Water-soluble and biocompatible protein carbon dots (P-CDs) were simply prepared from egg white by a rapid one-step neutralization heat reaction. Unexpectedly, the thus-fabricated P-CDs could present excitation-dependent tunable fluorescence that could be quenched specifically by Fe3+ and Fe2+ ions with obvious color changes. A high-throughput fluorimetric platform was thereby developed by coating the P-CDs onto a capillary array for detection of total iron ions in fish blood samples, with a linear concentration range of 0.25-60.00 μM and a detection limit of 0.085 μM. Moreover, it can allow for the fast evaluation of total iron ions in fish blood samples, showing recovery efficiencies of 97.25%-99.84%. Such a facile fabrication route for P-CDs from egg white by a rapid neutralization reaction may open a new door for preparing different CDs. More importantly, the developed fluorimetric method may be expected to have wide application in the fields of diagnosis of iron-related diseases, monitoring of environmental water, and ensuring aquatic product safety.