Christine Pernelle

Molecularly imprinted conducting polymer based electrochemical sensor for detection of atrazine.

An original electrochemical sensor based on molecularly imprinted conducting polymer (MICP) is developed, which enables the recognition of a small pesticide target molecule, atrazine. The conjugated MICP, poly(3,4-ethylenedioxythiophene-co-thiophene-acetic acid), has been electrochemically synthesized onto a platinum electrode following two steps: (i) polymerization of comonomers in the presence of atrazine, already associated to the acetic acid substituent through hydrogen bonding, and (ii) removal of atrazine from the resulting polymer, which leaves the acetic acid substituents open for association with atrazine. The obtained sensing MICP is highly specific towards newly added atrazine and the recognition can be quantitatively analyzed by the variation of the cyclic voltammogram of MICP. The developed sensor shows remarkable properties: selectivity towards triazinic family, large range of detection (10(-9) mol L(-1) to 1.5 x 10(-2) mol L(-1) in atrazine) and low detection threshold (10(-7) mol L(-1)).

7α- and 7β-hydroxy-epiandrosterone as substrates and inhibitors for the human 11β-hydroxysteroid dehydrogenase type 1

Abstract The human 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) catalyzes both the NADP(H)-dependent oxido-reduction of cortisol and cortisone and the inter-conversion of 7α- and 7β-hydroxy-dehydroepiandrosterone (DHEA) through a 7-oxo-DHEA intermediate. As shown with human liver and intestine fractions, 7α-hydroxy-epiandrosterone (7α-hydroxy-EpiA) and 7β-hydroxy-EpiA were readily inter-converted with no evidence for a 7-oxo-EpiA intermediate. Whether this inter-conversion resulted from action of the 11β-HSD1 or from an unknown epimerase is unresolved. Furthermore, whether these steroids could inhibit the cortisol–cortisone oxido-reduction remains a question. The recombinant human 11β-HSD1 was used to test these questions. NADP + supplementation only provided the production of 7β-hydroxy-EpiA out of 7α-hydroxy-EpiA with a V max / K M ratio at 0.1. With NADPH supplementation, both 7α-hydroxy-EpiA and 7β-hydroxy-EpiA were formed in low amounts from 7β-hydroxy-EpiA and 7α-hydroxy-EpiA, respectively. These inter-conversions occurred without a trace of the putative 7-oxo-EpiA intermediate. In contrast, the 7-oxo-EpiA substrate was efficiently reduced into 7α-hydroxy-EpiA and 7β-hydroxy-EpiA, with V max / K M ratios of 23.6 and 5.8, respectively. Competitive and mixed type inhibitions of the 11β-HSD1-mediated cortisol oxidation were exerted by 7α-hydroxy-EpiA and 7β-hydroxy-EpiA, respectively. The 11β-HSD1-mediated cortisone reduction was inhibited in a competitive manner by 7-oxo-EpiA. These findings suggest that the active site of the human 11β-HSD1 may carry out directly the epimeric transformation of 7-hydroxylated EpiA substrates. The low amounts of these steroids in human do not support a physiological importance for modulation of the glucocorticoid status in tissues.

Biological investigation using a shear horizontal surface acoustic wave sensor: Small “Click generated” DNA hybridization detection

We have used a 104 MHz lithium tantalate (LiTaO(3)) surface acoustic wave (SAW) sensor to investigate DNA probes grafting and their further hybridization with natural and click generated (Cg-DNA) oligonucleotides. Natural DNA targets of different strand lengths, tosyl-di(tri, tetra) thymidine and azido-di(tri, tetra) thymidine oligonucleotides were tested. In our case, and besides the follow-up of a 34mer DNA hybridization, we detected complementarity between natural DNA probes and azido-tetra-thymidine for the first time, whereas previous hybridization studies reported a minimal of 10-mer oligonucleotides recognition length. We also demonstrated that contrarily to natural DNA, the synthesized oligonucleotides present stable bonds with complementary DNA strands. Frequency responses of both grafting and hybridization have shown the same shape: an exponential decay with different time constants, (187±1)s and (68±19) s for grafting and hybridization respectively. We have also shown that recognition between DNA strands and tetranucleotide analogues is comparable to natural 34mer DNA bases and presents the same time constant within uncertainties.

Surface Acoustic Love Waves Sensor for Chemical and Electrochemical Detection

The present work is an experimental study of shear horizontal surface acoustic wave (SH-SAW) miniaturized sensors which offer a high potential for electrochemical applications in liquid environments and in real-time. Our devices consist of a 42° rotYX lithium tantalate (LiTaO3 ) substrate coated with an SU8 photoresist polymer in order to produce acoustic waveguides supporting a Love–wave. The sensors architecture and fabrication techniques are presented. Standard techniques employing continuous wave system and pulse mode measurements have shown the propagation of both surface skimming bulk waves (SSBW) and leaky SH-SAW (LSAW) on 42°rot YXLiTaO3 . A numerical calculation using a simple balanced summation waves model is presented. Taking into account waves reflections and our measured velocity values, the simulation is in accordance with measurement. A copper’s electrodeposition experiment was performed to estimate the sensitivity of SAW devices. The measured sensitivity of 0.38 cm2 .g−1 is discussed in the framework of previously published works concerning Love wave devices.Copyright