Sridhar G. Iyengar

Data from overlapping signals at an amperometric electrode using admittance vectors

Abstract A simple admittance vector presentation, common in telecommunication signal processing, is examined to separate mathematically two overlapping analytical amperometric signals. The method is based on a theoretical derivation of a constant potential amperometric electrochemical system experiencing an ac perturbation. For a given reaction at different concentrations of the electrochemically active species, the current measured during an ac perturbation at a particular frequency on a constant bias potential E dc , has constant phase angle ( φ ) of the admittance and only its magnitude ( Y ) changes with concentration. The complex admittance vector space is spanned by the basis vectors of the individual components of a mixture. The admittance measurement is thus given in terms of the contribution from these components. The concentration calibration may be computed by taking the distance to each admittance point. In the context of the conventional constant potential amperometric methods for detection of H 2 O 2 and ascorbic acid via their oxidation currents, where there is an inherent problem of interference and overlap of each electroactive species, their simultaneous estimation is taken as a model case to illustrate the methodology to extract the basis vectors for each species and obtain the concentration calibration vectors for the mixture. Evaluation of the use of the technique in complex mixtures is introduced.

Strategies for fabricating a biorecognition interface for a label free electrochemical immunosensor

An electrochemical interface for a label-free electrochemical immuno-biosensor was prepared by modifying electrodes with a mixed layer comprising a molecular wire (MW) and oligo(ethylene glycol) (OEG) molecules derived from in situ-generated aryl diazonium salts. The in situ-generated aryl diazonium salts were prepared in two different ways using either organic solvents or aqueous solutions. For organic phase surface modification, the corresponding amines of MW and OEG were dissolved in acetonitrile while for aqueous phase surface modification the corresponding amines of MW and OEG were dissolved in 0.5 M HCl acidic solution. Reduction of the aryl diazonium cations generates the corresponding aryl radicals which react with the carbon substrate, resulting in a covalent bond. Our results show that the interface generated in acidic aqueous conditions not only produced denser layers on the electrode surfaces, as determined by the passivation of the electrode towards the redox active species such as Fe(CN)63−/4− and Ru(NH3)62+/3+, but also has good responses for the detection of small molecules such as biotin.