New fluorescent dyes derivatized on a classical thiazole orange framework are able to show unexpectedly strong interaction signal and unusual binding selectivity with different structures of nucleic acid, particularly when bound with double-stranded DNA or G-quadruplex DNA. The present study reveals that these small binding ligands simply bearing an additional amino side group on its parent molecule of thiazole orange have almost no background fluorescence in solution. Conversely, they are able to produce an extremely strong yellow emission signal upon interaction with targeting nucleic acids in live cells. The induced fluorescence intensity was approximately 10–15 times stronger than that of thiazole orange. The dyes are therefore excellent fluorescent stains for bio-sensing and bio-imaging applications. It is particularly suitable for fluorescence microscopy experiments requiring very low working concentration (0.25 μM or less) targeting nucleic acids. This was demonstrated using pu27 G-quadruplex DNA, which has a low limit of detection (LOD = 3–4 nM) while thiazole orange was much higher (LOD = 48.7 nM) under the same conditions. In addition, it was found that structural modification on the quinolinium scaffold of thiazole orange was less effective than modification on the benzothiazole moiety. The findings of the present study provide important information for structural advancement of small molecules based on the widely used thiazole orange skeleton, resulting in analogues that are able to achieve higher sensitivity and selectivity for targeting at a specific class of nucleic acids. Computational docking studies were also conducted to illustrate the interaction behaviors of the dyes with different DNA structures.

在经典的噻唑橙骨架上衍生的新型荧光染料能够显示出意想不到的强相互作用信号和与核酸不同结构的异常结合选择性，特别是与双链DNA或G-四链体DNA结合时。本研究表明，这些小的结合配体仅在其噻唑橙的母体分子上带有一个额外的氨基侧基，在溶液中几乎没有背景荧光。相反，它们在与活细胞中的靶向核酸相互作用时能够产生极强的黄色发射信号。诱导的荧光强度大约是噻唑橙的荧光强度的10-15倍。因此，该染料是用于生物传感和生物成像应用的出色荧光染料。它特别适用于需要非常低的工作浓度（0.25μM或更小）靶向核酸的荧光显微镜实验。使用pu27 G-四链体DNA证明了这一点，在相同条件下，其检测限低（LOD = 3–4 nM），而噻唑橙的检测限高得多（LOD = 48.7 nM）。另外，发现噻唑橙的喹啉鎓骨架上的结构修饰不如苯并噻唑部分上的修饰有效。本研究的发现为基于广泛使用的噻唑橙骨架的小分子的结构改进提供了重要的信息，从而得到了能够针对特定类别的核酸实现更高灵敏度和选择性的类似物。