Carbon dots (CDs), revolutionary carbon-based nanomaterial, have demonstrated tremendous potential for applications across multiple areas. Chitin-rich shrimp shells are a sustainable and renewable resource, and their utilization can turn waste into treasure. This work is dedicated to efficiently preparing nitrogen-doped green fluorescent CDs (N-CDs) for multi-modal applications from waste shrimp shells by hydrothermal methods. The detailed spectroscopic characterization reveals that the N-CDs possess excellent optical properties. The quantum yield is as high as 33.2%. Specifically, the N-CDs show excellent selectivity and sensitivity in the quantitative detection of Fe