Development of an on-chip sample injection system with a 6-port valve incorporated in a microchip.

Micro-flow-injection analysis (μFIA) is amenable to high-throughput systems with lower consumption of sample and reagent volumes. On-chip sample injection methods are important to prevent reduced analytical performance associated with dead volumes and diffusion of sample solutions. In this study, we have developed an on-chip sample injection system with a small-sized 6-port valve incorporated on a microchip. The valve is made with a 3D printer and is a simple structure that can be easily operated manually. A sample solution in a loading channel can be injected by switching the valve from the load to injection position. Sample injection tests using resorufin solutions revealed that samples can be injected below 100 μL min, and the performance of the sample injection system is comparable to that of a commercially available injector. In addition, the sample injection system was successfully applied to a flow-based assay for hydrogen peroxide. The detection limit (3) of hydrogen peroxide was estimated to be 0.5 μM, and the assay time after sample injection was approximately 100 s. The developed sample injection system will be useful for various microfluidic-based analyses including μFIA.