Abstract
Currently most of the fluorogenic probes are designed for the detection of enzymes which work by converting the non-fluorescence substrate into the fluorescence product via an enzymatic reaction. On the other hand, the design of fluorogenic probes for non-enzymatic proteins remains a great challenge. Herein, we report a general strategy to create near-IR fluorogenic probes, where a small molecule ligand is conjugated to a novel γ-phenyl-substituted Cy5 fluorophore, for the selective detection of proteins through a non-enzymatic process. Detail mechanistic studies reveal that the probes self-assemble to form fluorescence-quenched J-type aggregate. In the presence of target analyte, bright fluorescence in the near-IR region is emitted through the recognition-induced disassembly of the probe aggregate. Based on this design, a fluorogenic probe for hCA II detection was constructed and was applied for the no-wash imaging of tumor cells for the detection of hypoxia-induced cancer-specific biomarker, transmembrane-type carbonic anhydrase IX. We have also created another fluorogenic probe which belongs to a class of fluorescent dyes called molecular rotors for the detection of human serum albumin (HSA), a key indicator for the early diagnosis of renal disease and for the cardiovascular disease in non-diabetic individuals. In aqueous buffer, molecular rotors show extremely weak fluorescence due to the unrestricted torsional rotation. In the presence of target analyte, bright fluorescence can be observed because of restricted torsional rotation. In the presence of albumin, the probe exhibits remarkable 400-fold fluorescence enhancement with high selectivity and sensitivity. The probe was successfully applied in the quantitative detection of urinary albumin.