Green production of multi-functional carbon dots from agricultural corn silk waste: application in heavy metal (Fe3+/Cu2+) fluorometric sensing and in vitro cytotoxicity.

Corn silk (CS), an abundant agricultural waste, is typically converted into carbon dots (CDs) through energy-intensive methods such as hydrothermal treatment and microwave-assisted synthesis. In contrast, this study introduces a novel, simple, non-thermal (non-synthetic), and chemical-free extraction strategy to produce CDs directly from corn silk at ambient conditions. The properties of the resulting CDs were comprehensively characterized using transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and photoluminescence (PL) spectroscopy. While existing literature extensively reports biomass-derived CDs as probes for Fe3+ detection, their application for Cu2+ sensing remains limited and often requires complex surface functionalization. Remarkably, our non-synthetic extracted CDs exhibit high sensitivity toward Cu2+ ions with a competitive limit of detection (LOD) of 33 nM. Furthermore, to elucidate the impact of processing conditions, we systematically investigated the hydrothermal carbonization of corn silk across a temperature gradient. Our findings reveal that the preparation method acts as a functional switch: the non-synthetic route enables Cu2+ sensing, while hydrothermal treatment optimizes Fe3+ detection at 200 °C and enhances antimicrobial activity at 240 °C. This work establishes the first energy-free, non-synthetic approach to transform corn silk into high-performance Cu2+ nanoprobes, providing a sustainable and tunable platform for converting biomass into multifunctional nanomaterials.