Srikanth Cheemalapati

Simultaneous electrochemical determination of dopamine and paracetamol on multiwalled carbon nanotubes/graphene oxide nanocomposite-modified glassy carbon electrode.

In the present study, multiwalled carbon nanotubes (MWCNT)/graphene oxide (GO) nanocomposite was prepared by homogenous dispersion of MWCNT and GO and used for the simultaneous voltammetric determination of dopamine (DA) and paracetamol (PA). The TEM results confirmed that MWCNT walls were wrapped well with GO sheets. The MWCNT/GO nanocomposite showed superior electrocatalytic activity towards the oxidation of DA and PA, when compared with either pristine MWCNT or GO. The major reason for the efficient simultaneous detection of DA and PA at nanocomposite was the synergistic effect between MWCNT and GO. The electrochemical oxidation of DA and PA was investigated by cyclic voltammetry, differential pulse voltammetry and amperometry. The nanocomposite modified electrode showed electrocatalytic oxidation of DA and PA in the linear response range from 0.2 to 400 µmol L(-1) and 0.5 to 400 µmol L(-1) with the detection limit of 22 nmol L(-1) and 47 nmol L(-1) respectively. The proposed sensor displayed good selectivity, sensitivity, stability with appreciable consistency and precision.

Amperometric glucose biosensor based on glucose oxidase dispersed in multiwalled carbon nanotubes/graphene oxide hybrid biocomposite

An amperometric glucose biosensor based on enhanced and fast direct electron transfer (DET) of glucose oxidase (GOx) at enzyme dispersed multiwalled carbon nanotubes/graphene oxide (MWCNT/GO) hybrid biocomposite was developed. The fabricated hybrid biocomposite was characterized by transmission electron microscopy (TEM), Raman and infrared spectroscopy (IR). The TEM image of hybrid biocomposite reveals that a thin layer of GOx was covered on the surface of MWCNT/GO hybrid composite. IR results validate that the hybrid biocomposite was formed through the electrostatic interactions between GOx and MWCNT/GO hybrid composite. Further, MWCNT/GO hybrid composite has also been characterized by TEM and UV-visible spectroscopy. A pair of well-defined redox peak was observed for GOx immobilized at the hybrid biocomposite electrode than that immobilized at the MWCNT modified electrode. The electron transfer rate constant (Ks) of GOx at the hybrid biocomposite was calculated to be 11.22s(-1). The higher Ks value revealed that fast DET of GOx occurred at the electrode surface. Moreover, fabricated biosensor showed a good sensitivity towards glucose oxidation over a linear range 0.05-23.2mM. The limit of detection (LOD) was estimated to be 28μM. The good features of the proposed biosensor could be used for the accurate detection of glucose in the biological samples.

Enhanced electrocatalytic oxidation of isoniazid at electrochemically modified rhodium electrode for biological and pharmaceutical analysis

A simple and sensitive electrochemical method has been proposed for the determination of isoniazid (INZ). For the first time, rhodium (Rh) modified glassy carbon electrode (GCE) has been employed for the determination of INZ by linear sweep voltammetry technique (LSV). Compared with the unmodified electrode, the proposed Rh modified electrode provides strong electrocatalytic activity toward INZ with significant enhancement in the anodic peak current. Scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM) results reveal the morphology of Rh particles. With the advantages of wide linearity (70-1300μM), good sensitivity (0.139μAμM(-1)cm(-2)) and low detection limit (13μM), this proposed sensor holds great potential for the determination of INZ in real samples. The practicality of the proposed electrode for the detection of INZ in human urine and blood plasma samples has been successfully demonstrated using LSV technique. Through the determination of INZ in commercially available pharmaceutical tablets, the practical applicability of the proposed method has been validated. The recovery results are found to be in good agreement with the labeled amounts of INZ in tablets, thus showing its great potential for use in clinical and pharmaceutical analysis.

Highly sensitive and selective determination of pyrazinamide at poly-L-methionine/reduced graphene oxide modified electrode by differential pulse voltammetry in human blood plasma and urine samples.

In this current study we used electrochemically active film which contains poly-L-methionine (PMET) and electrochemically reduced graphene oxide (ERGO) on glassy carbon electrode (GCE) for pyrazinamide (PZM) detection. The electrocatalytic response of analyte at PMET/ERGO/GCE film was measured using both cyclic voltammetry (CV) and differential pulse voltammetry (DPV). In addition, electrochemical impedance studies revealed that the smaller R(ct) value observed at PMET/ERGO film modified GCE which authenticates its good conductivity and faster electron transfer rate. The prepared PMET/ERGO/GCE film exhibits excellent DPV response towards PZM and the reduction peak current increased linearly with respect to PZM concentration in the linear range between 0.4 μM to 1129 μM with a sensitivity of 0.266 μA μM(-1) cm(-2). Real sample studies were carried out in human blood plasma and urine samples, which offered good recovery and revealed the promising practicality of the sensor for PZM detection. The proposed sensor displayed a good selectivity, repeatability, sensitivity with appreciable consistency and good reproducibility. In addition, the proposed electrochemical sensor showed good results towards the commercial pharmaceutical PZM samples.

Investigation of morphologies and characterization of rare earth metal samarium hexacyanoferrate and its composite with surfactant intercalated graphene oxide for sensor applications

Herein, we report a facile electrochemical approach for the hierarchical growth of samarium hexacyanoferrate (SmHCF) on surfactant intercalated reduced graphene oxide (SRGO). The fabricated SRGO/SmHCF modified glassy carbon electrode (GCE) has excellent electrocatalytic activity towards catechol (CC) sensor applications. The sunflower-like SmHCF microparticles were achieved by controlling the number of cycles during the electrodeposition process. In addition, the electrolyte plays a key role in the morphology of SmHCF and was investigated using different electrochemical techniques. The as-prepared SmHCF microparticles were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and Fourier transform infrared (FT-IR) spectroscopy. In addition, electrochemical impedance spectroscopy (EIS) was carried out to understand the mechanism of interfacial electrochemical reactions on the proposed SmHCF modified glassy carbon electrode (GCE). The obtained EIS data confirmed that the electron transfer rate at SmHCF/GCE was faster than bare GCE. The electrochemical detection of CC using the SRGO/SmHCF modified GCE was performed by cyclic voltammetry and difference pulse voltammetry. The fabricated modified GCE exhibits a good linear range from 50 μM to 250 μM, with a limit of detection (LOD) of 0.38 μM and a sensitivity of 0.430 μA μM−1 cm2 for the CC electrochemical sensor.

Electrochemical determination of selected antihypertensive and antituberculosis drugs at a tyrosine-modified electrode

A simple and sensitive electrochemical method was proposed for the determination of hydralazine hydrochloride (HDH), isoniazid (ISN), ethambutol hydrochloride (EBH) and pyrazinamide (PZM). For the first time, a tyrosine (Tyr)-modified glassy carbon electrode (GCE) was employed for the determination of HDH, ISN, PZM and EBH by the differential pulse voltammetric (DPV) technique. The proposed modified electrode showed strong electrocatalytic activity towards the above-mentioned drugs with a higher peak enhancement than that of an unmodified electrode. The practicality of the proposed electrode for the detection of HDH, ISN, PZM and EBH in human urine and blood serum samples was successfully demonstrated using the DPV technique. The applicability of the proposed method was verified with commercially available pharmaceutical tablets and the obtained results were in good agreement with the claimed label amounts of the tablets. From these results, it is clearly evident that the proposed electrode shows good catalytic activity towards HDH, ISN, PZM and EBH. In addition, this method could be used in the future for the accurate detection of HDH, ISN, PZM, and EBH in clinical and pharmaceutical industries.

Novel poly-L-lysine/carboxyl-group enriched graphene oxide/modified electrode preparation, characterization and applications for the electrochemical determination of meloxicam in pharmaceutical tablets and blood serum

Electrochemical determination of meloxicam (MLC) was successfully determined at a poly-L-lysine (PLL)/carboxylated graphene oxide (GO–COOH)/modified glassy carbon electrode (GCE) by cyclic voltammetry (CV) and differential pulse voltammetric (DPV) techniques. The fabricated film characterizations were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and electrochemical impedance spectroscopy (EIS). The PLL/GO–COOH/GCE was employed for the electrocatalytic oxidation of MLC and the oxidation current of MLC significantly increased when compared to the bare GCE, which clearly shows that the modified electrode shows better electrocatalytic activity than the unmodified GCE. The linear range of the determination of MLC has to be 4 to 104 μM. The low limit of detection (LOD) and sensitivity was found as 0.87 μM and 0.228 μA μM−1 cm−2. The analytical performance of this proposed sensor has been evaluated in commercially available pharmaceutical tablets and the practicality of the proposed sensor further demonstrated in a real blood serum sample. The obtained results for commercially available tablets were almost equal to the labelled claim of the tablets; from these results it was clearly evident that the proposed electrode shows good catalytic activity towards MLC.