“ELECTROANALYTICAL ASSESSMENT OF SOME BIOLOGICALLY IMPORTANT COMPOUNDS BY DEVELOPING BIOSENSORS”

Abstract

Background: Analytical Chemistry is an important branch of modern chemistry which deals with the separation and determination of the constituents present in the matter of interest. It involves the application of a range of techniques to assess the complete information about the analyte species present in a solution. The qualitative and quantitative assessments as well as structural assessments become very much reliable with the application of analytical techniques. A new branch of analytical chemistry is electroanalytical chemistry which can analyse a species depending upon its electrical properties with the help of an electrochemical cell. The electrical parameters like potential (E), current (I), charge (Q) and resistance (R) are related to the concentration (C) of the analyte. These types of electrochemical measurements for analytical purposes cover a wide range of applications in the field of biomedical analysis, environmental monitoring and industrial quality control. The electroanalysis can be done by a method called cyclic voltammetry which is considered as a sensitive, selective and versatile technique for the investigation of the redox process in the electrochemical system. In this system, the current is produced due to electron transfer between the solution and the electrode surface. A voltammogram gives information about adsorption or diffusioncontrolled processes in chemical reactions, the thermodynamics, and kinetics of heterogeneous electrochemical reactions. In our present study, we have focused only on the cyclic voltammetry technique for the determination of biologically active compounds by the use of different modified carbon paste electrodes. Objectives: To design electrochemical (bio) sensors by modifying bare carbon paste electrodes using different techniques so that a more sensitive, selective and simple electrochemical method can be developed to assess analytic species (drugs) in the solution. The effect of different modifier amount, pH, scan rate and concentration for the selected drugs are to be analyzed. Also the electrochemical behavior of the analytes (reversible/irreversible/quasi-reversible) and electrode processes (adsorption controlled/diffusion-controlled) are to be explored by using CV technique. The probable reaction mechanisms on the electrode surface are to be understood and to be illustrated. Method: All the investigations were done using an electrochemical workstation (model CH-Instrument-660c electrochemical analyzer USA) and connected to IBM PC and xv printer. The electrochemical cell, potentiostat and the recorder are the most important components of the workstation. Three-electrode cell system is as follows:  Reference Electrode- A saturated calomel electrode  Counter/Auxiliary Electrode- A platinum wire  Working Electrode- Various modified electrodes were prepared by using Niacinamide, Carbamazepine, Niacin and surfactant like CTAB. The electrochemical reactions were studied for different drugs by using BCPE and all the modified electrodes. The voltammograms were recorded at temperature 25±0.2 °C. Results: (i) Poly-Niacinamide/MCPE Sensor for Catechol (CC) The cyclic voltammetry (CV) behavior of Catechol was investigated with BCPE and poly-NA/MCPE. The effect of different scan rate, pH and concentration were studied. The modified electrode has shown higher sensitivity and better selectivity when compared to the BCPE, and a better lower detection limits of 1.49 μM. The study established that the electrochemical process is reversible, diffusion-controlled with involvement of equal number of protons and electrons. The probable electropolymerisation mechanism of niacinamide was proposed. (ii) CTAB-Immobilized/MCPE Sensor for Mesalazine(MSZ) The electro-oxidation behavior of MSZ was studied at CTAB/MCPE using cyclic voltammetry technique. The investigations included the study of the effect of pH variation, scan rate, and concentration of MSZ. The investigation revealed that the type of electrode reaction was quasi-reversible; adsorption controlled and involves equal number of protons and electrons transfer. Under optimal conditions, the lower limit of detection with CTAB immobilized MCPE was found to be 1.9×10-9 M. Thus, the present study was very impressive on account of used modifiers due to its affectability, selectivity, reproducibility and low LOD value. (iii) Carbamazepine (CZ)/MCPE Sensor for Paracetamol (PC) The electrochemical behaviour of paracetamol was investigated with modified carbamazepine film coated carbon paste electrode (CZ/MCPE) by CV technique. Under optimum conditions, the new modified electrode sensor showed good voltammetric responses of PC over varying concentration range and lower LOD was obtained at 0.24×10-6 M. Further parameters like scan rate and pH variation were optimized for the xvi analysis of PC. The overall study reveals that the PC electrochemical process is reversible; adsorption controlled and involves two proton-electron exchanges. The recovery test of paracetamol drug in tablet analysis was also done to conclude that the CZ/MCPE sensor can be effectively chosen for the selective resolve of PC in pharmaceutical samples. (iv) (Poly)-NC/CPE Sensor for Epinephrine (EP) with Uric Acid (UA) The oxidation of EP and UA were studied at (poly)-NC/CPE using a CV technique. The investigations included the study of the effect of pH variation, scan rate, and concentration of EP. The obtained results displayed the type of electrode reaction was irreversible, adsorption controlled and involves equal number of protons and electrons transfer. Under optimal conditions, the lower limit of detection of EP with (poly)- NC/CPE was found at 11.3×10-9 M. The applicability of the current methodology was successfully estimated by the quantification of EP in injection. Thus, the present study was very remarkable on account of used modifiers due to its affectability, selectivity and reproducibility. Conclusion: The present study has been carried out to give an explanation of the electrochemical behavior of four biologically active drugs such as; catechol, mesalazine, paracetamol, and epinephrine by preparing the modified electrodes. For each of the drugs we could establish the reaction mechanisms on the modified electrode surface and it has been observed that the electrode processes were either adsorption controlled or diffusion controlled and electrochemical behaviour of the analytes were reversible/irreversible/quasi-reversible. All the modified electrodes prepared were shown better selectivity and sensitivity as compared to BCPE. The lower detection limit for every drug was found to be enhanced when compared with the other modified electrodes reported earlier. The interference study was carried out and established a validated method for tablets and injections analysis