A fluorescence probe with near-infrared dual-emission for the ratiometric determination of homocysteine and cysteine

In the paper, an indocyanine-based near infrared fluorescence probe ( Cy5-A ) was reported, which showed a remarkably fluorescent response to homocysteine or cysteine in the PBS buffer-acetonitrile solution (9:1, v / v ) at room temperature. Furthermore, the increased concentration of homocysteine or cysteine caused the fluorescent intensity at 700 nm gradually enhanced, along with that at 660 nm decreased. Exhilaratingly, there was a ratio fluorescent response ( F 700 / F 660 ) to the concentration of homocysteine in the range of 40.0 to 200.0 μM with the limit of determination of 13.2 μM, or cysteine in the range of 10.0 to 100.0 μM with the limit of determination of 26.7 μM, respectively. The response mechanism of CyA-5 to homocysteine or cysteine was confirmed by 1 H NMR and MS, which was the cyclization reaction between the aldehyde group of CyA-5 with homocysteine or cysteine, inducing the near infrared dual-emission fluorescence signal. The fluorescent probe of CyA-5 exhibited good selectivity over other related amino acids and thiol-containing compounds. Therefore, the indocyanine-based dye of CyA-5 was a simple and efficient reaction-based fluorescence probe for the determination of homocysteine or cysteine in the serum samples with satisfactory results.