The invention is directed to a microfluidic device, which comprises distinct, parallel levels, including a first level and a second level. It further includes: a first microchannel, a second microchannel, and a node. This node comprises: an inlet port, a cavity, a via, and an outlet port. The cavity is formed on the first level and is open on a top side. The inlet port is defined on the first level; it branches from the first microchannel and communicates with the cavity through an ingress thereof. The outlet port, branches to the second microchannel on the second level. The via extends from the bottom side of the cavity, down to the outlet port, so the cavity may communicate with the outlet port. In addition, the cavity comprises a liquid blocking element to prevent an aqueous liquid filling the inlet port to reach the outlet port.