A new strategy for the detection and discrimination of sulfhydryl amino acids through liquid crystals sensing platform with Cu(ClO4)2

A facile, low-cost and label-free liquid crystals (LCs) sensing platform laden with Cu(ClO 4 ) 2 was herein established for detection and distinction of sulfhydryl amino acids, namely cysteine (Cys) and homocysteine (Hcy). When introducing Cys or Hcy to the fluid interface with Cu(ClO 4 ) 2 , the optical appearance of LCs exhibited a bright-to-dark transition, which coupled to the interactions between Cu 2+ and the sulphydryl of amino acids. Concomitantly with, the orientation of LCs varied from tilted to homeotropic state. Besides, this sensor system did not respond to other nineteen amino acids that make up human proteins. The detection limit of Cys and Hcy is around 0.01 mg/mL (~82.5 μM) and 0.05 mg/mL (~370.0 μM), respectively. Compared with Cys, the as-prepared LCs sensing platform shows a higher detection limit and longer response time for Hcy, based on which these two sulfhydryl amino acids can be distinguished from each other. This can be attributed to the additional methylene for Hcy, resulting in formation of a five-membered ring Hcy thiolactone which may not chelate with Cu 2+ . The LCs-based analytical platform constructed in this work can provide a convenient and label-free method for detecting and differentiating sulfhydryl amino acids.