Tyrosinase (Tyr) has been used frequently for the detection of phenolic compounds. The development of a biosensor based on this enzyme-integrated carbon nanotube (CNT) epoxy composite electrode (CNTECE) is described in order to perform measurements of catechol. The enzyme is immobilized into a matrix prepared by dispersion of multi-wall CNT (MWCNT) inside the epoxy resin forming a CNT epoxy-biocomposite (CNTEC-Tyr). The use of CNT improves the electronic transference between the enzyme and the electrode surface. The modified electrode was characterized electrochemically by amperometric and voltammetric techniques. An applied potential of -200 mV vs. Ag/AgC1 applied to the biocomposite based electrode was found to be optimal for electrochemical reduction of the enzymatic reaction products (quinones). The biosensor modified with MWCNT is also compared with a tyrosinase biosensor based on a graphite epoxy-composite (GECE-Tyr) showing a sensitivity of 294 microA/mM cm(2), a detection limit of 0.01 mM for a signal-to-noise ratio of 3 in a concentration range of 0.0-0.15 mM catechol with a response time of 20 s and an RSD of 8% (n = 3). The electrodes were stable for more than 24 h. A 90% increase of the signal indicated that the response is better with the biocomposite based on carbon nanotubes rather than with the graphite.

International audienc

No abstract

Gamma-ray spectra with energies up to 1.3 MeV have been detected for the first time with 1-cm-thick Hg12 semiconductor detectors at room temperature. The spectra can be taken using a "long," 10 vsec, or a llshort,ll 0.5 vsec, charge collection time. The latter has produced better results with better peak efficiency, higher peak-to-valley ratio, and fewer low energy counts with little sacrifice in resolution. Spectra for energies between 100 keV and 1.3 MeV and descriptions of the techniques for their acquisition are presented. The thick detectors need a conditioning treatment, which is described, prior to showing spectral response.-1.

Gamma-ray s p e c t r a with energies up t o 1 . 3 MeV have been d e t e c t e d f o r t h e first time with l-cm-thick HgI2 semiconductor d e t e c t o r s a t room temperature.The s p e c t r a can be taken using a 10 u s , o r a llshort,l' 0.5 u s , charge c o l l e c t i o n time. The l a t t e r has produced b e t t e r r e s u l t s with b e t t e r peak e f f i c i e n c y , higher peak-to-valley r a t i o , and fewer low energy counts with l i t t l e s a c r i f i c e i n r e s o l u t i o n . Spectra f o r energies between 100 key and 1.3 MeV and d e s c r i p t i o n s o f t h e techniques f o r t h e i r a c q u i s i t i o n a r e presented. The t h i c k d e t e c t o r s need a conditioning treatment, which i s described, p r i o r t o showing s p e c t r a l response. DISCLAIMER ! -----T h k n p~n~a s p e p . R d~a n -n t o f w k~W a n -o f t h a u n l t a d S~G w a m m e n t .Nalrher the United Smsr Cbwnmont mr any wncy thereof, nor any ef Hlalr amployeas, mskesanv warraw, sxpraa or lmplled. or srrunar m y lapal 1IQillN or r e l l m , tor tha amlracv. the publisher and/or r e c i p i e n t acknowledges t h e U.S. Government's r i g h t t o r e t a i n a nonexclusive royalty-free l i c e n s e i n and t o any copyright covering t h i s paper. Reference t o a company o r product name does not imply approval o r recommendat i o n of t h e product by t h e U.S. Department of Energy t o t h e exclusion of o t h e r s t h a t may be s u i t a b l e . DISCLAIMER