Preparation And Biosensing Properties Of Fluorescent Sensors Based On Water-soluble Cationic Hydrazine Derivatives

Fluorescent chemical sensors can be used for a series of process that are closely related with human life, for example, food analysis, process control and environmental monitoring, etc. Compared with other analytical methods, fluorescence-based sensing has many prominent advantages, including high sensitivity, good selectivity, simple operation and fast response. In recent years, a great number of fluorescent sensors have been developed for detecting various targets. Currently, those used for identification of biological molecules are receiving increasing attention and interests, since they can provide potential for medical diagnostic applications.Heparin is a biological anionic polysaccharide, and plays an important role in many life processes. The most widely applied field for heparin is anticoagulant in surgical and post-treatment to prevent thrombosis. Protamine is rich in arginine and contains a lot of positive charges. It has the ability to combine with anionic heparin by their strong electrostatic interactions, and to ease the anticoagulant effect arising from overdose of heparin. There are a great deal of methods that have been reported for detection of heparin and protamine. At present, in the area of fluorescence detection, researchers have developed different types of fluorescent sensors for detecting heparin, but few are reported for the detection of protamine. Therefore, in my dissertation, I propose to use cationic water-soluble probes based on pyrene derivatives to develop fluorescent sensors for sensing both heparin and protamine with high sensitivity. The present dissertation covers the following two parts that have been conducted.In the first part, an imidazolium-modified pyrene derivative, IPy, was used as a fluorescent sensor, which contains two positive charges and one pyrene unit. The cationic fluorescent probe could interact with anionic heparin via electrostatic interaction to bring about blue-to-green fluorescence changes as monomer emission significantly decreases and excimer increases. The binary combination of IPy and heparin could be used as another fluorescent sensor, and further used for green-to-blue detection of protamine since heparin prefers to bind to protamine instead of probe due to its stronger affinity with protamine. The cationic probe shows high sensitivity to heparin with a low detection limit of 8.5 nM (153 ng/mL) and its combination with heparin displays high sensitivity to protamine with a detection limit as low as 15.4 nM (107.8 ng/mL). Moreover, both processes can be performed in serum solutions, indicating possibility for practical applications. The simple cationic pyrene-based probe can function as a highly sensitive ratiometic sensor for both heparin and protamine in aqueous environment.In the second part, we have designed and synthesized an imidazolium-modified bispyrene-based fluorescent probe, DPI, which contains two positive charges and two pyrene moieties that are connected using a flexible spacer containing carbonyl groups and amine groups. The basic photophysical behavior of DPI in both water and SDS aqueous solutions were examined. Steady-state emission measurements reveal that the excimer emission is formed through intermolecular interaction. Moreover, the probe itself shows strong aggregation behavior in aqueous solution by emitting strong excimer emission. SDS concentration effect measurements also find that the fluorescence emission of DPI could be well-modulated by the anionic surfactant assemblies. Based on our previous work using surfactant assemblies encapsulated fluorescent probe for sensing arginine, we propose to construct a supramolecular fluorescent sensor for protamine based on the binary system of DPI and SDS assemblies. At the same time, the possibility of using the aggregation of the amphiphilic molecule itself for sensing application also attracts our interests.