Enhancement mechanism of FCLAa-1O2 chemiluminescence by human serum albumin

Fluoresceinyl Cypridina Luciferin Analog (FCLA) is a reactive oxygen species (ROS) specific chemiluminescence (CL) probe. Its detection efficiency of singlet oxygen ( 1 O 2 ) could be significantly enhanced in the presence of human serum albumin (HSA). The enhancement mechanism of HSA-FCLA CL is studied in the current work by means of direct CL measurement and spectroscopy. The results show that, FCLA can combine with HSA. HSA is an effective 1 O 2 quencher. It can react with 1 O 2 and produce a protein carbonyl group with an elevated energy state. The HSA protein carbonyl group can transfer its energy to FCLA in the FCLA-HSA complex. Via this irradiative de-excitation pathway of the excited FCLA, luminescence production from FCLA is greatly enhanced, in addition to the chemiluminescence from the direct interaction of FCLA and 1 O 2 . FCLA has been reported for cancer diagnosis in vivo. Considering HSA is a natural protein that is present in all parts of a human body, the efficacy of FCLA used in vivo is expected to be enhanced through the coupling of FCLA and HSA.