基于碱性胱氨酸水溶液在恒温水浴条件下可形成荧光性分子聚集体的特性, 发展一种荧光光谱直接检测胱氨酸含量的新方法。 实验结果表明, 将pH 9.0的0.01 mol·L-1的胱氨酸溶液, 于90 ℃恒温水浴热处理12 h后, 胱氨酸分子可形成大小为12.5nm粒径的荧光分子聚集纳米团簇(FANC)结构, 并发射蓝绿色荧光。 采用荧光光谱(FL)、 透射扫描电镜(TEM)和质谱(MS)对FANC的荧光性能和结构进行表征, 并初步探讨光致发光机理。 FANC在410 nm最佳激发波长条件下, 于508 nm处具有最佳的荧光发射信号, 体系的平均荧光寿命为6.028 ns, 荧光量子产率为8.48%。 FANC在水溶液中具有稳定的光漂白性、 酸碱稳定性和光谱不依赖性质, 粒子的Zeta电位为-57 mV, 结合150 nm的水合粒径结果, 表明形成的团簇表面亲水且带负电荷。 质谱结果显示体系中存在多种胱氨酸分子间脱水形成的分子碎片, 因此推测FANC是胱氨酸分子在水溶液环境中因分子间作用力形成分子聚集体。 基于FANC的荧光强度和原料胱氨酸的浓度在1.0×10-5～6.0×10-4 mol·L-1范围内呈良好的线性关系, 可将该方法用于胱氨酸片中含量的测定, 结果与中国药典中记载的滴定比色法相吻合。 相比于其他检测方法, 该方法具有操作简便, 检测限低, 精确度高等优点。

We first reported a strategy for promoting fluorescent aggregation nanocluster of cystine molecule by heating in constant temperature bath and this performance could be used for detecting quantity of cystine. The effects of pH value, reaction time and temperature on the system were investigated and the mechanism of photoluminescence was discussed. The results suggested that the non-fluorescent molecule was assembled to form Fluorescent Aggregated Nanoclusters (FANC) by heating the pH 9.0 0.01 mol·L-1 cystine solution at 90 ℃ for 12 hours, and its aqueous solution showed a maximum absorption at 410 nm and a fluorescence emission at 508 nm. The fluorescence performance and structure of FANC were characterized by fluorescence spectroscopy (FL), transmission electron microscopy (TEM) and mass spectrometry (MS). The average fluorescence lifetime of the FANC aqueous system is 6.028 ns and the fluorescence quantum yield is 8.48%. Moreover, FANC has stable photobleaching, acid-base stability and spectral dependence in aqueous solution. TEM images showed that the fluorescent FANC has a size of 12.5 nm, however, DLS size distribution of FANC is about 150 nm, suggesting that the aggregates of cystine has a hydrophilic surface. Zeta potential result is -57 mV, demonstrating that the nanocluster has a negative charge. Additionally, the results of mass spectrometry showed that there are molecular fragments formed by the intermolecular dehydration of cystine in the system. Therefore, we can further speculate that FANC is an inner molecular aggregation of cystine to form the supramolecular vesicles in the aqueous solution environment due to intermolecular forces. The relative fluorescence peak intensity of FANC and the concentration of cystine showed a good linear relationship in a certain range of 1.0×10-5～6.0×10-4 mol·L-1, and the detection limit of 4.559×10-9 mol·L-1(3S0/K). The proposed method was applied to the quantitative analysis of cystine tablet. The results were consistent with the titration result of Chinese Pharmacopoeia. Compared with other detection methods, this new method has the advantages of simple operation, low detection limit and high precision.