Microsoft Word - Lecture3M11.docx

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چکیده

These sensors employ redox reactions to quantify the amount of an analyte. The current flowing through the system or the potential difference between the electrodes as a result of the oxidation and reduction reactions involving the analyte are used for its quantification in the sample. The electrochemical sensors do not suffer from the drawbacks of optical sensors. They have more stable output, have high sensitivity, fast response and suffer from lesser interferences. Also, it is tedious to tag the analyte with any fluorescent label and hence electrochemical measurements are often used for sensing applications. The various electrochemical parametes that could be monitored are: • Conductometric measurements, which measures changes in the conductance of the system due to the presence of the analyte • Potentiometric measurements, which measures the electrical potential difference between a working and reference electrode. The reference electrode is one whose potential remains invariant during the entire duration of measurement. The working electrode undergoes significant change in its potential even for small changes in the analyte concentration. Potentiometric measurements are also carried out to monitor the accumulation of charge at zero current created by selective binding of the analyte at the electrode surface. The electrode may be selective for certain ions or gases and these include F , I , CN , Na + , K + , Ca 2+ , H + , NH4 + , CO2, NH3etc. • Amperometric measurements, which involves measuring the current generated by electrochemical oxidation or reduction of electroactive species at a constant applied potential. Fast measurements, sensitivity (ability to sense even 10 -9 M concentration) and ability to perform measurements on turbid/opaque solutions are its advantages over conventional optical sensors. However pH-sensing mechanisms require weakly buffered or non-buffered solutions and this is a drawback for this category of sensors.

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تاریخ انتشار 2013