Electroanalysis at the micro-and nano-length scale

The small physical size of microelectrodes allows the dimension of the electrochemical cell to be dramatically reduced allowing direct measurements to be performed in nanoliter and even picoliter volumes. 

Systems, Lab-on-a-chip, microvials, Battmes Fuel Cells 

Another approach to confining the volume is to use vials that have picoliter volumes (7). These can be fabricated with lithographic techniques. Electrochanical experiments using a standard reduction-oxidation couple, ferrocene-carboxylic acid, have been performed in volumes as small as 1 pL. Peak-shaped voltanunetry and an increase in the current on the reverse wave of the cycUc voltammogram are observed in the voltammetric response when ultrasmall volumes (16 pL or less) are used. This deviation from bulk microelectrode behavior is observed only at slower scan rates in the smaller microvials. The voltammetric behavior in the small-volume experiments depends on the scan rate, vial size, and analyte concentration. A physical model based on restriction of analyte in these well-defined 

Irrespective of the sample volume, the amount of sample probed in an electrochemical experiment depends on the timescale. This sensitivity arises because, for solution phase reactants, diffusion is typically the dominant mode of mass transport. When the response is under semi-infinite linear diffusion control, the thickness of the diffusion layer, 3, is given by equation (6.1.5.1). Taking a typical diffusion coefficient of 1 X 10 cm sec in aqueous solution, equation (6.1.5.1) indicates that for a conventional electrochemical experiment employing an electrode of 3 mm diameter and an electrolysis time of 1 sec, a volume of approximately 10 pL will be electrolyzed. In contrast, for a 5-pm radius microelectrode and a 50-psec electrolysis time, the volume will be less than 30 fL  

Microelectrodes have been used in combination with classical analytical techniques, such as anodic stripping voltammetry (ASV) to determine the concentration of a wide range of analytes, especially metal ions (18, 19). However, here we focus on more contemporary approaches that modify the surface of the microelectrode to produce sensors. 

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