Nitrocefin is a chromogenic cephalosporin substrate which is used for detection of β-lactamases. β-lactamases are enzymes produced by various microbes that mediate resistance to β-lactam antibiotics such as penicillins and  cephamycins. Comparing to other methods for β-lactamases detection, nitrocefin is more sensitive while using few materials and inexpensive equipment. The color change by nitrocefin can be followed quantitatively by measuring changes in absorption between 380 to 500 nm region[1].

Reference:
[1] O'Callaghan, Cynthia H et al.  Novel Method for Detection of B-Lactamases by Using a Chromogenic Cephalosporin Substrate. Antimicrobial Agents and Chemotherapy. 1972 Apr; 1(4):283-288.