Surface waters screen-printed electrodes

In this section, we discuss about the screen printed electrode (SPE) based AChE sensors for the selective determination of OP and CA pesticides. In the past decades, several attempts were made by the researchers to develop SPE based pesticide sensors, where the enzyme AChE was immobilized either directly onto the electrode or above other matrices incorporated SPE surfaces. Both approaches resulted in the good, rapid detection of OP and CA pesticides. Earlier, Hart et al. employed AChE/SPE to detect OP and CA pesticides [21], They measured the enzyme activity from the rate of hydrolysis of acetylthiocholine iodide. Three polymers such as hydroxyethyl cellulose, dimethylaminoethyl methacrylate, and polyethyleneimine were used as enzyme immobilization matrices. Initially, electrodes were exposed to drops of water or pesticide solution, dried and their activity was screened after 24 h. They found that, when the enzyme matrix was hydroxyethyl cellulose, electrode activity inhibited both by water as well as by pesticides. While with co-polymer matrix, a significant response towards pesticides alone was observed. Further, the long-term storage stability of electrodes was highest when the enzyme matrix consisted of the co-polymer. The electrodes retained their activity for nearly one year. In contrast, the electrodes made of hydroxyethyl cellulose or polyethyleneimine possess less stability. 

Electrochemical immunosensors have been widely used for environmental analysis in amperometric, potentiometric, and conductimetric configurations. Amperometric immunosensors measure the current generated by oxidation or reduction of redox substances at the electrode surface, which is held at an appropriate electrical potential. Wilmer et al. measured concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) in water by using an amperometric immunosensor with a limit of detection of 0.1 Jtg L-1 (Wilmer et al., 1997). Some examples of new developments are the disposable screen-printed electrodes for the detection of polycyclic aromatic hydrocarbons (PAHs)... 

The aim of this work is to demonstrate how the screen printed electrodes (SPEs) can be used for on site heavy metals monitoring in surface waters in the frame of the WFD. The sensors used consist of mercury-coated screen-printed electrodes coupled with square wave anodic stripping voltammetry (SWASV) (Palchetti et al., 1999). Three metals Cu, Cd, and Pb which are classically analysed in water matrices have been considered. Moreover, Cd and Pb belong to the priority substances list of the WFD. Performance criteria of the device are first established to evaluate the level of confidence of the method. The potential use of the device and its main advantages are then highlighted through two illustrative field applications. 

Electrode surface activation can be improved simply by electrochemical pretreatment. Determination of nitroaromatic compounds in water and soil spiked samples have been reported at electrochemically activated carbon-fiber microelectrodes. No interference was found from compounds such as hydrazine, phenolic compounds, carbamates, triazines or surfactants. The detection limit obtained can be approximately 0.03 iigml-1 for all the nitroaromatic compounds (Agui et al. 2005). Chen and coworkers reported an effective field-deployable tool for detecting nitroaromatic compounds with an electrochemically pre-anodized screen-printed carbon electrode (SPE) (Chen et al. 2006). 

Biosensors based on enzymes have high sensitivity and selectivity. A variety of microbial biosensors have also been developed. However, it still remains a great challenge to develop a rapid, inexpensive but sensitive method for real samples. Compared to enzymatic biosensors, development of a highly satisfactory microbial biosensor is still hampered because they suffer from long response time, low sensitivity, and poor selectivity. The trends for the development of biosensors lie in miniaturization of the devices, nanotechnology, and biotechnology. Disposable screen-printed sensors have been developed for industrial wastes or natural water. Metal nanoparticles can enhance the electron transfer between redox center in proteins and electrode surface and show promise for detection... 

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