The surface of electrodes can be modified in the following ways:
(1) Adsorption (Chemisorption)
A method that uses the same kind of valence forces involved in formation of chemical compounds, where the film is strongly adsorbed, or chemisorbed, onto the surface of the electrode, yielding monolayer coverage. This approach involves substrate-coupled self-assembled monolayers (SAMs), where molecules are spontaneously chemisorbed to the surface of the electrode, resulting in a microscopic superlattice structure of layers formed on it
(2) Covalent bonding
A method that uses chemical agents to create a covalent bond between one or more monomolecular layers of the chemical modifier and the electrode surface. The common agents to use in this method include organosilanes and cyanuric chloride.
(3) Polymer film coating
A method that uses one of the following to hold electron-conductive and nonconductive polymer films on the electrode surface:
Chemisorption and low solubility in the contacting solution
Physical anchoring in a porous electrode
This method includes removing chemical species (substrate) from self-assembled monolayers (SAMs) to allow adsorbing molecules on the electrode surface independently of the original substrate structure. The polymer films can be organic, organometallic or inorganic, and it can either contain the chemical modifier or have the chemical added to the polymer in a latter process.
(4) Composite
A method that has the chemical modifier mixed with an electrode matrix material. An example for this method is having an electron-transfer mediator (the chemical modifier) mixed with carbon particls in a carbon paste electrode (the electrode matrix).
Carbon paste, glassy carbon paste, glassy carbon etc. electrodes when modified are termed as chemically modified electrodes. Chemically modified electrodes have been employed for the analysis of organic and inorganic species.
