Graphene Based Printable Conductive Wax for Low‐Power Thermal Actuation in Microfluidic Paper‐Based Analytical Devices

Abstract Wax printing is one of the most widely used techniques to print hydrophobic barriers on hydrophilic microfluidic paper‐based analytical devices (µPADs) based on its simplicity, speed, and low cost, allowing large‐scale production. Nonetheless, its function is just passive, without any action on fluids. Thus, this work proposes multifunctional hydrophobic composites based on conductive graphene nanoplatelets (GNPs) integrated into the wax matrix to allow a dual role of barrier and heater, the latter being required in a large variety of temperature‐sensitive reactions and microfluidic applications. The effect of GNP weight content on the physicochemical properties of the wax, printed wax, and generated heating are evaluated. Wax prints with mechanical stability and adequate impregnation through the paper are obtained after post‐thermal curing. With respect to the functional response, controlled temperatures ranging from room temperature to ≈107 °C can be achieved after just 10 s. Two proofs of concept are presented involving thermochromic inks, specific printed systems designs, and low‐power batteries. The benefits of µPADs allied to the increased functionality and performance of the developed waxes, hold great promise to meet the requirements for a next generation of versatile, effective, and accurate µPADs for an increasing number of applications.