 90 ± 1.52 minutes at 50 ˚C, 36 ± 2.51 minutes at 60 ˚C and18 ± 1.52 minutes at 80˚C. Surface displayed BhCA displayed remarkable reusability retaining 100% activity even after 15 cycles. Surface displayed BhCA displayed highly alkali stable nature like free counterpart in solution. The alkali stability of the surface-displayed BhCA was comparable to its free counterpart in solution. Furthermore, the study investigated the impact of different metal ions, modulators, and detergents on the whole-cell biocatalysts. The present work represents the first report on surface display of CA utilising the AIDA-1 autotransporter.

Carbonic anhydrase as a tool to mitigate global warming

The global average temperature breaks the record every year, and this unprecedented speed at which it is unfolding is causing serious climate change which in turn impacts the lives of humans and other living organisms. Thus, it is imperative to take immediate action to limit global warming. Increased CO₂ emission from the industrial sector that relies on fossil fuels is the major culprit. Mitigating global warming is an uphill battle that involves an integration of technologies such as switching to renewable energy, increasing the carbon sink capacity, and implementing carbon capture and sequestration (CCS) on major sources of CO₂ emissions. Among all these methods, CCS is globally accepted as a potential technology to address this climate change. CCS using carbonic anhydrase (CA) is gaining momentum due to its advantages over other conventional CCS technologies. CA is a metalloenzyme that catalyses a fundamental reaction for life, i.e. the interconversion of bicarbonate and protons from carbon dioxide and water. The practical application of CA requires stable CAs operating under harsh operational conditions. CAs from extremophilic microbes are the potential candidates for the sequestration of CO₂ and conversion into useful by-products. The soluble free form of CA is expensive, unstable, and non-reusable in an industrial setup. Immobilization of CA on various support materials can provide a better alternative for application in the sequestration of CO₂. The present review provides insight into several types of CAs, their distinctive characteristics, sources, and recent developments in CA immobilization strategies for application in CO₂ sequestration.

Bio-imprinted magnetic cross-linked polyphenol oxidase aggregates for enhanced synthesis of L-dopa, a neurodegenerative therapeutic drug

Bio-imprinted magnetic cross-linked enzyme aggregates (i-m-CLEAs) of polyphenol oxidase (PPO) obtained from potato peels were prepared using amino-functionalized magnetic nanoparticles. Bio-imprinting is being used to improve the catalytic efficiency and conformational stability of enzymes. For bio-imprinting, PPO was incubated with different imprint/template molecules (catechol, 4-methyl catechol and l-3,4-dihydroxy phenylalanine) before cross-linking with glutaraldehyde. CLEAs imprinted with 4-methyl catechol showed maximum activity as compared with non-bio-imprinted magnetic CLEAs (m-CLEAs). They were further characterized by scanning electron microscopy and confocal microscopy. In bio-imprinted m-CLEAs, half-life (t_1/2) of PPO significantly improved (364.74 min) as compared to free PPO (43.58 min) and non-bio-imprinted m-CLEAs (266.54 min). Bio-imprinted m-CLEAs showed excellent thermal and storage stability as well as reusability. The CLEAs preparation were used for the synthesis of l-3,4-dihydroxyphenylalanine (L-dopa, a therapeutic drug to treat neurodegenerative disorder) and a remarkable increase in L-dopa yield (23.5-fold) was obtained as compared to free enzyme. A cost effective and reusable method has been described for the production of L-dopa.

Magnetic combi CLEA for inhibition of bacterial biofilm: A green approach

In the present study different enzymes (α- amylase, trypsin, cellulase, horse-radish peroxidase and pectinex ultra clear) were studied for bacterial biofilm inhibition and Pectinex ultra clear showed best inhibition. So, m-combi-CLEA of Pectinex ultra clear was developed by cross linked enzyme aggregate (CLEA) formation on APTES (3-aminopropyltriethoxysilane) modified iron oxide nanoparticles. Different parameters were optimized and it was observed that 0.4 mg/ml of protein (containing 25 U/mg cellulase activity), 0.5 mg/ml BSA and 10 mM glutaraldehyde when incubated for 3 h gives 100% enzyme activity using ethanol as the precipitant. The CLEA formed were thermally more stable as compared to free enzyme. m-combi-CLEA of Pectinex ultra clear shows 75-78% biofilm inhibition of E. coli and S. aureus. Furthermore, m-combi-CLEA can be reused till 4 cycles with same efficiency. The carbohydrate contents of E. coli biofilm decreased from 64.629 μg to 6.23 μg and for S. aureus biofilm, it decreased from 58.46 μg to 5.52 μg when treated with m-combi CLEA in comparison to untreated biofilms. FTIR, darkfield illumination Fluorescence Microscopy, and Scanning Electron Microscopy was further used for characterization.

Development of low-cost paper-based biosensor of polyphenol oxidase for detection of phenolic contaminants in water and clinical samples

In the present work, polyphenol oxidase (PPO) enzyme was purified from potato peel using three-phase partitioning (TPP). In this method, ammonium sulfate and t-butanol were added to precipitate the protein/enzyme from the crude aqueous extract. The PPO enzyme precipitated as an interfacial layer between the upper organic solvent phase and lower aqueous phase. Different purification parameters such as crude extract to t-butanol ratio, ammonium sulfate concentration, temperature, and pH were optimized for TPP. About 69% PPO enzyme activity was recovered in a single step of TPP with 9.2-fold purification. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis profile of partially purified PPO enzyme showed molecular weight in the range of about 30-40 kDa. The PPO enzyme was then investigated for the fabrication of a portable, cost-effective, and disposable colorimetric paper biosensor or colorimetric "test strips" for detection of phenolic contaminants. PPO and a chromophore reagent (3-methyl-2-benzothiazolinone hydrazine) generated a range of color in the presence of phenolic compounds (catechol, phenol, p-cresol, 4-methyl catechol) within 15 min, and limit of detection was found to be 0.5 μM. The biosensor worked in a broad range of pH from 3 to 11 and showed good storage stability at 25 °C and 4 °C for 30 days with no significant loss of activity. The biosensor was also applied on environmental water and urine sample to show reliability of biosensor.

Proteomics Analysis of Escherichia coli Treated with Nanosilver: An Approach to Analyze the Bactericidal Action

Background :

Silver nanoparticles pose high antibacterial properties against multi drugresistant and non-resistant bacteria. However, bacteria acquire resistance against chemically synthesized silver nanoparticles after repeated exposure. Therefore, there is an inevitable need to understand the mechanistic behavior of silver nanoparticles.

Objective:

In this study, we have performed a complete proteomic analysis of Escherichia coli after the treatment with silver nanoparticles to find out the mechanism of bactericidal action of silver nanoparticles (AgNPs).

Methods:

Silver nanoparticles were synthesized using Artemisia annua leaf extract and incubated with Escherichia coli to elucidate the antibacterial assay by determining MIC and the effect on the growth pattern. Further total genome proteins were isolated from control and silver nanoparticles treated bacteria, which were identified by LC MS and Label free quantification analysis technique.

Results::

Total identified proteins were 293, out of which 11 proteins were exclusively present in treated bacteria; these are the proteins mainly expressed in stress conditions. Fold change analysis shows that 65 proteins were upregulated where stress proteins are overexpressed while membrane proteins were downregulated.

Conclusions:

This study reveals that silver nanoparticles inhibit the expression of cellular proteins and cause cell death. Such a study may be helpful in designing drugs against resistant microbes.

Perioperative intravenous contrast administration and the incidence of acute kidney injury after major gastrointestinal surgery: prospective, multicentre cohort study

BACKGROUND

This study aimed to determine the impact of preoperative exposure to intravenous contrast for CT and the risk of developing postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery.

METHODS

This prospective, multicentre cohort study included adults undergoing gastrointestinal resection, stoma reversal or liver resection. Both elective and emergency procedures were included. Preoperative exposure to intravenous contrast was defined as exposure to contrast administered for the purposes of CT up to 7 days before surgery. The primary endpoint was the rate of AKI within 7 days. Propensity score-matched models were adjusted for patient, disease and operative variables. In a sensitivity analysis, a propensity score-matched model explored the association between preoperative exposure to contrast and AKI in the first 48 h after surgery.

RESULTS

A total of 5378 patients were included across 173 centres. Overall, 1249 patients (23·2 per cent) received intravenous contrast. The overall rate of AKI within 7 days of surgery was 13·4 per cent (718 of 5378). In the propensity score-matched model, preoperative exposure to contrast was not associated with AKI within 7 days (odds ratio (OR) 0·95, 95 per cent c.i. 0·73 to 1·21; P = 0·669). The sensitivity analysis showed no association between preoperative contrast administration and AKI within 48 h after operation (OR 1·09, 0·84 to 1·41; P = 0·498).

CONCLUSION

There was no association between preoperative intravenous contrast administered for CT up to 7 days before surgery and postoperative AKI. Risk of contrast-induced nephropathy should not be used as a reason to avoid contrast-enhanced CT.

Development of sustainable and reusable silver nanoparticle-coated glass for the treatment of contaminated water

Water contaminants like pathogenic microbes and organic pollutants pose a serious threat to human and aquatic life forms; thus, there is an urgent need to develop a sustainable and affordable water treatment technology. Nanomaterials especially metal nanoparticles have extensive applications in wastewater treatment, but the recovery and aggregation of nanoparticles in solution is a major limitation. In the present work, green synthesized silver nanoparticles were covalently immobilized on a glass surface to prevent aggregation of nanoparticles and to enhance their applicability. Fourier transform infrared (FTIR) of silver nanoparticle (AgNP)-coated glass shows peaks of Si-O-Si, Si-O-C, and Ag-O at 1075 cm^-1, 780 cm^-1, and 608 cm^-1 respectively which confirms the immobilization/conjugation of nanomaterial on glass surface. The surface morphology of immobilized AgNP was studied using scanning electron microscopy (SEM) which reveals nanoparticles are spherical and uniformly distributed on glass surface. The AgNP-coated glass was used for the removal of textile dyes in solution; the result indicates approximately 95% of textile dyes were removed after 5 h of treatment. Removal of microbial contaminants from Yamuna River was studied by optical density analysis and confirmed by fluorescence dye staining. The AgNP-coated glass was also studied for their reusability and the data indicates 50% removal of microbes up to the 5th cycle. To further enhance the applicability, the inhibition of bacterial biofilms were analyzed by dark-field illumination with a fluorescence microscope. Thus AgNP-coated glass can be used in the development of food/water storage containers and in textile industries.

Ampicillin Silver Nanoformulations against Multidrug resistant bacteria

The present study reported a single step synthesis of silver nanoparticles using ampicillin (Amp-AgNps), a second-generation β lactam antibiotic to get nanoformulation having dual properties that of antibiotic and silver. The Amp-AgNps was characterized by UV-VIS spectroscopy, TEM, XRD, FTIR and TGA. FTIR and TGA results suggested that amine group of Ampicllin reduce the metalic silver into nano form. These results were further validated by computational molecular dynamics simulation. The antibacterial potential of Amp-AgNps was investigated against sensitive and drug resistant bacteria. MIC of Amp-AgNps against 6 different bacterial strains were in the range of 3–28 µg/ml which is much lower than the MIC of ampicillin (12–720 µg/ml) and chemically synthesized silver nanoparticles (280–640 µg/ml). The repeated exposure to drugs may lead to development of resistance mechanism in bacteria against that drug, so the efficacy of Amp-AgNps after repeated exposure to bacterial strains were also studied. The results indicate that bacterial strains do not show any resistance to these Amp-AgNps even after exposure up to 15 successive cycles. The biocompatibility of these Amp-AgNps was checked against cell lines by using Keratinocytes cell lines (HaCaT).

Removal of toxic contaminants from water by sustainable green synthesised non-toxic silver nanoparticles

The study describes the synthesis of silver nanoparticles using 21 different plant extracts having medicinal properties. Molecular ultraviolet-visible spectroscopy shows that the λ_max of nanoparticles synthesised by different plant extracts varied and ranged between 400 and 468 nm. The ultraviolet results revealed that although synthesis of nanoparticles occurred by all plant extracts successfully, their size varies, this was further confirmed by differential light scattering. The synthesised nanoparticles were investigated for their antimicrobial properties. The most promising silver nanoparticles Ocimum sanctum and Artemisia annua assisted were further characterised using transmission electron microscopy and energy dispersive X-ray spectroscopy (EDX). EDX data confirms that synthesised nanoparticles are highly pure. Further these two plant assisted nanoparticles were studied for chemocatalytic and adsorptive properties. The silver nanoparticles from Ocimum sanctum can catalyse the reduction of 4-nitrophenol (63%) within 20 min in the presence of NaBH₄, whereas Artemisia annua assisted silver nanoparticles did not show significant chemocatalytic activity. Both the promising nanoparticles can efficiently adsorb textile dyes from aqueous solutions. These synthesised nanoparticles were also exploited to remove microbial and other contaminants from Yamuna River water. The nanoparticles show excellent antimicrobial properties and can be reused repeatedly.

Antibacterial efficacy of Ocimum sanctum leaf extract-treated iron oxide nanoparticles

Iron oxide nanoparticles (IONPs) were preparedviaa co-precipitation method and were then characterized and evaluated for their antibacterial activity after modification withOcimum sanctumleaf extract.

Screening of cyanobacterial extracts for synthesis of silver nanoparticles

Improvement of reliable and eco-friendly process for synthesis of metallic nanoparticles is a significant step in the field of application nanotechnology. One approach that shows vast potential is based on the biosynthesis of nanoparticles using micro-organisms. In this study, biosynthesis of silver nanoparticles (AgNP) using 30 cyanobacteria were investigated. Cyanobacterial aqueous extracts were subjected to AgNP synthesis at 30 °C. Scanning of these aqueous extracts containing AgNP in UV-Visible range showed single peak. The λ max for different extracts varied and ranged between 440 and 490 nm that correspond to the "plasmon absorbance" of AgNP. Micrographs from scanning electron microscope of AgNP from cyanobacterial extracts showed that though synthesis of nanoparticles occurred in all strains but their reaction time, shape and size varied. Majority of the nanoparticles were spherical. Time taken for induction of nanoparticles synthesis by cyanobacterial extracts ranged from 30 to 360 h and their size from 38 to 88 nm. In terms of size Cylindrospermum stagnale NCCU-104 was the best organism with 38 and 40 nm. But in terms of time Microcheate sp. NCCU-342 was the best organism as it took 30 h for AgNP synthesis.

Cellulase assisted synthesis of nano-silver and gold: Application as immobilization matrix for biocatalysis

In the present study, we report in vitro synthesis of silver and gold nanoparticles (NPs) using cellulase enzyme in a single step reaction. Synthesized nanoparticles were characterized by UV-VIS spectroscopy, Dynamic Light Spectroscopy (DLS), Transmission Electron Microscopy (TEM), Energy-dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD), Circular Dichroism (CD) and Fourier Transform Infrared Spectroscopy (FTIR). UV-visible studies shows absorption band at 415nm and 520nm for silver and gold NPs respectively due to surface plasmon resonance. Sizes of NPs as shown by TEM are 5-25nm for silver and 5-20nm for gold. XRD peaks confirmed about phase purity and crystallinity of silver and gold NPs. FTIR data shows presence of amide I peak on both the NPs. The cellulase assisted synthesized NPs were further exploited as immobilization matrix for cellulase enzyme. Thermal stability analysis reveals that the immobilized cellulase on synthesized NPs retained 77-80% activity as compared to free enzyme. While reusability data suggests immobilized cellulase can be efficiently used up to sixth cycles with minimum loss of enzyme activity. The secondary structural analysis of cellulase enzyme during the synthesis of NPs and also after immobilization of cellulase on these NPs was carried out by CD spectroscopy.

Alpha amylase assisted synthesis of TiO₂ nanoparticles: structural characterization and application as antibacterial agents

The enzyme alpha amylase was used as the sole reducing and capping agent for the synthesis of TiO2 nanoparticles. The biosynthesized nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopic (TEM) methods. The XRD data confirms the monophasic crystalline nature of the nanoparticles formed. TEM data shows that the morphology of nanoparticles depends upon the enzyme concentration used at the time of synthesis. The presence of alpha amylase on TiO2 nanoparticles was confirmed by FTIR. The nanoparticles were investigated for their antibacterial effect on Staphylococcus aureus and Escherichia coli. The minimum inhibitory concentration value of the TiO2 nanoparticles was found to be 62.50 μg/ml for both the bacterial strains. The inhibition was further confirmed using disc diffusion assay. It is evident from the zone of inhibition that TiO2 nanoparticles possess potent bactericidal activity. Further, growth curve study shows effect of inhibitory concentration of TiO2 nanoparticles against S. aureus and E. coli. Confocal microscopy and TEM investigation confirm that nanoparticles were disrupting the bacterial cell wall.

Immobilization of cellulase on TiO2 nanoparticles by physical and covalent methods: a comparative study

Immobilization of cellulase from Aspergillus niger on TiO2 nanoparticles was studied by two different approaches--physical adsorption and covalent coupling. A. niger was selected, as it is generally non-pathogenic, is found in nature in the broad range of habitats and produces cellulase extracellulary. For covalent method, TiO2 nanoparticles were modified with aminopropyltriethoxysilane (APTS). The adsorbed and covalently immobilized enzymes showed 76% and 93% activity, respectively, as compared to the free enzyme. The catalytic efficiency V(max)/K(m) increased from 0.4 to 4.0 after covalent attachment, whereas in adsorption method, it increased slightly from 0.4 to 1.2. The covalently-immobilized and adsorbed cellulase lost only 25% and 50% of their activity, respectively after 60 min of incubation at 75 degrees C. The reusability and operational stability data also showed that covalent coupling increased the stability of the enzyme. The presence of enzyme on TiO2 nanoparticles was confirmed by Fourier-transform infrared spectroscopy. The high-resolution transmission electron microscopy (HR-TEM) and atomic force microscopy (AFM) studies indicated aggregation of enzyme when adsorbed on TiO2 surface and a monolayer of enzyme in covalent attachment. In conclusion, covalently attached cellulase retained good activity and thermal stability, as compared to physically adsorbed enzyme. The lower amount of enzyme activity and thermal stability in case of physically adsorbed immobilized enzyme was due to aggregation of the enzyme after adsorption on TiO2 nanoparticles, as revealed by HR-TEM and AFM. Thus, TiO2 nanoparticles could be suitable candidates for immobilization of cellulase for industrial applications like paper, textile, detergent and food industries.

Modulation of antioxidant machinery in α-tocopherol-enriched transgenic Brassica juncea plants tolerant to abiotic stress conditions

The antioxidant machinery in plants consists of several components with unique or overlapping functions that combat the deleterious production of reactive oxygen species (ROS) induced by stress conditions. Tocopherols are a group of powerful antioxidants having additional roles in signaling and gene expression, with α-tocopherol being the most potent form. In the present study, we used wild-type (WT) and α-tocopherol-enriched transgenic (TR) Brassica juncea plants grown under salt, heavy metal, and osmotic stress to compare their relative tolerance to these stresses and to assess the effects of increased α-tocopherol content on the other antioxidative enzymes and molecules. The oxidative damage caused by induced stress was lower in TR plants compared to WT plants as assessed by their higher relative water content and lower electrolyte leakage, malondialdehyde content as well as H(2)O(2) accumulation. Lesser superoxide and H(2)O(2) accumulation was also observed by histochemical staining in TR seedlings exposed to stress. Though no significant differences were evident under normal growth conditions, TR plants showed higher activities and transcript levels of antioxidant enzymes superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase than WT plants under similar stress conditions. A decrease in ascorbate and glutathione content with marginally higher reductive ratios of these compounds was also observed in TR plants under the stress conditions. Our findings implicate the role of higher α-tocopherol levels in conferring better tolerance against salt, heavy metal, and osmotic stresses and also establish the existence of interplay between this lipid-soluble antioxidant and other water-soluble components of plant antioxidant defense.

TL behavior of topaz-glass composite in various irradiation fields

Topaz is a natural hard silicate mineral that has the potential to be used as a thermoluminescent dosimeter (TLD). It is difficult to manufacture chips of topaz and problematic to use its powder as TLDs. Topaz-glass composite (in the form of pellets) can be made easily and applied for radiation dosimetry. To produce pellets of topaz-glass composite in 2:1 wt (%), topaz powder was combined with commercial glass. The pellets with 6 mm diameter and 1 mm thickness were sintered in a furnace at 900°C for 1 h. The composite pellets were irradiated with x-ray and gamma photons and alpha and beta particles. The pellets yielded two peaks in the glow curve; Peak 1 at temperature range 150-160°C and Peak 2 at 250-260°C. The intensity of Peak 2 rose linearly with the increase in absorbed dose. The intensity of Peak 2 was comparable with peaks for photons and beta irradiation but relatively low for alpha exposure. The reproducibility of the intensity of Peak 2 was within 5-8%. Two months after irradiation of the pellets, the fading of the intensity of Peak 2 was found to be about 7%. The topaz-glass composite can be used effectively and efficiently for dosimetry of alpha, beta, and gamma radiation.

Preparation, characterization and biocatalytic activity of a nanoconjugate of alpha amylase and silver nanoparticles

The primary challenge in developing nanoparticle based enzymatic devices is to be able to chemically immobilize an enzyme, which will retain its activity or improve its function while being attached to the nanoparticle. This would be of even greater significance if the whole process could be performed under benign conditions without having to resort to functionalization of key molecules at various steps. In the present study the conjugates of amylase and silver nanoparticles were synthesized using neem leaf extract as the reducing and stabilizing agent. The silver nanoparticles were characterized using Surface Plasmon Resonance Spectra, Dynamic Light Spectroscopy (DLS), Fourier Transform Infrared Spectroscopy (FTIR), Circular Dichroism (CD) and Surface Tunneling Microscopy (STM). The silver nanoparticles retained 85% amylase activity. The nanobiocatalyst was further characterized in terms of kinetic parameters and thermal stability. It was thermally more stable as compared to the free alpha amylase enzyme.

Effects of wild-type and α-tocopherol-enriched transgenic Brassica juncea on the components of xenobiotic metabolism, antioxidant status, and oxidative stress in the liver of mice

Alpha (α)-tocopherol is the most biologically active and preferentially retained form of vitamin E in the human body and is known for its antioxidant and gene regulatory functions. Its increased intake is implicated in protection against diseases that involve an oxidative stress component. We have evaluated the chemopreventive potential of a diet supplemented with natural α-tocopherol-enriched transgenic (TR) Brassica juncea seeds. The modulation of phase I and phase II xenobiotic metabolism and of antioxidative enzymes was compared in the livers of mice fed on a control diet or on a diet supplemented with 2, 4, and 6 % (w/w) of wild-type (WT) or TR seeds. A dose-dependent increase in the specific activities of these enzymes was observed in those animals fed on diet supplemented with TR seeds. In comparison, an increase in the specific activities of antioxidative enzymes was substantial only at higher doses of WT seeds. Consequently, oxidative stress measured in terms of lipid peroxidation and lactate dehydrogenase activity was found to be lower in the case of mice fed with the supplemented diet. However, the chemopreventive potential of TR seeds was more pronounced than that of WT seeds. This study demonstrates the feasibility of fortifying diets with natural α-tocopherol for chemopreventive benefits by means of transgenic manipulation of a commonly used oilseed crop.

Immobilization of enzymes by bioaffinity layering

Bioaffinity immobilization exploits the affinity of the enzyme to a macro-(affinity ligand). Such a macro-(affinity ligand) could be a lectin, a water-soluble polymer, or a bioconjugate of a water-soluble polymer and the appropriate affinity ligand. Successive layering of the enzyme and the macro-(affinity ligand) on a matrix allows deposition of a large amount of enzyme activity on a small surface. Illustrative protocols show affinity layering of a pectinase and horseradish peroxidase on Concanavalin A-agarose and Concanavalin A-Sephadex matrices, respectively.

Observation of superparamagnetism to flux closure behaviour in ZnO nanoparticle agglomerates

In this paper we have tried to understand the nature of magnetism in ZnO nanoparticle samples with an intrinsic 50 ppm trace of Fe impurity. When the samples are annealed we observe formation of nanoparticle agglomerates and the size increases with annealing temperature. When the sample is annealed at 600 °C we observe superparamagnetic behaviour, and the magnetic hysteresis along with the coercive field below the blocking temperature is almost independent of the cooling field. When the sample is annealed at 900 °C we observe reduction of saturation magnetization but the magnetic hysteresis and the coercive field are now dependent on the cooling field, indicating magnetic correlation and ordering within the agglomerated nanograins. We propose a simple model that explains the reduction of magnetization as being due to a vortex-state-like flux closure formation.