Laser-Induced Direct Patterning of Free-standing Ti₃C₂-MXene Films for Skin Conformal Tattoo Sensors

The discovery of stable two-dimensional (2D) materials has effectuated a rapid evolution of skin conformal sensors for health monitoring via epidermal electronics. Among the newly discovered 2D materials, MXene stands out as a solution-processable 2D material allowing easy fabrication of highly conductive thin films with the potential to realize flexible skin conformal sensors. Here, we present a successful demonstration of a Ti₃C₂-MXene resistor as an extremely sensitive strain sensor in the form an ultrathin skin mountable temporary tattoo. The skin conformability and form factor afforded by the sensor promises inconspicuous and continuous monitoring of vital health parameters of an individual, like the pulse rate, respiration rate, and surface electromyography. The sensor serves as a single conduit for sensing the respiration rate and pulse, dispensing with the need of mounting multiple sensors. Its remarkably high sensitivity with a gauge factor of ∼7400 has been ascribed to development of nanocracks and their propagation through the film upon application of strain. The fast response and highly repeatable sensor follows easy fabrication steps and can be patterned into any shape and size using a laser.