Automatic sequential fluid handling with multilayer microfluidic sample isolated pumping

Thermodynamic Characterization of a Highly Transparent Microfluidic Chip with Multiple On-Chip Temperature Control Units

Indium tin oxide (ITO) is a functional material with great transparency, machinability, electrical conductivity and thermo–sensitivity. Based on its excellent thermoelectric performance, we designed and fabricated a multilayer transparent microfluidic chip with multiple sets of on–chip heating, local temperature measurement and positive on–chip cooling function units. Temperature control plays a significant role in microfluidic approaches, especially in the devices that are designed for bioengineering, chemical synthesis and disease detection. The transparency of the chip contributes to achieve the real–time observation of fluid flow and optical detection. The chip consists of a temperature control layer made with an etched ITO deposited glass, a PDMS (polydimethylsiloxane) fluid layer, a PDMS cooling and flow control layer. The performances of the ITO on–chip microheaters, ITO on–chip temperature sensors and two coolants were tested and analyzed in different working conditions. The positive on–chip heating and cooling were proved to be area-specific under a large temperature–regulating range. This PDMS–ITO–glass based chip could be applied to both temporal and spatial stable temperature–regulating principles for various purposes.

Fabrication of a Three-Layer PDMS Pneumatic Microfluidic Chip for Micro Liquid Sample Operation

The emphasis of this paper lies in the fabrication of a three-layer polydimethylsiloxane chip for micro liquid sample operation. In this paper, the microchannels with a rectangular control layer cross section are fabricated based on a dry-film negative photoresist mold, while the microchannels with a rounded liquid layer cross section are fabricated by a positive photoresist reflow mold. The relationships between temperature and the time of reflow and the arc level of the liquid layer mold are discussed. Different ratios, curing temperatures, and curing times are used to fabricate the two PDMS layers to improve their toughness and plasticity separately. The PDMS slabs with microstructure networks are treated with oxygen plasma to improve their surface properties. The improved surface properties serve to reduce the temperature and time, and improve the sealing strength, which is as effective as adding PDMS in varying ratios. The micro liquid sample operation experiments show that high levels of pinching off and mixing performances on pneumatic microfluidic chips are obtained more easily.

Automatic sequential fluid handling with multilayer microfluidic sample isolated pumping

To sequentially handle fluids is of great significance in quantitative biology, analytical chemistry, and bioassays. However, the technological options are limited when building such microfluidic sequential processing systems, and one of the encountered challenges is the need for reliable, efficient, and mass-production available microfluidic pumping methods. Herein, we present a bubble-free and pumping-control unified liquid handling method that is compatible with large-scale manufacture, termed multilayer microfluidic sample isolated pumping (mμSIP). The core part of the mμSIP is the selective permeable membrane that isolates the fluidic layer from the pneumatic layer. The air diffusion from the fluidic channel network into the degassing pneumatic channel network leads to fluidic channel pressure variation, which further results in consistent bubble-free liquid pumping into the channels and the dead-end chambers. We characterize the mμSIP by comparing the fluidic actuation processes with different parameters and a flow rate range of 0.013 μl/s to 0.097 μl/s is observed in the experiments. As the proof of concept, we demonstrate an automatic sequential fluid handling system aiming at digital assays and immunoassays, which further proves the unified pumping-control and suggests that the mμSIP is suitable for functional microfluidic assays with minimal operations. We believe that the mμSIP technology and demonstrated automatic sequential fluid handling system would enrich the microfluidic toolbox and benefit further inventions.