T. Madhusudana Reddy

Sol–gel immobilized biosensor for the detection of organophosphorous pesticides: A voltammetric method

Organophosphorous compounds are important neuroactive molecules whose presence exhibits significant analytical challenges. An acetylcholinesterase (AChE) based amperometric biosensor was developed by silica sol-gel film immobilization of the enzyme onto the carbon paste electrode. The mono enzyme biosensor was used for the determination of two organophosphorous compounds such as methyl parathion (MP) and acephate in 0.1M phosphate buffer (pH 7.0). The substrate used was acetylthiocholine chloride (ASChCl) confirmed the formation of thiocholine and it was electrochemically oxidized giving significant increase in anodic peak current around at 0.60 V versus calomel electrode. The influence of pH, enzyme loading and substrate concentration on the response of the biosensor was investigated. The monoenzyme biosensor provided linearity to methyl parathion and acephate in the concentration range of 0.1-0.5 ppb and 50-750 ppb with an incubation time of 20 min and 4 min. The detection limits under the optimum working conditions were found to be 0.08 ppb for methyl parathion and 87 ppb for acephate. The sensor shows good operational stability 89% of its original activity for 60 successive measurements.

Voltammetric behavior of Cefixime and Cefpodoxime Proxetil and determination in pharmaceutical formulations and urine

Electrochemical reduction behavior of cephalosporins, Cefixime (CF) and Cefpodoxime Proxetil (CP) have been studied by using different voltammetric techniques in Britton-Robinson buffer system. Two well defined cathodic waves are observed for both the compounds in the entire pH range. Number of electrons transferred in the reduction process was calculated and the reduction mechanism is proposed. The results indicate that the process of both the compounds is irreversible and diffusion-controlled. The peak currents for CF and CP are found to be linear over the range of concentration 6.0 x 10(-8) to 1.2 x 10(-5) mol l(-1) and 8.8 x 10(-8) to 1.1 x 10(-5) mol l(-1), respectively. The lower detection limits are found to be 4.6 x 10(-8) and 8.52 x 10(-8) mol l(-1) for the two compounds. A differential pulse voltammetric method has been developed for the determination of these drugs in pharmaceutical formulations and urine samples.

Acetylcholinesterase based biosensor for monitoring of Malathion and Acephate in food samples: A voltammetric study

Acetylcholinesterase (AChE) biosensor was developed through silica sol-gel (SiSG) immobilisation of AChE on the carbon paste electrode (CPE) and used as working electrode. AChE catalyses the cleavage of acetylthiocholine chloride (ASChCl or substrate) to thiocholine, which was oxidised to give a disulphide compound by dimerisation at 0.60V versus saturated calomel electrode. All the experiments were carried out in 0.1M phosphate buffer solution (PBS) at pH 7.0 and 0.1M KCl solution at room temperature. The limit of detection and limit of quantification values were found to be 0.058ppm, 0.044ppm and 0.194ppm, 0.147ppm for Malathion and Acephate, respectively. The response of the biosensor showed a good linearity range with an incubation time of 4min for Malathion and Acephate, respectively. This biosensor was used for the direct determination of pesticides without any pretreatment and it requires less time for analysis.

A novel electrochemical biosensor based on horseradish peroxidase immobilized on Ag-nanoparticles/poly(l-arginine) modified carbon paste electrode toward the determination of pyrogallol/hydroquinone

A novel electrochemical biosensor for the determination of pyrogallol (PG) and hydroquinone (HQ) has been constructed based on the poly l-arginine (poly(l-Arg))/carbon paste electrode (CPE) immobilized with horseradish peroxidase (HRP) and silver nanoparticles (AgNPs) through the silica sol-gel (SiSG) entrapment. The electrochemical properties of the biosensor were characterized by employing the electrochemical techniques. The proposed biosensor showed a high sensitivity and fast response toward the determination of PG and HQ around 0.18V. Under the optimized conditions, the anodic peak current of PG and HQ was linear with the concentration range of 8μM to 30×10(-5)M and 1-150μM. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 6.2μM, 20μM for PG and 0.57μM, 1.92μM for HQ respectively. The electrochemical impedance spectroscopy (EIS) studies have confirmed that the occurrence of electron transfer at HRP-SiSG/AgNPs/poly(l-Arg)/CPE was faster. Moreover the stability, reproducibility and repeatability of the biosensor were also studied. The proposed biosensor was successfully applied for the determination of PG and HQ in real samples and the results were found to be satisfactory.

Voltammetric behavior of some fluorinated quinolone antibacterial agents and their differential pulse voltammetric determination in drug formulations and urine samples using a β-cyclodextrin-modified carbon-paste electrode

A voltammetric determination of ofloxacin (OF), norfloxacin (NF), gatifloxacin (GF), and lomefloxacin (LF) at a β-cyclodextrin-modified carbon-paste electrode (CDMCPE) is described. A large increase in the peak currents was observed in cyclic voltammetry (CV) and differential pulse voltammetry (DPV) of OF, NF, GF, and LF at CDMCPE compared with a bare carbon-paste electrode (CPE). These increases in the peak currents were attributed to the complex formation of the quinone group of the drugs with β-cyclodextrin. CV studies indicate that the process is irreversible and adsorption-controlled. The experimental parameters which influence the peak current responses of OF, NF, GF, and LF were studied. The reduction peak currents of OF, NF, GF, and LF change linearly over the common concentration range from 3.2 × 10−8 to 2 × 10−5 M, with a common correlation coefficient and limit of detection of 0.9995 and 2.4 × 10−8 M, respectively, in pH 4.0 Britton-Robinson (BR) buffer at an accumulation time of 160 s. The interference of metal ions in the peak current response was also studied. The modified electrode exhibited good sensitivity and stability. The proposed method was applied to the determination of OF, NF, GF, and LF in both commercially available drugs and spiked human urine samples.

A novel horseradish peroxidase biosensor towards the detection of dopamine: a voltammetric study.

A polymerized film of glycine (Gly) was prepared on the surface of carbon paste electrode (CPE) through the cyclic voltammetry (CV) technique. A novel biosensor for the determination of dopamine (DA) has been constructed based on horseradish peroxidase (HRP) and multiwalled carbon nanotubes (MWCNTs) immobilizing on Poly (Gly)/CPE through silica sol-gel (SiSG) entrapment. CV measurements were employed in order to understand the feasibility of poly (Gly) as an electron carrier between the immobilized peroxidase and the surface of CPE. By using differential pulse voltammetry (DPV) the calibration curves of DA was obtained in the range of 15-865 μM. The limit of detection (LOD) and limit of quantification (LOQ) of DA was found to be 6×10⁻⁷ M and 2×10⁻⁶ M respectively. The apparent Michaelis-Menten constant (Km(app)) was found to be 0.5 mM and illustrated that the good biological activity of the fixed enzyme. Electrochemical impedance spectroscopy (EIS) results confirmed the rapid electron transfer and also the immobilization of enzyme on the electrode surface. The biosensor showed high sensitivity, selectivity and reproducibility. This method has been used to determine DA in the presence of various interferences and in clinical preparations.

Differential Pulse Adsorptive Stripping Voltammetric Determination of Nifedipine and Nimodipine in Pharmaceutical Formulations, Urine, and Serum Samples by Using a Clay‐Modified Carbon‐Paste Electrode

Abstract A simple, rapid, and selective differential pulse adsorptive stripping voltammetric (DPAdSV) method has been developed for the determination of nifedipine and nimodipine based on reduction of an aromatic nitro group in the drugs at a bare carbon‐paste electrode (CPE) and a clay‐modified carbon‐paste electrode (CMCPE). Compared with a bare CPE, CMCPE gave the highest sensitivity in the present developed method. The analytical parameters that affect the electrode reaction process have been studied in terms of pH of the supporting electrolyte, accumulation time, accumulation potential, and composition of a modifier on the adsorptive stripping response by using differential pulse voltammetry. When CMCPE was used, the peak current vs. concentration relationship was found to be linear over the range 4.6 × 10−10–2 × 10−7 M and 5.4 × 10−10–4 × 10−7 M, with a limit of detection (LOD) 3.9 × 10−10 and 4.8 × 10−10 M, and correlation coefficient of 0.9996 and 0.9998 for nifedipine and nimodipine, respectively. The method was applied successfully for the direct determination of nifedipine and nimodipine in tablet dosage forms, urine, and serum samples.

Electrochemical sensing of paracetamol and its simultaneous resolution in the presence of dopamine and folic acid at a multi-walled carbon nanotubes/poly(glycine) composite modified electrode

A facile and sensitive nanocomposite sensor was developed based on the electropolymerization of glycine (Gly) onto the surface of a glassy carbon electrode (GCE) using cyclic voltammetry (CV) followed by drop casting multi-walled carbon nanotubes (MWCNTs). The developed nanocomposite sensor (MWCNTs/poly(Gly)/GCE) was characterized using an electrochemical impedance spectroscopy (EIS) technique. The developed nanocomposite sensor offered high catalytic activity in sensing the paracetamol (PC) individually and simultaneously in the presence of dopamine (DA) and folic acid (FA). The limit of detection (LOD) and limit of quantification (LOQ) were found to be 5 × 10−7 M and 1.7 × 10−6 M respectively with a dynamic range from 5 × 10−7 to 1 × 10−5 M. The fabricated sensor showed good precision and accuracy with a relative standard deviation of 1.28%. The proposed composite sensor was successfully applied towards the determination of PC in human blood serum and pharmaceutical samples.

Electrocatalytic boost up of epinephrine and its simultaneous resolution in the presence of serotonin and folic acid at poly(serine)/multi-walled carbon nanotubes composite modified electrode: A voltammetric study.

The present paper describes the new strategy for the development of nanosensor based on dropcasting of multi-walled carbon nanotubes (MWCNTs) followed by electropolymerization of serine (ser) onto the glassy carbon electrode (GCE). The developed nanocomposite sensor was abbreviated as poly(ser)/MWCNTs/GCE and was characterized by using electrochemical impedance spectroscopy (EIS) technique. The EIS results confirmed the fast electron transfer rate at the surface of poly(ser)/MWCNTs/GCE. The proposed sensor exhibited good catalytic activity towards the sensing of epinephrine (EP) individually and simultaneously in the presence of serotonin (5-HT) and folic acid (FA) in 0.1M phosphate buffer solution (PBS) at pH7.0. The limit of detection (LOD) and limit of quantification (LOQ) of EP was found to be 6×10(-7)M and 2×10(-6)M respectively. The fabricated sensor showed excellent precision and accuracy with a relative standard deviation (RSD) of 4.86%. The proposed composite sensor was effectively applied towards the determination of EP in human blood serum and pharmaceutical injection sample.

Electrochemical determination of sparfloxacin in pharmaceutical formulations and urine samples using a β-cyclodextrin modified carbon paste electrode

Abstract The electrochemical behavior of Sparfloxacin at β-cyclodextrin modified carbon paste electrode (CDMCPE) has been studied. Compared with bare carbon paste electrode (CPE), the β-cyclodextrin modified carbon paste electrode exhibited a marked enhancement of current response of Sparfloxacin. Cyclic voltammetric (CV) studies indicate that the process was irreversible and adsorption controlled. To obtain a good sensitivity, the instrumental and accumulation variables were studied using Differential Pulse Voltammetry (DPV). A linear calibration plot was obtained over the 0.043–60 μM range with a correlation coefficient of 0.999 in pH 3.0 Britton Robinson buffer with a detection limit of 0.04 μM by using DPV. The peaks from the techniques CV and DPV are attributed to the complex formation of quinone group of the drug with β-cyclodextrin. The repeatability and reproducibility of the methods were within 7.52, 7.68% RSD for peak currents and 0.52, 0.60% RSD for peak potentials using CDMCPE. Quantitative analysis was performed by the standard addition method for Sparfloxacin in both urine and available pharmaceutical formulations. A spectrophotometric method was used as a reference method to assess the accuracy. Results obtained through spectrophotometric method were comparable to those obtained by CDMCPE.