Biochips – fundamentals and applications - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 303

11.4.3 Electrochemical detection
11.4.3.1 Amperometry
11.4.3.2 Potentiometry
11.4.3.3 Impedimetry
11.5 Lab-on-chips
11.5.1 Theory of microfl uidics
11.5.2 Components in lab-on-chip systems
11.5.3 Fabrication of BioMEMS
11.5.4 Applications
11.5.4.1 Cell sorting system
11.5.4.2 Combinatorial synthesis for drug screening and materials discovery
11.5.4.3 Chemical and biological analysis
11.6 References
11.1 INTRODUCTION
The biochip, a bio-microarray device, has been extensively studied and developed to
enable large-scale genomic, proteomic and functional genomic analyses. A biochip
comprises mainly three types: DNA microarray, protein microarray, and microfl uidic
chip. The promise of microarrays, a miniaturized device, lies in the spatially addressable
grid of specifi c binding sites, implying that hundreds or thousands of unique binding
events can be analyzed simultaneously. The microfl uidic chip is used to process ana-
lyte sample such as transportation, separation, and purifi cation. With the integration of
microarray and microfl uidic systems, a micro total analysis system, sometimes called a
lab-on-chip system, is produced. Advances of nanotechnology continuously reduce the
size of the biochip. This in turn reduces the manufacturing cost and increases the high
throughput capability. Due to the benefi ts of low expense, high throughput and mini-
aturization, this technology has great potential to be a crucial and powerful tool for clin-
ical research, diagnostics, drug development, toxicology studies, and patient selection
for clinical trials.
It was the work of Gilbert and Sanger that turned the biochip concepts into a reality
through their DNA sequencing approach which is still widely used today. As biochips
evolve throughout the years, their size decreases. This decrease is largely due to the
combination of DNA sequencing chemistry with electric current and micropore aga-
rose gels. Due to the small size of the hybridization array and the small amount of
target present, it is a challenge to acquire the signals from a DNA array. The signals
must fi rst be amplifi ed before they can be detected by the imaging devices. Polymerase
Chain Reaction, invented by Kary Mullis in 1983, provides a means to amplify signals,
thus solving the problems of small size hybridization array and small amount of target
present. Three years later, Leroy Hood brought the biochip technology to another new
height by using fl uorescence-based DNA sequencing to facilitate the automation of
reading DNA sequence. In the early 1990s, companies like Affymetrix, Motorola, and
Hyseq enabled mass production of DNA microarray chips by using photolithographic