Fig. 1. (A and B) Time-dependent fluorescence spectra changes of POP (2 μM) upon treatment with Cys (100 equiv.) and GSH (10 equiv.), respectively, in PBS (10 mM, pH 7.4) at 37 °C. (C and D) Fluorescence intensity changes of POP (2 μM) treated with various amino acids (200 μM), reducing agents (200 μM), ROS (100 μM) and metal ions (500 μM). (1) POP; (2) His; (3) Glu; (4) Asp; (5) Val; (6) Phe; (7) Tyr; (8) Ala; (9) Ser; (10) Leu; (11) Arg; (12) Pro; (13) Thr; (14) Glu; (15) Trp; (16) Ile; (17) Lys; (18) DTT; (19) Vc; (20) HS^– for (C) and Cys for (D); (21) GSH for (C) and HS^– for (D); (22) ONOO^–; (23) H₂O₂; (24) NaOCl; (25)OH˙; (26) KO₂; (27) NO; (28) HNO; (29) K⁺; (30) Ca²⁺; (31) Na⁺; (32) Mg²⁺; (33) Al³⁺; (34) Zn²⁺; (35) Cd²⁺; (36) Cu²⁺; (37) Fe²⁺; (38) Fe³⁺; (39) Cys for (C) and GSH for (D). For (A and C) λ_ex = 450 nm; for (B and D) λ_ex = 580 nm. Slits: 5/5 nm.