Red-emitting benzo[e]indolium probes for HSA based on the TICT characteristics

Human serum albumin (HSA) is the most abundant protein in human blood plasma. It plays an important role in many physiological functions, and the increase or decrease of HSA can exhibit the conditions of human health. Therefore, the accurate detection of HSA with high selectivity and sensitivity has a great clinical importance. We herein developed four red-emitting benzo[e]indolium fluorescent dyes, Ll-L4, for probing HSA in a physiological buffer or human urine. Satisfactorily, L2 and L4 showed high selectivity and excellent sensitivity for HSA in both PBS buffer and human urine. L2 was completely embedded in the alpha-helices from subdomain IIA (Sudlow site I) of HSA, and the limit of detection (LOD) was 13.43 mg L-1 in PBS and 8.91 mg L-1 in urine, respectively. However, L4 inserted into the alpha-helices from subdomain IIA and IIIA (Sudlow site II) of HSA, and exhibited a lower LOD (1.75 mg L-1 in PBS, 1.50 mg L-1 in urine). Furthermore, the high tolerance of environmental pH and anti-interference of L2 and L4 enabled us to develop the promising molecular probes for HSA.