Browsing by Author "Syed Hadi Hasan"

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A Facile and Simple Strategy for the Synthesis of Label Free Carbon Quantum Dots from the latex of Euphorbia milii and Its Peroxidase-Mimic Activity for the Naked Eye Detection of Glutathione in a Human Blood Serum
(American Chemical Society, 2019) Daraksha Bano; Vijay Kumar; Vikas Kumar Singh; Subhash Chandra; Devendra Kumar Singh; Pradeep Kumar Yadav; Mahe Talat; Syed Hadi Hasan
Herein a green synthetic route has been developed for the synthesis of water-soluble CQDs by facile single-step hydrothermal treatment of latexes of E. milii plant for the first time. This methodology is zero-cost; uses ultrapure water as a green solvent; does not use strong concentrated acid; and avoids the use of post surface passivating agents. The as-prepared CQDs exhibited excellent optical properties, including high QY up to 39.2%, resistance to high salt strength, and long time photostability. Furthermore, the as-prepared CQDs served as an intrinsic peroxidase-mimic activity to catalyze the chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB) associated with H 2 O 2 , which resulted into a blue-colored reaction with a characteristic absorbance peak at 652 nm. Afterward, the proposed TMB-based oxidation system act as a probe for the detection of GSH and offers the high selectivity relative to the different amino acids and various other interfering agents which can be easily seen with naked eye. The limit of detection (LOD) was found to be 5.3 nM in a linear range 0.02 to 0.1 μM of GSH concentration which showed to be superior under the optimal condition as compared with another probe. To demonstrate the practical feasibility for the GSH detection, the present system was successfully applied on human blood serums with good recovery. © 2018 American Chemical Society.
Biosynthesis of silver nanoparticles from the novel strain of Streptomyces Sp. BHUMBU-80 with highly efficient electroanalytical detection of hydrogen peroxide and antibacterial activity
(Elsevier Ltd, 2017) Rajeev Kumar Gupta; Vijay Kumar; Ravi Kumar Gundampati; Manisha Malviya; Syed Hadi Hasan; Medicherla V. Jagannadham
The use of a microbial supernatant has become a potential source for the eco-friendly and rapid synthesis of nanoparticles. In this study, we have targeted to synthesize silver nanoparticles (AgNPs) using extracellular secretion of Streptomyces sp. The strain was successfully isolated from the soil samples and identified as Streptomyces sp. BHUMBU-80 on the basis of morphological, biochemical and Phylogenetic analysis. The synthesized AgNPs was characterized using several modern characterizing techniques such as UV-vis Spectroscopy, FTIR spectroscopy, SEM, EDX spectroscopy, TEM, XRD and XPS. The presence of characteristics SPR band at 450 nm confirmed the synthesis of AgNPs. The FTIR spectra confirmed the involvement of various functional groups present in culture supernatant responsible for the reduction of Ag+ ions into Ag0. SEM and TEM analysis confirmed the presence of spherical AgNPs with an average size of 21 ± 1 nm. The XPS analysis confirmed the presence of two individual peaks which attributed to the Ag 3d3/2 and Ag 3d5/2 binding energies corresponding to the presence of metallic silver. The electrochemical studies of the green synthesized AgNPs using a glassy carbon electrode showed the superior electrocatalytic activity towards the reduction of H2O2. The calibration plot was established for H2O2 in the concentration range from 50 μM to 1000 μM with 50 μM detection limit, at a signal-to-noise ratio of 3 in a three-electrode cell with a Pt plate as the counter electrode. Additionally, the AgNPs also showed potent antibacterial activity against pathogenic bacteria like E. coli, and S. aureus. © 2017 Elsevier Ltd. All rights reserved.
Bright-blue-emission nitrogen and phosphorus-doped carbon quantum dots as a promising nanoprobe for detection of Cr(vi) and ascorbic acid in pure aqueous solution and in living cells
(Royal Society of Chemistry, 2018) Vikas Kumar Singh; Virendra Singh; Pradeep Kumar Yadav; Subhash Chandra; Daraksha Bano; Vijay Kumar; Biplob Koch; Mahe Talat; Syed Hadi Hasan
Highly fluorescent nitrogen and phosphorus-doped carbon quantum dots (N,P-CQDs) were synthesized via a one-step hydrothermal method and fully characterized via various techniques such as TEM, DLS, FT-IR, P-XRD and XPS analysis. The as-synthesized N,P-CQDs showed excellent optical properties and exhibited bright blue colour under UV-light with CIE coordinate (0.20, 0.22) along with a high quantum yield of 73%, due to which they could act as on-off fluorescent nanoprobes for the selective and sensitive detection of highly toxic Cr(vi) below its permissible limit via the inner filter effect (IFE) and static quenching mechanism. In addition, Cr(vi) could be reduced to lower valent chromium species. Therefore, the N,P-CQDs + Cr(vi) system further acted as a selective off-on sensor for reductant ascorbic acid (AA) because it reduced Cr(vi) to Cr(iii) species, resulting in the elimination of IFE and recovery of fluorescence of N,P-CQDs. Notably, this system possesses excellent biocompatibility and negligible cytotoxicity; therefore, it can be potentially applied for fluorescence imaging of intracellular Cr(vi) and ascorbic acid (AA) in living cells and complex biological systems. © 2018 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Effective removal of fluoride from water by coconut husk activated carbon in fixed bed column: Experimental and breakthrough curves analysis
(Elsevier B.V., 2018) Mahe Talat; Sweta Mohan; Viney Dixit; Devendra Kumar Singh; Syed Hadi Hasan; Onkar Nath Srivastava
The bio-waste coconut husk was converted into activated carbon through merely treating with KOH and thus obtained activated carbon was characterized by XRD, TGA, SEM and TEM analysis. The prepared activated carbon having very high surface area (1448 m2/g) was utilized as an adsorbent for the removal of fluoride (F-) from water. Fluoride adsorption experiments were performed on the laboratory-scale column at different bed height, flow rates, and F- concentrations to explore the potential of prepared adsorbent and it was found to be very efficient adsorbent as it showed high adsorption capacity 6.5 mg/g at pH 5, F- concentration 10 mg/L and adsorbent dose 1.4 g/L. Various breakthrough models i.e. Bed Depth Service Time (BDST), Thomas and Yoon–Nelson were applied on breakthrough data to analyze the breakthrough curves. The high R2 values obtained for the BDST model revealed its validity for this adsorption system. Breakthrough curves were successfully analyzed and described by both Thomas and Yoon–Nelson models. The exhausted adsorbent was efficiently regenerated with the 10% NaOH solution and regenerated adsorbent showed remarkable uptake capacity with a slight reduction in adsorption performance up to the 3 cycles. Life factor calculation indicated that adsorbent bed would have sufficient bed capacity up to 8.3 cycles to avoid breakthrough at time t = 0 and the bed would be completely exhausted after 9.0 cycles. © 2018
Enzymatic detection of mercuric ions in ground-water from vegetable wastes by immobilizing pumpkin (Cucumis melo) urease in calcium alginate beads
(2008) Om Prakash; Mahe Talat; Syed Hadi Hasan; Rajesh K. Pandey
Present report describes a quick and simple test based on enzyme inhibition for the detection of mercury in aqueous medium by urease immobilized in alginate beads. Urease was extracted from the discarded seeds of pumpkin (Cucumis melo) and was purified to apparent homogeneity (5.2-fold) by heat treatment at 48 ± 0.1 °C and gel filtration through Sephadex G-200. The homogeneous enzyme preparation (Sp activity 353 U/mg protein, A280/A260 = 1.12) was immobilized in 3.5% alginate leading to 86% immobilization. Effect of mercuric ion on the activity of soluble as well as immobilized enzyme was investigated. Hg2+ exhibited a concentration-dependent inhibition both in the presence and absence of the substrate. The alginate immobilized enzyme showed less inhibition. There was no leaching of the enzyme over a period of 15 days at 4 °C. The inhibition was non-competitive and the Ki was found to be 1.26 × 10-1 μM. Time-dependent interaction of urease with Hg2+ exhibited a biphasic inhibition behavior in which approximately half of the initial activity was lost rapidly (within 10 min) and reminder in a slow phase. Binding of Hg2+ with the enzyme was largely irreversible, as the activity could not be restored by dialysis. The significance of the observations is discussed. © 2007 Elsevier Ltd. All rights reserved.
Fluorometric sensing probe using carbon quantum dots for selective detection of doxycycline antibiotic
(Springer, 2025) Deepak Kumar; Subhash Chandra; Vivek V. Kumar; Pradeep Kumar Yadav; Syed Hadi Hasan
Due to the sturdy photoluminescence and absorption, CQDs emerged as a suitable candidate for optical sensing probe. The present study deals with the synthesis of blue-fluorescent Carbon Quantum Dot (TAA-CQD) using tannic acid and glycine as novel precursors. The TAA-CQD were synthesised hydrothermally with the high production yield and QY to be 86.12 and 21%, respectively, and an average particle size of 1.9 nm. The TAA-CQD aqueous solution displays excitation-dependent fluorescence emission in the excited range from 420 to 650 nm. The CIE co-ordinates in a highly blue region at (0.14, 0.19) confirmed the synthesised TAA-CQD were blue in fluorescent. Fluorescence of TAA-CQD was stable under all pH range, resisted the high ionic strengths condition and stable over 8 months. Furthermore, the fluorescent TAA-CQD was capable in detecting a tetracycline-classed antibiotic Doxycycline (DXY) along with remarkable selectivity and sensitivity. The measures limit of detection (LOD) was very low 2.42 mM in comparison to other methods. Moreover, the applicability of the proposed work has been fruitfully employed on the pharmaceutical waste. Thus, our designed TAA-CQD based fluorescence sensing system hold great promise for the advanced sensing materials in the detection of DXY and we believe that our approach will be promising and viable in a clinical applications. © The Author(s), under exclusive licence to Korean Carbon Society 2025.
Green Synthesis of Fluorescent Carbon Quantum Dots from Azadirachta indica Leaves and Their Peroxidase-Mimetic Activity for the Detection of H 2 O 2 and Ascorbic Acid in Common Fresh Fruits
(American Chemical Society, 2019) Pradeep Kumar Yadav; Vikas Kumar Singh; Subhash Chandra; Daraksha Bano; Vijay Kumar; Mahe Talat; Syed Hadi Hasan
In the present study, an ecofriendly and zero-cost approach has been demonstrated for the preparation of carbon quantum dots by one-pot hydrothermal treatment of leaf extracts of neem (Azadirachta indica). The as-synthesized neem carbon quantum dots (N-CQDs) exhibited high fluorescent quantum yields (QYs) up to 27.2%. Moreover, N-CQDs also act with a peroxidase-like-mimetic activity toward the oxidation of peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in association with hydrogen peroxide (H 2 O 2 ). Further, the kinetics of peroxidase-like catalytic activity follows the Michaelis-Menten and ping-pong pathway. In addition, the H 2 O 2 sensitive TMB oxidation motivated the colorimetric detection of H 2 O 2 which showed linearity from 0.1 to 0.5 mmol/L with a detection limit (LOD) of 0.035 mmol/L. Furthermore, the blue colors of oxidized TMB (ox-TMB) were selectively reduced in native TMB with ascorbic acid (AA) without any interference of other reducing agents. The linear range of AA detection was lying between 5 and 40 μM with a LOD up to 1.773 μM. The practicability assay of the proposed sensing system toward the detection of AA was also investigated in real sample analysis such as common fruits which showed good sensitivity to the presence of AA. Therefore, this convenient, ecofriendly, and cost-effective peroxidase-based sensing system opens a new platform for analysis of AA in real samples and in complex biological systems. Copyright © 2018 American Chemical Society.
Highly sensitive electrochemical sensing of ascorbic acid (vitamin C) using Pd-doped MnO2 supported on carbon quantum dots (Pd-MnO2@CQD) in water and fruit juices
(Springer, 2025) Deepak Kumar; Daraksha Bano; Subhash Chandra; Bharat Kumar; V. Sampath Sampath Kumar; Pradeep Kumar Yadav; Syed Hadi Hasan
The Pd-MnO2 nanoparticles attached to carbon quantum dots nanocomposite were synthesized using the green synthesis and hydrothermal process. Characterization of the as-prepared nanocomposite was intensively performed by FT-IR, powder XRD, XPS, and HR-TEM analysis. The synthesized nanomaterial was further examined for its selective and sensitive ascorbic acid (ASA) sensing using a Pd-MnO2@CQD modified glassy carbon electrode (GCE). The Pd-MnO2@CQD nanocomposite exhibits a distinct and improved peak current of ASA when compared to electrodes treated with Pd-MnO2 and bare GCE. The designed sensor has excellent performance, with a linear range of 10–1500 μM, a low detection limit of 0.14 μM (S/N = 3), a high sensitivity of 1.9671 μAµM−1 cm−2. Furthermore, the constructed sensor demonstrates good sensitivity for detecting ASA in a variety of real samples. © The Author(s), under exclusive licence to The Japan Society for Analytical Chemistry 2025.
Mustard seeds derived fluorescent carbon quantum dots and their peroxidase-like activity for colorimetric detection of H 2 O 2 and ascorbic acid in a real sample
(Elsevier B.V., 2019) Subhash Chandra; Vikas Kumar Singh; Pradeep Kumar Yadav; Daraksha Bano; Vijay Kumar; Vinay Kumar Pandey; Mahe Talat; Syed Hadi Hasan
Herein, we were synthesized fluorescent carbon quantum dots via facile one-step hydrothermal treatment of mustard seeds (M-CQDs). It showed excellent optical property with fluorescent quantum yield 4.6%. The as-prepared M-CQDs exhibited peroxidase-like mimetic activity and catalyzed the oxidation of chromogenic substrate 3,3‘,5,5‘-tetramethylbenzidine (TMB) in the presence of H 2 O 2 to produce a blue color reaction mixture with the prominent peak at 652 nm. Furthermore, the peroxidase-like catalytic performance of M-CQDs followed the steady-state kinetics behavior and exhibited similar catalytic activity as that of natural enzyme Horseradish peroxidase (HRP). In addition to this, the double reciprocal plot showed a parallel line which suggested the occurrence of Ping-Pong type of mechanism. The H 2 O 2 dependent oxidation of TMB was helpful for the colorimetric detection of H 2 O 2 in the linear range of 0.02–0.20 mM with the limit of detection (LOD) of 0.015 mM. Interestingly, the oxidized TMB (ox-TMB) was further reduced to native TMB by the reducing agent ascorbic acid. Hence M-CQDs showed its potential towards the selective and sensitive detection of ascorbic acid in the linear range of 10–70 μM having a correlation coefficient of 0.998 with LOD of 3.26 μM. The practical feasibility of the proposed detection method of AA was also investigated in common fresh fruits. © 2018 Elsevier B.V.
Nitrogen doped fluorescent carbon quantum dots for on-off-on detection of Hg2+ and glutathione in aqueous medium: Live cell imaging and IMPLICATION logic gate operation
(Elsevier B.V., 2019) Vikas Kumar Singh; Virendra Singh; Pradeep Kumar Yadav; Subhash Chandra; Daraksha Bano; Biplob Koch; Mahe Talat; Syed Hadi Hasan
The present work describes the synthesis of N-CQDs via one step hydrothermal methods. The synthesized N-CQDs was fully characterized by TEM, P-XRD, FT-IR, XPS and Zeta sizer. It exhibited excitation independent emission behaviour with fluorescent quantum yield of 41% respect to quinine sulphate standard. The excellent optical properties of N-CQDs made it fluorescent probe for turn off detection of toxic heavy metal ion Hg2+ with good selectivity and sensitivity. The limit of detection was found to be 0.08 μM with correlation coefficient (R2 = 0.992). After addition of various reducing agent such as amino acid, EDTA and GSH in the quenched solution of N-CQDs + Hg2+, the fluorescence property was selectively recovered in the presence of GSH and hence the quenched solution further acts as selective turn on sensing of GSH up to lower limit of 2.0 μM with correlation coefficient (R2 = 0.996). The on-off-on sensing behaviour of N-CQDs was utilized for the implication of logic gate in absence and presence of Hg2+ and GSH to construct the molecular switches. The MTT assay of N-CQDs was performed on MCF-7 cancer cell line to check their applicability in biological system and the result showed negligible cytotoxicity and good permeability. The cell imaging on MCF-7 cells visualized in dichromic region (blue and green). Therefore, it could be smart material for sensing of heavy toxic metal as well as cell imaging application. © 2019 Elsevier B.V.
Nitrogen/sulfur-co-doped carbon quantum dots: a biocompatible material for the selective detection of picric acid in aqueous solution and living cells
(Springer, 2020) Subhash Chandra; Daraksha Bano; Priyadarshika Pradhan; Vikas Kumar Singh; Pradeep Kumar Yadav; Devanjan Sinha; Syed Hadi Hasan
Here, a fast and eco-friendly one-pot hydrothermal technique is utilized for the synthesis of nitrogen/sulfur-co-doped fluorescent carbon quantum dots (NS-CQDs) from a simple precursor of citric acid (CA) and thiosemicarbazide (TSC). The obtained NS-CQDs exhibited strong blue emission under UV light, with fluorescence quantum yield (QY) of ~37.8%. The Commission internationale de l’eclairage (CIE) coordinates originated at (0.15, 0.07), which confirmed the blue fluorescence of the synthesized NS-CQDs. Interestingly, the prepared NS-CQDs were successfully used as a selective nanoprobe for the monitoring of environmentally hazardous explosive picric acid (PA) in different nitro- and non-nitro-aromatic derivatives of PA. The mechanism of the NS-CQDs was also explored, and was posited to occur via the fluorescence resonance electron transfer (FRET) process and non-fluorescent complex formation. Importantly, this system possesses excellent biocompatibility and low cytotoxicity in HeLa cervical cancer cells; hence, it can potentially be used for PA detection in analytical, environmental, and pathological applications. Furthermore, the practical applicability of the proposed sensing system to pond water demonstrated the feasibility of our system along with good recovery. [Figure not available: see fulltext.] © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
Peroxidase mimetic activity of fluorescent NS-carbon quantum dots and their application in colorimetric detection of H2O2 and glutathione in human blood serum
(Royal Society of Chemistry, 2018) Vikas Kumar Singh; Pradeep Kumar Yadav; Subhash Chandra; Daraksha Bano; Mahe Talat; Syed Hadi Hasan
Interest is growing in the development of artificial enzymes to overcome the drawbacks of natural enzymes. Herein, we have synthesized nitrogen-sulphur dual-doped carbon quantum dots (NS-CQDs) via a one-step hydrothermal method; the NS-CQDs possess excellent optical properties and a high fluorescent quantum yield (46%). Significantly, the NS-CQDs exhibited peroxidase mimetic enzyme activity without support from metals or polymeric materials and efficiently catalyzed the oxidation of peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2 to produce a blue solution with an absorption maximum at 652 nm. Mechanistic studies suggest that the small size and high electron density of NS-CQDs play vital roles and accelerate the reduction of H2O2 to generate OH radical, which facilitates the oxidation of TMB. The catalytic activity is based on Michaelis-Menten kinetic behavior, and steady state kinetic analysis suggests that the NS-CQDs exhibit a higher affinity for H2O2 than TMB, similar to the natural enzyme horseradish peroxidase (HRP). Moreover, the catalytic pathway follows a ping-pong mechanism. Therefore, these findings offer a worthy platform for colorimetric detection of H2O2 in a linear range of 0.02 mM to 0.1 mM with a limit of detection of 0.004 mM. Interestingly, the blue colour of oxidized TMB showed excellent selectivity over non-thiolate biological molecules, especially amino acids, and glutathione can be detected up to 0.07 μM via colorimetric and fluorimetric assays. Additionally, this system showed excellent recovery (96.0-108.3%) of GSH from human blood serum. Thus, the proposed sensing system is simple, convenient, and straightforward and can be potentially applied for real time monitoring of H2O2 and glutathione in biological samples. © 2018 The Royal Society of Chemistry.
Photo-induced rapid biosynthesis of silver nanoparticle using aqueous extract of Xanthium strumarium and its antibacterial and antileishmanial activity
(Korean Society of Industrial Engineering Chemistry, 2016) Vijay Kumar; Ravi Kumar Gundampati; Devendra Kumar Singh; Medicherla V. Jagannadham; Shyam Sundar; Syed Hadi Hasan
The current work describes the biosynthesis of stable AgNPs using aqueous extract of Xanthium strumarium (AEX) which act as both reducing as well as a stabilizing agent. The biosynthesis was confirmed by UV-visible spectroscopy where the presence of SPR band at λmax 436 nm corresponded to the existence of AgNPs in reaction mixture. The optimum conditions for biosynthesis of AgNPs were 30 min of sunlight exposure time, 3.0% (v/v) of AEX inoculum dose and 3.5 mM AgNO3 concentration. The synthesized AgNPs was characterized by HRTEM, SAED, FESEM, EDX, XRD, AFM, and FTIR which showed potent antibacterial and antileishmanial activity. © 2016 The Korean Society of Industrial and Engineering Chemistry.
Photoinduced green synthesis of silver nanoparticles with highly effective antibacterial and hydrogen peroxide sensing properties
(Elsevier B.V., 2016) Vijay Kumar; Ravi Kumar Gundampati; Devendra K. Singh; Daraksha Bano; Medicherla V. Jagannadham; Syed Hadi Hasan
In this study, an eco-friendly and sustainable green route was employed for the synthesis of stable silver nanoparticles (AgNPs) using aqueous leaf extract of Euphorbia hirta (AEE) as both reducing as well as a stabilizing agent. The synthesis of AgNPs was confirmed by UV–visible spectroscopy which produced a prominent SPR band at λmax 425 nm after 25 min of sunlight exposure. The AgNPs thus synthesized were optimized using one factor at a time approach, and these optimized conditions were 25 min of sunlight exposure time, 5.0% (v/v) of AEE inoculum dose and 3.0 mM of AgNO3 concentration. The Field Emission Scanning Electron Microscopy (FE-SEM) and High Resolution Transmission Electron Microscopy (HRTEM) analysis confirmed the presence of spherical AgNPs with average size 15.5 nm. The crystallinity was determined by X-ray Diffractometer (XRD) and Selected Area Electron Diffraction (SAED) pattern. Chemical and elemental compositions were determined by Fourier Transformed Infrared Spectroscopy (FTIR) and Energy Dispersive X-ray Spectroscopy (EDX) respectively. The Atomic Force Microscopy (AFM) images with average roughness 1.15 nm represented the lateral and 3D topological characteristic of AgNPs. The AgNPs thus synthesized showed effective antibacterial activity against gram negative and gram positive bacteria as well as hydrogen peroxide sensing property with a minimum detection limit of 10− 7 M. © 2016
Pyrene-fluorescein-based colour-tunable AIE-active hybrid fluorophore material for potential live cell imaging applications
(Royal Society of Chemistry, 2017) Vikas Kumar Singh; Ritika Prasad; Biplob Koch; Syed Hadi Hasan; Mrigendra Dubey
A novel hybrid fluorophore (FHPY) has been synthesized based on a condensation reaction of two standard fluorescent hydrophobic-hydrophilic molecules, viz. pyrene and fluorescein, with an objective to tune the aggregation-induced emission (AIE) along with the morphology. Owing to the distinct photophysical properties of pyrene and fluorescein, the hybrid FHPY dramatically exhibits a fluorescence change from colourless to yellow-green via a blue colour upon varying the volume fraction of water (poor solvent) in methanol (good solvent). FHPY has exhibited not only AIE, but also an outstanding quantum yield (ΦF) of 97% at a 70% water fraction in methanol (70-:-30, v/v). We attribute the reason behind the tuning of the AIE and quantum yield to the opening of the lactam ring of fluorescein as well as to the amassing of hydrophobic pyrene at a certain water fraction. The mechanism involved in the AIE has been well supported by detailed UV-vis, fluorescence, lifetime, SEM, AFM, DFT, PXRD and 1H NMR experiments. In addition, FHPY serves as a good candidate for the live cell imaging of HeLa cells. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2017.
Response surface design for the optimization of enzymatic detection of mercury in aqueous solution using immobilized urease from vegetable waste
(2009) Om Prakash; Mahe Talat; Syed Hadi Hasan
Soluble and alginate immobilized urease was utilized for detection and quantitation of mercury in aqueous samples. Urease from the seeds of pumpkin, being a vegetable waste, was extracted and purified to apparent homogeneity (sp. activity 353 U/mg protein; A280/A260 = 1.12) by heat treatment at 48 ± 0.1 °C and gel filtration through Sephadex G-200. Homogeneous enzyme preparation was immobilized in 3.5% alginate leading to 86% immobilization, no leaching of enzyme was found over a period of 15 days at 4 °C. Urease catalyzed urea hydrolysis by soluble and immobilized enzyme revealed a clear dependence on the concentration of Hg2+. Inhibition caused by Hg2+ was non-competitive (Ki = 1.2 × 10-1 μM for soluble and 1.46 × 10-1 μM for alginate immobilized urease.). Time-dependent inhibition both in presence and in absence of Hg2+ ion revealed a biphasic inhibition in activity. For optimization of this process response surface methodology (RSM) was utilized where two-level-two-full factorial (22) central composite design (CCD) has been employed. The regression equation and analysis of variance (ANOVA) were obtained using MINITAB® 15 software. Predicted values thus obtained were closed to experimental value indicating suitability of the model. 3D response surface plot, iso-response contour plot and process optimization curve were helpful to predict the results by performing only limited set of experiments. © 2008 Elsevier B.V. All rights reserved.
Synthesis of highly fluorescent nitrogen-rich carbon quantum dots and their application for the turn-off detection of cobalt (II)
(Elsevier B.V., 2019) Daraksha Bano; Vijay Kumar; Subhash Chandra; Vikas Kumar Singh; Sweta Mohan; Devendra Kumar Singh; Mahe Talat; Syed Hadi Hasan
In this study, we have reported easy and economical synthesis of highly fluorescent nitrogen-rich carbon quantum dots (N-CQDs). The as-prepared N-CQDs displayed strong blue color emission along with CIE co-ordinate index (0.15, 0.14). The N-CQDs possess comparatively high QY of 57% using quinine sulfate as a standard. Furthermore, the as-prepared N-CQDs defend against the high salt strength and longtime photostability over the six months of incubation. Apart from this, the as-prepared N-CQDs responded as a sensor for the ‘turn-off’ detection of Co2+ along with the detection limit of 0.12 μM over a linear range from 0.5 to 3 μM. The mechanistic study proved the detection of Co2+ was based on the IFE, static quenching, aggregation, and complex formation between the amino group of N-CQDs and Co2+. Moreover, the fluorescence of the quenched N-CQDs can reappear and get ‘turn-on’ by using GSH, AA, EDTA, and cyst; thus, the prepared N-CQDs could further execute as a probe for the Co2+ detection. Inspired by these outstanding properties, the as-prepared N-CQDs were also successfully employed for the practical application toward monitoring the trace level of Co2+ in a vitamin B-12 sample. © 2019 Elsevier B.V.
Water hyacinth biomass (WHB) for the biosorption of hexavalent chromium: Optimization of process parameters
(North Carolina State University, 2010) Syed Hadi Hasan; Deeksha Ranjan; Mahe Talat
Water hyacinth (Eichhornia crassipes) biomass has been used for many years for the remediation of heavy metals. The present study successfully utilizes the dried powdered biomass of the aerial part (stem and leaves) of water hyacinth for biosorption of hexavalent chromium. The effect of various parameters (viz. pH, initial metal ion concentration and temperature) on the removal of Cr(VI) was studied by conducting only 15 sets of sorption runs using Box-Behnken Design (BBD). The pH had a negative and temperature and concentration had positive effects on uptake of chromium. The predicted results (obtained using an empirical linear polynomial model) were found to be in good agreement (R2 = 99.8%) with the experimental results. The predicted maximum removal of Cr(VI) (91.5181 mg/g) can be achieved at pH 2.0, initial metal ion concentration 300 mg/L, and temperature 40 °C. The sorption capacity of sorbent was also calculated using a Langmuir sorption isotherm model and was found to be 101 mg/g at 40 °C and pH 2.0.