nan Rosy

Molecularly imprinted sensor based on o-aminophenol for the selective determination of norepinephrine in pharmaceutical and biological samples

An electrochemical sensor has been developed for the selective determination of norepinephrine (NE) using the molecularly imprinted technique. The imprinted polymer film at the surface of glassy carbon electrode is prepared by the electropolymerization of o-aminophenol in the presence of NE. Imprinted polymer film was characterized by atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The imprinted sensor showed a well-defined anodic peak at a potential of ~198 mV in phosphate buffer of pH 7.2 using square wave voltammetry. A linear increase in peak current was found with the increasing concentration of NE in the range from 50×10(-9) to 10×10(-6)mol L(-1)and the limit of detection (3σ/b) was found to be 4.9×10(-10)mol L(-1). The imprinted sensor has been successfully employed to ascertain the content of NE in the commercially available pharmaceutical preparations. The biological applicability of the developed sensor has been delineated by the determination of NE in human plasma and urine samples using the standard addition method. The proposed sensor exhibited high degree of selectivity for NE in comparison to other structurally similar biomolecules present in biological samples, along with long term stability, good reproducibility and excellent capacity of regeneration of molecular recognition sites.

Gold nanoparticles decorated poly-melamine modified glassy carbon sensor for the voltammetric estimation of domperidone in pharmaceuticals and biological fluids

The electrochemical response of an unmodified glassy carbon (GCE), poly-melamine/GCE and gold nanoparticle (AuNP)/poly-melamine/GCE is compared in the present protocol for the sensitive and selective determination of domperidone (DOM). The AuNPs were synthesized in the laboratory and characterized using UV-visible spectroscopy and Transmission Electron Microscopy (TEM). Melamine was electropolymerized onto the glassy carbon surface using cyclic voltammetry and was investigated using Field Emission Scanning Electron Microscopy (FE-SEM) and Electrochemical Impedance Spectroscopy (EIS). The AuNP/poly-melamine/GCE exhibited the best electrochemical response among the three electrodes for the electro-oxidation of DOM, that was inferred from the EIS, cyclic and square wave voltammetry. The modified sensor showed a sensitive, stable and linear response in the concentration range of 0.05-100µM with a detection limit of 6nM. The selectivity of the proposed sensor was assessed in the presence of high concentration of major interfering molecules as xanthine, hypoxanthine, and uric acid. The analytical application of the sensor for the quantification of DOM in pharmaceutical formulations and biological fluids as urine and serum was also investigated and the results demonstrated a recovery of >95% with R.S.D of <5%.

Determination of 8-Hydroxydeoxyguanosine: A potential biomarker of oxidative stress, using carbon-allotropic nanomaterials modified glassy carbon sensor.

A voltammetric sensor for the determination of 8-Hydroxydeoxyguanosine (8-OHdG); an important, sensitive and integral biomarker of oxidative stress and related pathological conditions like carcinogenesis, renal disorders, mental retardations, diabetes etc. has been fabricated. The synergistic behavior of two allotropic forms of carbon, which are electrochemically reduced graphene oxide (ErGO) and multiwalled carbon nanotubes (MWCNTs), has been exploited for the surface modification. The resulting modified surface has been characterized using Field Emission Scanning Electron Microscopy, X-ray diffraction, Electrochemical Impedance Spectroscopy and voltammetric behavior. The fabricated sensor exhibited excellent electrocatalytic effect towards oxidation of 8-OHdG and also showed substantial increment in sensitivity. The modified sensor showed a sensitivity of 0.1965µA/µM in the linear range of 3-75µM, whereas, a slope of 0.0046µA/µM was obtained for unmodified GCE. A limit of detection as low as 35nM has been obtained using the glassy carbon surface modified sensor. The proposed method was also successfully applied for the quantification of 8-OHdG in the presence of common interfering biomolecules like ascorbic acid, uric acid, xanthine, hypoxanthine etc. and also in human urine samples.

A melamine based molecularly imprinted sensor for the determination of 8-hydroxydeoxyguanosine in human urine

A sensitive and facile molecular imprinted sensor has been fabricated using edge plane pyrolytic graphite (EPPG) for the determination of an important oxidative DNA damage product, 8-hydroxydeoxyguanosine (8-OHdG). The molecularly imprinted polymer film was fabricated by electropolymerization of melamine in the presence of 8-OHdG, on glutaraldehyde/poly 1,5-diaminonaphthalene modified EPPG. The imprinted sensor surface was characterized by using Field Emission Scanning Electron Microscopy, Electron Impedance Spectroscopy, Cyclic Voltammetry, Square Wave Voltammetry and UV-visible spectroscopy. The calibration response was linear over a concentration range of 20×10-9-3×10-6M of 8-OHdG with sensitivity and limit of detection (3σ/b) as 10.59µM/µA and 3×10-9M respectively. The common metabolites in urine, like uric acid, ascorbic acid, xanthine, hypoxanthine do not interfere up to 100-fold concentration. The imprinted sensor is also successfully employed for the determination of 8-OHdG in human urine sample of a renal failure patient.

Structural and electrochemical characterization of carbon ion beam irradiated reduced graphene oxide and its application in voltammetric determination of norepinephrine

Irradiation of reduced graphene oxide (rGO) sheets using a 50 MeV C4+ ion beam has been implemented to create defects. The changes in the charge transfer resistance (RCT) and structural variations in rGO upon irradiation have been studied using electrochemical impedance spectroscopy (EIS), Raman spectroscopy and field emission scanning electron microscopy (FE-SEM). Irradiation of rGO with the 50 MeV C4+ ion beam resulted in three fold decreased charge transfer resistance (RCT 32.91 Ω) in comparison to 93.42 Ω corresponding to pristine rGO. Electrochemical properties of irradiated rGO have been further investigated by developing an irradiated rGO modified glassy carbon electrode (GCE) for the analysis of norepinephrine (NE). Voltammetric experiments showed that irradiated rGO modified GCE (irradiated rGO/GCE) exhibited superior response towards NE oxidation in comparison to both the pristine rGO/GCE and bare GCE. Thus, NE has been quantified using irradiated rGO/GCE in a linear concentration range of 1–200 μM with a detection limit of 50 nM. Detection sensitivities corresponding to bare, pristine rGO and irradiated rGO modified GCE were 0.0173, 0.1335 and 0.769 μA μM−1, respectively, demonstrating substantial improvement in sensing and electrocatalytic behaviour of rGO on exposure to the ion beam. To ensure the analytical applicability of the fabricated sensor it has been successfully applied for the estimation of norepinephrine (NE) in injections, human urine and serum samples and achieved a recovery >93% with an R.S.D. < 3.5%.

Glutaraldehyde sandwiched amino functionalized polymer based aptasensor for the determination and quantification of chloramphenicol

In the present work, the crosslinking property of glutaraldehyde (GA) is exploited to construct a 1,5-diaminonaphthalene (1,5-DAN) modified aptamer based sensor for the determination and quantification of chloramphenicol (CAP). The sensor was fabricated by electro-polymerizing 1,5-DAN on the edge plane pyrolytic graphite (EPPG) followed by immobilization of CAP selective aptamer on the amino functionalized polymer modified EPPG surface using GA, which resulted in covalent linkage with the –NH2 groups of the aptamer as well as those present on the polymerized electrode surface. Resulting GA sandwiched aptasensor leads to a tremendous improvement in the stability and sensitivity of the sensor in comparison to one fabricated without crosslinking. Characterization of the modification protocol was done using scanning electron microscopy (SEM), quartz crystal microbalance (QCM) analysis, and electrochemical impedance spectroscopy (EIS). Under optimized parameters, CAP was detected in a linear working range of 50–500 fM with the detection limit and sensitivity of 11 fM (n = 3, R.S.D = 0.15%) and 0.023 μA fM−1 respectively. The practical utility of the developed aptasensor has also been demonstrated by analysing CAP in complex matrix like urine, commercially available pharmaceutical samples and the Rosetta cells supernatant. The observed results suggests that the present electrochemical aptasensor is suitable for the detection of CAP in medicines, diagnosis of chloramphenicol resistant bacteria and virus, as well as for checking its adulteration in food and other dietary supplements.

A carbon ion beam irradiated MWCNT/AuNPs composite sensor for a sensitive assay of purine-nucleosides of DNA

Multi-walled carbon nanotube (MWCNT) and gold nanoparticle (AuNPs) composite modified glassy carbon (MWCNT/AuNPs/GC) was irradiated with a high energy carbon ion beam and the surface morphology of the irradiated sensor was analysed using Raman spectroscopy, FE-SEM and Electrochemical Impedance Spectroscopy (EIS). The irradiated MWCNT/AuNPs/GC sensor has been applied for the electrochemical investigation of deoxyguanosine (dGuo) and deoxyadenosine (dAdo) by using square wave voltammetry and cyclic voltammetry. The irradiated sensor has been found to exhibit an excellent electrocatalytic activity, leading to an enhancement in the peak currents of dGuo and dAdo. The peak potentials also shifted to less positive potentials as compared to the unirradiated MWCNT/AuNPs/GC (pristine). The peak current of dGuo and dAdo was found to be linear in the range of 1–500 μM and detection limits of 126 and 109 nM, respectively, were observed. The practical utility of the irradiated sensor has been demonstrated by the determination of dGuo and dAdo in the DNA samples extracted from herring sperm and a MCF7 cell line (human breast cancer cells). Further, the carbon beam irradiated sensor displayed high sensitivity and reproducibility and has been found to be suitable in clinical diagnosis.