Abstract: In this study, ninhydrin/titanium dioxide nanomaterials were constructed by using Sol-Gel method. These nanomaterial were then used as direct-reading colorimetric materials and printed on the surface loci of thin layer plate where theanine would migrate according to its retardation factor (R_f). In addition, ethanol: acetic acid developing system was chosen as developing reagent, the extraction solution of tea after being decolorized by ethyl acetate was analyzed by thin layer chromatography (TLC) via direct-reading colorimetric reaction. The results showed that the current direct-reading strip could effectively separate several amino acids in tea extraction under optimized conditions. The new constructed colorimetric nanomaterials had achieved a sensitive direct-reading coloration results for the target amino acid theanine, and the color spots on the strip were uniform and clear after self-coloration. Moreover, its color depth had a clear semi-quantitative relationship with its concentration. The current colorimetric strip has a serial of advantages including safety, easy-operation, convenient and low cost, and has a broad application prospect in fields such as quality identification of agricultural products and on-site rapid detection of amino acids.

Key words: green tea, theanine, direct-reading colorimetric strips, thin layer chromatography