Browsing by Author "Rashmi Madhuri"

Now showing 1 - 13 of 13

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.
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.
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 polymer-modified electrochemical sensor for simultaneous determination of copper and zinc
(2011) Deepak Kumar; Rashmi Madhuri; Mahavir Prasad Tiwari; Pankhuri Sinha; Bhim Bali Prasad
A procedure for the simultaneous determination of copper and zinc using molecularly imprinted polymer-modified sensor is developed. The linear range of copper and zinc was observed in the concentration window 0.098-23.80 μg L-1, with detection limits (S/N=3) as low as 0.0275 μg L-1 (zinc) and 0.0159 μg L-1 (copper). © 2011 VBRI press.
Multiwalled carbon nanotubes bearing 'terminal monomeric unit' for the fabrication of epinephrine imprinted polymer-based electrochemical sensor
(2013) Bhim Bali Prasad; Amrita Prasad; Mahavir Prasad Tiwari; Rashmi Madhuri
Carbon-nanotubes play a pivotal role in molecularly imprinted polymer technology for inculcating conducting property, high surface to volume ratio, and maximum porosity in the film texture. Contrary to the non-covalent heterogeneous dispersion of pure (unmodified) multiwalled carbon nanotubes in the imprinted polymer film, the homogeneous distribution of their functionalized derivative was found more effective to augment the sensitivity of the measurement. This could be made feasible using multiwalled carbon nanotubes bearing terminal monomeric unit (termed as "CNT-mer") for the polymerization (one CNT-mer in each repeating unit). In this work, the CNT-mer entails a N-hydroxyphenyl maleimide functionality to be utilized in the chain propagation with simultaneous imprinting of epinephrine in the polymeric network. This system, when casted on the tip of a pencil graphite electrode, responded a highly sensitive and selective response for epinephrine, prevalent in aqueous and real samples at ultratrace level (linear range 0.09-5.90ngmL-1, limit of detection 0.02ngmL-1, S/N=3), without any cross-reactivity and matrix effects. The proposed sensor is advantageous in obtaining enhanced differential pulse anodic stripping voltammetric current vis-a-vis the corresponding imprinted sensor modified with randomly dispersed flocculated multiwalled carbon nanotubes bundles. While the latter might restrict the interlayer diffusion of analyte in the film, the former sensor facilitated high diffusivity with the channelized electron transport to respond higher current. The CNT-mer dispersed sensor was found to be stable and rugged against mechanical stress and can be used, after regeneration, for more than hundred consecutive experiments in clinical settings. © 2013 Elsevier B.V.
Nonhydrolytic sol-gel derived imprinted polymer-multiwalled carbon nanotubes composite fiber sensors for electrochemical sensing of uracil and 5-fluorouracil
(Elsevier Ltd, 2012) Bhim Bali Prasad; Deepak Kumar; Rashmi Madhuri; Mahavir Prasad Tiwari
The present work describes an exciting method for the generation of stable silica-molecularly imprinted polymer (MIP) composite fibers, via a non-hydrolytic sol-gel simple route, using carboxylated multi-walled carbon nanotubes. The modified MIP-composite fibers were used as an electrochemical sensor for the selective and sensitive analysis of ultra-trace level of 5-fluorouracil and uracil in aqueous, blood plasma, and pharmaceutical samples. Such sensors could be considered cost-effective, renewable, disposable, and reliable for in-field and clinical studies, without any cross-reactivity and matrix effect from real samples [limit of detection (3σ, aqueous solution); 1.30ngmL-1, 5-fluorouracil and 0.56ngmL-1, uracil]. © 2012 Elsevier Ltd. All rights reserved.
Sol-gel derived multiwalled carbon nanotubes ceramic electrode modified with molecularly imprinted polymer for ultra trace sensing of dopamine in real samples
(2011) Bhim Bali Prasad; Deepak Kumar; Rashmi Madhuri; Mahavir Prasad Tiwari
A new class of composite electrodes made of sol-gel derived ceramic-multiwalled carbon nanotubes is used for the growth of a nanometer thin film adopting "surface grafting-from approach". For this the multiwalled carbon nanotubes-ceramic electrode surface is first modified with an iniferter (benzyl N,N-diethyldithiocarbamate) and then dopamine imprinted polymer, under UV irradiation, for differential pulse anodic stripping voltammetric sensing of dopamine in aqueous, blood serum, cerebrospinal fluid, and pharmaceutical samples (detection limit 0.143-0.154 ng mL-1, 3σ), without any cross reactivity, interferences and false-positive contributions. Such composite electrodes offer higher stability, electron kinetics, and renewable porous surface of larger electroactive area (with insignificant capacitance) than carbon ceramic electrodes. Additional cyclic voltammetry (stripping mode) and chronocoulometry experiments were performed to explore electrodics and kinetics of electro-oxidation of dopamine. © 2011 Elsevier Ltd. All rights reserved.