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Basic Components of an LoC
The component devices that make up an LoC are (Figure 3):
- Electrophoresis: Separation columns
- Microfluidics: Channels, valves-pumps & mixers
- Chem-bio detectors and sensors
- Microfluidic chips
Figure 3: LoC elements [1].
1. Electrophoresis
This is a method of separating large molecules (i.e., DNA fragments, blood, or other proteins) from a mixture of similar molecules by passing an electric field toward an electric pole (anode or cathode) in a liquid on various media (e.g., paper, glass, gel, liquid). It is used to separate and purify biomolecules. Each molecule travels through the medium at a different rate—depending on its electrical charge and size—and toward either the anode or the cathode at a characteristic speed (Figure 4).
2. Microfluidics
This custom application of fluidic technology is applied with conventional micromachining techniques, such as wet etching; dry etching; deep, reactive ion etching; sputtering; anodic bonding; and fusion bonding to make flow channels, flow sensors, chemical detectors, separation capillaries, mixers, filters, pumps and valves for various LoCs (Figure 4).
Flow in microchannels is laminar, which allows selective treatment of cells in microchannels, or arrays, as well as biochemical reactions. The integration of microelectronics, micromechanical, and microoptics onto the same substrates allows automated device control, which reduces human error and operation costs.
3. Chem-Bio Detectors and Sensors
Detectors, sensors, and electrodes can be ChemFET and BioFET C-MOS devices with special membranes or diffusions to make them sensitive to chemical or biological molecules. The sensors and electrodes are electrical elements that are sensitive to various chemical or biological molecules, plated with gold, silver, platinum, palladium, etc., and their salts (Figure 5).
4. Microfluidic Chips
A microfluidic chip is a set of microchannels etched or molded into a material (glass, silicon, or polymer, such as PDMS). Microchannels form the microfluidic chip connected in order to achieve the desired features (mix, pump, sort, control bio-chemical environment, etc.). Networks of microchannels are connected to the outside by inputs (inlets) and outputs (outlets) pierced through the chip (interface between the macro and micro world).
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