General criteria for designing of an electrochemical sensing device:
• Potentiometric sensors need extra electrode materials which must be free from
interferences while Amperometric and voltammetric techniques, species to be
determined must be electroactive in the potential range of sensors. Sometimes
inert, supporting electrolytes are also needed to be added to consolidate the
current perturbation.
• Concentration of analytical species must be determined carefully.
• The results obtained should be reliable and easily reproducible.
• The rate of electrode degradation with time and fouling of electrode surfaces
should be kept in mind while deciding the electrode materials.
• Sensors must respond fast and should be calibrated easily.
• The extremely low detection limit for the sensors gives additional advantages to
these electrochemical sensors.
4 New Developments in Electrochemical Sensing
Techniques
4.1 Screen Printed Electrochemical Sensors
Screen printing techniques are old methods applied for textiles and art. However in
recent researches it has been applied for the modification of electrode surfaces to
make them stable, reproducible and easily disposable in mass production. Pastes most
commonly used in screen printed electrodes are of silver or carbon ink. Silver ink is
mainly used for conductivity purpose while carbon ink is used for working electrodes. Carbon ink is simple, chemically inert and easily modified. Some SPEs
employ Gold paste but it is less cost effective as compared to carbon electrodes. Au
forms self-assembled layers (SALs) on the surface of electrodes and therefore have
much application in sensing devices [60]. Application of SPEs in electrochemical
sensing ranges from pH sensing, organic compounds, heavy metals, radioactive
wastes as well as biological samples. They can be used for replacement of Glass
electrodes in pH sensing devices [61]. Three-electrode system was applied for
sensing pH and was much more sensitive than two-electrode systems [62]. Nickel
oxide bulk modified SPEs are applied for detection of hydroxide ion change [63].
Disposable CdS modified SPEs electrode are used to measure dissolved oxygen
concentration by electro-chemiluminescence method [64]. MnO 2 based SPEs sensing
devices are used to determine the nitrate ions in the sample [65]. In-situ determination
of phenolic compounds and their derivatives was done using SPEs because their
simple design, fast response, high sensitivity and low cost. However electro-oxidation
of phenols leads to surface passivation and hence hinder the electron transfer
mechanisms. Graphene or carbon based nanomaterials have been proved to be outstanding material for screen-printing of electrodes due to their high tensile strength,
Materials in Electrochemical Detection of Water Pollutants
171
• Potentiometric sensors need extra electrode materials which must be free from
interferences while Amperometric and voltammetric techniques, species to be
determined must be electroactive in the potential range of sensors. Sometimes
inert, supporting electrolytes are also needed to be added to consolidate the
current perturbation.
• Concentration of analytical species must be determined carefully.
• The results obtained should be reliable and easily reproducible.
• The rate of electrode degradation with time and fouling of electrode surfaces
should be kept in mind while deciding the electrode materials.
• Sensors must respond fast and should be calibrated easily.
• The extremely low detection limit for the sensors gives additional advantages to
these electrochemical sensors.
4 New Developments in Electrochemical Sensing
Techniques
4.1 Screen Printed Electrochemical Sensors
Screen printing techniques are old methods applied for textiles and art. However in
recent researches it has been applied for the modification of electrode surfaces to
make them stable, reproducible and easily disposable in mass production. Pastes most
commonly used in screen printed electrodes are of silver or carbon ink. Silver ink is
mainly used for conductivity purpose while carbon ink is used for working electrodes. Carbon ink is simple, chemically inert and easily modified. Some SPEs
employ Gold paste but it is less cost effective as compared to carbon electrodes. Au
forms self-assembled layers (SALs) on the surface of electrodes and therefore have
much application in sensing devices [60]. Application of SPEs in electrochemical
sensing ranges from pH sensing, organic compounds, heavy metals, radioactive
wastes as well as biological samples. They can be used for replacement of Glass
electrodes in pH sensing devices [61]. Three-electrode system was applied for
sensing pH and was much more sensitive than two-electrode systems [62]. Nickel
oxide bulk modified SPEs are applied for detection of hydroxide ion change [63].
Disposable CdS modified SPEs electrode are used to measure dissolved oxygen
concentration by electro-chemiluminescence method [64]. MnO 2 based SPEs sensing
devices are used to determine the nitrate ions in the sample [65]. In-situ determination
of phenolic compounds and their derivatives was done using SPEs because their
simple design, fast response, high sensitivity and low cost. However electro-oxidation
of phenols leads to surface passivation and hence hinder the electron transfer
mechanisms. Graphene or carbon based nanomaterials have been proved to be outstanding material for screen-printing of electrodes due to their high tensile strength,
Materials in Electrochemical Detection of Water Pollutants
171