The Fundamental Researches On Fast Detection Technology Based On Molecular Recognition

Food safety is an important social problem, which directly influences national economy, people's livelihood and social stability. Recent years, the high incidence of food safety events attracts much attention. Therefore, it is imperative to accelerate the exploitation of rapid, sensitive and stable detection technologies and products of food safety.In recent years, detection and analysis technique for pesticide, veterinary drug and additive rudimental are chromatograph/mass spectrum tandem detecting technique, immunology and biological method. But they are greatly constrained by high price of instrument, long time of experiment, complex pretreatment, limited units of test sample, high level of skill and other factors, so they could not meet the food safety requirements. The paper explored new ideas of rapid detection technique based on molecular recognition. The article taken the hot issues of food safety——melamine as key point and designed and synthesised a molecular probes to interact with melamine. The paper also explored the recognition process of intermolecular interaction.The preliminary visualization sensor was designed and constructed, and several tests were performed to detect the concentration of melamine in solution. All these settled the foundation for the further rapid detection methodology based on molecular recognition.The main research work is as follows:(1) The design, synthesis and characterization of host molecules for recognition.1,12-diorotate diaminododecane (DDO) was synthesized by L-orotic acid and 1,12-dodecanediamine and the structure of DDO was characterized by fourier transform infrared spectrometer (FTIR) and nuclear magnetic resonance (NMR). The properties and self-aggregation behavior of DDO in water were determined by dynamic light scattering (DLS), fluorescence spectroscopy, isothermal titration calorimetry (ITC), transmission electron microscope (TEM) and electrochemical workstation. The experiment results showed that DDO itself could form vesicles easily in aqueous solutions with molecular recognition function moieties. Meanwhile, vesicles formation in DDO/conventional surfactant mixed systems was studied. ITC and TEM results revealed that vesicles existing in the above mixed systems, indicating the strong vesicle formation ability in DDO/conventional surfactant mixed systems, especially in SDS/DDO mixed system. Moreover, it was identified that sodium bromide could induce the transition from vesicle to abundant aggregation behaviors, including filiform texture, reticular formation and so on. Therefore, the size and shape of vesicles could be controled by varying conditions. In conclusion, DDO had great potential as a host molecular for detecting melamine. These settled the foundation for the further application study. (2) The interaction of melamine and DDO during the recognition process.It was found that melamine had favorable fluorescence property which exaion wavelengthλex=250 nm and the emission wavelengthλem=360 nm. Meanwhile, DDO interacts with melamine though complementary hydrogen bonding easily based on its proton acceptors and donors characters in hydrophilic group. Intermolecular interaction between DDO and melamine lead to fuorescence quenching of melamine. It was also found that the fluorescence of melamine was quenched more effectively by the spontaneously formed vesicles than by the monomers of the surfactant. Two mechanisms were involved in the fluorescence quench process. At lower concentration (5×10-5 mol/L), the fluorescence of melamine was found to be quenched by static complex formation. While at higher concentration (2×10-3mol/L), both static and dynamic quenching mechanisms coexisted in interaction process. Thermodynamic parameters measured by ITC showed that the free energy (ΔG) was negative, indicating that binding of DDO molecules with melamine was favorable energetically.Transverse relaxation T2 measured by low field pulsed NMR showed that a loose bonding between melamine and water, implying hydrogen bond formation between DDO and melamine. All of the results evidenced the molecular recognition taking place between DDO and melamine.(3) Application research of melamine visualization sensor preliminary.Polydiacetylene vesicles were selected as carrier of DDO dectecting melamine. The functional molecules DDO were successfully incorporated into the polydiacetylene vesicles by interaction between hydrophobic chains, therefrom, constructing a vesicle which set detection and discoloration as one. The process of molecular recognition could be reflected by the color change of polydiacetylene vesicles. Thus, DDO molecular already realised detecting melamine preliminary. These provided a fast, efficient, green way to detect melamine in food system and constructed a new platform to comprehensive, rapid, accurate food safety testing.