Near-infrared Squarylium Cyanine Dyes For Highly Selective Detection Of Proteins By The Character Of Its Gathered Control

In recent years,selective detection and visualization of specific proteins are important in clinical diagnostics and biological research. For protein sensing, small-molecule-based fluorescent turn-on probes are preferable because of their high sensitivity, simplicity and detection with high-throughput. Herein we demonstrated two small molecular fluorescent dyes(SQ-Biotin and SQ-P) which can self-assemble into non-fluorescent probe in aqueous solution for near infrared turn-on detection of avidin protein. The two probes detect avidin and BSA respectively in near infrared region. The probe SQ-Biotin consisting of a hydrophobic squaraine(SQ) as fluorophore and a specific and strong protein ligand(biotin) formed self-assembled aggregates in aqueous solution(fluorescence off), and the aggregates of the probe disassembled in response to the target protein(avidin) through the specific protein-ligand interaction(fluorescence on). The experiments showed that the fluorescence intensities at 665 nm were linearly proportional tothe concentration of avidin over the range of 0.76-1.46 μM. The detection limit was calculated to be about 70 n M. The conversion of the aggregation of SQ-Biotin was confirmed by field emission scanning electron microscopy(FESEM) and atomic force microscope(AFM). SQ-Biotin showed good selectivity to avidin over other proteins, enabling turn-on fluorescent detection of avidin in near-infrared region.Meanwhile, the design mechanism of SQ-P to detect BSA is similar to that of SQ-Biotin. The experiment showed that the fluorescence intensities at 673 nm were linearly proportional to the concentration of avidin over the range of 0-20 μM; The detection limit was calculated to be about 70 nM; The conversion of the aggregation of SQ-Biotin was confirmed by field emission scanning electron microscopy(FESEM) and atomic force microscope(AFM); SQ-Biotin showed good selectivity to avidin over other proteins; SQ-P combined with BSA on its site Ⅱ; More importantly, SQ-P can detect not only BSA in aqueous solution but also in the cells.