We report a study on the minimum microfluidic channel dimension in which gallium-based liquid metal alloy can be filled. Based on the non-toxicity of gallium-based liquid metal, it was expected to be utilized in many applications. Specifically, in order to possess advantages of its liquid property, there are several efforts to use it in microfluidic-based applications. However, due to its high surface tension of the liquid metal, the applicable dimension of the microfluidic channel has been simply limited. In order to investigate the minimum channel dimension, we have fabricated three different thick (5, 10, and 25 μm) PDMS-based microfluidic channel with various widths in the range from 20 μm to 3 μm using SU-8 mold technique. We successfully filled the liquid metal into as small as 3 urn wide channel with 25 urn thickness which has a rectangle cross section of 75 μm2. As a demonstration of the filling of liquid metal, we transferred the shape of channel in which liquid metal is filled, to positive photoresist by liquid metal-based photolithography.

We report a study of the surface properties of 2D and 3D micro-structures, for the purpose of fabrication of bio-chip array/wells for isolation of single cell or small group of cells. The components of the microstructure are polydimethylsiloxane (PDMS) and/or parylenes, which are the commonly used materials in biological researches. To fabricate micro-array/wells, five methods based on MEMS technology were conducted. An optimum fabrication method was successfully found and the 3D micro-well chip only consisting of PDMS was realized for cells isolation. To reveal the nature of cell adhesion and repellency on the substrate, atomic force microscopy (AFM), contact angle and x-ray photoelectron spectroscopy (XPS) methods have been carried out to analyze the physical and chemical properties of the material surfaces.

This paper presents the development of a disposable plastic biochip incorporating smart passive microfluidics with embedded on-chip power sources and integrated biosensor array for applications in clinical diagnostics and point-of-care testing. The fully integrated disposable biochip is capable of precise volume control with smart microfluidic manipulation without costly on-chip microfluidic components. The biochip has a unique power source using on-chip pressurized air reservoirs, for microfluidic manipulation, avoiding the need for complex microfluidic pumps. In addition, the disposable plastic biochip has successfully been tested for the measurements of partial oxygen concentration, glucose, and lactate level in human blood using an integrated biosensor array. This paper presents details of the smart passive microfluidic system, the on-chip power source, and the biosensor array together with a detailed discussion of the plastic micromachining techniques used for chip fabrication. A handheld analyzer capable of multiparameter detection of clinically relevant parameters has also been developed to detect the signals from the cartridge type disposable biochip. The handheld analyzer developed in this work is currently the smallest analyzer capable of multiparameter detection for point-of-care testing.