Tuning the fluorescence response of surface modified CdSe quantum dots between tyrosine and cysteine by addition of p-sulfonatocalix[4]arene

Abstract

A simple identification method of L-tyrosine (Tyr) and L-cysteine (Cys) using gemini surfactant coated CdSe quantum dots by using a fluorescent spectroscopic technique is proposed. The gemini surfactant modified QDs show a selective fluorescence response between Tyr and Cys by addition of p-sulfonatocalix[4]arene (pSCA). The CdSe QDs coated with gemini surfactant [C₁₂H₂₅N⁺(CH₃)₂(CH₂)₄(CH₃)₂N⁺C₁₂H₂₅]·2Br⁻ (GS) obviously responds to Tyr. While in the presence of pSCA, it shows selectivity to Cys due to the cooperation of gemini surfactant coated QDs (GS-QDs) and pSCA. Under optimal conditions, it is found that the luminescence of the GS-QDs enhanced by Tyr in a concentration-dependent fashion is described by a Langmuir binding isotherm equation in the range 5 × 10⁻⁸–10⁻⁵ M. In the presence of pSCA, the luminescence of the GS-QDs enhanced by Cys in a concentration-dependent fashion can also be described by a Langmuir binding isotherm equation in the range 10⁻⁸–10⁻⁴ M. The possible mechanism is discussed.