RESUMEN
By electron beam evaporation, noble metals (Au, Co, Pt, and Ag) with 2 and 4 nm nominal thicknesses were coated onto multi-walled carbon nanotube layers. The metals were in the form of nanoparticles mounted onto the side walls of carbon nanotubes (CNTs) to create a metal/CNT junction. The CNTs were directly grown on patterned Pt-electrode alumina substrates through chemical vapor deposition to produce a resistivity-based ammonia gas sensor. The metallic surface-modified CNT-based sensors were found sensitive to NH3 gas at room temperature. Compared with pristine CNT sensor, the response of Au/CNTs sensor increased slightly, whereas the responses of the Pt/CNTs, Co/CNTs, and Ag/CNTs increased by two, three, and more than four times, respectively.
RESUMEN
The determination of diuron, atrazine, desisopropylatrazine (DIA) and desethylatrazine (DEA) were investigated using conductometric tyrosinase biosensor. Tyrosinase was immobilised on the biosensor sensitive part by allowing it to mix with bovine serum albumin (BSA) and then cross-linking in saturated glutaraldehyde (GA) vapour for 30min. The determination of pollutants in a solution was performed by comparison of the output signal (i.e percentage of the enzymatic activity) of the biosensor before and after contact with pollutants. The measurement of the enzymatic activity was performed using 4-chlorophenol, phenol and catechol substrates and response times ranging from 1 to 5min were observed. A 4-chlorophenol substrate was used to detect pesticides. A 30min contact time of the biosensor in the pollutant solution was used. Under the experimental conditions employed, detection limits for diuron and atrazine were about 1ppb and dynamic range of 2.3-2330 and 2.15-2150ppb were obtained for diuron and atrazine, respectively. A relative standard deviation (n=3) of the output signal was estimated to be 5% and a slight drift of 1.5muSh(-1) was observed. The 90% of the enzyme activity was still maintained after 23 days of storage in a buffer solution at 4 degrees C.