Rajiv Prakash

A New Solid‐State pH Sensor and Its Application in the Construction of all Solid‐State Urea Biosensor

A new solid-state pH sensor is developed using neutral poly(3-cyclohexyl thiophene) assembled over a Pt disk electrode. The new sensor is developed following two different approaches; 1) the neutral poly(3-cyclohexyl thiophene) dissolved in chloroform and subsequent coating on to a Pt disk electrode; 2) the neutral polymer is incorporated into plasticized poly(vinyl chloride) matrix membrane. In both cases the polymer modified electrode is sensitive to pH and a reversible super Nernstian behavior is observed. The typical response of the pH sensor and its reversibility are reported. The polymer coated electrode is subsequently used to construct an all solid-state urea sensor. The construction of this new urea sensor involves the following two major steps; a) 20 µL of urease solution (40 mg /mL) is allowed to assemble overnight at 4u2005°C over neutral poly (3-cyclohexyl thiophene) modified electrode; b) an organically modified sol-gel layer is allowed to form over the urease adsorbed polymer modified electrode. The new solid-state urea sensor provides excellent reproducibility of the measurements and is stable for 3 months when stored at 4u2005°C under dry condition. The typical response of the solid-state urea sensor and the calibration plot of urea analysis are reported.

Estimation of Copper in Natural Water and Blood Using Anodic Stripping Differential Pulse Voltammetry over a Rotating Side Disk Electrode

Rotating disk electrode voltammetry (RDEV) in conjunction with anodic stripping differential pulse voltammetry (ASDPV) with a special type of gold side disk electrode has been evaluated for the direct estimation of copper in natural water (i.e. river water and underground water) as well as in whole blood without any pretreatment. Copper is quantified with high reproducibility and reliability even below 5u2005ppb without any interference of the common ions or organic materials dissolved in the samples, i.e., natural water and blood. The voltammetric measurements were carried out using a conventional three electrodes cell (i.e., gold as working, platinum as auxiliary and Ag/AgCl as reference electrodes) and the acidified sample. The major problem due to hydrogen evolution at cathode during the deposition of copper ions specially in acidified blood sample is overcome with the help of special design of rotating side disk gold electrode. A new type of rotating side disk electrode was designed to avoid the problem of gas bubbles interference in the stripping voltammetry. The shape, position and the rotation speed of the side disk electrode were optimized as per the requirement in the mild acidic condition. A simultaneous estimation of the zinc, lead and copper is also performed in aqueous sample with KCl as supporting electrolyte. The special design of working electrode and the modified voltammetric conditions are enhanced the sensitivity and reproducibility of the copper estimation at low ppb level with negligible interference.

Electrochemical and spectroscopic studies of metal cyclam complexes with thiocyanate. Evidence for mixed ligand complex formation

Complexes of NiII, CoII and CuII containing the macrocyclic ligand, 1,4,8,11-tetraazacyclotetradecane (cyclam), and their ability to form mixed ligand complexes with thiocyanate have been studied. These complexes in a 1:2 mole ratio, exhibit new absorption peaks at 450, 538 and 512 nm respectively. Addition of thiocyanate to the nickel–cyclam complex (1:2:5 mole ratio) led to the formation of a purple complex, exhibiting three distinct new absorption peaks at 330, 455 and 662 nm. A purple complex (1:2:10 mole ratio) separated, having absorption peaks at 352, 503 and 693 nm in CHCl3. The CoII–cyclam complex with thiocyanate in the same mole ratio exhibits two absorption peaks at 437 and 519 nm without appearance of any precipitate. The CuII–cyclam complex with thiocyanate did not form a mixed ligand complex. Electrochemical studies also confirmed the complex formation of NiII–cyclam with the thiocyanate with the appearance of two new oxidation peaks close to 1.25 and 1.60 V versus Ag/AgCl in H2O and CHCl3. The CoII–cyclam complex with thiocyanate exhibited an oxidation peak at 1.2 V versus Ag/AgCl, while no peak was observed for the CuII–cyclam complex with thiocyanate. Based on spectroscopic and electrochemical studies the geometry of the complex has been evaluated.