Fabrication and thermoresistive behavior characterization of three-dimensional silver-polydimethylsiloxane (Ag-PDMS) microbridges in a mini-channel

Polydimethylsiloxane (PDMS) microstructures, such as micro-pillars, have versatile applications as actuators in microfluidic devices. With the addition of functional materials, e.g., silver (Ag) particles, PDMS structures can also attain sensing properties such as electrical conductance. In this paper, we introduce a fabrication technique using sacrificial agar to develop novel double-side hinged PDMS and Ag-PDMS microstructures, called three-dimensional microbridges, suspended in the middle of a PDMS channel. The technique offers simple and consistent fabrication of high aspect ratio (∼44) microbridges with diameters of 90-200 μm. The design has advantages of yielding electrically-conductive Ag-PDMS microbridges in the bulk of the channel with accessible terminals at channel sidewalls for connection to external electrical instruments. This allowed us to investigate the electrical performance of Ag-PDMS microbridges and their thermoresistive behavior for future applications as temperature sensors. It was found that 70% Ag-PDMS microbridges with various diameters have electrical resistances in the range of 10-110 Ω, while demonstrating an exponential increase in resistance in response to the temperature of the fluid rising from 18 °C to 51 °C. These functionalized and three dimensional microbridges can be embedded in microfluidic devices and utilized as integrated sensors for measuring the bulk properties of fluids or the existence of target biological substances in the fluid.