Microfluidics Based Biochips

Other Unique Engineering Ideas
Microfluidics-based biochips are soon expected to revolutionize laboratory procedures involving molecular biology. The main advantage of microfluidics is utilizing scaling laws for new effects and better performance. These advantages are derived from the microscopic amount of fluid a microfluidic device can handle.

1. Description

2. Why

3. How

4. Future Trends

5. Related Links

Useful Links Microfluidics 

Description

Biochip is a generic term used to describe miniaturized devices based on a combination of microfabrication technology and life sciences. These devices are primarily based on microfluidics technology. The biochips employ miniaturization of biological separation and assay techniques to an extent that multiple and complex analyses can be accomplished on a "chip" small enough to fit the palm of the hand the so-called "lab on a chip" or micro total analysis systems (µTAS).A typical biochip system consists of several microfluidic components, such as pumps, dispensers, microvalves, interconnects, multiplexers, etc. There are several issues that needs to be addressed while designing various components of a system, such as:

  • Liquid filling - elimination of bubbles, channel geometry selection (hydrophobic vs. hydrophilic surfaces, dynamic contact angle and capillary effects), elimination of residue, etc
  • Liquid dispensing - control liquid droplet sizes, proper selection of actuation mechanism
  • Valving - passive vs. active valves, leakage minimization
  • Multiplexing - design of channel geometry, selection of critical pressure for liquid splitting
  • Mixing - selection of passive vs. active mixing modes, minimization of sample dispersion

Why

Very tiny quantities (nanoliters) of sample and reagents are transported through micron sized channels on the chip, where they undergo mixing, reaction etc. and are subjected to analysis by techniques such as mass spectrometry, fluorescence detection, immunoassay, or virtually any conventional laboratory analysis technique.At small scales (channel diameters of around 100 nanometers to several hundred micrometers) some interesting and unintuitive properties appear. The Reynolds number, which characterizes the presence of turbulent flow, is extremely low, thus the flow will remain laminar.Thus, two fluids joining will not mix readily via turbulence, so diffusion alone must cause the two fluids to mingle.

How

Microfluidics is the science of designing, manufacturing, and formulating devices and processes that deal with volumes of fluid on the order of nanoliters (symbolized nl and representing units of 10-9 liter) or picoliters (symbolized pl and representing units of 10-12 liter). The devices themselves have dimensions ranging from millimeters (mm) down to micrometers (µm), where 1 µm = 0.001 mm.

  • Microfluidics hardware requires construction and design that differs from macroscale hardware.
  • It is not generally possible to scale conventional devices down and then expect them to work in microfluidics applications.
  • When the dimensions of a device or system reach a certain size as the scale becomes smaller,
  • the particles of fluid, or particles suspended in the fluid, become comparable in size with the apparatus itself.
  • These dramatically alters system behavior

Capillary action changes the way in which fluids pass through microscale-diameter tubes, as compared with macroscale channels. In addition, there are unknown factors involved, especially concerning microscale heat transfer and mass transfer, the nature of which only further research can reveal.The behavior of fluids at the microscale can differ from 'macrofluidic' behavior in that factors such as surface tension, energy dissipation, and fluidic resistance start to dominate the system. Microfluidics studies how these behaviors change, and how they can be worked around, or exploited for new uses.

Liquid Filling

Void entrapments (presence of bubbles) is an often-confronted problem in the design of microarrays and microfluidic chips. Occurrence of these bubbles can be avoided through careful design of the chip, control of the filling process, and selection of material (hydrophobic vs. hydrophilic).

Liquid Dispensing

Controlled sample dispensing is the first-step in most microarray and several microfluidic chip applications. Precise metering of dispensed sample (droplet) is of necessary importance for quantitative measurements. Methods used for sample dispensing include piezoelectric actuators or pin-based spotting techniques.

Valving

Surface tension effects are dominant at small length scales prevalent in microfluidic devices. Hydrophobic surfaces act as "passive" (because of an absence of moving parts) valves and are being increasingly used for flow control in these systems.

Mixing

Fluid flow phenomena in microfluidic devices are generally in the laminar regime with very low Reynolds numbers (<10). As a result, the mixing rate is controlled by the rate of diffusion. Because of the limited area available in lab-on-a-chip devices, innovative methods need to be employed to achieve the desired extent of fluid mixing.These include winding serpentine channels and complex multiplexing structures to provide increased residence time as well as added mixing due to bend-induced vortices. These systems, as well as active mixing based devices such as the bubble pump (shown below) can be easily modeled and optimized using our expertise.

Future Trends

Lab-On-A-CD devices use centrifugal forces generated by rotation of the CD to provide the driving force for fluid transport. CFDRC engineers have developed the expertise in designing lab-on-a-CD systems to model and determine the optimal rotation speeds for precisely controlled fluidic motion on the CD.

Keywords

Fluid dynamics, Nanotechnology, Micro-fluidics, Biotechnology,Lab-On-A-CD, bioassays.

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