NBD-Pen is the first fluorescence probe for lipid radicals with high selectivity and sensitivity (λex: 470 nm, λem: 530 nm). NBD-Pen directly detects lipid radicals in living cells by turn-on fluorescence. NBD-Pen decreases inflammation, apoptosis, and oxidative stress markers. NBD-Pen can be studied in various disease models such as hepatic carcinoma.