The disclosure provides chromogenic and fluorogenic compounds comprising amino acid or peptide appendages that are capable of detecting an activity in a bioassay. Also provided herein are methods for detecting a biological activity in a sample with the subject chromogenic and fluorogenic compounds. In one embodiment, provided herein is a method for detecting endotoxin in a sample. Further provided herein are kits including the subject chromogenic and fluorogenic compounds for detecting a biological activity in a sample.