Chemistry Reference
In-Depth Information
Figure 14.6
Scheme of the disposable heavy metal microchip. (a) The entire chip including the sensor array
and the microfluidic channels; (b) the magnified picture of the three-electrode sensor, and (c) the customized
detection chips along with the chip. Reproduced from [99] with permission from Elsevier, © 2008.
device is depicted in Figure 14.6. Low values of detection limits of 8 ppb for Pb(II) using 60 s deposition
time, and 9.3 ppb for Cd (II) for 90 s deposition time were achieved. The sensor chip was applied to the in
situ monitoring of Cd (II) concentration in environmental samples of soil pore and ground water, and to the
online direct measurement of Cd (II) concentration in biological and clinical samples, such as cell culture
media in its native environment [99].
Microfabrication techniques nowadays allow the design of unique structures that can be tailor-made for
specific application [98]. Furthermore, multiple channel networks make possible the introduction and mixing
of reagents with zero dead volume connections. Also, theoretically, the small dimensions of these systems
allow enhancements in the separation performance with respect to conventional systems. In particular, the
development of micro-fabricated capillary electrophoresis (CE) chips and their use for rapid biochemical
analysis have demonstrated that this separation technique is also enhanced through miniaturization. Moreover,
electrochemical detection is ideally suited for miniaturization to the microchip format. Photolithographic
techniques used to construct the microchips can also be used to fabricate reproducible and inexpensive
microelectrodes for these applications. A major challenge for electrochemical detection on microchips is the
ability to isolate the detection potential from the separation field. Furthermore, microfabrication technology
offers the possibility for creating multiple electrode detectors and arrays on a very small scale which can be
used for monitoring various analytes simultaneously or for selective detection of analytes via chemically
reversible redox reactions [98]. An illustrative example of a capillary electrophoresis micro-analytical chip
with integrated electrodes for sample injection, separation and electrochemical detection is the one designed
