Biomedical and Environmental Application of Microfluidic Devices

Many studies have been done in the microfluidic fields, especially for biomedical and environmental application in the world.In this paper, two practical topics in our group will be presented mainly; automated paper device for sequential multistepsandwich enzyme-linked immunosorbent assays (ELISA) and high-sensitive ultra-compact elemental analyzer utilizing liquid electrode plasma (LEP) in a microfluidic channel.
Sandwich-type ELISA is a commonly used for biochemical analysis. This assay requires, however, a multistep process of mixing, washing, and incubation so that the entire process is laborious and time consuming.Our device was fabricated on one piece of the NC membrane and consists of several solution pathways (channel) separated by barrier-lines, and of a small amount of the reagents, such as antibodies (Abs) and substrates. When the one end of the device dips into an analyte solution, the solution migrates along with the channel by capillary action, dissolves and conveys the pre-spotted reagents, separates and mixed again in a proper timing designed by delay channel, and then the multi-reagent steps in the sequence for ELISA can be performed automatically.
The developed device successfully demonstrates determination of the levels of human chorionic gonadotropin (hCG) with a simple one-step manual operation, ease of use, and reducing the assay time and reagents consumption.
We also developed a high-sensitive ultra-compact elemental analyzer utilizing LEP. A channel whose center was made narrower was fabricated on a quarts glass chip. Solution samples were introduced into the channel and a high voltage (800~1500 V) was applied to the solution from the both ends of the channel. The sample solution was locally heated by confined electric current at the narrower part, to evaporate and to make discharge with element specific spectra. From the spectra, we can measure the elemental concentration in the sample. This method requires neither plasma gas nor nebulizer, and is very compact. The limit of detection for Cd and Pb were derived as 0.5 ppb and 5 ppb, respectively, in 0.1 M HNO3. Those values were low enough for the environmental analysis applications.