"Drop-and-Sip" fluid handling technique for the reagent-release capillary (RRC)-based capillary-assembled microchip...

The experimental conditions of the sample delivery inside the reagent-release capillary-based capillary-assembled microchip (RRC-based CAs-CHIP) were optimized and the reagent release procedure in the RRC is discussed. Recently, our group introduced the basic concept of the "drop-and-sip" fluid handling technique (Anal. Chem., 2007, 79, 908). A microliter volume of sample solution is dropped on the inlet hole and is sipped into another hole, producing a sample plug flow in the main poly(dimethyl siloxane) (PDMS) channel, concurrently filling each sensing capillary that faces the main PDMS channel. However, the detailed evaluation of the successful sample delivery condition and the reagent release behavior in the RRC has not been fully discussed. Under our experimental conditions, ca. 0.6 - 2.4 s of sample plug-RRC contact time allowed the successful sample introduction into the RRC by capillary force without any reagent leakage or disturbance of the sample plug flow. On the other hand, reagent release behavior inside the RRC is governed by both convective and diffusive mass transport, which leads to a faster mixing time of the sample with reagents immobilized inside the RRC compared to that expected from the simple diffusion alone.