Design and Fabrication of a Ligase Detection Reaction (LDR) Microchip With an Integrated Passive Micromixer

The ligase detection reaction (LDR) is a technique that can distinguish low-abundant mutant DNAs from wild-type DNAs. LDR is usually carried out on DNAs amplified using the polymerase chain reaction (PCR). In the realization of modular microfluidic systems, the DNA output of the PCR handed off to the LDR chip needs to be mixed with LDR reagents before continuing the reaction. Polymer, continuous flow ligase detection reaction (CFLDR) devices with integrated passive micromixers, were designed, fabricated and tested. The devices each consisted of: a passive mixer for mixing a PCR sample, a cocktail of primers, and ligase, an enzyme of DNA; an incubator channel (95°C) for preheating the mixture; and a thermal cycling channel for the LDR. The devices were produced by hot embossing polycarbonate (PC) substrates with brass mold inserts manufactured by micro-milling. Experiments using food dyes showed that the appropriate mixture concentrations were delivered to the preheating channel in both the pulling and pushing modes.