Sensitive naked-eye sensor for thiol-containing amino acids

Abstract

Amino acids are of significant importance to the reversible redox reactions. As building blocks for protein, the thiol-containing amino acids levels, such as cysteine (Cys) and homocysteine (Hcy), have been directly linked to some diseases and cancers, such as Alzheimer's disease, neural tube defect and cardiovascular disease. The organic dyes or fluorophore molecules with a formyl group were sensitive to Cys or Hcy, which react with the Cys or Hcy to form a five or six-membered ring. Diarylethene 1-1-[2-methyl5-(9,9-n-Hexyl-fluoren-2-yl)-3-thienyl]-2-[(2-methyl-5-formyl)-3-thienyl] perfluorocy clopentene experienced reversible reaction when alternate exposure of UV and visible light in Figure 1, A. Upon the UV irradiation, the colorless solution in open-ring state changed to turquoise in closed-ring state within seconds. The absorption spectral changes of 1b accompanied with Cys/Hcy titration were recorded in DMF (20 μM), and the results were shown in Figure 1, B and Figure 1,C. When Cys were added into theDMF solution of 1b from 0 to 200 μM, the absorption spectrum of 1bwas changed remarkably (Figure 1, B). Upon addition of Cys, the absorbance at 635 nm of 1b significantly decreased with a new absorbance peak increase at 443 nm, corresponding to solution color change from turquoise to pale yellow so that it could be readily visualized bythe eye. However, the absorption spectrum of 1bwas changed differently when Hcy was added into the DMF solution. As shown in Figure 1,C, the absorbance at 635 nm of 1b decreases with the increase of Hcy concentration from 0 to 200 μM, and a broader absorption band emerged from 285 nm to 385 nm and 420 nm to 600 nm. Simultaneously, the color changed from turquoise to light brick-red. Therefore, compound 1 is a potential application in rapid and sensitive naked-eye sensor to detect Cys or Hcy, even the mixture of other kinds of amino acid.