What have we done?

We search on various types of process that is actually happening in the process of microfluidics.

The topics we searched on are:
Laser-induced fluorescence (LIF)
Laser Doppler Velocimetry (LDV)
Photolithography
Photoresist
Electrophoresis (capillary electrophoresis)
Electro-osmosis
Particle Image Velocimetry (PIV)
Lab-on-a-chip


What have we learnt?

We have learnt about the various processes by sharing each of our work to get a head start for our project.

Laser-induced fluorescence (LIF)
Spectroscopic method used for studying structure of molecules, detection of selective species and flow visualization and measurements.
The species that is to be examined is excited with help of a laser. The wavelength is often selected to be the one at which the species has its largest cross section.
Excited species will after some time, usually in the order of few nanoseconds to microseconds, de-excite and emit light at a wavelength larger than the excitation wavelength.
This light, fluorescence, is measured.

Laser Doppler Velocimetry (LDV)
Also known as Laser Doppler Anemometry (LDA)
Technique for measuring the direction and speed of fluids like air and water
Used in clinical research as a mechanism to partially quantify blood flow in human tissues such as skin.
Within the clinical environment, LDV is referred to as Laser Doppler flowmetry (LDF.)
Gained popularity because it is simple to use, painless and non-invasive.
LDV crosses two beams of collimated, monochromatic, and coherent laser light in the flow of the fluid being measured. The two beams are usually obtained by splitting a single beam, thus ensuring coherency between the two.
The two beams are made to intersect at their waists (the focal point of a laser beam), where they interfere and generate a set of straight fringes.
The sensor is then aligned to the flow such that the fringes are perpendicular to the flow direction. As particles pass through the fringes, they reflect light (only from the regions of constructive interference) into a photodetector (typically an avalanche photodiode),
Since the fringe spacing d is known (from calibration), the velocity can be calculated to be u = f x d
where f is the frequency of the signal received at the detector

Photolithography
Also known as optical lithography
Is a process used in microfabrication to selectively remove parts of a thin film (or the bulk of a substrate).
Uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical on the substrate.
A series of chemical treatments then engraves the exposure pattern into the material underneath the photoresist. In a complex integrated circuit (for example, modern CMOS), a wafer will go through the photolithographic cycle up to 50 times.
Shares some fundamental principles with photography, in that the pattern in the etching resist is created by exposing it to light, either using a projected image or an optical mask.
This step is like an ultra high precision version of the method used to make printed circuit boards. Subsequent stages in the process have more in common with etching than to lithographic printing.
It is used because it affords exact control over the shape and size of the objects it creates, and because it can create patterns over an entire surface simultaneously.
Its main disadvantages are that it requires a flat substrate to start with, it is not very effective at creating shapes that are not flat, and it can require extremely clean operating conditions.

Photoresist
A light-sensitive material used in several industrial processes, such as photolithography and photoengraving to form a patterned coating on a surface.
Photoresists are classified into two groups, positive resists and negative resists.
Most commonly used at wavelengths in the ultraviolet spectrum or shorter (<400 efficiency="output/input" eqe="(electrons/sec)/(photons/sec)">