Regulating the aromatic structure in carbon dots to enhance the internal filter effect for sensitive on-site monitoring of anthrax biomarkers.

Anthrax, a fatal infectious disease caused by Bacillus anthracis (B. anthracis), poses a significant threat to public health. Herein, a novel type of carbon dots rich in π → π∗ transitions (R-CDs) was developed to fabricate an R-CDs/Eu3+ hybrid for the rapid on-site detection of the B. anthracis biomarker dipicolinic acid (DPA). The R-CDs/Eu3+ hybrid exhibits two distinct fluorescence responses to DPA: (1) quenching of the R-CDs fluorescence due to the internal filter effect, and (2) enhancement of Eu3+ fluorescence resulting from the antenna effect and the protective role of R-CDs, enabling ratiometric detection of DPA over a range of 0.1-100 μM with excellent selectivity. Furthermore, a portable, cost-effective device based on the hybrid was developed, enabling in-filed detection of DPA in lake water and real-time monitoring of DPA release from bacterial spores, which holds great promise for monitoring pathogenic biomarkers, with significant implications water safety and human health.