Eco-conscious scalable interconnects and embedded capacitive sensors for non-contact microfluidic monitoring

A capacitive sensor detects solids or liquids without physical contact, using the same principle as touchscreens. In this study, screen-printed capacitive sensors (SPCSs) were developed for non-contact fluid sensing in microfluidic channels. SPCSs were fabricated by printing carbon–graphene ink onto hydrophilic polyethylene terephthalate (PET) and polylactic acid (PLA) substrates via roll-to-roll rotary screen printing. Microfluidic channels were created by laser-cutting pressure-sensitive adhesive films and laminated onto SPCSs through pressure bonding, or hot embossed onto PLA or cellulose acetate (CA) and solvent-bonded to form integrated devices. Flexible carbon–graphene interconnects were incorporated to enable integration of additional components (e.g., bioenzymatic fuel cells, BFCs) and facilitate easier separation for recycling. Performance was demonstrated through sequential multichannel fluid filling experiments with electrical readouts. Potential applications include monitoring air bubbles, reagent dissolution, dilution, and liquid movement without labels or optical analysis. Sustainability considerations guided material selection and fabrication, reducing environmental impact through PLA-based microfluidics and printing on the unused non-hydrophilic side of PET. Integration of metal-free paper-based BFCs provided a fully sustainable power source for low-power electronics. These BFCs, being recyclable and compostable, further minimize the device’s environmental footprint.