Freeform Green Electronics: From Macadamia Nut Shell Waste to Multifunctional Sensors Based on Conformal Direct Laser Writing

A critical challenge in developing sustainable green electronics is achieving uniform fabrication and high performance on the curved, irregular surfaces of natural biomass waste. To address this, a conformal direct laser writing (CDLW) strategy is reported to manufacture multifunctional green sensors directly on macadamia nut shells. By optimizing the laser energy threshold to balance lignocellulose conversion and gasification, uniform porous laser-induced graphene (LIG) with a low sheet resistance of 119 Ω/sq was successfully patterned on the rigid, nondevelopable shells. The resulting multifunctional device integrates sensing and energy storage capabilities. The sensors exhibit high sensitivity and linearity (R² = 99.31%) for pressure, fast thermal response (−15 to 55 °C), and stable capacitance variation for humidity detection (0.017 to 82 nF within 19 s). Furthermore, integrated LIG supercapacitors demonstrated sufficient output to power a 3 mm LED. Crucially, the environmental compatibility was validated, as the decomposition products of discarded sensors promoted tomato seed germination, providing a sustainable, closed-loop pathway for high-performance green electronics.