One of the major interests in bio-chip like Lab-on-a-chip is to reduce the time for testing by mixing the infinitesimal quantity of the specimen and the reactant as fast as possible.
The flow inside the micro fluid element is extremely slow and it obstructs mixing. Therefore, it is an important task to manufacture an efficient micro-mixer. Below picture shows a fluorescent image observed in the cross section of the flow in a micro-mixer using Confocal Microscopy. In spite of the growing importance and contribution of flow visualization technique in developing microfluidic element, a standard and quantitative test technique has not been devised owing to a lack of relevant studies in the aspect of flow visualization.  
 
Cross section of flow in micro mixer
 
 
The most widely authorized method to solve this problem is micro-PIV developed in US
in1988, of which applies common measurement method of PIV to microscale fluid. In order to catch the fluid micro scale, Micro-PIV adds the tracking particle under 1¥ìm in diameter, generally 100~300nm to the fluid field, and illuminates with pulsed laser beam twice. The tracking particle which follows the fluid is excited by the laser beam and emits fluorescence, and the velocity of the particle can be computed by processing the two consecutive particle images.
 
 
Below picture shows the distribution of the flow speed inside a microchannel (300mmx50mm) measured by micro-PIV, and well represents the microscale structure of 3-dimensional distribution of the flow speed. With this flow information, we can predict or verify the fluidic feature and performance of micro-mixer.
One example of measurement by Micro-PIV
 
 
 
Confocal Microscopy has been originally developed for the observation of intracellular
structure, but recently it is widely applied to 3-D micro-structure observation of semiconductor parts and materials as it complements the defects of the general optical microscope and SEM (Scanning Electron Microscope).The general optical microscope can get only 2-D image for a cross section of a structure, and SEM which can make a 3-D observation has the defect that the specimen can be seriously damaged in the preparation processes.So, in order to observe the change of the 3-D structure in a living cell like a metabolism phenomenon, Confocal Microscopy has been developed.The principle of Confocal Microscopy as in below picture is that it strains out the light which passes through a certain cross section of the specimen, that is, the image only in a certain cross section using pinholes installed on the light path from the specimen to the detector.
 
 
 
At this point, a 3-D image is reconstructed by moving the pinholes to the direction of the specimen thickness properly. Confocal Microscopy is classified into Stage scanning type, Beam scanning type and Spinning disk type according to how the pinholes are moved. One of the Beam scanning types, LaserScanning Confocal Microscope(LSCM) is generally used, and a schematic is given below.