Green synthesis of biomass-derived carbon dots for the construction of portable test strips and hydrogel sensors for Cr(VI) sensing in environmental water samples

Chromium (Cr), especially Cr(VI), is a notorious heavy metal pollutant with high toxicity, posing serious threats to ecosystems and human health. Recently, biomass-derived carbon dots (B-CDs) have emerged as promising materials in the field of sensing due to their low cost, environmental friendliness, and good optical properties. Developing a simple, sensitive, selective, and portable sensing platform based on B-CDs for the efficient detection of Cr(VI) in real environmental water samples is urgently required. Here, nitrogen-doped blue-fluorescent B-CDs were successfully synthesized via a one-step hydrothermal method utilizing loofah biomass as the carbon source and ethylenediamine as the nitrogen source. The as-prepared B-CDs possess abundant surface functional groups, excellent water solubility, remarkable fluorescence stability, and high selectivity toward Cr(VI). The B-CDs exhibit a wide linear detection range for Cr(VI) from 10 to 1000 μmol L −1 with a low detection limit of 194 nmol L −1 . The quenching mechanism was determined to be an internal filter effect. This method has been effectively applied to the accurate analysis of real water samples. Furthermore, portable paper-based and hydrogel-based sensors incorporating B-CDs have been developed, enabling convenient on-site detection of Cr(VI) in practical scenarios.