Browsing by Author "Mahavir Prasad Tiwari"

Now showing 1 - 20 of 29

A dual-template imprinted polymer-modified carbon ceramic electrode for ultra trace simultaneous analysis of ascorbic acid and dopamine
(2013) Bhim Bali Prasad; Darshika Jauhari; Mahavir Prasad Tiwari
A dual-template imprinted polymer film containing dispersed multiwalled carbon nanotubes was exploited in the fabrication of a typical, reproducible, and rugged carbon ceramic electrode, adopting "surface grafting from" approach for the growth of a nanometer thin coating on its surface. For this, chloro groups were first introduced at the exterior surface of silica-carbon composite electrode through sol-gel modification using (3-chloropropyl)-trimethoxysilane, followed by an iniferter (sodium diethyl dithiocarbamate) initiated photopolymerization of functional monomer (2,4,6-trisacrylamido-1,3,5-triazine), mixed templates (ascorbic acid and dopamine), and cross-linker (ethylene glycol dimethacrylate), in the presence of multiwalled carbon nanotubes. The modified sensor was validated for the simultaneous analysis of ascorbic acid and dopamine in aqueous, blood serum, cerebrospinal fluid, and pharmaceutical samples, using differential pulse anodic stripping voltammetric technique. The oxidation peak potentials for both analytes were found to be well apart approximately by 300mV, which was large enough to allow selective and sensitive analysis of one in the presence of other, without any cross reactivity, interferences and false-positives. The detection limits realized by the proposed sensor, under optimized conditions, were found to be as low as 2.24ngmL-1 for ascorbic acid and 0.21ngmL-1 for dopamine (S/N=3). Such stringent limits could be considered suitable for the primitive diagnosis of several chronic diseases, in clinical settings. © 2013 Elsevier B.V.
An insulin monitoring device based on hyphenation between molecularly imprinted micro-solid phase extraction and complementary molecularly imprinted polymer-sensor
(2014) Mahavir Prasad Tiwari; Bhim Bali Prasad
Molecularly imprinted micro-solid phase extraction fiber was developed by modifying molecularly imprinted polymer film on the surface of silica fiber exploring "grafting via surface attached monomer" (method I) and "grafting via sol-gel" (method II) approaches. The latter approach was found to be inferior to the former one in terms of the sensitivity of insulin detection [method I, LOD=0.009ngmL-1; method II, LOD=0.064ngmL-1, RSD=1.21%]. Notably, either of the techniques, molecularly imprinted micro-solid phase extraction or complementary sensor, was found to be incompetent to monitor the stringent level of insulin in the real samples. However, the combination of these techniques has been found quite suitable for achieving the high detection sensitivity of ultra-trace insulin in human blood serum and Huminsulin injection, without any non-specific (false-positives) contributions. The proposed hyphenated device could serve as a possible marker for risk of developing type 2 diabetes mellitus and diabetic coma due to insulin resistance in human beings. © 2014 Elsevier B.V.
Ascorbic acid imprinted polymer-modified graphite electrode: A diagnostic sensor for hypovitaminosis C at ultra trace ascorbic acid level
(2011) Bhim Bali Prasad; Deepak Kumar; Rashmi Madhuri; Mahavir Prasad Tiwari
A new kind of molecularly imprinted polymer-modified graphite electrode was fabricated by "grafting-to" approach, incorporating sol-gel technique, for the detection of acute deficiency in serum ascorbic acid level (SAAL), manifesting hypovitaminosis C. The modified electrode exhibited ascorbic acid (AA) oxidation at less positive potential (0.0 V) than the earlier reported methods, resulting in a limit of detection as low as 6.13 ng mL -1 (RSD = 1.2%, S/N = 3). The diffusion coefficient (1.096 × 10-5 cm2 s-1), rate constant (7.308 s -1), and Gibb's free energy change (-12.59 kJ mol-1) due to analyte adsorption, were also calculated to explore the kinetics of AA oxidation. The proposed sensor was found to enhance sensitivity substantially so as to detect ultra trace level of AA in the presence of other biologically important compounds (dopamine, uric acid, etc.), without any cross interference and matrix complications from biological fluids and pharmaceutical samples. © 2011 Elsevier B.V. All rights reserved.
Biomimetic piezoelectric quartz sensor for folic acid based on a molecular imprinting technology
(2011) Rashmi Madhuri; Mahavir Prasad Tiwari; Deepak Kumar; Aparna Mukharji; Bhim Bali Prasad
A novel molecularly imprinted polymer (MIP)-modified quartz crystal microbalance (QCM) sensor with high selectivity has been developed for the determination of folic acid via activator generated-atom transfer radical polymerization (AGET-ATRP) technique. It requires an alkyl halide (R-X) as an initiator, a transition metal complex as a catalyst, and an amine as reducing agent. Herein, chlorosilane was used as initiator which was grafted onto the self assembled monolayer modified-quartz crystal surface followed by the addition of pre-polymer mixture which latter underwent thermal cross-linking resulting in MIP-modified QCM sensor. The linear working range (quantification) was found to be 0.6-26.0 μg L-1, with the detection limit as low as 0.08 μg L-1 (S/N=3). ©2011 VBRI press.
Double imprinting in a single molecularly imprinted polymer format for the determination of ascorbic acid and dopamine
(2011) Mahavir Prasad Tiwari; Rashmi Madhuri; Deepak Kumar; Darshika Jauhari; Bhim Bali Prasad
A new molecularly imprinted polymer - carbon composite fiber is constructed using reversible addition-fragmentation chain transfer polymerization technique. The fiber was evaluated as a sensor for the simultaneous determination of ascorbic acid and dopamine at ultratrace level, in aqueous samples, without any cross-reactivity. The binding characteristics of ascorbic acid and dopamine were also evaluated by differential pulse cathodic stripping voltammetry. © 2011 VBRI press.
Doubly imprinted polymer nanofilm-modified electrochemical sensor for ultra-trace simultaneous analysis of glyphosate and glufosinate
(Elsevier Ltd, 2014) Bhim Bali Prasad; Darshika Jauhari; Mahavir Prasad Tiwari
A rapid, selective, and sensitive double-template imprinted polymer nanofilm-modified pencil graphite electrode was fabricated for the simultaneous analysis of phosphorus-containing amino acid-type herbicides (glyphosate and glufosinate) in soil and human serum samples. Since both herbicides respond overlapped oxidation peaks and only glyphosate is prone to nitrosation, n-nitroso glyphosate and glufosinate were used as templates for obtaining the well-resolved quantitative differential pulse anodic stripping voltammetric peaks on the proposed sensor. Toward sensor fabrication, a nano-structured polymer film was first grown directly on the electrode via initial immobilization of gold nanoparticles at its surface. This was followed by linking of monomeric (N-methacryloyl-l-cysteine) molecules through S-Au bonds. Subsequently, these molecules were subjected to free radical polymerization, in the presence of templates, cross linker, initiator, and multiwalled carbon nanotubes as pre-polymer mixture. The modified sensor observed wide linear ranges (3.98-176.23ngmL-1 and 0.54-3.96ngmL-1) of simultaneous analysis with detection limits as low as 0.35 and 0.19ngmL-1 (S/N=3) for glyphosate and glufosinate, respectively, in aqueous samples. The respective oxidation peak potentials of both analytes were found to be substantially apart by 265mV. This enabled the simultaneous determination of one target in the presence of other, without any cross reactivity, interferences, and false-positives, in real samples. © 2014 Elsevier B.V.
Electrochemically grown imprinted polybenzidine nanofilm on multiwalled carbon nanotubes anchored pencil graphite fibers for enantioselective micro-solid phase extraction coupled with ultratrace sensing of d- and l-methionine
(2013) Bhim Bali Prasad; Amrita Srivastava; Indu Pandey; Mahavir Prasad Tiwari
An alternative method is presented for the modification of pencil graphite fibers using surface imprinting technology. In this new approach, we have adopted surface initiated electropolymerization of benzidine monomer, with simultaneous imprinting of template (d- and l-methionine), on carboxylated multiwalled carbon nanotubes anchored pencil graphite fiber. This yielded a nanostructured ultrathin imprinted film (58.3nm) uniformly coated all along the perimeter and length of pencil graphite fiber, for micro-solid phase extraction with substantial adsorption capability. The same film is coated over the exposed tip of the pencil graphite fiber to serve as a complementary molecularly imprinted polymer-sensor. Both extraction and sensing devices are not capable to measure the stringent limit (0.016ngmL-1) of clinical detection of methylenetetrahydrofolate reductase (MTHFR) gene mutation caused by acute methionine depletion, when used alone. However, on combination of both techniques, a successful enantioselective analysis of d- and l-methionine with excellent analytical figures of merit [limit of quantitation range: 0.03-30.00ngmL-1, limit of detection: 0.0098ngmL-1 (RSD=2.04, S/N=3)] could be achieved without any problem of non-specific false-positive contribution and cross-reactivity, in real samples. © 2012 Elsevier B.V.
Enantioselective separation and electrochemical sensing of d- and l-tryptophan at ultratrace level using molecularly imprinted micro-solid phase extraction fiber coupled with complementary molecularly imprinted polymer-fiber sensor
(2011) Bhim Bali Prasad; Mahavir Prasad Tiwari; Rashmi Madhuri; Piyush Sindhu Sharma
Highly efficient enantioselective separation and quantitative recoveries of d- and l-tryptophan in aqueous and real samples can be achieved, with a monolithic molecularly imprinted polymeric fiber that serves both for micro-solid phase extraction and ultratrace sensing, without any false-positive (non-specific) contribution and cross-reactivity, in the range of 0.15-30.00ngmL-1 with detection limit as low as 0.0261ngmL-1 (relative standard deviation=0.64%, signal/noise=3). The proposed method combining molecularly imprinted micro-solid phase extraction fiber and a complementary molecularly imprinted polymer-carbon composite fiber sensor is proven to be useful for clinical diagnosis of stress-related diseases caused by acute tryptophan depletion. © 2010 Elsevier B.V.
Enatioselective quantitative separation of d- and l-thyroxine by molecularly imprinted micro-solid phase extraction silver fiber coupled with complementary molecularly imprinted polymer-sensor
(2010) Bhim Bali Prasad; Mahavir Prasad Tiwari; Rashmi Madhuri; Piyush Sindhu Sharma
Thyroxine is a known disease biomarker which demands a highly sensitive and selective technique to measure ultratrace level with enantiodifferentiation of its optical isomers (d- and l-), in real samples. In this work, an approach of hyphenation between molecularly imprinted micro-solid phase extraction and a complementary molecularly imprinted polymer-sensor was adopted for enantioseparation, preconcentration, and analysis of d- and l-thyroxine. In both techniques, the same imprinted polymer, coated on a vinyl functionalized self-assembled monolayer modified silver wire, was used as the respective extraction fiber as well as sensor material. This combination enabled enhanced preconcentration of test analyte substantially so as to achieve the stringent limit [limit of detection: 0.0084ngmL-1, RSD=0.81%, S/N=3 (d-thyroxine); 0.0087ngmL-1, RSD=0.63%, S/N=3 (l-thyroxine)] of clinical detection of thyroid-related diseases, without any problems of non-specific false-positive contribution and cross-reactivity. © 2010 Elsevier B.V.
Highly selective and sensitive analysis of dopamine by molecularly imprinted stir bar sorptive extraction technique coupled with complementary molecularly imprinted polymer sensor
(2013) Bhim Bali Prasad; Amrita Srivastava; Mahavir Prasad Tiwari
This paper reports a combination of molecularly imprinted stir bar sorptive extraction and complementary molecularly imprinted polymer-sensor for the analysis of dopamine as a biomarker of several neurodegenerative diseases occurred at ultra trace level. This exploited iniferter initiated polymerization via "surface grafting-from" approach onto magnetic stir bar (for sorptive extraction) and multiwalled carbon nanotubes-ceramic electrode (for detection). Such hyphenation helped dual pre-concentration of dopamine in aqueous, biological and pharmaceutical samples. This enabled high sensitivity to achieve the stringent limit [limit of detection: 4.9ngL-1, RSD=2.4%, S/N=3, cerebrospinal fluid] of clinical detection, without any problems of non-specific contributions and cross-reactivity. © 2013 Elsevier Inc.
Highly selective and sensitive analysis of γ-aminobutyric acid using a new molecularly imprinted polymer modified at the surface of abrasively immobilized multi-walled carbon nanotubes on pencil graphite electrode
(2013) Bhim Bali Prasad; Amrita Prasad; Mahavir Prasad Tiwari
This work describes the development of an electrochemical sensor based on a new molecularly imprinted polymer for the detection of γ-amino butyric acid at ultra-trace level. This is comprised of a thin imprinted film exploiting an abrasive immobilization of functionalized multi-walled carbon nanotubes on the tip of a pencil graphite electrode. For the reason that γ-aminobutyric acid is an electro-inactive species, its o-pthalaldehyde/sulphite derivative was used as a template for imprinting polymer made from a typical functional monomer (5-fluorouracil-N-acetylacrylamide) and cross-linking agent (ethylene glycol dimethacrylate) in the porogen, dimethyl sulphoxide. The electrodics of the template was explored using various techniques, viz., cyclic voltammetry, differential pulse anodic stripping voltammetry, and chronocoulometry. The template detection, in terms of γ-aminobutyric acid, at stringent limits of clinical settings was feasible by differential pulse anodic stripping voltammetry technique in the linear concentration range, 0.75-205.19 ng mL -1 (correlation coefficients 0.999, detection limits 0.28 ng mL -1), without any cross-reactivity and false positives in aqueous, human serum, and cerebrospinal fluid. © 2013 Elsevier Ltd. All rights reserved.
Highly sensitive and selective hyphenated technique (molecularly imprinted polymer solid-phase microextraction-molecularly imprinted polymer sensor) for ultra trace analysis of aspartic acid enantiomers
(2013) Bhim Bali Prasad; Amrita Srivastava; Mahavir Prasad Tiwari
The present work is related to combination of molecularly imprinted solid-phase microextraction and complementary molecularly imprinted polymer-sensor. The molecularly imprinted polymer grafted on titanium dioxide modified silica fiber was used for microextraction, while the same polymer immobilized on multiwalled carbon nanotubes/titanium dioxide modified pencil graphite electrode served as a detection tool. In both cases, the surface initiated polymerization was found to be advantageous to obtain a nanometer thin imprinted film. The modified silica fiber exhibited high adsorption capacity and enantioselective diffusion of aspartic acid isomers into respective molecular cavities. This combination enabled double preconcentrations of d- and l-aspartic acid that helped sensing both isomers in real samples, without any cross-selectivity and matrix complications. Taking into account 6×104-fold dilution of serum and 2×103-fold dilution of cerebrospinal fluid required by the proposed method, the limit of detection for l-aspartic acid is 0.031ngmL-1. Also, taking into account 50-fold dilution required by the proposed method, the limit of detection for d-aspartic acid is 0.031ngmL-1 in cerebrospinal fluid. © 2013 Elsevier B.V.
Imprinted polymer-carbon consolidated composite fiber sensor for substrate-selective electrochemical sensing of folic acid
(2010) Bhim Bali Prasad; Rashmi Madhuri; Mahavir Prasad Tiwari; Piyush Sindhu Sharma
Molecularly imprinted polymers (MIPs) are often electrically insulating materials. Due to the presence of diffusion barrier(s) in between such MIP coating and electrode surface and the absence of a direct path for the conduction of electrons from the binding sites to the electrode, the development of electrochemical sensor is significantly restricted. The direct use of MIPs those possess intrinsic electron-transport properties, is highly limited. These problems are resolved by the design of an original, substrate-selective MIP-fiber sensor that combines conventional insulating MIP and conducting carbon powder in consolidated phase. A layer of conducting carbon particles, arranged orderly as 'carbon strip', is inducted in the polymer for direct electronic conduction. MIP-carbon composite (monolithic fiber) in this work is prepared via in situ free radical polymerization of a new monomer (2,4,6-trisacrylamido-1,3,5-triazine, TAT) and subsequent cross-linkage with ethylene glycol dimethacrylate, in the presence of carbon powder and template (folic acid), at 55°C in a glass capillary. The detection of folic acid with the MIP-fiber sensor was found to be specific and quantitative (detection limit 0.20ngmL-1, RSD=1.3%, S/N=3), in aqueous, blood serum and pharmaceutical samples, without any problem of non-specific false-positive contribution and cross-reactivity. © 2010 Elsevier B.V.
Imprinting molecular recognition sites on multiwalled carbon nanotubes surface for electrochemical detection of insulin in real samples
(2010) Bhim Bali Prasad; Rashmi Madhuri; Mahavir Prasad Tiwari; Piyush Sindhu Sharma
An insulin-imprinted polymer was synthesized over the surface of vinyl group functionalized multiwalled carbon nanotubes, using phosphotidylcholine- containing functional monomer and cross-linker. Phosphotidylcholine is a major component of all biological membrane; its incorporation in polymer backbone assures water-compatibility, bio-compatibility and specificity to molecularly imprinted nanomaterials, without any cross-reactivity or interferences from biological sample matrices. An electrochemical sensor fabricated by modifying multiwalled carbon nanotubes-molecularly imprinted polymer onto the pencil graphite electrode, was used for trace level detection of insulin in aqueous, blood serum, and pharmaceutical samples (detection limit 0.0186 nmol L -1, S/N = 3), by differential pulse anodic stripping voltammetry. Additional cyclic voltammetry (stripping mode) and chronocoulometry experiments were performed to explore electrodics and kinetics of electro-oxidation of insulin. © 2010 Elsevier Ltd All rights reserved.
Layer-by-layer assembled molecularly imprinted polymer modified silver electrode for enantioselective detection of d- and l-thyroxine
(2010) Bhim Bali Prasad; Rashmi Madhuri; Mahavir Prasad Tiwari; Piyush Sindhu Sharma
The present work describes a new, simple, and easy method for the generation of stable molecularly imprinted sites in polymeric film, combining self-assembled monolayer and Layer-by-layer approaches through thermal cross-linking of the layered structures, onto the surface of silver electrode. Modified silver electrodes demonstrate enantiodifferentiation and sensitive (detection limits 0.0060ngmL-1 for l- and 0.0062 for d-thyroxine) determination of d- and l-thyroxine with the help of differential pulse anodic stripping voltammetric technique. The binding kinetics of thyroxine was explored using anodic stripping cyclic voltammetry and chronocoulometry. The sensor was also validated for d- and l-thyroxine determinations in biological and pharmaceutical samples. © 2010 Elsevier B.V.
Metal ion mediated imprinting for electrochemical enantioselective sensing of l-histidine at trace level
(2011) Bhim Bali Prasad; Deepak Kumar; Rashmi Madhuri; Mahavir Prasad Tiwari
Enantioselective trace level sensing of l-histidine (limit of detection, 1.980ngmL -1, S/N=3) was feasible with the use of a typical, reproducible, and rugged complex imprinted polymer-based pencil graphite electrode, in aqueous samples. In the present instance, the Cu 2+ ion-mediated imprinting of l-histidine in an molecularly imprinted polymer motif actually helped upbringing electrocatalytic activity to respond an enhanced differential pulse anodic stripping voltammetric oxidation peak of l-histidine, without any cross-reactivity and false-positive, in real samples. The proposed sensor could be considered suitable for the practical applications in biomarking histedinemia, a disease associated with l-histidine metabolic disorders, in clinical settings. © 2011 Elsevier B.V.
Molecularly imprinted micro solid-phase extraction technique coupled with complementary molecularly imprinted polymer-sensor for ultra trace analysis of epinephrine in real samples
(Elsevier, 2014) Bhim Bali Prasad; Amrita Srivastava; Amrita Prasad; Mahavir Prasad Tiwari
A simple hyphenation approach was adopted to obtain a new molecularly imprinted micro solid-phase extraction fiber (as a selective extraction tool) and complementary molecularly imprinted polymer coated pencil graphite electrode (as a detection tool) for the selective and sensitive analysis of epinephrine, which is a disease biomarker prevalent at ultra trace level in biological fluids. In both extraction and detection processes, the functionalized multiwalled carbon nanotubes (CNT-mers) were preferred to multiwalled carbon nanotubes (unmodified) in order to obtain a stable homogeneously dispersed imprinted polymer matrix of better electroconductivity and adsorptive characteristics. The hyphenation of both tools helped dual pre-concentration of epinephrine so as to achieve the stringent limit [limit of detection: 0.002ngmL-1, S/N=3] of clinical detection, without any problems of non-specific contributions and cross-reactivity. © 2013 Elsevier B.V.
Molecularly Imprinted Nanomaterial-Based Highly Sensitive and Selective Medical Devices
(John Wiley and Sons, 2012) Bhim Bali Prasad; Mahavir Prasad Tiwari
Molecular imprinting provides a unique opportunity for the creation of three-dimensional cavities with tailored recognition properties. Over the past decade, the molecularly imprinted polymer (MIP) field has expanded considerably across a variety of disciplines, leading to novel approaches and many potential applications. The application of the imprinting approach to novel polymeric formats offers new insights and attractive methods for the preparation of synthetic receptors. In particular, MIP technology provides a means for ready access to nanostructured polymeric materials of predetermined selectivity. The versatility of the technique has attracted the attention of many workers for developing nanomaterials, with biological or biomimetic properties, for ultimate use in therapeutics and medical devices. The state-of-the art of ÌÉÑ-based nanomaterials may set a new trend in the development of chemical sensors, and that will have a big impact on the future of nanoscience. In fact, the exotic properties of nanostructured materials, such as high surface/volume ratio, functionalization ability, favorable electronic and thermal features, and electrocatalytic characteristics have paved the way of designing many fabrication strategies for sensors and biosensors. In this monograph, we present a useful guide to all researchers who are interested in exploiting MIP technology for potential applications in the development of nanostructured sensors as highly sensitive and selective medical devices. © 2012 Scrivener Publishing LLC.
Molecularly Imprinted Polymer as Advanced Material for Development of Enantioselective Sensing Devices
(Wiley Blackwell, 2014) Mahavir Prasad Tiwari; Bhim Bali Prasad
Chiral recognition is a fundamental property of many biological molecules. The enantiodifferentiation of the sensor signal requires the interaction of the determined chiral compound (one or a mixture of enantiomers) and a selector. Th is interaction is controlled by at least three binding centers, whose mutual arrangement and characteristics of interactions with one of the enantiomers control the selectivity of recognition. Molecular imprinting provides a unique opportunity for the creation of three-dimensional cavities with tailored recognition properties. Over the past decade, the molecularly imprinted polymer (MIP) field has expanded considerably across a variety of disciplines, leading to novel approaches and many potential applications. The application of the imprinting approach to novel polymeric formats offers new insights and attractive methods for the preparation of synthetic receptors for chiral recognition. The state-of-art of MIP-based chiral polymers may set a new trend in the development of chiral sensors, and that will have a big impact on the future of enantio-sensing. In this chapter, we present a useful guide to all researchers who are interested in exploiting MIP technology for potential applications in the development of chiral sensors as highly sensitive and selective devices. © 2014 Scrivener Publishing LLC. All rights reserved.
Molecularly imprinted polymer based enantioselective sensing devices: A review
(Elsevier, 2015) Mahavir Prasad Tiwari; Amrita Prasad
Chiral recognition is the fundamental property of many biological molecules and is a quite important field in pharmaceutical analysis because of the pharmacologically different activities of enantiomers in living systems. Enantio-differentiating signal of the sensor requires specific interaction between the chiral compounds (one or a mixture of enantiomers) in question and the selector. This type of interaction is controlled normally by at least three binding centers, whose mutual arrangement and interacting characteristics with one of the enantiomers effectively control the selectivity of recognition. Molecular imprinting technology provides a unique opportunity for the creation of three-dimensional cavities with tailored recognition properties. Over the past decade, this field has expanded considerably across the variety of disciplines, leading to novel transduction approaches and many potential applications. The state-of-art of molecularly imprinted polymer-based chiral recognition might set an exotic trend toward the development of chiral sensors. The objective of this review is to provide comprehensive knowledge and information to all researchers who are interested in exploiting molecular imprinting technology toward the rational design of chiral sensors operating on different transduction principles, ranging from electrochemical to piezoelectric, being used for the detection of chiral compounds as they pose significant impact on the understanding of the origin of life and all processes that occur in living organisms. © 2014 Elsevier B.V.