Isoindole-functionalized carbon dots as a highly sensitive fluorescent probe for manganese detection in tea samples

Isoindole-CDs probe synthesized via rapidly gram-scale self-exothermic method. • Isoindole groups enhance oxidation by Mn(VII), enabling ultra-sensitive detection. • Achieved LOD of 2.45 ng mL −1 for Mn(VII) in various tea samples. Manganese (Mn) is an essential trace element for human health, but excessive intake can lead to neurotoxicity. Tea is a major dietary source of Mn, necessitating sensitive and reliable methods for its quantification. In this work, a novel fluorescent probe based on isoindole-functionalized carbon dots (Iso-CDs) was developed for the highly sensitive detection of total Mn in tea samples. The Iso-CDs were synthesized via a two-step strategy: first, amino-rich nitrogen-doped carbon dots (NH₂-CDs) were rapidly prepared on a gram scale using a self-exothermic reaction with locust powder as the precursor; then, the surface amino groups were reacted with o-phthalaldehyde (OPA) and 4-mercaptophenylboronic acid (MPBA) to construct electron-rich isoindole moieties on the CD surface. The resulting Iso-CDs exhibited strong blue fluorescence at 427 nm. The isoindole group is more susceptible to oxidation by Mn(VII) compared to the original amino groups, enabling an efficient fluorescence quenching response. Under optimized conditions, the fluorescence quenching ratio showed a good linear relationship with Mn(VII) concentration in the range of 10–800 ng mL −1 , with a detection limit as low as 2.45 ng mL −1 . The proposed method was successfully applied to the determination of total Mn in various tea samples, yielding satisfactory recoveries. This work provides a rational surface engineering strategy for designing highly sensitive CDs-based fluorescent probes and demonstrates its practical potential for food safety monitoring. Download: Download high-res image (350KB) Download: Download full-size image