C. Martelet

Electrochemical impedance probing of DNA hybridisation on oligonucleotide-functionalised polypyrrole

We report a new approach for detecting DNA hybridisation using non faradaic electrochemical impedance spectroscopy. The technique was applied to a system of DNA probes bearing amine groups that are immobilized by covalent grafting on a supporting polypyrrole matrix functionalised with activated ester groups. The kinetics of the attachment of the ss-DNA probe was monitored using the temporal evolution of the open circuit potential (OCP). This measurement allows the determination of the time necessary for the chemical reaction of ss-DNA probe into the polypyrrole backbone. The hybridisation reactions with the DNA complementary target and non complementary target were investigated by non faradaic electrochemical impedance spectroscopy. Results show a significant modification in the Nyquist plot upon addition of the complementary target whereas, in presence of the non complementary target, the Nyquist plot is not modified. The spectra, in the form of Nyquist plot, were analysed with the Randles circuit. The transfer charge resistance R(2) shows a linear variation versus the complementary target concentration. Sensitivity and detection limit (0.2nM) were determined and detection limit was lower of one order of magnitude than that obtained with the same system and measuring variation of the oxidation current at constant potential.

Development of a urea biosensor based on a polymeric membrane including zeolite

A urea biosensor has been prepared by covalent biding of urease directly to the surface of an ammonium-sensitive field effect transistor (FET).The NH4 + -sensitive membrane is based on a zeolite-incorporated polymeric membrane biosensor (clinoptilolite). The sensitivity of ammoniumxa0 detection is sub-nernstian (32mV/pNH4 +) but the ISFET presents a high selectivity, which is interesting for measurements in biological media. The grafting of urease to the NH4 +-sensitive membrane was permorfed by cross-linking with glutaraldehyde .The sensitivity of the urea ENFET is 15V/purea and this remains stable over 15 days with a detection limit of 3x10-5 M. Finally, in order to test feasibility of the urea biosensor for environmental applications, the remaining activity of the urease was determined after exposure to enzyme inhibiting heavy metals ions such as Hg(II).Using these urea biosensors, a detection limit of less than 5 x 10-8 M was obtained for Hg(II).

Enhanced ionodetection by using polyethyleneimine as an insulator material

Abstract Thin polyethyleneimine (PEI) films were deposited on p-silicon-based transducers. The polymer acts at the same time as the insulator and the sensitive membrane of an electrolyte/insulator/semiconductor (EIS) structure. Electrochemical measurements such as potentiometric or capacitance and impedance spectroscopy analyses were performed to investigate the sensitivity of this device towards ions. The PEI-modified silicon was used as copper and pH sensor. Sensitivities recorded in both cases were close to a Nernstian response: 45 mV/pH and 26 mV/pCu. Impedance spectroscopy allowed to propose equivalent circuits for the EPS structure, and has lead to a better understanding of the mass-transfer mechanisms, which are involved during the interactions between the electroactive species and the polymeric insulator.