Dr. Mamta Raj
Verified @gmail.com
iit roorkee
RESEARCH INTERESTS
electrochemical sensors biosensors nanomaterials conducting polymer
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Vivek Yadav, Mamta Raj, and Rajendra N. Goyal
The Electrochemical Society
Jay Gautam, Mamta Raj, and Rajendra N. Goyal
The Electrochemical Society
Mamta Raj and Rajendra N. Goyal
Elsevier BV
Abstract A sensitive voltammetric biosensor based on silver nanoparticles (AgNPs) and electrochemically reduced graphene oxide (ErGO) nanocomposite modified pyrolytic graphite (AgNPs:ErGO/PG) has been prepared to determine the effect of caffeine (CAF) on the concentration of estradiol (EST) in the child-bearing aged women (18–35 yr). The modified surface was characterized by Transmission Electron Microscopy (TEM), Field Emission Scanning Electron Microscopy (FE-SEM), Electrochemical Impedance Spectroscopy (EIS), Raman Spectroscopy, cyclic voltammetry (CV) and square wave voltammetry (SWV). The modified sensor exhibited exceptional electrocatalytic effects towards the oxidation of EST and CAF with a significant enhanced peak current. The linear calibration curves were found in the concentration range of 0.001–175 μM and 0.001–200 μM for EST and CAF respectively and the limits of detection were found as 0.046 nM, and 0.54 nM. The common metabolites present in the biological fluid matrix i.e. ascorbic acid (AA), uric acid (UA), xanthine (XT) and hypoxanthine (HX) did not interfere in the simultaneous determination of EST and CAF. The analytical applicability of the proposed sensor has been exhibited by analyzing EST and CAF in the human serum and urine samples of five women of child-bearing age.
Mamta Raj, Jong-Min Moon, Rajendra N. Goyal, Deog-Su Park, and Yoon-Bo Shim
Elsevier BV
A sensitive voltammetric sensor based on palladium nanoparticles (PdNPs) and poly-bromocresol green (pBG) composite layer immobilized on amide functionalized single-walled carbon nanotubes (AmSWCNTs) modified pyrolytic graphite (PdNPs:pBG/AmSWCNTs/PG) has been prepared for the simultaneous determination of adenosine triphosphate (ATP) catabolites, inosine (INO), hypoxanthine (HX), xanthine (XT), and uric acid (UA). The modified PdNPs:pBG/AmSWCNTs/PG was characterized by electrochemical experiments and surface analysis, which exhibited exceptional electrocatalytic effects towards the oxidation of INO, HX, XT, and UA with a significant enhanced peak current and well resolved peaks separation for all the analytes. The linear calibration curves were obtained in the concentration range of 0.001-175 µM, 0.001-200 µM, 0.001-150 µM, and 0.001-200 µM and limits of detection were found as 0.95 nM, 1.04 nM, 1.07 nM, and 0.43 nM corresponding to INO, HX, XT, and UA, respectively. The common metabolites present in the biological fluids did not interfere in the determination. The applicability of the proposed sensor was successfully demonstrated by determining INO, HX, XT, and UA in the human plasma and urine and the obtained results were validated by using HPLC.
M. Amal Raj and S. Abraham John
Elsevier
Abstract In the last decade, remarkable advances in the field of electrochemical sensors based on graphene and its composites have been depicted. Graphene, a new 2D nanomaterial with outstanding physical, chemical, and electrochemical properties, is an efficient electrode material for creating new sensing assays due to its large conductivity, fast heterogeneous electron transfer, and large surface area. Graphene-modified electrodes prepared by different methods have been used for the successful determination of various biomolecules with high sensitivity and selectivity in the past few years. In this chapter, after a brief introduction to the properties, synthetic methods of graphene and its derivatives, and the importance of various biomolecules, the current development on graphene-based electrochemical sensors is discussed. The implications of graphene on the development of modern electrochemical sensors are also discussed. Finally, future prospects on graphene as advanced electrocatalysts are highlighted.
N. S. K. Gowthaman, M. Amal Raj, and S. Abraham John
American Chemical Society (ACS)
The attachment of nitrogen-doped graphene (NG) on glassy carbon electrode (GCE) followed by electrodeposition of copper nanostructures (CuNSs) is described in this paper. Nitrogen-doped graphene oxide (N-GO) was prepared by intercalating melamine into graphene oxide (GO) by sonication. The doping of nitrogen was confirmed from the characteristic peaks at 285.3 and 399 eV in the XPS corresponding to the C–N bond and nitrogen, respectively. The presence of amine groups on the N-GO was exploited to attach them on GCE via Michael’s reaction. Subsequently, N-GO was electrochemically reduced to form NG by reducing the oxygen functionalities present on the N-GO. Then, the CuNSs on the NG modified electrode was prepared by electrodeposition at various applied potentials with different deposition times. The homogeneous deposition of cubic, spherical, quasidendritic, and dendritic NS at the applied potentials of 0, −0.10, −0.30, and −0.40 V, respectively, was evidenced from scanning electron microscopy (SEM) studie...
Mamta Raj, Pankaj Gupta, Rajendra N. Goyal, and Yoon-Bo Shim
Elsevier BV
Abstract A novel and sensitive electrochemical method has been developed for the simultaneous determination of dopamine (DA) and 5-hydroxytryptamine (5-HT) using graphene (GR) and poly 4-amino-3-hydroxy-1-naphthalenesulfonic acid modified screen printed carbon sensor. The electrochemical measurements were studied using cyclic voltammetry, square wave voltammetry, whereas the surface morphology of the modified sensor was characterized by Electrochemical Impedance Spectroscopy and Field Emission scanning electron microscopy. The fabricated sensor facilitated the analysis of DA and 5-HT in the concentration range 0.05–100 μM and 0.05–150 μM with the detection limit of 2 nM and 3 nM respectively. The fabricated sensor has been explored for the determination of 5-HT in the plasma samples and the selectivity of the proposed work has been proved by the analysis of DA and 5-HT in the presence of common metabolites present in biological fluids. The analytical applicability of the fabricated sensor has also been successfully demonstrated for the simultaneous detection of DA and 5-HT in the pharmacological formulations, human urine and blood samples.
Mamta Raj, Pankaj Gupta, Neeta Thapliyal, and Rajendra N. Goyal
Wiley
A novel, facile fabrication, based on electrochemically reduced graphene oxide (ErGO), grafted with Pt nanoparticles and Nafion hybrid nano-composite (ErGO-Pt/Nafion) on the surface of edge plane pyrolytic graphite (EPPG) has been reported. The fabricated sensor has been used for the sensitive and selective determination of efavirenz (EFZ), a well-known drug for HIV infections. The ErGO-Pt/Nafion film was characterized by Field Emission Scanning Electron Microscopy (FE-SEM), Energy-dispersive X-ray spectrometry (EDS) and Electrochemical Impedance Spectroscopy (EIS). The experimental results reveal that the modified sensor displays an excellent electrocatalytic activity towards the oxidation of EFZ and exhibits a large linear dynamic relationship in the range of 0.05 μM to 150 μM, with a detection limit of 1.8 nM. Practical utility of the developed sensor has been demonstrated by determining the EFZ in biological fluids and pharmaceutical samples and a low detection limit with high sensitivity observed makes it valuable for the clinical diagnosis.
Mamta Raj and Rajendra N. Goyal
The Electrochemical Society
Mamta Raj and Rajendra N. Goyal
Elsevier BV
Abstract A sensitive and selective edge plane pyrolytic graphite sensor, modified using poly-melamine and poly-glutamic acid (p-Mel-Glu/EPPG) co-polymeric film through a single electropolymerization step, has been fabricated for the determination of 2-Thioxanthine (2-TX). The extremely sensitive interlinked polymeric film formed at the surface of pyrolytic graphite was characterized by using Field Emission Scanning Electron Microscopy, Electrochemical Impedance Spectroscopy, Cyclic Voltammetry and Square Wave Voltammetry techniques. The sensing surface exhibited electrocatalytic effects towards the oxidation of 2-TX, by displaying the significant enhancement in the sensitivity in terms of an increase in the peak current and shift of the peak potential to less positive potentials. The proposed method exhibited linear relation of the peak current in the concentration range of 0.5–150 μM and the limit of detection and limit of quantification were found as 1.0 nM and 3.4 nM, respectively. The developed approach has successfully been applied for the quantification of 2-TX in the presence of common interferents present in the urine.
Rosy, Mamta Raj, and Rajendra N. Goyal
Elsevier BV
Abstract A 4-amino-3-hydroxy-1-naphthalenesulfonic acid (AHNSA) and reduced graphene oxide (rGO) based polymer nanocomposite (PNC) has been electrodeposited directly on the surface of glassy carbon electrode (GCE) using cyclic voltammertry. The electrochemical reduction of graphene oxide (GO) to rGO and the synthesis of PNC have been inspected using FE-SEM, TEM and Raman spectroscopy. The modified GCE was further used for the voltammetric quantification of Tryptophan (Trp) in the presence and absence of 5-hydroxytryptamine. The PNC modified sensor exhibited improved sensing and electrocatalytic properties in comparison to unmodified GCE, rGO modified GCE and AHNSA modified GCE. The fabricated sensor showed a linear calibration plot in the range of 0.5–200 μM with sensitivity and limit of detection (L.O.D.) of 0.0451 μA μM −1 and 316 nM (n = 3) respectively in comparison to 0.19 μA μM −1 and 2.54 μM (n = 3) respectively for unmodified GCE. The proposed method was also successfully applied for the determination of Trp in commercially available pharmaceutical formulations, human urine and plasma samples.
M. Amal Raj, N.S.K. Gowthaman, and S. Abraham John
Elsevier BV
To reduce the side effects in the medication of Parkinson and Asthma, pyridoxine (PY) is administered along with l-3,4-dihydroxyphenyl alanine (l-dopa) and theophylline (TP), respectively. However, excessive dosage of PY leads to nervous disorder. Thus, a sensitive and selective electrochemical method was developed for the determination of PY in the presence of major interferences including TP, l-dopa, ascorbic acid (AA) and riboflavin (RB) using electrochemically reduced graphene oxide (ERGO) film modified glassy carbon electrode (GCE) in this paper. The ERGO fabrication process involves the nucleophilic substitution of graphene oxide at basic pH on amine terminal of 1,6-hexadiamine which was pre-assembled on GCE followed by electrochemical reduction. The electrocatalytic activity of the ERGO modified electrode was examined towards the oxidation of PY. It greatly enhanced the oxidation current of PY in contrast to bare and GO modified GCEs due to facile electron transfer besides π-π interaction between ERGO film and PY. Since TP and l-dopa drugs antagonize the drug action of PY, ERGO modified GCE was also used for the simultaneous determination of PY and l-dopa and PY and TP. Further, the selective determination of PY in the presence of other water soluble vitamins such as ascorbic acid and riboflavin was also demonstrated. Using amperometry, detection of 100nM PY was achieved and the detection limit was found to be 5.6×10(-8)M (S/N=3). The practical application of the present method was demonstrated by determining the concentration of PY in human blood serum and commercial drugs.
Srinivasan Kesavan, M. Amal Raj, and S. Abraham John
Elsevier BV
The current study describes the electrografting of 2,4-diamino-1,3,5-triazine (AT) groups at the surfaces of glassy carbon electrode (GCE) and indium tin oxide (ITO) through in situ diazotization of melamine. The presence of AT groups at the surface of the electrode was confirmed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Furthermore, graphene oxide (GO) was self-assembled on AT grafted GCE. The oxygen functional groups present on the surface of GO were electrochemically reduced to form an electrochemically reduced graphene oxide (ERGO) on AT grafted electrode surface. Raman spectra show the characteristic D and G bands at 1340 and 1605 cm(-1), respectively, which confirms the successful attachment of GO on AT grafted surface, and the ratio of D and G bands was increased after the electrochemical reduction of GO. EIS shows that the electron transfer reaction of [Fe(CN)6](3-/4-) was higher at the ERGO modified electrode than at bare, AT grafted, and GO modified GCEs. The electrocatalytic activity of ERGO was investigated toward the oxidation of methylxanthines. It shows excellent electrocatalytic activity toward these methylxanthines by not only shifting their oxidation potentials toward less positive potentials but also enhancing their oxidation currents.
Mamta Raj, Pankaj Gupta, and Rajendra N. Goyal
The Electrochemical Society
M. Amal Raj and S. Abraham John
Royal Society of Chemistry (RSC)
Electrochemically reduced graphene oxide film catalyzed electroless deposition of gold nanoparticles.
M. Amal Raj and S. Abraham John
Elsevier BV
Abstract We report the electrochemical determination of urate lowering therapeutic drug, allopurinol (AP) using the electrochemically reduced graphene oxide (ERGO) modified glassy carbon electrode (GCE). The ERGO modified GCE was fabricated by self–assembling graphene oxide (GO) on 1,6-hexadiamine (HDA) modified GCE by the electrostatic interaction between the positively charged amine group and the negatively charged GO layers followed by the electrochemical reduction of GO layers at negative potential. XPS results confirmed the attachment of GO and its electrochemical reduction. The electrochemical behavior of AP was examined at ERGO modified electrode in the presence of ascorbic acid (AA) and uric acid (UA). It was found that ERGO modified electrode not only enhanced the oxidation currents of AP, AA and UA but also showed stable signals for them for repetitive potential cycles. The present modified electrode was successfully used to determine these analytes simultaneously in a mixture. Selective determination of AP in the presence of high concentrations of AA and UA was also demonstrated at ERGO modified GCE. Using amperometry, detections of 40 and 200 nM of UA and AP were achieved and the detection limits were found to be 9.0 × 10−9 M and 1.1 × 10−7 M, respectively (S/N = 3). Further, the practical application of the present modified electrode was demonstrated by simultaneously determining the concentrations of AA, UA and AP in human blood serum and urine samples.
M. Amal Raj and S. Abraham John
Elsevier BV
This paper describes the fabrication of graphene on glassy carbon electrode (GCE) by electrochemical reduction of graphene oxide (GO) attached through 1,6-hexadiamine on GCE and the simultaneous determination of structurally similar four purine derivatives using the resultant electrochemically reduced GO (ERGO) modified electrode. The electrocatalytic activity of ERGO was investigated toward the oxidation of four important purine derivatives, uric acid (UA), xanthine (XN), hypoxanthine (HXN) and caffeine (CAF) at physiological pH. The modified electrode not only enhanced the oxidation currents of the four purine derivatives but also shifted their oxidation potentials toward less positive potentials in contrast to bare GCE. Further, it successfully separates the voltammetric signals of the four purine derivatives in a mixture and hence used for the simultaneous determination of them. Selective determination of one purine derivative in the presence of low concentrations other three purine derivatives was also realized at the present modified electrode. Using differential pulse voltammetry, detection limits of 8.8×10(-8)M, 1.1×10(-7)M, 3.2×10(-7)M and 4.3×10(-7)M were obtained for UA, XN, HXN and CAF, respectively. The practical application of the modified electrode was demonstrated by simultaneously determining the concentrations of UA, XN, HXN and CAF in human blood plasma and urine samples.
M. Amal Raj and S. Abraham John
American Chemical Society (ACS)
We report a simple, facile, and reproducible method for the fabrication of electrochemically reduced graphene oxide (ERGO) films on glassy carbon electrode (GCE) by the self-assembly method. The graphene precursor, graphene oxide (GO), was self-assembled on GCE through a diamine linker which was preassembled on GCE by electrostatic interaction between the positively charged amine and the negatively charged layers of graphene oxide (GO). The oxygen functional groups present on the surface of GO were electrochemically reduced to retain the aromatic backbone of graphene. The attachment of GO followed by its electrochemical reduction was confirmed by ATR-FT-IR spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Raman spectra show that the intensity ratio of D and G bands was increased after the electrochemical reduction of GO. XPS results reveal that the carbon-to-oxygen ratio was increased af...
M. Amal Raj, S. Brillians Revin, and S. Abraham John
Elsevier BV
This paper describes the synthesis of 4-amino-6-hydroxy-2-mercaptopyrimidine capped gold nanoparticles (AHMP-AuNPs) in aqueous medium and their immobilization on indium tin oxide (ITO) electrode modified with (3-mercaptopropyl)trimethoxysilane (MPTS) sol-gel for the determination of tannic acid (TA). The high resolution transmission electron microscopy (HR-TEM) images show that the particles are spherical in shape with a diameter of ~6 nm. The heterogeneous electron transfer rate constant (k(et)) of [Fe(CN)₆]³⁻/⁴⁻ at ITO/MPTS/AHMP-AuNPs electrode was found to be 1.14×10⁻⁷ m/s. This value was much higher than the values obtained at ITO/MPTS (4.94×10⁻⁹ m/s) and bare ITO (8.79×10⁻⁸ m/s) electrodes, indicating that the electron transfer reaction was faster at AuNPs modified electrode. Further, the ITO/MPTS/AHMP-AuNPs electrode shows excellent electrocatalytic activity toward TA oxidation when compared to bare ITO electrode. This was understood from the obtained higher heterogeneous rate constant (k(s)) value at AuNPs modified electrode (7.35×10⁻⁵ m/s) than at bare ITO electrode (5.45×10⁻⁶ m/s). Using the amperometry method, detection of 20 nmol/L TA was achieved. The practical application of the present method was demonstrated by determining the concentration of TA in commercial beer samples.
A. John Jeevagan, M. Amal Raj, and S. Abraham John
Royal Society of Chemistry (RSC)
In this paper, we report the synthesis of gold nanorods (GNRs) both in solution and on ITO and Au substrates using non-peripheral amine functionalized nickel(II) phthalocyanine capped gold nanoparticles (4α-NiIITAPc-AuNPs) as a seed solution. The GNRs formed in solution show transverse and longitudinal waves at 526 and 761 nm, respectively. The high-resolution transmission electron microscopy (HR-TEM) studies show the presence of GNRs in addition to few spherical AuNPs. The average aspect ratio of GNRs was found to be 4.5 ± 0.3. Further, the GNRs were also grown on the Au and ITO substrates by seed mediated growth method using (3-mercaptopropyl)-trimethoxysilane sol–gel as a linker. The 4α-NiIITAPc-AuNPs were first self-assembled on ITO or Au surface modified with MPTS sol–gel film and then immersed in a GNR growth solution, to form surface grown GNRs. The growth of GNRs on the MPTS sol–gel film modified ITO surface was monitored by UV-vis spectroscopy. The 4α-NiIITAPc-AuNPs attached on ITO surface shows a surface plasmon resonance band at 550 nm. The intensity of this band increases and an additional shoulder band around 680 nm was observed while increasing the immersion time of the 4α-NiIITAPc-AuNPs modified ITO surface into the growth solution. After 24 h, the 4α-NiIITAPc-AuNPs modified ITO surface shows a broad wave around 680 nm along with a band at 550 nm. Similarly, Au modified electrode also showed characteristic transverse and longitudinal absorption bands for GNRs which confirm the successful growth of GNRs on Au surface. The surface grown GNRs were characterized by atomic force microscopy, ATR-FT-IR, cyclic voltammetry and impedance spectral studies. Finally, the electrocatalytic activity of GNRs grown Au electrode was examined by studying the oxidation of L-tyrosine.
M. Amal Raj, S. Brillians Revin, and S. Abraham John
Elsevier BV
4-(Dimethylamino)pyridine capped gold nanoparticles (DMAP-AuNPs) were synthesized in aqueous medium and then immobilized on 1,6-hexanedithiol (HDT) modified Au electrode for the selective determination of 3,4-dihydroxyphenylacetic acid (DOPAC) in the presence of ascorbic acid (AA). The synthesized DMAP-AuNPs were characterized by UV-visible spectroscopy and high resolution-transmission electron microscopy (HR-TEM). The HR-TEM images showed that the nanoparticles are spherical in shape with a diameter of ∼12 nm. The DMAP-AuNPs immobilized on HDT modified electrode was characterized by cyclic voltammetry and impedance spectroscopy. Impedance spectra show that the electron transfer reaction was more facile at the AuNPs modified electrode when compared to bare and HDT modified Au electrodes. The application of DMAP-AuNPs modified electrode was demonstrated by selective determination of DOPAC in the presence of high concentration of AA at pH 4. Using amperometry method, 40 nM detection of each AA and DOPAC was achieved. The current response was increased linearly with increasing AA and DOPAC in the concentration range of 40×10(-9) to 10×10(-5) M and a detection limit was found to be 5.6×10(-10) M and 3.7×10(-10) M (S/N=3) for AA and DOPAC, respectively. The present modified electrode was also successfully used for the determination of 40 nM DOPAC in the presence of 2500-fold excess of common interferents such as Na(+), Mg(2+), Cu(2+), Ca(2+), NH(4)(+) urea and glucose.