Multiplexed electrical sensor arrays in microfluidic networks

A major limitation of many microfluidic platforms is their inability to perform large scale, real time, sensing, routing, or scheduling of the materials moving through them. This paper seeks to address the first of these deficiencies by introducing a multiplexed sensing architecture capable of monitoring the movement of liquid droplets in large microfluidic networks. We describe the design and fabrication of the sensor array, as well as its integration and testing in microfluidic networks. Individual sensors consisting of small electrical components (resistors, capacitors, or conduction gaps) are addressed using a multiplexing approach that allows an array of m × n sensors to be supported by only m + n + 1 electrical contacts, as compared to the 2 × m × n contacts traditionally necessary. For example, a multiplexed 10 × 10 array of sensors can be operated with 21 contacts, as opposed to the 200 contacts needed in a traditional configuration. The multiplexing relies on the fact that each sensing element is connected to two electrical leads, and each electrical lead is connected to multiple sensing elements. Here we show the principle using a 4 × 4 multiplexed arrays of resistive and capacitive sensors to monitor the passage of discrete liquid plugs through a microfluidic network.