Carbon dioxide (CO₂) is a universal indicator of biological, chemical, and physiological processes, yet it plays a multifaceted role, from regulating global climate to reflecting human cellular activities. The accurate and continuous measurement technologies of CO₂ have evolved along separate paths: environmental CO₂ monitors to biomedical sensors for respiratory or blood gas assessment. While environmental monitoring and clinical capnography are well established, translating these technologies to continuous, non-invasive transcutaneous CO₂ (tcCO₂) sensing remains challenging due to skin-interface instability, humidity interference, and diffusion-limited transport. This perspective will discuss design principles from ambient CO₂ sensors with emerging materials and architectures for wearable tcCO₂ platforms. This perspective also discusses sensor technologies and methods, their integration into systems, the physiological and skin-interface challenges, and the engineering trade-offs for wearables. We also outline recent advances, identify key gaps, and propose a roadmap for future wearable CO₂ sensors for transcutaneous monitoring.

Health monitoring of structures and people requires the integration of sensors and devices on various 3D curvilinear, hierarchically structured, and even dynamically changing surfaces. Therefore, it is highly desirable to explore conformal manufacturing techniques to fabricate and integrate soft deformable devices on complex 3D curvilinear surfaces. Although planar fabrication methods are not directly suitable to manufacture conformal devices on 3D curvilinear surfaces, they can be combined with stretchable structures and the use of transfer printing or assembly methods to enable the device integration on 3D surfaces. Combined with functional nanomaterials, various direct printing and writing methods have also been developed to fabricate conformal electronics on curved surfaces with intimate contact even over a large area. After a brief summary of the recent advancement of the recent conformal manufacturing techniques, we also discuss the challenges and potential opportunities for future development in this burgeoning field of conformal electronics on complex 3D surfaces.